Outcomes Using Cryoablation for Postoperative Pain Control in Children Following Minimally Invasive Pectus Excavatum Repair

Abstract

Purpose:

Pain is the main factor that determines the postoperative course for patients undergoing pectus bar placement. Cryoablation of the intercostal nerves has been suggested to mitigate this pain. We instituted a protocol for using intercostal cryoablation and report our early results compared to our immediately previous cohort.

Materials and Methods:

A retrospective study was conducted on patients undergoing minimally invasive repair for pectus excavatum between January 1, 2017, and August 21, 2017. Demographic data, anthropometrics, operative times, type and duration of patient analgesia, and postoperative length of stay were collected. Descriptive statistics were performed with all means reported ± standard deviations. Comparisons between groups were analyzed on STATA using T-tests with a P value <.05 determined as significant.

Results:

Twenty-eight patients were treated for pectus excavatum during the study period with 9 (32%) undergoing cryoablation. Mean number of rib spaces ablated was 5 ± 0.53 with no reported intraoperative complications. Mean operative time was 30 minutes longer in the cryoablation group (P = .00). Days to only oral pain medication was shorter in the cryoablation group, (1.22 ± 0.66 day versus 2.63 ± 0.68 day, P = .00). Length of stay, in days, was shorter in the cryoablation group (1.4 ± 0.72 days versus 4.0 ± 1.0 days, P = .00). There were no reported complications from cryoablation or bar placement during the study period. Days to discontinuation of oral narcotics were less in the cryoablation group (8.2 ± 7.0 versus 18.2 ± 10.4, P = .00).

Conclusion:

Cryoablation after pectus bar placement dramatically decreases narcotic usage and postoperative length of stay.

Introduction

Pectus excavatum is the most common chest wall deformity in children, with an incidence of 1 in 1000 children.¹ The modern treatment for severe pectus excavatum is operative correction with a substernal bar. This operation provides an immediate correction of the chest wall defect and has excellent short- and long-term results. However, repair creates immediate remodeling of the chest wall where the pressure against the bar is equal to the force required to push out the defect. The pressure and pain from this is immense, protracted, and is often the sole issue during the patient's postoperative hospital course. Once the pain is under control with oral medications alone, patients go home. In our recent experience, most of which had protocolized pain management pathways for both epidural and patient-controlled analgesia (PCA), the average hospital length of stay was 4.5 days.²

After extensively investigating the outcomes and differences with epidural and PCA,^3–7 early reports of cryoablation to mitigate pain after bar placement made it clear that it was time to explore a new strategy altogether.^8,9 Cryoablation had been previously reported to effectively treat pain, including neuralgias, postthoracotomy pain, pelvic pain, and others.^10,11 Recently, it has emerged in a few small series in patients undergoing bar repair for pectus excavatum with excellent results.^8,9 A retrospective study of 26 patients showed a reduction in length of stay and less IV narcotics when compared to epidural.⁹ Herein, we report our early experience with cryoablation compared to our most recent experience with epidural or PCA.

Materials and Methods

Following IRB approval (#17080504), a retrospective chart review of all patients treated for pectus excavatum with bar placement from January 1, 2017, to August 21, 2017, was performed. Patient lists were obtained from our department operative log that identified patients undergoing a minimally invasive pectus excavatum repair.

Data were collected, including demographics, Haller and corrective indices, presenting symptoms, operative details, cryoablation details, and type and duration of patient analgesia (epidural, PCA, or cryoablation). The patients' postoperative courses were also reviewed, including complications, time to regular diet, duration of hospital stay, time to transition to oral pain medication, and nurse max pain score (0–10 scale assessed every 2 hours).

At our institution, cryoablation is applied in the operating room thoracoscopically through a probe placed directly on the target nerve. We use the same side incisions that we use for bar placement and place a 5 mm port at the posterior aspect of the incision and insert the probe directly through the chest wall at the anterior aspect of the incision (Fig. 1). The probe is bent slightly to facilitate the angle and the tip is brought out from the protective sheath about 2 cm and bent manually (Fig. 2). We start by placing the CryoICE probe (©AtriCure, Inc., Mason, OH) at the top of the fourth interspace and initiate the freeze, which occurs for 120 seconds, at which the machine triggers the thaw that lasts a few seconds. We then move down sequentially to freeze T4–T7 bilaterally (Fig. 3).

