Elastomeric Pain Pumps as an Adjunct for Postoperative Pain Control After Minimally Invasive Repair of Pectus Excavatum

Abstract

Introduction:

Pectus excavatum is a common congenital anomaly in the pediatric population. During the postoperative period, pain control is one of the top priorities. As a result, multiple techniques for pain control have been developed, including thoracic epidural analgesia, multimodal analgesia (MM), and elastomeric pain pump (EPP) placement. The purpose of this study was to evaluate the effectiveness of pain control using EPP as an adjunct to MM after the minimally invasive repair of pectus excavatum (MIRPE).

Methods:

We identified all pediatric patients undergoing MIRPE from June 2017 to July 2018. MM was employed in all patients; some patients additionally received subpleural EPP as adjuncts to postoperative analgesia. We reviewed pain scores, length of stay, opioid use, and complications.

Results:

During the study period, a total of 62 patients were included. The study cohort was divided into 15 patients undergoing MM alone versus 47 patients undergoing subpleural EPP placement plus MM (EPP + MM). Median pain scores were lower in the EPP + MM group (2.9 versus 4.2, P < .05). There was a significant reduction of total inpatient opioid use in the EPP + MM group (357.6 mg versus 466.9 mg, P = .03). There was no difference in median length of stay or complications. We found no significant difference between subpleural versus subcutaneous placement of the infusion catheters.

Conclusion:

The use of subpleural EPP as an adjunct to MM is an effective way to reduce pain and opioid use after MIRPE without increased risk of complications.

Type of Study:

Retrospective study with comparison group.

Introduction

Pectus excavatum is a common congenital chest wall abnormality that results from disturbances in the growth of the costal cartilages and sternum. It occurs in about 1 in 400 to 1 in 1000 live births.^1–5 It is often recognized during early childhood with an increase in the severity of the deformity as skeletal growth becomes more rapid.^1,3,5 Pectus excavatum has historically been corrected with one of two procedures, the open Ravitch approach, along with multiple subsequent modifications, and more recently, the minimally invasive repair of pectus excavatum (MIRPE) or “Nuss procedure.”^2,4 The MIRPE allows forceful repositioning of the sternum using steel or titanium bars positioned underneath the chest wall that place a significant force on the ribs and costochondral cartilages.^2,5,6 However, this force, and the dissection itself, result in significant postoperative pain for the patient specifically in the early postoperative period, which have shown to affect hospital length of stay.^5–7

To optimize pain control, multiple strategies have been employed including both oral and intravenous analgesia, thoracic epidural analgesia, ultrasound-guided intercostal nerve blocks, and more recently, cryoablation of intercostal nerves.^3,8,9 Cryoanalgesia has shown some promising results; however, it is expensive, and there is still some concern about long-term sequelae from it. On the other side, continuous infusion of local anesthetics, through elastomeric pain pumps (EPP), for example, has been described as effective for postoperative analgesia following thoracotomy with the advantage of reducing the incidence of respiratory depression, nausea, vomiting, pruritus, and urinary retention compared with epidural analgesia or opioid use.^8,10–14 This method has been well described in adults; however, in children, this method has been limited to certain populations such as open cardiac surgery and scoliosis surgery with some promising results.^14,15

The pain management strategies at our institution have evolved over time from the sole use of epidural analgesia to the development of a multimodal analgesia (MM) protocol that forfeits the use of epidural catheters.⁹ To improve pain control, we began using subpleural elastomeric infusion pump catheters (On-Q Pain Relief System; Avanos, Irvine, CA) at our institution in 2017. The pump consists of a flow-limiting valve that provides continuous infusion of the anesthetic to nearby tissues. The aim of this study was to evaluate the quality of pain control provided by infusion pump catheters in comparison with our postoperative MM protocol after MIRPE.⁹

Materials and Methods

Patients and data collection

Following approval by the Phoenix Children's Hospital Institutional Review Board (IRB) and Ethics Committee (IRB 18-131), a retrospective chart review was performed on children who underwent MIRPE from June 2017 to July 2018. We excluded all the patients with previous repair. Patient demographics, postoperative intravenous and oral opioid and nonopioid analgesic use, length of hospital stay, surgical complications, reoperations, and outpatient data were recorded.

