Towards standardized measurement of adverse events in spine surgery: conceptual model and pilot evaluation

BACKGROUND: Independent of efficacy, information on safety of surgical procedures is essential for informed choices. We seek to develop standardized methodology for describing the safety of spinal operations and apply these methods to study lumbar surgery. We present a conceptual model for evaluating the safety of spine surgery and describe development of tools to measure principal components of this model: (1) specifying outcome by explicit criteria for adverse event definition, mode of ascertainment, cause, severity, or preventability, and (2) quantitatively measuring predictors such as patient factors, comorbidity, severity of degenerative spine disease, and invasiveness of spine surgery. METHODS: We created operational definitions for 176 adverse occurrences and established multiple mechanisms for reporting them. We developed new methods to quantify the severity of adverse occurrences, degeneration of lumbar spine, and invasiveness of spinal procedures. Using kappa statistics and intra-class correlation coefficients, we assessed agreement for the following: four reviewers independently coding etiology, preventability, and severity for 141 adverse occurrences, two observers coding lumbar spine degenerative changes in 10 selected cases, and two researchers coding invasiveness of surgery for 50 initial cases. RESULTS: During the first six months of prospective surveillance, rigorous daily medical record reviews identified 92.6% of the adverse occurrences we recorded, and voluntary reports by providers identified 38.5% (surgeons reported 18.3%, inpatient rounding team reported 23.1%, and conferences discussed 6.1%). Trained observers had fair agreement in classifying etiology of 141 adverse occurrences into 18 categories (kappa = 0.35), but agreement was substantial (kappa ≥ 0.61) for 4 specific categories: technical error, failure in communication, systems failure, and no error. Preventability assessment had moderate agreement (mean weighted kappa = 0.44). Adverse occurrence severity rating had fair agreement (mean weighted kappa = 0.33) when using a scale based on the JCAHO Sentinel Event Policy, but agreement was substantial for severity ratings on a new 11-point numerical severity scale (ICC = 0.74). There was excellent inter-rater agreement for a lumbar degenerative disease severity score (ICC = 0.98) and an index of surgery invasiveness (ICC = 0.99). CONCLUSION: Composite measures of disease severity and surgery invasiveness may allow development of risk-adjusted predictive models for adverse events in spine surgery. Standard measures of adverse events and risk adjustment may also facilitate post-marketing surveillance of spinal devices, effectiveness research, and quality improvement

Unilateral blindness after prone lumbar spine surgery

VISUAL loss after nonocular surgery is a rare but devastating perioperative complication. 1 It has been documented in a wide variety of procedures, the most common of which are cardiopulmonary bypass, head and neck operations, and prone spine operations. 2 Ischemic optic neuropathy is the most common diagnosis in these cases. Factors believed to be associated with its occurrence are large intraoperative blood loss, long duration in the prone position, and intraoperative hypotension and anemia. 3,4 We present a case of unilateral posterior ischemic optic neuropathy occurring after an uneventful prone lumbar spine operation in a relatively healthy man who did not have decreased blood pressure and hematocrit perioperatively. Case Report A 58-yr-old, 80-kg man presented for an L2-L3 posterior spinal instrumentation and fusion. The patient had a 22-pack-year history of tobacco, but had stopped smoking at the age of 36 yr. He had undergone radiation therapy for Graves disease 10 yr previously but was not noted to be proptotic at the time of presentation. Preoperative hematocrit was 50% (high end of normal at our institution), and baseline blood pressure was 134/92 mmHg (mean arterial pressure [MAP], 106 mmHg). A 12-lead electrocardiogram showed normal sinus rhythm with left ventricular hypertrophy and left atrial enlargement. Fentanyl (3 g/kg), propofol (2.5 mg/kg), and lidocaine (0.5 mg/kg) were used for induction of anesthesia. Rocuronium (1 mg/kg) was administered for muscle relaxation before tracheal intubation. Isoflurane (0.8 -0.9% end-tidal) in a 50:50 air:oxygen mixture and a sufentanil infusion ) were used for anesthetic maintenance. The patient was turned prone onto a Wilson frame with his head supported solely by a soft foam cushion with a cutout for the eyes, nose, and mouth. The head was slightly dependent with an approximate 15°tilt from the longitudinal axis of the body. After turning prone, a low-dose phenylephrine infusion (0.01%) was administered for the majority of the 6.5-h case and was titrated at a rate of 1.67 g · kg Ϫ1 · min Ϫ1 or less to maintain an MAP of predominately 80 -90 mmHg (range, 70 -95 mmHg), despite adequate volume replacement. At the time of initiation of the phenylephrine infusion, 2,000 ml crystalloid had been administered to the patient (calculated fluid deficit, 1,440 ml), and urine output was 600 ml. The requirement for phenylephrine was thought to result from loss of vascular tone during general anesthesia. The eyes were checked approximately every 30 min throughout the procedure. The patient was turned supine after approximately 320 min in the prone position and was noted to have an extremely edematous face. He underwent extubation uneventfully after confirmation of a leak around his endotracheal tube with the cuff deflated and was transported to the recovery room. Estimated blood loss for the case was 800 ml, and urine output was 700 ml. Eight thousand milliliters crystalloid was administered intraoperatively. No blood products were administered. The hematocrit at the end of the procedure was 40% in the operating room and 39% in the recovery room. That evening, the patient was noted to be comfortable, with intact lower extremity motor and sensory function. Early the next morning, the patient reported decreased vision in his left lateral field to the orthopedic service for the first time. He had noted blurry vision in the recovery room the day before, but did not verbalize any complaints because he thought it was caused by residual anesthesia. An ophthalmology consult was obtained. There were no signs of facial bruising or trauma. Fundoscopic examination yielded normal results bilaterally. An afferent pupillary defect was present in the left eye, and visual acuity was decreased to 20/800 compared with 20/20 on the right. Intraocular pressures were 18 mmHg bilaterally. Laboratory workup revealed a normal erythrocyte sedimentation rate and negative syphilis serologies. A magnetic resonance image of the head, performed approximately 24 h after surgery, was read by the radiologist as a probable lesion in the left posterior optic nerve on the T2-weighted images, but it could not be confirmed because of lack of enhancement. Fine sections through the optic nerve were not obtained because magnetic resonance imaging was performed on a "stroke protocol." Re-review of the image with a neuroradiologist did not reveal any definitive lesions. Visual evoked potentials and electroretinography were not performed. The final diagnosis was posterior ischemic optic neuropathy. No treatment was recommended by the ophthalmologic consultants. At the time of discharge, the visual acuity in his left eye had improved to 20/400. At 3 weeks' follow-up, the patient's ophthalmologic examination revealed a pale optic disc and a persistent relative afferent pupillary defect in the left eye. Color vision was significantly decreased in the left eye, and the visual field was still restricted with an inferotemporal quadrant defect, but central visual acuity had improved to 20/60. Six months after the injury, the left eye had improved central visual acuity to 20/25 and improved color vision but remained with a persistent temporal field deficit