Study On Promoting The Moisture Output Of HME During Mechanical Ventilation

Objective: To investigate how to promote the moisture output of heat and moisture exchanger (HME) during mechanical ventilaition.Methods: First,it was observed that how the changes of tidal volume(TV) and fresh gas flow(FGF) affect the temperature and humidity of the breathing circuit in vitro. That mean the changes of temperature and humidity were recorded , when the FGF jumped from 1L/(F1)min to 3 L /min(F3) with the TV of 480ml(V1) or 600ml(V2). And it's also recorded when the TV was altered from 480ml to 600ml with the FGF of 1L/min or 3 L /min. Then , two types of HME were utilized to study the variation of the temperature and humidity of the breathing circuit, when some saline water was added to the patient side of HME at different FGF and TV settings. Step one, with the settings of 480ml TV and 1L/min or 3L/min FGF, six observation groups were set up: V1F1S2,V1F1S3,V1F1S4 and V1F3S2,V1F3S3,V1F3S4 . The HMEs in those groups were sprinkled saline water 2ml(S2),3ml(S3),4ml(S4) respectively during mechanical ventilation . Step two, with the settings of 600ml TV and 1L/min or 3L/min FGF, six observation groups were set up: V2F1S2, V2F1S3,V2F1S4 and V2F3S2,V2F3S3,V2F3S4 . The HMEs in those groups received saline water 2ml (S2) ,3ml(S3) ,4ml(S4) respectively during mechanical ventilation . when the Corrugated matrix breathing filters were tested, all the steps come into practice. Just step one was took within anesthesia breathing filters, and the added water was 2ml, 4ml, 6ml respectively. The setting was breathing rate 12/min, I:E=1:2.First of all, the machine must keep running in the absence of HME for a minute. Recorded the time and the airway pressure (P1) shown on the anesthesia machine's screen, when the values shown on the temperature and humidity recorder stabilized. The mean temperature(T1) and humidity(H1) were computed by the data in three minutes before the time point from the database stored in the recorder at the end of the experiment. We got the mean ambient temperature (Tr1) by the same way from the monitor. The T1,H1 and Tr1 were regarded as basal value. And then, suspend the ventilation and connect the HME between the breathing circuit and the circuit joint. Operate the machine without any change in settings. When the temperature and humidity in the breathing circuit to be stable, record the time and the airway pressure (P2). The mean temperature (T2) , mean humidity(H2) in the breathing circuit and the mean ambient temperature (Tr2) at the time were computed by the same way .Then disconnect the breathing circuit, and spray a certain amount of saline water at room temperature uniformly in patient side of HME with 10ml syringe, and run the machine again with connected circuit. Record the time and the airway pressure(P3). After continuous ventilation and observation for some time, end the experiment and download all the data from the recorder. Calculate the mean temperature(T3), humidity(H3) and ambient temperature (Tr3) in a period of time .Results:When the TV was set as 480ml or 600ml and changed the FGF , the Relative Humidity(RH) in the circuit decreased by 10% approximately. However, the RH increased by 2-5% with the FGF 1L/min or 3 L/min after changing the TV. The ambient temperature in these groups did not differ significantly, but the humidity in the circuit achieved significance compared to the previous after the injection of saline water. When using EM as the research object, 4ml saline made the highest level average RH in one hour in the circuit, but the airway pressure significantly increased by about 3cmH2O. The RH decreased faster at FGF 3L/min, so did the airway pressure. When using GL as the research object, the RH in group V1F1S6 reached the peak value 61.2%. The mean RH was 56.9% in two hours, remained at 55% or more in three hours. When the FGF was 3L/min, the group of V1F3S6 raised the RH more than the rest groups. The average RH was 50.6% in two hours. Five hours later, the RH in the circuit was close to the basal value.Conclusions: The gas from Hospital central gas supply system hold a certain of temperature and humidity, not all Low-temperature drying. Low flow of fresh air helps to maintain the relative humidity of the breathing circuit, and the change in tidal volume also have some effects on the humidity. The additional water in the HME will help to raise the humidity output. It will increase the airway pressure at the same time for the Corrugated matrix breathing filters, but not for the anesthesia breathing filters. The measures have certain clinical significance for lung protection.