The aim of this study was to assess changes in the acid-base equilibrium of pleural fluid during the first 2 hours after thoracentesis and to determine whether, as with arterial blood, it is important to keep the fluid on ice.
Patients and methodsA prospective, descriptive, comparative study was performed in 53 consecutive patients with pleural effusion. Thoracentesis was performed and pleural fluid was collected in 5 heparinized syringes to determine the pH, PO2, and PCO2 at baseline and at 30, 60, 90, and 120 minutes. In the first 26 patients, pleural fluid was collected in a further 4 syringes that were kept on ice prior to performing the same measurements at 30, 60, 90, and 120 minutes.
ResultsThe patients had a mean (SD) age of 70 (14) years, 66% were smokers, 72% were men, 63% had right-sided pleural effusion, 85% had unilateral effusion, and 15% had massive effusion. In 10 patients the effusion was a transudate, in 35 it was lymphocytic, and in 8 it was neutrophilic. The etiology was benign in 34 cases and neoplastic in 19 cases. The baseline pH was 7.35 (0.1) and baseline values of PO2 and PCO2 were 57.8 (20) mm Hg and 53.7 (15) mm Hg, respectively. No significant changes were observed in the first 2 hours for either pH or PCO2, whereas PO2 did undergo a significant change over this period. The difference between the baseline value and the value obtained at 120 minutes was 0.005 (0.02) for pH, 12.5 (19) mm Hg for PO2, and 0.8 (3) mm Hg for PCO2, with correlation coefficients of 0.97, 0.49, and 0.98, respectively. Comparison of values by simple regression analysis did not reveal a significant difference in the changes in pH, PO2, or PCO2 associated with keeping samples on ice. Multivariate analysis revealed that neoplastic effusion and a higher red blood cell count in pleural fluid had a significant influence on pH changes.
ConclusionsThe pH and PCO2 of pleural fluid did not change significantly during the first 2 hours following thoracentesis, whereas PO2 did undergo a significant change. Keeping samples on ice during this period is unnecessary. Only a higher red blood cell count in pleural fluid and neoplastic effusion had a limited effect on changes in the pH of samples from our patients during the first 2 hours following thoracentesis.
Valorar los cambios en el equilibrio ácido-base del líquido pleural durante las primeras 2 h de la toracocentesis y la importancia de su conservación en hielo como ocu-rre en la sangre arterial.
Pacientes y métodosEstudio prospectivo, descriptivo y comparativo de 53 pacientes consecutivos con un derrame pleural. Se realizó toracocentesis con extracción del líquido pleural en 5 jeringas heparinizadas para determinar el pH, presión arterial de oxígeno (PO2) y de anhídrido carbónico (PCO2) basales, a los 30, 60, 90 y 120 min. En los primeros 26 pacientes se obtuvieron 4 jeringas que se conservaron en hielo y se realizaron las mismas determinaciones en el tiempo.
ResultadosLOS pacientes tenían una edad media (± des-viación estándar) de 70 ± 14 años, el 66% eran fumadores, el 72% varones, un 63% tenía un derrame derecho, un 85% unilateral y el 15% masivo. En 10 casos era un trasudado, en 35 exudado linfocitario y en 8 neutrofílico. La etiología fue benigna en 34 casos y neoplásica en 19. El valor basal del pH fue de 7,35 ± 0,1, y los de PO2y PCO2 de 57,8 ± 20 y 53,7 ± 15 mmHg, respectivamente, y no presentaron cambios significativos durante las primeras 2 h, a excepción de la PO2. El pH presentó una diferencia entre su valor basal y a los 120 min de 0,005 ± 0,02, la PO2 de 12,5 ± 19 mmHg y la PCO2 de 0,8 ± 3 mmHg, con unos coeficientes de correlación de 0,97, 0,49 y 0,98, respectivamente. El estudio comparativo y la regresión simple no demostraron una influencia sig-nificativa de la conservación en hielo en los cambios de pH, PO2 o PCO2. Una etiología neoplásica y un mayor número de hematíes influyeron de forma significativa en los cambios de pH en el análisis multivariante.
ConclusionesEl pH y la PCO2 pleurales no presentaron cambios significativos durante las primeras 2 h de la toracocentesis, a diferencia de la PO2. La conservación en hielo no estaría indicada durante este período. Sólo un nümero más elevado de hematíes o una etiología neoplásica tuvieron una influencia limitada en los cambios de los valores del pH de nuestros pacientes en las primeras 2 h.
