Non-invasive Technology for Early Signal Detection of Hypoxemia With ORI During Intubation

*Severe hypoxaemia is the most common serious adverse event during endotracheal intubation (ETI) in patients admitted to the intensive care unit (ICU), consistently reported around 25%. Preoxygenation is universally recommended as a risk-minimisation measure. While effective in the operating room, preoxygenation is more complex in critically ill patients, most notably those with acute hypoxic respiratory failure, as the low functional residual capacity (FRC) carries a risk of denitrogenation being confined to the healthy lung parenchyma, so that the FeO2 (Fraction of expired oxygen) no longer reflects the partial pressure of oxygen in arterial blood (PaO2). In these patients, 8 minutes of preoxygenation using a bag-valve-mask (BVM) device failed to change PaO2 levels noticeably. Increasing the BVM time was unhelpful, as the increase in PaO2 achieved in some patients was offset by decreases in others.

Non-invasive ventilation (NIV) has theoretical advantages for preoxygenation and has been shown to provide higher PaO2 values in hypoxic patients compared to a non-rebreathing (NRB) mask. However, use of NIV has several contraindications including consciousness alterations and agitation, and drawbacks such as gastric distension.

Apnoeic oxygenation which has been updated is a method consisting in continued oxygenation during laryngoscopy to extend the safe apnoea time. High-flow nasal oxygen (HFNO) therapy ensuring high and stable FiO2 (fraction of inspired oxygen) values by delivering oxygen flows above 60 L/min is another innovation shown to improve oxygenation in hypoxaemic patients. The effect of HFNO for preoxygenation, however, is less clear, as one study suggested benefits vs. NRB mask in patients with moderate hypoxaemia but another found no significant difference vs. BVM in patients with PaO2/FiO2 ratios below 200. No large randomised trial has compared preoxygenation methods. The latest recommendations of the Difficult Airway Society suggest than "In hypoxaemic patients, CPAP (continuous positive airway pressure) and non-invasive ventilation (NIV) may be beneficial."

As preoxygenation is a cornerstone of safety for intubation in the ICU, several recent trials have investigated different devices (non-rebreather mask, non-invasive ventilation, high flow nasal cannula, bag valve mask) with conflicting results. A main reason for those results is that efficiency of the preoxygenation period cannot be evaluated in the ICU in opposite to the operating room : gas monitoring are not available in ICU and even if it was the case, high flow demand from the patient, and agitation will make it inefficient. Additionally, desaturation is frequent (from 10% up to 50%) during intubation in ICU and lead to morbidity and mortality; so anticipation of desaturation is a major concern for ICU's physician because it's impacting care (face mask ventilation, early insertion of subglottic device).

The oxygen reserve index (ORI) (Masimo Corp., Irvine, CA, USA) is a new parameter that indicates real-time oxygenation reserve status in mild hyperoxemia range [partial pressure of oxygen (PaO2) of about 100-200 mmHg). ORI can be measured non-invasively by applying an exclusive sensor on a finger; the ORI is a nondimensional index that changes according to the oxygenation reserve status of the patient. It uses a value range of 0.00-1.00.