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

Hygrometric Performance of 113 Passive Humidifiers: ISO Standard Method Versus Psychrometry

Background: Passive humidifiers, also known as heat-and-moisture exchangers (HMEs) are used to warm and humidify inspired gases delivered during mechanical ventilation. Recent data demonstrate that the evaluation and selection of these devices is not optimal, leading to severe complications, such as endotracheal tube occlusions. The aim of the study was to assess the humidification performances of a large number of commercially available devices, with the psychrometric method, and to compare the results with manufacturer's data. Methods: We assessed 113 devices using a bench test that simulated physiological ventilation conditions. Seventy-one devices were described by the manufacturers as HME without or with filtration properties (HMEF) and 42 as antimicrobial filters. Among the 71 HME/HMEF, 60% were foam-based, 32% were paper-based, 6% were fiber-based, and 1 had carbon media (HMEF with inhaled sedation function). Three hygrometric measurements using the psychrometric method for each device were performed after reaching a steady state and compared with manufacturers' data (based on the International Organization for Standardization [ISO] method). Results: Among the 71 HME/HMEF tested, only 24 (34%) delivered absolute humidity above 28 mg H2O/L. Nineteen percent of the foam-based and 57% of the paper-based HME/HMEF delivered desired levels of humidity. Humidification data provided by manufacturers were available for 59 HME/HMEFs. In all but one device, humidity output was overestimated using the ISO method. The median (interquartile) difference between our measurements and the manufacturers' data were 6.0 (3.8-8.7) mg H2O/L for devices described as HMEs (P < .001). Poor performing devices were detected only with the psychrometric method. Conclusions: Several HME/HMEFs performed poorly and should not be used for prolonged mechanical ventilation. The values determined by independent assessments were lower than values reported by manufacturers. Evaluation of a passive humidifier using the current ISO method does not guarantee provision of adequate humidification.

Ventilatory changes during the use of heat and moisture exchangers in patients submitted to mechanical ventilation with support pressure and adjustments in ventilation parameters to compensate for these possible changes: a self-controlled intervention study in humans

OBJECTIVE

To evaluate the possible changes in tidal volume, minute volume and respiratory rate caused by the use of a heat and moisture exchanger in patients receiving pressure support mechanical ventilation and to quantify the variation in pressure support required to compensate for the effect caused by the heat and moisture exchanger.

METHODS

Patients under invasive mechanical ventilation in pressure support mode were evaluated using heated humidifiers and heat and moisture exchangers. If the volume found using the heat and moisture exchangers was lower than that found with the heated humidifier, an increase in pressure support was initiated during the use of the heat and moisture exchanger until a pressure support value was obtained that enabled the patient to generate a value close to the initial tidal volume obtained with the heated humidifier. The analysis was performed by means of the paired t test, and incremental values were expressed as percentages of increase required.

RESULTS

A total of 26 patients were evaluated. The use of heat and moisture exchangers increased the respiratory rate and reduced the tidal and minute volumes compared with the use of the heated humidifier. Patients required a 38.13% increase in pressure support to maintain previous volumes when using the heat and moisture exchanger.

CONCLUSION

The heat and moisture exchanger changed the tidal and minute volumes and respiratory rate parameters. Pressure support was increased to compensate for these changes.

Heat and moisture exchangers versus heated humidifiers for mechanically ventilated adults and children

BACKGROUND

Invasive ventilation is used to assist or replace breathing when a person is unable to breathe adequately on their own. Because the upper airway is bypassed during mechanical ventilation, the respiratory system is no longer able to warm and moisten inhaled gases, potentially causing additional breathing problems in people who already require assisted breathing. To prevent these problems, gases are artificially warmed and humidified. There are two main forms of humidification, heat and moisture exchangers (HME) or heated humidifiers (HH). Both are associated with potential benefits and advantages but it is unclear whether HME or HH are more effective in preventing some of the negative outcomes associated with mechanical ventilation. This review was originally published in 2010 and updated in 2017.

OBJECTIVES

To assess whether heat and moisture exchangers or heated humidifiers are more effective in preventing complications in people receiving invasive mechanical ventilation and to identify whether the age group of participants, length of humidification, type of HME, and ventilation delivered through a tracheostomy had an effect on these findings.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials, MEDLINE, Embase and CINAHL up to May 2017 to identify randomized controlled trials (RCTs) and reference lists of included studies and relevant reviews. There were no language limitations.

SELECTION CRITERIA

We included RCTs comparing HMEs to HHs in adults and children receiving invasive ventilation. We included randomized cross-over studies.

DATA COLLECTION AND ANALYSIS

We assessed the quality of each study and extracted the relevant data. Where possible, we analysed data through meta-analysis. For dichotomous outcomes, we calculated the risk ratio (RR) and 95% confidence interval (95% CI). For continuous outcomes, we calculated the mean difference (MD) and 95% CI or standardized mean difference (SMD) and 95% CI for parallel studies. For cross-over trials, we calculated the MD and 95% CI using correlation estimates to correct for paired analyses. We aimed to conduct subgroup analyses based on the age group of participants, how long they received humidification, type of HME and whether ventilation was delivered through a tracheostomy. We also conducted sensitivity analysis to identify whether the quality of trials had an effect on meta-analytic findings.

