Changing heat and moisture exchangers after 96 hours rather than after 24 hours: a clinical and microbiological evaluation

Humidification and heating of inhaled gas in patients with artificial airway. A narrative review

Instrumentation of the airways in critical patients (endotracheal tube or tracheostomy cannula) prevents them from performing their function of humidify and heating the inhaled gas. In addition, the administration of cold and dry medical gases and the high flows that patients experience during invasive and non-invasive mechanical ventilation generate an even worse condition. For this reason, a device for gas conditioning is needed, even in short-term treatments, to avoid potential damage to the structure and function of the respiratory epithelium. In the field of intensive therapy, the use of heat and moisture exchangers is common for this purpose, as is the use of active humidification systems. Acquiring knowledge about technical specifications and the advantages and disadvantages of each device is needed for proper use since the conditioning of inspired gases is a key intervention in patients with artificial airway and has become routine care. Incorrect selection or inappropriate configuration of a device can have a negative impact on clinical outcomes. The members of the Capítulo de Kinesiología Intensivista of the Sociedad Argentina de Terapia Intensiva conducted a narrative review aiming to show the available evidence regarding conditioning of inhaled gas in patients with artificial airways, going into detail on concepts related to the working principles of each one.

Effectiveness of heat and moisture exchangers in preventing ventilator-associated pneumonia in critically ill patients: a meta-analysis

BACKGROUND

Patients may acquire ventilator-associated pneumonia (VAP) by aspirating the condensate that originates in the ventilator circuit upon use of a conventional humidifier. The bacteria that colonize the patients themselves can proliferate in the condensate and then return to the airways and lungs when the patient aspirates this contaminated material. Therefore, the use of HME might contribute to preventing pneumonia and lowering the VAP incidence. The aim of this study was to evaluate how the use of HME impacts the probability of VAP occurrence in critically ill patients.

METHODS

On the basis of the acronym "PICO" (Patient, Intervention, Comparison, Outcome), the question that guided this review was "Do critically ill patients under invasive mechanical ventilation present lower VAP incidence when they use HME as compared with HH?". Two of the authors of this review searched the databases PUBMED/Medline, The Cochrane Library, and Latin-American and Caribbean Literature in Health Sciences, LILACS independently; they used the following keywords: "heat and moisture exchanger", AND "heated humidifier", AND "ventilator-associated pneumonia prevention". This review included papers in the English language published from January 1990 to December 2012.

RESULTS

This review included ten studies. Comparison between the use of HME and HH did not reveal any differences in terms of VAP occurrence (OR = 0.998; 95% CI: 0.778-1.281). Together, the ten studies corresponded to a total sample of 1077 and 953 patients in the HME and HH groups, respectively; heterogeneity among the investigations was low (I(2) < 50%). Information about the outcome mortality was available in only eight of the ten studies. The use of HME and HH did not afford different results in terms of mortality (OR = 1.09; 95% CI: 0.864-1.376). The total sample size was 884 and 762 patients, respectively. Heterogeneity among the studies was low (I(2) = 0.0%).

CONCLUSION

Current meta-analysis was not sufficient to definitely exclude an associate between heat and moisture exchangers and VAP. Despite the methodological limitations found in selected clinical trials, the current meta-analysis suggests that HME does not decrease VAP incidence or mortality in critically ill patients.

Humidification during mechanical ventilation in the adult patient

Humidification of inhaled gases has been standard of care in mechanical ventilation for a long period of time. More than a century ago, a variety of reports described important airway damage by applying dry gases during artificial ventilation. Consequently, respiratory care providers have been utilizing external humidifiers to compensate for the lack of natural humidification mechanisms when the upper airway is bypassed. Particularly, active and passive humidification devices have rapidly evolved. Sophisticated systems composed of reservoirs, wires, heating devices, and other elements have become part of our usual armamentarium in the intensive care unit. Therefore, basic knowledge of the mechanisms of action of each of these devices, as well as their advantages and disadvantages, becomes a necessity for the respiratory care and intensive care practitioner. In this paper, we review current methods of airway humidification during invasive mechanical ventilation of adult patients. We describe a variety of devices and describe the eventual applications according to specific clinical conditions.

