Mechanical Ventilation with or without 7-Day Circuit Changes

A Randomized Controlled Trial

  1. Marin H. Kollef;
  2. Steven D. Shapiro;
  3. Victoria J. Fraser;
  4. Patricia Silver;
  5. Denise M. Murphy;
  6. Ellen Trovillion;
  7. Mona L. Hearns;
  8. Rodger D. Richards;
  9. Lisa Cracchilo; and
  10. Linda Hossin
  1. From Washington University School of Medicine, Barnes Hospital, and Jewish Hospital, St. Louis, Missouri. Requests for Reprints: Marin H. Kollef, MD, Pulmonary and Critical Care Division, Washington University School of Medicine, Box 8052, 660 South Euclid Avenue, St. Louis, MO 63110. Acknowledgments: The authors thank Daniel P. Schuster, MD, for his review of the manuscript and Darnetta M. Baker, RRT, for her personal communication.
     
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    Abstract

    Objective: To determine whether a practice of not routinely changing ventilator circuits in patients who require prolonged mechanical ventilation is associated with an increased incidence of nosocomial pneumonia.

    Design: Randomized controlled trial.

    Setting: Intensive care units in two university-affiliated teaching hospitals.

    Patients: 300 patients admitted to an intensive care unit who required mechanical ventilation for more than 5 days.

    Intervention: Patients were randomly assigned to receive either no routine ventilator circuit changes or circuit changes every 7 days.

    Measurements: The primary outcome measure was the incidence of ventilator-associated pneumonia. Other outcome measures included duration of mechanical ventilation, length of hospital stay, and hospital mortality.

    Results: 147 patients were randomly assigned to receive no routine ventilator circuit changes, and 153 patients were randomly assigned to receive circuit changes every 7 days. The two groups were similar at the time of randomization with regard to demographic characteristics, intensive care unit admission diagnoses, and severity of illness. Ventilator-associated pneumonia was seen in 36 patients (24.5%) receiving no routine changes and in 44 patients (28.8%) receiving changes every 7 days (relative risk, 0.85 [95% CI, 0.55 to 1.17]). No statistically significant differences for hospital mortality, intensive care unit mortality, death during mechanical ventilation, death in patients with ventilator-associated pneumonia, or mortality directly attributed to ventilator-associated pneumonia were found between the two treatment groups (P ≥ 0.11). Patients receiving changes every 7 days had 247 circuit changes costing a total of $7410; patients receiving no routine changes had a total of 11 circuit changes costing $330.

    Conclusion: The elimination of routine ventilator circuit changes can reduce medical care costs without increasing the incidence of nosocomial pneumonia in patients who require prolonged mechanical ventilation.

    Nosocomial pneumonia is the leading cause of death among all hospital-acquired infections [1]. The estimated incidence of nosocomial pneumonia in intensive care units ranges from 10% to 65%; most studies [2-6] show case fatality rates of more than 20%. Ventilator-associated pneumonia specifically refers to nosocomial pneumonia that develops in a mechanically ventilated patient and that was not present at the time of airway intubation [7]. Various clinical risk factors have been associated with an increased incidence of ventilator-associated pneumonia, either because they predispose the patient to bacterial colonization of the oropharynx and stomach (for example, the administration of antacids or histamine-2-receptor antagonists) or because they facilitate aspiration of contaminated contents from these sites (for example, supine positioning) [1, 2, 8, 9].

    Craven and colleagues [10] first showed that the frequency of ventilator circuit changes also influences the incidence of ventilator-associated pneumonia. They found that changing circuits every 24 rather than every 48 hours was independently associated with the occurrence of nosocomial pneumonia [10]. This association has been attributed to increased manipulation of the patient, the endotracheal tube, and the ventilator circuit, which results in increased aspiration of contaminated tubing condensate or upper airway secretions [10, 11]. More recently, several groups of investigators have found that ventilator circuits can be used safely for more than 48 hours without increasing the incidence of nosocomial pneumonia [12-16]. However, because of limitations in the design of these studies and the small number of patients prospectively examined, the Centers for Disease Control and Prevention has given no clear recommendation for the maximum length of time that ventilator circuits can safely be left in place during prolonged mechanical ventilation [17]. This has resulted in the development of ambiguous guidelines about the frequency with which ventilator circuits should be changed [18, 19] and in a call for well-designed investigations to resolve this issue [20].

