Minimum alveolar anesthetic concentration

Dose-Response Characteristics The Concept of Minimum Alveolar Anesthetic Concentration the Continuum of CNS Depression... 

During inhalation anesthesia, the partial pressure of the inhaled anesthetic in the brain equals that in the lung when steady-state conditions are achieved. Therefore, at a given level (depth) of anesthesia, measurements of the steady-state alveolar concentrations of different anesthetics provide a comparison of their relative potencies. The volatile anesthetic concentration is the percentage of the alveolar gas mixture, or partial pressure of the anesthetic as a percentage of 760 mm Hg (atmospheric pressure at sea level). The minimum alveolar anesthetic concentration (MAC ) is defined as the... 

Eger El II, Saidman U, Brandstater B Minimum alveolar anesthetic concentration A standard of anesthetic potency. Anesthesiology 1965 26 756. [PMID 5844267]... 

Sonner JM, Antognini JF, Dutton RC, et al. Inhaled anesthetics and immobility mechanisms, mysteries, and minimum alveolar anesthetic concentration. Anesth Analg. 2003 97 718-740. 

Dose-Response Characteristics The Minimum Alveolar Anesthetic Concentration (MAC)... 

Eger II, E. I., Koblin, D. D., Laster, M. J., Schurig, V., Juza, M., Ionescu, P., and Gong. D. (1997) Minimum alveolar anesthetic concentration values for the enantiomers of isoflurane differ minimally. Anesth, Analg. 85, 188-192. 

The term minimum alveolar anesthetic concentration (MAC) was coined by Merkel and Eger (1963) as an index to compare various anesthetic agents. 

Issues in the design and interpretation of minimum alveolar anesthetic concentration studies were discussed by Sonner (2002). 

Fang et al. (1997) found that maturation decreases ethanol minimum alveolar anesthetic concentration more than desflurane MAC in rats. 

Doquier et al. (2003) studied the minimum alveolar anesthetic concentration of volatile anesthetics in rats as tools to assess antinociception in animals. 

Ide et al. (1998) used airway occlusion in cats as a noxious respiratory stimulus that induces a visceral sensation of choking for determination of minimum alveolar anesthetic concentrations during halothane, isoflurane, and sevoflurane anesthesia. These values were compared with MAC values for somatic noxious stimuli such as toe pinch or tetanic stimulus. The authors recommended this method as a new concept for MAC determination. 

Eger El II, Saidman LJ, Brandstater B (1965) Minimum alveolar anesthetic concentration a standard of anesthetic potency. Anesthesiol 26 756-763... 

Eger El II, Ionescu P, Laster MJ et al. (1999) Minimum alveolar anesthetic concentration of fluorinated alkanols in rats relevance to theories of narcosis. Anesth Analg 88 867-876... 

Eger El II, Xing Y, Laster M et al. (2003) Halothane and isofluroane have additive minimum alveolar concentration (MAC) effects in rats. Anesth Analg 96 1350-1353 Fang Z, Gong D, Ionescu P et al. (1997) Maturation decreases ethanol minimum alveolar anesthetic concentration (MAC) more than desflurane MAC in rats. Anaesth Analg 84 852-858... 

Gong D, Fang Z, Ionescu P et al. (1998) Strain minimally influences anesthetic and convulsant requirements of inhaled compounds in rats. Anesth Analg 87 963-966 Hall RI, Murphy MR, Hug CC (1987) The enfluorane sparing effect of sufentanyl in dogs. Anesthesiol 67 518-525 Ide T, Sakurai Y, Aono M, Nishino T (1998) Minimum alveolar anesthetic concentrations for airway occlusion in cats A new concept of minimum alveolar anesthetic concentration-airway occlusion response. Anaesth Analg 86 191-197... 

Ebert TJ, Messana ED, Uhrich TD, Staacke TS. Absence of renal and hepatic toxicity after four hours of 1.25 minimum alveolar anesthetic concentration sevoflurane anesthesia in volunteers. Anesth Anaig 1998 86(3) 662-7. 

C. Minimum Alveolar Anesthetic Concentration (MAC) The potency of inhaled anesthetics is best measured by the minimum alveolar anesthetic concentration (MAC), defined as the alveolar concentration required to eliminate the response to a standardized painful stimulus in 50% of patients. Each anesthetic has a defined MAC (see Table 25-2), but tWs value may vary among different patients depending on age, cardiovascular status, and use of adjuvant drugs. Estimations of MAC value suggest a relatively steep dose-response relationship for inhaled anesthetics. MACS for infants and elderly patients are lower than those for adolescents and young adults. When several anesthetic agents are used simultaneously, their MAC values are additive. 

A Concept of Anesthetic Dose Based on Partial Pressure-Minimum Alveolar Concentration... 

A comparison of the minimum alveolar concentration (MAC) with the oil-gas partition coefficient of several inhalational anesthetic agents. 

