In Reply:-We thank Dr. Oxorn for his interest in our report. During pregnancy, our patient's mild limitation of exercise tolerance remained essentially unchanged, and echocardiography showed a left ventricular outflow tract gradient of 15 mmHg. Although the response to amyl nitrite may provide some measure of severity, its use is not universal, it is not commonly used in our institution, and there are few data to support its safe use in pregnancy. We concur with Dr. Oxorn that hypovolemia, increased contractility, and vasodilation may worsen the condition. However, sympathetic stimulation associated with painful labor also may have detrimental consequences, and therefore adequate analgesia for the first stage and a controlled second stage of labor is important. By using a small dose of intrathecal fentanyl followed by a dilute epidural infusion, we obtained satisfactory analgesia without adverse hemodynamic changes. We anticipated that any changes that were to occur would be gradual and amenable to early intervention. In this respect, the predictive value of an amyl nitrite provocative test is unknown. In this case, our estimation of the risks of traditional methods of central neuraxial anesthesia prompted us to consider our modified approach.
Warwick D. Ngan Kee, F.A.N.Z.C.A.
Kwok M. Ho, M.R.C.P.
Department of Anaesthesia and Intensive Care; Chinese University of Hong Kong; Prince of Wales Hospital; Shatin; Hong Kong
(Accepted for publication September 4, 1997.)