The amount of fentanyl (ng/kg/min) administered during general anesthesia was less in the PVB group (12.81, SD ±7.73) than in the port infiltration group (16.57, SD ±7.50) (P = 0.007). Postoperatively, the total hydromorphone PCA requirement was not different (P = 0.549) although the amount of PCA hydromorphone consumption at 8 to 12 hours was greater in the PVB group (P = 0.040) than in the port infiltration group. There was no statistically significant difference in other opioid consumption (Table 2).
Linear mixed-effects model analysis of ME over time showed a significant main effect for time only (P < 0.0001). ME consumption decreased over time for both groups until 8 hours, but then consistent with the hydromorphone PCA results, ME increased for the PVB group but not for the port infiltration group. After 12 hours, both groups used less medication (Fig. 2).
The subjects were further evaluated by the presence of shoulder pain: PVB and no shoulder pain, PVB and shoulder pain, port infiltration and no shoulder pain, and port infiltration and shoulder pain. In the PVB group, patients who developed shoulder pain self-administered more hydromorphone PCA (ng/kg/min) between 4 and 8 hours (P = 0.028) and during the first 8 hours (P = 0.035). This relation was not seen in the port infiltration group (Table 3).
Pain Scores and Satisfaction Scores
There was no statistically significant difference in VAS pain scores at hours 4 (P = 0.537), 8 (P = 0.165), 12 (P = 0.217), or 18 (P = 0.299) after the administration of local anesthetic. Pain scores at 24 hours’ discharge time were greater in the PVB group (42.18, SD ±28.73) compared with the port infiltration group (29.98, SD ±25.91, P = 0.045). There was no statistically significant difference in the mean pain scores in the first 12 hours (P = 0.333) and overall pain scores (P = 0.196). There was, however, no statistically significant difference in the mean subject satisfaction scores (PVB group, 81.66, SD ±16.91; port infiltration group, 83.83, SD ±19.97 [P = 0.594]).
Linear mixed-effects model analysis of VAS pain scores showed that the between-group effect was not significant (P = 0.280) and that there was no significant time effect (P = 0.906) (Fig. 3, A). We then examined the relationship between pain just before surgery (preoperative pain) and pain after surgery. The subjects were subdivided into 4 groups: PVB with no preoperative pain (23 subjects), PVB with preoperative pain (18 subjects), port infiltration with no preoperative pain (27 subjects), and port infiltration with preoperative pain (15 subjects). There was no significant time effect (P = 0.333), but the between-group effect was significant (P = 0.002) (Fig. 3, B).
At hours 4, 8, 12, and 24, the mean pain scores were greater in the port infiltration group for the subjects who reported preoperative pain compared with the subjects who did not have preoperative pain. This relation was not seen in the PVB group (Table 4).
There was no difference in incisional (P = 0.555), visceral (P = 0.229), or gas pain (P = 0.353) between the groups (Table 5). More subjects reported shoulder pain in the PVB group (32; 78.05%) than in the port infiltration group (24; 57.14%) (P = 0.042). There was no difference in subjects’ age (P = 0.243), sex (P = 0.131), BMI (P = 0.943), anesthesia (P = 0.095), and surgical time (P = 0.741) between those who had or had no shoulder pain.
Model analysis showed that ME (P = 0.722) and time (P = 0.409) were not associated with shoulder pain, but the incidence of shoulder pain was significantly different between the PVB and the port infiltration groups (P = 0.022). The odds of having shoulder pain were 0.490 (95% confidence interval, 0.269–0.893) lower for the port infiltration group than for the PVB group.
Local Anesthetic Administration
The total amount of ropivacaine administered was 2.35 mg/kg (SD ±0.51) in the PVB group and 1.61 mg/kg (SD ±0.34) in the port infiltration group (P < 0.001).
