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Lack of nonshivering thermogenesis in infants anesthetized with fentanyl and propofol.

Abstract：

BACKGROUND:Sweating, vasoconstriction, and shivering have been observed during general anesthesia. Among these, vasoconstriction is especially important because-once triggered-it minimizes further hypothermia. Surprisingly, the core-temperature plateau associated with vasoconstriction appears to preserve core temperature better in infants and children than adults. This observation suggests that vasoconstriction in anesthetized infants may be accompanied by hypermetabolism. Consistent with this theory, unanesthetized infants rely on nonshivering thermogenesis to double heat production when vasoconstriction alone is insufficient. Accordingly, the authors tested the hypothesis that intraoperative core hypothermia triggers nonshivering thermogenesis in infants. METHODS:With Ethics Committee approval and written parental consent, the authors studied six infants undergoing abdominal surgery. All were aged 1 day to 9 months and weighed 2.4-9 kg. Anesthesia was maintained with propofol and fentanyl. The infants were mechanically ventilated and allowed to cool passively until core (distal esophageal) temperatures reached 34-34.5 degrees C. Oxygen consumption-the authors' index of metabolic rate-was recorded throughout cooling. Because nonshivering thermogenesis triples circulating norepinephrine concentrations, arterial blood was analyzed for plasma catecholamines at approximately 0.5 degree C intervals. Thermoregulatory vasoconstriction was evaluated using forearm-fingertip, skin-surface gradients, with gradients exceeding 4 degrees C, indicating intense vasoconstriction. The patients were subsequently rapidly rewarmed to 37 degrees C. Regression analysis was used to correlate changes in oxygen consumption and plasma catecholamine concentrations with core temperature. RESULTS:All patients were vasoconstricted by the time core temperature reached 36 degrees C. Further reduction in core temperature to 34-34.5 degrees C did not increase oxygen consumption. Instead, oxygen consumption decreased linearly. Hypothermia also failed to increase plasma catecholamine concentrations. CONCLUSIONS:Even at core temperatures approximately 2 degrees C below the vasoconstriction threshold, there was no evidence of nonshivering thermogenesis. This finding is surprising because all other major thermoregulatory responses have been detected during anesthesia. Infants and children thus appear similar to adults in being unable to increase metabolic rate in response to mild intraoperative hypothermia.

journal_name

Anesthesiology

journal_title

Anesthesiology

authors

Plattner O,Semsroth M,Sessler DI,Papousek A,Klasen C,Wagner O

doi

10.1097/00000542-199704000-00006

subject

Has Abstract

pub_date

1997-04-01 00:00:00

pages

772-7

issue

eissn

0003-3022

issn

1528-1175

journal_volume

pub_type

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Lack of nonshivering thermogenesis in infants anesthetized with fentanyl and propofol.