Effects of Intermittent Positive Pressure Ventilation on Cardiopulmonary Function in Horses Anesthetized with Total Intravenous Anesthesia Using Combination of Medetomidine, Lidocaine, Butorphanol and Propofol (MLBP-TIVA)

Effects of intermittent positive pressure ventilation (IPPV) on cardiopulmonary function were evaluated in horses anesthetized with total intravenous anesthesia using constant rate infusions of medetomidine (3.5 mu g/kg/hr), lidocaine (3 mg/kg/hr), butorphanol (24 mu g/kg/hr) and propofol (0.1 mg/kg/min) (MLBP-TIVA). Five horses were anesthetized twice using MLBP-TIVA with or without IPPV at 4-week interval (crossover study). In each occasion, the horses breathed 100% oxygen with spontaneous ventilation (SB-group, n=5) or with IPPV (CV-group, n=5), and changes in cardiopulmonary parameters were observed for 120 min. In the SB-group, cardiovascular parameters were maintained within acceptable ranges (heart rate: 33-35 beats/min, cardiac output: 27-30 l/min, mean arterial blood pressure [MABP]: 114-123 mmHg, mean pulmonary arterial pressure [MPAP]: 28-29 mmHg and mean right atrial pressure [MRAP]: 19-21 mmHg), but severe hypercapnea and insufficient oxygenation were observed (arterial CO2 pressure [PaCO2]: 84-103 mmHg and arterial O-2 pressure [PaO2]: 155-172 mmHg). In the CV-group, normocapnea (PaCO2: 42-50 mmHg) and good oxygenation (PaO2: 395-419 mmHg) were achieved by the IPPV without apparent cardiovascular depression (heart rate: 29-31 beats/min, cardiac output: 17-21 l/min, MABP: 111-123 mmHg, MPAP: 27-30 mmHg and MRAP: 15-16 mmHg). MLBP-TIVA preserved cardiovascular function even in horses artificially ventilated.