use, that the safety features are active and the electrical hazards are removed. intravenous anesthetic is delivered either by bolus doses or an infusion pump. there are also many smaller instruments used in airway management and monitoring the patient. the common thread to modern machinery in this field is the use of fail-safe systems that decrease the odds of catastrophic misuse of the machine. monitoring an anesthetic machine with integrated systems for monitoring of several vital parameters. patients under general anesthesia must undergo continuous physiological monitoring to ensure safety. in the us, the american society of anesthesiologists (asa) has established minimum monitoring guidelines for patients receiving general anesthesia, regional anesthesia, or sedation. these include electrocardiography (ecg), heart rate, blood pressure, inspired and expired gases, oxygen saturation of the blood (pulse oximetry), and temperature. in the uk the association of anaesthetists (aagbi) have set minimum monitoring guidelines for general and regional anesthesia. for minor surgery, this generally includes monitoring of heart rate, oxygen saturation, blood pressure, and inspired and expired concentrations for oxygen, carbon dioxide, and inhalational anesthetic agents. for more invasive surgery, monitoring may also include temperature, urine output, blood pressure, central venous pressure, pulmonary artery pressure and pulmonary artery occlusion pressure, cardiac output, cerebral activity, and neuromuscular function. in addition, the operating room environment must be monitored for ambient temperature and humidity, as well as for accumulation of exhaled inhalational anesthetic agents, which might be deleterious to the health of operating room personnel. sedation further information: sedation sedation (also referred to as dissociative anesthesia or twilight anesthesia) creates hypnotic, sedative, anxiolytic, amnesic, anticonvulsant, and centrally produced muscle-relaxing properties. from the perspective of the person giving the sedation, the patient appears sleepy, relaxed and forgetful, allowing unpleasant procedures to be more easily completed. sedatives such as benzodiazepines are usually given with pain relievers (such as narcotics, or local anesthetics or both) because they do not, by themselves, provide significant pain relief. from the perspective of the subject receiving a sedative, the effect is a feeling of general relaxation, amnesia (loss of memory) and time passing quickly. many drugs can produce a sedative effect including benzodiazepines, propofol, thiopental, ketamine and inhaled general anesthetics. the advantage of sedation over a general anesthetic is that it generally does not require support of the airway or breathing (no tracheal intubation or mechanical ventilation) and can have less of an effect on the cardiovascular system which may add to a greater margin of safety in some patients.: 736 regional anesthesia further information: conduction anesthesia sonography guided femoral nerve blockbackflow of cerebrospinal fluid through a spinal needle after puncture of the arachnoid mater during spinal anesthesia when pain is blocked from a part of the body using local anesthetics, it is generally referred to as regional anesthesia. there are many types of regional anesthesia either by injecting into the tissue itself, a vein that feeds the area or around a nerve trunk that supplies sensation to the area. the latter are called nerve blocks and are divided into peripheral or central nerve blocks. the following are the types of regional anesthesia:: 926–31 infiltrative anesthesia: a small amount of local anesthetic is injected in a small area to stop any sensation (such as during the closure of a laceration, as a continuous infusion or "freezing" a tooth). the effect is almost immediate. peripheral nerve block: local anesthetic is injected near a nerve that provides sensation to particular portion of the body. there is significant variation in the speed of onset and duration of anesthesia depending on the potency of the drug (e.g. mandibular block, fascia iliaca compartment block). intravenous regional anesthesia (also called a bier block): dilute local anesthetic is infused to a limb through a vein with a tourniquet placed to prevent the drug from diffusing out of the limb. central nerve block: local anesthetic is injected or infused in or around a portion of the central nervous system (discussed in more detail below in spinal, epidural and caudal anesthesia). topical anesthesia: local anesthetics that are specially formulated to diffuse through the mucous membranes or skin to give a thin layer of analgesia to an area (e.g. emla patches). tumescent anesthesia: a large amount of very dilute local anesthetics are injected into the subcutaneous tissues during liposuction. systemic local anesthetics: local anesthetics are given