Use of nonheparinized syringes for collecting pleural fluid samples

Factors influencing the measurement of pleural fluid pH

PURPOSE OF REVIEW

Pleural fluid pH measurement is important in the management of patients with exudative pleural effusions, especially in guiding treatment of parapneumonic effusions. Common variations in the method used to sample pleural fluid affect the accuracy of the value obtained. This article reviews the effects of these variations.

RECENT FINDINGS

Pleural fluid pH is decreased by exposure to acidic fluids, such as retention of local anesthetic or heparin in the syringe or sampling following infiltration of local anesthetic. Exposure of the sample to air leads to an increase in pH. If immediate analysis is not possible, delay of up to 4 h does not cause a significant change in pH, even when the sample is kept at room temperature. It is essential that a blood gas analyzer is used to obtain accurate pH measurement.These factors have less effect on the glucose concentration, which may be used to guide management if an accurate pH value is not available.

SUMMARY

Several common variables in collection method can lead to a clinically significant alteration in the pH value obtained. An evidence-based method for sampling and handling pleural fluid in order to obtain an accurate pH measurement is described.

Use of Heparinized versus Non-Heparinized Syringes for Measurements of the Pleural Fluid pH

BACKGROUND

Pleural fluid (PF) pH measurement is important for establishing a diagnosis and for guiding clinical management. The current standard practice is to collect PF samples for pH measurement in heparinized syringes at room temperature and to instantaneously process these samples.

OBJECTIVE

The purpose of this study is to investigate the effect of collecting PF in heparinized versus non-heparinized syringes at room temperature on PF pH measurements when processed at various time intervals.

METHODS

From 50 consecutive thoracenteses, 1 ml of PF was collected anaerobically in each of six 3-ml syringes. Only three syringes were coated with heparin. The samples were processed for PF pH measurements at time 0 (T(0)) and 1 h (T(1)) and 2 h (T(2)) after collection. All specimens were preserved at room temperature, until the measurements were carried out in duplicates by a calibrated blood gas analyzer.

RESULTS

PF pH values were significantly lower with heparinized versus non-heparinized syringes at all time intervals (T(0): pH heparinized = 7.378 +/- 0.107 vs. pH non-heparinized = 7.390 +/- 0.108; T(1): pH heparinized = 7.378 +/- 0.115 vs. pH non-heparinized = 7.389 +/- 0.111; T(2): pH heparinized = 7.367 +/- 0.105 vs. pH non-heparinized = 7.389 +/- 0.121). In the heparinized syringes, there was a significant decrease in PF pH values at T(2) versus T(0) and T(1). There were no significant changes in PF pH values over time in the non-heparinized syringes.

CONCLUSIONS

For serial PF pH measurements, the same type of syringes (either heparinized or non-heparinized) should be consistently used. With heparinized syringes, processing of PF pH measurements should be performed within 1 h after collection.