[Influence of the method used to obtain pleural fluid on the determination of the Acid-base balance]. / Importancia de la forma de obtención del líquido en la determinación del equilibrio ácido-base pleural.

OBJECTIVE: To analyze the methods used in our hospital for obtaining pleural fluid to determine the acid-base balance and to evaluate the clinical repercussions of each method. METHODS: Initially we studied the methods used by physicians in our hospital to collect pleural fluid for determination of the acid-base balance. In a second phase, we performed a prospective, descriptive, comparative study with the participation of 71 patients with pleural effusions in order to compare the acid-base balance according to the technique used to obtain the fluid. RESULTS: Pleural fluid was obtained using 3 methods: a) direct extraction using a heparinized syringe (group 1); b) extraction using a 20 mL syringe with subsequent aspiration from this syringe into a heparinized syringe (group 2); and c) filling a heparinized syringe from the 20 mL syringe (group 3). The only significant differences between group 1 and groups 2 and 3 were an increase in the pleural PO2 and oxygen saturation. The difference in the mean pH between groups 1 and 2 was 0.009 (95% confidence interval: -0.39 to 0.02; P=.5) and between groups 1 and 3 was 0.007 (95% confidence interval: -0.38 to 0.023; P=.6). The correlations between findings for PO2, pH, and PCO2 obtained in the different groups were statistically significant, with values superior to .95 in the last 2 variables. CONCLUSIONS: Physicians who perform thoracentesis in our hospital use different methods for obtaining fluid to determine the pleural acid-base balance. The 3 methods analyzed show no significant differences with regard to pH or PCO2. Pleural fluid may be obtained by a single puncture with a large-volume syringe, subsequently transferring the fluid to a heparinized syringe without this significantly affecting the pH or PCO2, thus reducing the number of manipulations and the risk of complications.

Importancia de la forma de obtención del líquido en la determinación del equilibrio ácido-base pleural / Influence of the method used to obtain pleural fluid on the determination of the acid-base balance

OBJETIVO: Analizar las formas de obtención del líquido para determinar el equilibrio ácido-base pleural en nuestro medio y su influencia o relevancia clínica. MÉTODOS: En una primera fase se describieron las formas en que los médicos de nuestro hospital obtenían el líquido para determinar el equilibrio ácido-base pleural. En una segunda fase se realizó un estudio prospectivo, descriptivo y comparativo de 71 pacientes con derrame para comparar el equilibrio ácido-base pleural según las formas de obtención. RESULTADOS: El líquido pleural se obtenía de 3 formas distintas: a) extracción directa con jeringa heparinizada (grupo I); b) extracción con jeringa de 20 ml, aspirando de esta jeringa con la jeringa heparinizada (grupo II), o c) llenando la jeringa heparinizada con la jeringa de 20 ml (grupo III). Se observó un aumento significativo sólo en los valores de la presión parcial (PO2) y saturación de oxígeno entre el grupo I y los grupos II o III. La diferencia de las medias del pH entre los grupos I y II fue de 0,009 (intervalo de confianza del 95%, -0,039 a 0,02; p = 0,5), y entre los grupos I y III, de 0,007 (intervalo de confianza del 95%, -0,038 a 0,023; p = 0,6). Las correlaciones entre los distintos grupos de la PO2, pH y presión parcial de anhídrido carbónico (PCO2) fueron estadísticamente significativas y con valores superiores a 0,95 en las 2 últimas. CONCLUSIONES: Los médicos que realizan las toracocentesis en nuestro hospital procesan de formas distintas el líquido para determinar el equilibrio ácido-base pleural. Las 3 formas analizadas no mostraron diferencias significativas en cuanto al pH y la PCO2. La obtención del líquido puede realizarse con una única punción con jeringas de mayor capacidad, para posteriormente llenar la jeringa heparinizada, sin que se modifiquen de forma significativa los valores del pH y la PCO2, y con una disminución del número de manipulaciones y el riesgo de complicaciones

OBJECTIVE: To analyze the methods used in our hospital for obtaining pleural fluid to determine the acid-base balance and to evaluate the clinical repercussions of each method. METHODS: Initially we studied the methods used by physicians in our hospital to collect pleural fluid for determination of the acid-base balance. In a second phase, we performed a prospective, descriptive, comparative study with the participation of 71 patients with pleural effusions in order to compare the acid-base balance according to the technique used to obtain the fluid. RESULTS: Pleural fluid was obtained using 3 methods: a) direct extraction using a heparinized syringe (group 1); b) extraction using a 20 mL syringe with subsequent aspiration from this syringe into a heparinized syringe (group 2); and c) filling a heparinized syringe from the 20 mL syringe (group 3). The only significant differences between group 1 and groups 2 and 3 were an increase in the pleural PO2 and oxygen saturation. The difference in the mean pH between groups 1 and 2 was 0.009 (95% confidence interval: -0.39 to 0.02; P=.5) and between groups 1 and 3 was 0.007 (95% confidence interval: -0.38 to 0.023; P=.6). The correlations between findings for PO2, pH, and PCO2 obtained in the different groups were statistically significant, with values superior to .95 in the last 2 variables. CONCLUSIONS: Physicians who perform thoracentesis in our hospital use different methods for obtaining fluid to determine the pleural acid-base balance. The 3 methods analyzed show no significant differences with regard to pH or PCO2. Pleural fluid may be obtained by a single puncture with a large-volume syringe, subsequently transferring the fluid to a heparinized syringe without this significantly affecting the pH or PCO2, thus reducing the number of manipulations and the risk of complications