Thermoregulatory Vasoconstriction During Propofol/Nitrous Oxide Anesthesia in Humans

Abstract

To determine the thermoregulatory effects of propofol and nitrous oxide, we measured the threshold for peripheral vasoconstriction in seven volunteers over a total of 13 study days. We also evaluated the effect of vasoconstriction on oxyhemoglobin saturation (SpO2). Anesthesia was induced with an intravenous bolus dose of propofol (2 mg/kg), followed by an infusion of 180 micrograms.kg-1 x min-1 for 15 min, and maintained with 60% nitrous oxide and propofol (80-160 micrograms.kg-1 x min-1). Central and skin surface temperatures and SpO2 (using two different pulse oximeters) were measured continuously; plasma propofol concentrations and arterial PO2 were measured at 15-min intervals. Volunteers were cooled with a circulating water blanket until definitive peripheral vasoconstriction was detected. The tympanic membrane temperature triggering vasoconstriction was considered the thermoregulatory threshold. Vasoconstriction developed on seven study days during propofol/nitrous oxide anesthesia at a central temperature of 33.3 +/- 1.0 degrees C (mean +/- SD) and plasma propofol concentration of 3.9 +/- 1.1 micrograms/mL. The thresholds during anesthesia were significantly lower than those during the control period (36.7 +/- 0.3 degrees C), but the correlation between plasma propofol concentrations and vasoconstriction thresholds was poor. On the remaining six study days, vasoconstriction did not develop despite central temperatures ranging from 32.1 to 32.7 degrees C. Corresponding propofol concentrations were 4.1-10.9 micrograms/mL. These data suggest that anesthesia with propofol, in typical clinical concentrations, and 60% nitrous oxide substantially inhibits thermoregulatory vasoconstriction. Vasoconstriction increased SpO2 by approximately 2% without a significant concomitant change in PO2. The observed increase in SpO2 probably reflects decreased transmission of arterial pulsations to venous blood in the finger.

Pulse oximetry: fundamentals and technology update

“…A similar effect was found following administration of propofol/nitrous oxide anesthesia, leading to alteration of peripheral vascular tone and concomitant changes in skin temperature 55. The observed increase in SpO 2 probably reflects decreased transmission of arterial pulsations to venous blood in the finger,55 but it can also be speculated that the effect is related to the calibration process. Changes in scattering parameters due to changes in microcirculation can interfere with the relationship between the measured parameter R and SaO 2 (Equation 4), which was obtained in healthy subjects under normal thermal conditions.…”

“…Local hyperthermia resulted in a significant decrease in SpO 2 , while during local hypothermia SpO 2 increased 56. A similar effect was found following administration of propofol/nitrous oxide anesthesia, leading to alteration of peripheral vascular tone and concomitant changes in skin temperature 55. The observed increase in SpO 2 probably reflects decreased transmission of arterial pulsations to venous blood in the finger,55 but it can also be speculated that the effect is related to the calibration process.…”

“…Low perfusion induced by vasoconstriction, which results in a decreased PPG signal, is also associated with an increase in SpO 2 value 55–57. Local hyperthermia resulted in a significant decrease in SpO 2 , while during local hypothermia SpO 2 increased 56.…”

The effects of two rewarming strategies on heat balance and metabolism after coronary artery bypass surgery with moderate hypothermia

“…The interthreshold range is only about 0.2aeC in awake humans (15). Anesthetics decrease the vasoconstriction threshold (16)(17)(18) and increase the sweating threshold (19,20) and general anesthesia hence augments the interthreshold range to about 4aeC. In addition, most general anesthetics cause vasodilatation and reduce heat production, resulting in a decrease of the body heat content.…”

L’administration im d’une prémédication de dropéridol atténue l’hypothermie peropératoire

“…Since the patients' environment was based on institutional and Japanese standards, the ambient temperature measured in the present study was higher than that of most previous studies. [19][20][21] Higher ambient temperatures would keep peripheral temperatures higher. In fact, peripheral temperature FIGURE 3 Time course of skin (index fingertip) blood flow.…”