Operative technique

A double-lumen endotracheal tube was placed by an anesthesiologist to allow for unilateral and bilateral pulmonary ventilation. Bilateral incisions were made on the lateral chest wall and extended through the muscular layer. Submuscular pockets were created for bar placement. The mediastinal cavity was accessed, and under thoracoscopic visualization, two bars were placed to correct the defect in most of the cases due to severity of the defect. The bars were secured in place with permanent braided sutures around the ribs. The use or not of EPP was based on surgeon's individual expertise and preference.

Elastomeric pump infusion catheters on peel-away sheath trocars were then tunneled within the chest wall just beneath the pleura under direct thoracoscopic vision through bilateral stab incisions on the inferior anterolateral chest wall (Fig. 1). The pumps were filled with 550 mL of 0.25% bupivacaine or 0.2% ropivacaine and continuously provided postoperative infusion. The dosage was weight-based (0.0403 mL/hour/kg/dose for 0.25% bupivacaine and 0.2 mL/hour/kg/dose for 0.2% ropivacaine) with a maximum dosage of 14 mL/hour. The total dosage was divided between the two catheters in a Y-configuration. The catheters were secured to the skin with clear tape. The catheters were removed before discharge from the hospital.

FIG. 1.

Right intrathoracic view of subpleurally placed elastomeric pain pumps.

Postoperative management

The postoperative pain management strategy included MM for the patients as per our published protocol.⁸ All patients received general anesthesia and patient-controlled anesthesia with either demand only or continuous plus demand infusion of hydromorphone (or fentanyl if allergic). They also received a clonidine patch, gabapentin, ketamine, and dexmedetomidine infusions, and one dose of intravenous methadone. After 24 hours, the patient-controlled anesthesia was discontinued, and the patient was transitioned to 10–20 mg/day of oxycodone. Ketorolac and diazepam were given also as part of the protocol. Once adequate pain control was achieved, the patients were transitioned to oral medications (ibuprofen, acetaminophen, and oxycodone) and then discharged.

Statistical analyses

Demographic and clinical characteristics within each of the groups are reported as medians (interquartile ranges [IQRs]) for continuous covariates and frequencies (percentages) for categorical variables. Our two comparison groups were patients undergoing MM alone versus patients undergoing MM and EPP placement (EPP + MM). The Kruskal–Wallis test compared the continuous covariates between the three groups, whereas chi-squared or Fisher's exact test compared the categorical variables. Multivariable linear regression was used to ascertain estimated differences in morphine equivalence between the both analgesia groups using multimodal as the reference group. The multivariable linear mixed model calculated differences in pain scores between the analgesia groups over time. Both models were adjusted for age, gender, body mass index (BMI), length of stay, correction index, and total operating room (OR)/surgical time. Further adjustments of baseline pain scores were included in the linear regression model, whereas total morphine equivalence was added to the linear mixed model. All P values were two-sided, and P < .05 was considered statistically significant. All data analyses were conducted using STATA version 14 (STATA Corp, College Station, TX, USA).

Results

During the study period, a total of 62 patients were included. The study cohort was divided into 15 patients undergoing MM alone versus 47 patients undergoing EPP placement plus MM (EPP + MM). Demographics are summarized in Table 1. There was no difference in preoperative characteristics, such as age, gender, symptoms, or severity of the disease (Haller and Correction indices).

Table 1.

Demographics

Variable	MM (N = 15)	EPP + MM (N = 47)	P
Age, years, median (IQR)	15.4 (13.8–16.5)	15.2 (13.9–16.7)	.80
Gender: male (%)	12 (80.0)	35 (74.5)	.76
Height, cm, median (IQR)	169.3 (164.6–180.2)	171.5 (165.9–175.4)	.89
Weight, kg, median (IQR)	51.8 (46.7–65.6)	53.8 (46–59.3)	.87
BMI, kg/m², median (IQR)	18.9 (16.4–20.6)	18.3 (16.7–19.7)	1.0
Shortness of breath: yes (%)	12 (80.0)	41 (87.2)	.67
Pain: yes (%)	8 (53.3)	26 (55.3)	1.0
Palpitations: yes (%)	1 (6.67)	0 (0.0)	.24
Haller Index, median (IQR)	4.28 (3.72–5.20)	4.50 (3.80–5.80)	.35
Correction Index, median (IQR)	29 (25–39)	35 (25–43)	.32

BMI, body mass index; IQR, interquartile range; MM, multimodal analgesia.