FIG. 1.

Cryoablation configuration.

FIG. 2.

Bent probe.

FIG. 3.

Cryoablation.

In patients who did not undergo cryoablation, either PCA or epidural was used based on discussion among the patient, family, surgeon, and anesthesiologist, usually with review of institutional data. All patients utilized the same oral pain control regimen after discontinuation of epidural or PCA patient analgesia, and in those who underwent cryoablation. The oral regimen consisted of extended-release oxycodone (Oxycontin) 10 mg initiated every 12 hours and oxycodone 0.05–0.15 mg/kg (max 10 mg) every 3 hours available for breakthrough pain. Once the patient's pain was controlled utilizing solely oral medication, they were discharged home with a prescription for an oxycontin taper (3 days of 10 mg BID, 3 days of 5 mg BID, and 3 days of 5 mg daily) and oxycodone for breakthrough pain control.

Descriptive statistics was performed with all means reported ± standard deviations. Comparisons between groups were analyzed on STATA (StataCorp 2017. Stata Statistical Software: Release 15. College, Station, TX: StataCorp LLC) using T-tests with a significance of <.05.

Results

Twenty-eight patients were treated for pectus excavatum during the study period with 9 (32%) undergoing cryoablation. The remaining 19 (67%) patients utilized a combination of epidural and/or PCA for pain control. Epidurals were used in 8 patients and PCAs in 11 patients, while an additional 3 PCAs were used in epidural patients who did not have adequate pain control. There was no difference in the mean BMI between groups, 18.7 ± 2.1 in no cryoablation versus 17.6 ± 2.0 in cryoablation (P = .22). The cryoablation group had deeper defects with higher Haller index and Correction index (Table 1).

Table 1.

Demographics

	No cryoablation (n = 19)	Cryoablation (n = 9)	P
Male	17 (90%)	9 (100%)	.33
BMI^a	18.7 (2.1)	17.6 (2.0)	.22
Haller index^a	4.2 (0.8)	6.3 (4.3)	.04^*
Corrective index^a	32.3 (10.7)	45.5 (14.7)	.01^*

Reported as mean (SD).

Statistically significant.

Expectedly, mean operative time was on average 30 minutes longer with cryoablation and was shorter in patients who did not undergo cryoablation (Table 2).

Table 2.

Operative Outcomes

	No cryoablation (n = 19)	Cryoablation (n = 9)	P
Operative time (minutes)^a	64.2 (13.3)	98.4 (17.0)	.00^*
Number of ribs ablated^a		5 (0.5)
Left		5 (0.5)
Right		4.8 (0.6)
Postoperative analgesia
Epidural	8 (42%)
PCA	11 (57%)
Time to oral pain control (days)^a	2.63 (0.6)	1.22 (0.6)	.00^*
Hospital length of stay (days)^a	4.0 (1.0)	1.4 (.72)	.00^*
Time to discontinuation of oral narcotics (days)^a	18.2 (10.4)	8.2 (7.0)	.00^*
Readmissions	0 (0%)	1 (11%)

Reported as mean (SD).

Statistically significant.

PCA, patient-controlled analgesia.

There were no reported intraoperative complications. Days to only oral pain medication was shorter in the cryoablation group, (1.2 ± 0.66 day versus 2.6 ± 0.68 day, P = .00). Hospital length of stay was shorter in the cryoablation group (1.4 ± 0.72 days versus 4.0 ± 1.0 days, P = .00) with 6 (67%) from the cryoablation group leaving on postoperative day (POD) 1. There were no reported complications from cryoablation or of bar placement during the study period. One patient in the cryoablation group was readmitted with a pneumothorax that was monitored for 2 days without intervention. Days to discontinuation of oral narcotics were less in the cryoablation group (8.2 ± 7.0 versus 18.2 ± 10.4, P = .00) (Table 2). Average maximum nurse-assessed pain score was less in the cryoablation group on POD 0, similar on POD 1, and less throughout the remainder of the patient's postoperative stay (Table 3).

