Induction techniques that reduce redistribution hypothermia: a prospective, randomized, controlled, single blind effectiveness study

Abstract

Background: While much effort has been devoted to correcting intraoperative hypothermia, less attention has been directed to preventing redistribution hypothermia. In this study, we compared three different anesthetic induction techniques to standard IV propofol inductions (control) in their effect on reducing redistribution hypothermia.

Methods: Elective, afebrile patients, age 18 to 55 years, were randomly assigned to one of four groups (n = 50 each). Group "INH/100" was induced with 8% sevoflurane in 100% oxygen, Group "INH/50" with 8% sevoflurane in 50% oxygen and 50% nitrous oxide, Group "PROP" with 2.2 mg/kg propofol, and Group "Phnl/PROP" with 2.2 mg/kg propofol immediately preceded by 160 mcg phenylephrine. Patients were maintained with sevoflurane in 50% nitrous oxide and 50% oxygen in addition to opioid narcotic. Forced air warming was used. Core temperatures were recorded every 15 min after induction for 1 h.

Results: Compared to control group PROP, the mean temperatures in groups INH/100, INH/50, and Phnl/PROP were higher 15, 30, 45 and 60 min after induction (p < 0.001 for all comparisons), averaging between 0.39 °C and 0.54 °C higher. In group PROP, 60% of patients had at least one temperature below 36.0 °C in the first hour whereas only 16% did in each of groups INH/100, INH/50, and Phnl/PROP (p < 0.0001 in each group compared to PROP).

Conclusions: In this effectiveness trial, inhalation inductions with sevoflurane or with prophylactic phenylephrine bolus prior to propofol induction reduced the magnitude of redistribution hypothermia by an average of 0.4 to 0.5 °C in patients aged 18 to 55 years.

Trial registration: Retrospectively registered on clinical-trials.gov as NCT02331108 , November 20, 2014.

Keywords: Anesthesia induction; Hypothermia; Inhalation anesthesia induction; Inhalation induction; Intraoperative hypothermia; Intravenous anesthesia induction; Intravenous induction; Perioperative hypothermia; Postoperative hypothermia; Redistribution hypothermia.

Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig. 1

Consort Diagram. Eleven patients consented but were never randomized and not studied: 9: The first author was not available to perform the induction. 1: The case changed from a general anesthetic to a sedation case. 1: The surgeon did not want that patient to be in a clinical study. Five patients were induced and then withdrawn from analysis* because of protocol violations: 1: Airway difficulty during induction. 1: Additional propofol required; 2: Patients received more than 300 mL unwarmed IV fluid. 1: Forced air warming malfunction. *Four patients were withdrawn before T15 so that they had no post-induction temperature measurements. In one patient, there was only one temperature measurement at T15. This patient received more than 300 mL unwarmed IV fluid

Fig. 2

Mean Temperature ± SD and Number (n) in Each Group at Each Time Point (°C). In the three successive time intervals (T15 to T30, T30 to T45, and T45 to T60), the percentage of patients (all groups combined) whose temperature decreased were (37.5, 14.4, and 14.2% respectively). The percentage of patients whose temperature increased were (39.0, 55.4, and 59.1% respectively). The remaining patients had no temperature changes within these time intervals