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CE Article

Effect of Backrest Elevation on the Development of Ventilator-Associated Pneumonia

	Abstract

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• Background Ventilator-associated pneumonia is a common complication of mechanical ventilation. Backrest position and time spent supine are critical risk factors for aspiration, increasing the risk for pneumonia. Empirical evidence of the effect of backrest positions on the incidence of ventilator-associated pneumonia, especially during mechanical ventilation over time, is limited.

• Objective To describe the relationship between backrest elevation and development of ventilator-associated pneumonia.

• Methods A nonexperimental, longitudinal, descriptive design was used. The Clinical Pulmonary Infection Score was used to determine ventilator-associated pneumonia. Backrest elevation was measured continuously with a transducer system. Data were obtained from laboratory results and medical records from the start of mechanical ventilation up to 7 days.

• Results Sixty-six subjects were monitored (276 patient days). Mean backrest elevation for the entire study period was 21.7°. Backrest elevations were less than 30° 72% of the time and less than 10° 39% of the time. The mean Clinical Pulmonary Infection Score increased but not significantly, and backrest elevation had no direct effect on mean scores. A model for predicting the Clinical Pulmonary Infection Score at day 4 included baseline score, percentage of time spent at less than 30° on study day 1, and score on the Acute Physiology and Chronic Health Evaluation II, explaining 81% of the variability (F=7.31, P=.003).

• Conclusions Subjects spent the majority of the time at backrest elevations less than 30°. Only the combination of early, low backrest elevation and severity of illness affected the incidence of ventilator-associated pneumonia.

Notice to CE enrollees:A closed-book, multiple-choice examination following this article tests your understanding of the following objectives: Discuss recommendations for backrest elevation for the prevention of ventilator-associated pneumonia Describe the study findings related to backrest elevation Identify significant factors found in the study that influenced the development of ventilator-associated pneumonia

The degree of backrest elevation and the time spent supine are critical risk factors for aspiration, which increases the risk for ventilator-associated pneumonia (VAP).^4–7 Lower backrest elevations are associated with an increase in the incidence of aspiration of gastric contents, a major risk factor for VAP. The recommendations⁸ of the Centers for Disease Control and Prevention for prevention of VAP include elevation of the head of the bed at an angle of 30° to 45°. More recently, the Joint Commission on Accreditation of Healthcare Organizations proposed an intensive care unit (ICU) core measure related to prevention of pneumonia that includes the number of days of mechanical ventilation in which the head of a patient’s bed is elevated 30° or more.⁹ However, only 3 reports^5,10,11 provide empirical evidence of the unique effect of backrest positions on the incidence of VAP, and in these studies, backrest positions were assessed for a short time.

The Centers for Disease Control and Prevention recommends use of backrest elevations of 30° to 45° to prevent ventilator-associated pneumonia.

 

Patients’ body position is a key component of nursing care and can significantly affect the development of VAP, as well as the morbidity and mortality associated with VAP. Because of the risks associated with the use of supine positioning in patients treated with mechanical ventilation, the relationships between (1) level of backrest position and time spent in lower positions (<30° elevation) and (2) the development of VAP should be examined. Therefore, the purpose of this study was to describe the relationship between back-rest elevation and the development of VAP.

	Methods

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Design and Sample
This nonexperimental, longitudinal, descriptive pilot study was conducted in the medical respiratory ICU at Virginia Commonwealth University Health Systems, Richmond, Va. The ICU is a 12-bed unit with about 1000 admissions each year, and approximately 50% of the patients admitted require mechanical ventilation. All patients admitted to the unit who were intubated within the previous 24 hours and were receiving mechanical ventilation were reviewed for potential enrollment in the study. Patients with a diagnosis of pneumonia at the time of intubation were excluded. Because reintubation increases the risk for VAP,^12,13 patients who had had an endotracheal intubation during their current hospital admission were also excluded. On the basis of a mean VAP incidence of 25%, we expected that a sample size of 60 would be large enough to include approximately 15 patients in whom VAP would develop. We anticipated that a sample of this size would be sufficient to indicate the effect of backrest elevation on the development of VAP over time.

