TREATMENT OF HYPOTENSION AFTER HYPERBARIC TETRACAINE SPINAL-ANESTHESIA - A RANDOMIZED, DOUBLE-BLIND, CROSS-OVER COMPARISON OF PHENYLEPHRINEAND EPINEPHRINE

Background: Despite many advantages, spinal anesthesia often is follow ed by undesirable decreases in blood pressure, for which the ideal tre atment remains controversial. Because spinal anesthesia-induced sympat hectomy and management with a pure alpha-adrenergic agonist can separa tely lead to bradycardia, the authors hypothesized that epinephrine, a mixed alpha- and beta-adrenergic agonist, would more effectively rest ore arterial blood pressure and cardiac output after spinal anesthesia than phenylephrine, a pure alpha-adrenergic agonist Methods: Using a prospective, double-blind, randomized, cross-over study design, 13 Pat ients received sequential infusions of epinephrine and phenylephrine t o manage hypotension after hyperbaric tetracaine (10 mg) spinal anesth esia Blood pressure, heart rate, and stroke volume (measured by Dopple r echocardiography using the transmitral time-velocity integral) were recorded at baseline, 5 min after injection of tetracaine, and before and after management of hypotension with epinephrine and phenylephrine . Cardiac output was calculated by multiplying stroke volume x heart r ate. Results: Five min after placement of a hyperbaric tetracaine spin al anesthesia, significant decrease in systolic (from 143 +/- 6 mmHg t o 125 +/- 5 mmHg; P < 0.001), diastolic (from 81 +/- 3 to 71 +/- 3; P < 0.001), and mean (from 102 +/- 4 to 89 +/- 3; P < 0.001) arterial pr essures occurred. Heart rate (75 +/- 4 beats/ min to 76 +/- 4 beat/min ; P = 0.9), stroke volume (115 +/- 17 to 113 +/- 13; P = 0.3), and car diac output (8.0 +/- 1 l/m to 8.0 +/- 1 l/m; P = 0.8) did not change s ignificantly after spinal anesthesia. Phenylephrine was effective at r estoring systolic blood pressure after spinal anesthesia (120 +/- 6 mm Hg to 144 +/- 5 mmHg; P < 0.001) but was associated with a decrease in heart rate from 80 +/- 5 beats/min to 60 +/- 4 beats/min CP < 0.001) and in cardiac output from 8.6 +/- 0.7 l/m to 6.2 +/- 0.7 l/m (P < 0.0 03). Epinephrine was effective at restoring systolic blood pressure af ter spinal anesthesia (119 +/- 5 mmHg to 139 +/- 6 mmHg; P < 0.001) an d was associated with an increase in stroke volume from 114 +/- 12 ml to 142 +/- 17 (P < 0.001) and cardiac output from 7.8 +/- 0.6 l/m to 1 0.8 +/- 1.1 l/m (P < 0.001). Conclusions: Epinephrine management of te tracaine spinal-induced hypotension increases heart rate and cardiac o utput and restores systolic arterial pressure but does not restore mea n and diastolic blood pressure. Phenylephrine management of tetracaine spinal-induced hypotension decreases heart rate and cardiac output wh ile restoring systolic, mean, and diastolic blood pressure.