IJCS | Volume 31, Nº3, May/ June 2018

245 Cordeiro et al. Respiratory mechanics and oxygenation International Journal of Cardiovascular Sciences. 2018;31(3)244-249 Original Article Physical therapy prescribed correctly during the preoperative and postoperative periods of cardiac surgery providesmajor benefits for patientswith heart disease and may reduce substantially the occurrence of complications during these periods. With these potential benefits, the inclusion of physical therapists becomes fundamental in the hospital environment. However, there is scarce information in the literature regarding the impact of changes in respiratory mechanics on the duration of invasive MV (IMV) and whether this would increase the duration of stay in the intensive care unit (ICU). Based on these considerations, this study aimed to evaluate the association between respiratory mechanics with oxygenation and duration of IMV and ICU hospitalization in patients in the postoperative period of cardiac surgery. Methods This was a prospective cohort study conducted with patients admitted to the Instituto Nobre de Cardiologia / Santa Casa de Misericórdia in the period between February and June 2016. The study was approved by the Research Ethics Committee at Faculdade Nobre (CAAE 51208115.1.0000.5654), and all patients signed an informed consent form in the preoperative period. The inclusion criteriawere individuals of both genders, aged 18 years or older, undergoing cardiac surgery (coronary-artery bypass grafting [CABG], aortic and/or mitral valve replacement, andcorrectionof cardiacdisease), whounderwent sternotomy and extracorporeal circulation (ECC) under IMV in the immediate postoperative period. The exclusion criteria were: (a) hemodynamic instability requiring vasopressors at high concentration, (b) nonevaluable respiratory mechanics (for example, interaction with the MV), (c) progression to death during the ICU period, (d) sedation required for more than 48 hours, (e) absence of arterial catheter for collection of blood sample, and (f) refusal to participate in the research and to sign the informed consent form. Patients whomet the inclusion criteria were evaluated at the moment of admission to the ICU, soon after leaving the operating room. After receiving the initial support from the health care team, the physiotherapist on call evaluated the ventilatory mechanics and obtained from the ventilator (Vela, Viasys Healthcare, Critical Care Division, Palm Springs, CA, USA) the values related to peak and plateau pressure, static compliance of the respiratory system, and airway resistance. During this evaluation, the patients remained in the supine positionwith the bed-head raised to aminimumof 30º while still under the effect of the surgical anesthesia, receiving ventilation at a controlled volumemode (6mL/ kg) with an inspiratory flow of 40 L/min, respiratory rate of 15 mpm, pause duration of 1 second, fraction of inspired oxygen (FiO 2 ) of 100%, and positive end- expiratory pressure (PEEP) of 5 cm H 2 O. To calculate the static compliance, we used the formula tidal volume / (plateau pressure - PEEP) and to calculate resistance, the formula (peak pressure - plateau pressure) / flow. Immediately after evaluating the ventilatorymechanics, the physician on call collected a sample of arterial blood through a catheter inserted into the radial artery. The sample was analyzed with a blood gas analyzer and the results related to arterial oxygen pressure (PaO 2 ) and FiO 2 were recorded. Levels of PaO 2 were divided by those of FiO 2 , yielding the oxygenation index. After these assessments, the patients continued to receive support according to the routine procedures of the unit, including the maintenance of strategies for weaning and decisions about the patient’s discharge to the ward. The researchers refrained from interfering with the decisions and were limited to taking notes about the IMV duration (from ICU admission to extubation) and ICU stay. Statistical analysis The analysis was performed using SPSS 20.0, and the data are represented as mean and standard deviation. Normality was tested with the Kolmogorov-Smirnov test. Categorical variables were analyzed with the chi- square test and numerical variables (IMV duration, length of ICU stay, static compliance, resistance, and gas exchange) with Pearson’s correction test. P values < 0.05 were considered statistically significant. Results Between February and June 2016, a total of 64 patients were hospitalized to undergo cardiac surgery. Of these, 14 were excluded from the study due to nonevaluable ventilatorymechanics (10 patients) or for refusing to sign the informed consent (4 patients). Therefore, we included 50 patients (52% women) with a mean age of 57.5 ± 13.5 years, who underwent cardiac surgery at Instituto Nobre de Cardiologia / Santa Casa de Misericórdia em Feira de Santana , Bahia (Brazil).