Effect Of P_ETCO₂ On Cerebral Oxygen Saturation In Patients In The Beach Chair Position

Purpose:The beach chair position is commonly used for both arthroscopic and open shoulder surgery.This technique position the shoulder in an anatomic upright position facilitating shoulder joint access and visualization.The position also provides improved airway access,diminished bleeding,and reduced risk of brachial plexus injury.However,there has been concern cerebral blood flow and perfusion in the beach chair position with shoulder arthroscopy for some time.Reduction in cerebral perfusion pressure below critical thresholds of duration and severity may result in permanent neurologic injury.Near-infrared spec-troscopy?NIRS?is a noninvasive and continuous technique that offers the potential for cerebral perfusion monitoring,in which cerebral oxygenation reflecting the balance between cerebral metabolic supply and demand can be assessed.During BCP surgery,postural decreases in rSO₂ were related to both arterial pressure and P_ETCO₂.The aim of this investigation was to assess the impact of different P_ETCO₂ on cerebral oxygenation during BCP surgery.Method:We select 62 inpatients undergoing arthroscopic shoulder surgery in the BCP with general anaesthesia of Taishan medical school affiliated hospital during july,2016 to february,2018,39 of which are male and 23 are female.Patients were randomized to a low pressure group(ventilated to P_ETCO₂ of 30-32mmHg)or a high pressure group(ventilated to P_ETCO₂ of 40-42mmHg).Anaesthetic management was standardized in both groups.Intraoperative monitoring basic vital signs consist of electrocardiography,pulse oximetry,capnography,bispectral index monitoring,and arterial blood pressure.Baseline values were obtained while patients were breathing a 6L/min inspired gas mixture via a face mask.The patients were induced and intubated with midazolam,sufentanil,etom-idate,cisatracurium iv.The sevoflurane concentration was adjusted to achieve bis values of 40-60 and to maintain mean arterial pressure within 20%of baseline values.In two groups,an initial volume of 8ml/kg was established immediately after tracheal intubation and respiratory rate was adjusted to achieve appropriate P_ETCO₂ targets.Values of MAP,HR,SPO₂,rSO₂(and P_ETCO₂ and BIS after induction of anaesthesia)were measured continuously and recorded until the time of tracheal extubation.At the same time,the episodes of patients CDEs and recovery were recorded,including the time of extubation,recovery time and any episodes of nausea and vomiting.The different of rSO₂ in the two groups was investigated by comparing the perioperative period and recovery of two groups.Results:1.The two groups were similar in all preoperative patient characteristics,including age,sex,height,weight,baseline haemoglobin values?Table 1?.There was no significant difference between the baseline values of preoprative vital signs in the two groups,inc-luding HR,MAP,SPO2,rSO2?Table 2?.Intraoperative management characteristics of the control and high pressure groups are presented in Table 3.There were no significant dif-ferences observed between groups in total anaesthesia time,total BCP time,total op-eration time,use of intraoperative sufentanyl and Cisatracurium besilate,or fluid admi-nistration and blood loss.Endtidal sevoflurane concentrations did not differ between the groups and depth of anaesthesia was similar between the groups?no significant differences in BIS values,data not shown?.Significant differences in P_ETCO₂ endpoints were achi-eved in the control and high pressure groups,with most patients maintained within the P_ETCO₂ goals established throughout the intraoperative period?Fig 2?.HR,MAP,SPO2did not change significantly from baseline measures,and there were no statistically significant differences between the groups at any time.The number of patients requiring phenylephrine treatments,as well the total doses of phenylephrine,were similar between the groups?Table 4?.2.Baseline rSO₂ did not differ between the control and high pressure groups.rSO₂values in the high pressure group did not decrease over time.The incidence of CDEs was higher in the low pressure group?59.3%?than it was in the high pressure group?10%?.3.Clinical recovery date did not differ between the groups.Low pressure group?28%?higher than high pressure group?6.3%?in the incidence of nausea.The incidence of vomiting was low in both groups and not significantly different.Conclusion:1.rSO₂ is better maintained during BCP shoulder surgery when patients are venti-lated to an P_ETCO₂ of 40–42mmHg compared with an P_ETCO₂ of 30–32 mmHg.2.Hyperventilation will reduce rSO₂ when patients are undergoing BCP surgery with general anaesthesia.