The V/Q ratio of patients without obvious cardiopulmonary diseases is normal. PETCO2 can reflect PaCO2 to some extent. Normal PETCO2 is 5%, while 1%CO2 is about 1 1Kpa(7.5mmHg). Therefore, PETCO2 is 5Kpa(38mmHg). When the ventilation function changes, PETCO2 approaches PACO2 and PaCO2. Therefore, the gradual increase of PETCO2 is a very rapid and sensitive index reflecting insufficient ventilation, and it is specific. When there is a difference between PETCO2 and PaCO2, its sensitivity and specificity decrease. Because the clinical manifestations of hypoventilation are insensitive and nonspecific, PETCO2 waveform has high value in auxiliary diagnosis [3]. Mostly because the VT setting is small. It may also be caused by a leak in the circuit.
(2) Maintain normal ventilation.
When using a ventilator under general anesthesia or respiratory insufficiency, the ventilation volume can be adjusted according to PETCO2 _ 2 to avoid hypercapnia or hypocapnia caused by insufficient and excessive ventilation.
(3) Determine the position of trachea
At present, there are three recognized correct methods to prove that the endotracheal tube is in the trachea: 1, and the catheter must be seen in the glottis, and 2, the figure of PETCO2 can be seen. Clinical use of fiberoptic bronchoscope is the "gold standard" to judge the position of catheter, but it is inconvenient to use. PETCO2 can judge the position of catheter quickly, intuitively and sensitively, especially suitable for nasal intubation in oral surgery. Ran Qihua and others used PETCO2 waveform guidance. When the catheter is close to the glottis, the waveform will be more obvious, thus guiding the catheter to insert into the glottis. If the catheter is inserted into the esophagus, the PETCO2 waveform cannot be observed. Therefore, petco _ 2 has a high auxiliary diagnostic value for catheter straying into esophagus, and it is one of the methods to prove that catheter is in trachea. Fengxing et al. [7] further improved it and used petco _ 2 to judge the position of trachea. According to the fact that petco _ 2 is not specific, it is easy to make the stomach swell due to excessive ventilation under the mask, drink beverages containing CO2, and take antacids. So they used chest petco _ 2 to determine the position of the catheter. Its value lies in: (1) the waveform is intuitive, characteristic and of high value, which is more helpful to quickly and accurately judge the catheter position than PETCO2 after artificial ventilation; (2) It is helpful to judge the accumulation of CO2 in the body during non-ventilation, especially when the intubation time is long, the body does not suffer from hypoxia, but CO2 accumulates. Therefore, after no ventilation time exceeds 90 seconds, the intubation operation should be terminated and the mask should be given again. 3. See the normal compliance ring (PV ring), which can avoid the misjudgment of tracheal catheter entering esophagus by mistake.
(four) timely detection of mechanical failure of ventilator.
Such as joint shedding, ring leakage, catheter distortion, tracheal obstruction, valve failure and other mechanical failures. The pattern of PETCO2 can be changed clinically. It is common that respiratory and circulatory joints fall off and leak between endotracheal tube and threaded tube, between threaded tube and anesthesia machine, or at the joint of breathing sac. The operation of craniofacial surgery is easy to cause joint detachment, which is often difficult for observers to find because of occlusion. For example, when monitoring PETCO2, we can find that the carbon dioxide waveform disappears in time. When the catheter is twisted and folded, the airway is blocked and the valve fails, the waveform of carbon dioxide will disappear or decrease obviously, and the airway pressure will increase sharply. At this time, as long as the blockage can be found and eliminated in time, it can turn the corner. If with the increase of PETCO2 _ 2, the catheter is partially blocked, accompanied by the increase of airway pressure, sharp pressure waveform and lower platform, the blockage should be lifted in time. Wu Weiping [9] thinks that continuous monitoring of PETCO2 _ 2 is superior to other monitoring methods such as SpO2 _ 2 and expiratory tidal volume, and has the advantages of more timely and accurate detection of airway obstruction such as tracheal tube distortion, blockage, catheter detachment, catheter displacement and respiratory ring disconnection, so it is not necessary to monitor expiratory tidal volume during general anesthesia of tracheal intubation, especially during surgery; The anesthesiologist is far away from the patient's head, so it is of great significance to find it in time during tracheal general anesthesia, to deal with airway obstruction, to maintain the patient's airway patency and to ensure the patient's O2 supply.
(5) Adjust ventilator parameters to guide the removal of ventilator: (1) Adjust ventilation; (2) Choose the best PEEP value. Generally speaking, PEEP with the smallest PETCO2 value is the best PEEP value; (3) Petco _ 2 is a continuous noninvasive monitoring, which can be used to guide the temporary stop of ventilator. When SpO2 _ 2 and petco 2 are normal during spontaneous breathing, the ventilator can be removed; Attention should be paid to the existence of abnormal PETCO2, and blood gas control should be applied if necessary.
(6) monitoring the changes of CO2 production in the body; Intravenous injection of a large amount of NahCO2, NaHCO2 and PETCO2 increased significantly, which is one of the indexes reflecting cardiac output. Re-inhalation, elevated body temperature, sudden loosening of tourniquet and malignant hyperthermia will all increase the production of CO2. In addition, the rapid increase of PETCO2 is an early indicator of malignant hyperthermia sensitivity.
(seven) to understand the changes of alveolar volume and pulmonary blood flow.
PaCO 2 is PaCO 2 with blood perfusion in alveoli, and PetCO 2 is PaCO 2 with ventilation. If PetCO _ 2 is lower than PaCO _ 2, PetCO _ 2 rises or CO2 waveform rises obliquely, which indicates that the alveolar void volume increases and the pulmonary blood flow decreases. Fang et al. [1 1] reported that when lying on the side, the invalid volume will change whether breathing is controlled or spontaneous, and the upper lung is in good condition at this time.
(eight) monitoring cycle function
Shock, cardiac arrest and pulmonary infarction, pulmonary blood flow decreases or stops, CO2 concentration rapidly becomes zero, CO2 waveform disappears, PETCO2 disappears, and PETCO2 drops rapidly for more than 30 seconds, which indicates cardiac arrest. PETCO2 is an important non-invasive monitoring index to judge whether precordial compression is effective in resuscitation first aid, and its prognosis value is great. At this time, the level of PETCO2 and cardiac output change accordingly.