Postoperative pulmonary complications (PPCs) remain a frequent event after pump-on cardiac surgery and are mostly characterized by postoperative hypoxemia.These complications are significant contributors to prolonged intensive care unit admissions and an escalation in in-hospital mortality rates.

The dual impact of general anesthesia with invasive mechanical ventilation results in ventilator-induced lung injury, while cardiac surgery introduces additional pulmonary insults. These include systemic inflammatory responses initiated by cardiopulmonary bypass and ischemic lung damage consequent to aortic cross-clamping. Contributing factors such as blood transfusions and postoperative pain further exacerbate the incidence of PPCs by increasing the permeability of the alveolar-capillary barrier and disrupting mucociliary functions, often culminating in pulmonary atelectasis.

Protective ventilation strategies, inspired by acute respiratory distress syndrome (ARDS) management protocols, involve the utilization of low tidal volumes (6-8mL/kg predicted body weight). However, the uniform application of low tidal volumes, especially when combined with the multifactorial pulmonary insults inherent to cardiac surgery, can precipitate surfactant dysfunction and induce atelectasis.

The role of pulmonary surfactant in maintaining alveolar stability is critical, necessitating continuous synthesis to sustain low surface tension and prevent alveolar collapse. The most potent stimulus for surfactant secretion is identified as the mechanical stretch of type II pneumocytes, typically induced by larger tidal volumes.

This background sets the foundation for a research study aimed at assessing the safety and efficacy of incorporating sighs into perioperative protective ventilation. This approach is hypothesized to mitigate postoperative hypoxemia and reduce the incidence of PPCs in patients undergoing scheduled on-pump cardiac surgery.

The purpose of this single center, parallel group, randomized controlled study is to evaluate the effect of a perioperative sigh ventilation strategy on postoperative outcomes during the first 7 days following cardiac surgery. The study will include 192 adult patients undergoing scheduled on-pump cardiac surgery. The sigh ventilation approach will combine sigh ventilation and lung protective ventilation (6-8 ml/kg/pbw) from intubation to extubation. It will be compared to a conventional approach without sigh ventilation, with lung protective ventilation and positive end-expiratory pressure (PEEP) setting same as the intervention arm. The primary endpoint is the Spo2/Fio2 ratio during the initial post extubation hour. The secondary endpoints are postoperative pulmonary complications and hospital length of stay .

Inclusion Criteria:

• Elective cardiac surgery with general anesthesia
• Conventional cardiopulmonary bypass and aortic cross clamp
• Providing written informed consent by the patient himself/herself or the next of kin

Exclusion Criteria:

• Emergent surgery including aortic dissection, cardiac rupture and active endocarditis surgery
• Left ventricular assist device implantation
• Patients anticipated to require intraoperative support with Extracorporeal Membrane Oxygenation (ECMO) or Intra-Aortic Balloon Pump (IABP)
• Chronic pulmonary disease requiring long-term home oxygen therapy
• Receiving invasive mechanical ventilation within 7 days prior to surgery
• Preoperative shock
• Obstructive Sleep Apnea Syndrome (OSAS) requiring intermittent non-invasive ventilatort support
• Preoperative left ventricular ejection fraction<40%
• Pulmonary arterial systolic pressure>50 mmHg
• Redo surgery