An alternative strategy for infection control of anesthesia breathing circuits: a laboratory assessment of the Pall HME Filter

Anesthesia Management and Perioperative Infection Control in Patients With the Novel Coronavirus

Anesthesiologists have a high risk of infection with COVID-19 during perioperative care and as first responders to airway emergencies. The potential of becoming infected can be reduced by a systematic and integrated approach that assesses infection risk. The latter leads to an acceptable choice of materials and techniques for personal protection and prevention of cross-contamination to other patients and staff. The authors have presented a protocolized approach that uses diagnostic criteria to clearly define benchmarks from the medical history along with clinical symptoms and laboratory tests. Patients can then be rapidly assigned into 1 of 3 risk categories that direct the choice of protective materials and/or techniques. Each hospital can adapt this approach to develop a system that fits its individual resources. Educating medical staff about the proper use of high-risk areas for containment serves to protect staff and patients.

Guidelines for the management of hospital-acquired pneumonia in the UK: report of the working party on hospital-acquired pneumonia of the British Society for Antimicrobial Chemotherapy

These evidence-based guidelines have been produced after a systematic literature review of a range of issues involving prevention, diagnosis and treatment of hospital-acquired pneumonia (HAP). Prevention is structured into sections addressing general issues, equipment, patient procedures and the environment, whereas in treatment, the structure addresses the use of antimicrobials in prevention and treatment, adjunctive therapies and the application of clinical protocols. The sections dealing with diagnosis are presented against the clinical, radiological and microbiological diagnosis of HAP. Recommendations are also made upon the role of invasive sampling and quantitative microbiology of respiratory secretions in directing antibiotic therapy in HAP/ventilator-associated pneumonia.

Bacterial filters in respiratory circuits: an unnecessary cost?

OBJECTIVE

To evaluate the efficacy of bacterial filters (BF) to decrease pneumonia associated with mechanical ventilation (MV).

DESIGN

Prospective, randomized study.

SETTING

A 24-bed medicosurgical intensive care unit in a 650-bed tertiary hospital.

PATIENTS

A total of 230 patients who needed MV for >24 hrs.

INTERVENTIONS

A total of 114 patients were ventilated with BF and 116 without BF.

MEASUREMENTS

Throat swab and tracheal aspirate were taken at the moment of admission and twice a week until discharge. We considered the following infectious events: pneumonia, respiratory infection, which comprises pneumonia or tracheobronchitis, and respiratory colonization-infection complex, which comprises respiratory infection or colonization. All infectious events were classified as endogenous or exogenous based on throat flora.

MAIN RESULTS

Both groups of patients (ventilated with and without filters) were similar in age, sex, Acute Physiology and Chronic Health Evaluation II score, diagnostic group, days of MV, and mortality. There was no difference in the percentage of patients who developed pneumonia (24.56% with BF and 21.55% without BF), respiratory infection (33.33% vs. 28.44%), or colonization-infection (42.10% vs. 43.96%). The number of infectious events per 1000 days of MV were also similar in both groups: pneumonia (17.41 with BF and 16.26 without BF), respiratory infection (24.62 vs. 21.48), and colonization-infection (36.63 vs. 36). There were also no differences in incidence of infectious events by MV duration. Likewise, we did not find any differences in the number of exogenous events per 1000 days of MV: pneumonia, 2.40 with BF vs. 1.74 without BF; colonization-infection, 4.20 vs. 4.05.

CONCLUSIONS

Bacterial filters in ventilation circuits neither reduce the prevalence of respiratory infections associated with MV nor decrease exogenous infectious events; thus, their usage is not necessary.

Bacterial/viral filtration: let the breather beware!

