The Journal of Tehran University Heart Center Original Article The Effect of Low Tidal Volume Ventilation during Cardio- pulmonary Bypass on Postoperative Pulmonary Function Maryam Davoudi, MD, Afshin Farhanchi, MD, Ahmad Moradi, MD, Mohammad Hosein Bakhshaei, MD*, Gholamreza Safarpour, MD Ekbatant Hospital, Hamadan University of Medical Sciences, Hamadan, Iran. Received 23 January 2010; Accepted 09 May 2010 Abstract Background: Postoperative pulmonary dysfunction is one of the most frequent complications after cardiac surgery and it is believed to result from the use of cardiopulmonary bypass (CPB). In this study, we investigated the effect of low tidal volume ventilation during CPB on postoperative gas exchange and lung mechanics. Methods: This prospective randomized study included 100 patients undergoing elective coronary artery bypass grafting. In 50 patients, low tidal volume ventilation [tidal volume (TV) = 3 ml/kg, respiratory rate (RR) = 12/min, fraction of inspiratory oxygen (FIO2)= 1.0, positive end expiratory pressure (PEEP) = 5 cmH2O] was applied during CPB (group I); and in the other 50 patients (group II), the lungs were open to the atmosphere without ventilation. Measurements were taken preoperatively, after CPB, and before discharge. Results: Post-bypass PaO2 (just after CPB 85 versus75) was higher significantly in group I (P value < 0.05). Decrease in postoperative forced expiratory volume in 1 second (25% versus 30%) and forced vital capacity (32% versus 35%) was less significant in group I. Also, time to extubation (5 hrs versus 5.5 hrs) was shorter in group I. Conclusion: Continued low tidal volume ventilation during CPB improved post-bypass oxygenation and lung mechanics. J Teh Univ Heart Ctr 3 (2010) 128-131 Keywords: Cardiac surgical procedures • Cardiopulmonary bypass • Tidal volume • Ventilation • Respiratory function test Introduction Lung dysfunction after coronary artery bypass grafting (CABG) remains an important cause of postoperative morbidity despite continuing improvements in cardiopulmonary bypass (CPB) techniques and postoperative intensive care.1 Pulmonary dysfunction not only prolongs mechanical ventilation, intensive care in intensive care unit(ICU), and total duration of hospitalization time but it also increases treatment costs.2 The etiology of pulmonary dysfunction after open heart surgery is thought to be multi factorial, occurring as a result of the combined effects of anesthesia, CPB, and surgical trauma. CPB in particular is known to activate the inflammatory process, resulting in increased pulmonary capillary permeability and damage to lung parenchyma.1 Even after uncomplicated cardiac surgery, a midline sternotomy causes significant reductions in total lung capacity, vital capacity, forced expiratory volume in 1 second (FEV ), and functional residual capacity. 1 These changes may give rise to postoperative atelectasis and frequently at least mild hypoxemia.3 Atelectasis in the post- bypass period is the main cause of intrapulmonary shunt and poor arterial oxygenation.2 The physiologic disturbance after CPB can be categorized into abnormal gas exchange and poor lung mechanics.1 Most interventions focus specially on airway management, *Corresponding Author: Mohamad Hosein Bakhshaei, Assistant Professor of Anesthesiology, Hamadan University of Medical Sciences, Ekbatan Hospital, Hamadan, Iran. 6515737461. Tel: +98 811 8251338. Fax: +98 811 8268034. E-mail: bakhshaei@umsha.ac.ir. 128