Spread of spinal anesthesia in patients having perianal surgery in the jackknife position: effects of baricity of 0.5% bupivacaine and positioning during and after induction of spinal anesthesia.

Study Objective: To compare the influence of baricity and patient positioning during onset of subarachnoid block in patients placed in the prone, jackknife position with head-down tilt of 15 degrees .

Design: Randomized study.

Setting: Operating room of Tonami General Hospital.

Patients: 180 ASA physical I and II patients (134 men and 46 women), aged 18 to 54 years, scheduled for elective perianal surgery.

Interventions: Patients were randomly divided into 6 groups (n = 30 each) based on baricity (hyperbaric or isobaric) of 0.5% bupivacaine (5 mg) and duration of the sitting position (two, 5, or 10 min) after injection.

Measurements: Sensory block levels were examined by pinprick at 0, 5, 10, 20, and 60 minutes after jackknife positioning. Systolic blood pressure and heart rate were also recorded.

Main Results: After jackknife positioning, sensory block levels progressively increased until 15 or 20 minutes in all groups. Regardless of baricity of bupivacaine, sensory block levels were higher at 10 through 60 minutes in the two-minute sitting groups than in the 5-minute or 10-minute sitting groups (P < 0.01 and P < 0.01, respectively), and in the 5-minute sitting groups than in the 10-minute sitting groups (P < 0.05). The mean highest sensory block levels were T5, T9, and T11 in the two-minute, 5-minute, and 10-minute sitting groups, respectively.

Conclusion: Patient positioning, not baricity of bupivacaine, significantly affected the cephalad spread of spinal anesthesia, and a 10-minute period in the sitting position limits the maximum cephalad spread to T11.