Measurement and Quantification of Key Variables
  Backrest Elevation.   The elevation of the head of the bed measured in degrees was recorded continuously, and data were downloaded every 10 minutes, from the time of admission to the study through day 7 of mechanical ventilation or until extubation for patients extubated before day 7. We developed a 2-transducer system for measuring the elevation (Figure 1) and pilot tested the system for accuracy and reliability.¹⁴ Two pressure transducers, one attached to the bed frame just distal to the head of the bed gatch (the point at which the frame elevates) and another attached to the bed frame at the top of the bed, were used to monitor the differential head pressure between the 2 pressure channels, which was then used to calculate the height of the head of the bed. The amount of time patients spent out of bed and off the unit was recorded, and data collected during these periods were not used in the data analysis.

View larger version (8K): [in this window] [in a new window]   Figure 1 Calculation for continuous measurement of backrest elevation: D1 = (P1 – P2) x 1.36. = sin–1 (D1/D2). P1 = the pressure to the bed gatch in millimeters of mercury. P2 = the pressure to the head of the bed in millimeters of mercury. D1 = (P1 – P2) = the height of the bed in centimeters. 1.36 = the conversion factor from millimeters of mercury to centimeters of water, and D2 = the distance between transducers in centimeters. The intravenous bag serves as a constant source of pressure on the transducer that changes only with changes in backrest position.

  Ventilator-Associated Pneumonia.   VAP is pneumonia in a patient receiving mechanical ventilation that was neither present nor developing at the time of intubation, so that clinical evidence of VAP occurs 48 hours or more after intubation.¹⁵ In this study, the CPIS¹⁶ was used as the measure of VAP. The CPIS is based on 6 easily measured variables: body temperature, white blood cell count, number of tracheal secretions, oxygenation (calculated as Pa O₂ divided by the fraction of inspired oxygen), findings on chest radiographs (radiologist’s report), and results of cultures of tracheal aspirates. The tracheal secretions score, a component of the CPIS, is an estimation of the total secretions per day and is calculated on the basis of nurses’ estimates of the quantity of secretions, from 0 to 4+ (none, scant, minimal, moderate, large; documented on the flow sheet), for each aspiration and then totaled for a 24-hour period. Cultures of tracheal aspirates were evaluated by using a microscopic examination (Gram stain) and semiquantitative culture of endotracheal secretions.

Each variable is assigned points (0, 1, 2), and a total CPIS (range 0–12) is obtained, providing a range of scores for data analysis. The CPIS has been used by others^17,18 and can be used to describe the development of VAP over time, thereby enhancing the ability to describe the relationship between backrest position and development of VAP over time. Pugin et al¹⁶ found a good correlation between CPIS values and quantitative samples of bronchial alveolar lavage fluid obtained via (1) bronchoscopy (r = 0.84) and (2) a "blind" nonbronchoscopic method (r = 0.76). Papazian et al¹⁹ compared CPIS values and results of bronchoscopic and blind sampling techniques with histological data for the diagnosis of VAP and found a sensitivity of 72% and a specificity of 85% for the CPIS for diagnosis of VAP. The CPIS also was predictive of the presence of pneumonia (P < .001) versus other causes of pulmonary infiltrates in liver transplant recipients.²⁰ However, using a CPIS greater than 5 as a diagnostic cutoff, Schurink et al²¹ recently compared CPIS values with quantitative cultures of bronchoalveolar lavage fluid in 99 patients and found a sensitivity of 83% and a specificity of 17% for diagnosis of VAP. Overall, the CPIS expands clinical judgment by including the elements of chest radiography and bacteriology and allows use of a noninvasive measure to quantify the development of pneumonia.

VAP is a multifaceted process involving a variety of risk factors. Therefore, data were also collected to evaluate a number of cofactors associated with the development of VAP, including demographics, severity of illness (score on the Acute Physiology and Chronic Health Evaluation II [APACHE II]),²² oral health status, nutritional information (number and type of enteral feedings recorded as hours fed per day for patients with continuous feedings), gastric pH, previous use of antibiotics, type of and reason for intubation, and intensity of nursing care during the study period. Oral health status was evaluated by summing the number of decayed, missing, and filled teeth (DMF score). The intensity of nursing care was evaluated by using the Therapeutic Intervention Scoring System,²³ a scoring system based on the number and intensity of interventions required for a patient’s care each day.

