Author: Michael Vlessides
Interscalene nerve blocks may be the standard of care in patients undergoing shoulder surgery, but in obese patients the approach is associated with a significant increase in respiratory complications and other morbidity, a Canadian research team has found. In its place, they suggested patient-specific postoperative pain management that considers the increased risk for respiratory complications posed by a higher body mass index (BMI).
“As many of us know, the interscalene block is the current standard of pain control in shoulder surgery in the ambulatory setting,” said Carla Y. Henderson, MD, a resident at the University of Ottawa, in Ontario. “Nevertheless, the deposition of local anesthetic from performing this block invariably freezes the phrenic nerve as well, which can impair diaphragmatic function.
“And although the majority of patients don’t have any adverse events related to this, there are certain populations that may be more prone to complications from having loss of phrenic nerve function,” Dr. Henderson said. “Specifically, obese patients are prone to additional postoperative complications as a whole, and may be more prone to respiratory complications with the involvement of the phrenic nerve when placing this block.”
The investigators sought to clarify the potential compounding effects of obesity and interscalene nerve blocks on recovery, outcomes and respiratory complications in patients undergoing shoulder surgery. To that end, Dr. Henderson and her colleagues collected demographic and clinical outcomes data from the charts of 2,067 patients who underwent shoulder surgery between 2007 and 2016, at three academic hospitals in Toronto.
Both obese patients (BMI ≥30 kg/m2) and nonobese patients (BMI <30 kg/m2) were propensity-matched based on baseline characteristics such as age, sex, BMI, surgical procedure and Charlson Comorbidity Index score. A variety of outcomes were examined, including PACU time, occurrence of severe hypoxemia in the PACU, duration of in-PACU oxygen supplementation, unplanned hospital admission, unplanned ICU admission and hospital length of stay. A total of 996 patients were successfully matched and included in the cohort, including 182 patients with a BMI of 30 kg/m2 and higher, and 814 patients with a BMI lower than 30 kg/m2.
Results Highly Significant
As Dr. Henderson reported at the 2018 Joint World Congress on Regional Anesthesia and Pain Medicine and annual meeting of the American Society of Regional Anesthesia and Pain Medicine (abstract 5066), obese patients who received the interscalene block experienced a longer PACU stay, greater occurrence of hypoxemia in the PACU, requirement for more PACU oxygen supplementation, a greater risk for unplanned hospital and ICU admissions, and a longer hospital stay after ambulatory shoulder surgery (Table).
|Table. Outcomes of Interscalene Block, by Body Weight|
|Outcome||BMI ≥30 kg/m2(n=182)||BMI <30 kg/m2(n=814)||P Value|
|PACU time, minutes||209±184||129±117||<0.00001|
|Risk for severe hypoxemia in PACU (O2saturation <90%), n||41 (22.5%)||13 (1.6%)||<0.00001|
|Duration of PACU O2 supplementation, minutes||146±137||33±29||<0.00001|
|Unplanned hospital admission, n||20.2 (12.1%)||17 (2.1%)||<0.00001|
|Unplanned ICU admission, n||5 (2.7%)||2 (0.2%)||0.004|
|Hospital length of stay, hours||7.8±1.7||6.3±1.2||<0.00001|
|BMI, body mass index; O2, oxygen|
Some of the findings proved notable to the researchers. “We were surprised to find an increase of approximately 50% in PACU time for obese patients,” Dr. Henderson said. “Unplanned hospital admission from compromised respiratory status—which some people define as a failure of ambulatory surgery because they require an inpatient admission—was also higher in obese patients, both to the hospital and to the intensive care unit.”
These results led the investigators to reconsider how they approach obese individuals undergoing shoulder surgery. “Given these findings, as well as our colleagues’ previous work with sleep apnea and obesity, we believe they’re additive components in this very specific population undergoing shoulder surgery,” Dr. Henderson said. “Although there’s obviously a drive to initiate evidence-based clinical guidelines for ambulatory shoulder surgery with interscalene block, obese patients may actually benefit from having a different approach or a different model of care to handle their specific respiratory needs.”
The presentation prompted considerable discussion among Dr. Henderson’s audience, including one attendee who asked why patients with BMIs less than 30 kg/m2 were kept in the PACU for more than two hours. “Two hours would be considered standard in terms of meeting criteria for ambulatory surgery in our center,” Dr. Henderson said. “In this cohort, all patients received a block plus general anesthesia, so part of this is recovery time from general anesthesia.”
“If you’re looking at the compounding effect of obesity and interscalene block, do you not need a control group of patients who are just obese?” asked Robert S. Weller, MD, a professor of anesthesiology and the section head of regional anesthesia at Wake Forest Baptist Health, in Winston-Salem, N.C. “Did you look at that kind of control, or did everyone get an interscalene block?”
“We were unable to capture charts during our time frame where the patient did not have the interscalene block,” Dr. Henderson replied. “To my knowledge, no comparison of those two groups exists. Part of that is that it’s somewhat unethical to refuse to offer a gold standard regional anesthesia option to patients on that basis.”
“Have these results changed the practice pattern in your institution to move perhaps toward suprascapular blocks or other forms of regional anesthesia?” asked Sean W. Dobson, MD, PhD, an assistant professor of anesthesiology at Wake Forest Baptist Health.
“That’s part of what I would actually encourage people to consider,” Dr. Henderson replied. “The suprascapular block provides noninferior analgesia—not surgical anesthesia—to the interscalene block when combined with multimodal analgesia. Nevertheless, it generally reduces the risk of having any major phrenic nerve involvement. Still, the analgesia is not going to be as good with the suprascapular block alone, and there’s always still a chance of phrenic nerve involvement.”
In the end, the researchers recognized that obese patients may need individual attention when it comes to nerve blocks for shoulder surgery. “I think we should consider moving to other blocks in these patients, and considering whether everybody needs to have different blocks based on their own specific comorbidities,” she concluded.