Cardiac tamponade and different modes of artificial ventilation

Cardiac tamponade after open-heart surgery often occurs in a situation when the patient is still mechanically ventilated and needs circulatory support with catecholamines. To evaluate the effects of different modes of artificial ventilation and dopamine on cardiac tamponade, an experimental study was carried out in seven mongrel dogs. In pentobarbital - N2O anaesthesia, a cardiac tamponade of 20 mmHg was produced by injecting 120-200 ml of normothermic saline into the pericardium. Intermittent positive pressure ventilation (IPPV) and positive end-expiratory pressure (PEEP) ventilation with frequencies of 12 and 20 were tested before and after producing the tamponade. Cardiac tamponade produced a significant fall in arterial pressure and cardiac output, a significant rise in central venous pressure and only a slight increase in pulmonary arterial pressure. PEEP with the slower ventilation frequency of 12 produced additional, significant falls in cardiac output and systemic arterial pressure, which were not noted with the ventilation frequency of 20 and PEEP. Dopamine infusion increased the cardiac output by increasing the heart rate during tamponade. It is concluded that PEEP ventilation with a slow frequency should not be used if cardiac tamponade is suspected after open-heart surgery, and that dopamine has a favourable effect on haemodynamics even in the presence of a severe cardiac tamponade.