Source: SIFIC 2023 "National Infection Control and Drug-Resistant Infection" Joint Conference, Infection Control Practice and Information.

Whether the internal circuits of ventilators need routine disinfection is a controversial topic, and the implementation varies greatly in each hospital and each department. At the SIFIC 2023 "National Infection Control and Drug-Resistant Infection" Joint Conference, the necessity of routine disinfection of the internal circuits of ventilators was discussed from multiple angles, based on standards, specifications, and references.

Relevant standard requirements

1. "Clinical Application of Ventilator" (WS392-2012): Appendix C ---- Ventilator Cleaning and Disinfection C.2.7 If the infection of the patient using the ventilator is suspected to be related to the ventilator pipeline, the pipeline and accessories should be replaced, cleaned, disinfected and disposed of in time, and the ventilator should be disinfected if necessary.

2. "Beijing Ventilator Cleaning and Disinfection Guidelines" stipulates that for the detachable parts of the internal gas circuit of the ventilator, the cleaning and disinfection effect is better after disassembly. The specific disinfection method of the internal gas circuit is simply clarified by the engineer for regular maintenance according to the characteristics of the ventilator.

3. "Intensive Care Unit Hospital Infection Prevention and Control Specifications" (WS/T509-2016): 11.4 Disinfection of ventilators and accessories, as follows: Disinfection of the internal pipeline of the ventilator is carried out according to the manufacturer's instructions.

4. "Guidelines for the diagnosis and treatment of hospital-acquired pneumonia and ventilator-associated pneumonia in adults in China" (2018 edition): Cluster prevention, strengthening the cleaning and disinfection of the internal and external pipes of the ventilator, combined with other core intervention measures, can significantly reduce the average ventilation time and hospitalization days of patients receiving mechanical ventilation, and reduce the incidence, mortality and (or) costs of VAP (ventilator-associated pneumonia).

5. The main resource allocation suggestions in the annex of the "Shanghai Expert Consensus on Hospital Infection Management in the "New Normal of the Epidemic": The operating room should be equipped with an internal pipe disinfection machine for anesthesia machines, and the operating room and ICU should be equipped with an internal pipe disinfection machine for ventilators.  6. A study in the United States showed the implementation of a strict ventilator care policy, including routine replacement of breathing circuits and external bacterial filters and replacement of internal bacterial filters (every 4-8 weeks), etc.

The ventilator circuit may be contaminated.

The risk score of ventilators in the ISO 14971 Medical Device Risk Management Standard is 12 points, the highest risk medical device. The risk of ventilators may come from functional failures such as abnormal ventilation parameters and alarm failure, or from droplets or aerosols carrying pathogens in the internal components of the ventilator, resulting in infections such as ventilator-associated pneumonia in patients on the machine.

However, according to relevant research reports, only 44.41% of hospitals in China disinfect the internal air circuit of ventilators. The internal circuit of the ventilator may be contaminated because the mechanically ventilated patient is connected to the ventilator circuit to form a closed loop, and bacteria in the lower respiratory tract are easily colonized in the ventilator circuit with choking or reverse respiratory airflow. Studies have shown that pathogens can contaminate the entire ventilator circuit system after mechanical ventilation for several hours.

In addition, relevant studies have shown that the internal circuit of the ventilator is seriously contaminated with pathogens. Qiu Kai et al. sampled and cultured the internal circuit of the ventilator to observe the growth of pathogens in different periods. The results showed that many pathogens grew in the internal circuit of the ventilator, and the contamination at the exhalation end was more obvious than that at the inhalation end, and the number of pathogens was positively correlated with the mechanical ventilation time. The pathogen culture identification was mainly Gram-negative bacilli, and Gram-positive cocci and fungi were cultured in the internal circuits of some ventilators. In addition, the bacterial culture of different parts of the ventilator pipeline was consistent with that of the lower respiratory tract secretions. The results suggested that the ventilator circuit may be contaminated during the entire mechanical ventilation process.

Professor Hu Bijie's team investigated the contamination of the internal circuits of anesthesia machines in 10 hospitals in Shanghai and found that the internal circuits of anesthesia machines were seriously contaminated. The import bacteria load of 121 anesthesia machines was as high as 34.7%, and the export contamination rate was 27.3%. The colonization of microorganisms on the inner surface of anesthesia machines in some hospitals reached 100,000 CFU/cm², and filamentous fungi were detected in 12 specimens, posing a serious risk of microbial contamination. Different pathogens survived for a long time in the ventilator pipeline. Staphylococcus aureus can survive for up to 7 months (210d) in the ventilator pipeline, and Klebsiella pneumoniae can survive for up to 30 months (900d). Cross-infection is prone to occur when different patients reuse the same ventilator, and cross-use can lead to VAP.

