<prompt> Minimum alveolar concentration MAC of an anesthetic agent means it produces lack of reflex response to skin incision in___ of subjects.255075100  <response>: Ans. b 50. Ref. Shorttext book, Anaesthesia, 2nd ed., 54-55Anesthetic potency of volatile anesthetics is measured by MAC. MAC represents the alveolar concentration of an anesthetic at one atmosphere that prevents movement in 50 percent of the subjects in response to pain.MINIMUM ALVEOLAR CONCENTRATION MAC - MAC 1 potency of drug For determination of MAC in humans, the usual stimulus used is surgical skin incision. It represents after a short time the partial pressure of the anesthetic in the central nervous system CNS and it is therefore the most useful index of anesthetic potency. MAC is age-dependent, being lowest in newborns, reaching a peak in infants, and then decreasing progressively with increasing age. The MAC can also be altered following administration of opioids. As a rule of thumb, the addition of every one percent of alveolar nitrous oxide to another inhalation anesthetic will decrease in the MAC of that gas about one percent. Increases in MAC result from hyperthermia and hypernatremia. Decreases in MAC can result from hypothermia, hyponatremia, pregnancy, hypotension, and drugs such as lithium, lidocaine, opioids, and alpha2 agonists.Minimum alveolar concentration of inhaled anesthetics in 100 oxygen:- Halothane 0.74 percent- Enflurane 1.68 percent- Isoflurane 1.15 percent- Desflurane 6.3 percent- Sevoflurane 2.0 percent- Nitrous oxide 104 percent Factors increasing MACFactors decreasing MACDrugs decreasing MAC1 Hyperthermia2 MAO inhibitors3 Hypernatremia4 Alcohol abuse chronic1 Hyperthermia2 Hypoxia3 Metabolic acidosis4 Pregnancy5 Alcohol abuse acute.1 Opiods, Pancuronium2 Propofol, Ketamine3 Benzodiazepines4 Barbiturates, Lidocaine5 Clonidine. 