Near-infrared Spectroscopy-Based Clinical Algorithm Applicability During Spinal Neurosurgery and Postoperative Cognitive Decline. Summary of the Doctoral Thesis
Authors:   ,   Rīga Stradiņš University, Mūrniece Sniedze 
Published: June 2023

In patients undergoing spinal surgery in prone position, physiological changes can occur in multiple organ systems. Pressure on pelvis, abdomen and thorax reduces systemic venous return, thereby decreasing cardiac output and increasing pressure in vertebral blood vessels, thus promoting intraoperative bleeding. Concomitantly, lung compliance decreases. The latter noxious factors hamper blood flow and oxygen delivery to the brain. The brain is highly dependent on adequate oxygen delivery, thus, tissue injury, and even cell death may occur already 5 minutes after cerebral ischemia. Postoperative cognitive decline is a potential complication, which may lead to long-term consequences. The exact aetiology and pathophysiology of postoperative cognitive disturbances is not known. Despite intraoperative cerebral ischemia could be a contributing factor to consider, the brain remains one of the least monitored organs intraoperatively. The aim of the present study was to evaluate the effect of the intraoperative use of a near-infrared spectroscopy-based clinical algorithm on outcome, especially on postoperative cognitive decline. We included 64 adult patients, scheduled for elective spinal neurosurgery in the prone position. All the patients underwent general anaesthesia and regional cerebral oxygen saturation (rScO2) was monitored intraoperatively by means of an INVOS 4100 cerebral oximeter. Patients were randomised into a study group and a control group. In patients of the study group, a near-infrared spectroscopy-based clinical algorithm was used to restore adequate cerebral oxygen saturation when noticing a drop of 20 % from preoperative baseline of cerebral oxygen saturation, or a fall in regional cerebral oxygen saturation below an absolute value of 50 %. In the control group, intraoperative cerebral oxygen saturation was monitored blindly without using the near-infrared spectroscopy-based clinical algorithm. In both groups, before and after the surgery, cognitive function was evaluated using Montreal Cognitive Assessment Scale (MOCA). Preoperative haemoglobin (Hb) and haematocrit (Hct) concentrations also were noticed, as well as intraoperative mean arterial pressure (MAP), expiratory end-tidal carbon dioxide (EtCO2) levels, peripheral oxygen saturation (SpO2), intraoperative blood loss and length of operation. In our study, in three patients – two in the study group and one in the control group, intraoperative cerebral desaturation was observed. Two study group patients were 54 and 57 years old. In one study group patient, cerebral saturation fell for 29 % from baseline values and also under an absolute value of 50 %; in the other study group patient, we noticed a cerebral oxygen saturation drop of 27 % below preoperative baseline. The NIRS-based clinical algorithm was initiated. No changes in rScO2 were observed after the first step, which according to the algorithm, was an assurance of correct head positioning. The next step was a raise in mean arterial pressure in both patients, as assessed by ephedrine administration. After the second step rScO2 values raised above the threshold, and no further intervention was necessary. Mean arterial pressure in the patients at the time of cerebral desaturation was 95 mmHg and 62 mmHg, respectively vs. 124 mmHg and 104 mmHg preoperatively. None of the patients showed postoperative cognitive decline – MOCA score remained unchanged pre- and postoperatively. In one control group patient, in whom intraoperative cerebral desaturation occurred, but the NIRS-based clinical algorithm was not applied, we detected a rScO2 drop of 21 % from the preoperative baseline values. The patient was 24 years old and showed a postoperative MOCA score decline of 4 points (from 29 points preoperatively to 25 points postoperatively). In the present study, we found a correlation between lower intraoperative rScO2 values and higher patient age, larger intraoperative blood loss, higher preoperative mean arterial pressure and lower preoperative MOCA score. In our study, 45.5 % patients from the control group, where cerebral oximetry was monitored blindly, no NIRS algorithm was applied, showed postoperative cognitive decline, compared to the study group where postoperative cognitive decline was observed in 21.4 % of patients. No correlation was found between intraoperative cerebral oxygenation and postoperative cognitive function. However, patients, who had a rScO2 decrease of > 10 % in any stage of surgery experienced a lower median MOCA score after the surgery. Near-infrared spectroscopy together with NIRS-based clinical algorithm is useful to manage intraoperative cerebral oxygen desaturation and to avoid postoperative cognitive disturbances.