[Effects of mechanical ventilation and controlled spontaneous respiration on pulmonary function during short duration of general anesthesia with tracheal intubation].

OBJECTIVE: To evaluate the effects of mechanical ventilation on pulmonary function during short duration of general anesthesia with tracheal intubation, and assess the safety of controlled spontaneous respiration during general anesthesia. METHODS: Fifty-three adult patients (aged 18-55 years, ASA physical status I-II) scheduled for elective unilateral tympanoplasty were randomly assigned into mechanical ventilation group (group M, n=28) and spontaneous respiration group (group S, n=25). Anesthesia induction was performed in group M with intravenous propofol (2 mg/kg), fentanyl (3 microg0.05). The pH and SpO(2) [ (97.9-/+1.00)% at the lowest] and PaO(2) in group S were significantly lower and the PaCO(2) was higher than those in group M (P<0.05). In group S, the pH values were 7.274-/+0.025 and 7.331-/+0.039, PaCO(2) values were 60-/+6 and 53-/+5 mmHg, and PETCO(2) values were 53-/+ 6 and 48-/+7 mmHg, and the PaO(2) values were 143-/+37 and 165-/+49 mmHg immediately and 150 min after the intubation, respectively. These values were considered safe under the concept of permissive hypercapnia. No significant differences were found in the P(A-a)DO(2), RI, VD/VT and TFC between or within the two groups (P>0.05), nor were moving, bucking, swallowing and awareness recorded during the surgical procedures. CONCLUSION: In essentially normal lungs, short-term mechanical ventilation during general anesthesia with tracheal intubation does not damage the lung functions, and spontaneous respiration can offer sufficient oxygen supply without causing harmful carbon dioxide retention.