Prediction of arterial blood gas values from arterialized earlobe blood gas values in patients treated with mechanical ventilation

Background/objective: Arterial blood gas (ABG) analysis is useful in evaluation of the clinical condition of critically ill patients; however, arterial puncture or insertion of an arterial catheter may sometimes be difficult and cause many complications. Arterialized ear lobe blood samples have been described as adequate to gauge gas exchange in acute and chronically ill pediatric patients.

Purpose: This study evaluates whether pH, partial pressure of oxygen (PO(2)), partial pressure of carbon dioxide (PCO(2)), base excess (BE), and bicarbonate (HCO(3)) values of arterialized earlobe blood samples could accurately predict their arterial blood gas analogs for adult patients treated by mechanical ventilation in an intensive care unit (ICU).

Setting: A prospective descriptive study.

Methods: Sixty-seven patients who were admitted to ICU and treated with mechanical ventilation were included in this study. Blood samples were drawn simultaneously from the radial artery and arterialized earlobe of each patient.

Results: Regression equations and mean percentage-difference equations were derived to predict arterial pH, PCO(2), PO(2), BE, and HCO(3)-values from their earlobe analogs. pH, PCO(2), BE, and HCO(3) all significantly correlated in ABG and earlobe values. In spite of a highly significant correlation, the limits of agreement between the two methods were wide for PO(2). Regression equations for prediction of pH, PCO(2), BE, and HCO3- values were: arterial pH (pHa) = 1.81+ 0.76 x earlobe pH (pHe) [r = 0.791, P < 0.001]; PaCO(2) = 1.224+ 1.058 x earlobePCO(2) (PeCO(2)) [r = 0.956, P < 0.001]; arterial BE (BEa) = 1.14+ 0.95 x earlobe BE (BEe) [r= 0.894, P < 0.001], and arterial HCO(3)- (HCO(3)-a) = 1.41+ earlobe HCO(3)(HCO(3)-e) [r = 0.874, P < 0.001]. The predicted ABG values from the mean percentage-difference equations were derived as follows: pHa = pHe x 1.001; PaCO(2) = PeCO(2) x 0.33; BEa = BEe x 0.57; and HCO(3)-a = HCO(3)-e x 1.06.

Conclusions: Arterialized earlobe blood gas can accurately predict the ABG values of pH, PCO(2), BE, and HCO(3)- for patients who do not require regular continuous blood pressure measurements and close monitoring of arterial PO(2) measurements.