Veterinary Clinical Services
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Veterinary Clinical Services |
1999 ACLAM forumAnesthesia monitoring systemsSimon S. Young MA, VetMB, PhD, DVA, DiplECVA. Schering-PloughResearch Institute, Kenilworth, NJ, USA
Why monitor during anesthesia?The ideal anesthetic agent would produce reversible unconsciousness and analgesia (i.e. absence of response to painful stimuli) with no effect on other homeostatic measurements. Unfortunately, no anesthetic drugs meet this standard and they all affect other body systems to some extent. The most important and serious side effect of anaesthetic drugs is depression of respiration and the cardiovascular system. There are two reasons why these side effects are important:
Point (1) affects the way in which anaesthetic drugs are given. Compared to other drugs, anaesthetic are highly toxic. The therapeutic index of propofol, for example, is 4.5 (Glen and Hunter 1984). This range is comparable to that seen with normal inter-animal variability, which means that what is an effective dose for one animal may be ineffective for another (i.e. they don't go to sleep) and too large for others (marked cardiovascular and respiratory depression). Smith (1993) noted considerable variability in the depth of anesthesia in laboratory animals. The only way that these drugs can be used safely is to administer them on an individual basis and observe (or monitor) their effects in that particular animal. Since we know that our anesthetic drugs will produce significant side effects, and these side effects are serious for the animal, we must treat the side effects if necessary. Some treatments can be applied "blindly" with little monitoring of their effect. For example, it is recommended that supplemental oxygen is given to all anesthetized animals whether or not they are hypoxaemic. The rationale for such blind treatment is that inhalation of an oxygen-rich mixture will not harm animals if they are not hypoxic and will benefit animals that are. Vender et al. (1995), for example, showed that rats anesthetized with a standard regimen become hypoxaemic and this can be reversed with oxygen supplementation. Even with this apparently innocuous procedure there are problems. Firstly, prolonged administration of oxygen is harmful (Hall and Clarke 1991 p.49) and when oxygen is given for hours or days the inspired concentration must be titrated against arterial oxygen saturation. Secondly, and much more important, administration of oxygen does not guarantee that an animal will not become hypoxaemic. if its airway is obstructed no amount of supplemental oxygen will help. Thus arterial oxygenation should be monitored during anesthesia even if supplemental oxygen is given. When we consider the other main side effect of anesthesia, cardiovascular depression, the argument for monitoring is even more compelling. Anaesthetic agents in general depress the myocardium and cause peripheral vasodilatation. Both of these effects lead to hypotension, although the degree depends upon the state of the circulation and the health of the animal (Booke et al. 1996, Goodchild and Serrao 1989). In addition, there will be other causes of hypotension such as blood loss and vascular compromise. Mild hypotension is tolerated by healthy animals but prolonged moderate hypotension (mean arterial pressure < 6OmmHg) produces renal shutdown. if this persists for a long time the animal can go into renal failure. In large animals, a mean arterial pressure of < 60 mmHg is insufficient to perfuse the muscles and leads to post-anaesthetic myopathy (Lindsay et al. 1989). if the blood pressure falls further, vital organ perfusion is affected. Cerebral autoregulation is lost at a mean pressure of 60 mmHg (Aitkenhead and Smith 1990 p.605) and myocardial perfusion is dependent upon an adequate diastolic pressure (Aitkenhead and Smith 1990 p. 55). If perfusion of the heart or brain is compromised the animal will rapidly deteriorate and die. There are, therefore, good reasons to control blood pressure during anesthesia. In order to control any physiological variable we need to be able to do two things: (1) measure it, and (2) change it if necessary. In the case of blood pressure control, we measure it with a variety of techniques detailed below. We can alter blood pressure in several ways: fluid administration, positive inotropes (such as dobutamine) and reducing the depth of anesthesia will increase blood pressure. Reduction of blood pressure is rarely needed in veterinary anesthesia but is common in human anesthesia and vasodilators (e.g. sodium nitroprusside) are widely used. The same arguments can be applied to other less critical parameters such as body temperature. General anesthetics interfere with temperature regulation both by depressing the hypothalamic centers and by suppressing heat generation mechanisms such as shivering. Mild to moderate hypothermia does not kill animals but leads to other problems, the most important being prolonged recovery from anesthesia. Again, to control body temperature and maintain it at the normal level we need to have a means of