MAIN RESULTS

We included 34 trials with 2848 participants; 26 studies were parallel-group design (2725 participants) and eight used a cross-over design (123 participants). Only three included studies reported data for infants or children. Two further studies (76 participants) are awaiting classification.There was no overall statistical difference in artificial airway occlusion (RR 1.59, 95% CI 0.60 to 4.19; participants = 2171; studies = 15; I2 = 54%), mortality (RR 1.03, 95% CI 0.89 to 1.20; participants = 1951; studies = 12; I2 = 0%) or pneumonia (RR 0.93, 95% CI 0.73 to 1.19; participants = 2251; studies = 13; I2 = 27%). There was some evidence that hydrophobic HMEs may reduce the risk of pneumonia compared to HHs (RR 0.48, 95% CI 0.28 to 0.82; participants = 469; studies = 3; I2 = 0%)..The overall GRADE quality of evidence was low. Although the overall methodological risk of bias was generally unclear for selection and detection bias and low risk for follow-up, the selection of study participants who were considered suitable for HME and in some studies removing participants from the HME group made the findings of this review difficult to generalize.

AUTHORS' CONCLUSIONS

The available evidence suggests no difference between HMEs and HHs on the primary outcomes of airway blockages, pneumonia and mortality. However, the overall low quality of this evidence makes it difficult to be confident about these findings. Further research is needed to compare HMEs to HHs, particularly in paediatric and neonatal populations, but research is also needed to more effectively compare different types of HME to each other as well as different types of HH.

Heat and moisture exchangers (HMEs) and heated humidifiers (HHs) in adult critically ill patients: a systematic review, meta-analysis and meta-regression of randomized controlled trials

BACKGROUND

The aims of this systematic review and meta-analysis of randomized controlled trials are to evaluate the effects of active heated humidifiers (HHs) and moisture exchangers (HMEs) in preventing artificial airway occlusion and pneumonia, and on mortality in adult critically ill patients. In addition, we planned to perform a meta-regression analysis to evaluate the relationship between the incidence of artificial airway occlusion, pneumonia and mortality and clinical features of adult critically ill patients.

METHODS

Computerized databases were searched for randomized controlled trials (RCTs) comparing HHs and HMEs and reporting artificial airway occlusion, pneumonia and mortality as predefined outcomes. Relative risk (RR), 95% confidence interval for each outcome and I ² were estimated for each outcome. Furthermore, weighted random-effect meta-regression analysis was performed to test the relationship between the effect size on each considered outcome and covariates.

RESULTS

Eighteen RCTs and 2442 adult critically ill patients were included in the analysis. The incidence of artificial airway occlusion (RR = 1.853; 95% CI 0.792-4.338), pneumonia (RR = 932; 95% CI 0.730-1.190) and mortality (RR = 1.023; 95% CI 0.878-1.192) were not different in patients treated with HMEs and HHs. However, in the subgroup analyses the incidence of airway occlusion was higher in HMEs compared with HHs with non-heated wire (RR = 3.776; 95% CI 1.560-9.143). According to the meta-regression, the effect size in the treatment group on artificial airway occlusion was influenced by the percentage of patients with pneumonia (β = -0.058; p = 0.027; favors HMEs in studies with high prevalence of pneumonia), and a trend was observed for an effect of the duration of mechanical ventilation (MV) (β = -0.108; p = 0.054; favors HMEs in studies with longer MV time).

CONCLUSIONS

In this meta-analysis we found no superiority of HMEs and HHs, in terms of artificial airway occlusion, pneumonia and mortality. A trend favoring HMEs was observed in studies including a high percentage of patients with pneumonia diagnosis at admission and those with prolonged MV. However, the choice of humidifiers should be made according to the clinical context, trying to avoid possible complications and reaching the appropriate performance at lower costs.

Potential infection risk from thyroid radiation protection

OBJECTIVES

Thyroid shields that are worn for personal radiation protection in the operating room are often exposed above the sterile gown and are likely a bacterial source of wound infections. We would like to determine what bacteria may be present on the portion of the thyroid shield, which is facing the operative table.

METHODS

Community thyroid shields were collected from around the operative rooms. The shields were then cultured on the side, which faces the patient and operative table. The shields where then cleaned with a readily available cleaner and again cultured to evaluate the reduction of bacterial load. Samples were cultured on nonselective media for 72 hours.

RESULTS

Thirty-two total thyroid shields were cultured before and after cleaning. Before cleaning, 81% of thyroid shields grew out at least 1 type of bacteria with 90% being coagulase negative staphylococcus. Postcleaning culturable contamination was reduced by 70% (P < 0.05).

CONCLUSIONS

The thyroid shield that is often visible above the neckline is contaminated with strains of bacteria that are commonly implicated in postoperative infections. Cleaning the thyroid shield with readily available cleaners can significantly reduce the bacterial burden as detectable by culture. Based on the primary research question, this article is a basic science article.

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.

A survey on oral care practices for ventilator-assisted patients in intensive care units in 3A hospitals of mainland China

Oral hygiene is a critical element of patient care, particularly among patients who need ventilator-assisted equipment. The objective of this study was to explore the current status of oral care practices, attitudes, education and knowledge among intensive care unit (ICU) nurses caring for ventilator-assisted patients in 3A hospitals in mainland China. To achieve this aim, an 18-item self-assessment questionnaire was mailed to head ICU nurses in 189 Grade 3A hospitals. Additional data were collected through in-person interviews at 38 ICUs throughout Sichuan, Shanxi, Jiangsu provinces, as well as Chongqing and Beijing. We found that most ICUs conducted oral examinations at patient admission, and that this care was largely provided by nurses. The most common oral care methods were foam swabs and mouth rinse containing antibiotics or disinfectants. Although the majority of ICUs provided continuing training for oral care, and most training was conducted by head nurses, the content and scope of training were not consistent among the hospitals in the study. The most popular sources of oral care knowledge were academic journals, Internet and professional books. Overall, it is clear that an evidence-based oral care standard manual is urgently needed for oral practice in ICUs in mainland China.

