Controversies when using mechanical ventilation in obese patients with and without acute distress respiratory syndrome

Heart-lung crosstalk in acute respiratory distress syndrome

Acute Respiratory Distress Syndrome (ARDS) is initiated by a primary insult that triggers a cascade of pathological events, including damage to lung epithelial and endothelial cells, extracellular matrix disruption, activation of immune cells, and the release of pro-inflammatory mediators. These events lead to increased alveolar-capillary barrier permeability, resulting in interstitial/alveolar edema, collapse, and subsequent hypoxia and hypercapnia. ARDS not only affects the lungs but also significantly impacts the cardiovascular system. We conducted a comprehensive literature review on heart-lung crosstalk in ARDS, focusing on the pathophysiology, effects of mechanical ventilation, hypoxemia, and hypercapnia on cardiac function, as well as ARDS secondary to cardiac arrest and cardiac surgery. Mechanical ventilation, essential for ARDS management, can increase intrathoracic pressure, decrease venous return and right ventricle preload. Moreover, acidemia and elevations in transpulmonary pressures with mechanical ventilation both increase pulmonary vascular resistance and right ventricle afterload. Cardiac dysfunction can exacerbate pulmonary edema and impair gas exchange, creating a vicious cycle, which hinders both heart and lung therapy. In conclusion, understanding the heart-lung crosstalk in ARDS is important to optimize therapeutic strategies. Future research should focus on elucidating the precise mechanisms underlying this interplay and developing targeted interventions that address both organs simultaneously.

Perioperative Pulmonary Atelectasis: Part I. Biology and Mechanisms

Pulmonary atelectasis is common in the perioperative period. Physiologically, it is produced when collapsing forces derived from positive pleural pressure and surface tension overcome expanding forces from alveolar pressure and parenchymal tethering. Atelectasis impairs blood oxygenation and reduces lung compliance. It is increasingly recognized that it can also induce local tissue biologic responses, such as inflammation, local immune dysfunction, and damage of the alveolar-capillary barrier, with potential loss of lung fluid clearance, increased lung protein permeability, and susceptibility to infection, factors that can initiate or exaggerate lung injury. Mechanical ventilation of a heterogeneously aerated lung (e.g., in the presence of atelectatic lung tissue) involves biomechanical processes that may precipitate further lung damage: concentration of mechanical forces, propagation of gas-liquid interfaces, and remote overdistension. Knowledge of such pathophysiologic mechanisms of atelectasis and their consequences in the healthy and diseased lung should guide optimal clinical management.

Adoption of low tidal volume ventilation in the emergency department: A quality improvement intervention

BACKGROUND

Ventilator tidal volumes of >8 mL/kg of predicted body weight (PBW) may increase the risk of lung injury. We sought to evaluate the impact of a quality improvement intervention among intubated Emergency Department (ED) patients to protocolize the prescription of low tidal volume ventilation.

METHODS

In this before-and-after study, the average tidal volume delivered to ED patients receiving volume assist-control ventilation was compared before (2007-2014) and after (2015-2016) implementation of a ventilator initiation protocol (the quality improvement intervention). The intervention emphasized 1) measurement of the patient's height to calculate PBW and therefore tailor the tidal volume to estimated lung size (<8 mL/kg PBW), and 2) focused education and reference materials for ED physicians and respiratory therapists.

RESULTS

Among ventilated ED patients meeting inclusion criteria in the before (N = 2185) and after (N = 774) cohorts, the mean (±SD) tidal volume decreased from 9.0 ± 1.4 mL/kg to 7.2 ± 0.9 mL/kg PBW following the intervention (absolute difference 1.8 mL/kg, 95% confidence interval 1.7 to 1.9 mL/kg, p < 0.001). The proportion of patients receiving low tidal volume ventilation increased after the intervention (72%), as compared to before (23%). Low tidal volume ventilation continued to be utilized at 24 h after ICU admission in patients who remained intubated in the cohort following the intervention (mean tidal volume 7.3 mL/kg PBW).

CONCLUSIONS

Pairing a ventilator initiation protocol with focused education and resources for emergency physicians and respiratory therapists was associated with a significant reduction in tidal volume delivered to ED patients.