Airway Management

## **Chapter 2** Hypoxia and Paraoxygenation

*Suresh Kumar Singhal and Manisha Manohar*

## **Abstract**

Hypoxemia whether critical or not is a complication associated with airway management. The abruptness with which the hypoxic events can occur during airway management in anticipated as well as unanticipated difficult airways provide very little time to the airway managers to avoid the whirlpool of complications that can ensue if hypoxia persists. An understanding of the etiology and mechanisms of hypoxemia and the techniques that can ensure oxygenation for a prolonged time provide a safe window to think and execute the airway management plans. Paraoxygenation is one such technique that ensures an uninterrupted oxygen supply to the patient after the onset of apnoea and prolongs the safe apnoea time significantly.

**Keywords:** hypoxia, hypoxemia, paraoxygenation, apneic oxygenation, safe apnea time, NODESAT, THRIVE, barotrauma

## **1. Introduction**

Perioperative hypoxia occurs due to variety of causes. An anesthesiologist has to diagnose as well as treat the hypoxic events in a very short frame of time before the development of critical hypoxemia. An understanding of the causes and the pathophysiology of types of hypoxia is a prerequisite for successful management of hypoxic episodes. The technique of Paraoxygenation, also known as apneic oxygenation has found use in anaesthesia as well as critical care. This technique can be easily applied in patient population at risk of hypoxia with easily available equipments like nasal prongs, end bronchial catheters, RAE tube inside the operating theatres. Although associated with various complications, Paraoxygenation prolongs the duration of apnea without desaturation and buys time for the airway management before the development of critical hypoxemia**.**

## **1.1 Literature search**

PubMed, Googlescholar, manual searches were used to find the relevant articles. The following key words were used for the search: apnoeicoxygenation, paraoxygenation, difficult intubation, hypoxia, hypoxemia, aventilatory mass flow.

## **1.2 Aim**

This chapter focuses on understanding the pathophysiology of hypoxia and the role of paraoxygenation in various aspects of anaesthesiology and critical care.

## **Hypoxia**

I.Definition

II.Classification

III.Clinical effects of hypoxia

## **Paraoxygenation**

I.Physiologic basis

II.Prerequisite

III.Techniques

IV. Clinical application

V.Complications

## **2. Hypoxia**

## **2.1 Definition**

Although used synonymously quite often, the term hypoxia and hypoxemia are different and should be used in appropriate clinical scenarios. Hypoxemia is the arterial PO2 below what is expected normal for a patient's age while hypoxia is decreased level of tissue oxygenation. Hypoxia and Hypoxemia do not always coexist e.g., Hypoxia in cyanide poisoning is due to the defective utilisation of oxygen despite having normal oxygen levels in the blood.

## **2.2 Classification of hypoxia**

*1. Hypoxic hypoxia (Hypoxemia)*: is defined as arterial Pao2 less than 60 mmHg or SaO2 < 90%. Hypoxemia is one of the most feared and common complication related to tracheal intubation that can occur suddenly in the perioperative period. Hypoxemic episodes can occur during induction, maintenance, extubation and post extubation period (**Figures 1** and **2**).

## *2.2.1 Causes of hypoxemia*

i. Hypoxemia due to the patient factors: Airway obstruction in unconscious patient is mostly due to tongue falling back against posterior pharynx and is commonly seen in patients with history of obstructive sleep apnea. Secretions/blood in the airway, laryngospasm, bronchospasm, glottic edema due to airway instrumentation, aspiration of vomitus, retained throat pack, external pressure on the trachea due to a neck hematoma can lead to critical hypoxemia.

#### **Figure 1.**

*Classification of hypoxia.*

#### **Figure 2.**

*Common causes of perioperative hypoxemia.*

ii. Hypoxemia due to the equipment factors: Delivery and monitoring of the anaesthetic gases to the patient is done through a series of equipment. Any fault with the functioning of the equipment e.g.: pipeline, oxygen cylinder, anaesthesia machine, anaesthesia circuit, pulse oximetry can lead to the development of hypoxemia

## **2.3 Clinical effects of hypoxemia**

The cardiovascular response to hypoxemia is a product of neural, humoral and direct effects. The neural reflex which is excitatory is mediated by aortic, carotid chemoreceptors, baroreceptors and central cerebral stimulation while the humoral reflex which is vasoconstrictive is mediated by release of catecholamines and renin angiotensin release. The direct local vascular effect of hypoxia is seen late and is manifested as inhibitory and vasodilatory effect. Mild arterial hypoxemia causes generalised activation of the sympathetic nervous system and release of catecholamines leading to an increase in heart rate, stroke volume and myocardial contractility. With the onset of moderate hypoxemia local vasodilation begins to predominate and systemic vascular resistance and blood pressure begin to decrease, however heart rate increases due to the hypotension induced stimulation of baroreceptors. With severe hypoxemia the local depressant effect dominates and blood pressure falls rapidly, pulse slows down, shock develops and heart either fibrillates or becomes asystolic [1] (**Figure 3**).

## *2.3.1 Mechanisms of hypoxemia [2]*

**Figure 3.** *Mechanisms of hypoxemia.*

Paco2 and the condition is called SHUNT. Hypoxemia seen in pulmonary carbon dioxide is largely due to the right to left shunting of the blood

*2. Anaemic hypoxia*: Anaemic hypoxia is characterised by decreased oxygen carrying capacity of the blood either due to low haemoglobin or due to presence of abnormal haemoglobin (carboxyhaemoglobin, methaemoglobin). A reduction in the haemoglobin concentration of the blood is accompanied by a corresponding decline in the oxygen carrying capacity of the blood. Although Pao2 is normal in anaemic hypoxia, the absolute quantity of the oxygen transported per unit volume of the blood is diminished. As the anaemic blood passes through the capillaries the usual quantity of oxygen is removed from it and Pao2 and saturation in the venous blood decline to a greater extent than normal. Presence of carbon monoxide in the blood leads to the formation of carboxyhaemoglobin there by reducing the amount of oxyhaemoglobin. The arterial oxygen decreases in proportion to the increase in carboxyhaemoglobin reflecting the ability of Carbon monoxide to block oxygen binding to haemoglobin.

*3. Ischemic or stagnant hypoxia or Hypokinetic hypoxia*: Decreased cardiac output or sluggish blood flow either due to heart failure, shock, or haemorrhage leads to stagnant hypoxia. The blood remains in the tissues for a greater period of time leading to increased extraction of oxygen. The Pao2 is usually normal but the venous and the tissue po2 values are reduced as a consequence of reduced tissue perfusion and greater tissue extraction.

*4. Histotoxic hypoxia*: is due to the inability of the tissue to utilise oxygen despite adequate availability of oxygen in the blood. Cyanide induced inhibition of cytochrome oxidase halts the process of oxidative metabolism in mitochondria leading to an increased uptake of pyruvate by mitochondria resulting in excess production of lacticacid.

The process of intubation inherently makes the patient prone to hypoxemia due to the reduced functional residual capacity (FRC) insupine position, hypoventilationdue to anaesthetic agents and deliberately induced apnoeawith musclerelaxants. Hypoxemia can develop with startling abruptness during the perioperative period without giving much time for the patient rescue. Oxygenating a patient prior to the induction of anaesthesia is called Preoxygenation. Adequate preoxygenation prolongs the duration of apnoea without desaturation (DAWD) by building up the oxygen reserve in the functional residual capacity which acts like a reservoir from where the oxygen can be extracted and delivered to blood thereby avoiding the desaturation to critical levels. Preoxygenation is currently the standard of care in all patients undergoing general anaesthesia. However, conventional preoxygenation techniques may be inadequate in providing a safe apnoeic period (time from apnoea onset to spo2 90%) in all patient's

population especially the one with high oxygen requirements (paediatric, obstetric, obese) or those with difficult airways. In order to supplement preoxygenation and to prolong the safe apnoea time further Para oxygenation or apnoeic oxygenation can be used as a useful adjunct to preoxygenation.

