title: Meperidine and skin surface warming additively reduce the shivering threshold: a volunteer study.
abstract: BACKGROUND
  Mild therapeutic hypothermia has been shown to improve outcome for patients after cardiac arrest and may be beneficial for ischaemic stroke and myocardial ischaemia patients. However, in the awake patient, even a small decrease of core temperature provokes vigorous autonomic reactions-vasoconstriction and shivering-which both inhibit efficient core cooling. Meperidine and skin warming each linearly lower vasoconstriction and shivering thresholds. We tested whether a combination of skin warming and a medium dose of meperidine additively would reduce the shivering threshold to below 34 degrees C without producing significant sedation or respiratory depression.
  
  
  METHODS
  Eight healthy volunteers participated on four study days: (1) control, (2) skin warming (with forced air and warming mattress), (3) meperidine (target plasma level: 0.9 mug/ml), and (4) skin warming plus meperidine (target plasma level: 0.9 mug/ml). Volunteers were cooled with 4 degrees C cold Ringer lactate infused over a central venous catheter (rate asymptotically equal to 2.4 degrees C/hour core temperature drop). Shivering threshold was identified by an increase of oxygen consumption (+20% of baseline). Sedation was assessed with the Observer's Assessment of Alertness/Sedation scale.
  
  
  RESULTS
  Control shivering threshold was 35.5 degrees C +/- 0.2 degrees C. Skin warming reduced the shivering threshold to 34.9 degrees C +/- 0.5 degrees C (p = 0.01). Meperidine reduced the shivering threshold to 34.2 degrees C +/- 0.3 degrees C (p < 0.01). The combination of meperidine and skin warming reduced the shivering threshold to 33.8 degrees C +/- 0.2 degrees C (p < 0.01). There were no synergistic or antagonistic effects of meperidine and skin warming (p = 0.59). Only very mild sedation occurred on meperidine days.
  
  
  CONCLUSIONS
  A combination of meperidine and skin surface warming reduced the shivering threshold to 33.8 degrees C +/- 0.2 degrees C via an additive interaction and produced only very mild sedation and no respiratory toxicity.
authors.affiliation: Department of Anaesthesiology, University of Bern, CH-3010 Bern, Switzerland. study@kimberger.at
authors.forename: Oliver
authors.initials: O
authors.lastname: Kimberger
authors.forename: Syed Z
authors.initials: SZ
authors.lastname: Ali
authors.forename: Monica
authors.initials: M
authors.lastname: Markstaller
authors.forename: Sandra
authors.initials: S
authors.lastname: Zmoos
authors.forename: Rolf
authors.initials: R
authors.lastname: Lauber
authors.forename: Corinne
authors.initials: C
authors.lastname: Hunkeler
authors.forename: Andrea
authors.initials: A
authors.lastname: Kurz
mesh_terms: D000328:Adult; D006358:Hot Temperature; D006801:Humans; D007036:Hypothermia, Induced; D008614:Meperidine / Q000097:blood / Q000494:pharmacology*; D009294:Narcotics / Q000097:blood / Q000494:pharmacology*; D012768:Shivering / Q000187:drug effects* / Q000502:physiology; D012881:Skin Temperature / Q000502:physiology*; D014661:Vasoconstriction / Q000187:drug effects* / Q000502:physiology
chemical_list: D009294:Narcotics; D008614:Meperidine