CORRELATION OF VENOUS BLOOD GAS WITH ARTERIAL BLOOD GAS VALUES IN PATIENTS ADMITTED TO EMERGENCY DEPARTMENT

Introduction:

ABG is of utmost value for monitoring and driving the management of patients with multiple diseases. Though extremely useful, it has its own limitations and adverse effects like increased risk of errors in sample collection, over or under heparinization, mixing of venous blood, and delay in analysing. Drawing arterial blood is a very painful procedure and can be an issue in critically ill patients who have to undergo repeated procedures. Indwelling arterial catheters may cause bloodstream infections, local thrombosis, arterial vasospasm, aneurysm formation and rarely, thrombosis of radial artery leading to ischemia. We planned this study to check whether venous blood gas analysis can replace ABGs.

Methods:

Cross sectional observational hospital-based study. Sample size was 200. Inclusion criteria was age 18 years and above, admitted to ED. Two simultaneous samples were taken, from radial artery followed by a venous sample. Patients with abnormal Allen’s test, coagulopathy, thrombocytopenia and peripheral vascular disease were excluded.

Results:

200 patients were studied. Spearman rank coefficient was used for correlation between ABG and VBG parameters. Univariate regression equations were derived to predict arterial values from their venous counterparts. Further, venous values were arterialized using these equations and then compared with observed arterial values to find any significant difference. 

Mean venous pH was 7.35 and mean arterial pH was 7.39. Mean difference was 0.04. Venous pH correlated well with arterial pH (correlation coefficient 0.673, p< 0.0001). Univariate equation was derived, which was arterial pH= 3.518+0.526*pH (Venous). Using this equation, arterialized and arterial pH had no significant difference (p =0.327) 

Mean venous pCO2 was 41.18 while mean arterial pCO2 was 37.5 mmHg. Mean difference was 3.68. Venous pCO2 also had a good correlation with its arterial counterpart (correlation coefficient was 0.683, p<0.0001). Univariate equation was derived, which was arterial pCO2= 8.933+0.694*pCO2 (mmHg) (Venous). Arterialized and arterial pCO2 had no significant difference (p =0.255). 

Mean venous bicarbonate was 22.62 mmol/L while mean arterial bicarbonate was 22.1mmol/L. Correlation coefficient was 0.775 (p< 0.0001), that is, venous bicarbonate had an extremely high correlation with arterial bicarbonate. Univariate equation was derived, which was arterial bicarbonate = 4.231+0.79*Bicarbonate (Venous) (mmol/L). Using this equation, arterialized and arterial bicarbonate had no significant difference (p =0.399) 

Mean venous pO2 was 45.28 mmHg and mean arterial pO2 was 87.64mmHg. Correlation was poor between the two, with correlation coefficient of 0.134 (p=0.058). Univariate equation was derived, which was arterial pO2= 69.355+0.404*PvO2 (mmHg). However, the arterialized values of pO2 and actual PaO2 had significant difference (p=0.028). 

Mean arterial SpO2 was 90.54% and mean venous SpO2 was 65.77%. Correlation was poor between the two, 0.121 (p =0.088). Univariate equation was derived, which was arterialized SpO2= 87.695+0.043*SpO2 (%)(Venous). However, the arterialized values of SpO2 and SpO2 had significant difference (p=0.028). 

Conclusions:

Venous bicarbonate values had the highest correlation with corresponding arterial values followed by pCO2 and pH. Arterialized values of venous HCO3-, pCO2 and pH were not significantly different and can be used in emergency and critical care setting, where we are not really concerned about PaO2.

I have no potential conflict of interest to disclose.

I did not use generative AI and AI-assisted technologies in the writing process.