The Effectiveness of High Flow Nasal Cannula Versus Noninvasive Ventilation and Conventional Oxygen Therapy

Reintubation after liberation from mechanical ventilation (MV) is a wellknown adverse event seen in different patients subtypes(post surgical, trauma,medical) as well as in surgical and medical intensive care units (ICUs) .The cumulative probability of reintubation , following planned and unplanned extubation , in 185 ICUs in the United States ,reached up to 10 % and 90% occurred within the first 96 hours (4 days) after first extubation , the median time to reintubation was 15 hours.

Proper timing for extubation is crucial to minimize extubation failure and about 12 to 14% of patients planned for extubation would require reintubation within 48 to 72 hours, mostly within the first 24 hours \& in a multivariate analysis, duration of MV more than 7 days prior to extubation, ineffective cough, and severe systolic left ventricular dysfunction were independent factors associated with extubation failure, whereas ,in another study,age and underlying diseases were other factors associated with higher extubation failure with rates reaching up to 34% in patients 65 yrs or older, those with chronic respiratory or cardiac disorders and the condition was specifically associated with significant rapid clinical deterioration and worsening of daily organ dysfunction scores reflecting a direct effect of reintubation on patient outcomes. Mortality risk is reported to be five times higher in patients who require reintubation after extubation from MV.

Postextubation sequential oxygen devices applied as first-line therapy after extubation include noninvasive ventilation (NIV) , high-flow nasal cannula (HFNC) and conventional oxygen therapy (COT).

COT delivered via masks and nasal prongs has been widely used as the main sequential supportive oxygen therapy administered to patients after extubation . However, the maximal oxygen flow rates that these devices can deliver are limited with maximum flow rate up to 15 L/min only, which is usually far lower than the demands that postextubation patients would require . The fraction of inspired oxygen (FiO2) delivered by COT is unstable because of the entertainment of room air and dilution of the inspired oxygen .

Potential benefits of NIV include the ability to provide a relatively consistent and wider range of FiO2 compared with COT . Moreover, NIV creates an extrinsic positive end expiratory pressure which aids in recruitment of collapsed alveoli.

The American College of Chest Physicians/American Thoracic Society (ACCP/ATS) clinical practice guidelines for liberation from MV in the critically ill highlight the importance of usage of preventive (NIV) in patients at high risk of reintubation and emphasizing its impact on improving oxygenation, ventilation, decreasing hospital mortality, length of hospital stay, and incidence of ventilator associated pneumonia (VAP) . Evidence suggest that NIV may prevent postextubation respiratory failure and avoid reintubation if it is applied soon after extubation. On the other hand, this strategy is associated with worse outcomes if applied after development of postextubation acute respiratory failure (ARF). In addition, intolerance to NIV is quite common in clinical practice, eye irritation, skin damage, interruption in diet and clearance of airways secretion are common adverse events and can worsen the patient's outcome. These limitations urge investigators to explore other alternative oxygen delivery devices and search for potential roles in improving clinical outcomes in the post extubation setting.

High flow nasal cannula (HFNC) is a novel, high flow oxygen device with established efficiency, it is well tolerated by patients, easily applied and can provide fully humidified, heated, high-flow rates up to 60 L/min, a constant high fraction of inspired oxygen (FiO2) (0.21 - 1.0) and flow-dependent continuous positive airway pressure (2-5 cm H2O) which , in turn , increases end-expiratory lung volume and aids in alveolar recruitment and reduces atelectasis, subsequently improving ventilation-perfusion mismatch . The continuous high flow of oxygen guarantees both higher tidal volume with adequate minute ventilation and sufficient oxygenation improves inspiratory flow dynamics and decrease work of breathing by improving thoracoabdominal synchrony. In addition, pharyngeal dead space washout effect decreases carbon dioxide in a faster manner. Finally, the heated humidification flow creates physiological conditions preserving mucosal integrity, reducing mucosal inflammation, and facilitating clearance of secretions, thereby improving the oxygenation, and further decreasing the risk of atelectasis.

Several studies have investigated these available devices and compared their efficacy in lowering reintubation rates after extubation, but results are conflicting and inconsistent and no study could conclude that either HFNC, NIV or COT is superior to prevent reintubation. One randomized controlled trial (RCT) reported that HFNC was associated with a lower rate of reintubation in low-risk patients compared to COT. Another RCT in high-risk non-hypercapnic patients and concluded that HFNC could not decrease rate of reintubation compared with COT. A third study showed that HFNC and NIV are equally effective in lowering reintubation rate.

In Egypt, researchers have also studied and compared the effectiveness of these modalities in different clinical ICU settings with comparable efficacies between three devices. The objective of the current work is to compare the rate of reintubation after extubation using HFNC versus NIV and COT as sequential respiratory support.