#3 Cerebral protection for the preclinical evaluation of a vascular graft in sheep carotid artery model
A protocol for cerebral protection without systemic hypothermia to aid the safe, smooth and fast recovery of sheep used for the preclinical evaluation of a prosthetic vascular graft in the carotid artery is presented in this study. Ten adult Ramnad white sheep (33.8± 3.2 kg) were green grass deprived and anticoagulated from 5 days prior to surgery with aspirin 150 mg and clopidogrel 75 mg till the end of the study. After anesthetic premedication and endotracheal intubation, the animals were ventilated at the rate of 12 breaths/min and tidal volume of 12 ml/kg. Ten minutes prior to carotid artery clamping (right unilateral internal carotid artery) which was performed after heparinisation, pharmacologic mitigation was done for cerebral protection with a total dose of thiopentone 50 mg (2.5%), 8 mg dexamethasone, 100 mg hydrocortisone and 15 ml (7.5% w/v) sodium bicarbonate as i/v bolus and 250 ml dextran 40 (10% w/v) at 40 ml/hour as i/v drip. Mean values of arterial pressure and heart rate were 94±16 mmHg and 88±11 min-1 respectively, over the entire intra operative period. A moderate alkalosis which occurred in all animals under anaesthesia was postulated to supplement cerebral protection and was corrected by reducing the respiratory rate and tidal volume to 10 breaths/min and 10ml/kg respectively. Significant variation in pH (p<0.05) was observed at 90, 120, 150 and 180 minutes after induction of anaesthesia. Significant variation in MAP (p<0.05) was observed at 180 minutes after premedication, which was related to alkalosis and resultant hypokalemia and was effectively corrected with 31±7 meq potassium chloride (40 meq in 500 ml ringer lactate). The total procedure lasted 126±18 minutes and total unilateral right carotid arterial clamping time was 36.7±6.5 minutes. 28±5 minutes after spontaneous respiration, the animals were extubated and moved to the postoperative cage. Three doses of nadroparine 3800 IU s/c at 12 hour intervals were given postoperatively. All animals were free from any neurological deficits, which showed the effectiveness of the perioperative protocol encompassing the cerebral protective medication.
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