Water Uptake Performance of Hygroscopic Heat and Moisture Exchangers after 24-Hour Tracheostoma Application

OBJECTIVE

After total laryngectomy, patients suffer from pulmonary complaints due to the shortcut of the upper airways that results in decreased warming and humidification of inspired air. Laryngectomized patients are advised to use a heat and moisture exchanger (HME) to optimize the inspired air. According to manufacturers' guidelines, these medical devices should be replaced every 24 hours. The aim of this study is to determine whether HMEs still function after 24-hour tracheostoma application.

STUDY DESIGN

Assessment of residual water uptake capacity of used HMEs by measuring the difference between wet and dry core weight.

SETTING

Tertiary comprehensive cancer center.

SUBJECTS AND METHODS

Three hygroscopic HME types were tested after use by laryngectomized patients in long-term follow-up. Water uptake of 41 used devices (including 10 prematurely replaced devices) was compared with that of control (unused) devices of the same type and with a control device with a relatively low performance.

RESULTS

After 24 hours, the mean water uptake of the 3 device types had decreased compared with that of the control devices. For only one type was this difference significant. None of the used HMEs had a water uptake lower than that of the low-performing control device.

CONCLUSION

The water uptake capacity of hygroscopic HEMs is clinically acceptable although no longer optimal after 24-hour tracheostoma application. From a functional point of view, the guideline for daily device replacement is therefore justified.

Effect of heat and moisture exchangers on the prevention of ventilator-associated pneumonia in critically ill patients

Ventilator-associated pneumonia (VAP) remains one of the major causes of infection in the intensive care unit (ICU) and is associated with the length of hospital stay, duration of mechanical ventilation, and use of broad-spectrum antibiotics. We compared the frequency of VAP 10 months prior to (pre-intervention group) and 13 months after (post-intervention group) initiation of the use of a heat and moisture exchanger (HME) filter. This is a study with prospective before-and-after design performed in the ICU in a tertiary university hospital. Three hundred and fourteen patients were admitted to the ICU under mechanical ventilation, 168 of whom were included in group HH (heated humidifier) and 146 in group HME. The frequency of VAP per 1000 ventilator-days was similar for both the HH and HME groups (18.7 vs 17.4, respectively; P = 0.97). Duration of mechanical ventilation (11 vs 12 days, respectively; P = 0.48) and length of ICU stay (11 vs 12 days, respectively; P = 0.39) did not differ between the HH and HME groups. The chance of developing VAP was higher in patients with a longer ICU stay and longer duration of mechanical ventilation. This finding was similar when adjusted for the use of HME. The use of HME in intensive care did not reduce the incidence of VAP, the duration of mechanical ventilation, or the length of stay in the ICU in the study population.

Trocador de calor e umidade: proteção contra infecções pulmonares? Estudo piloto

O objetivo deste trabalho foi realizar um estudo bacteriológico comparativo entre os sistemas de umidificação aquoso aquecido (UAA) e filtro trocador de calor e umidade (FTCU) quanto à colonização bacteriana e a incidência de infecção respiratória em pacientes submetidos à ventilação mecânica (VM). Trata-se de uma pesquisa prospectiva, controlada e randomizada, na qual 15 pacientes internados na Unidade de Terapia Intensiva (UTI) foram distribuídos em dois grupos. O primeiro fez uso de UAA (n=7) e o outro de FTCU (n=8). Foram coletadas amostras da secreção traqueal, condensado do circuito e FTCU na admissão do paciente, no quarto e oitavo dias, e realizada análise bacteriológica dos mesmos. Quanto às características antropométricas, não observou-se diferenças entre os grupos estudados. A prevalência de pneumonia associada à ventilação (PAV) foi de 57,1% no UAA e 62,5% no FTCU. Ao realizar a análise bacteriológica quantitativa entre eles, não foram observadas variações, sugerindo não haver diferença na prevenção de PAV entre os sistemas de umidificação; porém a presença das mesmas bactérias na secreção traqueal e no condensado e ausência destas na membrana do FTCU podem indicar que a principal fonte de contaminação é o próprio paciente.

