In Reply:-Dr. Langevin correctly points out that the animal data do not consistently support the clinically observed phenomenon of uterine relaxation resulting from administration of nitroglycerin in human parturients. Dr. Shin et al. [1]found a dose-dependent reduction of contractility in isolated human uterine muscle segments exposed to nitroglycerin in vitro, but the mean dose to abolish spontaneous contractions was 4.5 x 10 sup -4 M (250 micro gram in the 12 ml bath), far exceeding commonly used clinical doses. This may be a result of the scarcity of vascular endothelium present in these preparations.
Dr. Langevin also states that administration of nitroglycerin definitely reduces maternal blood pressure. In our experience, the administration of 50-100 micro gram of nitroglycerin intravenously or 800 micro gram sublingually has not resulted in decreased maternal blood pressure consistently, or even frequently, in urgent clinical settings. These include tetanic uterine contraction, extraction of a breech twin, or manual extraction of placenta. I suspect that the anxiety engendered by rapid interventions such as maternal position changes, increased intravenous fluid administration, application of supplemental oxygen, and summoning the obstetrician ameliorate the vasodilatory effects of the nitroglycerin. This is in contrast to our recent trial using nitroglycerin spray in the setting of elective external version of breech position. [2]We saw a high percentage of patients respond with decreased blood pressure (4 of 10 patients experienced a decrease of 20% or greater). It is unclear whether this was in response to the nitroglycerin or mechanical compression from vigorous attempts, and certainly deserves further investigation.
Elizabeth Bell, M.D., M.P.H.
Assistant Professor of Anesthesiology
Division of Women's Anesthesia; Duke University Medical Center; Box 3094; Durham, North Carolina 27710
(Accepted for publication May 21, 1997.)
