How to deal with incorrect tidal volume of dre anesthesia machine

　　When using the dre anesthesia machine, if the tidal volume is set at 500 but the test value is 400, look at the bellows scale at 600. Who should we trust in this situation, and which one is more accurate? Indeed, it can be very embarrassing to encounter such a situation. When this happens, you have to believe in yourself. For doctors to judge according to the breath sound, this is the most basic skill of doctors, but now more and more equipment, many doctors can not make their own judgment after leaving the equipment. For the device, if the flow detector functions normally, the test value shall prevail. As for the scale of the bellows, it is the most inaccurate, and the scale of some bellows is itself very thick. Then how much tidal volume error is appropriate, it is generally believed that the error up and down within 10%, clinically acceptable.

　　What are the factors that affect the accuracy of tidal volume in dre anesthesia machine?

　　The compliance of the respiratory system, fresh air flow, leakage of the respiratory system, the position of the flow sensor in the respiratory system and airway resistance are all factors that affect the accuracy of tidal volume.

　　compliance

　　Due to the compressibility of gases and the expansibility of certain elements of the respiratory system, not all ventilators deliver gas into the patient's lungs. Part of the gas provided by the ventilator is used to increase the pressure of the respiratory system to reach the peak inspiratory pressure without reaching the patient. The higher the peak inspiratory pressure, the greater the tidal volume loss.

　　Fresh air flow

　　During inhalation, all fresh gas guided by the dre anesthesia machine to the respiratory system will be mixed with the gas provided by the ventilator and then administered to the patient. The higher the volume of fresh gas, the greater the tidal volume.

　　Sink leakage

　　Respiratory system sink leakage during inhalation reduces the tidal volume provided. For a well-maintained respiratory system, the leak is usually so small that it is negligible when calculating tidal volume compensation.

　　Location of the flow sensor

　　When the flow sensor is located at the proximal end, i.e. on the patient's side of the "Y" joint, the ventilator will only measure the patient's exhaled tidal volume. If the flow sensor is placed at the remote end, i.e., at the exhalation check-valve port of the absorber, the ventilator measures the patient's exhalation tidal volume plus a portion of the patient's compliance flow between the intake and exhalation valves of the absorber and the patient. This compliant flow is also shown to the patient.

　　The tidal volume measured at the distal end is always artificially higher than that measured at the proximal end, and when a standard patient loop pipe (75-100cm) is connected between the absorber and the patient, the difference is usually small, about 2-3ml/cmH2O. Adding flow to the loop, such as connecting a humidifier to the suction branch, will increase the difference in tidal volumes measured near and far.

　　Airway resistance

　　High gas resistance (e.g. due to small trachea or other airway obstruction) reduces the tidal volume provided by the ventilator to the patient. In situations of high inspiratory flow, a tidal volume provided may be restricted from reaching the lungs, causing the excess portion of this tidal volume to reside in the respiratory system. You can determine whether airway resistance in your ventilator is a contributing factor in the following ways: High airway resistance is a contributing factor if the measured tidal volume increases as the inspiratory flow is reduced or the inspiratory pause function is activated.

　　These respiratory factors can cause the measured tidal volume indicated on the screen to differ from the value you set with the tidal volume knob. At work, the control of the ventilator is adjusted to compensate for these factors, so the measured and displayed tidal volume is an indicator of the level of breathing you want to use, but sometimes you may want to calculate an expected tidal volume.

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