Canadian Journal of Anesthesia, Vol 32, 272-277, Copyright © 1985 by Canadian Anesthesiologists' Society

Clinical Reports: End-Tidal Carbon Dioxide Tension and Temperature Changes After Coronary Artery Bypass Surgery

¹ Department of Anaesthesia, Montreal Heart Institute, Montreal, Quebec, Canada

Address correspondence to: Dr. J.G. Maillé, Montreal Heart Institute, 5000 east, Belanger Street, Montreal, Quebec, HIT 1C8, Canada.

Variations in end-tidal carbon dioxide partial pressure (PetCO₂) and temperature were measured for six hours following coronary artery bypass surgery in twenty patients. In the recovery room, the patients were mechanically ventilated with a tidal volume of 12 ml·kg^-1. Arterial blood gases were drawn every two hours, and the respiratory frequency was adjusted to maintain arterial carbon dioxide pressure (PaCO₂) in the range of 30-45 mmHg. Naso-pharyngeal temperature was recorded every 30 minutes, and PetCO₂ was measured continuously. The mean difference between temperature-corrected arterial and end-tidal CO₂ pressure measurements was 3.2 mmHg (SD = 2.8; r = 0.963). This difference did not vary with time, temperature or PCO₂. The largest temperature increases (mean 1.7°C/hour) occurred at a mean of 253 minutes after the end of surgery. End-tidal PCO₂ increased markedly as temperature rose, in spite of a coincident increase in ventilation and then decreased as temperature stabilized. Large increases in CO₂ production, caused by the metabolic demands during rewarming, most likely account for these changes. It is concluded that end-tidal CO₂ recordings are reliable, and can help in maintaining normocarbia during the short but unstable period associated with rewarming following cardiac surgery.

Key Words: ANAESTHESIA: cardiovascular • TEMPERATURE: body • VENTILATION: postoperative, carbon dioxide tension