Device-Related Infections in Critically Ill Patients. Part II: Prevention of Ventilator-Associated Pneumonia and Urinary Tract Infections

Device utilization in critically ill patients is responsible for a high risk of complications such as catheter-related bloodstream infections (CRBSI), ventilator-associated pneumonia (VAP) and urinary tract infections (UTI). In this article we will review the current status of data regarding the prevention of VAP and UTI. The results of the more recent (5 years) randomized controlled trials are reviewed and discussed. General recommendations include staff education and use of a surveillance program with a restrictive antibiotic policy. Adequate time must be allowed for hand washing and barrier precautions must always be used during device manipulation. Specific measures for VAP prevention are: 1) use of multi-use, closed-system suction catheters; 2) no routine change of the breathing circuit; 3) lubrication of the cuff of the endotracheal tube (ET) with a water-soluble gel; 4) maintenance of patient in semi-recumbent position to improve chest physiotherapy in intubated patients. Specific measures for UTI prevention include: 1) use of a catheter-valve instead of a standard drainage system; 2) use of a silver-alloy, hydro gel-coated latex urinary catheter instead of uncoated catheters. Biofilm represents a new variable: the capacity of bacteria to organize a biofilm on a device surface can explain the difficulty in preventing and eradicating an infection in a critically ill patient. More clinical trials are needed to verify the efficacy of prevention measures of ICU infections.

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.

Comparison of two different types of heat and moisture exchangers in ventilated patients

Study Objectives:

To compare the efficacy of two different types of Heat and Moisture Exchangers (HME filters) in reducing transmission of infection from the patient to ventilator and vice versa and also its cost effectiveness.

Design:

Randomized, controlled, double blind, prospective study.

Patients and Methods:

60 patients admitted to the ICU from May 1, 2007 to July 31, 2007 of either sex, age ranging between 20 and 60 years, requiring mechanical ventilation were screened for the study. Following intubation of the patients, the HME device was attached to the breathing circuit randomly by the chit-in-a box method. The patients were divided into two groups according to the HME filters attached.

Results:

Both the groups were comparable with respect to age and sex ratio. In Type A HME filters, 80% showed growth on the patient end within 24 h and in 27% filters, culture was positive both on the patient and the machine ends. The organisms detected were Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa and co-related with the endotracheal aspirate culture. After 48 h, 87% filters developed organisms on the patient end, whereas 64% filters were culture positive both on the patient and the machine end. In Type B HME filters, 70% showed growth on patient's end after 24 h. Organisms detected were S. aureus, E. coli, P. aeruginosa and Acinetobacter. Thirty percent of filters were culture negative on both the patient and machine ends. No growth was found on the machine end in any of the filters after 24 h. After 48 h, 73% of the filters had microbial growth on the patient end, whereas only 3% filters had growth (S. aureus) on the machine end only. Seven percent had growth on both the patient as well as the machine ends. The microorganisms detected on the HME filters co-related with the endotracheal aspirate cultures.

Conclusion:

HME filter Type B (study group) was significantly better in reducing contamination of ventilator from the patient as compared to Type A (control group), which was routinely used in our ICU. Type B filter was found to be effective for at least 48 h. This study can also be applied to patients coming to emergency department (ED) and requiring emergency surgery and postoperative ventilation; and trauma patients like flail chest, head injury etc. requiring ventilatory support to prevent them from acquiring ventilator-associated pneumonia (VAP).

Paradoxical ventilator associated pneumonia incidences among selective digestive decontamination studies versus other studies of mechanically ventilated patients: benchmarking the evidence base

Introduction

Selective digestive decontamination (SDD) appears to have a more compelling evidence base than non-antimicrobial methods for the prevention of ventilator associated pneumonia (VAP). However, the striking variability in ventilator associated pneumonia-incidence proportion (VAP-IP) among the SDD studies remains unexplained and a postulated contextual effect remains untested for.

Methods

Nine reviews were used to source 45 observational (benchmark) groups and 137 component (control and intervention) groups of studies of SDD and studies of three non-antimicrobial methods of VAP prevention. The logit VAP-IP data were summarized by meta-analysis using random effects methods and the associated heterogeneity (tau²) was measured. As group level predictors of logit VAP-IP, the mode of VAP diagnosis, proportion of trauma admissions, the proportion receiving prolonged ventilation and the intervention method under study were examined in meta-regression models containing the benchmark groups together with either the control (models 1 to 3) or intervention (models 4 to 6) groups of the prevention studies.

Results

The VAP-IP benchmark derived here is 22.1% (95% confidence interval; 95% CI; 19.2 to 25.5; tau² 0.34) whereas the mean VAP-IP of control groups from studies of SDD and of non-antimicrobial methods, is 35.7 (29.7 to 41.8; tau² 0.63) versus 20.4 (17.2 to 24.0; tau² 0.41), respectively (P < 0.001). The disparity between the benchmark groups and the control groups of the SDD studies, which was most apparent for the highest quality studies, could not be explained in the meta-regression models after adjusting for various group level factors. The mean VAP-IP (95% CI) of intervention groups is 16.0 (12.6 to 20.3; tau² 0.59) and 17.1 (14.2 to 20.3; tau² 0.35) for SDD studies versus studies of non-antimicrobial methods, respectively.

Conclusions

The VAP-IP among the intervention groups within the SDD evidence base is less variable and more similar to the benchmark than among the control groups. These paradoxical observations cannot readily be explained. The interpretation of the SDD evidence base cannot proceed without further consideration of this contextual effect.