Airway humidification with a heat and moisture exchanger in mechanically ventilated neonates

OBJECTIVE

We set out to evaluate the efficacy of passive inspiratory gas conditioning in mechanically ventilated neonates and compared it with that of a heated humidifier (HH).

DESIGN

Prospective, randomized, controlled study.

SETTING

Neonatal and pediatric intensive care unit.

PATIENTS

Fourteen mechanically ventilated neonates nursed in incubators.

INTERVENTIONS

The HH was set to deliver a temperature of 37 degrees C and an absolute humidity of 40 mgH(2)O/l at the incubator entrance. Inspired temperature (T degrees ) and absolute humidity (AH) were measured by the psychometric method, transpulmonary pressure (Tpres) by means of a differential pressure transducer. Measurements were performed at 5, 10, and 15 min.

MEASUREMENTS AND RESULTS

The values of T degrees were significantly higher using the HH (34.6+/-1.6 degrees C) than the heat and moisture exchanger (HME) (33.8+/2.3, p<0.001). The values of AH were significantly higher using the HH (36.6+/-2.5 mgH(2)O/l) than the HME (32.4+/-2.8 mgH(2)O/l, p<0.001). No significant changes were observed in transpulmonary pressure. A significant positive correlation was observed between incubator temperature and the temperature delivered by the HH (R(2)=0.61, p<0.001).

CONCLUSIONS

The use of HMEs in neonates made it possible to achieve an absolute humidity of 28 mgH(2)O/l or more and a temperature of 30 degrees C or more. Higher values are obtained using a HH.

Comparison of manufacturers’ specifications for 44 types of heat and moisture exchanging filters

BACKGROUND

Although heat and moisture exchanging filters (HMEF) are recommended for use during anaesthesia, the criteria for choosing a filter are not clearly defined. Manufacturers offer many different types of HMEF with various technical characteristics. We compared the technical specifications provided by the manufacturers for different types of HMEF.

METHODS

Filter manufacturers were asked to provide technical information. Additional information was obtained from websites. Information about 44 filters (16 mechanical and 28 electrostatic) was collated.

RESULTS

Filter performances were estimated with different sizes of microorganism and durations of challenge. Twenty-eight filters had not been tested by independent laboratories. For 12 of the filters, information obtained from websites and from the manufacturers differed. Most filter specifications claimed high efficiency, particularly for filtration, microbial challenge number and test duration. Electrostatic filters used in anaesthesia were claimed to have high filtration efficiency, similar to the efficiency provided by mechanical filters. Excluding moisture output values did not alter the general conclusions.

CONCLUSIONS

Technical aspects of the tests, international standards, and independent validation should be considered when a filter is chosen.

Efficacy of heat and moisture exchangers in preventing ventilator-associated pneumonia: meta-analysis of randomized controlled trials

OBJECTIVE

Several randomized controlled trials (RCT) have examined the effect of antibacterial humidification strategies, particularly the replacement of heated humidifiers (HH) by heat and moisture exchangers (HME), in preventing ventilator-associated pneumonia (VAP). The present meta-analysis reviews these RCTs.

METHODS

RCTs were identified by searching the Medline and Cochrane Central Register of Controlled Trials databases from 1990 to 2003. We included RCTs using HMEs in the treatment group and HHs in the control group and reporting the incidence of pneumonia as a study outcome. Two investigators independently abstracted key data on design, population, intervention and outcome of the studies.

RESULTS

Between 1990 and 2003 eight RCTs met the inclusion criteria of this analysis. Pooling the results from these studies revealed a reduction in the relative risk of VAP in the HME group (0.7), particularly in MV with a duration of at least 7 days (five RCTs, relative risk 0.57).

CONCLUSIONS

This meta-analysis found a significant reduction in the incidence of VAP in patients humidified with HMEs during MV, particularly in patients ventilated for 7 days or longer. This finding is limited by the exclusion of patients at high risk for airway occlusion from some of the studies. Moreover, contraindications (tenacious secretions, airway obstructive disease, hypothermia) and technical issues of HMEs must be considered. Further RCTs are necessary to examine the wider applicability of HMEs and their extended use.

