Venous vs Arterial Blood Gases in Acute Exacerbation of COPD

Hussain Ahmad, Mukhtiar Zaman, Rukhsana Javed Farooqi, Saadia Ashraf


Background: Arterial blood gases are necessary for management of
respiratory failure in patients with acute exacerbation of COPD. Venous blood
gas analysis may be a less invasive potential alternative. The objective of our
study was to determine the accuracy of venous blood gases in the diagnosis of
hypercapnic respiratory failure and to determine the correlation between
arterial and venous PH, PCO2 and HCO3.

Methodology: All adult patients presenting to Pulmonology department
between November 2018 and March 2019 with COPD exacerbation having
SPO < 90% were included. Patients in shock, arrhythmia, diabetic 2 ketoacidosis, renal failure, bleeding disorder or unwilling for blood sampling
were excluded. Paired arterial and venous blood samples were obtained and
analyzed on the spot via blood gas analyzer. The sensitivity, specificity and
diagnostic accuracy of VBGs were calculated via SPSS 19, by taking PCO2
>45mm of Hg as cut off value to diagnose hypercapnia using ABGs as the gold
standard. Correlation between arterial and venous PH, PCO2 and HCO3 were 
calculated via Pearson correlation.

Results: We enrolled 87 patients, with mean age of 51yrs (+ 8.89 SD) and male to female ratio of 1: 2.2. The mean venous minus arterial PH (7.39-7.40) was -0.13. The mean venous minus arterial PCO (60-54) was 6mm of Hg. The 2
sensitivity of venous PCO in the diagnosis of hypercapnia was 97.95%, 2 specificity 66.66%, PPV 80%, NPV 96% and diagnostic accuracy of 82.7%.
There was a strong correlation between arterial and venous PH (r =0.83), HCO 3 (r=0.63) and PCO2 (r=0.92). 

Conclusion: VBGs instead of ABGs can be used as a screening test for
detection of hypercapnia in hemodynamically stable patients presenting with
acute exacerbation of COPD and VBGs indices (PH, PCO2 and HCO3 ) can 
provide guidance about the severity of acid base disturbance.


Arterial blood gases; Venous blood gases; Hypercapnia; COPD exacerbation

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