CONSECUTIVE CHANGES IN CUTANEOUS BLOOD FLOW, TEMPERATURE, METABOLISM AND HEMATOCRIT READINGS DURING PROLONGED ANESTHESIA WITH MORPHINE AND BARBITAL

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Abstract
Subcut. temps. were recorded with needle thermocouples connected with a Leeds and Northrup micromax recorder. When subcutaneous temperature of paws or ears was constant, blood flow was estimated from relationship of subcut. temp. to air and rectal temps. Subcut. temps. approximating air temps. indicated minimal blood flow; those near rectal temps. maximal blood flow. Immediately following a sudden change of blood flow the new rate of flow was estimated by comparison of ensuing rate of change of subcutaneous temp. with that observed following onset of a known change of blood flow. Estimation of blood flow through skin over trunk or over large muscle masses in terms of subcut. temp. was less satisfactory apparently because of the high rate of conduction of heat directly from deeper structures. Pre-anesthetic rectal temp. in 21 dogs ranged from 37.5[degree]-39.7[degree] with an av. of 38.5[degree]C. Anesthesia with morphine alone caused immediate and frequently maximal increase in cutaneous blood flow and decline in rectal temp. to 34[degree]-37[degree] C, often followed in 1 to 3 hours by a sharp reduction in cutaneous blood flow. The latter apparently was secondary to temp. regulating reactions induced by the drop in rectal temp. Sodium barbital, sodium pentobarbital and chloralosane caused a similar initial increase in cutaneous blood flow and a drop of 0.5[degree]-1.5[degree] in rectal temp. and subsequent decrease in cutaneous blood flow; and, in addition, induced an increase in O2 consumption, often associated with shivering, and a rise of rectal temp. to 38.6[degree]-40.5[degree] within 3-11 hrs. Anesthesia with morphine plus barbital accentuated the initial drop of rectal temp. Hematocrit readings showed little change with morphine alone, but with either morphine and a barbiturate or one of the barbiturates alone the hematocrit reading dropped 5-10 cell vol. % within a few minutes after anesthesia and then slowly returned to and often above normal during period of reduction of cutaneous blood flow and rise of rectal temp. Changes in rectal temp. and cutaneous blood flow were minimized by maintaining rectal temp. between 38[degree] and 39[degree] and were often abolished by elevating rectal temp. to 39[degree]-40[degree] by warming the animal board. The heating had, however, no significant influence upon the initial decline and subsequent rise of the hematocrit reading. Both heart rate and mean arterial blood pressure were higher under Na barbital anesthesia than under the other anesthetic combinations. Because of the above sequence of events during anesthesia with any of these drugs it was recommended that a control period of at least 3 to 4 or more hours elapse following anesthetization before proceeding with experimental studies, if hematocrit, O2 consumption, rectal temp., or cutaneous blood flow are to be studied.

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