## **3. Paraoxygenation**

Para oxygenation is the technique of providing uninterrupted oxygen supply to the patient after the onset of apnoea in order to prolong the safe apnoea time especially in patients with difficult airways to provide adequate time to the anaesthesiologist for uninterrupted execution of the attempts to secure the airway. Paraoxygenation is also known as apnoeic oxygenation.

## **3.1 Physiologic basis of para oxygenation:**

*Aventilatory mass flow [3]/diffusion respiratio [4]/apnoeic diffusion of oxygen [5]*: The oxygen consumption of a health adult is 250 ml/min while the carbon dioxide production is 200 ml/min. Inapnoeic patients the extraction of oxygen from the alveoli continues at the rate of 250 ml/min while carbon dioxide delivery to the alveoli is 21 ml/min thereby causing the alveolar pressure to become sub atmospheric leading to a generation of pressure gradient which enables the movement of additional administered oxygen provided the airway is patent. Preoxygenation facilitates the process of apnoeic oxygenation by denitrogenating the alveoli. In the absence of adequate preoxygenation, the persistence of nitrogen in the lungs along with the accumulating carbon dioxide will diminish the pressure gradient available for the mass flow of oxygen into the alveoli thereby hastening the onset of hypoxemia. The persistent delivery of 100 percent oxygen prevents the renitrogenation of the alveoli during the apnoea. The sub atmospheric pressure also promotes carbon dioxide transfer from blood to the alveoli. The degree of oxygen extraction from the alveoli exceeds the degree of carbon dioxide return to the alveoli since carbon dioxide is buffered in the body but with time the alveolar accumulation of carbon dioxide reaches a critical level beyond which the pressure gradient is reduced thereby reducing the aventilatory mass flow of oxygen.

## **3.2 Prerequisite for para oxygenation**

*Hypoxia and Paraoxygenation DOI: http://dx.doi.org/10.5772/intechopen.106827*

> cannula, nasopharyngeal catheter, rigid bronchoscope, catheter placed in trachea, endobronchial catheters, front of neck catheter, channels located in direct and video laryngoscopes.

4.*Oxygen source*: Auxiliary port in the anaesthesia machine or an oxygen cylinder in case of intubations done in out of operating room settings can be used for the oxygen denitrogenating supply.

## **3.3 Techniques**

Various techniques for administration of paraoxygenation have been described. Oxygen can be delivered at different locations in the upper and lower airway during apnoea: Devices can be placed at following sites: Nares, nasopharynx, oropharynx, oral cavity, trachea, Primarybronchi (**Figure 4**).

1.NODESAT: Nasal oxygenation during efforts securing a tube

## *3.3.1 NODESAT: Nasal oxygenation during efforts securing a tube.*

NODESAT was first described by Levitan [6], as a method to extend the safe apnea time during rapid sequence anaesthesia in the emergency department. Inappropriately sized nasal cannula is used to administer the standard unwarmed and dry oxygen at the rate of 15 litres/min while attempts for intubating the trachea by conventional

**Figure 4.** *Techniques of paraoxygenation.*

## **Figure 5.**

*(a) NODESAT during preoxygenation; (b) NODESAT during intubation.*

laryngoscopy or video laryngoscopy or flexible fibreoptic bronchoscope are being made. Unlike other techniques, this technique does not require any special equipment and can be easily done in the operating theatre with nasal prongs and auxiliary oxygen port. However, they can impair the face mask seal during bag mask ventilation. The administration of dry, cold oxygen at high flows can lead to mucosal injury and mucociliary dysfunction (**Figure 5**).

## *3.3.2 Direct pharyngeal oxygen insufflation:*

Para oxygenation can be achieved by using any device that administers oxygen to the pharynx (**Figure 6**).

**Figure 6.** Naso-Flo *(Medis medical CO Ltd).*

## *Hypoxia and Paraoxygenation DOI: http://dx.doi.org/10.5772/intechopen.106827*

*Nasopharyngeal catheter*: A nasopharyngeal catheter advanced into the nasopharynx can be used to deliver oxygen during apnoea. The distance from the nares to the tragus of the ear is measured as taken as depth of the catheter insertion. Achar et al [7] found nasopharyngeal catheters to be more effective than nasal prongs in delivering oxygen during apnoea. The Naso-Flo®(Medis medical CO Ltd) is soft silicone nasopharyngeal airway device that allows for direct oxygen delivery into the pharynx, while humidification vents positioned towards the distal tip facilitate heat and moisture transfer.

*Buccal oxygen delivery device. As described by Andrew Heard et al. [8] (a) RAE tube (b) RAE tube cut above murphy's eye (c) Standard oxygen tubing connected from the cut end to the oxygen source. The Blunt proximal end (connector detached) is placed in the buccal space with the tube angle apposed to the side of the mouth.*

*Buccal oxygen delivery*: An inexpensive, readily available method of apneic oxygenation was described by Andrew Heard et al. [8]. A 3.5 mm south facing Ring Adair and Elwin (RAE) tube was cut above the murphy's eye. Standard oxygen tubing was connected from the cut end to the auxiliary oxygen outlet on the anaesthesia machine. The blunt proximal end was placed in the buccal space with the tube angle opposed to the left side of the mouth. The tube was fixed to the external cheek to maintained the position. This method of buccal oxygen delivery provided a viable alternative to the nasal route (**Figure 7**).

## *3.3.3 THRIVE: Trans nasal humidified rapid insufflation ventilatory exchange:*

Patel and Nourae, in 2013, introduced the delivery of warm and humidified high flow nasal oxygen using OPTIFLOW™ system (Fischer and Paykellhealth care LTD Auckland, newzealand). Not only the apnea time were prolonged but the rate of rise of carbondixoide was found to be one third of what was expected [9]. This suggested a physiology supplementing classic apneic oxygenation. The clearance of carbondioxide can be explained by the interaction of cardiogenic oscillations and turbulent primary supraglottic vortex [10].

*Primary supraglottic vortex*: High-flow nasal oxygen enters the nose at 70-90 L/min, loops around the soft palate, and exits through the mouth. This creates a highly turbulent 'primary supraglottic vortex" which has the following effects:

It replenishes the pharynx with oxygen and prevents entrainment of room air.

It effectively bypasses the upper airways which ordinarily account for approximately 50% of the resistance of the entire respiratory system to airflow [11]. By effectively breathing 'directly from the glottis', work of breathing is reduced by approximately 50% [12].

It also generates a positive airway pressure which in turn reduces upper airway collapsibility and distal airway atelectasis [13].

The primary vortex does not, however, extend deep into the trachea and cannot by itself account for the observed level of gaseous exchange.

*Cardiogenic oscillations*: The compression and expansion of the small airways is brought about by the blood leaving and entering the thoracic cavity with each heartbeat [14]. The typical amplitude of a 'cardiogenic breath' is around 7-15 ml per heartbeat [10]. Ordinarily, cardiogenic oscillations result in small-volume mass movement of gases within the trachea.

