Correlation Analysis Between End-tidal PCO₂ Measurements With Sidestream Capnography And Arterial Carbon Dioxide

Objective:Respiration is one of the most important functions of the human body, Carbon dioxide is produced in the tissues by aerobic and anaerobic metabolism, transported to the lung by blood, and eliminated from the lung. Monitoring respiratory function is very important for the patients who are undergoing general anesthesia. Monitoring the CO2 in the blood is an important parameter of respiratory function. The normal partial pressure of carbon dioxide in the arterial blood(Pa CO2) is 4.5k Pa-6.0k Pa(35mm Hg-45 mm Hg). The Pa CO2 is the most accurate parameter of human body. The Pa CO2 is usually obtained by the arterial blood gas analysis. In clinical, we usually use arterial blood gas analysis to measure the Pa CO2 and to evaluate the respiration function. But the blood gas analysis is invasive, the complications content arterial injury, infection, false aneurysm, et al. And blood gas analysis can only measure the Pa CO2 intermissionly. The detection technique of the partial pressure of end-tidal carbon dioxide(Pet CO2) is non-invasived and can measure the CO2 consecutively. Today, we measure the Pet CO2 by the absorption spectrum of infra-red light, the technique can response swiftly and conveniencely. According to the position of sensor, the detection method of Pet CO2 can be divided into two kinds, the sidestream type and the mainstream type. The mainstream capnometer has an airway adaptor cuvette. The cuvette is part of the respiratory pathway and incorporates an infrared light source and sensor that senses carbon dioxide absorption to measure Pa CO2. The sidestream capnometer aspirates tidal airway gas continually to analysis CO2. The sensor is not directly connected to the respiratory pathway. It can work without tracheal intubation. It is more convenient than the mainstream type. There has a large number of literature reports, that the Pet CO2 and Pa CO2 have good consistency by the mainstream capnometer under certain conditions. But there has few reports about the dependability of the sidestream capnometer and the correlation between Pet CO2 and Pa CO2 by the sidestream capnometer. It is extremely important to monitor CO2 in neurosurgical operation. In the craniocerebral operations, the CO2 can effect the p H of brain extracellular fluid(ECF), thus affecting the cerebral blood flow(CBF). When the Pa CO2 between 2.7k Pa-8k Pa(20mm Hg-60 mm Hg), CBF will increase with the rise of Pa CO2. When the Pa CO2 change 1mm Hg, the CBF can increase 2%-3% or 1-2ml·100g·min-1. Through the monitoring of the Pet CO2 and Pa CO2 by the sidestream capnometer in craniocerebral operations, and analysing their regularity, the study provide a theoretical reference of the noninvasive clinical application by sidestream capnometer.Methods:From February 2013 to March 2015, 40 adult patients were chosen, who did the craniocerebral operation in our hospital. There has no gender restriction, and the ASA anesthesia classification were I or II, all the patients have no cardiovascular or respiratory system diseases, and the intracranial pressure is normal. The craniocerebral operations which have minor effect to the respiration and cirulation were chosen. All the operations were in supine position. With intravenous general anesthesia, respiration was controlled by respiratory machine and respiratory rate was 12 times·min-1, and inhalational oxygen fluence was 1.5L·min-1, respiratory ratio was 1:2, tidal volume was 6-8ml·kg-1. The arterial blood was sampled with special arterial blood gas needle through the radial artery. The samples were analysed by the GEM Premier3000 blood gas analyzer to measure the values of Pa CO2 at 15 minutes(T1), 30 minutes(T2), 60 minutes(T3) after mechanical ventilation. The real-time monitoring of the concentration of CO2 in the respiratory passage can be obtained by the Bene View T5 monitor of Shenzhen Mairei company. Through its inbuilt CO2 measurement module. It also can obtain the Pet CO2 and show the waveform. The SPSS 13.0 statistical software was used to analysis the data. The measurement data was expressed by mean±standard deviation(x± s). Pet CO2 and Pa CO2 were analyzed by linear correlation analysis, the test level of α=0.05.Results:There have good correlation between Pet CO2 and PaCO2 at 15 minutes(T1)、30 minutes(T2)、60 minutes(T3) after mechanical ventilation.(T1 time,r1=0.808,P1<0.05;T2 time, r2=0.786,P2<0.05;T3 time,r3=0.773, P3<0.05).Conclusions:The partial pressure of end-tidal carbon dioxide by sidestream measurements and arterial carbon dioxide have good correlation. We can use the sidestream Pet CO2 measurements comprehend the respiration functional status of the patients intraoperative.