Hemodynamic and respiratory effects in sheep subjected to four ventilation types and anesthetized with isoflurane or propofol

Abstract

The objective of this study was to examine the effects of various ventilation modalities in sheep anesthetized with isoflurane or propofol. Twelve healthy adult crossbred ewes, aged 12 months and weighing 32±5 kg, were used in the study. After instrumentation with conscious animals in the right lateral decubitus position, they were administered morphine (0.3 mg kg^-1) and detomidine (20 mcg kg^-1) as preanesthetic medication. General anesthesia was induced with propofol (4 mg kg^-1), followed by intubation. The sheep were then allocated into two groups: PG (n=6), which received continuous infusion of propofol (0.5 mg kg^-1 min^-1) for maintenance; and IG (n=6), which was maintained with isoflurane inhalation anesthesia (1.3 V %). Each group underwent four different ventilation modalities for 30 min: spontaneous ventilation (SV), volume-cycled mechanical ventilation (VV), pressure-cycled mechanical ventilation (PV), and pressure-cycled mechanical ventilation with positive end-expiratory pressure (PPV). Heart rate and cardiac index were higher in the IG, while systemic vascular resistance was higher in the PG. Hemoglobin levels, intrapulmonary shunt fraction, and tidal volume were higher in the PG. Both groups developed metabolic alkalosis. Isoflurane anesthesia resulted in greater hypotension, reduced lung compliance, increased airway resistance, lower PaO₂, and higher PaCO₂ values across all ventilation modalities. In contrast, PPV led to improved lung compliance, oxygenation index, and higher PaO₂ values, with lower intrapulmonary shunt fractions. The study concluded that propofol and PPV provide greater hemodynamic stability in anesthetized sheep.