Depth of anesthesia is determined by the concentration of anesthetic agent that reaches the brain. Brain concentration, in turn, depends on the solubility and transport of the anesthetic agent in the bloodstream and on its partial pressure in inhaled air. Anesthetic potency is usually expressed as a minimum alveolar concentration (MAC), defined as the percent concentration of anesthetic in inhaled air that results in anesthesia in 50% of patients. As shown in Table 9.6, nitrous oxide, N2O, is the least potent of the common anesthetics. Fewer than 50% of patients are immobilized by breathing an 80 20 mix of nitrous oxide and oxygen. Methoxyflurane is the most potent agent a partial pressure of only 1.2 mm Hg is sufficient to anesthetize 50% of patients, and a partial pressure of 1.4 mm Hg will anesthetize 95%. 

Petrenko AB, Tsujita M, Kohno T et al. (2007) Mutation of alG T-type calcium channels in mice does not change anesthetic requirements for loss of the righting reflex and minimum alveolar concentration but delays the onset of anesthetic induction. Anesthesiology 106 1177-1185... 

The potency of inhaled anesthetics is defined quantitatively as the minimum alveolar concentration (MAC), which is the concentration of anesthetic gas needed to eliminate movement among 50% of patients challenged by a standardized skin incision. The MAC is... 

A method for determining minimum alveolar concentration of anesthetic in the rat was published... 

Eger et al. (1988) determined minimum alveolar concentration of fluorinated anesthetics in pigs. 

Waizer PR, Baez S, Orkin LR (1973) A method for determining minimum alveolar concentration of anesthetic in the rat. Anesthesiol 39 394-397... 

Cyclopropane is an inhalational anesthetic gas. Its minimum alveolar concentration (MAC) is 9.2%. Because of the risk of explosion, it is usually administered by closed circuit (1). 

In 45 adult patients undergoing elective surgery, the 2-adrenoceptor agonist dexmedetomidine in a concentration of 0.7 ng/ml reduced the minimum alveolar concentration of sevoflurane required to suppress movement to skin incision by 17%, but a plasma concentration of 0.39 ng/ml had no effect (58). The larger reductions in isoflurane requirements found in earlier studies of dexmedetomidine were probably due to the use of potent opioids and intravenous induction as part of the anesthetic. 

The minimum alveolar concentrations of sevoflurane required to suppress movements and adrenergic responses to surgery in the presence of the potent opioid fentanyl have been quantified in 226 adults (59). Fentanyl 3 ng/ml and 6 ng/ml reduced sevoflurane requirements to suppress movement to pain by 61% and 74%, respectively, and requirements to suppress the adrenergic responses to pain by 83% and 91%, respectively. There was no further reduction in sevoflurane requirements at concentrations of fentanyl above 6 ng/ml. The degree of interaction was similar to that seen in previous studies of other volatile anesthetic + opioid combinations. 

The potency of inhalation agents can be compared using their respective MAG values. The MAG is the minimum alveolar concentration of an inhalation anesthetic (percentage concentration at sea level) that would prevent movement in response to a surgical incision in 50% of subjects. At equilibrium, the concentration of the inhalation agent in the pulmonary alveoli correlates well with the partial pressure of the anesthetic in the brain, while the inspired concentration of the anesthetic and the concentration of the anesthetic in the blood do not correlate well with brain partial pressure. In order to achieve surgical... 

Tendillo F J, Mascias A, Santos M et ai 1997 Anesthetic potency of desflurane in the horse determination of the minimum alveolar concentration. Veterinary Surgery 26 354-357... 

Anesthetic Biood Gas Partition Coefficient Minimum Alveolar Concentration (%) Metabolism... 

Minimum alveolar concentration (MAC) is the anesthetic concentration that eliminates the response in 50% of patients exposed to a standardized painful stimulus. In this table, MAC is expressed as a percentage of the inspired gas mixture. 

A) Anesthetic potency is quantitated by the minimum alveolar concentration (MAC) that causes 50% of subjects to fail to respond to a standardized painful stimulus General anesthesia is associated with increased blood pressure and total peripheral resistance... 

The minimum alveolar concentration (MAC) is defined as the conoentration at 1 atmosphere of anesthetic in the alveoli that is required to produce immobility in 50% of adult patients subjected to a surgical incision. A further inorease to 1.3 MAC frequently will oause immobility in 99% of patients. At equilibrium, the conoentration (or partial pressure) of an anesthetic in the alveoli is equal to that in the brain, and it is this concentration in the brain that probably most olosely reflects the concentration at the site responsible for the anesthetio aotions. Thus, the MAC often is used as a measure of the potenoy of individual anesthetic agents. The MAC of many of the volatile and gaseous anesthetics in use today is shown in Table 18.2. 

The physical properties of inhalational anesthetics are provided in Table 19.2. Note that desflurane, compared to other agents, has a boiling point that is close to normal room temperature and a vapor pressure that is close to atmospheric pressure at sea level. These properties dictated a new type of vaporizer that heats the agent to 39°C in order to meter the flow of desflurane vapor into the gas flow stream. The minimum alveolar concentration (MAC) of halothane, from Table 19.2 indicates that the agent is the most potent of the agents available today with desflurane as the least potent. 

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