Hemodynamics and myocardial metabolism under deliberate hypotension. An experimental study in dogs.

Coronary blood flow, cardiac work and metabolism were studied in dogs under sodium nitroprusside (SNP) and trimetaphan (TMP) deliberate hypotension (20% and 40% mean pressure decrease from baseline). Regarding the effects of drug-induced hypotension on coronary blood flow, aortic and coronary sinus metabolic data (pH, pO2, pCO2) we could confirm that nitroprusside hypotension could be safely used to 30% mean blood pressure decrease from control, trimetaphan hypotension to 20% mean blood pressure decrease. Cardiac work was significantly reduced during SNP hypotension. Myocardial O2 consumption and O2 availability were directly dependent on the coronary perfusion. Careful invasive monitoring of the blood pressure, blood gases and of the ECG ST-T segment is mandatory.

Autoregulation of myocardial blood flow under controlled hypotension in the dog.

The autoregulation of myocardial blood flow was studied under: (a) haemorrhagic hypotension (mean pressure decrease 40% from baseline); (b) drug-induced hypotension with sodium nitroprusside or trimetaphan (40% pressure decrease); (c) drug-induced hypotension (40% pressure decrease) after moderate blood loss of 20%. Dogs were used in experiments under general anaesthesia with sodium thiopentone and artificially ventilated with N2O/O2 (70%, 30%) and pancuronium. Under haemorrhagic hypotension, the flow was pressure-dependent from the beginning. During nitroprusside hypotension, there was autoregulation of coronary flow to the level of mean pressure decrease 30% from control. Under trimetaphan, a constant flow persisted to the level of mean pressure decrease 20% from the baseline. Identical changes were seen during drug-induced hypotension after moderate blood loss (20%). Central venous pressure, cardiac output, left ventricular stroke work and minute work changes are demonstrated. Blood gas data pH, PO2, PCO2 in the aortic and coronary sinus under drug-induced hypotension are compared with control groups. There is a level of autoregulation of myocardial blood flow under hypotension. This level can be unfavourably changed in cases with hypertension and coronary obstructive diseases.