Assessing breathing effort in mechanical ventilation: physiology and clinical implications

Abstract

Recent studies have shown both beneficial and detrimental effects of patient breathing effort in mechanical ventilation. Quantification of breathing effort may allow the clinician to titrate ventilator support to physiological levels of respiratory muscle activity. In this review we will describe the physiological background and methodological issues of the most frequently used methods to quantify breathing effort, including esophageal pressure measurement, the work of breathing, the pressure-time-product, electromyography and ultrasound. We will also discuss the level of breathing effort that may be considered optimal during mechanical ventilation at different stages of critical illness.

Physiology of the Respiratory Drive in ICU Patients: Implications for Diagnosis and Treatment

“…The respiratory drive directly determines breathing effort when neuromuscular transmission and respiratory muscle function are intact. We define breathing effort as the mechanical output of the respiratory muscles, including both the magnitude and the frequency of respiratory muscle contraction [1].…”

“…Normal values for EA di are not yet known, but it is proposed that an amplitude of at least 5 μV per breath in ICU patients is likely sufficient to prevent development of diaphragmatic disuse atrophy [1].…”

“…This requires tight control of ventilation by the respiratory centers in the brain stem. The respiratory drive is the intensity of the output of the respiratory centers, and determines the mechanical output of the respiratory muscles (also known as breathing effort) [1,2].…”

Esophageal Manometry

“…Otherwise, chest wall compliance can be estimated as 4% of predicted vital capacity per cm H 2 O. 14,60,61 Predicted vital capacity is based on sex, height, and weight, and it can be calculated using several online calculators; E cw is the inverse of chest wall compliance, measured in L/cm H 2 O.…”

Ventilator Graphics: Scalars, Loops, & Secondary Measures

“…The use of direct bedside monitors has been proposed to better assess WOB and to monitor spontaneous efforts more closely while fine-tuning the level of ventilatory support. [77][78] Through the use of an esophageal balloon, intrapleural pressure measurements can be estimated and WOB can be calculated by integration of the P-V plot. [77][78] WOB techniques have been recommended to accurately adjust ventilation settings, optimize gas exchange, and minimize unwarranted patient exertion.…”