Cardiorespiratory function during thoracic anaesthesia: a comparison of two-lung ventilation and one-lung ventilation with and without PEEP5.

Previous studies have shown that, in patients undergoing thoracic surgery, a relatively high positive end-expiratory pressure (PEEP of 10 cmH2O = PEEP10) has no beneficial effect on oxygenation during one-lung ventilation (OLV). In the present investigation, cardiorespiratory function was examined in 11 patients intubated endobronchially and undergoing thoracotomy. Comparison was made between two-lung ventilation (TLV) and OLV and between zero end-expiratory pressure and PEEP5 during OLV. Cardiac output was determined to obtain information of the total oxygen delivery (cardiac output times arterial O2 content. The change from TLV to OLV was accompanied by a marked fall in PaO2 and a marked rise in shunt, whereas no significant change was observed in mean cardiac output. Oxygen delivery also remained unchanged due to relatively small decrease in SaO2 (arterial oxygen saturation) and maintenance of cardiac output. The application of PEEP5 during OLV produced no significant changes in these parameters. The findings in individual patients demonstrated the relative importance of cardiac output in determining oxygen delivery during OLV. A significant negative correlation was found between inspiratory airway pressure and cardiac index during OLV.