Procedure
The study protocol was reviewed and approved by the university’s institutional review board. For each patient who met the inclusion criteria, the study was explained to the patient’s legally authorized representative and written consent was obtained. Backrest elevation, heart rate, and blood pressure were continuously monitored from time of admission to the study through day 7 of intubation or until extubation. All continuous data were automatically downloaded every 10 minutes during the study period. For each patient, the CPIS was determined 3 times during the study: within 24 hours of intubation (at the time of admission into the study), at 72 to 96 hours after intubation (during day 4 of mechanical ventilation), and at 144 to 168 hours after intubation (during day 7 of mechanical ventilation).

Early-onset VAP occurs during the first 4 days of continuous mechanical ventilation, whereas late-onset VAP occurs after 4 days of continuous mechanical ventilation.²⁴ Data related to other risk factors for VAP were also collected and included ventilator support data (ventilator mode, rate, type of support, use of positive end-expiratory pressure, use of pressure-support ventilation, fraction of inspired oxygen, Pa O₂, and arterial oxygen saturation), enteral nutrition data (use, route, rate, and type of enteral feedings and highest daily gastric pH during the preceding 24 hours), and administration of antibiotics, histamine blockers, antacids, sucralfate, and vasopressors.

Data Analysis
Descriptive statistics were used to summarize the characteristics of the study population; percentages for discrete variables and means and SDs for continuous variables were calculated. Summaries for backrest elevation, nutritional data, and oral care interventions were generated for each study day.

A general forward-selection multiple regression analysis was used to determine an appropriate model for predicting the CPIS at day 4 (72–96 hours after intubation). Day 4 was chosen because the sample size at day 7 was small because of attrition (extubation or patients’ deaths). Predictor variables tested in the model included a baseline CPIS measure, angle measurements (percentage of time at <10°, <20°, <30°, and <45° elevation on study day 1 and mean percentage of time spent at <10°, <20°, <30°, and <45° elevation during study days before CPIS measurement on day 4), as well as other important explanatory variables (APACHE II score; use of enteral feedings; number of enteral feedings and number of mouth care interventions before determination of the CPIS; the patient’s age; use of antibiotics before intubation; number of decayed, missing, and filled teeth; intubation process [urgent, emergent, or elective]; and reason for intubation). The final model was chosen because the overall analysis of variance F ratio and adjusted R² were the highest. Finally, model assumptions were checked by examining both the residual (a measure of the discrepancy between observed and predicted values) by predicted plot, the normal quantile plot of the residuals, and regression diagnostics.

	Results

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Characteristics of the Sample
The 66 patients in the sample (mean age 55 years, 58% men) were intubated primarily because of respiratory failure (Table 1). Patients remained in the study for a mean of 4.2 days and were monitored for up to 7 days, for a total of 276 patient days. A total of 37 subjects were in the study on day 4, and 21 remained in the study on day 7 when the CPIS was determined.

The average backrest elevation in 276 patient days of mechanical ventilation was 21.7°.

 

Ventilator-Associated Pneumonia
Of the 37 subjects in the study on day 4, 31 had complete data for CPIS calculation and 8 (26%) of those had VAP (according to the CPIS). On day 7, 5 (31%) of the 16 remaining patients with complete data for calculation of the CPIS had VAP. Because of the small sample size on day 7, day 4 data were used for analysis of factors affecting VAP. The mean CPIS increased from day 1 to day 4 and continued to increase through day 7, but the increases were not significant (Table 2).

