The Relationship Between Volume Status, Hydration, and Radiographic Findings in the Diagnosis of Community-Acquired Pneumonia

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Original Research

The Relationship Between Volume Status, Hydration, and Radiographic Findings in the Diagnosis of Community-Acquired Pneumonia

J Fam Pract. 2000 September;49(9):833-837

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Our retrospective study appears to be the first to specifically address the relationship between pneumonia, hydration status, rehydration, and the effect on the radiographic appearance of pneumonia. Our results show an association between an elevated admission BUN level, volume of fluids given, and a worsening of the radiographic appearance of CAP. A future prospective study could teach us more about diagnostic strategies for CAP, including any situations in which repeated radiographs are helpful.

We were not able to address the question of whether the radiographic findings of pneumonia can be completely masked by dehydration and subsequently expressed by rehydration; our findings, however, suggest that there may be some basis for this premise.

Limitations

Our study has a number of limitations. There is an inherent selection bias in our retrospective process: Patients who received only one chest radiograph because of misdiagnosis, management decision, or other reasons were excluded from the study. Follow-up chest radiographs within a few days are generally not indicated and are not obtained in clinically stable patients who may only show worsening or improving patterns on radiograph.^6,13 Also, the retrospective nature of the study precluded the collection of a uniform database or uniform evaluation of possible etiologic agents. Viral and mycoplasma pneumonias are well documented to have a lag between onset of symptoms and evolution of radiographic findings,⁹ that may have led to inappropriate group assignment or complete exclusion from the study. The determination of the presence, progression, or nonprogression of radiographic findings is somewhat subjective and may affect our results. Our data are based on the reported radiograph interpretation from a randomly assigned radiologist. Interobserver agreement between radiologists for the determination of infiltrates on chest radiographs was found to be only 80% in a recent study.²¹ Finally, hydration status was difficult to determine. Although the BUN level was significantly higher in the P group than in the NP group, BUN level is not a specific marker for dehydration or intravascular volume status. The higher serum sodium levels of the P group, while not achieving statistical significance, may have been a better marker of total body water status. Although fluid volume depletion and dehydration are very different clinical problems,²² the determination of which condition was present, and the severity of that condition, was not possible in our study. Although statistically significant, the difference in fluid intake between the 2 groups may not be clinically significant. Furthermore, dehydration alone has been shown to adversely affect lung host defense in rats.²³ If applicable to humans, this could also unexpectedly affect our results.

Conclusions

To our knowledge, this study is the first to try to define the relationship of fluid volume status and radiographic progression of CAP in humans. The retrospective nature of our study leads to several limitations and potential sources of bias, but it appears to show that there is a correlation between markers of fluid volume status, hydration, and the evolution of the radiographic findings. A prospective clinical study is needed to further define this relationship.

Acknowledgments

Our work was funded by a grant from the Clinical Research Center of the Medical Center of Central Georgia. We wish to thank Jennifer K. Rayhill for her assistance in preparing this manuscript.