An alternative method of increasing PCO2 using apnoea and continuous positive airway pressure

We have examined the use of continuous positive airway pressure (CPAP) and apnoeic oxygenation for restoration of spontaneous breathing at the end of anaesthesia after controlled ventilation. We studied 45 adult patients without a history of acute or chronic respiratory disturbances. Anaesthesia was induced with thiopentone or propofol and maintained with nitrous oxide and enflurane in oxygen. The patients were normocapnic during artificial ventilation. At the end of surgery, the lungs were ventilated for 5 min with oxygen and then given a CPAP of 8 cm H2O. Spontaneous ventilation was regained after a mean of 5 min and an arterial blood sample was obtained at the third breath. All patients were well oxygenated (PO2 mean 43.5 kPa, range 21-76 kPa) when spontaneous ventilation started. The pH was close to 7.28 in most cases (mean 7.28, range 7.21-7.32), and PCO2 varied in the range 6.6-9.9 kPa (mean 7.9 kPa). It is concluded that the method is safe with regard to oxygenation and acid-base balance.