Patient Selection for Spine Surgery: Preoperative Optimization

Background

The goals of most spinal surgeries are to decompress, physiologically align, and stabilize the spine. In addition to the technical aspects of a case, a surgeon’s important role in patient selection and risk stratification cannot be understated. Although patient-specific factors such as age and race are generally considered nonmodifiable risk factors, comorbidities such as smoking, diabetes, anemia, and obesity are potential targets for intervention. Assuming a patient’s cardiac and pulmonary risk factors are controlled, the surgeon’s role in preoperative optimization is paramount to a successful outcome. In addition, with renewed focus on reducing surgical costs by minimizing hospital length of stay, as well as public reporting of surgeon performance, preoperative optimization has become extremely important for quality metrics and payers. ^,

In this chapter we identify specific, evidence-based areas for intervention that have shown direct correlation with decreased complication rates, reduced surgical site infections, and improved patient outcomes after spinal surgery.

Diabetes Mellitus

Diabetes mellitus is a hormonally-mediated endocrine disorder of poor blood glucose control and insulin resistance. Prolonged hyperglycemia has been directly correlated with poor outcomes in virtually every medical and surgical specialty. ^, Pathophysiologically, glucose is a biologically active molecule that glycosylates proteins in the bloodstream and tissue. Hemoglobin, in particular, is a target for glycosylation that leads to impaired oxygen and nutrient delivery to tissues from a micro- and macrovascular perspective. Although different clinical forms of diabetes exist in the general population, type 2 diabetes mellitus is the most prevalent in the spine surgery population. Type 2 diabetes mellitus, in and of itself, is an independent risk factor for accelerated degenerative changes in the intervertebral discs and spinal column. Numerous studies have identified uncontrolled diabetes as a strong risk factor for pseudarthrosis after cervical and lumbar fusion surgery, postoperative surgical site infection, delayed and poor wound healing, and prolonged length of stay. ^{, ,} Satisfactory glucose control, as measured by HbA1c, is essential before any elective spine surgery. ^{, , ,}

This was highlighted in a study by Epstein which demonstrated higher rates of morbidity and adverse in-hospital events in diabetic patients who underwent spinal surgery. In this retrospective study, which examined a Nationwide Inpatient Sample (NIS) from 1988 to 2003, diabetics who underwent lumbar fusion had higher rates of infection, blood transfusion, hospital-acquired pneumonia, and in-hospital mortality, greater costs, and longer length of stay compared with matched nondiabetics. Similar findings were found in diabetics who underwent anterior and/or posterior cervical decompression and fusion. These findings were supported by additional studies by Walid and colleagues who found that patients with HbA1c greater than 6.1% were at risk for increased length of stay and greater healthcare costs after lumbar decompression and fusion surgery. ^, Furthermore, even patients with subclinical elevations in HbA1c were at risk for adverse outcomes and increased healthcare resource utilization compared with nondiabetics. The authors of this study recommended the use of HbA1c as part of the routine preoperative work-up for spine patients. These findings were echoed by Underwood and colleagues who determined that patients with an HbA1c greater than 8% demonstrated poor surgical outcomes and complications.

In the adult spinal deformity literature, the results have been surprisingly mixed. Cho and colleagues published a small retrospective study examining outcomes in 23 diabetics and 23 nondiabetic controls over two years and found no significant difference in outcomes. Alternatively, in a large NIS from 2002 to 2011 Shin and colleagues found that uncontrolled diabetes mellitus was a risk factor for postoperative hemorrhage, acute kidney injury, deep vein thrombosis, and mortality.

With these factors in mind, there is generally strong evidence to suggest that patients with poor glucose control measured by elevated HbA1c levels before elective surgery fare worse on virtually all parameters than normoglycemic patients and have increased healthcare resource utilization. ^{, , ,} Screening spine patients for serum blood glucose and HbA1c levels before elective surgery, therefore, may be warranted. Patients with HbA1c greater than 8% may benefit from referral to a diabetes specialist for further management and stratification of cardiovascular risk. In the postoperative period, patients should resume their home oral diabetes medications in addition to an insulin sliding scale, if needed, to maintain normoglycemia.