During THRIVE, this small volume is flushed into the supraglottic vortex during cardiogenic 'expiration', is removed, and replaced by 100% oxygen. Cardiogenic 'inspiration' moves this oxygen towards the distal airways and also entrains turbulence, which enhances intratracheal mixing. e.g.

Volume of a 'cardiogenic breath' to be 12 ml per heartbeat, Heart rate:70 beats per minute.

840 ml of gas which contains CO2 is removed, and is replaced with 100% oxygen. This is not enough to achieve full CO2 clearance. That is why carbondioxide still accumulates during THRIVE, but at a slower rate than with classical apnoeic oxygenation.

THRIVE is administered through a standard commercially available high flow oxygen delivery system e.g. Optiflow (Fischer and Paykel health care), Airvo, Airvo2 (Fischer and Paykel health care). It consists of a flowmeter, humidifier, heating system, heated non condensing circuit, and an oxygen connector for gas supply. Some

## *Hypoxia and Paraoxygenation DOI: http://dx.doi.org/10.5772/intechopen.106827*

of the ventilators. e.g Bellavista ventilators, IMT medical, Switzerland available in the market have an inbuilt system that provides the high flow oxygen therapy as well as invasive ventilation modes (**Figures 8**–**10**).

**Figure 8.** *Nasal prongs for high flow nasal oxygenation.*

**Figure 10.** *Bellavista ventilator (IMT, medical, Switzerland).*

## *3.3.4 Others*

*Endobronchial catheters*: Endobronchial catheters are placed in the main stem bronchi. The catheter placedeither in right or left main stem bronchi or in both the bronchi can be used for apnoeic oxygenation**.** Babinski et al. used two polyethylene catheters (2.5 mm OD) with angulation of 20 degree for the right side and 30 degree for the left were placed in the bronchi under fibreoptic guidance for endobronchial apnoeic oxygenation. Humidified oxygen was delivered at 0.6 to0.7 L/min. The authors found the adequate oxygenation was maintained till 30 minutes with a mean co2 rise at rate 0.6mmhg/min [15] (**Figure 11**).

Dual use laryngoscopes: Dual use laryngoscopes are specifically designed to allow for the insufflation of oxygen during laryngoscopy. The miller port American profile

**Figure 11.** *ShileyEndobronchial suction catheters( COVIDIEN, MEDTRONIC) with color coded connectors.*

**Figure 12.** *Miller port American profile blade (Sun MED LLC).*

conventional blade (Sun Med LLC) is commercially available laryngoscope that has an integrated tube that permits the delivery of oxygen and other gas mixtures during laryngoscopy (**Figure 12**).

*Tracheal tube introducer*: An Eschmann tracheal tube introducer was used by Millar et al. for administering apnoeic oxygenation. Two holes were drilled at both the end of the Eschmann gum elastic bougie (SIMSportex, Hythe Kent, UK) and apnoeic oxygenation was tested on an anaesthetic simulator model. The modified bougie was positioned 2–3 cm beyond the vocal cords with 8 l/min of oxygen flowing through it. The time taken for the oxygen saturation to fall was significantly prolonged when modified gum elastic bougie was used for apnoeic oxygenation [16]. COOKS airway exchange catheter (AEC) has a blunt tip which is a traumatic to internal structures. The lumen and distal side ports are designed to deliver oxygen. The removable Rapi-Fit Adapter permits oxygen delivery during an airway exchange procedure. Although cook's airway is intended for tracheal tube exchange, it can also be used to paraoxygenate the airways (**Figure 13a**–**c**).

*Intratracheal catheters:* A retrospective study was conducted by Rudlof and Hohenhorst [17] analysing 47 patients who underwent apnoeic oxygenation at 0.5 l/min using a catheter inserted into the trachea. The median Spo2 at the end of the apnoeic period was found to be 100 percent. The mean apnoea time was found to be 24.7 min with no adverse effects.

## **3.4 Clinical applications of paraoxygenation/apnoeic oxygenation**

See **Figure 14.**

## *3.4.1 Routine elective endotracheal intubation*

Para oxygenation through nasal or nasopharyngeal catheter prolongs the safeapnoea time and also decreases the degree of desaturation during induction of anaesthesia and endotracheal intubation in adult ASA 1–2 patients undergoing anaesthesia for elective surgery [18]. Apnoeic oxygenation has been shown to be associated with increased per intubation oxygen saturation, decreased rate of hypoxemia and first pass intubation success [19]. During one lung ventilation, apneic oxygenation of the deflated lung through a suction catheter can reduces the likelihood of hypoxemia and need for resumption of double lung ventilation [20, 21].

**Figure 13.**

*Cooks airway exchange catheter (cook medical). (a) Cook's Airway exchange catheter; (b) Distal end of Cook's AEC Designed to deliver oxygen; and (c) distal lumen of the cooks airway exchange catheter.*

**Figure 14.** *Clinical applications of paraoxygenation.*

#### *3.4.2 Difficult airway management*

Awake intubation: Awake fibreoptic intubation is indicated in cases with anticipated difficult airways. Even though the procedure can be done with local anaesthesia, sedation is often required to improve the patient tolerance and cooperation. Sedative induced apnea, can lead to hypoventilation, and upper airway obstruction during awake fibreoptic intubation in difficult airway resulting in critical oxygen desaturation. Paraoxyygention can be used as an effective tool to ensure adequate oxygenation while the airway is being navigated by the scope. Schroeder et alevaluated a special oropharyngeal oxygenation device (OOD), allowing a continuous laryngeal oxygen insufflation during and parallel with bronchoscopy [22]. Apnoeic laryngeal oxygenation in a preoxygenated manikin with both oxygen insufflation via the OOD and the bronchoscope kept oxygen saturation in the test lung at 95% over 20 min. Oxygen insufflation via OOD or bronchoscope was found to be more effective than nasal oxygen insufflation.

*Physiologically difficult airway*: Peri intubation hypoxia is more common in physiologically difficult airways e.g., paediatric, obstetric and obese patient population. Obesity leads to decreased in function residual capacity, increases atelectasis and shunting in the dependent region of the lung. Resting metabolic rate, work of breathing and minute oxygen demand however are increased. This combination of the factors makes the obese patient prone to hypoxemia during the induction of the induction of anaesthesia. Oxygen insufflation at 15 l/min through nasopharyngeal airway and standard nasal cannula can significantly increase the safe apnea time during induction of anaesthesia in obese patients [23].

Although apnoeic oxygenation is extensively studied in the adult population, very few studies have been conducted on the paediatric population, there is evidence that apnoeic oxygenation is a simple easy to apply intervention that can decrease hypoxemia during paediatric endotracheal intubation. Not only it increases the time until desaturation but also reduced the overall incidence of hypoxia during laryngoscopy in paediatric population [24].

Difficult airway society and obstetric anaesthetist association guidelines issued in 2015 for the management of difficult tracheal in obstetric patients emphasised on the role of apnoeic oxygenation via nasal cannula, nasopharyngeal catheter or mask [25]. AIDA Arecommends the universal use of 15 L/min oxygen insufflation via nasal cannula for obstetric general anaesthesia they recommend the use of nasal prongs to insufflate oxygen during the apnoeic period in patients with difficult airway [26].

*Tubeless anaesthesia*: Managing the shared airway in the glottic and subglottic pathologies presents a challenge to the anaesthesiologist as well as the surgeon. Tubeless anaesthesia with apnoeic oxygenation allows a good access and visualisation of the glottis without oxygen desaturation. Apneic oxygenation enables tubeless anaesthesia for extended period of time. Vocalcordbiopsy, balloon dilation of subglottic stenosis has been done using this technique. Apnoeic oxygenation with nasal cannula and THRIVE has been found to be safe and feasible for the endoscopic management of subglottic stenosis in short glottic surgical procedures [27].

