Exploring the Feasibility of Calculating Expected pCO2 From Venous Blood Gas Samples Alone in Intensive Care Patients

Abstract

Introduction This study highlights the significance of assessing acid-base balance and gas exchange in intensive care patients. The research investigates the applicability of using the "expected (pCO 2 = HCO 3 + 15)" formula, derived from venous blood gas samples, as an alternative to Winter's formula and practical formula. The study emphasizes the importance of identifying the primary acid-base abnormality accurately and efficiently for appropriate clinical intervention in critically ill patients. Methods This study included 400 adult patients admitted to the Anesthesia Clinic in the Third Stage Anesthesia and Reanimation Intensive Care Unit at Hitit University Erol Olçok Training and Research Hospital between April 2020 and July 2023. Blood gas samples were collected simultaneously from both arterial lines and venous catheters. Patients under 18 years, pregnant women, hemodialysis patients, and those with missing data were excluded. The study aimed to calculate the expected partial pressure of carbon dioxide (pCO 2 ) values using Winter's formula and simple formula for both arterial and venous blood gas samples and assess potential correlations between them. Results The results showed a narrow range for arterial pH values (7.12-7.72), a wider distribution for pCO 2 values (17.90-81.30 mmHg), and a moderate dispersion for HCO 3 values (12.80-44.33 mmol/L). Both Winter's and simple formulas were applied to estimate the expected pCO 2 values, showing strong positive correlations between arterial and venous pH, pCO 2 , and HCO 3 values. The scatterplot illustrated a very high level of association (Pearson's correlation coefficient, r = 1) between the expected pCO 2 values derived from both formulas using arterial and venous blood gas samples. Conclusion The clinical study demonstrates that estimating expected pCO 2 values in mixed acid-base disorders can be achieved using a simple and convenient formulation, eliminating the need for arterial blood gas sampling and its associated complications.

High-Flow Nasal Cannula Versus Noninvasive Ventilation as Initial Treatment in Acute Hypoxia: A Propensity Score-Matched Study

“…Notably, a majority of first available blood gases were venous, which may be less accurate than arterial blood gases for measuring P co 2 ( 25 , 26 ). Dividing patients into categories based on the comparison of measured to expected P co 2 , rather than using exact P co 2 values, may help decrease inaccurate judgments based on venous blood gases ( 27 ). Also, given some patients were treated with HFNC or NIV immediately on ED arrival, it was not always possible to isolate the pretreatment severity of illness.…”

“…using exact Pco 2 values, may help decrease inaccurate judgments based on venous blood gases (27). Also, given some patients were treated with HFNC or NIV immediately on ED arrival, it was not always possible to isolate the pretreatment severity of illness.…”