The Effect of Position on PaCO2 and PETCO2 in Patients Undergoing Cervical Spine Surgery in Supine and Prone Position.

BACKGROUND: As per American Society of Anesthesiologists guidelines, continuous monitoring of end tidal carbon dioxide (PETCO2) is recommended as standard II basics of anesthetic monitoring especially to ensure adequate ventilation during all anesthetics. Continuous monitoring of PETCO2 can also be used as a guide to maintain the partial pressure of carbon dioxide in arterial blood (PaCO2) to desired level during the surgery. AIMS AND OBJECTIVES: To study the effect of position on PaCO2 and PETCO2 during cervical spine surgery in prone position. MATERIALS AND METHODS: Following institutional ethical committee approval and written informed consent, a prospective study was conducted in 40 patients of 18 to 60 years and of American Society of Anesthesiologists I and II scheduled for cervical spine surgery in prone position. In operating room, the patient is connected to standard monitoring and intravenous access was secured. A 20 G arterial cannula was placed. General anesthesia administered and oral endotracheal intubation done. Baseline values of systolic blood pressure, diastolic blood pressure, mean arterial pressure, heart rate, temperature, SpO2, Ppeak, Pmean, and Pplateau were measured in supine position. For each patient the capnometer was calibrated before use. The P(a-ET)CO2 was calculated in supine position (S1). The PaCO2 and ETCO2 were measured after prone positioning P1, at each subsequent hour (P2, P3, P4), and on completion of the procedure in supine position (S2). The mean values were used for further analysis. RESULTS: The PETCO2 and PaCO2 decreased significantly in cervical spine surgery patients with change of position from supine to prone with no significant change in arterial to end tidal CO2 gradient (P(a-ET)CO2). CONCLUSIONS: PETCO2 can be used as a reliable guide to estimate PaCO2 during cervical spine procedures in prone position.