    We did a randomized, controlled trial to compare the effect and cost-efficacy of routine and no routine ventilator circuit changes in patients having prolonged mechanical ventilation. Our main goals were to determine 1) the incidence and outcome of ventilator-associated pneumonia in patients receiving scheduled ventilator circuit changes and 2) whether this incidence was increased in patients whose ventilator circuits remained unchanged.

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    Methods

    Study Location and Patients

    The study was conducted at two university-affiliated teaching hospitals: Barnes Hospital (900 beds) and Jewish Hospital (450 beds). During a 7-month period (June 1994 to December 1994), all patients receiving mechanical ventilation in the intensive care units of these hospitals (surgical, trauma, medical, cardiothoracic, and neurosurgical units at Barnes Hospital; surgical, medical, and cardiothoracic units at Jewish Hospital) were potentially eligible for this investigation. Patients were entered into the trial if they were older than 18 years and had received mechanical ventilation for more than 5 days. Mechanical ventilation for more than 5 days was predetermined, on the basis of our previous experience at these institutions [2, 21], to be necessary so that a more homogeneous cohort of patients requiring prolonged mechanical ventilation could be accrued.

    Patients were excluded if they were likely to be extubated within 24 hours of randomization, if they had transferred from other hospitals and had already received mechanical ventilation for more than 24 hours, if they had had lung transplantation, or if they had active hemoptysis. Barnes Hospital and Jewish Hospital share the same respiratory therapy and infection control departments. The study was approved by the Washington University School of Medicine Human Studies Committee and the Institutional Review Board of Jewish Hospital. Both waived the requirement for informed consent because this study was a quality assessment of two low-risk practices already in clinical use.

    Study Design

    Patients were randomly assigned to receive no routine ventilator circuit changes or circuit changes every 7 days within 24 hours of meeting eligibility criteria. A schedule of changing ventilator circuits every 7 days was selected on the basis of available clinical data [12-16] and our survey of 16 regional medical centers (DM Baker. Unpublished communication). Stratification according to hospital site was done before randomization to control for differences in patient populations and health care personnel. Randomization within each hospital was done using opaque, sealed envelopes, which were opened at the time each patient was enrolled in the study.

    For the purposes of this investigation, ventilator circuits were defined to include gas delivery tubing, humidifier water reservoirs, water traps, and medication delivery devices (such as metered-dose inhaler chambers or adapters). Ventilator circuits could be changed at any time, at the discretion of individual care providers (physicians, nurses, and respiratory therapists), secondary to a mechanical failure of the ventilator circuit (such as an air leak) or visible soil (such as that resulting from hemoptysis or aspirated emesis). Scheduled ventilator circuit changes were done during the evening or night shifts to minimize the identification of individual patient group assignments to blinded investigators. All nonscheduled circuit changes were done when an appropriate indication for the circuit change (that is, a mechanical defect or soil) was identified. Patients transferred to the operating room for a surgical procedure (such as tracheotomy) or to diagnostic radiology received the same mechanical ventilator and circuit when they returned to the intensive care unit.