*Bronchoscopy:* Apnoeic oxygenation can be done in patient undergoing rigid bronchoscopy with passive oxygen insufflation through the side port of the bronchoscope or a tracheal catheter [28, 29]. High flow administration of oxygen via side sport of bronchoscope risk barotrauma if the path for gas egress becomes obstructed even for brief period.

*Critical care:* Recent guidelines for the management of airway in critical care patients have recommended that nasal oxygen should be applied throughout the airway management. If the standard nasal cannula is used it should be applied during preoxygenation with a flow of 5 L/min while awake and increased to 15 L/min when the patient loses conscious. A high flow nasal cannula can also be used if already in place [30].

 During this time oxygen is insufflate through the tracheal tube via a catheter to prevent hypoxemia.

## *3.4.3 Emergency intubation*

Patients requiring emergency airway management are at a greater risk of hypoxemia due to underlying lung pathology, high metabolic requirements, high respiratory drive or inability to protect the airway. Rapid sequence intubation in critically ill patients is associated with episodes of hypoxia. Apneic oxygenation has been shown to reduce the incidence of desaturation in patient undergoing rapid sequence intubation in emergency [31]. A systematic review to investigate the effect of apnoeic oxygenation on incidence of clinically significant hypoxemia during emergency endotracheal intubation concluded that paraoxygentaion reduces the incidence of hypoxemia in emergency endotracheal intubation and supported the inclusion of apnoeic oxygenation in everyday practice (**Figure 15**) [32].

## **3.5 Complications of paraoxygenation**

*Hypercarbia*: During Para oxygenation carbon dioxide cannot be vented out. Co2 levels continue to rise leading to an increase in PH and development of respiratory acidosis [15, 33, 34]. Paco2 levels increase with a speed of 1.1–3.4 mmHg. Mean CO2 levels can reach as high as 160 mmHg [33]. However, with THRIVE the rate of carbon dioxide accumulation is less than that seen in classic apnoeicoxygenation [9]. The

**Figure 15.** *Complications of paraoxygenation.*

#### *Hypoxia and Paraoxygenation DOI: http://dx.doi.org/10.5772/intechopen.106827*

effects of hypercarbia are versatile ranging from tachycardia, increased cardiac output, increased cerebral blood flow. Prolonged apnoeic oxygenation should be avoided in patients with contraindication to hypercapnia e.g., cardiac arrythmia, hemodynamicinstability, raised intracranial pressure. Para oxygenation interrupts the early detection of rise of carbon dioxide. Since the end-tidal carbon dioxide monitoring cannot be done during apnea, transcutaneous carbon dioxide measurements may help in minimizing the risk and optimal utilization of Para oxygenation [35].

*Acidosis*: Gradual increase in the carbon dioxide levels leads to respiratory acidosis however, during testing for brain death in addition to respiratory acidosis, a mild metabolic acidosis of unknown cause also develops during apnoeic oxygenation [36].

*Accidental awareness*: Apnoeicoxygenation does not deliver volatile agents to the lung. Hence adequate anaesthesia during the airway management should be ensured to avoid accidental awareness [37]. Total intravenous anaesthesia {TIVA} can be used during paraoxygenation to avoid the accidental awareness during this procedure. Tubeless anaesthesia with apnoeic oxygenation for the short glottic procedures also requires the administration of intravenous anaesthesia to ensure adequate depth during the procedure.

NODESAT, direct pharyngeal insufflation delivers dry and cold oxygen to the respiratory tree. Administration of dry and cold gases can induce bronchoconstriction in patients with asthma [38]. Airway resistance is increased to reduce the airflow in the upper and trachea to protect the lungs from the challenge of dry and cold gases [39, 40]. Dry gases cause excessive water loss by the nasal mucosa [41]. This may reduce the nasal mucociliary clearance rate due to the changes in the rheological properties or adhesiveness of the nasal mucus and slowing of ciliary pulses [42]. High flow dry gases result in inspissated secretions that can cause life threatening airway obstruction [43].

*Barotrauma*: Apnoeic oxygenation is a widely accepted method for apnea testing in brain death. During the apnea testing, ventilator assistance is discontinued and oxygen is delivered into the trachea via an oxygen catheter placed at the level of carina while waiting for the spontaneous respiratory movements. Apnea testing related pneumothorax was first reported by Bar joseph et al. [44]. In order to avoid pneumothorax authors proposed that the oxygen flow rates should not exceed 6 l/min, oxygen catheter diameter should be narrower than the diameter of the endotracheal tube and the tip of the oxygen catheter should not exceed the tip of the endotracheal tube to avoid wedge position in the trachea. A case of pneumothorax and pneumomediatinum was reported by saposnik et al. [45] during apnea testing. Vivien et al. [46] proposed that a 12 french catheter should be advanced only 5 cm into the endotracheal tube and oxygen flow rates should not exceed 8 l/min to avoid pneumothorax during apnea testing. Barotraumacan occur if there is no clear route for egress of gases during apnoeicoxygenation.AT- piece or a self-inflating bag valve system can be used as an alternative technique to conductapnoeatest. Serious air leak syndromes have been reported with the use of high flow especially in paediatric age group. HFNC is being used as a respiratory support for preterm infants. HFNC is being used as an alternative to nasal continuous positive airway pressure (CPAP) and in particular to prevent postextubation failures. A case of tension pneumocephalus in a preterm infant was reported by Iglesias et al. [47] as a complication during HFNC ventilation. Significant neurological impairment was detected and support was eventually withdrawn. Clinicians need to be aware of this rare but possible complication during HFNC therapy, as timely diagnosis and treatment can prevent neurological sequelae. Paying close attention to flow rate, nasal cannula size and insertion, regularly checking insertion depth

**Figure 16.** *Paraoxygenation: Preparation to execution.*

can help to avoid these complications. Cases of pneumo-orbitus [48], epistaxis, subcutaneous emphysema, oesophageal rupture, gastric rupture [49, 50] have all been reported with use of apneic oxygenation.

## **4. Conclusion**

Perioperative critical hypoxia is one of the most feared complication an anesthesiolgist may come across. These episodes often occur abruptly and demand prompt intervention to avoid irreversible damage. Management of these lifethreatening situations requires simultaneous diagnosis and treatment of hypoxia. Differentiating between the patient factors and the machine factors leading to hypoxic event is imperative. Paraoxygenationor apneic oxygenation techniques can help to buy time, avoid panic and execute airway securing strategies by delaying the development of critical hypoxemia. Routine application of paraoxygenation techniques in everyday clinical practice and a knowledge of various equipments that can be used to administer paraoxygenation to the patient can help prevent the nightmare of critical hypoxic perioperative events (**Figure 16** and **Table 1**).

