Metabolic effects of i.v. propacetamol, metamizol or external cooling in critically ill febrile sedated patients

Abstract

SummaryWe have measured the metabolic response to sequential administration of propacetamol, metamizol and/or external cooling in 20 febrile patients under sedation and analgesia and during mechanical ventilation. There was no change in temperature (TЊ) after propacetamol therapy, whereas after metamizol only a small decrease was noted (from 38.9 (SEM 0.2) to 38.5 (0.3) ЊC; P:0.02). External cooling produced a significant decrease in TЊ (39.1 (0.2) to 37.1 (0.2) ЊC; P:0.0001) accompanied by a decrease in energy expenditure (EE) (2034 (73) to 1791 (88) kcal day 91 ; P:0.004). Heart rate and minute ventilation decreased significantly in parallel. There were no other changes in haemodynamics or pulmonary gas exchanges. We conclude that propacetamol and metamizol did not produce a clinically significant decrease in TЊ in febrile ICU patients whereas external cooling decreased both TЊ and EE. The parallel decrease in body temperature and EE seemed to be related to opioid administration or sedation, or both. (Br. J. Anaesth. 1997; 78: 23-127 Fever in critically ill patients is related frequently to either the systemic inflammatory response syndrome (SIRS) or infection. Usually fever is treated with antipyretic drugs, often paracetamol or metamizol. External cooling by different methods, such as sponging the body surface with ice-cooled water, is also used. 1 Even if reducing fever is still controversial from an immunological point of view, there is little doubt that patient comfort and metabolic demand can be improved by this procedure. 2 Indeed, a previous study in critically ill patients demonstrated diminished oxygen consumption related to decreased body temperature improving the oxygen demand-delivery ratio. 3 However, body cooling in healthy humans results in shivering which increases energy expenditure (EE).The aim of this study was to measure EE as an integrated indicator of body metabolic activity after reduction in temperature. Our hypothesis was that external cooling may induce an increase in EE, in contrast with drugs which, by resetting the thermoregulatory set point, decrease EE. Therefore, we designed a prospective, unblinded, crossover study to evaluate the respective effects of centrally acting drugs (propacetamol or metamizol) or external physical cooling in febrile ICU patients. Patients and methodsThe study was approved by the Ethics Committee of our institution. The requirement for informed consent was waived by the committee who judged that the therapies were applied independently by the attending physician and were accepted in clinical practice, and no invasive measurements were made. We studied 20 patients undergoing mechanical ventilation via a tracheal tube, with a rectal temperature greater than 38.5 ЊC and in whom the physician in charge wished to decrease fever. No patient had an inspired oxygen fraction greater than 0.6, a pneumothorax or a broncho-pleural fistula. Patients' lungs were ventilated with a Veolar-Hamilton (Hamilton Bonaduz, Switzerland) or Engström-Erica ventilator (Engström,...

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