systemically (orally or intravenous) to relieve neuropathic pain. a 2018 cochrane review found moderate quality evidence that regional anesthesia may reduce the frequency of persistent postoperative pain (ppp) from three to 18 months following thoracotomy and three to 1 months following caesarean. low quality evidence was found three to 12 months following breast cancer surgery. this review acknowledges certain limitations that impact its applicability beyond the surgeries and regional anesthesia techniques reviewed. nerve blocks further information: nerve block when local anesthetic is injected around a larger diameter nerve that transmits sensation from an entire region it is referred to as a nerve block or regional nerve blockade. nerve blocks are commonly used in dentistry, when the mandibular nerve is blocked for procedures on the lower teeth. with larger diameter nerves (such as the interscalene block for upper limbs or psoas compartment block for lower limbs) the nerve and position of the needle is localized with ultrasound or electrical stimulation. evidence supports the use of ultrasound guidance alone, or in combination with peripheral nerve stimulation, as superior for improved sensory and motor block, a reduction in the need for supplementation and fewer complications. because of the large amount of local anesthetic required to affect the nerve, the maximum dose of local anesthetic has to be considered. nerve blocks are also used as a continuous infusion, following major surgery such as knee, hip and shoulder replacement surgery, and may be associated with lower complications. nerve blocks are also associated with a lower risk of neurologic complications compared to the more central epidural or spinal neuraxial blocks.: 1639–41 spinal, epidural and caudal anesthesia further information: neuraxial blockade and history of neuraxial anesthesia central neuraxial anesthesia is the injection of local anesthetic around the spinal cord to provide analgesia in the abdomen, pelvis or lower extremities. it is divided into either spinal (injection into the subarachnoid space), epidural (injection outside of the subarachnoid space into the epidural space) and caudal (injection into the cauda equina or tail end of the spinal cord). spinal and epidural are the most commonly used forms of central neuraxial blockade. spinal anesthesia is a "one-shot" injection that provides rapid onset and profound sensory anesthesia with lower doses of anesthetic, and is usually associated with neuromuscular blockade (loss of muscle control). epidural anesthesia uses larger doses of anesthetic infused through an indwelling catheter which allows the anesthetic to be augmented should the effects begin to dissipate. epidural anesthesia does not typically affect muscle control. because central neuraxial blockade causes arterial and venous vasodilation, a drop in blood pressure is common. this drop is largely dictated by the venous side of the circulatory system which holds 75% of the circulating blood volume. the physiologic effects are much greater when the block is placed above the 5th thoracic vertebra. an ineffective block is most often due to inadequate anxiolysis or sedation rather than a failure of the block itself.: 1611 acute pain management a patient-controlled analgesia infusion pump, configured for epidural administration of fentanyl and bupivacainefor postoperative analgesia nociception (pain sensation) is not hard-wired into the body. instead, it is a dynamic process wherein persistent painful stimuli can sensitize the system and either make pain management difficult or promote the development of chronic pain. for this reason, preemptive acute pain management may reduce both acute and chronic pain and is tailored to the surgery, the environment in which it is given (in-patient/out-patient) and the individual.: 2757 pain management is classified into either pre-emptive or on-demand. on-demand pain medications typically include either opioid or non-steroidal anti-inflammatory drugs but can also make use of novel approaches such as inhaled nitrous oxide or ketamine. on demand drugs can be administered by a clinician ("as needed drug orders") or by the patient using patient-controlled analgesia (pca). pca has been shown to provide slightly better pain control and increased patient satisfaction when compared with conventional methods. common preemptive approaches include epidural neuraxial blockade or nerve blocks. one review which looked at pain control after abdominal aortic surgery found that epidural blockade provides better pain relief (especially during movement) in the period up to three postoperative days. it reduces the duration of postoperative tracheal intubation by roughly half. the occurrence of prolonged postoperative mechanical ventilation and myocardial infarction is also reduced by epidural analgesia. risks and complications