[Assessment of 44 heat and moisture exchange filters. What to choose?]

OBJECTIVES

If the use of heat and moisture exchange filter (HMEF) in anaesthesia is recommended by the French Society of Anaesthesia and Intensive Care (SFAR), the criteria's choice are not clearly defined. Many HMEF are proposed by manufacturers which technical characteristics are different.

STUDY DESIGN

The aim of this study was to evaluate the HMEF using items of the American Association of Respiratory Care (AARC) and technical dossiers.

METHODS

All manufactures producing filters have been contacted to give their technical dossiers. Forty-eight filters have been analyzed (13 mechanical filters, 31 electrostatic filters). Each item has been scaled 0, 5 or 10. The final result was on 10.

RESULTS

Seventeen filters had a note superior to 5. There were 8 mechanical filters and 9 electrostatic filters. The difference between the filters was the size of the micro-organisms tested and the duration of the test. Some filters were not tested by independent laboratories (N = 8). There were differences between the commercial documentation and on Internet and the technical dossiers (N = 12).

DISCUSSION

We noted the good quality of the filters particularly concerning criters recommended by the Sfar (filter medium, filtration efficiency, microbial challenge number and duration of the test). The electrostatic filters recently used in anaesthesia have high performance concerning filtration efficiency. To supprime the moisture output criteria did not change the results.

CONCLUSIONS

Criteria's used by manufactures to evaluate there filters are not always precised or too restrictive. The technical tests, the international norms, the certificates of validation, the ergonomic qualities and the definition of our needs are the main elements of choice of a filter.

Heat and moisture exchangers in mechanically ventilated intensive care unit patients: a plea for an independent assessment of their performance

OBJECTIVE

To determine whether use of a hygroscopic and hydrophobic heat and moisture exchanger (HME) for 7 days without change affects its efficiency in long-term, mechanically ventilated, chronic obstructive pulmonary disease (COPD) patients.

DESIGN

Prospective, randomized, controlled clinical study comparing two combined HMEs.

SETTING

Medical intensive care unit at a university teaching hospital.

PATIENTS

Long-term, mechanically ventilated, COPD patients compared with non-COPD patients.

INTERVENTIONS

In the first part of the study, COPD patients were studied with the Hygroster HME changed once a week. For the second part, the Hygroster was assessed in non-COPD patients and compared with the Hygrobac HME used in COPD and non-COPD patients for 1 wk without change. Devices could be changed if hygrometric measurements indicated insufficient humidity delivery.

MEASUREMENTS AND MAIN RESULTS

Daily measurements were recorded for inspired gas temperature and relative and absolute humidity. Ventilatory variables, clinical indicators of efficient humidification, were also recorded. No tracheal tube occlusion occurred. However, contrary to the manufacturer advertisement, the Hygroster experienced surprisingly low values for absolute humidity in both COPD and non-COPD patients. Such events did not occur with the Hygrobac. Absolute humidity with the Hygroster was constantly and significantly lower during the 7-day study period than with the Hygrobac. Absolute humidity measured in COPD patients was identical to that measured in the rest of the study population with both HMEs.

CONCLUSIONS

Manufacturer specifications and bedside measurements of absolute humidity differed considerably for the Hygroster, which in certain instances did not achieve efficient humidification in both COPD and non-COPD patients. This did not occur with the Hygrobac, which performed well throughout the 7-day period in both COPD and non-COPD patients. Our results speak for independent and evaluation of HMEs.

Randomized clinical trial of extended use of a hydrophobic condenser humidifier: 1 vs. 7 days

OBJECTIVE

To determine whether extended use (7 days) would affect the efficiency on heat and water preservation of a hydrophobic condenser humidifier as well as the rate of ventilation-acquired pneumonia, compared with 1 day of use.

DESIGN

Prospective, controlled, randomized, not blinded, clinical study.

