Servo ventilator 300

Six Swedish landrace pigs with a mean weight of 61 ± 1.8 kg were fasted overnight with free access to water. Premedication was performed with an intramuscular injection of Xylazine (Rompun® vet. 20 mg/ml; Bayer AG, Leverkusen, Germany; 2 mg/kg) mixed with ketamine (Ketaminol® vet. 100 mg/ml; Farmaceutici Gellini S.p.A., Aprilia, Italy; 20 mg/kg) in their stables, and a peripheral iv access was established in the earlobe. The pig was then transferred to the laboratory and placed in supine position on the operating table. Oral intubation was performed using a 7.5 size endotracheal tube after anesthesia induction with sodium thiopental (Pentothal; Abbott Laboratories, North Chicago, IL, USA) and pancuronium bromide (Pavulon; N.V. Organon, Oss, the Netherlands). Anesthesia was maintained with a ketamine (Ketaminol® vet), midazolam (Midazolam Panpharma®, Oslo, Norway), and fentanyl (Leptanal®, Lilly, France) infusion. Fluid loss was compensated by continuous infusion of Ringer’s Acetate. Mechanical ventilation was established with a Siemens-Elema ventilator (Servo Ventilator 300, Siemens, Solna, Sweden).

Ventilator settings (Servo Ventilator 300, Siemens) were as follows: upper airway pressure limit: 20 cm H₂O, typical pressure generation above PEEP: 6–9 cm H₂O, respiratory rate: 80 breaths/min; and PEEP: 1 cm H₂O. Animals were constantly monitored during MV. Continuing care included expressing the animals’ bladders, rotating the animals to prevent blood pooling, and suctioning the airway to prevent mucus plugs. At the start of MV, animals received an intramuscular injection of glycopyrrolate (0.08 mg/kg) to decrease airway mucus secretions during MV. Animals also received a maintenance dose of glycopyrrolate (0.04 mg/kg) every two hours. Body temperature was read by a rectal thermometer and maintained at 37°C by resting animals on a recirculating water blanket. Heart rate was monitored by electrocardiograph. Following the initiation of MV, the carotid artery was cannulated to measure blood pressure. Blood samples (~100 μL) were taken from this catheter to ensure blood gas homeostasis was maintained during MV. If blood gas parameters changed, either tidal volume and/or oxygen concentration of the inspired air was increased to return to homeostasis. To maintain a surgical plane of anesthesia, sodium pentobarbital diluted in saline was constantly infused into a catheter in the jugular vein (~10 mg/kg/hr).

We used a ventilator (Servo-300 ventilator, Siemens Elema, Solna, Sweden) with a humidifier and a disposable circuit (DAR Neonatal, Medtronic, Dublin, Ireland) which were configured based on the manufacturer’s recommendation (Fig. 4).