Abstracts of Posters Presented at the International Anesthesia Research Society; 72nd Clinical and Scientific Congress; Orlando, FL; March 7-11, 1998: Obstetric Anesthesia
Introduction. Isoproterenol is suggested to be a safer and more effective test-dose for the detection of intravascular placement of epidural catheters than epinephrine in laboring patients. However, epidural epinephrine favors the uptake of local anesthetics and opioids into the spinal cord and decreases the vascular uptake, thereby increasing the intensity and the duration of their neural blockade. The addition of isoproterenol, because of its beta 2-mimetic action, could increase the vascular absorption, and shorten the quality and duration of anesthesia. The present study was undertaken to determine the effects of adding isoproterenol to local anesthetics on the quality and duration of analgesia.
Methods. Following IRB approval, written informed consent was obtained from 80 healthy laboring, pregnant patients at term (ASA 1, 2). The 80 women were randomly divided into two groups, receiving either 12.5 mg bupivacaine with 7.5 [micro sign]g sufentanil and 12.5 [micro sign]g epinephrine (E), or 12.5 mg bupivacaine with 7.5 [micro sign]g sufentanil and 5 [micro sign]g isoproterenol (I) epidurally. For each woman a set of three coded ampoules containing 10 ml was prepared. Contraction pain was measured before epidural analgesia and at 5 min intervals for 15 minutes after each epidural administration of 10 ml of the study solution, and for every hour after the beginning of the study. We used a 100-mm visual analogue scale (VAS) ranging from 0 (no pain) to 100 (worst pain imaginable pain). Injection time was always noted. Statistical analysis was performed using student t-testing and repeated measures analysis of variance.
Results. The total study population consisted of 80 patients of which 78 patients were analysed. Demographic data did not differ between the two groups. The VAS scores were less for the first 15 min after each injection with isoproterenol. The VAS scores did not differ on hourly evaluation. Analgesia after each administration lasted significantly longer in patients receiving epinephrine (Table 1). Due to this difference more patients in group I received a fourth epidural administration.
Discussion. Isoproterenol added to a mixture of local anesthetics and sufentanil shortens the duration of analgesia without affecting the quality of analgesia.