Monitoring and preventing diaphragm injury

Abstract

Purpose of review: The present review summarizes developments in the field of respiratory muscle monitoring, in particular in critically ill patients.

Recent findings: Patients admitted to the ICU may develop severe respiratory muscle dysfunction in a very short time span. Among other factors, disuse and sepsis have been associated with respiratory muscle dysfunction in these patients. Because weakness is associated with adverse outcome, including prolonged mechanical ventilation and mortality, it is surprising that respiratory muscle dysfunction largely develops without being noticed by the clinician. Respiratory muscle monitoring is not standard of care in most ICUs. Improvements in technology have opened windows for monitoring the respiratory muscles in critically ill patients. Diaphragm electromyography and esophageal pressure measurement are feasible techniques for respiratory muscle monitoring, although the effect on outcome remains to be investigated.

Summary: Respiratory muscle dysfunction develops rapidly in selected critically ill patients and is associated with adverse outcome. Recent technological advances allow real-time monitoring of respiratory muscle activity in these patients. Although this field is in its infancy, from a physiological perspective, it is reasonable to assume that monitoring respiratory muscle activity improves outcome in these patients.

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FIGURE 1

Monitoring of respiratory muscle function using esophageal pressure (Pes). Tracings of flow, airway pressure (Paw), Pes and gastric pressure (Pga) under different conditions. (a) Patient on controlled mechanical ventilation. Pes increases during mechanical inspiration. There is no decrease in Pes before mechanical inspiration, indicating absence of respiratory muscle activity. Note the perturbations in Pes resulting from cardiac activity. (b) Patient–ventilator asynchrony during pressure support ventilation; arrow indicates an autotriggered breath. Note the absence of a deflection in Pes in this breath, which is present in the other two breaths. (c) Weaning patient during a successful spontaneous breathing trial with T-piece, showing negative Pes and positive Pga swings during inspiration. (d) Weaning patient during a failed spontaneous breathing trial with T-piece. Note the increase in Pga during the expiratory phase to compensate for diaphragm weakness or high intrinsic positive end-expiratory pressure. Note that in this case, the decrease in Pes at the beginning of inspiration (e.g. the breath just after T = 3 s) results from both relaxation of the abdominal muscles (note decrease in Pga) and contraction of the diaphragm.

FIGURE 2

Monitoring diaphragm function using processed EMG. Tracings of flow, airway pressure (Paw), electrical activity of the diaphragm (EAdi) and transdiaphragmatic pressure (Pdi) under different conditions. (a) Patient–ventilator asynchrony during assist control ventilation. Arrow indicates a wasted effort following a machine-cycled breath. (b) Weaning patient during a failed spontaneous breathing trial with T-piece. Left panel shows tracings in first minute of the trial and right panel 25 min later. Note the increase in EAdi and Pdi. Subparts (c) and (d) represent same patient, ventilated with low (c) and high (d) pressure support. Note the decrease in EAdi resulting from a reduction in pressure support level. EMG, electromyography.