Four hundred ninety-eight single injections were performed in the PVB space with no serious complications (pleural puncture and/or pneumothorax). Four subjects (3 subjects in the PVB group and 1 subject in the port infiltration group) complained of minimal tenderness at the paravertebral injection sites, which resolved without any intervention. During the PVB injections, 6 vascular punctures (1 subject in the PVB group and 4 subjects in the port infiltration group) were recorded, but these incidents did not result in any bruising or recognizable local anesthetic toxicity symptoms.
No episodes of respiratory depression were reported. There was no difference in incidence of nausea (P = 0.319), emesis (P = 0.881), or itching (P = 0.185). In addition, there was no difference in administration of ondansetron (mg/kg) (P = 0.552) and diphenhydramine (mg/kg) (P = 0.406) between the study groups.
Our study is the first pediatric double-blinded prospective study in which we compared PVBs with incisional local anesthetic administration for postoperative pain control after LC. To ensure a reliable spread of medication, to decrease the risk of epidural spread and PVBs failure,14 we chose to perform 6 separate PVB injections. The primary results of our study differ from a previously published series in adults.6,9 Although we document a decrease in intraoperative use of fentanyl in the PVB group, we did not find any differences in quantitative or qualitative measures of postoperative pain. The fentanyl administered was statistically different, but a statistically significant difference may translate poorly to an actual benefit for the patient.
In the PVB group, there was an increase in hydromorphone PCA use 8 hours after the blocks, with several PVB subjects reporting an increase in pain 6 to 8 hours after the blocks. We had anticipated that the PVB analgesic effect would last 12 hours after local anesthetic injection9,15; however, in our pediatric population, the duration of paravertebral analgesia appeared to be shorter (6–8 hours).
In both groups, VAS pain scores were similar and did not change, despite a decrease in pain medication consumption over time. We found that the port infiltration group subjects with pain immediately before surgery reported more pain than subjects with no pain before surgery, but we cannot explain why we did not find the same relation in the PVB group.
The incidence of shoulder pain in our study was 67%. The reported incidence after adult LC is 30% to 40%. Shoulder pain is attributed to peritoneal stretching and diaphragmatic irritation.2 It can contribute to morbidity by increasing analgesic requirements postoperatively. We did not find any relation among surgery duration, BMI, overall opioid consumption, and shoulder pain, but in the PVB group, opioid consumption at 8 hours was less for the subjects with no shoulder pain. This may be a relative benefit of PVBs in subjects with no shoulder pain. Shoulder pain was more common in the PVB group. Both groups underwent injections in the paravertebral space and thus, we do not suspect a cause and effect relationship between PVBs and shoulder pain. High insufflation pressure has been associated with more postoperative pain.16 Children may be more susceptible to increased pressures because their diaphragms are thinner and thus may stretch more during standard insufflations.
In an attempt to ensure an adequate blinding of the study, maximizing the validity of the results, and to control for a placebo effect from the needle insertion per se, both groups received a therapeutic intervention (local anesthetic administration in the paravertebral space or at the instrument sites) and an “invasive” placebo intervention (saline administration in the paravertebral space or at the instrument sites). We felt that the lack of an invasive placebo would invalidate the study findings.
Invasive placebo is not without risks. We took all measures to ensure patient safety by performing the paravertebral techniques using only very well-trained faculty. The authors had not mastered pediatric paravertebral ultrasound technique when this study was designed, and therefore, this technique was not used. Normal saline solution was used to confirm the needle in the PVB space. A vessel injury from prevertebral muscle and/or paravertebral space was noted in both groups but did not result in any complications. The study drug was injected only after the needle was confirmed to not be in the blood vessel. None of the patients had any complications such us pneumothorax and/or pleural puncture. Mild tenderness at the PVB injection sites was reported in both groups but was self-resolving and did not require any interventions. Placing a dressing over the PVB needle insertion sites of both groups could have compromised double blinding and the validity of results.