Correlation between ventilator circuit contamination and VAP

Zhu Minghua et al. found that in 19 patients with VAP (ventilator-associated pneumonia), the condensation water collection cup at the air outlet, the inner wall of the expiration end interface of the threaded tube, the condensation water collection cup in the air supply pipe, and the ventilator humidification tank were closely related to the secretions of the lower respiratory tract. The consistency of bacterial culture was 66.48%, 63.45%, 40.26%, and 54.32% respectively. The emergence time of bacteria in the condensate water collection cup of the air supply pipeline and the ventilator humidification tank was consistent with the emergence time of lower respiratory tract pathogens. There is a causal relationship between ventilator circuit contamination and VAP. High-risk factors for ventilator-associated pneumonia VAP include cross-infection caused by contamination of respiratory equipment and hands. Multiple studies have shown that the use of ventilator internal circuit sterilizers to disinfect the ventilator's internal circuits is effective, can significantly reduce the number of microbial colonies, improve the pipeline qualification rate, and reduce the incidence of VAP in patients.

Breathing filters have no disinfecting effect

It is not recommended to routinely use respiratory filters for ordinary patients. The 2013 edition of the "Guidelines for the Diagnosis, Prevention and Treatment of Ventilator-Associated Pneumonia" states that "Respiratory filters installed at the exhalation end can increase inspiratory resistance and dead space, so they are not recommended for routine use for ordinary patients. For suspected or confirmed tuberculosis patients, bacterial filters should be placed at the exhalation end to avoid contaminating the ventilator and the surrounding environment."

Respiratory filters are a passive isolation measure. Various bacteria and viruses are still alive and attached to the filter membrane and instrument, making later processing difficult.

Respiratory filters are used by patients with special diseases (respiratory tract infections, etc.), but the bacterial filtration efficiency is less than 100%, and the respiratory filter only acts as a barrier between the patient and the machine, with no disinfection effect.

The internal tubing of the ventilator needs to be disinfected immediately after use by patients with special diseases.

Studies have shown that installing effective filters at the inlet and outlet of the ventilator can filter out 99% of particulate matter in the exhaled gas. However, for patients with severe contamination or special diseases, such as hepatitis B and HIV patients, in addition to the external piping that needs to be sterilized by high pressure, the internal piping also needs to be effectively disinfected and sterilized before it can continue to be used.

The most common infections caused by anesthesia respiratory equipment are respiratory bacterial infections, especially those caused by Mycobacterium tuberculosis and atypical mycobacteria. However, HBV and HCV infections have also been discovered recently, and HIV has been found to be contaminated on the ventilator. Anesthesia machines should be disinfected regularly. Patients with respiratory infections should use bacterial filters when using anesthesia machines, and the anesthesia machines should be disinfected immediately after use. Therefore, it is necessary to effectively disinfect the anesthesia and respiratory equipment used by patients.

Discussion on the disinfection method of the internal circuit of the ventilator

The disinfection schemes generally used for the non-detachable internal circuits of hospital ventilators are:

1. Chemical disinfectant disinfection: time-consuming, if disassembled, it will affect the air tightness.

2. High-temperature fumigation disinfection: time-consuming, if disassembled, it will affect the air tightness.

3. Ethylene oxide disinfection of some components that can be disassembled: time-consuming, need to be disassembled, easy to leave residue, affecting the air tightness.

None of the above schemes are suitable for disinfecting the internal piping of the ventilator.

The non-detachable parts of the hospital ventilator require a professional disinfection machine. "Guidelines for Disinfection of the Breathing Circuit of Anesthesia Machines for Perioperative Periods of New Crown Patients" Disinfection of the breathing circuit of anesthesia machines: It is recommended to use a compound alcohol disinfection machine, which is characterized by the fact that the anesthesia machine does not need to be disassembled. The air circuit of the ventilator is in a special position and contains a variety of precision electromagnetic components. Conventional disinfection methods cannot complete thorough disinfection. Chen Xuebin and others compared the currently commonly used disinfection modes in clinical practice and proposed the feasibility of using hydrogen peroxide vapor and ozone as disinfectants for the internal air circuit system of the ventilator.

To sum up, to prevent the ventilator from becoming a relay station for the spread of infection, it is necessary to promptly and thoroughly disinfect the inside of the ventilator circuit to prevent cross-infection and actively respond to hospital infection prevention and control!