Diaphragmatic Inspiratory Amplitude Measured by Ultrasonography as a Prognosticator for Postoperative Pulmonary Complications After Cardiac Surgery: a Prospective Observational Cohort Study

Cardiac surgery represents a critical intervention for various cardiovascular pathologies, yet it is frequently accompanied by a spectrum of postoperative complications.1 Amongst various morbidities, Post-Operative Pulmonary Complications (POPC) represent a significant clinical challenge leading to adverse outcomes like increased morbidity, mortality, and raised healthcare expenditures.2

Despite significant advancements in surgical methods and perioperative care protocols, POPCs still occur with the reported incidence of 3-16% after Coronary artery bypass grafting and 5-7% after valvular heart surgery.3 POPCs encompass various problems such as atelectasis, pneumonia, cardiogenic pulmonary oedema, acute respiratory distress syndrome, pneumothorax, pleural effusion, phrenic nerve injury and prolonged mechanical ventilation (PMV).2

The diaphragm, as the principal respiratory muscle, plays a pivotal role in maintaining pulmonary function.4 A normal diaphragmatic function is needed for optimal lung re- expansion post cardiac surgery, especially where the work of breathing is high (due to pain etc). Its function is also crucial in aiding efficacious respiratory secretion clearance through adequate coughing.2 Interventions that amplify the inspiratory muscle strength preoperatively (via an incentive spirometer), and usage of Non-invasive ventilation (NIV) in the postoperative period (via mechanical unloading) have demonstrated efficacy in attenuating the incidence of POPCs.2

Diaphragmatic dysfunction (DD) in the perioperative period of Cardiac surgery has an incidence of up to 20%.5 Diaphragmatic dysfunction after cardiac surgery constitutes a complex phenomenon with multifactorial aetiology, encompassing phrenic nerve injury (due to topical ice-slush usage, surgical trauma, or ligation of its blood supply during internal mammary artery dissection) and the deleterious inflammatory sequelae (from high level of cytokines and mitochondrial oxidative stress) associated with cardiopulmonary bypass (CPB).6

Transient diaphragm impairment is a frequent occurrence in the immediate aftermath of cardiac surgery and can be attributed to various perioperative factors, including sternotomy-associated pain, mechanical constraints on thoracic dynamics, electrolyte derangements, and intrathoracic fluid accumulations.7 However, a subset of patients manifest significant DD, which poses distinct challenges in clinical management and may exert profound ramifications on overall outcomes. Understanding the impact of DD on postoperative pulmonary function is imperative for optimizing patient care and clinical outcomes. Its occurrence has been linked to a spectrum of respiratory complications, ranging from pneumonia to difficulty in weaning from mechanical ventilation.7 Despite its clinical significance, it remains an under evaluated cause of POPCs.4