Heat and moisture exchangers and breathing system filters: their use in anaesthesia and intensive care. Part 2 - practical use, including problems, and their use with paediatric patients

Heat and moisture exchangers and breathing system filters are intended to replace the normal warming, humidifying and filtering functions of the upper airways. The first part of this review considered the history, principles of operation and efficiency of these devices. The aim of this part of the review is to summarise recent guidelines on the use of these devices and outline the problems that can occur. In particular, the effect of these devices on gas analysis, dead space, resistance to gas flow and blockage of the breathing system is considered. In children, it is important to consider the addition of dead space and resistance to gas flow. A body weight of 2.5 kg is probably the lower weight limit for use with heat and moisture exchangers, and 3 kg for filters. The resistance to gas flow of a heat- and moisture-exchanging filter added to a Mapleson F breathing system can cause a delay in the induction of anaesthesia.

Heated humidification versus heat and moisture exchangers for ventilated adults and children

BACKGROUND

Humidification by artificial means must be provided when the upper airway is bypassed during mechanical ventilation. Heated humidification (HH) and heat and moisture exchangers (HME) are the most commonly used types of artificial humidification in this situation.

OBJECTIVES

To determine whether HHs or HMEs are more effective in preventing mortality and other complications in people who are mechanically ventilated.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials (The Cochrane Library 2010, Issue 4) and MEDLINE, EMBASE and CINAHL (January, 2010) to identify relevant randomized controlled trials (RCTs).

SELECTION CRITERIA

We included RCTs comparing heat and moisture exchangers (HMEs) to heated humidifiers (HHs) in mechanically ventilated adults and children. We included randomized crossover studies.

DATA COLLECTION AND ANALYSIS

We assessed the quality of each study and extracted the relevant data. Where appropriate, results from relevant studies were meta-analysed for individual outcomes.

MAIN RESULTS

We included 33 trials with 2833 participants, 25 studies were parallel group design (n = 2710) and eight crossover design (n = 123). Only three included studies reported data for infants or children. There was no overall effect on artificial airway occlusion, mortality, pneumonia, or respiratory complications; however, the PaCO(2) and minute ventilation were increased when HMEs were compared to HHs and body temperature was lower. The cost of HMEs was lower in all studies that reported this outcome. There was some evidence that hydrophobic HMEs may reduce the risk of pneumonia and that blockages of artificial airways may be increased with the use of HMEs in certain subgroups of patients.

AUTHORS' CONCLUSIONS

There is little evidence of an overall difference between HMEs and HHs. However, hydrophobic HMEs may reduce the risk of pneumonia and the use of an HME may increase artificial airway occlusion in certain subgroups of patients. Therefore, HMEs may not be suitable for patients with limited respiratory reserve or prone to airway blockage. Further research is needed relating to hydrophobic versus hygroscopic HMEs and the use of HMEs in the paediatric and neonatal populations. As the design of HMEs evolves, evaluation of new generation HMEs will also need to be undertaken.

Humidification performance of 48 passive airway humidifiers: comparison with manufacturer data

INTRODUCTION

Heat and moisture exchangers (HMEs) are increasingly used in the ICU for gas conditioning during mechanical ventilation. Independent assessments of the humidification performance of HMEs are scarce. The aim of the present study was thus to assess the humidification performance of a large number of adult HMEs.

METHOD

We assessed 48 devices using a bench test apparatus that simulated real-life physiologic ventilation conditions. Thirty-two devices were described by the manufacturers as HMEs, and 16 were described as antibacterial filters. The test apparatus provided expiratory gases with an absolute humidity (AH) of 35 mg H(2)O/L. The AH of inspired gases was measured after steady state using the psychrometric method. We performed three hygrometric measurements for each device, measured their resistance, and compared our results with the manufacturer data.

RESULTS

Of the 32 HMEs tested, only 37.5% performed well (>or= 30 mg H(2)O/L), while 25% performed poorly (< 25 mg H(2)O/L). The mean difference (+/- SD) between our measurements and the manufacturer data was 3.0 +/- 2.7 mg H(2)O/L for devices described as HMEs (maximum, 8.9 mg H(2)O/L) [p = 0.0001], while the mean difference for 36% of the HMEs was > 4 mg H(2)O/L. The mean difference for the antibacterial filters was 0.2 +/- 1.4 mg H(2)O/L. The mean resistance of all the tested devices was 2.17 +/- 0.70 cm H(2)O/L/s.

CONCLUSIONS

Several HMEs performed poorly and should not be used as HMEs. The values determined by independent assessments may be lower than the manufacturer data. Describing a device as an HME does not guarantee that it provides adequate humidification. The performance of HMEs must be verified by independent assessment.

Which regions of the operating gown should be considered most sterile?

Various guidelines have been proposed regarding which portions of a surgical gown may be considered sterile. Unfortunately, the validity of these recommendations has not been definitively established. We therefore evaluated gown sterility after major spinal surgery to assess the legitimacy of these guidelines. We used sterile culture swabs to obtain samples of gown fronts at 6-inch increments and at the elbow creases of 50 gowns at the end of 29 spinal operations. Another 50 gowns were swabbed immediately after they were applied to serve as negative controls. Bacterial growth was assessed using semiquantitative plating techniques on a nonselective, broad-spectrum media. Contamination was observed at all locations of the gown with rates ranging from 6% to 48%. Compared with the negative controls, the contamination rates were greater at levels 24 inches or less and 48 inches or more relative to the ground and at the elbow creases. The section between the chest and operative field had the lowest contamination rates. Based on these results, we consider the region between the chest and operative field to be the most sterile and any contact with the gown outside this area, including the elbow creases, should be avoided to reduce the risk of infection.