measuring temperature (a thermometer) and controlling it (heating blankets, insulation etc). One common question with regard to monitoring is "How much monitoring do I need to use?". There is no one standard because the more invasive the procedure, and hence the more likely it is to interfere with normal homeostasis, the greater the need for monitoring. However, several attempts have been made to define minimum standards for both human and veterinary anesthesia. A key point is the importance of monitoring cardiovascular and respiratory function. The recommendations of the Association of Anesthetists of Great Britain and Ireland, for example, state that "Continuous monitoring of ventilation and circulation is essential. This may be performed by use of the human senses augmented, where appropriate, by the use of monitoring equipment". This minimum standard is directly applicable to veterinary anesthesia. In laboratory animal work it may be difficult to achieve even this level of monitoring, in an anesthetized mouse for example. The guidelines of the American Society of Anesthesiologists state that "During all anesthetics, the patient's oxygenation, ventilation, circulation and temperature shall be continually evaluated." and the guidelines emphasize the use of monitoring equipment to augment clinical observations. Another question asked is "How frequently do I need to monitor the animal?" This should be re-phrased to "How frequently do I need to write down physiological measurements?" because, as discussed above, cardiovascular and respiratory monitoring should be continuous. To be realistic, however, there is a difference between being aware that the heart rate is "about right" and actually counting the number of beats and writing it down. The former is an almost unconscious task that is performed by glancing at the ECG screen and noting that there is the usual number of QRS complexes on the screen. The latter takes time and concentration. Also, other less critical parameters such as temperature do not need to be measured continuously. Writing down the physiological variables on the anaesthetic record every 10 or 15 minutes is a good working standard. 5 minute intervals take up a significant proportion of the anesthetist’s time unless automatic monitors are used but are recommended for blood pressure monitoring in human anesthesia (Appendix). If readings are taken more than 15 minutes apart the animal can deteriorate between measurements. There is a temptation to "cut corners" on routine procedures and reduce the amount of monitoring used, in an effort to increase "efficiency" and throughput. This is not advisable. When looking at anesthetic disasters in veterinary medicine, two features are apparent. Firstly, the cases that die unnecessarily are not the complicated surgeries but the routine ones. The complicated (i.e. "interesting") cases are assigned to the most experienced staff and are well monitored. The boring neuterings are relegated to the most junior staff in the back room and forgotten - until something goes wrong. Secondly, anaesthetic disasters are not due to a single factor. The chance of the anesthetic machine suddenly failing and delivering a lethal gas mixture is extremely remote. Anesthetic disasters are due to a combination of events, none of which on its own seems important. The usual member of staff is sick so a new person is assigned to anesthesia. The batteries in the pulse oximeter were not replaced at the end of the previous day (the sick person had to leave early for a doctor's appointment), it fails after 5 minutes and replacement batteries are not to hand. All goes well until the oxygen tank runs out on the anaesthetic machine because the replacement anesthetist did not notice that the gauge (in an unfamiliar place) was reading low. The anesthetist has stepped away from the table for a couple of minutes to get some suture material from the next room. The problem with the oxygen is not seen until the surgeon notices dark blood oozing from the wound edge and calls the anesthetist back. By the time he/she has replaced the empty tank the animal is dead. This case may seem artificial but most veterinary anaesthetic misadventures involve similar factors. Not everything can be avoided but equipment problems can be reduced by purchasing good quality equipment, maintaining it and have spares on hand. A certain amount of "resource redundancy" is also advisable. Finally, it is important that staff are adequately trained in basic physiology and anesthesia so that they can recognize problems as they occur. Everyone anesthetizing animals should, for example, know that an oxygen saturation of <70% requires attention and be able to instigate appropriate corrective measures (check the airway, supply 100% oxygen and commence IPPV). This problem is most serious in laboratory animal anesthesia of rodents where the anesthesia is carried out by the principal investigator (PI) who often has no knowledge of, and very little interest in, animal anesthesia. Why do we need monitoring equipment?There are three main reasons why we need monitoring equipment to augment our senses.
