Passage of pathogenic microorganisms through breathing system filters used in anaesthesia and intensive care

A simple screening test of filtration efficiency for protecting the gas sampling line from coronavirus using fluorescent microspheres

BACKGROUND

During the coronavirus pandemic, preventing contamination of the anesthesia machine, critical to avoid cross-contamination between patients, has proven challenging when treating premature infants and neonates. While attaching a HEPA filter to the endotracheal tube will protect the anesthesia machine and the gas sampling line from contamination, this contribution to the dead space makes ventilation of these small patients challenging. Direct filtration of the gas sampling line eliminates this problem; however, appropriate filters are not readily available.

AIMS

Identify a small filter capable of filtering out particles of a size similar to the SARS-CoV-2 virus for the gas sampling line.

METHODS

We used fluorescence microspheres suspended in a solution for a challenge test to determine the filtration efficiency of various filters. The microspheres varied in diameter (0.02 µm, 0.042 µm, 0.109 µm, and 0.989 µm). A fluorescence plate reader was used to evaluate the degree of fluorescence intensity in the flow-through from various filters and referenced to the fluorescence intensity of the input.

RESULTS

AHEPA filter, as recommended as an anti-viral filter, effectively filtered all the particles tested. The B. Braun PERIFIX Flat Epidural Filter was the second most effective filter, filtering particles larger than 0.042 µm. Other filters tested did not filter fluorescence microspheres equivalent in size to a single coronavirus particle (0.07 µm).

CONCLUSIONS

Although the Food and Drug Administration (FDA) has not approved the Flat Epidural Filter for use as an anesthesia machine gas filter, our simple challenge test suggests that it could be used to effectively filter the anesthesia gas sampling line.

Anesthesia in patients with infectious disease caused by multi-drug resistant bacteria

PURPOSE OF REVIEW

Up to 50% of specific bacterial strains in healthcare admission facilities are multi-drug resistant organisms (MDROs). Involvement of anesthesiologists in management of patients carrying/at risk of carrying MDROs may decrease transmission in the Operating Room (OR).

RECENT FINDINGS

Anesthesiologists, their work area and tools have all been implicated in MDRO outbreaks. Causes include contamination of external ventilation circuits and noncontribution of filters to prevention, inappropriate decontamination procedures for nondisposable equipment (e.g. laryngoscopes, bronchoscopes and stethoscopes) and the anesthesia workplace (e.g. external surfaces of cart and anesthesia machine, telephones and computer keyboards) during OR cleaning and lack of training in sterile drug management.

SUMMARY

Discussions regarding the management of potential MDRO carriers must include anesthesia providers to optimize infection control interventions as well as the anesthesia method, the location of surgery and recovery and the details of patient transport. Anesthesia staff must learn to identify patients at risk for MDRO infection. Antibiotic prophylaxis, although not evidence based, should adhere to known best practices. Adjuvant therapies (e.g. intranasal Mupirocin and bathing with antiseptics) should be considered. Addition of nonmanual OR cleaning methods such as ultraviolet irradiation or gaseous decontamination is encouraged. Anesthesiologists must undergo formal training in sterile drug preparation and administration.

Bacterial and viral contamination of breathing circuits after extended use - an aspect of patient safety?

BACKGROUND

In the past, anaesthetic breathing circuits were identified as a source of pathogen transmission. It is still debated, whether breathing circuits combined with breathing system filters can be safely used for more than 1 day. The aim of this study was to evaluate the transmission risk of bacteria and also viruses via breathing circuits after extended use.

METHODS

The inner and outer surface of 102 breathing circuits used for 1 day and of 101 circuits used for 7 days were examined for bacteria and viruses. Additionally, 10 and 20 breathing circuits each were examined after use on patients with pulmonary virus infection and with multidrug-resistant organism (MDRO) colonisation/infection respectively. Bacteria were detected by standard microbiological procedures; PCR techniques were applied for herpes simplex virus, cytomegalovirus, influenza, parainfluenza and respiratory syncytial virus.

RESULTS

Endoluminal bacterial contamination of breathing circuits remained unchanged after 7-day vs. 1-day use (5.9% vs. 7.8%) [CI95%: -0.0886-0.0506, pnon-inferiority 0.0260]. Only outside surface contamination with bacteria belonging to environmental species or human flora increased (16.8 vs. 6.9%) [CI 95%: 0.0118 - 0.1876, pnon-inferiority 0.8660]. Viruses occurred on the patient side, but not in breathing circuits. No MDRO occurred in the 20 circuits after use on patients harbouring such germs.

CONCLUSION

Endoluminal contamination of breathing circuits with bacteria did not increase after extended use. No viruses were detected in the breathing circuits using filters. Based on our results, the extended use of ABC without exceptions appears safe, if a high level of anaesthesia workplace cleaning is secured.

The simultaneous use of a heat and moisture exchanger and a heated humidifier causes critical airway occlusion in less than 24 hours

PURPOSE

Heat and moisture exchangers (HMEs) and heated humidifiers (HHs) may be used together inadvertently. Such an incident occurred at our institution resulting in airway occlusion.

MATERIAL AND METHODS

A bench-top study was conducted to compare the incidence of airway occlusion when using (1) no airway humidification, (2) HME alone, (3) HH alone, and (4) both HME and HH in combination as part of a standard breathing circuit.

RESULTS

The simultaneous use of a HME and a HH was associated with a reduction in tidal volume (no airway humidification, P ≤ .05; HME alone, P ≤ .01; and HH alone, P ≤ .01) and an increased incidence of airway occlusion (no airway humidification, 0/7; HME alone, 0/7; HH alone, 0/7; and HME and HH in combination, 7/7; P < .0001).

CONCLUSIONS

The use of a HME and a HH in combination is likely to result in airway occlusion. Precautions should be taken to ensure that both systems are not used together in clinical practice.

Heat and moisture exchangers and breathing system filters: their use in anaesthesia and intensive care. Part 1 - history, principles and efficiency

Heat and moisture exchangers and breathing system filters are intended to replace the normal warming, humidifying and filtering functions of the upper airways when these structures are bypassed during anaesthesia and intensive care. Guidance on their use continues to evolve. The aim of this part of the review is to describe the principles of their action and efficiency and to summarise the findings from clinical and laboratory studies. Based on previous studies, an appropriate minimum target for moisture output is 30 and 20 g.m⁻³ for long-duration use in intensive care and short-duration use in anaesthesia, respectively. The practice of reusing a breathing system in anaesthesia, provided it is protected by a filter, assumes that the filter is effective. However, there is wide variation in the gas-borne filtration performance, and contaminated condensate can potentially pass through some filters under typical pressures encountered during mechanical ventilation.