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.

Humidification policies for mechanically ventilated intensive care patients and prevention of ventilator-associated pneumonia: a systematic review of randomized controlled trials

The Dutch Working Party on Infection Prevention (WIP) aimed to determine whether certain humidification policies are better than others in terms of prevention of ventilator-associated pneumonia (VAP) in mechanically ventilated intensive care unit (ICU) patients. Publications were retrieved by a systematic search of Medline and the Cochrane Library up to February 2006. All (quasi-) randomized trials and systematic reviews/meta-analyses comparing humidification methods in ventilated ICU patients were selected. Two reviewers independently assessed trial quality and extracted data. If the data was incomplete, clarification was sought from original authors and used to calculate the relative risk of VAP. Data for VAP were combined in the analysis, where appropriate, using a random-effects model. Ten trials were included in the review. In general, the quality of the trials and the way they were reported were unsatisfactory. The results did not show any benefit from specific humidification techniques in terms of reducing VAP. WIP do not recommend either passive or active humidifiers to prevent VAP, nor the type of passive humidifiers to be used. Regarding active humidification, WIP recommends using heated wire circuits. This is due to the theoretical consideration that less condensate reduces colonization and subsequent risk of spread throughout an ICU when condensate is removed.

Ventilator-associated pneumonia using a heated humidifier or a heat and moisture exchanger: a randomized controlled trial [ISRCTN88724583]

INTRODUCTION

Some guidelines to prevent ventilator-associated pneumonia (VAP) do not establish a recommendation for the preferential use of either heat and moisture exchangers (HMEs) or heated humidifiers (HHs), while other guidelines clearly advocate the use of HMEs. The aim of this study was to determine the incidence of VAP associated with HHs or HMEs.

METHODS

A randomized study was conducted in the intensive care unit of a university hospital involving patients expected to require mechanical ventilation for >5 days. Patients were assigned to two groups; one group received HH and the other group received HME. Tracheal aspirate samples were obtained on endotracheal intubation, then twice a week, and finally on extubation, in order to diagnose VAP. Throat swabs were taken on admission to the intensive care unit, then twice a week, and finally at discharge from the intensive care unit in order to classify VAP as primary endogenous, secondary endogenous, or exogenous.

RESULTS

A total of 120 patients were assigned to HMEs (60 patients) and HHs (60 patients); 16 patients received mechanical ventilation for less than five days and were excluded from the analysis. Data analysis of the remaining 104 patients (53 HMEs and 51 HHs) showed no significant differences between groups regarding sex, age, Acute Physiology and Chronic Health Evaluation II score, pre-VAP use of antibiotics, days on mechanical ventilation, and diagnosis group. VAP was found in eight of 51 (15.69%) patients in the HH group and in 21 of 53 (39.62%) patients in the HME group (P = 0.006). The median time free of VAP was 20 days (95% confidence interval, 13.34-26.66) for the HH group and was 42 days (95% confidence interval, 35.62-48.37) for the HME group (P <0.001). Cox regression analysis showed the HME as a risk factor for VAP (hazard rate, 16.2; 95% confidence interval, 4.54-58.04; P < 0.001).

CONCLUSION

The patients mechanically ventilated during more than 5 days developed a lower incidence of VAP with a heated humidifier than heat and moisture exchanger.

Ventilator-associated pneumonia: diagnosis, treatment, and prevention

While critically ill patients experience a life-threatening illness, they commonly contract ventilator-associated pneumonia. This nosocomial infection increases morbidity and likely mortality as well as the cost of health care. This article reviews the literature with regard to diagnosis, treatment, and prevention. It provides conclusions that can be implemented in practice as well as an algorithm for the bedside clinician and also focuses on the controversies with regard to diagnostic tools and approaches, treatment plans, and prevention strategies.

Under-humidification and over-humidification during moderate induced hypothermia with usual devices

OBJECTIVE

In mechanically ventilated patients with induced hypothermia, the efficacy of heat and moisture exchangers and heated humidifiers to adequately humidify the airway is poorly known. The aim of the study was to assess the efficacy of different humidification devices during moderate hypothermia.

DESIGN

Prospective, cross-over randomized study.

SETTINGS

Medical Intensive Care Unit in a University Hospital.

PATIENTS AND PARTICIPANTS

Nine adult patients hospitalized after cardiac arrest in whom moderate hypothermia was induced (33 degrees C for 24[Symbol: see text]h).

INTERVENTIONS

Patients were ventilated at admission (period designated "normothermia") with a heat and moisture exchanger, and were randomly ventilated during hypothermia with a heat and moisture exchanger, a heated humidifier, and an active heat and moisture exchanger.

MEASUREMENTS AND RESULTS

Core temperature, inspired and expired gas absolute and relative humidity were measured. Each system demonstrated limitations in its ability to humidify gases in the specific situation of hypothermia. Performances of heat and moisture exchangers were closely correlated to core temperature (r (2)[Symbol: see text]=[Symbol: see text]0.84). During hypothermia, heat and moisture exchangers led to major under-humidification, with absolute humidity below 25[Symbol: see text]mgH(2)O/l. The active heat and moisture exchanger slightly improved humidification. Heated humidifiers were mostly adequate but led to over-humidification in some patients, with inspiratory absolute humidity higher than maximal water content at 33 degrees C with a positive balance between inspiratory and expiratory water content.

CONCLUSIONS

These results suggest that in the case of moderate hypothermia, heat and moisture exchangers should be used cautiously and that heated humidifiers may lead to over-humidification with the currently recommended settings.

