In a comprehensive analysis of the ACS NSQIP® database, spreading across multiple surgical specialties, we found that a higher ASA PS, less than normal preoperative albumin levels and impaired preoperative functional capacity were associated with 30-day mortality in patients undergoing elective non-cardiac surgery. Despite significant advances in perioperative care, postoperative mortality remains high and although the ACS NSQIP® SRC provides an estimate of this risk, identification of specific risk factors is essential to implement targeted interventions and our analysis is such an attempt.
We identified less than normal preoperative serum albumin levels to be a significant predictor of postoperative mortality. Although serum albumin levels can be impacted by a multitude of conditions, in patients undergoing elective surgery, these could be considered surrogate markers of preoperative nutritional status. Low preoperative serum albumin levels have been found to be associated with significant risk of postoperative complications including poor wound healing, surgical site infections and mortality in various surgical populations.(9–11) However, most of these studies included both elective and emergency surgeries, or were confined to a sample involving specific pathologies and surgical procedures. In a large prospective observational study spread across forty-four tertiary care veterans affairs (VA) medical centers more than a decade ago, the authors concluded that serum albumin concentration is a better predictor of surgical outcomes than many other preoperative patient characteristics.(12) Despite awareness of the association of a low preoperative albumin with worse outcomes, over 10% of the patients in our cohort had less than normal albumin values prior to surgery.
Although the relationship of hypoalbuminemia and poor surgical outcome has been known for many years, the pathophysiology behind the relationship is unclear. Hypoalbuminemia may be an indicator of poor nutritional status, and hence contribute towards poor postoperative outcomes. Secondly, since albumin has antioxidant and carrier properties, a lack or deficiency thereof, might result in inadequate performance of these tasks, thus further pre-disposing to postoperative complications. Thirdly, since albumin is a known negative acute phase protein, hypoalbuminemia might represent a pre-existing amplified inflammatory status of the patient. Kim et al(13) reviewed this relationship in detail, explored the fallacies with these hypothesis and concluded that Interventions designed solely to correct preoperative hypoalbuminemia, in particular intravenous albumin infusion, do little to change the patient's course of hospitalization. In essence, it is the optimization of preoperative nutritional status that is important and whether elective surgery should be delayed until nutritional status has been optimized and preoperative serum albumin levels are normalized needs to be explored in future studies. A direct relationship between improvement in nutritional status and correction of serum albumin values has yet to be established.
Impaired preoperative FHS was another factor that was associated with a higher likelihood of postoperative mortality in our cohort. Functional health status is often defined as one’s ability to perform daily activities required to meet basic needs, fulfill usual roles, and maintain their health and well-being.(14) For documentation into the NSQIP database, patient charts are manually reviewed to determine the level of patient’s functional health status. Patients are placed into one of three categories: independent, partially dependent, and totally dependent. An independent patient is defined as one who does not require assistance from another person for any activities of daily living. A partially dependent patient requires some assistance from another person for activities of daily living regardless of use of prosthetics, equipment, and/or devices. Finally, a totally dependent patient requires total assistance for all activities of daily living. The best functional status demonstrated by the patient, within the 30 days prior to the principal operative procedure or at the time the patient is being considered a candidate for surgery is recorded.
Functional health status has been identified as a major risk factor for postoperative complications in isolated surgical cohorts(15, 16) and as part of the preoperative mortality predictor (PMP) in patients undergoing major abdominal surgery.(17) However, its association with mortality across all surgical procedures has not been explored before. Patients with poor functional capacity are generally sicker, tend to have more comorbidities, and may present later in their disease process, which may result in higher mortality. The decision to operate on patients with poor FHS should be thoroughly reviewed with a detailed preoperative workup and in patients in whom surgery is indicated, optimization pathways should be implemented. Functional health status is also an important determinant of preoperative cardiovascular non-invasive testing and forms an integral part of the American College of Cardiology (ACC)/American Heart Association (AHA) guidelines on perioperative cardiovascular evaluation and management of patients undergoing elective non-cardiac surgery.(18)
Improvement of FHS prior to elective surgery can be beneficial and pre-habilitation prior to major abdominal surgery was recently found to reduce overall and pulmonary morbidity.(19) However, in a systematic review of the impact of pre-habilitation programs in abdominal cancer surgery, no significant difference between patients undergoing pre-habilitation and standard care groups were observed.(20) There seems to be heterogeneity in the composition, mode of administration and the outcome measures of functional capacity that are used to evaluate the impact of pre-habilitation programs that may account for these incongruent findings.
The ASA Classification System, introduced in 1941, is routinely assigned to patients prior to procedures where an anesthesia professional is present, and application of this system has become a standard component of anesthetic practice worldwide. We found that a higher ASA physical status was associated with postoperative mortality and prior studies have also reported similar association.(21) Although, the ASA classification system is associated with inter-observer variability and can be inconsistent, it does demonstrate validity as a marker of patients' preoperative health status.(22, 23)
We believe that the strength of this study is the inclusion of a diverse population of patients who underwent varied surgical procedures. However, there are a few limitations. Our analysis is limited by our observed low mortality rate of 0.6%, likely due to the heterogeneity of surgical cases reported in the NSQIP database. Further, NSQIP audited cases are chosen randomly, and thus may not be reflective of the overall surgical case mix. In addition, the lack of reporting of intraoperative complications in the NSQIP database makes the evaluation of valuable data such as blood loss, transfusions, and anesthesia type, unfeasible. Also, the NSQIP database fails to report important clinical risk factors, such as frailty. The retrospective nature and analysis of surgical cases from a single center also limit the generalizability of our findings.