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The Spine Blog

Friday, April 5, 2019

Mortality After Surgery for Epidural Abscess

Spinal epidural abscesses (SEA) are occurring more frequently in our older, sicker population as well as in the increasing intravenous drug user population. These serious infections are difficult to treat and can result in neurological deficit, sepsis, and death. Treatment traditionally involved surgery and IV antibiotics for all epidural abscess patients, though recent literature suggests that medically stable patients without a neurological deficit can frequently be treated successfully with antibiotics alone. While the incidence of SEA is increasing, the absolute number of cases, particularly the number treated at a single institution, remains relatively low and makes powering studies on the topic difficult. In order to obtain a sufficient sample size to study the topic, Dr. Du and colleagues from Cleveland analyzed the NSQIP database and identified 1094 patients who underwent surgical treatment of SEA from 2011 to 2016. The NSQIP database includes outcomes and events up to 30 days following surgery, which allowed them to calculate a 30 day mortality rate of 3.7%. Risk factors for mortality included increased age, higher ASA class (indicating a greater comorbidity burden), diabetes, hypertension, respiratory disease, renal disease, bleeding disorder, metastatic cancer, thrombocytopenia, and receiving a perioperative blood transfusion. Multivariate analysis demonstrated that age over 60 years, diabetes, respiratory disease, renal disease, metastatic cancer, and thrombocytopenia were independent risk factors for mortality. Having 4 or more of these risk factors was associated with a 38% mortality compared to less than 1% mortality for patients with no risk factors. Seventy percent of deaths occurred within 2 weeks of surgery, though 10% occurred between 27 and 30 days post-operatively. Not surprisingly, cardiac arrest and septic shock were strongly associated with death.  

The authors have done a nice job using a database to study a topic that is very difficult to study using traditional chart review given the relatively low number of patients who undergo surgery for SEA at any single institution. Additionally, death is a good outcome to study using a large database as it is captured reliably. Nonetheless, the study has all of the limitations associated with a database study, notably that many relevant variables such as neurological status, intravenous drug use, and cause of death were not included. Additionally, the database does not record death beyond 30 days from surgery, yet the data makes it clear that patients were continuing to die at a significant rate even at 30 days out from surgery. The paper provides a good benchmark mortality rate following surgery for SEA. While it did identify risk factors for mortality, none of these come as a surprise, and all are indicative of systemic disease burden which increases mortality risk for all types of surgery. Surgeons need to decide which SEA patients should undergo surgery, and this paper does not help answer that question. While sicker SEA patients are at higher risk for mortality, it is unclear how surgery affects this risk. Some patients may have a survival advantage with surgery due to a higher chance of clearing their infection, while other patients may succeed with antibiotic treatment alone and have an increased risk of mortality due to the physiological stress of surgery. Most patients survive regardless of treatment, and a small minority are so sick that they will likely die however they are treated. To answer this question would require a huge database of patients treated with surgery and medical management that also includes a sufficient number of clinical variables that could be used to create an accurate predictive model. An RCT to address this question is not feasible. It is possible that a Medicare database analysis could provide some further insight, but this administrative database includes only billing data and likely misses some of the key clinical variables. For now, surgeons will probably continue to operate on most SEA patients with neurological deficit, sepsis, or failed medical management.

Please read Dr. Du's article in the April 15 issue. Does this change how you view the treatment of SEA? Let us know by leaving a comment on The Spine Blog.

Adam Pearson, MD, MS

Associate Web Editor