Because APACHE II score, percentage of time spent in backrest elevations less than 30° on day 1, and baseline CPIS appear in the model with significant pairwise interaction, the effect of these variables must be determined by analyzing these interactions. Contour plots were generated to illustrate the relationship between the CPIS on day 4 and these 3 predictor variables. Figure 2 shows the CPIS on day 4 for a baseline CPIS of 1. The CPIS value on day 4 consistently increases as the percentage of time spent at less than 30° elevation increases and as the APACHE II score increases. For a baseline CPIS of 2, Figure 3 shows a similar trend for the percentage of time spent at less than 30° elevation. The trend for APACHE II scores, however, is not as uniform. Note that according to the model (Figure 3), for patients who spent about 70% of the time or less at less than 30° elevation on day 1, the CPIS on day 4 remains fairly constant, whereas for those who spent more than 70% of time at less than 30° elevation on day 1, the CPIS on day 4 increases as the APACHE II score increases, thus highlighting the interaction between backrest elevation and APACHE II scores. For a baseline CPIS of 3, Figure 4 shows a similar trend for patients who spent more than 75% of the time at less than 30° elevation on day 1.

View larger version (25K): [in this window] [in a new window]   Figure 2 Predicted CPIS for day 4 and a baseline CPIS of 1. This contour plot represents the predicted CPIS response from the regression model for a baseline CPIS of 1 relative to the percentage of time spent at less than 30° elevation and the APACHE II score. The CPIS value on day 4 consistently increases as the percentage of time spent at less than 30° elevation increases and as the APACHE II score increases.

View larger version (24K): [in this window] [in a new window]   Figure 3 Predicted CPIS for day 4 and a baseline CPIS of 2. This contour plot represents the predicted CPIS response from the regression model for a baseline CPIS of 2 relative to the percentage of time spent at less than 30° elevation and the APACHE II score. The CPIS on day 4 consistently increases as the percentage of time spent at less than 30° elevation increases and as the APACHE II score increases. The predicted CPIS response is not consistent relative to the percentage of time spent at less than 30° elevation and the APACHE II score.

View larger version (22K): [in this window] [in a new window]   Figure 4 Predicted CPIS for day 4 and a baseline CPIS of 3. This contour plot represents the predicted CPIS response from the regression model for a baseline CPIS of 3 relative to the percentage of time spent at less than 30° elevation and the APACHE II score. Similar to Figure 2, the predicted CPIS response is not consistent relative to the percentage of time spent at less than 30° elevation and the APACHE II score.

Ventilator-associated pneumonia was more likely to develop in patients who were more seriously ill and spent greater time at backrest elevations of less than 30° during the first day of intubation.

 

	Discussion

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The purpose of this study was to describe the relationship between backrest elevation and the development of VAP. Mean backrest elevation in the study was similar to that reported by others^25–27 and was consistently lower than the recommended 30° to 45°.² Mean backrest elevation decreased over the study days, but the decrease was not significant. However, patients who remained intubated and thus were in the study longer were more likely to be severely ill, possibly resulting in lower back-rest positions because of the severity of illness.²⁵

In analyzing the effect of backrest elevation over time on VAP, we found that VAP was more likely to develop in patients who were more severely ill and had greater amounts of time at backrest elevations lower than 30° elevation during the first 24 hours after intubation. Therefore, the early hours of intubation appear to be the most critical for higher backrest elevations. Unfortunately, this period is also the time (first 24 hours of this study or first 24–48 hours after intubation) when patients are most likely to be lying flat because of procedures or unstable hemodynamic status.

Patients with greater illness severity (higher APACHE II scores) are more likely than patients with lower illness severity to require procedures or experience unstable hemodynamic status, dictating use of lower backrest positions. Effects of backrest position in the early ICU period were also studied by Torres et al,⁴ who found that patients in a semirecumbent position (ie, >45° elevation) had a reduced incidence of aspiration. Torres et al introduced radioactively labeled sulfur colloid into gastric contents and then measured the radioactivity of endobronchial secretions. Mean radioactive counts in endobronchial secretions were higher in samples obtained while patients were in the supine position than in samples obtained while patients were in the semirecumbent position. Moreover, the greater the length of time in lower backrest positions, the greater was the incidence of aspiration of gastric contents. Our findings, however, did not confirm these results beyond the first day of intubation. Rather, we found that the combination of time spent in low backrest elevations only on day 1 and higher APACHE II scores were significantly associated with VAP.

To reduce risk of ventilator-associated pneumonia, it is especially important to maintain backrest elevation of at least 30° during the first 24 hours of mechanical ventilation.

