Monitoring assisted ventilation in the hypoxemic patient

Abstract

During assisted ventilation in patients with hypoxemic respiratory failure and acute respiratory distress syndrome (ARDS), achieving a balance between ventilator support and patient effort is essential. Contemporary approaches favor light sedation and limited use of neuromuscular blocking agents: most recent evidence would suggest that spontaneous breathing should be encouraged for as long as possible, provided that excessive inspiratory effort does not injure the lungs or the diaphragm. While spontaneous breathing is beneficial in case of mild-moderate hypoxemia, it may become injurious in moderate-to-severe patients (PaO<inf>2</inf>/FiO<inf>2</inf> <150 mmHg), especially in cases of low respiratory system compliance. Monitoring drive, effort, patient-ventilator interaction, respiratory mechanics and lung stress helps detect and manage harmful inflation patterns, preventing self-inflicted lung injury. By analyzing the first effort against an end-expiratory occlusion, we can assess the respiratory drive intensity from the negative deflection of airway pressure in the first 100 ms (P0.1 ‒ optimal range: 1-4 cmH<inf>2</inf>O), and the inspiratory effort from the maximum negative deflection (ΔPocc ‒ optimal range: 5-14 cmH<inf>2</inf>O). Plateau pressure can be measured to estimate total lung stress and calculate respiratory system compliance and driving pressure: driving pressure values above 12 cmH<inf>2</inf>O are associated to increased mortality. These measurements can be performed bedside without additional equipment, and should be integrated for comprehensive understanding of patient's individual respiratory mechanics and workload. In this narrative review, we provide a practical overview of these monitoring techniques and their physiological rationale, aiming to guide safe and effective maintenance of spontaneous breathing during invasive ventilation in hypoxemic patients.