Processed intraoperative burst suppression and postoperative cognitive dysfunction in a cohort of older noncardiac surgery patients.

Postoperative cognitive dysfunction (POCD) is a decline in cognitive test performance which persists months after surgery. There has been great interest in the anesthesia community regarding whether variables generated by commercially available processed EEG monitors originally marketed to prevent awareness under anesthesia can be used to guide intraoperative anesthetic management to prevent POCD. Processed EEG monitors represent an opportunity for anesthesiologists to directly monitor the brain even if they have not been trained to interpret EEG waveforms. There is continued equipoise regarding whether any of the variables generated by the machines' interpretation of raw data are associated with POCD. Most literature has focused on the depth of anesthesia number, however recent studies have shown that processed depth may not be accurate in older age groups due to reduced alpha band power. Burst suppression is an encephalographic pattern of high voltage activity alternating with periods of electrical silence and is another marker of depth which can be obtained from commercial processed EEG monitors. We performed a prospective cohort study to determine whether burst suppression and burst suppression ratio as measured by the BIS Monitor (Bispectral Index, BIS Medtronic, Boulder CO), is associated with cognitive dysfunction 3 months after surgery. We recruited 167 elective surgery patients, 65 years of age and older, anticipated to require at least 2 day inpatient admission. Our main outcome measure was cognitive decline in composite z-score on the Alzheimer's Disease Research Center UDS Battery of at least 1 standard deviation 3 months after surgery relative to preoperative baseline. 14% experienced POCD, this group was older (72 [70, 74] versus 70 [67, 75] years), and had frailty scores as measured by the FRAIL Scale (2 [0, 3] versus 1 [0, 2]) and lower baseline z-scores (- 0.2 [- 0.6, 0.5] versus 0.1 [- 0.3, 0.5]). There was a univariable association between suppression ratio > 10 (SR > 10) and POCD (4.8 [0, 37.3] versus 15.4 [4.0-142.4] min), p = .038. However, after adjustment this relationship did not persist, only anesthetic technique, age, and pain remained in the model. In our cohort of older elective noncardiac surgery patients we found a marginal association between processed burst suppression (total burst suppression p = .067, SR > 5 p = .052, SR > 10.038) which did not persist in a multivariable model. Patients with POCD had almost twice the number of minutes of burst suppression, and three times the amount of time for SR > 5 and > 10. Our finding may be a limitation of the monitor's ability to detect burst suppression. The consistent trend towards more intraoperative burst suppression in patients who developed POCD suggests that future studies are needed to investigate the relationship of raw intraoperative burst suppression and POCD.Trial registry Clinical trial number and registry URL: Optimizing Postoperative Cognitive Dysfunction in the Elderly-PRESERVE, Clinical Trials Gov# NCT02650687; https://clinicaltrials.gov/ct2/show/NCT02650687 .

Intraoperative neurophysiological monitoring of T9-T10 fracture in a patient with morbid obesity and ankylosing spondylitis: A case report with literature review.

INTRODUCTION: As the prevalence of obesity continues to rise, there is a growing need to identify practices that protect overweight patients from injury during spine surgery. Intraoperative neurophysiological monitoring (IONM) has been recommended for complex spine surgery, but its use in obese and morbidly obese patients is understudied. CASE REPORT: This case report describes a patient with morbid obesity and ankylosing spondylitis who was treated for a T9-T10 3-column fracture with a planned, minimally invasive approach. Forty minutes after positioning the patient to prone, the IONM team identified a positive change in the patient's motor responses in the bilateral lower extremities and alerted the surgical team in a timely manner. It turned out that the pressure exerted by gravity on the patient's large pannus resulted in further dislocation of the fracture and narrowing of the spinal canal. The surgical team acknowledged the serious risk of spinal cord compression and, hence, immediately changed the surgical plan to an urgent, open approach for decompression and reduction of the fracture. The patient's lower extremities' motor responses improved after decompression. The patient was ambulatory on post-operative day 2 and pain-free at six-weeks with no other neurologic symptoms. SIGNIFICANCE: The use of IONM in this planned minimally invasive spine surgery for a patient with morbid obesity prevented potentially serious iatrogenic injury. The authors include a literature review that situates this case study in the existing literature and highlights a gap in current knowledge. There are few studies that have examined the use of IONM during spine surgery for morbidly obese patients. More research is needed to elucidate best practices for the use of IONM in spine surgery for morbidly obese patients.