Most clinicians believe that any device that is marketed as a "bacterial/viral filter" must necessarily be capable of capturing any individual bacteria or viruses that might be suspended within inhaled or exhaled gases. We were surprised to discover that this is, by no means, a justifiable assumption. This article describes testing methods that manufacturers employ to generate the often-misleading efficiency specifications that are claimed for some of these devices. We discuss articles that have documented the presence of airborne pathogens in the effluent of a ventilator circuit, and characterize the attributes that a competent filter must exhibit if it is to succeed in protecting patients and caregivers from incidental exposure to bacteria, viruses, aerosolized drugs, and endotoxins. This article continues with a discussion of the numbers of particles that are commonly produced with commercially available pneumatic nebulizers, the comparative performance characteristics of filters and heat/moisture exchanging filters (HMEFs), and the success or failure of various brands of HMEFs to comply with the guidelines recently developed by the Centers for Disease Control and Prevention for the management of patients who are harboring active tuberculosis. The presentation concludes with a description of the standards that apply to any filter that classifies as a high-efficiency particulate aerosol (HEPA) device, and demonstrates that the performance of filters/HMEFs in common clinical use can range from approximately 1/50th to > 30-fold the efficiency of a HEPA-grade device. Those who frequent the bedside of patients receiving ventilation might unwittingly be placing themselves at considerable risk of exposure to infectious microaerosols, but methods are available to dramatically decrease those risks.

Anesthesia breathing circuits protected by the DAR Barrierbac S breathing filter have a low bacterial contamination rate

PURPOSE

In order to reuse the same anesthesia breathing circuit for more than one patient, it has been proposed to add a breathing filter between the Y-piece and the artificial airway. The purpose of this study was to evaluate the in vivo bacterial filtration efficacy of an anesthesia filter in a usual clinical anesthesia setting.

METHODS

A sterile DAR Barrierbac S breathing filter was inserted at the Y-piece of a sterile single-use anesthesia breathing circuit before induction of general anesthesia. At the end of anesthesia, the breathing circuit connector of the filter and of the endotracheal tube connector were cultured separately on growth media (chocolate and blood agar). These were incubated for 48 hr and bacterial identification was conducted using standard methods.

RESULTS

Bacterial cultures were negative on both sides of the filter membrane of 1842 of the 2001 filters studied. Cultures were positive on the patient side of 104 filters. In two of those, the same bacteria were found on both the circuit side and the patient side of the filter. Therefore these data indicate a clinical effectiveness of 99.9% (confidence interval, CI 95%, 99.6-99.998%), and an in vivo filtration efficacy of 98.08% (CI 95%, 92.54-99.67%).

CONCLUSION

Using the upper limit of the CI, it can be assumed that the practice of using a sterile DAR Barrierbac S breathing filter for every patient while reusing the anesthesia breathing circuit would result in a cross contamination rate of the breathing circuit lower than once every 250 cases.

Humidification method that decreases condensate contamination in ventilator tubing

OBJECTIVE

To demonstrate combining unheated bubble-through humidifier with a heat-moisture exchanger filter for the purpose of decreasing condensate contamination in mechanical ventilator tubing.

DESIGN

Single-case, pretest and posttest.

SETTING

University-affiliated and nonprofit hospital.

PATIENT

A 32-year-old man with Pickwickian syndrome and pneumonia caused by Pseudomonas aeruginosa received mechanical ventilation for 14 days.

METHODS

Ventilator tubing was cultured in two 24-hour trials, using a pretest and posttest design, to assess tubing bacterial contamination during use of 2 humidification methods. In the first trial, a traditional heated bubble-through humidifier (HBH) was used for 24 hours. Before the start of the second trial, the "wet" tubing and the heated bubble-through humidifier were removed and replaced with clean equipment through the use of aseptic technique. The bubble-through humidifier was placed on the "cold," or unheated mode, and a heat-moisture exchanger filter was attached to the Y-connector of the ventilator tubing.

RESULTS

The heated bubble-through humidifier method revealed contamination of the ventilator tubing in 3 places with the patient's strain of P aeruginosa in addition to copious water condensate. The unheated bubble-through humidifier/heat moisture exchanger filter method demonstrated no bacterial contamination or condensate in the tubing.

CONCLUSION

It can be inferred that the humidification method using the combination of an unheated bubble-through humidifier and a heat moisture exchanger filter has the potential benefit of preventing "reseeding" of the patient's airway with contaminated condensate.

The potential for dissemination of Mycobacterium tuberculosis through the anesthesia breathing circuit

BACKGROUND

Respiratory pathogens that pass through the anesthesia breathing system potentially can infect other patients. This study was designed to determine if bacteria can pass through contemporary anesthesia breathing systems and if the environment within the machine is hostile to these organisms.

METHODS

Staphylococcus aureus, Pseudomonas aeruginosa, and Mycobacterium tuberculosis were nebulized into the expiratory limb of an anesthesia breathing circuit and collected from the inspiratory and expiratory limbs in an impinger system that provided a quantitative determination of the number of organisms entering the circuit and the number that would reach the patient in the inspiratory gas. Bacteria were collected before, during, and after nebulization. A second experiment determined if a saturated solution of soda lime was bactericidal.

