(mmv) allows spontaneous breathing with automatic adjustments of mandatory ventilation to the meet the patient's preset minimum minute volume requirement. if the patient maintains the minute volume settings for vt x f, no mandatory breaths are delivered. if the patient's minute volume is insufficient, mandatory delivery of the preset tidal volume will occur until the minute volume is achieved. the method for monitoring whether or not the patient is meeting the required minute ventilation (ve) differs by ventilator brand and model, but, in general, there is a window of monitored time, and a smaller window checked against the larger window (i.e., in the dräger evita® line of mechanical ventilators there is a moving 20-second window, and every 7 seconds the current tidal volume and rate are measured) to decide whether a mechanical breath is needed to maintain the minute ventilation. mmv is an optimal mode for weaning in neonatal and pediatric populations and has been shown to reduce long-term complications related to mechanical ventilation. pressure-regulated volume control pressure-regulated volume control is an imv based mode. pressure-regulated volume control utilizes pressure-limited, volume-targeted, time-cycled breaths that can be either ventilator- or patient-initiated. the peak inspiratory pressure delivered by the ventilator is varied on a breath-to-breath basis to achieve a target tidal volume that is set by the clinician. for example, if a target tidal volume of 500 ml is set but the ventilator delivers 600 ml, the next breath will be delivered with a lower inspiratory pressure to achieve a lower tidal volume. though prvc is regarded as a hybrid mode because of its tidal-volume (vc) settings and pressure-limiting (pc) settings fundamentally prvc is a pressure-control mode with adaptive targeting. continuous positive airway pressure continuous positive airway pressure (cpap) is a non-invasive positive pressure mode of respiratory support. cpap is a pressure applied at the end of exhalation to keep the alveoli open and not fully deflate. this mechanism for maintaining inflated alveoli helps increase partial pressure of oxygen in arterial blood, an appropriate increase in cpap increases the pao2. automatic positive airway pressure automatic positive airway pressure (apap) is a form of cpap that automatically tunes the amount of pressure delivered to the patient to the minimum required to maintain an unobstructed airway on a breath-by-breath basis by measuring the resistance in the patient's breathing. bilevel positive airway pressure bilevel positive airway pressure (bpap) is a mode used during non-invasive ventilation (niv). first used in 1988 by professor benzer in austria, it delivers a preset inspiratory positive airway pressure (ipap) and expiratory positive airway pressure (epap). bpap can be described as a continuous positive airway pressure system with a time-cycle change of the applied cpap level. cpap/apap, bpap, and other non-invasive ventilation modes have been shown to be effective management tools for chronic obstructive pulmonary disease, acute respiratory failure, sleep apnea, etc. often bpap is incorrectly referred to as "bipap". bipap is the name of a portable ventilator manufactured by respironics corporation; it is just one of many ventilators that can deliver bpap. medical uses bpap has been shown to be useful in reducing mortality and reducing the need for endotracheal intubation when used in people with chronic obstructive pulmonary disease (copd). high-frequency ventilation (active) the term active refers to the ventilator's forced expiratory system. in a hfv-a scenario, the ventilator uses pressure to apply an inspiratory breath and then applies an opposite pressure to force an expiratory breath. in high-frequency oscillatory ventilation (sometimes abbreviated hfov) the oscillation bellows and piston force positive pressure in and apply negative pressure to force an expiration. high-frequency ventilation (passive) the term passive refers to the ventilator's non-forced expiratory system. in a hfv-p scenario, the ventilator uses pressure to apply an inspiratory breath and then returns to atmospheric pressure to allow for a passive expiration. this is seen in high-frequency jet ventilation, sometimes abbreviated hfjv. also categorized under high frequency ventilation is high frequency percussive ventilation, sometimes abbreviated hfpv. with hfpv it utilizes an open circuit to deliver its subtidal volumes by way of the patient interface known as the phasitron. volume guarantee volume guarantee an additional parameter available in many types of ventilators that allows the ventilator to change its inspiratory pressure setting to achieve a minimum tidal volume. this is utilized most often in neonatal patients who need a pressure controlled mode with a consideration for volume control to minimize volutrauma. spontaneous breathing and support settings positive end-expiratory pressure positive end expiratory pressure (peep) is pressure applied upon expiration. peep is applied using either a valve that is connected to the expiratory port and set manually or a valve managed internally by a mechanical ventilator. peep is a pressure that an exhalation has to bypass, in effect causing alveoli to remain