Changes In Cerebral Oxygen Saturation Following Prone Positioning For Spinal Surgery With Positive End Experiatory Pressure Under Anaesthesia

Objective: Near-infrared cerebral oximeter(FORE-SIGHT)is an on-going,convincable,noninvasive monitoring tool for assessment of regional cerebral oxygenation,which has been widely used in different surgeries to find out a mismatch in cerebral perfusion,cerebral oxygenation in time and offer many advantages for monitoring cerebral oxygenation in the prevention of perioperative adverse events such as cerebral anoxia.Perioperative adverse events are common in the old patients for spinal surgery under anaesthesia because of operative trauma,position,inadequate tissue perfusion,and other stresses.PEEP could improve arterial oxygenation and pulmonary ventilation function.However,high levels of PEEP may result in impaired venous drainage,then affect the tissue perfusion and oxygenation.The purpose of this paper is to observe the changes of cerebral oxygen saturation in patients with different PEEPs undergoing spinal surgery in prone positioning,and discuss what level of PEEP can maintain better cerebral perfusion and oxygenation.Methods: Ninety patients who underwent elective spinal surgery were randomly assigned to different positions.There are 45 patients in the supine position with cervical spine surgery and 45 patients in the prone position with lumbar spine surgery.Exclusion criteria were as follows: pre-existing cerebrovascular disease;American Society of Anesthesiologists(ASA)physical status classification IV or V;injury/haematoma on the forehead;intracerebral lesions;haemoglobin concentration below 110g/L;They were divided into six groups with different positions and PEEPs: Group S0(supine position,PEEP=0 cmH2 O,n=15),Group S5(supine position,PEEP=5 cmH2 O,n=15),Group S10(supine position,PEEP=10 cmH2 O,n=15),Group P0(prone position,PEEP=0 cmH2 O,n=15),Group P5(prone position,PEEP=5 cmH2 O,n=15),Group P10(prone position,PEEP=10 cmH2 O,n=15).HR,MAP,PetCO2,Ppeak,Pmean,SctO2 were recorded before anesthesia induction(T1),after tracheal intubation(T2),at 30 min for mechanical ventilation with PEEPs(T3),at 60 min for mechanical ventilation with PEEPs(T4),at 90 min for mechanical ventilation with PEEPs(T5),and at 10 min after tracheal extubation(T6).When mean airway pressure was more than 35 mmHg or airway peak pressure more than 45 mmHg,the trial would stop.In the operation,the patient's head was placed carefully in a cushioned head-positioning device to ensure a straight head and neck position that would enable venous drainage and avoid neck compression.Anaesthesia was maintained with 0.7 to 1.0 age-adjusted minimum alveolar anaesthetic concentration of sevoflurane as calculated by the monitoring software and repeated injections of sufentanil and rocuronium at the discretion of the attending anaesthetist.Maintain an end-tidal carbon dioxide concentration(PetCO2)of 30 mmHg to 40 mmHg.Ephedrine was intravenous given in the dose of 6mg every time when patient's MAP decrease by thirty percent or when MAP was less than 60 mmHg.When patient ' s HR was less than 45 times every minute,atropine was intravenous given in the dose of 0.5mg every time.And when patient's MAP increase by thirty percent,perdipine was intravenous given in the dose of 0.5mg every time.Record the number of the cases patients using these drugs of the two groups.Results: There was no statistically significant difference(P>0.05)in HR and PCO2 in six groups;There was statistically significant difference(P<0.05)in Ppeak and Pmean in six groups and Ppeak and Pmean was higher when the levels of PEEPs increased;MAP was lower in Group S10 and Group P10 at T4 and T5 compared with T1,T2,T6(P<0.05)and there was statistically significant difference(P<0.05)comparing with group S0,S5,P0,P5;Group S5 and group P5 can improve the pulmonary function and maintain better cerebral perfusion and oxygenation than other groups;Group S10 and Group P10 may have influences on hemodynamic parameters and may use the vasoactive agents in more patients(P<0.05)although it can improve oxygenation.Conclusion: Mechanical ventilation with low tidal volume and PEEP(5cmH20)can improve the pulmonary function without influences on hemodynamic parameters and maintain better cerebral perfusion and oxygenation in the spinal surgery following prone position.