From the Guidelines
Yes, a venous blood gas (VBG) can provide a sufficiently accurate pH measurement to help determine diabetic ketoacidosis (DKA). According to the study published in Diabetes Care 1, the diagnostic criteria for DKA include a venous pH of 7.3, which suggests that venous blood gas can be used to determine the pH level for DKA diagnosis.
The study also mentions that during therapy for DKA, blood should be drawn every 2–4 h for determination of serum electrolytes, glucose, blood urea nitrogen, creatinine, osmolality, and venous pH (for DKA) 1. This indicates that venous pH is a reliable and sufficient measure for monitoring the resolution of acidosis in DKA patients.
Some key points to consider when using venous blood gas for DKA diagnosis include:
- Venous pH typically runs about 0.02-0.04 units lower than arterial pH, which is a clinically insignificant difference for DKA diagnosis purposes.
- In DKA, you're looking for a metabolic acidosis with pH typically below 7.30, elevated anion gap, hyperglycemia, and presence of ketones.
- The venous sample will reliably detect these significant pH derangements.
- Venous samples are less accurate for measuring oxygen levels, so if respiratory status assessment is needed, an arterial sample would be preferred.
Overall, venous blood gas can be a reliable and less invasive alternative to arterial blood gas for determining pH levels in DKA patients, and can be used in conjunction with other laboratory tests to diagnose and monitor DKA 1.
From the Research
Determining DKA using Venous Blood Gas
- The use of venous blood gas to determine pH in diabetic ketoacidosis (DKA) has been studied in several research papers 2, 3, 4, 5.
- A study published in 1998 found that venous blood gas measurements accurately demonstrate the degree of acidosis in adult patients presenting with DKA, with a high correlation between arterial and venous pH results (r = 0.9689) 3.
- Another study published in 2014 derived a predictive formula for arterial pH from serum venous bicarbonate level, finding that venous serum bicarbonate concentration of ≤20.6 mEq/L predicted arterial pH ≤7.3 with over 95% sensitivity and 92% accuracy 4.
- A review of the evidence supporting the use of venous blood gas assessment in DKA found that venous values can be clinically acceptable alternatives to arterial measurements, with reasonable evidence that venous and arterial pH have sufficient agreement to be clinically interchangeable in patients with DKA who are haemodynamically stable and without respiratory failure 5.
- However, it is noted that the measurement of blood gas pH, via arterial or venous sampling, may not substantially impact the management of the patient, especially if sodium bicarbonate administration is not being considered 2.
Comparison of Arterial and Venous Blood Gas Values
- Studies have shown that the difference between arterial and venous pH values is relatively small, with a mean difference of 0.03 (range 0.0 to 0.11) 3 and a weighted average difference of 0.02 pH units (95% limits of agreement -0.009 to +0.021 pH units) 5.
- The correlation between arterial and venous bicarbonate results has also been found to be high (r = 0.9543) 3, although further confirmation is needed to establish the agreement between venous and arterial bicarbonate in DKA 5.
Clinical Implications
- The use of venous blood gas to determine pH in DKA may be a viable alternative to arterial blood gas sampling, particularly in situations where arterial sampling is not feasible or is associated with increased risk 4, 5.
- However, the decision to use venous blood gas should be made on a case-by-case basis, taking into account the individual patient's clinical presentation and the availability of resources 2, 6.