Raised end-expiratory alveolar pressures during cardiac surgery

Increased end-expiratory pressure (EEP) is usually associated with expiratory obstruction. By pressing the "expiratory pause hold" button on the Servo ventilator 900C, EEP was measured at four stages during coronary bypass surgery: before sternotomy (I), after sternotomy with the sternal edges fully retracted (II), after completed extracorporeal circulation, sternal edges still retracted (III) and after sternal closure (IV). Five patients had EEP values > 3 cm H2O at stage I. EEP decreased after opening the sternum and was still low after extracorporeal circulation (stages II and III). However, sternal closure was associated with large increases in EEP (maximum value 22 cm H2O). Typically, patients in whom EEP exceeded 5 cm H2O at stage IV also had raised values at stage I. These patients had obstructive preoperative spirometry patterns and tended to be of shorter stature in relation to weight than patients in whom EEP did not exceed 5 cm H2O. The changes in EEP are believed to be caused by changes in lung volume as a result of opening and closing the sternum and by increased lung water after extracorporeal circulation.