Chest ACCP Member Benefits
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

Guest Access | Sign In via User Name/Password
This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF) Free
Right arrow Submit a response
Right arrow Alert me when this article is cited
Right arrow Alert me when eLetters are posted
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Add to My Personal Article Archive
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via ISI Web of Science (2)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Castro, D. J.
Right arrow Articles by Yusen, R. D.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Castro, D. J.
Right arrow Articles by Yusen, R. D.
(Chest. 1999;116:399-402.)
© 1999 American College of Chest Physicians

Modification of Pleural Fluid pH by Local Anesthesia*

David Jiménez Castro, MD; Gema Díaz, MD; Esteban Pérez-Rodríguez, MD, PhD; Edgardo Prieto, RN and Roger D. Yusen, MD

* From the Respiratory Disease Service (Drs. Castro, Díaz, Pérez-Rodríguez, and Mr. Prieto), Hospital Universitario Ramón y Cajal, Madrid, Spain; and the Division of Pulmonary and Critical Care Medicine (Dr. Yusen), Washington University School of Medicine, St. Louis, MO.

Correspondence to: David Jiménez Castro, MD, Servicio de Neumologia, Hospital Ramón y Cajal, Apartado 31057, E-28080 Madrid, Spain


   Abstract
TOP
 Abstract
Introduction
 Materials and Methods
 Results
 Conclusion
 References
 
Background: It is a common practice to anesthetize patients before performing a thoracentesis. We postulated that this technique may cause a clinically significant difference in the pH of the pleural fluid.

Methods: We compared two methods of determining pleural fluid pH. Fifty patients undergoing diagnostic or therapeutic thoracentesis were enrolled. Two 4-mL aliquots of pleural fluid were anaerobically collected into blood gas syringes containing heparin, one before (group A) and the other after (group B) anesthetizing the patient with 5 mL of 2% mepivacaine. pH was then determined on both samples using an arterial blood gas machine. Agreement analysis was performed overall and in subcategories of pH used to define complicated (< 7.1), borderline (7.1 to 7.3), or uncomplicated (> 7.3) parapneumonic effusions. We analyzed these same data stratified by the volume of pleural fluid in relationship to the size of the hemithorax (< 15% and > 15%).

Results: There was a statistical difference between the mean pH in both groups (group A, 7.32; group B, 7.28; p < 0.0001). There was a significant correlation between the two measures (r = 0.97; p < 0.0001). Using the pH subcategories, there was 45% discordance in classification for patients with parapneumonic effusions. The pH values obtained in group B wrongly predicted whether the patient required a chest tube in two of four cases (50%). In patients with effusions that occupied < 15% of the affected hemithorax, there was an 80% discordance in classification for patients with parapneumonic effusions, and the pH values obtained in group B wrongly predicted whether the patient required a chest tube in two of two cases (100%).

Conclusions: Local anesthesia is typically used before thoracentesis is performed. However, in cases of suspected parapneumonic effusions that occupy < 15% of the affected hemithorax, pH results may be significantly altered by use of local mepivacaine anesthesia.

Key Words: anesthesia • parapneumonic effusions • pleural fluid pH


   Introduction
TOP
 Abstract
 Introduction
Materials and Methods
 Results
 Conclusion
 References
 
Measurement of pleural pH is very useful in the diagnosis and management of parapneumonic and malignant pleural effusions.1 2 3 4 Adequate anesthesia is used prior to thoracentesis or closed pleural biopsy in order to decrease pain in patients. Occasionally, part of the anesthetic may be injected inside the pleural space, modifying the value of the pleural pH. To our knowledge, no studies have examined whether this practice alters the pH and thus potentially affects management. We prospectively compared the pH of the pleural fluid obtained before and after the use of local anesthesia in 50 consecutive cases.


   Materials and Methods
TOP
 Abstract
 Introduction
 Materials and Methods
Results
 Conclusion
 References
 
After informed consent was obtained, 50 patients undergoing diagnostic or therapeutic thoracentesis were enrolled. After the chest had been cleansed and draped, two 4-mL aliquots of pleural fluid were anaerobically collected, one before (group A) and the other after (group B) the patient was anesthetized with 5 mL of 2% mepivacaine. Different syringes were used to administer the anesthetic and to obtain the pleural fluid sample. pH was then determined on both samples using an arterial blood gas analyzer (model 995-Hb; AVL Medical Instruments; Roswell, GA). All samples were measured within 10 min of collection, and the before and after samples were collected within 5 min of each other.

The pH of mepivacaine was 6.09 (Beckman pHmeter; Beckman Instruments; Madrid, Spain).

The data were analyzed statistically using two-tailed Student's t test of pH values, and correlations were assessed using the Pearson product moment correlation coefficient.

Agreement was assessed using both conventional mathematical formulas5 and predefined limits of agreement based on clinical relevancy, as previously reported.6 Agreement between the pH pairs was assessed in function of the volume of pleural fluid with relation to the size of the hemithorax, which was visually assessed on chest radiograph and subjectively recorded as < 15% or > 15%.

For parapneumonic effusions, pH values were categorized into three groups (< 7.1, 7.1 to 7.3, and > 7.3) that correspond with complicated, potentially complicated, and uncomplicated effusions, respectively.4 Chest tube drainage is typically recommended for a complicated parapneumonic pleural effusion.7

Concordance of classification between these subgroups was compared between the pH pairs obtained with either technique.