Cardiovascular monitorsArterial blood pressureThere are two basic methods for measuring arterial blood pressure, direct and indirect. How do they work?Direct blood pressure measurement involves placing a catheter in an artery and connecting it to a transducer. In cats, rabbits and larger species the arteries are large enough to be cannulated percutaneously. A standard 22g or 24g venous catheter is suitable in many cases. Specialized arterial catheters, designed for human use, are available to make the task easier. One useful technique is the "wire-guided" or Seldinger method which makes it easier to advance the catheter up the artery. Arrow International (www.arrowintl.com) makes wire-guided arterial catheters. For smaller animals the artery has to be exposed surgically, the usual site being the femoral or carotid. Once the catheter has been placed in the vessel and secured, it is connected to a pressure transducer via a fluid-filled line. Drip tubing is often used but for the best results the tubing should be narrower and stiffer. It is important that there are no bubbles in the system. The transducer is connected to an amplifier and display unit, which shows the waveform and the systolic/diastolic/mean pressures calculated from the waveform. The shape of the waveform gives useful information about the state of the circulation, in particular the peripheral resistance. Indirect blood pressure involves inflating a cuff around the limb and monitoring the blood flow in the limb distal to the artery. The classic technique for monitoring the blood flow in humans is to listen for the Korotkoff sounds with a stethoscope. This cannot be done in animals because the arteries are too small. Blood flow can be monitored optically (e.g. on a rat's tail), using ultrasound (the Doppler system) or by the pulsations it induces in the cuff itself. The pressure in the cuff is measured with a mechanical gauge or a transducer. Automated systems such as the Dinamap are easy to use. A cuff is simply wrapped around the limb and the unit turned on. They work well in larger species such as dogs, primates and sheep but not in smaller species such as rabbits and rodents, and are marginal in cats. The Doppler system is more sensitive and works well in cats (Binns et al. 1995), but requires manual intervention to obtain a reading. Indirect systems for rodents do exist but are not used for routine anesthesia because they are fiddly to set up. They are used for research purposes. What do they tell us?The circulation should be monitored continuously during anesthesia (Wagner and Brodbelt 1997) and blood pressure measurement is one way to achieve this. The mean arterial pressure (MAP) is the overall judge of the state of the circulation. At the tissue level the fluctuations in arterial pressure are damped out so it is the MAP that determines how well tissues are perfused. As the MAP falls vital organ autoregulation and perfusion is lost. The susceptibility of tissues to poor circulation varies tremendously depending upon their metabolic rate. Skin, for example, is very tolerant of loss of perfusion whereas the heart, brain, retina and kidneys will not tolerate any significant ischaemia. The diastolic pressure (DAP) and the pulse pressure (PP, = SAP - DAP) give information about the degree of vasoconstriction and the adequacy of ventricular ejection. if the peripheral vessels dilate the DAP falls because arterial run-off increases. if cardiac ejection is good then SAP will be preserved and the low DAP leads to a large PP which can be felt as a bounding pulse. Conversely, if the animal is vasoconstricted then the DAP, SAP and MAP are all high. The PP is low so the pulse is paradoxically weaker. A low PP and low DAP indicates poor cardiac output. ElectrocardiogramHow does it work?The electrocardiogram (ECG or EKG) monitors the electrical activity of the heart. With each beat the atria and ventricles depolarize and repolarize. The depolarization and repolarization are synchronized in each chamber and thus the action potentials from each fiber summate, producing a signal that is large enough to be measured at the surface of the body. The electrical signal is picked up by electrodes, amplified and displayed on a screen. The ECG is always measured as the difference in voltage between two electrodes. Depending upon the placement of the electrodes the ECG has different shapes. If the electrodes are placed on each arm a lead I waveform is obtained. Lead II is measured from the right arm to the left leg, and lead III is measured from the left arm to the left leg. For anesthetic monitoring the lead configuration is largely irrelevant because we are not going to make detailed measurements of the complex heights and we just need a waveform that contains all the main components. A lead II type trace, with positive P, R and T wave is usually chosen. In theory only two electrodes are needed to record an ECG, since it is the voltage difference between the two electrodes. In practice a third ground electrode is needed to reject interference and the typical ECG lead arrangement for anesthetic monitoring has leads placed on the left (black connector) and right (white connector) arms and one leg (red connector). It is often easier to place the arm electrodes on either side of the chest rather than on the arms. The leg electrode can go on the inside of the thigh where the hair is tin. In primates, good results are also obtained by sticking the electrodes to the palms of the hands and feet. Getting a good electrical connection to the skin is not as simple as it appears. The ideal electrode should have a low resistance, a stable half-cell voltage and not harm the animal. The first two requirements need some explanation. The ECG machine will reject noise best if the electrodes have a low resistance, which in practical terms means they should have a reasonable surface area and the skin should be moistened with a conductive solution. The "half-cell" voltage or electrode potential is the voltage formed whenever a metallic conductor meets a conducting solution. The junction between the two forms one half of a battery and generates a characteristic voltage, the value of which depends upon the particular chemistry involved but which is always several hundred times greater than the ECG voltage. This voltage must be very stable if it is not to interfere with the ECG waveform. The ideal electrode uses silver coated with silver chloride, which has a stable half cell voltage and is compatible with the chloride ions in plasma. Commercial ECG electrodes have a piece of silver-plated foil in the center which is coated with saline gel and backed up by an adhesive pad. The problem with these electrodes is that they don't stick well to animals. We have had better success with electrodes designed for human "stress testing", which involves recording the ECG while the person exercises. These electrodes are much stickier than the normal ones. Electrodes used for veterinary work are often crude modifications of human leads. The problem is that the self-adhesive electrodes have a button connection in the middle and commercial ECG cables are made up with the corresponding clip. These clips are often cut off and other connectors substituted. "Crocodile" clips are commonly used but they are painful, they don't give a reliable contact, they have a high resistance and they corrode easily. Subcutaneous stainless steel needles are also used but they tend to fall out. Another problem with modifying the leads is that it is impossible to provide proper strain relief for the cable and it will inevitably break at the point where it is connected to the clip. In larger animals it is therefore best to use the original cable with human stress testing electrodes, but they are too big for rodents. A solution is to use pediatric electrodes on the paws and secure them with adhesive tape. What does it tell us?The electrocardiogram only monitors the electrical activity of the heart and the heart rate is derived from this. Electrocardiograms are not the first choice for cardiovascular monitoring because they tell you nothing about the mechanical function of the heart or the state of the circulation. They are essential for the diagnosis and treatment of arrhythmias, and ECG monitoring is advised during cardiac procedures such as catheterisation. They are useful in critical situations where the blood pressure has fallen so low that peripheral pulses are not palpable. Respiratory monitorsPulse oximeterHow does it work?The pulse oximeter shines red and infrared light through a thin piece of tissue such as the tongue and measures the relative absorption of the two wavelengths. From this it calculates the oxygen saturation, i.e. the ratio of oxyhaemoglobin to deoxyhaemoglobin, from absorption curves programmed into the device (Alexander, Teller and Gross 1989). What makes the pulse oximeter so useful is that it only looks at the pulsatile component of the light absorption, not the background level. The pulsatile change in tissue absorption is due to blood entering the arterioles and thus the pulse oximeter measures arterial oxygen saturation (Sa02%). What does it tell us?The pulse oximeter measures the adequacy of arterial oxygenation. Pulse oximeters are very useful monitors in anesthesia for two reasons. Firstly, arterial hypoxaemia is the final "common pathway" for many problems that occur in anesthesia such as hypoventilation, airway obstruction and equipment-related problems. A pulse oximeter can therefore pick up problems of different etiology. Secondly, hypoxia is a common and serious problem so noticing it early will prevent disasters. A pulse oximeter will detect hypoxaemia long before the animal becomes cyanosed. An added bonus is that they are relatively cheap (<US$1000) because the human market is so large. There are many pulse oximeters on the market, including some specifically designed for veterinary use. These are good because the clips are designed for animals' tongues rather than human fingers. The best site for the pulse oximeter clip varies between species. The tongue is the best site and works for larger species (Huss et al. 1995). The nasal septum can be used in pigs as well as the tall. In rodents the clip can be placed across the hind foot, and in primates the cheek works well. The absolute accuracy of pulse oximeters seems to be a little lower for animals than humans (Erhardt et al. 1990), but the trends are still important. In general a saturation of >95% is good. If it falls to <90% then the anesthetist should take note but corrective action may not be necessary, especially if the cause is known and self-limiting. When the saturation fails below <80% action should be taken to improve oxygenation. Tidal volume and respiratory rateThere are no good, inexpensive respiratory monitors on the market. Simple "beepers" are available which measure gas temperature at the endotracheal tube connector. They detect the change in temperature between inspiration and expiration. Such monitors are fiddly to set up and give no indication of depth of respiration. At the other end of the spectrum there are human multi-function anaesthetic monitors that measure airflow and airway pressure and calculate compliance (Datex Engstrom, Tewkesbury, MA) but they are expensive. Basic respiratory monitoring, therefore, tends to be based on clinical observations. If an anaesthetic circuit is used that has a reservoir bag then the rate can be counted and some idea of volume obtained by looking at the bag movements. In smaller animals this is not possible and one is limited to looking at chest movement. It is important to know the difference between normal and paradoxical respiration - inexperienced anesthetists often assume that because the chest is moving there must be airflow. A useful teaching aid is to occlude the endotracheal tube for a few breaths and note how the pattern of respiration changes. With normal respiration the abdomen and chest rise together. When the endotracheal tube is occluded there is paradoxical respiration: the abdomen moves in as the chest rises. Rabbits and rodents are commonly ventilated during anesthesia because it seems to improve their general condition, especially during long procedures. During ventilation the tidal volume and respiratory rate are controlled by the anesthetist and do not need to be monitored, but they should be set correctly! People using ventilators should know that carbon dioxide is the main stimulus for respiration, and that if the arterial carbon dioxide level is reduce below 354OmmHg the animal will not attempt to breathe. They should appreciate how altering the ventilator settings changes arterial carbon dioxide levels. A common mistake is to under-ventilate so that the animal fights the ventilator. This is misinterpreted as the animal being too light, and more anaesthetic is given. The end result is a hypercapnic animal that is too deeply anesthetized. Inappropriate ventilator settings also lead PIs to use neuromuscular blocking agents when they are not necessary. Expired carbon dioxideHow does it work?Carbon dioxide absorbs infrared light with a wavelength of 4.3m m. Light at this wavelength is shone through a gas sample and the absorption is proportional to the carbon dioxide concentration. A sample of respired gas is withdrawn from the anaesthetic circuit by a pump and analyzed inside the machine. One problem with these machines in rodents is that the gas sampling rate, about l00ml/minute, is too fast and removes excessive amounts of gas from the airway but the problem can be overcome (Larach et al. 1988). What does it tell us?A lot of information can be obtained from the continuous measurement of carbon dioxide. At the most basic level the regular rise in carbon dioxide at the end of respiration can be used to determine respiratory rate, and the regularity of respiration can also be assessed. The shape of the capnograph (the plot of carbon dioxide against time) is a good indicator of pulmonary function. The carbon dioxide level should rise rapidly during the first part of exhalation and then flatten off - the "alveolar plateau". If there is pulmonary disease or poor lung perfusion (secondary to poor cardiac output) the alveolar plateau disappears. The level of carbon dioxide at the end of expiration (end tidal carbon dioxide, etCO2) is normally within a few mmHg of the arterial carbon dioxide level. EtCO2 is very useful for assessing adequacy of ventilation both during spontaneous respiration and when using a ventilator. Volatile anesthetic concentrationHow does it work?Like carbon dioxide, the volatile anesthetic agents absorb infrared light. There are several absorption peaks that can be used, 10 - 13mm being a common one. Light at this wavelength is shone through a gas sample and the absorption is proportional to the anaesthetic vapor concentration. Absorption at other wavelengths may also be measured so that the agent being used can be identified automatically. One problem with these monitors for veterinary use is that methane produced by ruminants can interfere with the measurements (Moens and Gootjes 1993). Gas and anaesthetic vapor concentrations can also be measured using a different technology, mass spectrometry. Although these machines are expensive they will measure several gases simultaneously and they have a very fast response time. They tend to be used more for research work than clinical monitoring. What does it tell us?The monitor displays inspired and end tidal anaesthetic concentrations. The end tidal level is very close to the arterial level and it is the latter which determines depth of anesthesia. Thus when volatile agents are used as the main anaesthetic agent the depth of anesthesia can to some extent be estimated. The drawback is that the amount of volatile anaesthetic needed to abolish the response to a noxious stimulus (defined as the minimum alveolar concentration or MAC) varies between individual animals. For example, Eger et al. (1965) found that the MAC for halothane varied from 0.7 to 1.1% in 7 dogs. Nevertheless, MAC is a very useful way of comparing the potency of volatile anesthetics. Volatile anesthetic monitors are most useful when patients are anesthetized on rebreathing circuits such as the circle, because neither the inspired nor the expired anesthetic concentrations are known. They are particularly useful when animals are paralyzed with neuromuscular blocking agents because they provide some measure of security that the animal is adequately anesthetized. Non-rebreathing circuits are used almost exclusively in laboratory animal anesthesia and as long as a precision vaporizer is used the inspired anesthetic concentration is known. Arterial blood gasesHow does it work?The pH, PO2 and pCO2 of the sample are measured with specific electrodes. By equilibrating the sample against different CO2, mixtures the bicarbonate concentration is calculated. What does it tell us?Arterial blood gas analysis is the gold standard for assessing respiratory function. The gas exchange capability of the lung can be directly measured. The three main measurements made by the blood gas analyzer are used together to obtain a detailed picture of the state of the respiratory system. Oxygen: the PaO2 is the standard for measuring blood oxygenation. Decreases in PaO2 are due to hypoventilation, inspiration of hypoxic gas mixtures or impairment of gas exchange. Further information can be gained when the inspired oxygen level is changed from 21% to 100% and the PaO2 re-measured. Carbon dioxide: PaCO2 is set by the balance between CO2 production and CO2 elimination. During anesthesia, CO2 production is fairly constant so the arterial level is determined by elimination. If the lungs are healthy the etCO2 is a good substitute for PaCO2 but in pulmonary dysfunction the difference between them increases which is useful diagnostically. HCO3-, base excess, anion gap, pH: These all measure different aspects of acid-base balance. Animals with metabolic diseases may have acid-base disturbances and blood gas analysis can be used to monitor and treat them. A blood gas analyzer is not a routine piece of monitoring equipment. Interpretation of the results requires knowledge of pulmonary and renal physiology, and because the arterial sample has to be transported to the machine for analysis there is a delay in obtaining the results. However, a blood gas analyzer is invaluable for critical care patients, pulmonary research and advanced procedures such as cardiopulmonary bypass and transplantation. TemperatureHow does it work?A probe containing a thermocouple or thermistor is placed in the esophagus or rectum. The probe is connected to a small amplifier box which displays the core temperature. Infrared sensors that are placed in the ear are also available but best used for clinical examination rather than anesthesia. What does it tell us?Core body temperature. It is very important with laboratory animals to maintain body temperature. Hypothermia is the most common cause of delayed recovery from anesthesia. Body temperature can be maintained with heating lamps, electrical pads, warm air blowers or circulating water blankets. Water blankets are best because there is no risk of burning the animal. Hyperthermia is very rare in veterinary anesthesia. Horses and cows anesthetized outdoors in the summer can overheat. Malignant hyperpyrexia (MH) is a genetic disorder that is best known in pigs but also occurs in dogs. An MH attack in susceptible animals is triggered by some anesthetic drugs, the classic ones being halothane and suxamethomum. MH is usually fatal unless treated promptly with dantrolene. MH susceptible animals can be safely anesthetized by using a total intravenous technique. Neuromuscular blockadeHow does it work?Neuromuscular blocking agents act at the neuromuscular junction. By preventing transmission from the motor nerve to the motor end plate they paralyze all striated muscle. The degree of blockade can be monitored by stimulating a motor nerve and measuring the resultant muscular contraction. Nerve stimulators are simple electronic devices that produce a brief, variable amplitude electrical spike. The two electrodes are placed over a superficial motor nerve and when the machine produces a spike the motor nerve depolarizes. If