#### **Table 1.**

*Summary of techniques of paraoxygenation.*

## **Abbreviations**

## **Author details**

Suresh Kumar Singhal\* and Manisha Manohar Department of Anaesthesiology and Critical Care, Pt. B.D. Sharma Post Graduate Institute of Medical Sciences, Rohtak, India

\*Address all correspondence to<EMAIL_ADDRESS>
© 2022 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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## **Chapter 3**

## Anesthesia in Plastic Surgery: Intersurgical I-gel Placement in a Prone Position

*Judith Adrianne Deutsch, Kata Šakić, Dinko Bagatin, Johann Nemrava and Tomica Bagatin*

## **Abstract**

Anesthesia is a specialization which in past history has branched off of surgery. It needs to be very creative in its delivery, in order to accommodate the many operating positions, needed by the surgeon. The patient positions must also be safe and adequate for proper ventilation, throughout the operative procedure. There are times when multiple positions must be used, turning the patient over, even several times. Careful planning and team discussions prior to an operation are absolutely necessary, to form anesthetic and operative plans. The aim of the supraglottic airway device (Intersurgical i-gel) prone position induction method is to describe, detail and present its safe efficacy for certain planned operative procedures. Patient fasting preparation is a must, nil by mouth for 8 h. This method and sequence alleviates the use of muscle relaxants for patient rotation. This increases patient safety by keeping muscle tone normal, reduced drug use, minimizing rotation of the patient, and reduces possible injury of patient and among staff involved in rotating. Some may say induction in the prone position may be unsafe due to aspiration risks, but knowing anatomy and gravitational physics, in the event of any secretions projected, they will project forwards onto the operating table (through the gastric port of the i-gel), not into the tracheal area. This similar technique and principle are seen and used for the recovery position, to aid in free drainage of fluid from within the oral cavity. The method is used for a variety of operations worldwide and introduced in 2018 at Poliklinika Bagatin (PB). Approximately, 80 prone position inductions or 10% of all general anesthesias are performed every year at PB. More than 240 anesthesized patients in the prone position with an i-gel have used this method, since it was introduced. All have been with excellent results, minimal risk and appropriate ventilation of patients. I-gel placement in prone position was successful everytime. This method is advantageous to avoid multiple rotations of patients and avoid the use of muscle relaxants, otherwise used, with classic endotracheal intubation methods. The exact process will be discussed in more detail and described within the chapter.

**Keywords:** i-gel, prone position, patient safety, reduced rotation, faster preparation, esthetic plastic procedures, liposuction

## **1. Introduction**

Creative anesthesia and patient safety are the goals of accommodating surgeons and providing superior anesthesia. The entire team have the same focus, to complete an operation in the best possible manner and with exceptional results. Plastic surgery has high expectations for perfect results. There are numerous operative procedures being offered in esthetic plastic surgery, requiring various forms of anesthesia, in various positions. The anesthesia provided may be local, local with sedation (local potentiated), regional blocks and general. The choice of delivery can involve the patient's desires, but must be a safe method, in order to maximize comfort during the procedure. Some procedures may last several hours, and in these cases a balance between the patient's desires, comfort and safety must be weighed out, for the most optimal choice. Preoperative consultations and plans are discussed between the patient, surgeon, anesthesiologist and the entire team, to define the type of optimal anesthesia to be delivered, as well as surgical technicalities and specifics (instruments, devices, sutures) needed.

Preoperative preparations with the anesthesiologist can be challenging with patients who have specific disorders, chronic disease, previous operations, increased age, mobility issues, various drug therapies being taken, allergies and more. Preoperative testing, thromboprophylaxis, intraoperative active body warming, hydration are among other vitally important features of preoperative and intraoperative preparations that need to be considered.

Today many patients undergoing anesthesia, wish to complete as much as possible, while under one anesthesia. This needs to be assessed by both the surgeon and anesthesiologist for safety, logistics and feasibility. At times, a combination of operations, two body regions, can be performed. This significantly increases the duration of the anesthesia and operation. In some cases, this may not be possible, and a recommendation is made for the procedures to be performed separately.

Many individual clinics may be specialized in other specific types of esthetic plastic operations, offering even more procedures, not mentioned here. However, the list is comprised of the more common available procedures worldwide and what is offered at Poliklinika Bagatin (PB). Furthermore, these various procedures can involve different positions, which are challenging for the anesthesiologist and their team. Therefore, good preparation is key. The prone position can be a safe and great alternative induction position, reducing patient rotations, avoiding the use of muscle relaxants and increasing patient and staff safety.

## **2. Methods and procedures**

A deeper understanding of the methods and procedures, used worldwide and at PB, using prone position induction will be described. A detailed refresher of anatomy is recommended, for the anatomical placement differences between the endotracheal (ET) tube and i-gel intubation devices.

Anatomy of the airway is vitally important and needs to be protected, during any procedure. The pharynx is comprised of the nasopharynx, oropharynx and

*Anesthesia in Plastic Surgery: Intersurgical I-gel Placement in a Prone Position DOI: http://dx.doi.org/10.5772/intechopen.106538*

#### **Figure 1.**

*(A) Sagittal plane anatomy head; (B) vocal chords, epiglottis image without ET tube; (C) image of ET tube in place following intubation.*

laryngopharynx (**Figure 1A**) [1, 2]. The upper section, nasopharynx connects the nasal passages to the airway. The middle section, the oropharynx forms the mouth. While the lower portion, the laryngopharynx is the area with the entrance into the trachea passing the vocal chords (**Figure 1B**) [1, 2].

The process of intubation can comprise of an endotracheal tube, which is the most secure method of separating the airway from the gastrointestinal passages, or the use of laryngeal devices, which adequately ventilate but do not separate these passages (**Figure 2A** and **B**) [1, 2]. Both methods require complete sedation of the patient and placement onto an anesthetic machine for controlled or assisted ventilation. Standard monitoring (blood pressure, ECG, and pulse oximetry) should always be used, regardless of the anesthesia type and method chosen. Placement onto an anesthetic machine gives more diverse information, such as end tidal CO2, tidal volume, respiratory rate, various airway pressures and concentrations of anesthetic gases. Even more advanced monitoring (arterial pressures) can be used, depending on the complexity and duration of the procedure being performed, more often used within the hospital setting rather than outpatient clinics.

Other methods used at PB, such as local, local with added sedation (local potentiation) and regional blocks are used with mask or nasal oxygen tubing in spontaneously breathing patients. The various anesthetic methods can be used on their own or in combination, for optimum pain control coverage during and after procedures. Both surgeons and anesthesiologists can perform the local and regional anesthetic methods. However, intubation requires specific training and skills, and is usually reserved for anesthesiologists.

Placement of the ET tube involves the use of a laryngoscope, to move away soft tissues and the base of the tongue, gently lifting the epiglottis, in order to visualize the entrance into the trachea (**Figure 1B**) [1, 2]. The ET tube is then advanced, with care, into the trachea, passing the vocal cords (**Figure 1C**) [1, 2]. Fixation and final placement of the ET tube is confirmed by chest auscultation hearing equal breath sounds on either side of the chest and then securing it with medical tape or a tie.

#### **Figure 2.**

*(A) i-gel following intubation; (B) ET tube following intubation.*

Proper auscultation and fixation prevent accidental one lung ventilation and possible barotrauma (**Figure 2B**) [1, 2].

There are various generations of laryngeal devices available, however all have similar principles in their placement, with a variation in fixation of position (with or without a cuff). They all cover the entrance into the trachea and the esophagus. They do not separate or prevent spillage over into the tracheal area, which can cause concerns, potentially causing aspiration of fluids into the respiratory system (**Figure 2A**) [1, 2]. However, proper patient preparation can reduce spillage into this area.

The i-gel is a unique device, which is elegantly simple and requires no balloon inflation (**Figure 3**) [3].

Assistance to perform a mandibular thrust aids in the opening of the mouth. The placement of the i-gel follows the curvature of the tongue and the device is advanced into position after passing the tongue base. There usually is a final jolt, felt in the hand when the i-gel reaches its final snug position, felt similarly in supine and prone position placement. Thereafter it can be taped or tied to remain in position. The final choice, of which intubation method and device will be used, is decided by the anesthesiologist.

