EDITORIAL| VOLUME 164, ISSUE 4, P814-815, OCTOBER 2023
Lung-Protective Concept and Noninvasive Respiratory Support
Masaaki Sakuraya
Chest 2023; 164: 814-815
DOI:https://doi.org/10.1016/j.chest.2023.05.014
Noninvasive respiratory support (NIRS), which includes high-flow nasal cannula (HFNC) and noninvasive ventilation (NIV), has been used for initial respiratory treatment in patients with respiratory failure. However, conclusive evidence is insufficient for the use of NIRS in patients with de novo acute hypoxic respiratory failure (AHRF), which is characterized by significant hypoxemia in the absence of prior chronic respiratory disease.1 Previous network meta-analyses included studies in which more than one-half of the eligible patients had de novo AHRF.2,3 Thus, most of the included studies were performed in patients with respiratory failure of various causes, and the NIV strategies varied. Therefore, in previous network meta-analyses,2,3 NIV was divided according to the interfaces (face mask or helmet) or ventilation modes (CPAP or bilevel positive airway pressure) to address the heterogeneity of the NIV strategies.
In this issue of CHEST, Pitre et al4 conducted a network meta-analysis to evaluate NIV that was divided into four groups according to both interfaces and ventilation modes and compared it with HFNC and oxygen therapy. Regardless of the ventilation mode, a helmet interface was associated with lower risks of death and tracheal intubation, similar to the findings of a previous network meta-analysis.2 Because no previous network meta-analyses have assessed both critical (eg, death and intubation) and important (eg, patient comfort) outcomes, their findings provide an important rationale for treating patients with de novo AHRF receiving NIRS. However, as shown in the network map, although many studies have used NIV with face mask bilevel positive airway pressure, only a small number of studies used NIV with helmet or CPAP. Additionally, the current data do not provide conclusive evidence in the comparison of face mask and helmet interfaces for the improvement of discomfort by reducing leakage, which is considered an advantage of the helmet interface. Although further evaluation is required, the current evidence suggests that the use of a helmet interface can improve the patient outcomes. Nevertheless, when interpreting these findings, we should remember that NIV management with a helmet interface was more effective than management without it. Thus, understanding respiratory treatment in patients who receive helmet NIV is important to improve the clinical practice for patients with de novo AHRF.
Pressure support is not always necessary for patients with AHRF without hypercapnia. CPAP not only improves oxygenation by reducing V˙/Q˙ mismatch but also improves ventilation and reduces inspiratory effort. In most clinical trials that have compared helmet NIV with oxygenation therapy, CPAP was used as the initial ventilation mode.2,4 The previous network meta-analysis that evaluated NIV according to the ventilation modes suggested that CPAP might be the most effective NIRS for the reduction of the risk of death and intubation.3 In a network meta-analysis conducted by Pitre et al,4 patients who received helmet CPAP had the lowest point estimate in the reduction of the risk of death and intubation using oxygen therapy as a reference when compared with the other respiratory treatments. Furthermore, in a randomized controlled trial that compared the helmet and face mask interfaces in patients who underwent bilevel positive airway pressure,5 those patients with the helmet interface were set at a lower level of pressure support than those with the face mask. Considering that a larger tidal volume during NIV is associated with treatment failure in patients with AHRF,6, 7, 8 pressure support should be used carefully while monitoring the tidal volume. Moreover, patients with sustained strong inspiratory effort, which requires a high level of pressure support, may be at a high risk of treatment failure.8
Maintaining a positive airway pressure is also important. In patients with cardiopulmonary edema, which is one of the causes of AHRF, NIV is recommended to improve patient outcomes. The respiratory status is expected to recover within a short period in these patients. However, pulmonary edema caused by increased vascular permeability (eg, ARDS) takes longer to resolve. Because increased respiratory drive and inspiratory effort can lead to lung injury, these patients would have prolonged exposure to the risk of self-inflicted lung injury.9 In most trials that evaluated the face mask interface, NIV was not used continuously.2, 3, 4 The risk of lung injury would be even higher if those patients interrupt NIV use before improving their respiratory status. The use of HFNC during the NIV interval may be better for maintaining positive airway pressure. CPAP may also be superior to bilevel positive airway pressure in terms of the interaction between the patient and NIV and it is expected to be usable continuously.
Lung-protective strategies should be implemented even during NIRS. Further studies are needed to identify the appropriate monitoring methods and optimal targets for lung-protective strategies during NIRS. The level of positive end-expiratory pressure required varies among individual patients. When NIV is used at lower level of positive pressures, the face mask interface will be enough to maintain airway pressure. Sedative or opioid use improves tolerance, which can potentially lead to continuous use.10 Based on careful monitoring and assessment, appropriate strategies should be adopted to minimize the risk of lung injury. Although the helmet interface may be reasonable for the performance of NIV with the lung-protective concept, it is not a magic wand.