Variation in Arterial to End - Tidal Carbon Dioxide Tension Differences by Duration of Anesthesia and Position during Anesthesia

Han, Jong In

Abstract

BACKGROUND
The adquacy of ventilation can be monitored noninvasively, continuously, and in real time by using capnography. But the difference between arterial and end-tidal carbon dioxide tension was related to the presence or absence of lung disease, age, ASA class, systolic blood pressure and the other factors. The purpose of this study is to evaluate the effect of duration of anesthesia and position on the difference between arterial and end-tidal carbon dioxide tension. METHOD: 15 patients were selected for supine group(group 1) and 15 patients scheduled for spine surgery were selected for prone group(group 2). The anesthesia was induced by penthotal sodium(5mg/kg) and succinylcholine(2mg/kg). After intubation, anesthesia was maintained by demerol, midazolam, nitrous oxide and oxygen. The patients were ventilated mechanically with tidal volume 10mi/kg and respiration rate 12/min. Arterial and end-tidal carbon dioxide tension, heart rate, arterial blood pressure and esophageal temperature were estimated at 10min after induction of anesthesia. At 30min, 60min and 90min after placement in the position for operation and the end of the surgical procedure, these parameters were also measured. RESULT: 1) Arterial and end-tidal carbon dioxide tension decreased significantly at 30min, 60min and 90min after placement in the position for operation and the end of the surgical procedure in both group. 2) There was no statistically significantly difference in P(a-ET)CO2 between both group. But a gradual increase in mean P(a-ET)CO2 occured with maintenance of anesthesia in group 2. 3) No significant relationship was seen between mean P(a-ET)CO2 and heart rate, mean arterial pressure and temperature. CONCLUSION: We do not believe it is valid to assume that a constant arterial to end-tidal CO2 gradients exists when estimating PaCO2 from P(ET)CO2 when the patient is in the prone position for spine surgery.