Intravenous trimethaphan during epidural plus general anesthesia decreases the direct radial artery pressure lower than the brachial artery pressure.

ABSTRACT

STUDY OBJECTIVE: To determine whether vasodilators such as sodium nitroprusside (SNP) and trimethaphan (TMP) produce a pressure difference between the radial artery and the brachial artery during epidural plus general anesthesia or simple general anesthesia. DESIGN: Randomized study and prospective study. SETTING: Operating rooms of two hospitals. PATIENTS 36 and 6 adult patients in the first and second studies, respectively, who received spherical acetabular osteotomy with induced hypotensive anesthesia. INTERVENTIONS: In the first study, 18 patients received epidural plus general anesthesia (epidural group) and 18 patients received general anesthesia alone (general group). All patients received the hypotensive drugs for more than 50 minutes each. In the second study, 6 patients received TMP-induced hypotension for 20 minutes under epidural plus general anesthesia. MEASUREMENTS AND MAIN RESULTS: In the first study, radial intra-arterial blood pressure (RIBP) and tonometric blood pressure (TBP) calibrated with oscillometric blood pressure of the arm were compared. In the second study, RIBP and the brachial intra-arterial blood pressure (BIBP) were compared. In the first study, the bias between RIBP and TBP for systolic, mean and diastolic blood pressure were significantly less during TMP-induced hypotension in the epidural group (-11.5 +/- 2.5 (mean +/- SD), -6.0 +/- 3.1, and -2.8 +/- 3.7 mmHg, respectively] than during SNP-induced hypotension in the epidural group and SNP- and TMP-induced hypotension in the general group (p < 0.01). The precision of systolic and mean pressures were significantly greater during TMP-induced hypotension in the epidural group (11.8 +/- 2.3 and 7.1 +/- 1.9 mmHg, respectively) than the other three hypotension groups (p < 0.01). In the second study, the bias between RIBP and BIBP for systolic, mean, and diastolic pressures were significantly less (p < 0.01), and precision was significantly greater during hypotension than during normotension (p < 0.01). CONCLUSIONS: Our results demonstrate that TMP decreases the direct radial artery systolic and mean pressures to levels below the brachial artery systolic and mean pressures in patients who received epidural plus general anesthesia.