Effects of phenylephrine and ephedrine on pulmonary arterial pressure in patients with cervical or lumbar epidural anesthesia, or enflurane anesthesia.

The authors studied systemic and pulmonary hemodynamic changes with ephedrine (EP) or phenylephrine (PH) when used to normalize arterial hypotension resulting from acute sympathectomy due to cervical or lumbar epidural anesthesia, or enflurane anesthesia in 52 patients. Both EP (0.2±0.05 mg·kg-1) and PH (0.025±0.008 mg·kg-1) produced a significant increase in pulmonary arterial pressure (PAP) with a concomitant increase in arterial pressure (AP). In the patients anesthetized with cervical epidural block and NO2-O2, systolic PAP increased from 22±5 to 28±8 mmHg with EP and from 23±6 to 32±10 mmHg with PH in response to approximately 30 mmHg increase of AP, and the ratio of the increment of systolic PAP to systolic AP (ΔPAP/ΔAP) was 0.15±0.08 with EP and 0.20±0.13 with PH (P<0.05); these changes did not differ significantly from those observed in the patients having lumbar epidural or enflurane-N2O-O2 anesthesia. The influence on cardiac output (CO) differed significantly between EP and PH; EP increased CO in all three groups (P<0.05), while PH did not elicit any significant changes in CO. A significant relationship between PAP and AP was found in patients given EP; the regression equation was ΔPAP=0.22×ΔAP-2.9 (r=0.77). The relationship in patients given PH was less significant (r=0.38). The results indicated that EP and PH elicit pulmonary hypertensive effect similarly in the patients with a high level of epidural anesthesia and that although both drugs act differently (EP mainly due to increases in the blood flow and PH solely due to its pulmonary vasconstrictive action), the increases in PAP were predictable, to some extent, from the increase of AP in anesthetized humans without predominant cardiopulmonary disorders.