EPP placement + MM versus MM alone

Operative time was statistically significantly longer in the EPP + MM group when compared with the MM group (128 minutes [IQR 101–153] and 100 minutes [IQR 84–126], respectively). There was no difference in the median length of stay among both groups. There were no cases where interventions were needed or wound infection was encountered. Bar displacement as defined radiographically or with correction loss was not different among groups. One patient in the MM group had postoperative pneumonia diagnosed by chest radiograph and 1 patient in the EPP + MM group had bar displacement but did not require any intervention. There was no difference in the median follow-up between both groups: 19.3 weeks (IQR 6.86–52.3) in the MM group versus 36 weeks (IQR 12.6–52.4) in the EPP + MM group (Table 2).

Table 2.

Clinical Outcomes

Variable	MM (N = 15)	EPP + MM (N = 47)	P
Surgical time, minutes, median (IQR)	100 (84–126)	128 (101–153)	.014
Length of stay, days, median (IQR)	3 (3–4)	4 (3–5)	.24
Pleural drainage needed: yes (%)	0 (0.0)	0 (0.0)	N/A
Wound infection: yes (%)	0 (0.0)	0 (0.0)	N/A
Pneumonia: yes (%)	1 (6.67)	0 (0.0)	.24
Bar displacement: yes (%)	0 (0.0)	1 (2.13)	1.0
Total follow-up time, weeks, median (IQR)	19.3 (6.86–52.3)	36 (12.6–52.4)	.54

IQR, interquartile range; MM, multimodal analgesia; N/A, not applicable.

The median pain scores were lower in the EPP + MM group (2.9 [IQR 1.7–4.4]) when compared with the MM group (4.2 [IQR 3.2–5.3]) (Table 3). However, this tendency was initially not statistically significant but after adjusting for multiple clinical confounders (BMI, correction index, age, and gender), it reached statistical significance in the second model (P < .05). In terms of inpatient opioid use, total inpatient (both oral and intravenous) opioid use was lower in the EPP + MM group (357.6 [IQR 263.4–454.6]) when compared with the MM group (466.9 [IQR 331.4–548.4]). There was no statistical difference on the total oral opioid use (P = .53); however, the EPP + MM group used less intravenous opioids as inpatient (P = .02) (Table 4). The duration of the elastomeric pump was 72 hours for all the patients per our protocol.

Table 3.

Visual Analog Pain Score by Pain Modality

	Pain scores, median (IQR)	Model 1, exp(β) (95% CI)^a	P	Model 2, exp(β) (95% CI)^b	P
Pain modality
MM	4.23 (3.25–5.28)	REF		REF
EPP + MM	2.92 (1.71–4.42)	0.83 (0.66–1.07)	.15	0.80 (0.65–1.00)	.054

Model 1: exponentiated beta (95% CI) calculated using the linear mixed model to ascertain changes in VAS score over time adjusting for time and the patient-level random effect.

Model 2: exponentiated beta (95% CI) calculated using the linear mixed model to ascertain changes in VAS score over time adjusting for time and the patient-level random effect with further adjustments for age, gender, body mass index, length of stay, surgical/total operating room time, and total amount of morphine equivalents given.

CI, confidence interval; IQR, interquartile range; MM, multimodal analgesia; VAS, Visual Analog Scale.

Table 4.

Inpatient Opioid Use by Pain Modality

Variable	MM (N = 15)	EPP + MM (N = 47)
Total IV opioids, mg
Median (IQR)	84 (60–130.3)	63.1 (46.5–93.2)
Exp(β) (95% CI)^a	REF	0.64 (0.45–0.92)
P		.017
Total oral opioids, mg
Median (IQR)	120 (105–172.5)	150 (112.5–195)
Exp(β) (95% CI)^a	REF	1.07 (0.86–1.32)
P		.53
Total inpatient opioids, mg
Median (IQR)	466.9 (331.4–548.4)	357.6 (263.4–454.6)
Exp(β) (95% CI)^a	REF	0.78 (0.62–0.98)
P		.036

Exponentiated beta (95% CI) calculated using the linear regression to ascertain differences in morphine equivalents adjusting for age, gender, body mass index, length of stay, correction index, total operating room/surgical time, and baseline pain scores.

CI, confidence interval; IQR, interquartile range; IV, intravenous; MM, multimodal analgesia.