    The ventilators used for this study included Siemens Servo 900C (Siemens-Elema Ventilator Systems, Schaumburg, Illinois), Puritan-Bennett 700 Series (Puritan-Bennett Corporation, Carlsbad, California), and Bird 8400 Series ventilators (Bird Products Corporation, Palm Springs, California). All ventilators were equipped with wick-type humidifiers (Concha Therm III Plus, Hudson Respiratory Care, Inc., Temecula, California) filled with sterile irrigation water. All ventilator circuits were disposable (Hudson Respiratory Care, Inc., model 1613) and equipped with Y connectors. Each ventilator circuit had an attached trap for the collection of tubing condensate (Marquest Medical Products, Inc., Englewood, Colorado). As per our standard procedure, all ventilator circuits were monitored at least every 2 hours and water traps were emptied when full.

    Data Collection

    For all study patients, the following characteristics were prospectively recorded by one of the investigators: age, sex, diagnosis at hospital admission, indication for mechanical ventilation, Premorbid Lifestyle score, the ratio of arterial blood oxygen tension to the concentration of inspired oxygen (PaO 2: FIO 2), severity of illness based on APACHE II (Acute Physiology and Chronic Health Evaluation [22]) scores, the Organ System Failure Index, and the occurrence of a witnessed aspiration event. Specific processes of medical care examined to assess risk factors for ventilator-associated pneumonia were the administration of antacids or histamine-2-receptor antagonists, pharmacologic aerosol treatments during mechanical ventilation (such as bronchodilators, antibiotics, and mucolytics), fiberoptic bronchoscopy, surgical tracheostomy, and the number of ventilator circuit changes done and the indications for those changes (scheduled according to the study protocol, soil, or mechanical defect).

    Two of the investigators made daily rounds in the intensive care units of each hospital to identify eligible patients. Patients entered into the study were prospectively followed for the occurrence of ventilator-associated pneumonia until they were successfully weaned from mechanical ventilation, were discharged from the hospital, or died. All patients suspected by these investigators of having ventilator-associated pneumonia were prospectively and independently reviewed by another investigator who was blinded to the patient's treatment group assignment. The diagnosis of ventilator-associated pneumonia was strictly based on the predetermined criteria described below. Patients could not be entered into the study more than once during the same hospitalization, and only the first episode of ventilator-associated pneumonia was evaluated.

    In addition to the occurrence of ventilator-associated pneumonia, secondary outcomes assessed included the length of hospitalization, the duration of mechanical ventilation, hospital mortality, and mortality directly attributed to ventilator-associated pneumonia. All study variables were recorded in data collection books maintained at each of the participating hospitals.

    Definitions

    All definitions were selected prospectively as part of the original study design. The Premorbid Lifestyle score was used as previously defined [23]: Zero indicated that the patient was employed without restriction; 1 indicated that the patient was independent, fully ambulatory, not employed, or employed with restriction; 2 indicated that the patient had restricted activities, could live alone and get out of the house to do basic necessities, or had severely limited exercise ability; 3 indicated that the patient was housebound, could not get out of the house unassisted, could not live alone, or could not do heavy chores; and 4 indicated that the patient was bed- or chairbound. We calculated APACHE II scores on the basis of clinical data available from the 24-hour period before study enrollment (day 5 of mechanical ventilation).

    The Organ System Failure Index was modified from that used by Rubin and coworkers [24]. One point was given for acquired dysfunction of each organ system. Renal dysfunction was defined as a twofold increase in baseline creatinine level or an absolute increase in creatinine level of 176.8 µmol/L (2.0 mg/dL); hepatic dysfunction was defined as an increase in total bilirubin level to more than 34.2 µmol/L [2.0 mg/dL]; and pulmonary dysfunction was defined as 1) a requirement for mechanical ventilation for a diagnosis of pneumonia, chronic obstructive pulmonary disease, asthma, or pulmonary edema [cardiogenic or noncardiogenic], 2) a PaO 2 of less than 60 mm Hg while receiving a fraction of inspired oxygen of 0.50 or more, or 3) the use of at least 10 cm of water of positive end-expiratory pressure. Hematologic dysfunction was defined as the presence of disseminated intravascular coagulation, a leukocyte count of less than 1000 cells/mm3 (1.0 × 109/L), or a platelet count of less than 75 × 103/mm3 (75 × 109/L); neurologic dysfunction was defined as new focal deficit (such as hemiparesis after cerebral infarction) or new generalized process (for example, seizures or coma). Gastrointestinal dysfunction was defined as gastrointestinal hemorrhage requiring transfusion, new ileus, or diarrhea lasting more than 24 hours and unrelated to previous bowel surgery; and cardiac dysfunction was defined as acute myocardial infarction, cardiac arrest, or the new onset of congestive heart failure.

