OBJECTIVES: Respiratory muscle effort is an important determinant of pathophysiology and clinical outcomes in patients with acute hypoxemic respiratory failure receiving noninvasive respiratory support (NIRS). Excessive effort reflects an imbalance between ventilatory load and muscle capacity and has been associated with patient self-inflicted lung injury, treatment failure, and worse outcomes, particularly when escalation to invasive ventilation is delayed. This review provides a clinically focused synthesis of the physiological determinants, bedside assessment, and practical implications of respiratory muscle effort during NIRS. METHODS: We included physiological, translational and clinical studies evaluating the assessment and clinical implications of respiratory muscle effort in patients with AHRF receiving NIRS. Evidence was selected to emphasize clinical applicability and bedside relevance. RESULTS: Clinical signs and simple indices remain essential for early detection of increased respiratory effort but lack specificity. They are widely available, scalable, and low-cost, although they require clinical experience for accurate interpretation. Advanced monitoring-including oesophageal pressure measurement, respiratory muscle ultrasound, and electrical impedance tomography-provides physiological insight but is variably available, more resource-intensive, and requires expertise. A tiered approach to monitoring, integrating scalable bedside assessment with selective use of advanced tools, may represent a pragmatic framework for clinical implementation. NIRS modalities-including high-flow nasal oxygen, continuous positive airway pressure, and bilevel ventilation-affect respiratory effort through distinct mechanisms and may fail to adequately unload respiratory muscles if not carefully titrated. Persistently elevated effort may occur despite acceptable oxygenation and is associated with clinical deterioration. CONCLUSIONS: Respiratory muscle effort should be considered a key component of patient assessment during NIRS. Structured and repeated evaluation using a combination of clinical signs and, when available, advanced monitoring, may help identify harmful breathing patterns and support timely escalation of care. Future research should prioritise pragmatic monitoring strategies, actionable thresholds, and integration into routine practice across diverse healthcare settings. IMPLICATIONS FOR CLINICAL PRACTICE: Routine assessment of respiratory effort, integrating clinical observation with available monitoring tools, may improve titration of respiratory support, reduce the risk of delayed intubation, and support more individualized care in patients with AHRF. Embedding a tiered, feasibility-informed approach to respiratory effort monitoring may enhance translation from physiological insight to routine bedside care.
Fazzini et al. (Mon,) studied this question.