RESULTS

When the gas flow through the circuit was interrupted for < 1 h following the nebulization period, large numbers of microorganisms (1 x 10(3) to 1 x 10(5), around 100% of the nebulized organisms) were collected from the inspiratory gas. Soda lime itself was not bactericidal for any of the organisms tested, but solutions of this material with a pH of 12 were bactericidal.

CONCLUSION

Cross contamination between patients may occur unless the gas flow through the anesthesia breathing system is interrupted for > 1 h.

Clinical utility of hygroscopic heat and moisture exchangers in intensive care patients

OBJECTIVE

To compare the degree of bacterial circuit colonization, frequency of ventilator-associated pneumonia (VAP), character of respiratory secretions, rewarming of hypothermic patients, disposable costs, and air flow resistance in intensive care patients ventilated using either a heat and moisture exchanger (HME) or hot water (HW) humidifier circuit.

DESIGN

A prospective, randomized blinded trial of patients in the intensive care unit undergoing mechanical ventilation.

SETTING

A metropolitan teaching hospital.

PATIENTS

One hundred sixteen patients undergoing mechanical ventilation for a minimum period of 48 hrs were enrolled.

INTERVENTIONS

Patients were randomized to three ventilation groups using a) an HW circuit with a 2-day circuit change (n = 41); or b) a bacterial-viral filtering HME in the circuit, with either a 2-day (n = 42); or c) a 4-day circuit change (n = 33).

MEASUREMENTS AND MAIN RESULTS

Circuit colonization was assessed using quantitative culture of washings taken from the circuit tubing and semiquantitative culture of swabs from the Y connectors. Sixty-seven percent of HW circuits became contaminated compared with 12% in the two HME groups (p < .0001). Median colony counts were lower in the HME groups (p < .0001). If circuits at first circuit change were contaminated in the HW group, 89% of subsequent circuit changes became contaminated compared with 0% and 25% for the 2- and 4-day HME groups, respectively. The frequency of VAP, the time to resolution of admission hypothermia, and the volume and fluidity of secretions were similar for all groups. The resistance of the HME after 24 hrs of use was < 0.025 cm H2O/L at gas flows of 40 L/min. HME use resulted in a cost reduction of $1.48 (Australian)/day.

CONCLUSIONS

Circuits with a bacterial-viral filtering HME are less readily colonized by bacteria. Contamination is a random event. Humidification technique has no influence on the frequency rate of VAP, the effectiveness of rewarming, nor the character of the respiratory secretions. Breathing resistance is generally low and disposable costs are reduced when an HME is used.

An experimental set-up to test heat-moisture exchangers

OBJECTIVES

The purpose of this study was to build an experimental set-up to assess continuously the humidification, heating and resistance properties of heat-moisture exchangers (HMEs) under clinical conditions.

DESIGN

The experimental set-up consists of a patient model, measurement systems and a ventilator.

SETTING

Surgical ICU, University Hospital of Rotterdam.

MATERIALS

A clinically used HME.

MEASUREMENTS AND RESULTS

The air flow, pressure in the ventilation circuit, pressure difference over the HME, and partial water vapour pressure and temperature at each side of the HME were measured. The resistance, absolute humidity, humidification efficiency and temperature difference at the patient side of the HME were calculated. Measurements were performed during 24 h. The temperature output, humidity output and lung mechanics of the patient model were similar to values found in mechanically ventilated patients. The measurement system was in agreement with the ISO draft standard and was capable of measuring dynamic variation of water and heat exchange over the range of a clinically used ventilator setting.

CONCLUSION

The experimental set-up described is reliable for evaluating HMEs and can also be used for future clinical evaluation of HMEs. The main advantages of this set-up over those described previously are: (i) measurements of dynamic variations of water and heat exchange; (ii) on-line measurements of expiratory, as well as inspiratory resistance.

The effect of a heat and moisture exchange filter on sidestream spirometry in critically ill patients

Sidestream spirometry has enabled continuous on-line monitoring of the pulmonary mechanics in intubated patients. We studied the effect of the heat and moisture exchange filter (HMEF) on the displayed spirometry values of a commercial multiparameter pulmonary monitor in 35 stable ICU patients needing mechanical ventilatory support. There were statistically significant differences in tidal volumes, airway pressures, compliances and end-tidal CO2-values between the two sites of measurements on both sides on the HMEF. The effect of the HMEF was linear in almost every patient. However, the change of the displayed values was clinically of minor importance. In conclusion, we suggest that the HMEF can be safely used between the patient and the monitoring site in routine ventilatory monitoring of ICU patients.

Practical methods of cost containment in anesthesia and surgery

With the increasing focus of national attention on health care and health care costs, anesthesiologists, along with all other medical specialists, must become more cost conscious in their practice behaviors. This review describes the current concerns about health care in the United States, including a discussion of some of the forces causing the increase in health care spending. The role of anesthesiology in the increase in health care costs is discussed. Practical methods for controlling anesthesia costs are outlined, including reducing preoperative testing, decreasing blood product use, and employing more regional and local anesthetic techniques. Several ideas for reducing the costs of anesthetic gases and drugs, including low-flow anesthesia and less expensive alternative drugs, are presented. The final section describes the changes in anesthesia drug use that occurred from 1992 to 1993 at one health care center (St. Francis Regional Medical Center, Wichita, KS, which is associated with the University of Kansas School of Medicine-Wichita). These changes resulted in a 13% reduction in anesthesia drug costs, which amounted to a savings of $127,472. The largest decreases were in anesthetic gases (16%), resulting from an increase in the use of low-flow techniques, and in muscle relaxants (26%), resulting from a switch to older lower-cost drugs.

Ventilatory support of the neonatal foal

Many sick neonatal foals have respiratory failure secondary to perinatal hypoxia, sepsis, or pneumonia. These foals require ventilatory support to prevent respiratory embarrassment and other complications associated with chronic hypoxia and hypercapnia. This article discusses practical aspects of ventilatory therapy, such as choosing a candidate for mechanical ventilation, choosing the proper ventilatory mode, placing a foal on a ventilator, maintaining a foal on mechanical ventilation, and weaning from mechanical ventilation. This article details some of the techniques that have been developed based on experiences with mechanical ventilation of neonatal foals and encourages other clinicians to consider ventilatory therapy as a feasible option.

Humidification in the intensive care unit. Prospective study of a new protocol utilizing heated humidification and a hygroscopic condenser humidifier

STUDY OBJECTIVE

Determine the utility of a proposed algorithm in allowing safe, efficient humidification in mechanically ventilated patients using both a hygroscopic condenser humidifier (HCH) and heated humidifier (HH).

DESIGN

A prospective study using an algorithm to chose humidification devices based on physical examination and sputum characteristics.

SETTING

All patients admitted to the surgical ICU.

PATIENTS

One hundred twenty consecutive patients requiring mechanical ventilation (MV) were studied.

INTERVENTIONS

Patients were examined by the attending respiratory care practitioner and given either an HCH or HH. If patients demonstrated any of the following--thick or tenacious secretions, core temperature < 32 degrees C, or bloody secretions--they were given an HH. All others used an HCH. If any of the above conditions occurred during HCH use, the patient was given an HH.

MEASUREMENTS AND RESULTS

Duration of ventilation, incidence of nosocomial pneumonia, ventilator circuit colonization, and mortality were determined for patients in each group. Cost of humidification devices, number of suctioning procedures per day, and volume of saline solution instilled were also recorded. Initially, 27 percent (32/120) of patients used an HH and 73 percent (88/120) used an HCH. During the study, ten patients required changing to an HH during HCH use. Patients in the HH group were more likely to have preexisting lung disease and had a longer duration of ventilation (83 +/- 21 h) and higher mortality (21 percent). Patients in the HCH group were more likely to be postoperative, had shorter durations of ventilation (38 +/- 14 h), and lower mortality (9 percent). There was no difference in the incidence of nosocomial pneumonia between the two groups (9 percent vs 6 percent) and endotracheal tube occlusion did not occur in either group. Circuit colonization was common in the HH group (64 percent) but rate in the HCH group (5 percent). Cost per day was significantly less for the HCH group ($4 vs $19.80). Patients who required a change from HCH to HH did so at a mean of 5 days.

CONCLUSION

The proposed algorithm resulted in cost-efficient and safe application of humidification devices in patients in the surgical ICU.