The evaluation of factors affecting hemodynamic variability in mechanically-ventilated patients after cardiac surgery

Background: Optimizing cardiac preload is usually the first step in patients with unstable hemodynamic. However, it should be remembered that an unnecessary volume expansion may exacerbate the hemodynamic. In mechanically ventilated patients, the ventilatory induced hemodynamic variations (VIHV) can be used to predict the fluid requirement. These variations (called dynamic indices of cardiac filling pressure), are superior to static indices (central venous and pulmonary artery occlusion pressure) in diagnosing any volume requirement. We theorized that some conditions other than hypovolemia might affect these hemodynamic variations. Objectives: The current study aimed to discover these conditions in adult patients admitted to post-cardiac surgery ICU. Methods: This antegrade cross-sectional study was conducted on 304 adult patients who were admitted to ICU after elective cardiac surgery in a teaching hospital (Tabriz-Iran). During the first 3 hours of the admission, the systolic (∆SBP), diastolic (∆DBP), mean (∆MAP), and arterial blood pulse pressures (∆PP) were invasively monitored and calculated in percent value. Because of the return of spontaneous breathing in most of the patients, the calculations were done only during the first 3-hour. All patients with spontaneous breathing, irregular cardiac rhythm, or re-admission to OR in this period were excluded from the study. We recorded demographic and surgical characteristics, perioperative hemodynamic and echocardiographic, and complications data and surveyed the correlation between VIHV and perioperative data. Results: Two hundred and ninety two patients met the inclusion criteria. Coronary artery bypass grafting (CABG) was the most common surgery (64.4 %). Cardiopulmonary bypass (CPB) was used in 95.55% of the surgeries. In the first 24-hour, 51 patients required re-operation because of sternum closure, bleeding control, cardiac tamponade, and coronary artery revascularization. Mortality and morbidity occurred in 2 (0.68%) and 50 (17.12%) patients, respectively. Among VIHVs, the ∆PP had the most significant value. Thus, mean ∆PP was calculated and the correlation between its severity (≤ 20% vs. > 20%) and other values surveyed. It was high in patients with cardiac dysfunction and tamponade (P value < 0.001). No significant correlation was found between mean ∆PP severity and hemorrhage rate, fluid balance, need to vasoactive agents, blood products, or bleeding control, redo CABG or sternum closure surgery, time to tracheal extubation, ICU stay, and postoperative complications. Patients with closed sternum were the same as those with the unclosed sternum. Conclusions: The ∆PP was the most sensitive VIHV parameter. Cardiac dysfunction and tamponade increased ∆PP. Unclosed sternum did not affect its value. ∆PP value did not affect postoperative complications rate, time to tracheal extubation, or ICU stay.