Discussion
This study showed that continuous subfascial wound administration of ropivacaine combined to a multimodal systemic analgesia after caesarean section is more effective than placebo. Results showed a significant reduction in morphine consumption of 8.05 mg in the ropivacaine group. On VAS, pain at mobilisation 6 hours after surgery was significantly reduced with ropivacaine compared to placebo. A trend toward significance in favour of ropivacaine was observed for pain by VAS at rest 6 hours after surgery, at rest 12 hours after surgery and at mobilisation 48 hours after surgery. In contrast, no significant differences were observed on VAS for pain 2 hours and 72 hours after surgery, both at rest and at mobilisation. For adverse effects (post-operative nausea/vomiting and pruritus) and time of first ambulation, no significant differences were observed comparing ropivacaine to placebo continuous subfascial wound infusion.
In obstetric populations, although several studies assessed analgesic effects of continuous anaesthetic wound infusion after caesarean section, clear results are still lacking because of conflicting results. (3-13) Furthermore, most of these studies showed some important limitations and heterogenicity in their designs, regarding the local anaesthetic agent used (ropivacaine, bupivacaine, levobupivacaine), its mode of release (continuous infusion or PCA), the NSAID in adjunction and the multimodal systemic analgesics used (morphine, oxycodone, ketoprofen or diclofenac) and their mode of release (oral, intramuscular intravenous or intrathecal).
A Cochrane Collaborative systematic review published in May 2010 concluded that morphine consumption was decreased by 1.70 mg at 24 hours after caesarean section using anaesthetic wound infiltration compared to placebo. (7) This modest reduction compared to the 8.05 mg reduction in our study may be explained by selection bias. Indeed Bamigboye et al. (2009) included next to wound infusions studies, studies of wound infiltration with local anaesthetic or with NSAID. (7) Furthermore, in all of the included wound infusion studies, the catheter was placed above the fascia. (4,5,6) However, based on Rackelboom et al. (2010), better analgesia is obtained over 48 hours when ropivacaine and ketoprofen are infused below the fascia compared to administration above the fascia. (8) In this study, the multi-holded catheter was placed below the closed fascia transversalis and above the closed parietal peritoneum, to avoid intraperitoneal leakage.
In more recent studies, Kainu et al. (2012) found no benefit of continuous subfascial wound infusion with ropivacaine, which in their study failed to reduce the use of PCA administered oxycodone or pain scores compared to saline control. (10) The same conclusions were made in another randomized trial published by Reinikainen et al. (2014) where on the contrary ropivacaine was placed above the fascia and oxycodone not PCA administrated, possibly explaining the lack of efficacy from their ropivacaine infusion. (11) Conversely, Jolly et al. (2015) concluded that after caesarean section without subarachnoid morphine, continuous levobupivacaine compared to placebo subfascial wound infiltration decreased PCA administered morphine consumption (6.7 mg, P value = 0.02) and pain intensity. (12) Nevertheless, the unblinded design of their study may have leaded to biases. Finally, Lalmand et al. (2017) investigated the duration and effect of intrathecal analgesia and continuous subfascial ropivacaine wound infiltration versus a control group after caesarean delivery. The duration of postoperative analgesia was increased with intrathecal morphine (380 minutes) and ropivacaine wound infusion (351 minutes) compared with the control (247 minutes), without significant difference between the morphine and catheter group. Cumulative postoperative morphine consumption was also significantly lower in the morphine group and catheter group compared to the control group. (13) When comparing continuous ropivacaine wound infusion after caesarean delivery to epidural morphine analgesia on pain evaluated by VAS, O’Neill et al. (2012) concluded a better analgesia, a lower incidence of side effects, less need for nursing care and shorter duration stay using wound infusion. (9) Based on the important role in post-operative pain of diffuse visceral nociceptive afferents in peritoneal tissue, blockade by local anaesthetics could easily explain the dose reduction of systemic analgesics.
Continuous subfascial wound infusion seems to be well tolerated by patients. In this study we selected ropivacaine as local anaesthetic because of its lower systemic toxicity and its shorter half-life comparing to bupivacaine and levobupivacaine. The infusion rate was chosen based on the study of Beaussier et al. showing that a constant rate of 0.2 % ropivacaine at 10 mL/h was well tolerated and associated with a sufficient margin of safety in colorectal surgery. (14) Liu’s et al. meta-analysis concerning the use of continuous wound catheters delivering local anaesthetics reported a 1% technical pump failure rate and similar infection rates between active (0.7 %) and control groups (1.2 %). (15) Current study observed no technical failure and no infection issue, probably explained by the inadequate sample size for this purpose. The same concept can be applied to explain the fact that some of the secondary outcomes showed a trend in favour of the ropivacaine group without reaching the threshold of statistical significance: pain by VAS at rest 6 hours after surgery, at rest 12 hours after surgery and at mobilisation 48 hours after surgery. Nevertheless, a previous assessor-blinded trial already evidenced beneficial effects of continuous subfascial wound infusion with ropivacaine after caesarean delivery, using pain at rest and at mobilisation on VAS as primary outcome. (9)
The strengths of the current study include the prospective, randomized controlled, double-blind design and the robust and rigorous methodological approach of the study protocol. Furthermore, using analgesic consumption on PCA device instead of VAS as primary outcome is likely to be more objective for pain evaluation. As far as we know, no other randomized controlled, double-blind studies were published comparing the analgesic efficacy of continuous ropivacaine versus placebo subfascial wound infusion after caesarean delivery using morphine consumption on PCA as primary outcome. The limitation of this study is the monocentric design.
In conclusion, continuous ropivacaine subfascial wound infusion trough a multi-holded catheter can be considered as an effective method for pain management in a multimodal analgesic approach after caesarean delivery and this without increasing the incidence of side effects.