Effect of meperidine and skin surface warming on shivering

AORN Journal, July, 2007 by George Allen

Critical Care February 2007

Mild hypothermia (ie, core body temperatures between 33[degrees]C and 34[degrees]C [91.4[degrees] F and 93.2[degrees]F]) has been shown to provide substantial protection against cerebra] and myocardial ischemia, improve neurologic outcomes, and reduce mortality after cardiac arrest. Mild hypothermia is relatively easy to induce during general anesthesia because anesthetics profoundly impair thermoregulatory responses. Induction of mild hypothermia in fine awake patient, however, may be difficult. Minute reductions in core temperature trigger shivering, which impairs efficient core cooling. Consequently, numerous studies have investigated ways to lower the shivering threshold using medications and medication combinations including meperidine, buspirone, dexmedetomidine, clonidine, and nefopam. Additionally, nonpharmacological treatments, including arm and face warming and whole-body skin warming, have been investigated.

In contrast to other opioids, meperidine has been shown to have additional antishivering properties at equianalgesic doses and to inhibit shivering twice as much as vasoconstriction. When meperidine is used as a single medication, however, high plasma concentrations are needed to reduce the shivering threshold to below 34[degrees]C (93.2[degrees]F). Such high plasma concentrations can cause significant respiratory depression and sedation, which consequently mandates close patient monitoring in an intensive care unit (ICU). Skin warming, on the other hand, efficiently lowers thermoregulatory thresholds without causing side effects, but skin warming alone is not sufficient to allow induction of mild hypothermia. The purpose of this study was to test whether a combination of skin warming and a medium dose of meperidine would additively reduce the shivering threshold to below 34[degrees]C (93.2[degrees]F) without producing significant sedation or respiratory depression.

Eight healthy volunteers from the University Hospital of Berne, Switzerland, were recruited and participated on four study days:

* control day, in which a placebo was infused and no skin warming took place;

* skin warming day, in which participants' skin was warmed with a forced-air warming system and a water-circulating mattress, with mean skin temperature maintained at approximately 35.8[degrees]C (96.4[degrees]F) throughout the study day;

* meperidine day, in which meperidine was administered intravenously with a target plasma level of 0.9 mcg/mL; and

* meperidine plus skin warming day, in which meperidine was infused and participants' skin was warmed.

On all study days, participants were cooled using lactated Ringer solution at approximately 4[degrees]C (39.2[degrees]F), which was infused through a central venous catheter until the participant's shivering threshold was identified or 80 mL/kg of fluid had been administered.

Shivering threshold was identified by an increase in oxygen consumption of 20% above baseline. Sedation was assessed using the Observer's Assessment of Alertness/Sedation scale, in which points are assigned based on an assessment of the participant's responsiveness, speech, facial expression, and eyes, with a wide-awake score equaling 20 and a deeply sedated score equaling 9. Common statistical procedures, including the Friedman test and the Newman-Keuls test, were used to analyze the data.

FINDINGS. There was no difference for meperidine plasma levels between the meperidine day and the meperidine plus skin warming day (P = .42). Meperidine plasma levels remained stable throughout the study. Skin warming reduced the shivering threshold to 34.9[degrees]C [ or -] 0.5[degrees]C (94.8[degrees]F [ or -] 0.9[degrees]F) (P = .01). Meperidine reduced the shivering threshold to 34.2[degrees]C [ or -] 0.3[degrees]C (93.6[degrees]F [ or -] 0.5[degrees]F)P < .01) and produced only mild sedation. The combination of meperidine and skin warming reduced the shivering threshold to 33.8[degrees]C [ or -] 0.2[degrees]C (92.8[degrees]F [ or -] 0.4[degrees]F) (P < .01). There were no synergistic or antagonistic effects from meperidine and skin warming (P = .59).

CLINICAL IMPLICATIONS. The results of this study revealed that a combination of meperidine and skin surface warming reduced the shivering threshold to 33.8[degrees]C [ or -] 0.2[degrees]C (92.8[degrees]F 0.4[degrees] F) and produced only very mild sedation and no respiratory toxicity. Perioperative nurses and managers should understand that this combination can be considered as a feasible regimen for induction and maintenance of mild therapeutic hypothermia.

Kimberger O, Ali SZ, Markstaller M, et al. Meperidine and skin surface warming additively reduce the shivering threshold: a volunteer study. Crit Care [serial online]. 2007;11(1):R29. http://ccforum.com /content/11/1/R29. Accessed May 22, 2007.

This information is intended for general use only. The clinical implications are specific to the abstracted article only. Individuals intending to put these findings into practice are encouraged to review the original article to determine its applicability to their setting.