SETTING

Twelve-bed intensive care unit of a university hospital.

PATIENTS

One hundred and fifty-five consecutive patients undergoing mechanical ventilation for > or = 48 hrs.

INTERVENTIONS

After randomization, patients were allocated to one of the two following groups: a) heat and moisture exchangers (HMEs) changed every 24 hrs; b) HMEs changed only once a week. Devices in both groups could be changed at the discretion of the staff when signs of occlusion or increased resistance were identified.

MEASUREMENTS AND MAIN RESULT

Efficient airway humidification and heating were assessed by clinical variables (numbers of tracheal suctionings and instillations required, peak and mean airway pressures). The frequency rates of bronchial colonization and ventilation-acquired pneumonia were evaluated by using clinical and microbiological criteria. Endotracheal tube occlusion, ventilatory support variables, duration of mechanical ventilation, length of intensive care, acquired multiorgan dysfunction, and mortality rates also were recorded. The two groups were similar at the time of randomization. Endotracheal tube occlusion never occurred. In the targeted population (patients ventilated for > or = 7 days), the frequency rate of ventilation-acquired pneumonia was 24% in the HME 1-day group and 17% in the HME 7-day group (p > .05, not significant). Ventilation-acquired pneumonia rates per 1000 ventilatory support days were 16.4/1000 in the HME 1-day group and 12.4/1000 in the HME 7-day group (p > .05, not significant). No statistically significant differences were found between the two groups for duration of mechanical ventilation, intensive care unit length of stay, acquired organ system derangements, and mortality rate. There was indirect evidence of very little, if any, change in HME resistance.

CONCLUSIONS

Changing the studied hydrophobic HME after 7 days did not affect efficiency, increase resistance, or altered bacterial colonization. The frequency rate of ventilation-acquired pneumonia was also unchanged. Use of HMEs for > 24 hrs and up to 7 days is safe.

Risk factors for nosocomial pneumonia. Focus on prophylaxis

Despite an increased understanding of the pathogenesis of NP and advances in diagnosis and treatment, the risk, cost, morbidity, and mortality of NP remain unacceptably high. This article has identified strategic areas for primary and secondary prophylaxis that are simple and cost-effective. Realizing that the pathogenesis of NP requires bacterial colonization and the subsequent entry of these bacteria into the lower respiratory tree helps highlight the role of cross-infection and the importance of standard infection control procedures. Similarly the role of sedation and devices as risk factors can be reduced by minimizing the duration and intensity of sedation and length of exposure to invasive devices. Additional low-cost interventions that have been shown to be effective in preventing NP are the positioning of patients in a semirecumbent position and the appropriate use of enteral feeding, antibiotics, and selected medical devices. Prophylaxis of NP and VAP is carried out best by a multidisciplinary management team comprised of physicians (critical care, pulmonary medicine, infectious diseases, and primary care), critical care and infection control nurses, and respiratory therapists, even though this approach may result in decreased professional autonomy and freedom. This group should review the current guidelines, pathways, and standards for short-term and long-term prophylaxis of NP and VAP, then integrate them into and monitor their use for routine patient care. The risk factors and prophylaxis strategies for NP discussed in this article apply primarily to patients in acute care facilities, but also are relevant to alternative health care settings as well as the care of ill patients in ambulatory settings. The routine use of effective team policies for prophylaxis needs to be monitored by the Joint Commission for the Accreditation of Health Care or other agencies. Research to delineate the most effective and feasible strategies for prophylaxis NP has been compromised by insufficient funding and lack of adequate, randomized multicenter studies to enable generalizability of results. Effective strategies for prophylaxis have not been disseminated widely or implemented in hospitals. Successful short-term and long-term strategies for prophylaxis must be evaluated and implemented by a team of physicians, nurses, and respiratory therapists. More than 100 years ago, Sir William Osler warned health care providers, "Remember how much you don't know." The authors would add that clinicians have acquired significant knowledge about risk factors and prophylaxis of NP in the 1980s and 1990s, but prophylaxis as a theory rather than an action. If the tree has not been planted, the time is now.