    The diagnostic criteria for ventilator-associated pneumonia were modified from the work of Salata and colleagues [25]. Ventilator-associated pneumonia was defined as the occurrence of a new and persistent roentgenographic infiltrate along with either positive pleural or blood cultures for the organism recovered from the tracheal aspirate; roentgenographic cavitation; histopathologic evidence of pneumonia; or two of the following: fever, leukocytosis, and purulent tracheal aspirate. A new infiltrate was prospectively defined as one occurring more than 48 hours after the start of mechanical ventilation or within 48 hours of extubation. Persistence was defined as the infiltrate presenting on roentgenogram for at least 72 hours. Fever was defined as an increase in the core temperature of 1 °C or more and a core temperature of more than 38.3 °C. Leukocytosis was defined as a 25% increase in circulating leukocytes from baseline and a leukocyte count of more than 10 × 103/mm3 (10 × 109/L). Tracheal aspirates were considered purulent if a Gram stain showed more than 25 neutrophils per high-power field.

    Hospital mortality was defined as those patient deaths occurring in the initial hospital admission during which the patients were studied. Intensive care unit mortality was defined as any death occurring while a patient was in an intensive care unit. Mortality directly related to ventilator-associated pneumonia was predetermined to be present when a patient died during an episode of nosocomial pneumonia and the death could not be directly attributed to any other cause. Costs for ventilator circuit changes were based on 1995 costs of $30 per change, which included materials and the time of the respiratory therapists.

    Statistical Analysis

    We estimated sample size to provide 80% power to detect a 15% difference in the rate of occurrence of ventilator-associated pneumonia between the two groups. We used an α-error of 0.05 (two-tailed). On the basis of these assumptions, 134 patients were needed in each of the two study groups.

    All comparisons were unpaired and all tests of significance were two-tailed. Continuous variables were compared using the Student t-test for normally distributed variables and the Wilcoxon rank-sum test for non-normally distributed variables. The chi-square or Fisher exact test was used to compare categorical variables. The primary data analysis compared the incidence of ventilator-associated pneumonia between patients assigned to receive no routine ventilator circuit changes and patients assigned to receive circuit changes every 7 days. We confirmed the results of these tests, while controlling for specific patient characteristics (Table 1), using multiple logistic regression analysis [26] and a commercial statistical package [27].

    View this table:
    Table 1. Characteristics of Study Patients at the Time of Randomization and during the Study Period*

    A stepwise approach was used to enter new terms into the logistic regression model; 0.05 was set as the limit for the acceptance or removal of these terms. All potential confounding variables associated with ventilator-associated pneumonia were forced to enter the model regardless of statistical significance. Model overfitting was examined by evaluating the ratio of outcome events to the total number of independent variables in the final model, and specific testing for interactions between the individual variables was included in our analysis [28].

    Results of the logistic regression analysis are reported as adjusted odds ratios with 95% CIs. Relative risks and their 95% CIs were calculated using standard methods [29]. Values are expressed as the mean ±SD (continuous variables) or as a percentage of the group from which they were derived (categorical variables). All P values were two-tailed, and P values of 0.05 or less were considered to indicate statistical significance.

