Midodrine was effectively used for prophylaxis against hypotensive syndromes such as postural hypotension and intradialytic hypotension, and during the recovery phase of septic shock. In our study, we aimed to assess the efficacy of prophylactic administration of midodrine tablets before spinal anesthesia in reducing the occurrence of hypotension.
This randomized placebo-controlled study embraced 67 patients aged 18 to 40 years undergoing elective knee surgery under spinal anesthesia. Patients were randomized to midodrine group (given 10-mg tablets of midodrine) or placebo group (given placebo tablets), and tablets were administered 1 hour before spinal anesthesia (intrathecal injection of 12.5-mg 0.5% hyperbaric bupivacaine and 15-μg fentanyl). The primary outcome was the occurrence of hypotension, defined as a systolic blood pressure <90 mm Hg or <80% of baseline. Secondary outcomes were hemodynamic characteristics (mean arterial pressure [MAP] and heart rate [HR]) after spinal anesthesia, ephedrine dose, and occurrence of complications including bradycardia, vasovagal attacks, reactive hypertension nausea, vomiting, and shivering.
The number of patients who became hypotensive after spinal anesthesia was 5 (14.7%) in midodrine group versus 14 (42.4%) in the placebo group; relative risk (95% confidence interval) was 0.35 (0.14–0.85) (P = .021). The median (interquartile range) total dose of ephedrine was significantly lower in midodrine group 0 (0–10) mg than in placebo group (0 (0–15) mg; the Hodges-Lehmann median difference (95% confidence interval) was 0 (0–5) mg (P = .015). For MAP data, the group × time interaction was significant (P = .038), and the MAP was significantly lower in the placebo group than in the midodrine group after intrathecal injection at 2 minutes (P = .047), 10 minutes (P = .045), 15 minutes (P < .001), 20 minutes (P = .007), 30 minutes (P =.013), 45 minutes (P = .029), 60 minutes (P = .029), and at the end of surgery (P < .001). For HR data, the group × time interaction was nonsignificant (P = .807), and the difference in means (95% confidence interval) between groups collapsing over time was −1.4 (−3.1 to 0.2) beats/min (P = .096). There was no significant difference between the 2 groups regarding the occurrence of complications.
Prophylactic administration of 10-mg midodrine tablets before spinal anesthesia is an effective method in the prevention of hypotension in young adult patients undergoing elective orthopedic knee surgery.