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Purpose of Study
Nosocomial pneumonia is a common problem in intubated and ventilated patients. However, previous studies have not demonstrated clearly that nosocomial pneumonia results in increased mortality or prolongs hospitalization of these patients. The study sort to address these limitations of past researchers by performing a cohort study in which patients who developed nosocomial pneumonia and control subjects were carefully matched for the severity of underlying illness and other important variables.
Sample Size
The number of patients used in the study was 48 ventilated patients with nosocomial pneumonia. These patients were identified based on results of protected specimen brush quantitative culture and identification of intracellular organisms in cells recovered by bronchoalveolar lavage. The size of the sample was large enough given the number of major variables being investigated.
Reliability of Measurements
The measurements of major variables are valid and reliable since all adjustments to take care of any errors were made. The researchers used appropriate variables for matching cases and their respective controls. For age, (+ÂÂÂ_5 years), Simplified Acute Physiologic Score (+_3 points), indication for ventilator support, date of admission, and duration of risk exposure were used.
Data Collection
During the study, the following data was collected from the cases and controls; age, sex, dates of admission and discharge from ICU; prior location before admission to the ICU; severity of underlying medical conditions, stratified according to criteria of McCabe and Jackson as fatal, ultimately fatal, and nonfatal; indication for ventilator support, using the classification described by Zwillich and coworkers; the arterial oxygen pressure/inspired oxygen fraction ratio; the Simplified Acute Physiologic Score (SAPS); the APACHE II score; the Glasgow coma score; presence or absence of cardiac failure, renal failure, hepatic failure, hematologic failure, and neurologic failure at admission, diagnosed according to previously described definitions; duration of mechanical ventilation; results of bronchoalveolar lavage and results of quantitative cultures of specimens obtained by brush; patients outcome at the time of discharge, and postmortem examination findings. Controls were also put in place to match those under investigation. The amount of data collected was sufficient for conducting a meaningful analysis to come up with reliable findings.
Data Analysis
Statistical analysis of the data collected used the same criteria for diagnosis of pneumonia as that of prior data. The odds ratio for death was 2.50 for cases compared with that of controls while the mortality rate for controls was 30%. Measures to test the null analysis were also used. Moreover, McNemars test with continuity correction was used to determine whether the crude mortality rates of the cases and controls were significantly different. The study also used the risk ratio to measure relative risk of infection and in inducing death. The confidence interval (CI) of the risk ratio was found to be 95% by using Taylor series based weights. The stratified analysis of mortality was calculated using Mantel-Haenszel x2 statistic. The equality of length of stay between cases and controls, as well as the difference in medians were tested using the Wilcoxon sign rank test. Yates corrected x2 test was used in the evaluation of proportions in independent groups.
Validity of Results
The results of the study are reliable to a high degree owing to the methodology of data collection and analysis employed by the researchers. Possible sources of biases were taken care of by the introduction of controls and margin of error in the data collected. The size of the sample selected was large enough to warrant the credibility of the results obtained. The time period over which the study was conducted was sufficient to make meaningful observations, crucial for making/drawing meaningful conclusions. The results obtained also provide a cl4ear explanation of an issue that had not been addressed by other studies. The study findings are of great clinical significance since it emerged that there is big correlation between nosocomial pneumonia in ventilated patients and mortality, as well as elongation of hospitalization. The precision of measurement of effect was very high given the advanced methods of statistical analysis employed by the researchers in the interpretation of their findings. Generally, the confidence intervals were at an average of 95% and p value had a range of 0.2
0.2. The validity of the results is also reinforced by the fact that this study included all factors in the diagnosis of patients with pneumonia unlike past studies which relied fully on clinical criteria that resulted in over-diagnosis of pneumonia. The study used strict diagnostic criteria for the diagnosis of pneumonia as mentioned earlier. However, the findings/results of this study cannot be generalized to units in which the patient mix includes mostly patients being ventilated for respiratory failure associated with other medical conditions. This is because the patient mix in the study included a large number of patients being ventilated postoperatively.
Consistency of Results
The results obtained are consistent and has useful application for nurse practitioners. The results show that ventilator-associated pneumonia causes excess mortality independent of age and initial severity of illness, as well as extension of hospitalization (ICU). The results provide useful information about the relationship between pneumonia and mortality rates and elongated periods of hospitalization in the ICU due to pneumonia-related illnesses.
References
Fagon, J. Y., Chastre, J., Hance, A. J., Montravers, P., Novara, A., & Gilbert, C. (1993). Nosocomial pneumonia in ventilated patients: a cohort study evaluating attributable mortality and hospital stay. American Journal of Medicine, 94: 281-288.
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