The Effects Of Induced Hypothermia On Porcine Pulmonary Pathophysiology

Objective: Hypothermia is widely used in clinical work. We want to study the pulmonary effects when induced hypothermia on healthy individuals, in order to facilitate the protection of lung function and develope the basic research theory of hypothermia. Hypothermia is used in treatment of traumatic brain injury. The patients got serious traumatic brain injury may be the donors for lungs transplantation, we should pay more attention to how to optimize organ function. Our study will be the control to the study of donors organ under hypothermia.Methods: Thirty Swedish domestic pigs with a mean weight of 50 kg (range 48～52kg) were included in the study. Fifteen pigs for hypothermia group, fifteen for control group. Anesthesia was induced with an intramuscular injection of ketamine (30 mg/kg) and xylasin (4 mg/kg). Sodium thiopental (5～8 mg/kg) and atropine (0.015 mg/kg) were given intravenously before tracheotomy. Anesthesia and muscular paralysis were maintained with a continuous infusion of 10 ml/h of a NaCl (0.9%) solution containing ketamine (16mg/ml) and pancuronium (0.6 mg/ml). Then inserted endotracheal tube,connected to a Servo Ventilator, using pressure-regulated (max 30cmH2O = 23 mmHg) and volume-controlled IPPV, using a tidal volume of 15 ml/kg body weight, 20 breaths/min, a PEEP of 5 cmH2O (= 6 mmHg) and a FiO2 of 0.25. The endtidal CO2 was measured by CO2SMO Plus Respiratory Profile Monitor . Three catheters for blood pressure measurements and blood sampling were introduced via direct puncture of the right carotid artery and the right internal jugular vein . A median sternotomy was performed, Open pericardium, put a blood probe around pulmonary artery. Put one catheter in left atrium sinistrum, put another one in pulmonary artery for blood pressure measurements and blood sampling. We cooled the pigs by surface cooling with ice packs to 32.0℃core temperature. With rectal temperature fell down 1.0℃, Values of T , HR, AP, CVP, LAP, PAP, PetCO2 would be recorded.,Arterial and mixed venous blood gases were measured. Count PVR use formula"PVR=80×(mean pulmonary arterial pressure-mean left atrial pressure)/cardiac output". Superior lobe of left lung was cut for testing moisture capacity. Control group was deal with the same methods, keeping pigs'temperature around 37.0℃.Datas were expressed as means±SEM, analysis were done by SPSS 12.0, P < 0.05 was considered significant.Results: 1. Inducing hypothermia to pigs,With temperature fell to 32.0℃, HR will be slower ( P < 0.05 ) , PVR will be increased ( P < 0.05 ), MAP is stable ( P >0.05 ).2. With temperature fell to 32.0℃,PaCO2 and PvCO2 will significant decreased ( P < 0.05 ), Hgb and Hct will be increased ( P < 0.05 ),serum potassium will decreased ( P < 0.05 ). 3. Inducing hypothermia to pigs, With temperature fell to 32.0℃, moisture capacity of lung will be increased ( P < 0.05 );PaCO2 - PetCO2 gradient will be increased ( P < 0.05 );indicates pulmonary edema and dysfunction of ventilation.Conclusions: Hypothermia may increase PVR and cause complications such as pulmonary edema and dysfunction of ventilation.