Double-heater-wire circuits and heat-and-moisture exchangers and the risk of ventilator-associated pneumonia

OBJECTIVE

To compare the incidence of ventilator-associated pneumonia (VAP) in patients ventilated in intensive care by means of circuits humidified with a hygroscopic heat-and-moisture exchanger with a bacterial viral filter (HME) or hot-water humidification with a heater wire in both inspiratory and expiratory circuit limbs (DHW) or the inspiratory limb only (SHW).

DESIGN

A prospective, randomized trial.

SETTING

A metropolitan teaching hospital's general intensive care unit.

PATIENTS

Three hundred eighty-one patients requiring a minimum period of mechanical ventilation of 48 hrs.

INTERVENTIONS

Patients were randomized to humidification with use of an HME (n=190), SHW (n=94), or DHW (n=97).

MEASUREMENTS AND MAIN RESULTS

Study end points were VAP diagnosed on the basis of Clinical Pulmonary Infection Score (CPIS) (), HME resistance after 24 hrs of use, endotracheal tube resistance, and HME use per patient. VAP occurred with similar frequency in all groups (13%, HME; 14%, DHW; 10%, SHW; p=0.61) and was predicted only by current smoking (adjusted odds ratio [AOR], 2.1; 95% confidence interval [CI], 1.1-3.9; p=.03) and ventilation days (AOR, 1.05; 95% CI, 1.0-1.2; p=.001); VAP was less likely for patients with an admission diagnosis of pneumonia (AOR, 0.40; 95% CI, 0.4-0.2; p=.04). HME resistance after 24 hrs of use measured at a gas flow of 50 L/min was 0.9 cm H2O (0.4-2.9). Endotracheal tube resistance was similar for all three groups (16-19 cm H2O min/L; p=.2), as were suction frequency, secretion thickness, and blood on suctioning (p=.32, p=.06, and p=.34, respectively). The HME use per patient per day was 1.13.

CONCLUSIONS

Humidification technique does not influence either VAP incidence or secretion characteristics, but HMEs may have air-flow resistance higher than manufacturer specifications after 24 hrs of use.

Clinical and economic consequences of ventilator-associated pneumonia: a systematic review

BACKGROUND

Ventilator-associated pneumonia (VAP) is the most common nosocomial infection in critically ill patients. The clinical and economic consequences of VAP are unclear, with a broad range of values reported in the literature

OBJECTIVE

To perform a systematic review to determine the incidence of VAP and its attributable mortality rate, length of stay, and costs.

DATA SOURCE

Computerized PUBMED and MEDLINE search supplemented by manual searches for relevant articles, limited to articles published after 1990.

STUDY SELECTION

English-language observational studies and randomized trials that provided data on the incidence of VAP were included. Matched cohort studies were included for calculation of attributable mortality rate and length of stay.

DATA EXTRACTION

Data were extracted on patient population, diagnostic criteria for VAP, incidence, outcome, type of intensive care unit, and study design.

DATA SYNTHESIS

The cumulative incidence of VAP was calculated by combining the results of several studies using standard formulas for combining proportions, in which the weighted average and variance are calculated. Results from studies comparing intensive care unit and hospital mortality due to VAP, additional length of stay, and additional days of mechanical ventilation were pooled using a random effects model, with assessment of heterogeneity.

RESULTS

Our findings indicate a) between 10% and 20% of patients receiving >48 hrs of mechanical ventilation will develop VAP; b) critically ill patients who develop VAP appear to be twice as likely to die compared with similar patients without VAP (pooled odds ratio, 2.03; 95% confidence interval, 1.16-3.56); c) patients with VAP have significantly longer intensive care unit lengths of stay (mean = 6.10 days; 95% confidence interval, 5.32-6.87 days); and d) patients who develop VAP incur > or = USD $10,019 in additional hospital costs.

CONCLUSIONS

Ventilator-associated pneumonia occurs in a considerable proportion of patients undergoing mechanical ventilation and is associated with substantial morbidity, a two-fold mortality rate, and excess cost. Given these findings, strategies that effectively prevent VAP are urgently needed.

Impact of Humidification Systems on Ventilator-associated Pneumonia

RATIONALE AND OBJECTIVES

The respective influence on the incidence of ventilator-associated pneumonia of currently available systems used for warming and humidifying the gases delivered to mechanically ventilated patients, that is, heated humidifiers and heat and moisture exchanger filters, remains controversial.

METHODS

We addressed this question in a multicenter randomized study comparing heated humidifiers (with heated circuits) and filters in an unselected population of 369 intensive care patients receiving mechanical ventilation for more than 48 h.

MAIN MEASUREMENTS AND RESULTS

The diagnosis of pneumonia was confirmed according to strict microbiologic criteria. There was no difference in pneumonia rate between the two groups (53 of 184 [28.8%] versus 47 of 185 [25.4%] for humidifiers versus filters; p = 0.48), or in the incidence density of pneumonia (27.4/1,000 ventilatory days versus 25.3/1,000 ventilatory days for humidifiers versus filters; p = 0.76). The mean duration of mechanical ventilation did not differ between the two groups (14.9 +/- 15.1 versus 13.5 +/- 16.3 days for humidifiers versus filters, p = 0.36). Endotracheal tube occlusion occurred, respectively, in five patients and one patient in the humidifier and filter groups (p = 0.12). Intensive care mortality was identical in the two groups (about 33%).

CONCLUSION

These results suggest that both heated humidifiers and heat and moisture exchanger filters can be used with no significant impact on the incidence of ventilator-associated pneumonia and that other criteria may justify their choice.