There are several limitations to our study. Despite achieving a recruitment target for our study, we did not find a difference in total PCA hydromorphone consumption. The SD was much greater than anticipated, and an adequately powered study based on our findings would not be feasible.
The majority of subjects enrolled were adolescents (mean 13.4 years, SD ±2.2); previous studies have reported that pain assessment and management are difficult in hospitalized adolescents (11–18 years).17 Under these circumstances, we elected to use hydromorphone PCA consumption at 12 hours as our primary outcome. After PCA was discontinued, pain scores did not change much, but the amount of opioid administered decreased significantly, which raises the possibility that our subjects may have used the PCA demand option not only for incisional or visceral pain but also dosed in an effort to hasten ambulation, to relieve anxiety, or to improve their mood.
This study did not collect any information about psychosocial factors such as subjects’ catastrophizing attention to pain, pain behavior, anxiety, depression, or mood level. These variables influence pain scores and the decision regarding self-administration of pain medication and thereby confounded our results.18–21
Pain scores collected were specific to abdominal pain and not documented for specific shoulder pain. There were some subjects who complained more of shoulder pain than incisional, visceral, or gas pain.
We did not enroll any subjects with chronic abdominal pain, but in several cases the removal of the gallbladder did not lead to resolution of abdominal pain. These subjects may require long-term multidisciplinary interventions.
In conclusion, PVBs decreased intraoperative fentanyl consumption but were not superior to port site injections with local anesthetic for pain control after pediatric LC. Duration of analgesia after PVBs in our study was shorter than expected. Pain before surgery can influence self-reported postoperative pain scores. In this context, the analysis of pain medication consumption and postoperative pain scores should be complemented by knowledge of subjects’ catastrophizing thoughts about pain, depression, anxiety, and mood level. Shoulder pain was a potential confounding variable, unlikely to be impacted by either treatment strategies. Novel surgical strategies to prevent shoulder pain and associated opioid use should be encouraged.
The authors thank Barbara W. Brandom, MD, Professor of Anesthesiology Children’s Hospital, University of Pittsburgh Medical Center, and Jacques E. Chelly, MD, Professor and Vice Chairman of Clinical Research for the Department of Anesthesiology, University of Pittsburgh Medical Center Presbyterian–Shadyside Hospitals Aiken Medical Building, for their indispensable advice in preparation of the manuscript. We thank George K. Gittes, MD, Chair of Pediatric Surgery, Surgery-in Chief, Division of Pediatric Surgery, Children’s Hospital of Pittsburgh of University of Pittsburgh Medical Center, and R. Cartland Burns, MD, Associate Professor of Surgery, Division Chief, Division of General Surgery, Department of Surgery, Nemours Children’s Hospital in Orlando, Florida, for their support with this study. We express our gratitude to the surgeons, anesthesiologists, and pharmacists who supported this project and nurses who helped to collect the questionnaires. We thank Bedda Rosario, PhD, from the University of Pittsburgh for statistical analysis on this project. We also acknowledge Michael C. Young, technical manager, University of Pittsburgh, NAMHR of MHAUS, and Lendi Joy, Research Assistant, Children’s Hospital of Pittsburgh of University of Pittsburgh Medical Center, who assisted with statistical analysis.
Name: Mihaela Visoiu, MD.
Contribution: This author designed the study, conducted the study, collected and analyzed the data, and wrote the manuscript.
Attestation: Mihaela Visoiu has seen the original study data, reviewed the analysis of the data, approved the final manuscript, and is the author responsible for archiving the study file.
Name: Antonio Cassara, MD.
Contribution: This author helped conduct the study, collected the data, and helped write the manuscript.
Attestation: Antonio Cassara approved the final manuscript.
Name: Charles Inshik Yang, MD.
Contribution: This author helped design the study, collected and analyzed the data, and helped write the manuscript.
Attestation: Charles Inshik Yang approved the final manuscript.
This manuscript was handled by: James A. DiNardo, MD.
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