Correlation and agreement between arterial and central venous blood pH, PO2, PCO2 and HCO3- values of mechanically ventilated patients in intensive care unit: A prospective observational study☆,☆☆

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Abstract

Background:

The procedure for arterial blood sampling can be technically difficult with limitations and complications.

Aims:

To evaluate the correlation and agreement between arterial and central venous blood pH, PO2, PCO2 and HCO3- values and infer whether central venous blood gas (CVBG) values could replace arterial blood gas (ABG) values.

Design:

Prospective observational study.

Methods and Material:

A total of 100 samples were collected from 50 adult normotensive and normothermic patients requiring mechanical ventilation. Arterial blood was collected from radial artery and within 2 minutes central venous blood was withdrawn from the same patient. Correlation and agreement was tested using Pearson's Correlation and Bland Altman Analysis.

Results:

The pH, PO2, PCO2 and HCO3- of CVBG correlated significantly with arterial values (rpH = 0.88, p <0.001; rPO2 = 0.358, p < 0.05; rPCO2 = 0.470, p < 0.001 and rHCO3 = 0.714, p < 0.001). Regression equations were derived to predict AVG values from CVBG values as follows: Arterial pH = 0.879 × central venous pH + 0.9422 (constant), arterial PO2 = 0.421 × central venous PO2 + 114.4 (constant), R2 = 0.128, arterial PCO2 = 0.429 × central venous PCO2 + 24.627 (constant), R2 = 0.2205 and arterial HCO3 = 1.045 × central venous HCO3 + 3.402 (constant), R2 = 0.5101.The mean arterial minus venous difference for pH, PO2, PCO2, and bicarbonate was 0.053 ± 0.014, 56.04 ± 15.74, 2.20 ± 4.4 and 4.30 ± 1.64 respectively. Bland-Altman plots for agreement of pH, PO2, PCO2, and bicarbonate showed 95% limits of agreement of -0.04 to 0.146, -52.51 to 164.59, -26.61 to 31.01 and -7.0 to 15.6, respectively.

Conclusions:

The arterial pH, PO2, PCO2 and HCO3- values correlated well with central venous values. However, only the arterial pH value can replace the central venous pH value.

Antecedentes:

la toma de gases arteriales (GA) puede ser difícil con limitaciones y complicaciones.

Objetivo:

evaluar la correlación y concordancia entre valores de pH, PO2, PCO2 y HCO3- en sangre arterial y venosa central e inferir si valores de gases venosos centrales (GVC) pueden reemplazar valores de GA.

Diseño:

Estudio prospectivo observacional.

Materiales y Métodos:

se tomaron 100 muestras en 50 pacientes adultos normotensos y normotérmicos, que requirieron ventilación mecánica. Los GA se tomaron de la arteria radial y 2 minutos después se tomaron los GVC. Se evaluó la correlación y concordancia utilizando la Correlación de Pearson y Análisis de Bland Altman.

Resultados:

los valores venosos y arteriales de pH, PO2, PCO2 y HCO3- correlacionaron significativamente (rpH = 0.88, p < 0.001; rPO2 = 0.358, p < 0.05; rPCO2 = 0.470, p < 0.001 y rHCO3 = 0.714, p < 0.001). Las ecuaciones que predicen los valores de GA a partir de valores de GVC, son: pH arterial = 0.879 × pH venoso central + 0.9422; PO2 arterial = 0.421 × PO2 venoso central + 114.4, R2 = 0.128, PCO2 arterial = 0.429 × PCO2 venoso central +24.627, R2 = 0.2205 y HCO3 arterial = 1.045 × HCO3 venoso central + 3.402, R2 = 0.5101. La diferencia media de GA menos GVC de pH, PO2, PCO2, y bicarbonato fue de 0.053 ± 0.014, 56.04 ± 15.74, 2.20 ± 4.4 y 4.30 ± 1.64, respectivamente. Las gráficas de Bland-Altman para concordancia del pH, PO2, PCO2 y bicarbonato mostraron límites de concordancia del 95% de -0.04 a 0.146, -52.51 a 164.59, -26.61 a 31.01 y -7.0 a 15.6, respectivamente.

Conclusiones:

hubo correlación entre los valores de GA y GVC de pH, PO2, PCO2 y HCO3-. Sin embargo, solamente el pH venoso puede reemplazar el pH arterial.

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