Continuous spinal anesthesia: does low-dose plain or hyperbaric bupivacaine allow the performance of hip surgery in the elderly?

OBJECTIVES

This study was designed to assess the predictability of 5 mg bupivacaine to give a T10 sensory level when injected subarachnoid in elderly patients.

METHODS

Sixty-five patients aged 75 years or more, scheduled to undergo elective hip surgery, participated in the study. Patients were randomized to receive either 5 mg plain bupivacaine without epinephrine (isobaric group), or 5 mg hyperbaric bupivacaine (hyperbaric group). A 19-gauge catheter was inserted at the L3-4 interspace and threaded 4 cm cephalad in the subarachnoid space. Patients were placed in supine horizontal position and sensory level was assessed every 5 minutes over 20 minutes. Increments of 2.5 mg bupivacaine were given when sensory level did not reach T10 at the 20th minute.

RESULTS

After 20 minutes, the mean sensory level was T8.8 +/- 3.2 in the isobaric group and T7.2 +/- 4.3 in the hyperbaric group without significant difference. Hypotension, defined as greater than a 25% drop in mean arterial pressure, was not significantly different in the two groups: 37.5% and 42.4%, respectively. However, patients who developed hypotension were older (84.3 +/- 7.8 years) than the others (80.3 +/- 5.9 years), and cephalad spread of sensory anesthesia was higher in patients who developed a hypotension (T5.3 +/- 1.4 versus T9.5 +/- 4). In each group, sensory levels did not reach T10 in five patients after initial dose. Five had a sensory block that was too low in spite of incremental doses with the patient in the horizontal position. For the last three, an unintentional sacral placement of the catheter was proved radiologically.

CONCLUSIONS

The authors conclude that 5 mg bupivacaine is too high a dose in the elderly to limit the sensory blockade at T10 and avoid hypotension. In elderly patients, this dose allowed surgery to be performed, provided that the sensory level reached T10. When the initial dose only affects lumbar dermatomes, a caudal direction of the catheter must be evoked, and changing position must be preferred to incremental injections to reach thoracic levels.