[Effectiveness and hemodynamic mechanism of action of blood pressure lowering by intravenous labetalol in patients with a critical increase in blood pressure].

Labetalol (L) was intravenously given to ten patients with an acute elevation of arterial blood pressure above to 200 to 100 mmHg. Blood pressure was controlled in 9 of 10 patients (less than or equal to 170/100 mmHg) with 50 mg in 4, 100 mg in 4 and 200 mg L in 1 patient. In 9 responders, systolic pressure decreased from 207 +/- 20 to 161 +/- 9, diastolic pressure from 107 +/- 11 to 90 +/- 8, and mean pressure from 140 +/- 11 to 113 +/- 5 mmHg, and all pressures remained at these levels during a 25 min control period. Heart rate decreased significantly from 87 +/- 20 to 69 +/- 11 per min and cardiac index from 3.2 +/- 0.8 to 2.6 +/- 0.61/min x m2. Stroke volume index remained unchanged. Total peripheral resistance and pulmonary artery occlusion pressure were not significantly altered but tended to increase, resulting in a small shift to the right of the ventricular function curve. Pulmonary vascular resistance increased significantly from 236 +/- 108 to 314 +/- 132 dyn x sec x cm-5 and mixed venous oxygen saturation decreased from 70 +/- 5 to 65 +/- 8%. Peripheral resistance was considerably higher and cardiac index lower in patients with a heart rate below 70/min. We conclude that L effectively lowers the arterial blood pressure in hypertensive crisis, but the substance should not be used in patients with heart rates below 70/min, as in this case the beta-blocking effect may supervene resulting in a high-resistance low-output state.