Patient-controlled bupivacaine wound instillation following cesarean section: the lack of efficacy of adjuvant ketamine.

STUDY OBJECTIVE

To assess the analgesic efficacy of ketamine when administered as an adjuvant to bupivacaine for patient-controlled wound instillation following cesarean section.

DESIGN

Prospective, randomized, double-blind study.

SETTING

Large referral hospital.

PATIENTS

50 term parturients undergoing cesarean section.

INTERVENTION

In all cases, a standard spinal anesthetic was administered. On completion of the surgery, a multihole 20 G epidural catheter (B. Braun, Melsungen, Germany) was placed above the fascia such that the tip was sited at the point which demarcated 50% of the length of the surgical wound. Thereafter, the catheter was connected to a patient-controlled drug delivery device. The device was filled with either 0.125% bupivacaine (bupivacaine group) or 0.125% bupivacaine and ketamine (1 mg/mL) (bupivacaine-ketamine group). Postoperatively, wound instillation was performed via the patient-controlled analgesia device. During the first 6 postoperative hours, a co-investigator administered "rescue" morphine (2 mg IV). Thereafter, "rescue" dipyrone (1 g) was administered on patient request.

MEASUREMENTS AND MAIN RESULTS

At all time intervals, visual analog scale (VAS) for pain at rest, on coughing, and during leg raise were similar between the groups. All patients (100%) in both treatment groups received "rescue" morphine. Similarly, the number of doses of 2 mg "rescue" morphine administered was unaffected by patient randomization. The total "rescue" morphine administered during the first 6 postoperative hours was 11.2 +/- 4.6 mg versus 11.3 +/- 5.6 mg for the bupivacaine group and bupivacaine-ketamine group, respectively. The number of pump infusions during the 24-hour study period was 9 +/- 2 and 9 +/- 3 for the bupivacaine group and bupivacaine-ketamine group, respectively. The volume infused via the delivery device was similar between the groups (81 +/- 18 mL vs. 85 +/- 24 mL for the bupivacaine group and bupivacaine-ketamine group, respectively). Psychomental and cognitive function as measured by the Digit Symbol Substitution and Mini Mental Tests were unaffected by adjuvant ketamine administration. Patient satisfaction was similar between the groups.

CONCLUSION

Adjuvant local ketamine does not enhance bupivacaine-induced wound instillation following cesarean section.