The effect of positive end expiratory pressure on right ventricule function during coronary artery bypass surgery

Coronary artery bypass grafting (CABG) surgery is one of the most commonly performed major surgeries worldwide. Cardiac and respiratory complications are the most common causes of postoperative mortality and morbidity after CABG. Positive end expiratory pressure (PEEP) is frequently used for the prevention and treatment of respiratory complications after this procedure. While Optimal PEEP level has positive effects on respiratory mechanics and hemodynamic parameters, excessive levels of PEEP may play a negative role on both systems. Many methods have been described to determine the optimal PEEP levels. However, there are few studies investigating the relationship between PEEP and transesophageal echocardiography (TEE). TEE, has been gained acceptance as a useful hemodynamic monitoring tool and provides valuable information regarding right ventricle structure and function. Both strain and strain rate that are calculated using echocardiography provide direct assessment of myocardial contractility during systole and diastole. Speckle tracking echocardiography (STE) is a new strain analyze technique. Strain imaging provides reliable information in patients with myocardial ischemia, myocardial infarction, and valvular disease. The aim of this study is to evaluate the effects of different PEEP levels on right ventricle function using speckle tracking in patients undergoing CABG surgery. After Ethical and Research Committee of Baskent University Medicine and Health Association approval we prospectively analyzed 20 CABG surgery patients between May 2013 and September 2013. After initiation of mechanical ventilation and before sternotomy 5, 10, and 20 cmH2O of PEEP were applied sequentially in 5 minutes intervals. After 5 minutes of stabilization at each PEEP level four and two chamber images of right ventricle were recorded using TEE. The right ventricle diameter, velocity, longitudinal strain, strain rate, and fractional area change (RVFAC) were calculated and evaluated from the recorded images. Seventeen male (85%) and 3 female (15%) patients with the mean age of 60 years were studied. Intraoperative mean systolic (p = 0.918), diastolic (p = 0.765), and mean arterial blood pressure (p = 0.808), and heart rate (p=0,116) were not significantly different between any of the three PEEP levels. Mean RVFAC measurements were similar between 5 and 10 cmH2O PEEP (44.3% ± 5.4 and 41.8% ± 5.6, p=0.063). Compared with 5 and 10 cmH2O PEEP, mean RVFAC significantly decreased at 20 cmH2O PEEP (35.9% ± 4.9, p=0,001). Right ventricle velocity significantly reduced with incremental PEEP increases (5 cmH2O PEEP 8.0 ± 1.7 cm/sec, 10 cmH2O PEEP 7.2 ± 1.4 cm/sec, 20 cmH2O PEEP 5.8 ± 1.6 cm/sec; p < 0.05). Mean strain rate values at 5, 10, and 20 cmH2O PEEP levels were 1.2 ± 0.2 sec-1, 1.2 ± 0.2 sec-1, and 1.0 ± 0.3 sec-1, respectively 20 cmH2O PEEP when compare with 5 cmH2O PEEP (p=0,03). Mean right ventricle diameter measurements also decreased with incremental PEEP increases (3.9 ± 0.4 cm at 5 cmH2O PEEP, 3.8 ± 0.3 cm 10 cmH2O PEEP, and 3.7 ± 0.4 cm at 20 cmH2O PEEP), however this decrease was significantly different only between 20 cmH2O PEEP and other two PEEP levels (p = 0.01). Respective mean right ventricular strain values at 5, 10, and 20 cmH2O PEEP levels were 22.9% ± 3.1%, 23.8% ± 2.6%, and 18.9% ± 2.7%. Mean right ventricle strain value significantly decreased at 20 cmH2O PEEP when compared with other two PEEP levels (p<0,001 for both). In conclusion, in patients who had normal right ventricle function and underwent CABG incremental increases in PEEP level from 5 cmH2O to 10 cmH2O and 10 cmH2O to 20 cmH2O did not significantly change mean arterial systolic, diastolic, and mean pressures and heart rate. However, compared with other two PEEP levels, right ventricle functions in terms of strain, SR, right ventricle diameter, and RVFAC were significantly impaired at 20 cmH2O PEEP level.