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    Results

    Patients

    Three hundred five consecutive patients who required mechanical ventilation for more than 5 days were enrolled in the study. Because five patients were randomized on two different occasions during one hospitalization, their second study admissions were excluded. Thus, 300 patients were analyzed, of whom 147 (49%) received no routine ventilator circuit changes and 153 (51%) received changes every 7 days. At the time of randomization, no statistically significant differences were found between the two treatment groups for age, sex, ethnicity, Premorbid Lifestyle scores, APACHE II scores, the number of acquired organ system derangements, history of previous intubation, the ratio of arterial blood oxygen tension to the concentration of inspired oxygen, and diagnostic category (for example, surgical or nonsurgical) (Table 1). Patients receiving circuit changes every 7 days did have a significantly higher rate of tracheostomy than patients receiving no routine changes (P < 0.01). The two treatment groups had similar administration rates for antacids (11.1% compared with 13.6%; P = 0.51), histamine-2-receptor antagonists (26.8% compared with 30.6%; P = 0.47), and sucralfate (56.9% compared with 48.3%; P = 0.14). The distribution of other risk factors for ventilator-associated pneumonia were also similar in both groups (Table 1). No statistical differences were shown between the two treatment groups in the 14 diagnostic categories examined (Table 2).

    View this table:
    Table 2. Study Location and Diagnostic Categories

    Ventilator-Associated Pneumonia

    Eighty of the 300 study patients (26.7%) developed ventilator-associated pneumonia. These patients were more likely than patients without ventilator-associated pneumonia to have a surgical diagnosis (75.0% compared with 57.7%; P = 0.006) and to have had a tracheostomy (42.5% compared with 20.9%; P < 0.001). No other substantial differences were found between patients with and patients without ventilator-associated pneumonia for the study variables examined (Table 1).

    In the group randomly assigned to receive no routine ventilator circuit changes, 36 patients (24.5%) developed ventilator-associated pneumonia; 44 patients (28.8%) randomly assigned to receive 7-day circuit changes developed ventilator-associated pneumonia (relative risk, 0.85 [95% CI, 0.55 to 1.17]). Similar results were found when the analysis was stratified according to hospital (Barnes Hospital: relative risk, 0.84 [CI, 0.56 to 1.27]; Jewish Hospital: relative risk, 0.94 [CI, 0.37 to 2.38]). When we used multiple logistic regression analysis to control for all relevant confounders, the adjusted odds ratio assessing the relation between ventilator-associated pneumonia and treatment group assignment (receiving no routine ventilator circuit changes compared with receiving circuit changes every 7 days) was 0.68 (CI, 0.33 to 1.38).

    Among patients without a tracheostomy (n = 220), there was no statistical difference in the development of ventilator-associated pneumonia between patients assigned to receive no routine ventilator circuit changes (n = 119) and those assigned to receive 7-day circuit changes (n = 101; relative risk, 1.4 [CI, 0.84 to 2.40]). However, among patients with a tracheostomy (n = 80), ventilator-associated pneumonia occurred more often in patients assigned to receive 7-day circuit changes (n = 52) than in patients assigned to receive no routine circuit changes (n = 28; relative risk, 2.5 [CI, 1.30 to 4.77]).

    Multiple logistic regression analysis identified three factors as independent predictors for the development of ventilator-associated pneumonia for the entire study cohort: 1) requiring mechanical ventilation for more than 14 days (adjusted odds ratio, 5.1 [CI, 3.7 to 6.8]; P < 0.001); 2) 7-day ventilator circuit changes in patients with tracheostomy (an interaction effect suggesting that the influence of tracheostomy on ventilator-associated pneumonia depends on ventilator circuit changes) (adjusted odds ratio, 2.2 [CI, 1.5 to 3.1]; P = 0.009); and 3) having a surgical categorization (adjusted odds ratio, 2.0 [CI, 1.5 to 2.8]; P = 0.028). The individual terms making up the interaction between tracheostomy and circuit changes were also included in the logistic regression model but were not statistically significant (P > 0.2).