   Results
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
Conclusion
 References
 
Fifty patients (38 men and 12 women) from 23 to 84 years old (mean, 62.3 years old) with pleural effusions were included in the study. The general characteristics of the study population are shown in Table 1 .


View this table:
[in this window]
[in a new window]

  		Table 1. General Characteristics of the Study Population

 
There was a statistically significant difference in the mean pH values obtained before and after anesthetic administration (group A, 7.32; group B, 7.28; p < 0.0001); an r value of 0.97 implies that there is a strong correlation between the two measurement techniques (Fig 1 ). Agreement analysis of the differences yielded an SD of 0.04. Limits of agreement calculated using the standard statistical formula revealed that the pH value obtained after anesthetizing the patient could be as much as 0.06 pH units lower or 0.1 pH units higher than the pH obtained before administering anesthesia. Using a limit of the difference of 0.1 pH units, we found that the values obtained after the patient was anesthetized exceeded this limit 3 of 50 times (6%).



View larger version (31K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 1. A plot of the correlation between the two measurement techniques.

 
For parapneumonic effusions, the values obtained in group B wrongly predicted whether the patient required a chest tube in two of four cases (50%), according to Light's criteria.4

In 11 patients, the pleural effusion occupied < 15% of the affected hemithorax (Table 2 ). The SD of the differences in this subgroup was 0.06. The pH value obtained after anesthetic administration ranged from as much as 0.07 pH units lower or 0.17 pH units higher than the pH obtained before anesthetic administration. Using a limit of the difference of 0.1 pH units, we found that the values obtained after the patient was anesthetized exceeded this limit 2 of 11 times (18%). For patients with parapneumonic effusions, the values obtained in group B were not in the same pH subgroup as values obtained in group A 80% of the time. The pH values obtained in group B wrongly predicted whether the patient required a chest tube in two of two cases (100%), according to Light's criteria.4


View this table:
[in this window]
[in a new window]

  		Table 2. Characteristics of the Study Population with Pleural Effusion Volume > 15% of Hemithorax

 

   Conclusion
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Conclusion
References
 
Pleural fluid pH is typically used at the time of the thoracentesis to define the need of a chest tube in cases of parapneumonic pleural effusions. To date, there have been no studies to assess the influence of anesthesia on the values of pleural pH and its influence on the management of patients.

Although the pH of the fluid collected after the patients were anesthetized differed in a statistically significant way, the results of our study suggest that the absolute impact of local anesthesia on pleural fluid pH is not great, nor is the relative change in pH altered in a clinically meaningful way. However, there were clinically significant differences in those patients who had parapneumonic effusions, and this could alter clinical management in 50% of cases.

The clinically significant differences were even more important in patients with pleural effusions of < 15% of the affected hemithorax; in such cases, the pH values after the administration of anesthesia were not predictive of complicated vs uncomplicated parapneumonic effusions in any of the patients.

We postulate that part of the anesthetic solution may enter the pleural cavity. Because the pH of the anesthetic is significantly lower than the pH that is usually found in pleural effusions, there is an acidification of the pleural fluid; this acidification is even higher when the pleural effusion is small.

To conclude, we recommend administering anesthesia before performing thoracentesis except in cases of suspected parapneumonic effusions, especially if they occupy < 15% of the affected hemithorax.

Received for publication November 9, 1998. Accepted for publication March 17, 1999.


   References
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Conclusion
 References
 

  1. Heffner, JE, Brown, LK, Barbieri, C, et al (1995) Pleural fluid chemical analysis in parapneumonic effusions. Am J Respir Crit Care Med 151,1700-1708[Abstract]
  2. Sahn, SA, Good, JT, Jr (1988) Pleural fluid pH in malignant effusions. Ann Intern Med 108,345-349
  3. Light RW. Pleural diseases. 3rd ed. Baltimore, MD: Williams & Wilkins, 1995; 50–52, 129–142
  4. Sahn, SA, Light, RW (1989) The sun should never set on a parapneumonic effusion. Chest 95,945-947[Free Full Text]
  5. Bland, JM, Altman, DG (1986) Statistical methods for assessing agreement between two methods of clinical measurement. Lancet 1,307-310[CrossRef][ISI][Medline]
  6. Lesho, EP, Roth, BJ (1997) Is pH paper an acceptable, low-cost alternative to the blood gas analyzer for determining pleural fluid pH? Chest 112,1291-1292[Abstract/Free Full Text]
  7. Light, RW (1998) The management of parapneumonic effusions and empyema. Curr Opin Pulm Med 4,227-229[CrossRef][Medline]



This article has been cited by other articles:


Home page
 ThoraxHome page
C W H Davies, F V Gleeson, and R J O Davies
BTS guidelines for the management of pleural infection
Thorax, May 1, 2003; 58(90002): ii18 - 28.
[Full Text]

Home page
 Eur Respir JHome page
J. Alegre, J. Jufresa, R. Segura, A. Ferrer, L. Armadans, C. Aleman, R. Marti, E. Ruiz, and T. Fernandez de Sevilla
Pleural-fluid myeloperoxidase in complicated and noncomplicated parapneumonic pleural effusions
Eur. Respir. J., February 1, 2002; 19(2): 320 - 325.
[Abstract] [Full Text] [PDF]

This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF) Free
Right arrow Submit a response
Right arrow Alert me when this article is cited
Right arrow Alert me when eLetters are posted
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Add to My Personal Article Archive
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via ISI Web of Science (2)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Castro, D. J.
Right arrow Articles by Yusen, R. D.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Castro, D. J.
Right arrow Articles by Yusen, R. D.

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS