Adequate perioperative analgesia is an important requisite for improved patient outcome and functional recovery. Intensity of pain and the risk-benefit ratio of different analgesic modalities are procedure-related.[7
] Procedure-specific pain management strategies for laparoscopic cholecystectomy are currently being investigated.[8
] Hence, we assessed the efficacy and safety of PVB in laparoscopic cholecystectomy.
Analysis of our results revealed a significant decrease in intraoperative supplemental fentanyl consumption in the study group (mean requirements 38.6 μg vs 17.6 μg in the control and study groups, respectively; P
<0.05). Since general anesthesia was administered in the study group immediately after the PVB in most patients, the success of the block by the loss of pin-prick or temperature sensation could not be assessed. Hence, the finding of reduced intraoperative fentanyl requirement in the study group assumes greater clinical relevance. Similar results have been reported in thoracoscopic surgery in patients receiving single-dose, multilevel (six injections of 5 ml of 0.5% bupivacaine each) PVB.[9
] Naja et al
. (2004) assessed the efficacy of bilateral PVB in laparoscopic cholecystectomy but did not compare intraoperative analgesic requirements between the groups.[10
The mean VAS score at rest was significantly higher in the control group in the immediate postoperative period. More patients in the control group reported moderate to severe pain (92% compared to 44% in the study group; P<0.05) immediately after awakening, while a significant number of patients in the PVB group awoke pain free. Fifty-six percent (56%) of the patients in the study group had a VAS score <3 compared to 8% in the control group, (P<0.05) after the surgery.
These findings affirm that the pre-induction PVB was effective in reducing pain intensity in a significant number of patients in the study group because the mean VAS score at rest was less in the study group despite less intraoperative fentanyl consumption.
The subsequent mean VAS scores at rest were less in our study group at 2, 6, 12, and 24 hours postoperatively, but the difference was not statistically significant. This can be explained by the use of PCA morphine postoperatively in both the groups and the wearing off of the PVB. The patients in the control group required more PCA morphine in order to keep the VAS score <3 throughout the first postoperative day compared to those in the study group.
Dynamic pain relief is crucial to facilitate early recovery in the postoperative period. The efficacy of PVB in attenuating dynamic pain was assessed in this study by comparing VAS scores on coughing between the groups. The patients in the study group reported significantly less pain on coughing in the immediate postoperative period (mean VAS scores 5.24±1.5 and 7.04±1.24 in the study and control groups, respectively; P<0.001).
However, VAS scores on coughing were comparable between the two groups during the subsequent postoperative recordings (2, 6, 12, and 24 hours). These findings can again be attributed to the PCA morphine consumption in both the groups.
The mean VAS scores on coughing were higher than those at rest in both the groups at all intervals. However, unlike those at rest, the mean VAS scores on coughing at 2, 6, 12, and 24 hours postoperatively in both the groups were >3, thus reflecting inadequate analgesia on coughing. A high percentage of patients reported moderate pain (VAS score: 4-6) on coughing at 2, 6, 12, and 24 hours postoperatively in both the groups (64%, 64%, 72%, and 80% in Group A and 72%, 60%, 64%, and 64% in Group B, respectively).
These findings suggest that neither the PCA morphine could adequately relieve the pain on coughing in the control group, nor could the PVB result in adequate dynamic pain relief in the study group.
The results in our study group are in contrast with those observed in the PVB group by Naja et al
. (2004) because only 20%, 10%, and 14% of the patients reported mean VAS scores on coughing >3 in their study group at 6, 12, and 24 hours postoperatively.[10
] This difference in results can be explained by the use of a combination of lignocaine, bupivacaine, fentanyl, and clonidine for PVB in their study compared to bupivacaine only in our PVB group. Adjuvants such as fentanyl and clonidine are of proven efficacy in enhancing the quality and duration of analgesia following peripheral nerve blocks.[11
Patients in the PVB group in our study required significantly less PCA morphine compared to those in the control group, and the difference was significant statistically throughout the first postoperative day (mean cumulative PCA morphine requirements 16.80±3.37 mg vs 27.24±5.08 mg in the study and control groups, respectively; P<0.05).
The significant reduction in analgesic consumption for the first 24 hours in our study group was well beyond the reported duration of bupivacaine in peripheral nerve blocks. This finding may suggest the efficacy of PVB as a pre-emptive analgesic modality in laparoscopic cholecystectomy. Pre-incisional PVB may have led to inhibition of central sensitization and resulted in improved pain relief beyond the pharmacological duration of bupivacaine. In a study involving patients undergoing breast surgery, Greengrass et al
. (1996) reported improved analgesia for 24 hours in patients receiving PVB with bupivacaine alone.[12
] Kairaluoma et al
. (2000) also demonstrated that pre-incisional PVB resulted in reduction of the prevalence of chronic pain for one year following breast surgery.[13
Opioid-sparing effects of PVB
Laparoscopic cholecystectomy is now being increasingly performed on an outpatient basis, and hence effective analgesia with opioid-sparing attributes is being preferred to hasten postoperative recovery. The patients receiving PVB in our study required 38% less PCA morphine compared to those in the control group. Intraoperative supplemental fentanyl requirement in the study group was 54% less than the control group. Kehlet et al
. (2005) have extensively reviewed opioid-sparing effects of different regimens and remarked that approximately 30% reduction in opioid requirement was clinically significant.[14
An opioid-sparing analgesic technique should also result in decreased incidence of opioid-related side effects. Hence, we compared the occurrence of opioid-related adverse effects between the two groups.
PONV is one of the most unpleasant symptoms perceived by the patients following laparoscopic cholecystectomy. Patients in the PVB group reported significantly less PONV than those in the control group in the immediate postoperative period in our study. Rescue anti-emetic was required by 15 of 25 patients (60%) in the control group immediately postoperatively compared to only 9 of 25 patients (36%) in the study group. This difference reflects significant opioid-sparing benefit of PVB in terms of reduced PONV but did not attain statistical significance, presumably, due to the small sample size. Similar limitation of various trials assessing opioid-sparing analgesic regimens had been reported by Kehlet et al
. in 2005.[14
] They suggested that the different trials estimated the sample size in order to demonstrate a certain reduction in opioid requirements for effective analgesia, but, subsequently, found it insufficient to reflect a similar difference in opioid-related side effects. Requirement of a larger sample size was suggested in order to find a statistically significant difference in the side effects.
Baumgarten et al
. (2007) also remarked the efficacy of PVB in terms of reducing PONV after hernia surgery and recommended PVB as the anesthetic technique of choice in ambulatory hernia repair.[15
Urinary retention was noted in 2 of 25 patients in the control group compared to none in the study group. This can be attributed to the greater PCA morphine requirement in the control group.
Hence, in summary, the use of PVB in our study resulted in significantly better pain relief, reduced opioid requirements for the first 24 hours, and a decreased incidence of opioid-related side effects.
Complications related to PVB
We also aimed to assess the safety of PVB in our study. Karmakar (2001) in his review of PVB reported the following complications—pleural puncture, pneumothorax, epidural spread, injection into the subarachnoid space, intravascular injection, and Horner's syndrome.[16
None of the patients in the PVB group reported chest pain or breathlessness indicative of pneumothorax in our study. This could be attributed to the enhanced safety associated with the nerve-stimulator–guided technique of PVB. Improved safety with nerve-stimulator–guided technique has also been suggested in few previous studies.[17
] Ultrasound guidance has further enhanced the safety of PVB as illustrated in some recent studies.[19
Epidural and subarachnoid spread of local anesthetic injected into the paravertebral space has also been reported. One of 25 patients in our study probably had an epidural spread as reflected in the persistent intraoperative hypotension and mephentermine requirements. Klein et al
. (2002) also noted epidural spread in one of 24 patients receiving PVB for inguinal herniorrhaphy.[21