 

In a prospective, randomized, clinical trial, Drakulovic et al⁶ compared continuous semirecumbency (45° elevation) to no backrest elevation (0°) from intubation until the first weaning attempt and found a significantly greater incidence of VAP in patients without backrest elevation. However, these authors did not test the use of backrest elevations during various days of intubation as we did. Drakulovic et al⁶ and Kollef⁵ also found, as we did, that higher APACHE II scores were associated with the development of VAP. Additional factors, such as use and number of enteral feedings, number of mouth care interventions, oral status (number of decayed, missing, and filled teeth) at the time of admission, and the type of intubation (urgent, emergent, or elective) were not associated with the development of VAP.

Although the recommendations⁸ of the Centers for Disease Control and Prevention for VAP prevention include a backrest elevation of 30° to 45°, use of such an elevation is not common in practice,^25–27 and the rationale for use of lower backrest positions has not been clearly described. Other investigators did not find relationships between use of lower backrest elevations and unstable hemodynamic status,²⁶ type of enteral feeding,^26,27 or nurses’ inability to accurately estimate backrest position.²⁸ Further, Cook et al²⁹ investigated clinicians’ perspectives of the determinants and consequences of a semirecumbent position (backrest elevation >45°). They found that intensivists and nutritionists were familiar with semirecumbency as a strategy to prevent pneumonia, whereas other clinicians were not. Nurses thought physicians’ orders were the primary determinant of use of a semirecumbent position, whereas intensivists thought the main determinant was nurses’ preferences. Cook et al concluded that underutilization of semirecumbency for prevention of pneumonia is influenced by insufficient awareness of the benefit of this position, real and perceived deterrents, poor agreement about who is responsible for putting patients in a semirecumbent position, and lack of enabling and reinforcing strategies.

	Implications for Practice and Future Research

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Our results confirm previous data that indicated an association between backrest elevation and the incidence of VAP and particularly highlight the importance of elevated backrest positions early in the intubation period, especially for patients who are severely ill. Although instituting and maintaining changes in practice throughout a patient’s entire period of mechanical ventilation may be difficult, use of higher backrest positions specifically during the first 24 to 48 hours after intubation may be easier to implement consistently.

Potential problems with use of higher backrest positions include skin breakdown due to greater skin shear forces, the need for frequent repositioning of patients (pulling patients up in bed), and reduced comfort for patients. If use of higher backrest positions is focused on the first 24- to 48-hour period, compliance with the recommendation may be greater. Effective risk reduction for VAP most likely will require multiple interventions and a collaborative approach. However, maintenance of higher backrest elevations, especially in the first 24 to 48 hours after intubation, especially in patients who are severely ill, appears to be an effective, easily implemented first step.

Our results are limited by the small sample size and the lack of bronchoscopic evaluation for diagnosis of pneumonia, and the findings should be confirmed in future work. Use of higher backrest elevations and their effect on patients’ comfort and skin integrity need to be evaluated. In addition, optimal backrest positions (ie, 30° vs 45° elevation) also need to be determined.

The patients in our study primarily had early-onset VAP, and because of attrition, the effect of backrest on late-onset VAP was not evaluated. Because late-onset VAP results in a higher mortality rate,³⁰ investigation of the effect of backrest elevation on the development of VAP beyond 4 days of intubation is also important. Although culture of bronchial secretions obtained by using a bronchoscope and a protected specimen brush is the gold standard for diagnosis of VAP, the method is invasive, expensive, and not without risk. An ideal, reliable, and valid clinical method for diagnosis of VAP is not available, and although the CPIS is useful, continued work in this area is still needed. VAP is a multi-faceted process and will therefore require innovative and comprehensive approaches to address all possible aspects of prevention.

	ACKNOWLEDGMENTS

 
This research was supported by grant R15 NR07730 from the National Institute of Nursing Research (to MJG) and by the A.D. Williams Foundation of Virginia Commonwealth University.

To purchase reprints, contact The InnoVision Group, 101 Columbia, Aliso Viejo, CA 92656. Phone, (800) 809-2273 or (949) 362-2050 (ext 532); fax, (949) 362-2049; e-mail, reprints{at}aacn.org.

Commentary by Mary Jo Grap (see shaded boxes).

	REFERENCES

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