Assessment Through Transcutaneous Brain Oximetry (NIRS) of Two Preoxygenation Techniques

Hypoxemia secondary to the inability to secure the airway remains the main cause of anesthesia-related morbidity and mortality. Preoxygenation with 100% oxygen before induction of anesthesia is currently considered a standard of care and practiced routinely for all patients, and especially carefully for high-risk cases. It is an essential component of the rapid sequence induction technique. Common pre-oxygenation techniques include the 3 min tidal volume breathing (3TV) and the eight vital capacity, deep breaths (8DB). Their efficiency has been extensively assessed by measuring the rate of decline of SaO2 during apnea after induction/paralysis, with 'time to desaturation (to 95% or 90%) being the endpoint of many studies. This is arguably a surrogate endpoint for oxygen stores and Pandit et al. estimated the total amount of oxygen taken up by the body in these techniques using breath-by-breath gas analysis. An even more relevant measure is the impact of preoxygenation on tissue stores of oxygen, but this is difficult to quantify. Especially, given its vulnerability to hypoxemia due to its high energy requirements compared to the low energy reserves, the brain is particularly susceptible. Cerebral oximetry is a noninvasive monitoring technique that uses near-infrared spectroscopy (NIRS) to measure regional cerebral oxygen saturation (rScO2). Continuous rScO2 monitoring has shown to be useful in detecting mismatch of oxygen supply and demand in the brain and assessing cerebral autoregulation in real-time. This offers a means to measure tissue oxygenation in a relevant organ with pre-oxygenation. The primary aim of the present study was to test the hypothesis that different pre-oxygenation techniques result in different degrees of cerebral oxygenation as measured by rScO2 with the INVOSTM-5100-C. The investigators wished to compare the 3TV method with the 8DB method, as being the two methods that produced the highest increases in body oxygen stores in previous experiments; the null hypothesis that these would yield similar degrees of brain oxygenation. The investigators also wished to assess whether, regardless of the preoxygenation technique, there were differences between arterial PO2 and rScO2 dynamics with preoxygenation and subsequent apnoea.