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.

Influence of Ambient and Ventilator Output Temperatures on Performance of Heated-Wire Humidifiers

Although heated humidifiers are considered the most efficient humidification devices for mechanical ventilation, endotracheal tube occlusion caused by dry secretions has been reported with heated-wire humidifiers. We tested the hypothesis that inlet chamber temperature, influenced by ambient air and ventilator output temperatures, may affect humidifier performance, as assessed by hygrometry. Hygrometry was measured with three different humidifiers under several conditions, varying ambient air temperatures (high, 28-30 degrees C; and normal, 22-24 degrees C), ventilators with different gas temperatures, and two VE levels. Clinical measurements were performed to confirm bench measurements. Humidifier performance was strongly correlated with inlet chamber temperature in both the bench (p < 0.0001, r2 = 0.93) and the clinical study. With unfavorable conditions, absolute humidity of inspired gas was much lower than recommended (approximately 20 mg H2O/L). Performance was improved by specific settings or new compensatory algorithms. Hygrometry could be evaluated from condensation on the wall chamber only when ambient air temperature was normal but not with high air temperature. An increase in inlet chamber temperature induced by high ambient temperature markedly reduces the performance of heated-wire humidifiers, leading to a risk of endotracheal tube occlusion. Such systems should be avoided in these conditions unless automatic compensation algorithms are used.

Einfluss von aktiver und passiver Befeuchtung auf die beatmungsassoziierte nosokomiale Pneumonie

STUDY OBJECTIVE

Airway humidification of ventilated patients in an intensive care unit may be established by heated humidifying systems (active) or by the means of a (passive) heat and moisture exchange filter (HMEF). There is a controversial discussion about the influence of the type of humidification on the rate of ventilator-associated pneumonia (VAP). Among 3,585 patients both methods were tested over a period of 21 months in an open, non-randomized cohort study. The aim of the investigation was to compare the incidence of VAP caused by a change of humidification strategy.

METHOD

All patients in a 16-bed surgical intensive care unit who required mechanical ventilation, were included. In the first period (period AB) 1,887 cases were handled with a heated humidifier. During the second period (period PB) 1,698 patients were treated using a HMEF. Infection control was established according to the national Infection Surveillance Program (KISS) based on the CDC criteria for VAP.

RESULTS

During the period of 42 months, 99 cases of VAP were reported. The incidence for VAP was found to be 13.5 (AB) and 9.6 (PB) per 1,000 ventilator days, a rate of 32.3 and 22.4 VAP per 1,000 patients, respectively. The rate of VAP among the groups ( p=0.068) and the incidence of VAP per 1,000 ventilator days ( p=0.089) only just failed to reach a significant level, but in the group of patients requiring mechanical ventilation for more than 2 days, the difference did reach statistical significance ( p=0.012).

CONCLUSION

Our results showed that the rate of VAP could be significantly reduced by changing the strategy from active to passive humidification devices, especially concerning patients requiring long-term respirator therapy. A more physiological humidification and a reduced number of airway manipulations are discussed as a possible explanation.

Humidification in the long-term ventilated patient; a systematic review

This review aims to identify which method of humidification is most effective in Intensive Care patients intubated and ventilated for longer than 48hours with regard to the prevention of tracheal tube occlusion and the incidence of ventilator associated pneumonia (VAP). The Cochrane Library, Medline, CINAHL and Embase databases were searched for randomised controlled trials (RCTs) that compared any type of heated water humidifier with any type of heat moisture exchange (HME) filter. Two prospective RCTs met the inclusion criteria and were available to include in the main body of the review. These studies showed no difference in the rate of tracheal tube occlusion between devices but a significantly higher level of VAP with the heated humidifier. However, many potential studies were excluded from the review due to insufficient data within the published articles, and both included studies were undertaken in USA and excluded high risk patients. This limits the wide applicability of findings.

Long-term mechanical ventilation with hygroscopic heat and moisture exchangers used for 48 hours: a prospective clinical, hygrometric, and bacteriologic study

OBJECTIVE

To determine whether use of a hygroscopic heat and moisture exchanger (HME) for 48 hrs without change affects its efficiency and the level of bacterial colonization in long-term mechanically ventilated medical intensive care unit patients.

DESIGN

Prospective, randomized clinical study evaluating two hygroscopic HMEs.

SETTING

Medical intensive care unit at a university teaching hospital.

PATIENTS

Long-term mechanically ventilated medical intensive care unit patients, including chronic obstructive pulmonary disease patients.

INTERVENTIONS

Patients were randomly allocated to one of the two HMEs studied (Hygrolife and EdithFlex) and changed every 48 hrs. Devices in both groups could be changed if hygrometric measurements indicated insufficient humidity delivery.

MEASUREMENTS AND MAIN RESULTS

Daily measurements of inspired gas temperature and relative and absolute humidity. In addition, cultures of tracheal aspirations and both patient and ventilator sides of the device were performed after 48 hrs of use. Ventilatory variables and clinical indicators of efficient humidification were also recorded. Prolonged use of both HMEs was safe and efficient (no tracheal tube occlusion occurred). Mean duration of mechanical ventilation was 20 days. Both clinical indicators and hygrometric measurements showed that both devices performed well during 48 hrs. Absolute humidity with EdithFlex was significantly higher on day 0 and day 1 than with Hygrolife. Absolute humidity measured in chronic obstructive pulmonary disease patients was identical to that measured in the rest of the study population. Tracheal colonization and HME colonization were similar with both HMEs. Bacterial contamination of the ventilator side of both devices was markedly low.