Table 3.

Average Maximum Nurse Pain Score

	No cryoablation (n = 19)	Cryoablation (n = 9)	P
POD 0	6.5	4.0	.00^*
POD 1	5.1	5.4	.58
POD 2	6.1	3.3	.03^*
POD 3	5.7	0.0	—
POD 4	4.4	—	—
POD 5	3.0	—	—

Statistically significant.

POD, postoperative day.

When comparing patients who did not undergo cryoablation (Epi versus PCA), days to only oral pain medication was similar (2.8 ± 0.6 versus 2.4 ± 0.6, P = .19) as was hospital length of stay (4.25 ± 1.0 versus 3.9 ± 1.1, P = .51).

Discussion

Our study demonstrates that patients undergoing cryoablation had lower postoperative pain scores, shorter hospital length of stay, and shorter time to the start of oral pain control and subsequent discontinuation. Cryoablation forms an ice ball around the nerve causing transient vascular damage to the vasoneureum. This causes a change in the nerve's structure with axonal swelling called Mullerian degeneration, but leaves the myelin sheath and endoneurium intact. What results is a transient paresthesia that blunts the patient's pain response; however, this can take 24–36 hours to take full effect. When followed long term, these nerves show complete recovery in both structure and function with reported resolution of parathesias.^8,10,11

Several studies have been done to examine the most efficacious postoperative pain control measure, including two randomized controlled trials at our institution comparing epidural versus PCA. The first trial with 110 patients showed no difference in the mean hospital stay (4.2–4.5 days, P = .13) in the two groups. The pain scores were better with epidural for the first 2 days and better with PCA the last 2 days. The epidural group incurred far greater operation times and charges.³ One interpretation was that only the PCA should be used, another was that a better epidural was needed. We are in the process of describing a subsequent trial with a better protocol and two institutions. Even in this study, when the patients are followed closely under a prospective protocol, the average hospital stay was still about 4.5 days. Clearly, there appeared to be little room for substantive improvements without a different augment or strategy, which led to our adoption of cryoablation. In our pilot experience reported in this study, the cryoablation patients had demonstrative improvement in pain control despite having apparently deeper defects (Table 2). The process of cryoablation had a longer operative time as expected, but this difference seems to be decreasing as we gain experience. The freeze time for each nerve is 2 minutes, so the most rapidly this can be done is just under 20 minutes in total.

Examining our postoperative pain groups, there was a 37% rate of epidural failure in our noncryoablation group. We have seen a similar result with our previous studies with epidural. In pediatric hospitals where anesthesia experience in this procedure may be limited, this rate could be even higher.^3,4 Thus far, we have not seen a patient who has recovered in a manner that would imply the block did not work by staying until the fourth day.

While there was no significant difference in maximum pain scores POD 1, this may be due to the fact that cryoablation can take up to 24–36 hours to take effect in some patients; these patients do not look the same subjectively. These patients will be sitting up, playing videogames, and moving around the room and hallways, which are unusual for POD 1. This is why six cryoablation patients went home on POD 1, with no readmissions for pain control.

A previous study examined cryoablation as a method of controlling postoperative pain after a minimally invasive pectus excavatum repair in comparison to thoracic epidurals. In this study, they compared cryoablation to thoracic epidural catheters in 52 patients. They found a significant reduction in mean hospital length of stay from 5 to 3 days and a slightly higher rate of postoperative complications in the cryoablation group. The authors concluded that cryoablation was superior to thoracic epidural catheters and they comment that they have eliminated epidurals from their practice based on their results.⁹ Critiques of the study included a lack of standardized pain control protocol and short follow-up.¹² However, this study and our own indicate that cryoablation is useful to decrease hospital length of stay following minimally invasive pectus excavatum repair. As we develop our protocol and our experience, we would expect to see more improvements in overall length of stay and use of IV narcotics.