open and not fully deflate. this mechanism for maintaining inflated alveoli helps increase partial pressure of oxygen in arterial blood, and an increase in peep increases the pao2. pressure support pressure support is a spontaneous mode of ventilation also named pressure support ventilation (psv). the patient initiates every breath and the ventilator delivers support with the preset pressure value. with support from the ventilator, the patient also regulates their own respiratory rate and their tidal volume. in pressure support, the set inspiratory pressure support level is kept constant and there is a decelerating flow. the patient triggers all breaths. if there is a change in the mechanical properties of the lung/thorax and patient effort, the delivered tidal volume will be affected. the user must then regulate the pressure support level to obtain desired ventilation. pressure support improves oxygenation, ventilation and decreases work of breathing. also see adaptive support ventilation. other ventilation modes and strategies negative pressure ventilation main article: negative pressure ventilator negative-pressure ventilation stimulates (or forces) breathing by periodic application of partial vacuum (air pressure reduced below ambient pressure), applied externally to the patient's torso—specifically, chest and abdomen—to assist (or force) the chest to expand, expanding the lungs, resulting in voluntary (or involuntary) inhalation through the patient's airway. various "negative pressure ventilators" (npvs) have been developed to serve this function—most famously the "iron lung," a tank in which the patient lays, with only their head exposed to ambient air, while air pressure on the remainder of their body, inside the tank, is varied by pumping, to stimulate chest and lung expansion and contraction. though not in wide use today, npvs were the principal forms of hospital and long-term mechanical ventilation in the first half of the 20th century, and remain in limited use today. adaptive support ventilation adaptive support ventilation (asv) is the only commercially available mode that uses optimal targeting. this ventilation mode was invented and subsequently patented in 1991 by tehrani in this positive pressure mode of ventilation, the frequency and tidal volume of breaths of a patient on the ventilator are automatically adjusted and optimized to mimic natural breathing, stimulate spontaneous breathing, and reduce weaning time. in the asv mode, every breath is synchronized with patient effort if such an effort exists, and otherwise, full mechanical ventilation is provided to the patient. automatic tube compensation automatic tube compensation (atc) is the simplest example of a computer-controlled targeting system on a ventilator. it is a form of servo targeting. the goal of atc is to support the resistive work of breathing through the artificial airway neurally adjusted ventilatory assist neurally adjusted ventilatory assist (nava) is adjusted by a computer (servo) and is similar to atc but with more complex requirements for implementation. in terms of patient-ventilator synchrony, nava supports both resistive and elastic work of breathing in proportion to the patient's inspiratory effort proportional assist ventilation proportional assist ventilation (pav) is another servo targeting based mode in which the ventilator guarantees the percentage of work regardless of changes in pulmonary compliance and resistance. the ventilator varies the tidal volume and pressure based on the patient's work of breathing. the amount it delivers is proportional to the percentage of assistance it is set to give. pav, like nava, supports both restrictive and elastic work of breathing in proportion to the patient's inspiratory effort. liquid ventilation liquid ventilation is a technique of mechanical ventilation in which the lungs are insufflated with an oxygenated perfluorochemical liquid rather than an oxygen-containing gas mixture. the use of perfluorochemicals, rather than nitrogen, as the inert carrier of oxygen and carbon dioxide offers a number of theoretical advantages for the treatment of acute lung injury, including: reducing surface tension by maintaining a fluid interface with alveoli opening of collapsed alveoli by hydraulic pressure with a lower risk of barotrauma providing a reservoir in which oxygen and carbon dioxide can be exchanged with pulmonary capillary blood functioning as a high-efficiency heat exchanger despite its theoretical advantages, efficacy studies have been disappointing and the optimal clinical use of lv has yet to be defined. total liquid ventilation in total liquid ventilation (tlv), the entire lung is filled with an oxygenated pfc liquid, and a liquid tidal volume of pfc is actively pumped into and out of the lungs. a specialized apparatus is required to deliver and remove the relatively dense, viscous pfc tidal volumes, and to extracorporeally oxygenate and remove carbon dioxide from the liquid. partial liquid ventilation in partial liquid ventilation (plv), the lungs are slowly filled with a volume of pfc equivalent or close to the frc during gas ventilation. the pfc within the lungs is oxygenated and carbon dioxide is removed by means of gas breaths cycling in the lungs by a conventional gas ventilator.