Created in 2007, the i-gel is a versatile device capable of providing safe effective anesthesia in fasted patients, as mentioned earlier. The various operations it can be used for are for those lasting up to 4 h, ideally for procedures of the neck down and used with caution involving abdominal distention and pressures [3]. Prone position I-gel use adds a new dimension of possibilities for additional procedures on the backside of patients. The list of possible procedures can span from esthetic plastic

*Anesthesia in Plastic Surgery: Intersurgical I-gel Placement in a Prone Position DOI: http://dx.doi.org/10.5772/intechopen.106538*

**Figure 3.** *Intersurgical i-gel laryngeal device (flexibility).*

to abdominal, vascular, orthopedic, urology, gynecology, fiberoptic guidance, and numerous beneficial pediatric uses [3]. As with any anesthetic method complications can always arise. They can be of various intensities, from mild to severe, and these are mentioned further into the chapter. The anesthesiologist must weigh out the risks and benefits prior to every anesthesia they perform.

## **3. Comparison of supine and prone intubations**

The supine position, laying flat on the back with the head placed in a neutral position, is the most common intubating position. The patient, following intubation with either an ET tube or laryngeal device, can be moved into desired postions, to facilitate the operative areas. Caution with laryngeal device use, as some movements may cause displacement.

When performing a supine induction with an ET tube, a hypnotic, an opiate, and a muscle relaxant (paralytic) are given to aid in its placement. This completely relaxes (paralyzes) all the muscles in the body. In contrast, a supine induction with an i-gel requires just a hypnotic and opiates. Following intubation, the patient can then be placed into desired positions, extreme caution must be used not to cause injury, when the patient is fully relaxed and paralyzed.

The anesthesiologist is the voice of the team and sets the start of patient positioning and movements. All movements must be thoroughly planned and synchronized. This ensures that everyone involved moves at the same time, to avoid injuries.

Prone position induction begins with the patient placing themselves onto the operating table, in the most comfortable head and body position. A good visual image is, as if they are sunbathing (**Figure 4**).

**Figure 4.** *Patient oxygenation in prone position. Patient in prone position with i-gel.*

Their hands and arms are placed in extensions, in a somewhat relaxed forwards position. An added benefit of this method, is that the patient positions themselves, avoiding pressure points that can cause injury. This is especially important, when lying in position for a greater length of time. The induction can begin, when the patient has found their most comfortable body and head position. Another advantage is determining can they tollerate such a position. High BMI patients may have difficulty in ventilation but this can be visualized prior to anesthesia. Finding their most comfortable position is key. The operating table can be adjusted to help further. At PB, patients with an increased BMI are routine. Extreme BMI (over 40 kg/m2 ) patients are advised beforehand, to reduce weight and are guided by a nutritionist to prepare them, for future procedures.

Prone positioning induction, following patient position, intravenous access (can be placed earlier) and monitoring attachment, begins with preoxygenation. A mask with flowing oxygen is placed near the mouth of the patient, not too close to the mouth as to cause discomfort or stress. A hypnotic and an opiate drug are used. When the patient has lost eyelash reflexes and is asleep, the laryngeal device (i-gel) can be placed. The anesthetic technician assists in a gentle mandibular thrust, in order to open the mouth, while the anesthesiologist places the device into the pharynx. The use of your index finger to gently move the tongue away, if needed, to aid in i-gel placement is helpful. The sensation of the device "sitting into position "is similar as when applying the device in the supine position. Attachment to the anesthetic

## *Anesthesia in Plastic Surgery: Intersurgical I-gel Placement in a Prone Position DOI: http://dx.doi.org/10.5772/intechopen.106538*

machine, parameters and quality check of ventilation are the same. Often fixation of the i-gel is not necessary in the prone position, as the position itself prevents the i-gel displacement. The eyes, ears, and neck flexion/extension need to be checked. The operating table is then tilted up to 10–20° angle, in an anti-Trendelenburg position (head slightly higher than feet). This reduces potential secretions draining from the gastrointestinal tract. In the event of visible drooling, gentle suctioning around, through the gastric port and the main i-gel channel can be done. Remember that all patients using this technique need to be well fasted. It is also advisable to have a stretcher bed near by, in the event you need to turn the patient quickly over onto their back, for any reason.

The avoidance of muscle relaxants (paralytics), reduced rotations, better patient and staff protection are some of the reasons why many centers worldwide, and PB, are using this prone method, for planned and well fasted patients, in selected operations. At PB, only the Intersurgical i-gel is used for the prone position method.

Magnetic resonance imaging (MRI) can show anatomical coverage in a prone position, with the head turned to the right side (**Figure 5**, Courtesy of Special Hospital AGRAM, Zagreb, Croatia) [4].

The imaging done in this position, may have been the first of its kind. When compared to supine MRI imaging, the anatomy is similar. Unfortunately, due to the limitations of the radio frequency (RF) head coil, an image with a i-gel in place,

#### **Figure 5.**

*MRI image of prone position with head turned to the right side (courtesy of Special Hospital AGRAM, Zagreb, Croatia).*

in a prone position, was unattainable for safety reasons. Limited head and i-gel device space, in a prone position, were the main factors.

## **4. Possible complications of prone position**

The prone position, as with any intubating position, can have various complications [5–9]. The most common complications can be secretional aspiration, air leakage—improper fit of the i-gel device, increased abdominal and thoracic pressures, tongue swelling, tongue cyanosis, and hypoglossal nerve injury [10–15]. Mentioned earlier, is the importance of a patient being well fasted, to avoid obvious food aspirational risks. Secretions in a fasted patient can also cause aspiration, but to a reduced effect. This can be avoided to gently aspirate around and through the i-gel, if present.

Air leakage around the i-gel can occur, reducing tidal voume and compromising ventilation, if the i-gel is too small. A properly sized i-gel can alleviate this issue (sizing by weight on packaging).

Heavy BMI patients can have ventilation difficulty, due to increased abdominal and thoracic pressures. The anti-Trendelenburg position can be increased to reduce these pressures and aid in better ventilation. An added benefit, of the patient positioning themselves, is the ability to observe position tolerance, while they are still awake. For the increased BMI patients, in prone, the increased operation table adjustment was enough, to normalize the higher thoracic pressures, to have adequate ventilation throughout the procedures.

Patients with gastroesophageal reflux disease (GERD) have been done successfully, in prone with the i-gel during the first phase of a liposuction procedure at PB. However, upon rotation into a supine position they are intubated with an endotracheal tube, for the remainder of the operation. This is also true for planned extended liposuction with abdominoplasty. Following rotation into supine, a switch is made from i-gel to ET, with the addition of an urinary catheter to monitor output, as well as hydration.

Continuous suctioning through the i-gel port is not recommended. This could have an effect on ventilation values and the patient's attempts to breath spontaneously. Patients can and should be encouraged to breath spontaneously while in the prone position. This is also an effective method, for heavy BMI patients, to reduce abdominal and thoracic pressures.

Intersurgical the manufacturer of the i-gel device recommends a maximum 4 h of use [3]. This is mainly due to pressure sores developing in the parynx where the i-gel comes into direct contact with the mucosa and base of the tongue. With prone position the i-gel pressure points are in different areas as compared to the supine position. Therefore, an extended length of usage time is possible, up to an additional 2–3 h, after rotating from prone to supine. At PB, this is done often and with minimal or no issues. There have been a few incidences of regional numbness of the tonuge, minor swelling, throat soreness, which resolved in a few days or weeks, without permanent damage, and with no special interventions necessary. In some instances, a low dose of dexamethasone (8 mg) was sufficient to reduce swelling, if present. The patients were explained the causative factor and followed up, with all of them making a full recovery of these minor injuries. There have been documented complications, at other institutions, with laryngeal devices of premolar toothloss, tongue cyanosis and hypoglossal nerve injury [11, 14, 15]. However, at PB these more serious complications have not been observed. The majority of these serious complications involved classic laryngeal mask devices, not the i-gel, since the i-gel was created in 2007 [3].