no neuromuscular blocking agent has been given the muscles innervated by that nerve contract with a twitch. if the animal is fully paralyzed there will be no twitch, and as the drug wears off the twitch force will gradually increase to normal levels. The amplitude of the twitch can be assessed visually, or more objectively by measuring the force of contraction or the EMG produced by the contracting muscle. There is a great deal of literature on the interpretation of nerve stimulation because muscle relaxants are widely used in human anesthesia. What does it tell us?A nerve stimulator is an essential piece of equipment if you are using muscle relaxants in animals for recovery procedures. Before the animal wakes up from the anesthetic it is important to make sure that the effects of the muscle relaxant have worn off, and this is done using a nerve stimulator. The nerve stimulator can also be used to tell when supplementary doses of muscle relaxant are needed. References
Appendix AMERICAN SOCIETY OF ANESTHESIOLOGISTS: STANDARDS FOR BASIC ANESTHETIC MONITORING(Approved by House of Delegates on October 21, 1986 and last amended on October 21, 19981)These standards apply to all anesthesia care although, in emergency circumstances, appropriate life support measures take precedence. These standards may be exceeded at any time based on the judgment of the responsible anesthesiologist. They are intended to encourage quality patient care, but observing them cannot guarantee any specific patient outcome. They are subject to revision from time to time, as warranted by the evolution of technology and practice. They apply to all general anesthetics, regional anesthetics and monitored anesthesia care. This set of standards addresses only the issue of basic anesthetic monitoring, which is one component of anesthesia care. In certain rare or unusual circumstances, 1) some of these methods of monitoring may be clinically impractical, and 2) appropriate use of the described monitoring methods may fail to detect untoward clinical developments. Brief interruptions of continual# monitoring may be unavoidable. Under extenuating circumstances, the responsible anesthesiologist may waive the requirements marked with an asterisk (*); it is recommended that when this is done, it should be so stated (including the reasons) in a note in the patient's medical record. These standards are not intended for application to the care of the obstetrical patient in labor or in the conduct of pain management. STANDARD IQualified anesthesia personnel shall be present in the room throughout the conduct of all general anesthetics, regional anesthetics and monitored anesthesia care. OBJECTIVEBecause of the rapid changes in patient status during anesthesia, qualified anesthesia personnel shall be continuously present to monitor the patient and provide anesthesia care. In the event there is a direct known hazard, e.g., radiation, to the anesthesia personnel which might require intermittent remote observation of the patient, some provision for monitoring the patient must be made. In the event that an emergency requires the temporary absence of the person primarily responsible for the anesthetic, the best judgment of the anesthesiologist will be exercised in comparing the emergency with the anesthetized patient's condition and in the selection of the person left responsible for the anesthetic during the temporary absence. STANDARD IIDuring all anesthetics, the patient's oxygenation, ventilation, circulation and temperature shall be continually evaluated. OXYGENATIONOBJECTIVETo ensure adequate oxygen concentration in the inspired gas and the blood during all anesthetics. METHODS
VENTILATIONOBJECTIVETo ensure adequate ventilation of the patient during all anesthetics. METHODS
CIRCULATIONOBJECTIVETo ensure the adequacy of the patient's circulatory function during all anesthetics. METHODS1 .Every patient receiving anesthesia shall have the electrocardiogram continuously displayed from the beginning of anesthesia until preparing to leave the anesthetizing location. * 2.Every patient receiving anesthesia shall have arterial blood pressure and heart rate determined and evaluated at least every five minutes.* 3.Every patient receiving general anesthesia shall have, in addition to the above, circulatory function continually evaluated by at least one of the following: palpation of a pulse, auscultation of heart sounds, monitoring of a tracing of intra-arterial pressure, ultrasound peripheral pulse monitoring, or pulse plethysmography or oximetry. BODY TEMPERATUREOBJECTIVETo aid in the maintenance of appropriate body temperature during all anesthetics. METHODSEvery patient receiving anesthesia shall have temperature monitored when clinically significant changes in body temperature are intended, anticipated or suspected. #Note that "continual" is defined as "repeated regularly and frequently in steady rapid succession" whereas "continuous" means "prolonged without any interruption at any time."
1 To become effective July 1, 1999
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