[Hemodynamic effects of positive pressure breathing]

A decrease of cardiac output during artificial ventilation with PEEP has been reported in 30-100% of patients. The drop in cardiac output is caused by (I) a decrease of transmural filling pressures of both ventricles, (II) an increase in afterload of the right ventricle, (III) a change of left ventricular geometry caused by a right to left shift of the interventricular septum in face of an enlarging right ventricle. Afterload enhancement and right to left interdependance are effective on high PEEP levels only (above 15 cm H2O). Pulmonary occlusion pressure represents left ventricular filling pressure up to PEEP 10-15 cm H2O. A rise of cardiac output during PEEP may be seen (I) in patients with severe left ventricular failure, where hemodynamics may ameliorate with PEEP (II) in patients with very stiff lungs and low FRC before ventilation. A drop in mean arterial blood pressure was observed in a certain number of patients, while arterial pressure remained constant in others. PEEP should not be delivered to patients with arterial hypotension and hypovolimia before stabilisation of circulation and volume replacement. Regional blood flow is significantly altered during PEEP. In dog experiments a redistribution of peripheral blood flow was observed favouring the flow to brain, heart, adrenal glands small intestine and sceletal muscle and ischemia of stomach, thyroideal and fatty tissue blood flow. Within the kidney, a redistribution of blood flow away from the outer cortex compromises the kidney function (decrease of glomerula filtration, urine output and sodium excretion).(ABSTRACT TRUNCATED AT 250 WORDS)