    Bacterial isolates from the tracheal aspirates of the patients with ventilator-associated pneumonia were similar in the two treatment groups. The predominant organisms recovered included Pseudomonas aeruginosa (28.8%), Staphylococcus aureus (27.1%), Enterobacter species (13.6%), Klebsiella pneumoniae (8.5%), Haemophilus influenzae (6.8%), Acinetobacter species (6.8%), Escherichia coli (2.8%), Xanthomonas maltophilia (2.8%), and Streptococcus pneumoniae (2.8%).

    Secondary Outcomes

    The average duration of mechanical ventilation for the entire study group was 15.7 ±13.6 days. The duration of mechanical ventilation and the total length of hospital stay did not differ between the two treatment groups (Table 3). Patients assigned to receive circuit changes every 7 days had a total of 247 changes; patients assigned to receive no routine circuit changes had a total of 11 changes. Among patients assigned to receive circuit changes every 7 days, 237 (96.0%) of the changes were routine changes done according to the study protocol, 5 (2.0%) were done because of soilage of the tubing, 3 (1.2%) were done because of mechanical leaks, and 2 (0.8%) were due to human error. For patients assigned to receive no routine circuit changes, 5 circuits (45.5%) were changed because of soil, 2 (18.2%) were changed because of mechanical leakage, and 4 (36.3%) were changed as a result of human error. Total costs for ventilator circuit changes were $7410 in the group receiving changes every 7 days and $330 in the group receiving no routine changes.

    View this table:
    Table 3. Secondary Outcomes Measures*

    Mortality

    One hundred eleven patients died during their study hospitalization, yielding an overall hospital mortality rate of 37%. No statistically significant differences in the mortality rates during mechanical ventilation, intensive care unit admission, or entire hospitalization were found between the two study groups (Table 4). The hospital mortality rate for patients with ventilator-associated pneumonia (37.5%) was similar to that for patients without ventilator-associated pneumonia (36.8%) (relative risk, 1.02 [CI, 0.73 to 1.42]).

    View this table:
    Table 4. Mortality in the Study Groups
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    Discussion

    We found that a practice of not routinely changing ventilator circuits was not associated with an increased risk for nosocomial pneumonia compared with a practice of changing ventilator circuits routinely. Although hospital mortality, intensive care unit mortality, deaths during mechanical ventilation, and deaths in patients with ventilator-associated pneumonia were higher and deaths directly related to ventilator-associated pneumonia were lower in the group with no routine circuit changes (Table 4), none of these differences reached statistical significance (P ≥ 0.11). These results agree with those of Dreyfuss and colleagues [12], who found no difference in the incidence of ventilator-associated pneumonia when ventilator circuits were changed every 48 hours and when they were not changed routinely. Our results are unique in suggesting that patients with a tracheostomy may be at greater risk for the development of nosocomial pneumonia if they receive ventilator circuit changes (because of an interaction effect). The overall importance of this interaction, compared with the individual factors making it up, may be due to increased aspiration of contaminated tubing condensate in patients with tracheostomy who have more frequent manipulation of their ventilator circuits [30]. Additionally, gravitational factors (the point of attachment of the distal end of the ventilator circuit to a tracheostomy tube is lower than that of an orally placed endotracheal tube) could facilitate the occurrence of aspiration when ventilator circuits are changed [31].

    Our results support the findings of other investigators [3, 4, 32], who have identified duration of mechanical ventilation, presence of a tracheostomy, and surgery as important risk factors for ventilator-associated pneumonia. Because tracheostomy was present more often in patients assigned to receive ventilator circuit changes every 7 days, one might argue that circuit changes were effective in reducing the infection rate in this group (it would otherwise have increased because of the higher rate of tracheostomy) to a level similar to the infection rate in patients receiving no circuit changes. However, our stratified analysis of these patients does not support such an argument; it shows that changing ventilator circuits is associated with an increased occurrence of ventilator-associated pneumonia among patients with tracheostomy.

