Table 1.

Relationship of the Different Planes of Anesthesia and MAC.

CNS Function Lost	MAC Stage	Significance of Plane of Anesthesia	Status of CNS Functions	Functional Test in Mice	Approximate MAC Value	Vaporizer Dial Setting
Loss of memory	MACamnesia	Unable to form memories	Cerebral functions, spinal and autonomic reflexes intact	Difficult to assess in mice both experimentally and in clinical settings	0.25	0.3–0.5%
Loss of consciousness	MACawake	Unable to perceive pain	Cerebral functions anesthetized; spinal and autonomic reflexes intact	Mouse can be laid on its back and will not right itself	0.5	0.7–0.9%
Loss of motor response to a noxious stimulus	MAC	No motor response to a noxious stimulus; surgical plane of anesthesia (in veterinary medicine)	Cerebral functions and spinal reflexes anesthetized; autonomic reflexes intact	No movement in response to a noxious stimulus	1.0	1.3–1.8%
Blunted autonomic reflexes	MACBAR	Autonomic nervous system is not responsive to physiologic changes	Cerebral functions, spinal reflexes, and autonomic reflexes anesthetized	Experimentally, no change in serum epinephrine concentrations in response to a noxious stimulus, clinically no change in HR, RR, or BP in response to noxious stimulus	1.5	2.0–2.7%

This table presents different anesthetic planes and MAC relationship, which refers to the minimum alveolar concentration where 50% of animals lose a motor response to a noxious stimulus. The MAC value is dependent on multiple factors, including the severity of the noxious stimulus, where the stimulus is applied, and animal-specific factors. In veterinary medicine, the loss of a motor response to a noxious stimulus is commonly referred to as the surgical plane of anesthesia, while this would be considered a very deep plane of anesthesia in human patients.^{2,6,17,321,34,322} Please note that 2% isoflurane may blunt autonomic responses; therefore, supportive care, such as warmed fluid administration and other monitoring techniques (preventing hypothermia etc ), is warranted (discussed in anesthetic monitoring). MAC_BAR refers to the MAC which blocks autonomic responses. HR, RR, and BP indicate heart rate, respiratory rate, and blood pressure, respectively.