All in all, PB has had great success using the prone position induction method, for over 3 years, with minimal complications. As with all induction methods, anethesiologists must have a back up plan and always be prepared for the unexpected.

## **5. Induction for esthetic plastic procedures**

At PB a variety of esthetic plastic procedures are available. Some larger operations requiring general anethesia, may rotate patients several times, while for others only one patient position is necessary. For operations involving the head, neck, ears, face an ET intubating method is used, while for breast augmentation, reduction and lifting a laryngeal device (i-gel) is preferred. For some procedures, a combination of both can be used. The final choice lies in the decision of the anesthesiologist, however, for longer operative times, an ET tube is preferred [5, 6].

Since 2019, at Poliklinika Bagatin 756 various procedures have been performed during the pandemic era (**Table 1**).

Computer simulations using the VECTRA XT 3D, aid in displaying visual results of some postoperative procedures, before and after imaging. The VECTRA captures body images, 360° measurements and imaging, taking only a few seconds to produce a simulated image [16–18]. This is an added benefit where reconstructive plans can be worked out in detail with the surgeon and patient before the actual operation.

During the pandemic era, this was a challenging time. New protocols and safety precautions had to be created and followed. More online consultations were performed, followed by shorter in person visits, to reduce exposure risk. Masks, sanitizing gel, body temperature control, ozone devices, constant cleaning of offices, examination and operating rooms were the norm. Paradoxically, there was an increased interest in esthetic plastic procedures during this period. Perhaps, this was due to working from home. Patients were able to avoid taking off sick days for procedures, recovery was in the privacy of their home and not as noticeable, as it would be having to return to their workplace. The percentages of the most common procedures performed at Poliklinika Bagatin, during the pandemic era, are presented in **Figure 6**.

As seen from the table and graph, the prone position is used for total body liposuction (with or without abdominoplasty). The operations usually begin on the backside of the patient and following completion, the patients are turned around to complete

#### **Table 1.**

*Esthetic plastic operative procedures poliklinika bagatin from November 2019 to January 2022 (the pandemic era).*

**Figure 6.**

*Esthetic plastic operative procedures Poliklinika Bagatin during the pandemic era.*

the frontside [19, 20]. At this point, following roation, a decision will be made to the length of the procedure, whether to keep the i-gel in place for the remainder of the operation, or if an ET tube will be placed. If abdominoplasty is planned, an ET tube is placed (the procedure can be lengthy and last more than 4 h). However, if only liposuction is planned, often the i-gel will remain, as the procedure will last up to 2 h more in the new supine position.

Other uses of the i-gel are with breast augmenation procedures, in estimated operative times up to 4 h. If more time is expected, such as with reduction, lifting and lipofilling, then an ET tube is preferred.

Ritidectomy (Face Lifting), septorhinoplasty, cleft lip corrections, palatal expansion, and various dental procedures require intubation with an ET tube.

As a private clinic, PB needs to provide safe anesthesia and surgery at a highest level. Providing a method without the use of muscle relaxants reduces recovery time, reduces muscle fatigue, and helps patients be prepared for discharge. However, in the event they are not ready, other arrangements are in place to care for them until they can safely go home [7].

## **6. Conclusion**

This chapter reflects on a successful 3 year period, at PB, in which the prone position induction was introduced in 2018, for certain esthetic plastic procedures. The clinic has benefited from easier patient preparation, less patient rotation, reduced muscle relaxant (paralytic) drug use and increased safety for patients and staff.

Some clinicians may not believe in the i-gel as a reliable laryngeal device, and may reserve its use only for emergencies. However, the i-gel is an unique and extremely useful device, with a wider scope of delivery, that has changed anaethesia today [21]. This chapter explains that the i-gel can be used in uncommon induction positions safely. Future analysis of pulmonary pressure differences using the i-gel in prone and supine position, in the same patient after roation, are being gathered. Also, a study to compare tongue complications in prone and supine, with an i-gel in situ for 4 h is being developed. There are numerous fascinating aspects to observe and present with this method of intubation. Its use has been very reliable and valuable [9]. However, most importantly are the patient, staff and clinic benefits, using this safe and secure

method, for a variety of procedures. PB finds the i-gel a remarkable and useful device, and will continue to use it and the prone position induction method, for years to come, after their successful introduction.

## **7. Discussion**

After researching the use of i-gel in the prone position, we have found its usefulness in Japan, India, Germany, Netherlands, Denmark, Spain, Portugal, Poland, Croatia and even sporadic uses in the UK. A special thank you to all the colleagues who gave feedback about the use of i-gel in prone position. Initial experiences with this method, I personally observed in Porto, Portugal at the CICA Centar (a beautifully organized 1 day ambulatory surgery clinic) in 2014, and its use was routine. This method used Worldwide is intended for shorter duration procedures performed dorsally on the back, arms, legs ideally for any back side region. As asked by one editor, could it be used for spinal operations? Indeed, potentially it could be used for minor spinal procedures which are shorter in length, and not expected to develop serious complications intraoperatively, which would require converting to a deeper and more secure form of airway control and anesthesia. In the Netherlands this method of prone i-gel use is used for selected spinal operations since 2013 [22]. It is an excellent method to consider, for example, in lipoma excision, pilonidal sinus, achilles tendon heel repair, prone jackknife position for hemorroids, certain radiological exams or total body liposuction. Anesthesiologists are constantly faced with risks, never knowing when something may go awry. In general, being ultra prepared and choosing the least risky route, with patient safety as a leading determinate, are the mainstays of anesthetics. Throughout history most innovative new devices, techniques, methods, etc.… have been created to simplify and make our work easier. The technique, for PB, has been shown to be safe, reliable and a valuable alternative to the classic intubation and rotational methods being used. Regardless of the method used, patient's safety should come first. Remember, there can be many routes to get to our final destination, but get there safely. The ultimate choice lies with the anesthesiologist.

## **Author details**

Judith Adrianne Deutsch1 \*, Kata Šakić2,3, Dinko Bagatin4 , Johann Nemrava4 and Tomica Bagatin<sup>5</sup>

1 Anaesthesiology, Resuscitation and Intensive Care, Polyclinic Bagatin, Croatia

2 Faculty of Dental Medicine and Health Osijek, Anaesthesiology, Resuscitation and Intensive Care, University of Osijek, Croatia

3 School of Medicine University of Zagreb, Polyclinic Bagatin, Croatia

4 Faculty of Dental Medicine and Health Osijek, General and Plastic Reconstructive and Aesthetic Surgery, University of Osijek, Polyclinic Bagatin, Croatia

5 Faculty of Dental Medicine and Health Osijek, University of Osijek, Polyclinic Bagatin, Croatia

\*Address all correspondence to<EMAIL_ADDRESS>
© 2022 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Section 3


**Author details**

Haifeng Chen\*

Address all correspondence to<EMAIL_ADDRESS>
U.S. Food and Drug Administration, CFSAN/OARSA/DMB, Laurel, MD, USA

The views and opinions expressed in this article are those of the author and do not necessa‐ rily reflect the official views of the U.S. Food and Drug Administration (FDA).


