Cardiorespiratory dynamics of sedated pigs submitted to different inspired oxygen fractions under controlled mechanical ventilation

ABSTRACT

Background: Individuals submitted to situations of deep sedation have a marked decrease in their ventilatory capacity.The provision of adequate ventilation and oxygenation in critically ill patients submitted to sedation in intensive therapyhas been the subject of special care. In such cases, exposure to low inspired oxygen fractions (FIO2) is a factor that caninfl uence alveolar perfusion and respiratory performance. The aim of this study is to evaluate the effects of three inspiredoxygen fractions (80%, 60% or 40%) on the cardiorespiratory dynamics of pigs submitted to mechanical ventilation byintermittent positive pressure in deep sedation with propofol-remifentanil.Material, Methods & Results: Twenty crossbred pigs weighing between 17 and 25 kg and aged between 60 and 90 dayswere used. Each animal was submitted to deep sedation for 2h in randomly assigned FIO2 (80%, 60% or 40%). Scores suchas heart and respiratory rate, blood pressure, respirometry (PaO2, P(A-a)O2, PIP, Vmin), physiological dead space, pulmonaryshunt and blood gas analysis (pH, PaO2, PaCO2, HCO3) were observed, evaluated and compared. Patients were evaluatedafter sedation was induced with propofol (12 mg.kg-1) and remifentanil (1 mcg.kg-1). To maintain the level of sedation weused propofol (an average of 18 mg.kg-1.h-1) and remifentanil (0.5 mcg.kg-1.min-1). Intubation was preceded after the onsetof sedation to mechanical ventilation - volume-cycled, intermittent positive pressure. Patients received a tidal volume of10 mL.kg-1 and an IE ratio of 12, positive end-expiratory pressure of 4 cmH2O with three inspired oxygen fractions. Patients’ respiratory rate was adjusted so as to maintain end-tidal carbon dioxide pressure between 35 and 45 mmHg. Datawere subjected to analysis of variance for repeated measures followed by a Tukey test. Patients receiving a 40% oxygenconcentration showed an average heart rate higher than the others. Shunt levels...