Chest
Volume 126, Issue 6, December 2004, Pages 2022-2024
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Selected Reports
Diagnostically Significant Variations in Pleural Fluid pH in Loculated Parapneumonic Effusions

https://doi.org/10.1378/chest.126.6.2022Get rights and content

Study objectives:

Parapneumonic effusions are common, and measurement of pleural pH is one of the most useful measurements in assessing the need for tube drainage. Use of pleural pH assumes that a single measurement conveys a representative picture of pH throughout the effusion. Often effusions are multiloculated, and varying concentrations of nondiffusible acids such as lactic acid, if present in different concentrations, could mean clinically significant variations in pH between locules. If these differences were large, a single pH measurement could misrepresent the “stage” that the parapneumonic effusion had reached. We therefore set out to test the hypothesis that pH varies significantly between locules in complicated parapneumonic effusions.

Design:

The study was performed in seven consecutive patients presenting to our institution with complicated parapneumonic effusions.

Interventions:

In each case, pleural pH was measured in several separate pleural fluid locules, using ultrasound-guided pleural fluid sampling.

Results:

Significant variations were found in pleural fluid visual appearance, pH, and lactate dehydrogenase between locules in four of seven patients. Three of seven patients had variations, resulting in pH levels both above and below 7.2, which is the threshold used in our institution to indicate the need for tube drainage.

Conclusions:

This is the first reported series of variation in pleural pH between different locules in complicated parapneumonic effusions. These variations are clinically important and cast light on the mechanisms responsible for the acidosis seen in infected effusions. Physicians should be aware of this when making drainage decisions in these patients using the clinical picture and a single pH result alone.

Section snippets

Materials and Methods

We prospectively measured pleural fluid characteristics from seven consecutive patients with complicated parapneumonic effusions presenting to our respiratory unit (Oxford Centre for Respiratory Medicine, Oxford) over an 8-month period (December 2001 to August 2002). Patients are referred to the Oxford unit directly from general practitioners (60%), from other local hospital consultants (30%), and occasionally from respiratory consultants in other neighboring health authorities (< 10%).

Patients

Results

The seven patients studied had a median age of 67 years (range, 32 to 83 years). Four patients were men, and three patients were women, and they all presented with community-acquired complicated parapneumonic effusions. Five patients had received antibiotics prior to hospital admission. None had a medical history of pleural disease or cancer. Blood culture specimens were obtained in all cases, and all results were negative. Pleural fluid cytology was negative for malignancy in all cases.

The

Conclusions

We believe this is the first reported series of variation in pleural pH between different locules in complicated parapneumonic effusions. These variations are large, clinically important, and cast light on the mechanisms predominantly responsible for the acidosis seen in infected effusions.

In three of our patients, if only the first pleural fluid sample had been obtained showing the recorded pleural pH of > 7.2, it would have implied that they probably did not require chest tube drainage,

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Mr. Maskell is partly funded by a Medical Research Council (UK) grant.

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