    Controversy over the need for routine ventilator circuit changes, the time interval for such changes, and their effect on patient outcome has existed for almost two decades [20, 33]. Current economic pressures to downsize respiratory therapy departments, along with shrinking budgets for such services, have added to the importance of this controversy and to the need for appropriately designed investigations to resolve it [17]. Several preliminary reports have described the experiences of various hospitals that have lengthened the time intervals between routine ventilator circuit changes [13-16]. Despite documenting cost savings from such practices, these studies all suffer from having used retrospective control groups in their analyses of patient outcomes. The only prospective, controlled study of prolonged duration of ventilator circuit use examined 63 patients, limiting the power of the analysis [12]. Despite the limitations of the available clinical studies, increasing evidence suggests that institutional practices and policies are being changed in favor of the prolonged use of ventilator circuits in an attempt to reduce medical care costs [17, 34].

    Two important aspects of our study protocol, designed to optimize its safety, should be emphasized. First, ventilator circuits were changed whenever mechanical failure or soilage was noted. Second, we regularly monitored all ventilator circuits—at least every 2 hours—to ensure their integrity, to eliminate the accumulation of any condensate from within the tubing, and to empty the collection traps. This policy of regularly checking ventilator circuits was implemented, in part, to prevent the aspiration of contaminated liquid boluses that can predispose patients to the development of nosocomial pneumonia [30].

    An important goal of our investigation was to evaluate the cost-effectiveness of routine ventilator circuit changes among patients requiring prolonged mechanical ventilation. Compared with a policy of changing circuits every 7 days, we estimate that not routinely changing ventilator circuits will result in a combined cost savings of $18 300 per year for our two institutions. Additionally, because the incidence of ventilator-associated pneumonia was not increased by this practice, it is unlikely that these cost savings will be eroded by additional unforeseen costs for the treatment of excessive cases of nosocomial pneumonia [35, 36].

    Our study had several limitations. First, we used a clinical diagnosis of ventilator-associated pneumonia that could be established at the bedside [2, 25]. Although some investigators [37, 38] have warned that the incidence of ventilator-associated pneumonia may be overestimated when clinical criteria alone are used, the incidence of pneumonia in our study was lower than that reported by Dreyfuss and coworkers [12] and similar to that reported by other investigators [3, 9, 39] using bronchoscopy to obtain lower airway secretions for quantitative cultures. However, clinical criteria have been shown to be less accurate than lower airway sampling techniques in establishing the diagnosis of ventilator-associated pneumonia when tissue examination and culture are used as the diagnostic “gold standard” [40-42]. Second, we did not assess differences in bacterial colonization of the ventilator circuits among the two treatment groups. Previous investigations have shown that ventilator circuits become contaminated within 8 hours of use and that the frequency of ventilator circuit changes has little effect on their colonization [12, 33, 43]. Third, we did not evaluate all potential confounding variables that could influence the occurrence of nosocomial pneumonia (for example, previous antibiotic exposure). Finally, we limited our investigation to only one schedule of routine ventilator circuit changes (changes every 7 days). However, available clinical data [12-16] indicate that it is unlikely that our results would have been different had we selected another schedule of changes.

    We have shown that eliminating routine ventilator circuit changes is safe and cost-effective in patients having prolonged mechanical ventilation. If institutional procedures are changed on the basis of these findings, then cost savings in the care of mechanically ventilated patients should result. More importantly, eliminating routine circuit changes may allow respiratory therapists to use their time more effectively, doing tasks that have been shown to improve patient outcomes (such as monitoring patient-ventilator interactions, suctioning subglottic secretions, removing circuit tubing condensate, and positioning patients appropriately) [1, 9, 11, 44]. Rigorously designed future studies should be directed toward examining other standard but unproven respiratory therapy practices to determine whether doing “more” is better for patients who require prolonged mechanical ventilation [44].

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