CONCLUSIONS

These two purely hygroscopic HMEs provided safe and efficient humidification during a 48-hr period of use in long-term mechanically ventilated medical intensive care unit patients, including chronic obstructive pulmonary disease patients. In addition, they maintained ventilatory circuits clean, despite the absence of filtering media. The cost of mechanical ventilation is consequently reduced.

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.

Ventilator-associated pneumonia. Prevention, diagnosis, and therapy

Ventilator-associated pneumonia remains the nosocomial ICU infection of greatest concern. The authors have summarized the clinical trials that have assessed specific strategies to prevent VAP and the current controversies regarding the diagnosis and therapeutic approach to this condition. Improvements in care of patients who are at risk for or who have developed VAP will depend on the judicious application of this information for individual patients.

Tracheostomy management in the chronically ventilated patient

Tracheotomy is a fundamentally important technique for managing patients who require long-term mechanical ventilation. Appropriate application of tracheotomy requires a skilled approach for timing the procedure, selecting the appropriate tracheostomy tube appliance, caring for the artificial airway once it is in place, and assisting patients with their specialized needs, such as articulated speech, airway humidification, and oral nutrition. Preparing patients for airway decannulation after they have weaned from mechanical ventilation requires a similar level of skill and attention to detail.

Association between implementation of CDC recommendations and ventilator-associated pneumonia at selected US hospitals

BACKGROUND

To assess whether selected recommendations in the Centers for Disease Control and Prevention "Guideline for Prevention of Nosocomial Pneumonia" were being implemented and having an impact on the occurrence of ventilator-associated pneumonia (VAP) at US hospitals, we surveyed hospitals participating in the National Nosocomial Infections Surveillance (NNIS) system.

METHODS

We mailed a questionnaire to the infection control practitioner of each NNIS hospital in 1995 and used data from the NNIS system to calculate annual rates of VAP.

RESULTS

Of the 188 hospitals surveyed, 179 (95%) returned completed questionnaires. Of these, 175 (98%) had implemented the recommended change of mechanical-ventilator breathing circuits at 48-hour or greater intervals. Of 110 hospitals using the hygroscopic condenser-humidifiers or heat-moisture exchangers with ventilators, 102 (93%) changed the hygroscopic condenser-humidifiers or heat-moisture exchangers routinely, and of 98 hospitals using bubbling humidifiers, 96 (98%) used sterile water to fill these humidifiers. Other practices for which the guideline provides no recommendation and their frequency of use by NNIS hospitals include use of hygroscopic condenser-humidifiers or heat-moisture exchangers (110/179 [61%]) and use of bacterial filters in anesthesia machines (128/171 [61%]). There was a significant decrease in the VAP rate from 1987 to 1998.

CONCLUSION

Most NNIS hospitals had implemented selected recommendations in the Centers for Disease Control and Prevention "Guideline for Prevention of Nosocomial Pneumonia" before the final publication of the revised guideline. Further studies are needed to assess the impact of these recommendations on the occurrence of VAP.

A new device for 100 per cent humidification of inspired air

STATEMENT OF FINDINGS: A new humidifier for use during mechanical ventilation in endotracheally intubated patients is described and tested. The humidifier is based on a heat-moisture exchanger, which absorbs the expired heat and moisture and releases it into the inspired air. External heat and water are then added at the patient side of the heat-moisture exchanger, so that the inspired gas should reach 100% humidity (44 mg/l) at 37 degrees C. In bench tests using constant and decelerating inspiratory flow and minute volumes of 3-25 l the device gave an absolute humidity of 41-44 mg/l, and it reduced the amount of water consumed in eight mechanically ventilated patients compared with a conventional active humidifier. During a 24-h test period there was no water condensation in the ventilator tubing with the new device.

Therapy for ventilator-associated pneumonia

Pneumonia is a serious complication of mechanical ventilation. Pneumonia occurs despite the best efforts at prevention. Multiple methods available to prevent ventilator-associated pneumonia are reviewed, and ventilation-associated pneumonia (VAP) is divided into early versus late onset. The authors discuss the organisms associated with each of these situations, the empiric antibiotic choices, and specific issues related to antibiotic therapy such as resistance, pharmcodynamics, tissue penetration, and types of modifications necessary in empiric choice when the cause of VAP is identified.

Mechanical effects of heat-moisture exchangers in ventilated patients

Although they represent a valuable alternative to heated humidifiers, artificial noses have unfavourable mechanical effects. Most important of these is the increase in dead space, with consequent increase in the ventilation requirement. Also, artificial noses increase the inspiratory and expiratory resistance of the apparatus, and may mildly increase intrinsic positive end-expiratory pressure. The significance of these effects depends on the design and function of the artificial nose. The pure humidifying function results in just a moderate increase in dead space and resistance of the apparatus, whereas the combination of a filtering function with the humidifying function may critically increase the volume and the resistance of the artificial nose, especially when a mechanical filter is used. The increase in the inspiratory load of ventilation that is imposed by artificial noses, which is particularly significant for the combined heat-moisture exchanger filters, should be compensated for by an increase either in ventilator output or in patient's work of breathing. Although both approaches can be tolerated by most patients, some exceptions should be considered. The increased pressure and volume that are required to compensate for the artificial nose application increase the risk of barotrauma and volutrauma in those patients who have the most severe alterations in respiratory mechanics. Moreover, those patients who have very limited respiratory reserve may not be able to compensate for the inspiratory work imposed by an artificial nose. When we choose an artificial nose, we should take into account the volume and resistance of the available devices. We should also consider the mechanical effects of the artificial noses when setting mechanical ventilation and when assessing a patient's ability to breathe spontaneously.