Discussion

Since the introduction of the minimally invasive techniques to repair pectus excavatum, there have been many pain management strategies employed by providers, including intravenous and epidural analgesia, both opioid and nonopioid oral pain medications, percutaneous intercostal nerve blocks, muscle relaxants, sedatives, and cryoablation of intercostal nerves (8). We hypothesized that pain control could be improved with the implementation of pain management strategies that targeted the intercostal nerves, the likely source of postoperative pain, with the use of EPP. We observed that the addition of EPP to MM following MIRPE led to a decrease in the inpatient opioid use and intravenous opioid use when compared with the use of MM alone. Also, we found improvement in pain control postoperatively.

There was no increase in complications in our study secondary to pain pump use as demonstrated by a lack of statistically significant differences in the length of stay, pneumonia, wound infection, bar displacement, or need for pleural drainage, which are the most common complications after MIRPE with the decrease in narcotic use with improved pain scores. A randomized trial by Jaroszewski et al. evaluating pain management with epidural versus subcutaneous catheters following MIRPE in adults also did not find a significantly higher rate in complications, including pneumonia, pleural effusion, or pneumothorax in the subcutaneous catheter cohort.⁸

One potential drawback to the use of subpleural placement of elastomeric pump catheters is the increase in the OR time, which potentially could increase costs. In our series, there was an increase of about 20–30 minutes with the elastomeric pump placement due to increased technical difficulty. With increased experience and number of cases, this difference has reduced to about 5–10 minutes. We did not perform a cost-analysis, which might be needed to elucidate this point.

Subcutaneous infusion of local anesthetics has also been used following other chest wall procedures and has been found to be advantageous. Wheatley et al. demonstrated a reduction in narcotic use and pain scores in patients who received subcutaneous infusion of anesthetics following thoracotomy procedures compared with patients who received thoracic epidural anesthesia.¹⁶ Interestingly, the patients in the subcutaneous infusion cohort had a higher preoperative American Society of Anesthesiologists status, demonstrating the effectiveness and safety of this approach in procedures beyond MIRPE. Multiple additional studies have also demonstrated the advantage of subcutaneous infusion of anesthesia with a reduction in the incidence of respiratory depression, nausea, vomiting, pruritus, and urinary retention.^10–13,16

In children, Pontarelli et al. reported similar pain control with no change in the length of stay or overall pain regimen when comparing EPP and epidural for a wide range of incisions, including midline and transverse abdominal, Pfannenstiel, and thoracotomy in 136 patients.¹⁵ In terms of thoracotomy, to the best of our knowledge, our study is the second to largest to present the use of EPP in children. We show a decrease in pain scores and use of postoperative narcotics without any increase in complications when compared with a multimodal regimen. This is compatible with findings in children undergoing median sternotomy and scoliosis surgery when compared with placebo and a multimodal regimen, respectively.^17–19

Furthermore, Thaker et al. also demonstrated an improvement in patient care with infusion catheter placement following pectus excavatum surgery when compared with thoracic epidural placement in 124 patients. They found that infusion catheters were associated with shorter postoperative length of stay and no increase in postoperative complications.¹⁴ Our group has previously compared the use of MM versus epidural catheter placement with decreased length of stay and improved postoperative pain.⁹ We compare two different groups, but we evidenced a further decrease in opioid use with no difference in the length of stay.

In our study, we placed the EPP subpleurally with the aim to provide a more direct infusion of analgesic in the intercostal nerves. When compared with subcutaneous placement, this is a technique that is more time-consuming and technically more difficult. Initially, in our experience, we placed our pumps subcutaneously, but we switched due to this possible advantage. We did not have enough cases to compare both techniques. Further studies are needed with a larger number of patients to further delineate the true difference in pain control between subpleural and chest wall placement of the catheters.

Limitations

Our study is a nonrandomized retrospective study with its inherent limitations where the placement of EPP was performed by surgeon's preference. We also encountered some degree of interpatient variability of pain tolerance and self-assessment of the pain score. There were not enough data to evaluate for outpatient opioid consumption, which might be important. Finally, there were some cases where children remained with high degree of pain after day 3 and required refilling of the pump reservoir, which was not recorded in the electronic medical record.

Conclusion

EPP in addition to multimodal pain management is an effective adjunct for postoperative pain control in patients undergoing MIRPE. The addition of EPP placement improves pain scores and decreased opioid use without any increased complications or a significant increase in the length of stay. This technique can potentially be applied to other thoracoscopic procedures in the pediatric population.

Footnotes

Disclosure Statement

No competing financial interests exist.

Funding Information

No funding was received for this article.

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