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**34**


**Author details**

Dalip Singh India EnMS Consulting Pvt Ltd and AEE, Delhi, India

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**5. Summary**

This chapter presented observations showing that a jointed rock mass responds to temperature fluctuations. First, we presented a few examples of measurements observed at several monitoring stations around the world. The difficulty in field measurements is to isolate the effect of temperature from other environmental factors, such as water pressure in joints due to a freezing and thawing process. For this reason, Mount Masada is a preferred site for testing thermal mechanisms because of the prevailing desert conditions, where there is usually no pore pressure or freezing of underground water.

Then, a ratchet mechanism was used to explain how temperature changes can lead to cumulative displacement along a rock slope. Laboratory results of models of different sizes were presented, and the effect of the wedge size was demonstrated. Numerical analyses using 3DEC illustrate the effect of the wedge inside the tensile crack. We have seen that the wedge generally accelerates the cumulative response of the block system, and the maximum response occurs where the wedge length in about a third of the length of the sliding block.

The numerical analyses also make it possible to examine the contribution of daily and annual fluctuations. We saw that in the model of the block in Masada, the daily temperature fluctuations do not affect the block due to its large size. However, a sequence of several days with extreme temperatures for the season can lead to a cumulative response. Finally, based on the numerical analysis, rocks made of material with a high thermal expansion coefficient will respond more to the thermal mechanism.

### **Acknowledgements**

I thank Prof. Yossi Hazor for his support throughout the research. The laboratory work and the numerical analyses were carried out by Aviran Feldheim and Yuval Keissar, with the support of the Israel Science Foundation under contract no. ISF 1442/13. Christine Detournay from Itasca Consulting Group is thanked for her contribution.

## **Author details**

Dagan Bakun-Mazor Shamoon College of Engineering, Beer-Sheva, Israel

\*Address all correspondence to<EMAIL_ADDRESS>
© 2022 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

*Rock Slope Stability under Temperature Fluctuations DOI: http://dx.doi.org/10.5772/intechopen.108464*


**10. Enzymes for grape juice and wine production**

Grape (*Vitis vinifera*) production can be found on every continent except Antarctica because the vine plant is able to adapt to a wide range of environments, and because of the increasing importance of fermentation-based industries in the world economy. The grape berry has three major types of structures (**Figure 9**): pulp (80–85% of total weight), skin (7–11%), and seed (2–6%) [60], with the sheer bulk of juice being derived from the pulp, and remarkably, aromas and red grape juice colour is derived from the skin. Enological enzymes can be used at several stages in juice and wine processing and their application in the wine industry started in the 70s [61]. The main stages for winemaking are: a) pre-fermentation processing, b)

**Figure 8.** *Effect of 10 U PGzyme /ml at 40°C on the Hard-to-cook beans (HTCB) during soaking and cooking time [59].*

**Figure 9.** *Grape berry diagram and tissue organisation.*

fermentation, c) post-fermentation processing, and ageing. Enzymes can be used in the first and third stages to improve: juice extraction, clarification, filtration, colloidal stability (by preventing haze from forming later in processing), aroma extraction, and in the case of red grapes, to improve colour extraction.

#### *Fungal Pectinases in Food Technology DOI: http://dx.doi.org/10.5772/intechopen.100910*

Commercial pectolytic enzyme preparations commercialised for grape juice and wine production are actually complex mixtures of several enzymes that degrade the cell walls and middle lamella of grape tissues, as well as polysaccharide colloids of the produced grape juices. The main enzyme activity of commercial preparations is polygalacturonase (*exo*- and *endo*-PG) accompanied with pectin lyase (PNL) [62]. In addition, these commercial preparations contain other enzymes that act in synergy with the former activities, among which, cellulases, hemicellulases, and other glycosidases (α-L-rhamnosidase, α-L-arabinofuranosidase, β-D-glucosidase) potentiate the lytic effect of these commercial enzyme preparations. When grape berries are infected by the mould *Botrytis cinerea* (grey rot or "pourriture grise") it is recommended to use specific pectolytic preparations that also contain *exo* β-(1 ! 3) glucanases and β-(1 ! 6) glucanases that degrade the β-D-glucan macromolecules produced by the mould and responsible for grape juice and wine spoilage [63]. Currently, commercial pectolytic enzyme preparations for enological use come from fungi belonging to the *Aspergillus* [37] and *Trichoderma* [61] genera that possess the status of GRAS organisms. Moreover, the International Organisation of Vine and Wine (OIV) requires manufacturers to inform their customers if the enzymes supplied have been produced from genetically modified organisms (GMOs). This information must be given either on the product label or on the technical documentation (resolution OIV-OENO 485–2012) and currently, both consumers and winemakers are not in favour of the GMO origin.

The endogenous pectolytic activities of grape cells and those of the wine fermenting yeasts [64] also participate in the whole lytic process of grape tissues. It is worth noting that only a low percentage (about 11.5%) of indigenous fungi strains associated with grapes and wine have been reported to be able to produce significant amounts of extracellular pectinases under enological conditions. Those strains belonged to *Aureobasidium pullulans, Filobasidium capsuligenum* [65] and to the yeast species included in **Table 2**. Under winemaking conditions, ethanol and sulphurous anhydride can be present at concentrations reaching 15% (vol/vol) and 120 mg L�1 respectively, which are quite restrictive conditions for grape and yeast pectinase activities [66] and to a lower extent, also for pectinase activities produced by filamentous fungi. These organisms have evolved to infect plant cells, they are well adapted to overcome the plant cell barriers and to degrade vegetable cell walls and pectic substances, as demonstrated by the number of pectinase encoding genes identified in fungi.

#### **11. Grape processing and juice extraction**

Destemming and crushing of grape berries are the first mandatory procedures for grape juice extraction, and simultaneously maceration starts as grape skins are torn into smaller pieces. At this stage, commercial pectolytic enzyme preparations can be used to degrade the polysaccharides of cell walls and middle lamella, thus facilitate juice release, liberation of polyphenols (pigments, tannins) and aroma molecular precursors that are located at the skin cells [67]. Pectolytic enzymes used in enology are selected preparations that are active at the acidic pH of grape juices (pH 3.0–4.0) under enological conditions and within wide limits of temperature [68], although at lower temperatures (15–5°C) the pectolytic activity decreases [37]. Pectolytic enzymes allow better extraction of the juice, but they also allow better extraction of the components of skins and occasionally of seeds. As shown in **Figure 9**, the pulp intermediate zone is easily released and crushed, whereas the peripheral zone, which includes skin cells, is the most difficult to extract and needs extra pressure to release its components. If grapes are not ripe enough, extraction of vegetal and astringent compounds from skins and seeds will depreciate the juice

quality. In this case, the fruit should be processed without the addition of pectolytic enzymes and avoiding maceration procedures, and consequently, the yield will considerably decrease, but the obtained juice will be low in bitterness and astringency. Thus, we see that enzyme addition at this stage should be wisely used to improve grape varietal characteristics and give character to the juice and wine. Normally, the more the damage is done to the skin and internal berry cell walls, the greater the release of berry components. Consequently, both aromas and flavours increase.

In the case of red-wine making, red grape skins are allowed to be present during the alcoholic fermentation and the polyphenols responsible for the red colour and sensory properties such as astringency or mouth-filling, which include anthocyanins and tannins among others, are further extracted as the ethanol produced during the fermentation facilitates their release from skin cells [69]. In the case of white and rosé wines, grape musts are submitted to pressing avoiding further contact with skins and seeds.