title: Rectal temperature reflects tympanic temperature during mild induced hypothermia in nonintubated subjects.
abstract: BACKGROUND
  Mild induced hypothermia holds promise as an effective neuroprotective strategy following acute stroke and cardiac arrest. Dependable noninvasive measurements of brain temperature are imperative for the investigation and clinical application of therapeutic hypothermia. Although the tympanic membrane temperature correlates best with brain temperature, it is a cumbersome location to record from continuously in the clinical setting. Data are lacking regarding the relationship between rectal and tympanic temperatures in nonintubated humans undergoing induced hypothermia via surface cooling.
  
  
  METHODS
  We induced mild hypothermia in healthy volunteers using a novel surface cooling method (Arctic Sun Temperature Management System, Medivance, Inc., Louisville, CO). Core temperatures were recorded at the tympanic membrane (Ttym) and rectum (Trec). The gradient was defined as (Ttym-Trec). Controlled hypothermia was maintained for up to 300 minutes with a target Ttym of 34 degrees C to 35 degrees C; subjects were then actively rewarmed to a target Ttym of 36 degrees C over 1.5 to 3 hours.
  
  
  RESULTS
  Twenty-two volunteers (10 males and 12 females) 31 +/- 8 years of age were studied. Subjects showed a triphasic temperature response: induction, maintenance, and rewarming. The mean gradient at baseline was -0.1 +/- 0.3 degrees C and the maximum gradient increased to -0.6 +/- 0.4 degrees C at 105 minutes. During maintenance of hypothermia (from 150 to 300 minutes), the mean gradient was -0.3 +/- 0.5 degrees C (95% confidence limits, -1.2 degrees C to 0.6 degrees C).
  
  
  CONCLUSIONS
  : Our data suggest that Ttym and Trec are not related during the induction of hypothermia via surface cooling but correlate during the maintenance phase, with a -0.3 degrees C gradient. These findings support the use of rectal temperature as a measure of tympanic and, therefore, brain temperature during maintenance of induced hypothermia in nonintubated humans.
authors.affiliation: University of South Alabama Stroke Center, Mobile, 36617, USA. rzweifle@usouthal.edu
authors.forename: Richard M
authors.initials: RM
authors.lastname: Zweifler
authors.forename: Marc E
authors.initials: ME
authors.lastname: Voorhees
authors.forename: M Asim
authors.initials: MA
authors.lastname: Mahmood
authors.forename: Mel
authors.initials: M
authors.lastname: Parnell
mesh_terms: D000082:Acetaminophen / Q000494:pharmacology; D000328:Adult; D018712:Analgesics, Non-Narcotic / Q000494:pharmacology; D000701:Analgesics, Opioid / Q000494:pharmacology; D001831:Body Temperature / Q000502:physiology*; D005260:Female; D006801:Humans; D007036:Hypothermia, Induced; D008297:Male; D008614:Meperidine / Q000494:pharmacology; D012007:Rectum / Q000502:physiology*; D017694:Rewarming; D012768:Shivering; D014432:Tympanic Membrane / Q000502:physiology*
chemical_list: D018712:Analgesics, Non-Narcotic; D000701:Analgesics, Opioid; D000082:Acetaminophen; D008614:Meperidine