Limitations to our study include its retrospective nature and our small patient population. Another limitation is that pain control was not protocoled because this study was retrospective. To properly study the impact of cryoablation, we have begun a prospective observational study where the cryoablation patients will be compared to the epidural and PCA patients from our second randomized trial, so all the groups will be under protocol. This study also lacks long-term follow-up. It is reported that patients have resolution of their paresthesia with time; however, we were unable to capture this during our study. In our prospective study, we will be monitoring these patients throughout their 3-year course.

In conclusion, cryoablation improves pain control and shortens hospital length of stay in those undergoing minimally invasive pectus excavatum repair. Cryoablation has become our preferred method of pain control and we will continue to further investigate its benefits by utilizing a prospective observational study.

Footnotes

Acknowledgment

The authors would like to recognize and thank Yara Duran RN and Pete Muenks for their contributions and as our research coordinators.

Authors' Contributions

J.S.: Concept and design, data collection, data analysis and interpretation, drafting article, critical revision of article, approval of article, and statistics; L.A.B.: Drafting article, critical revision of article, and statistics; J.D.F., P.A., and D.L.M.: Concept and design, drafting article, critical revision of article, and approval of article; S.D.S.P.: Concept and design, drafting article, data analysis and interpretation, critical revision of article, and approval of article.

Disclosure Statement

No competing financial interests exist.

References

Ashcraft

, Holcomb

, Murphy

, Ostlie

(eds). Ashcraft's Pediatric Surgery. Sixth edition. London, New York: Saunders/Elsevier, 2014.

Gould

, Sharp

, Peter

, et al. The minimally invasive repair of pectus excavatum using a subxiphoid incision. Eur J Pediatr Surg, 2016; 27:002–006.

St Peter

, Weesner

, Weissend

, et al. Epidural vs patient-controlled analgesia for postoperative pain after pectus excavatum repair: A prospective, randomized trial. J Pediatr Surg, 2012; 47:148–153.

St Peter

, Weesner

, Sharp

, Ostlie

, Holcomb

. Is epidural anesthesia truly the best pain management strategy after minimally invasive pectus excavatum repair?. J Pediatr Surg, 2008; 43:79–82.

Gasior

, Weesner

, Knott

, Poola

, St Peter

. Long-term patient perception of pain control experience after participating in a trial between patient-controlled analgesia and epidural after pectus excavatum repair with bar placement. J Surg Res, 2013; 185:12–14.

Connelly

, Brown

, Kearns

, Anderson

, St Peter

, Neville

. Pupillometry: A non-invasive technique for pain assessment in paediatric patients. Arch Dis Child, 2014; 99:1125–1131.

Dalton

BGA

, Gonzalez

, Millspaugh

, Desai

, Sharp

, St Peter

. Pectus excavatum: Benefit of randomization. J Pediatr Surg, 2015; 50:1937–1939.

Kim

, Idowu

, Palmer

, Lee

. Use of transthoracic cryoanalgesia during the Nuss procedure. J Thorac Cardiovasc Surg, 2016; 151:887–888.

Keller

, Kabagambe

, Becker

, et al. Intercostal nerve cryoablation versus thoracic epidural catheters for postoperative analgesia following pectus excavatum repair: Preliminary outcomes in twenty-six cryoablation patients. J Pediatr Surg, 2016; 51:2033–2038.

10.

Trescot

. Cryoanalgesia in interventional pain management. Pain Physician, 2003; 6:345–360.

11.

Moorjani

, Zhao

, Tian

, Liang

, Kaluba

, Maiwand

. Effects of cryoanalgesia on post-thoracotomy pain and on the structure of intercostal nerves: A human prospective randomized trial and a histological study. Eur J Cardiothorac Surg, 2001; 20:502–507.

12.

Das

, Sadhasivam

. Response to intercostal nerve cryoablation versus thoracic epidural catheters for postoperative analgesia following pectus excavatum repair. J Pediatr Surg, 2017; 52:1076.