VBG Indications in Seizure Patients
Venous blood gas (VBG) analysis is NOT routinely indicated in patients presenting with seizures, but should be obtained in specific high-risk scenarios including status epilepticus with respiratory compromise, suspected metabolic acidosis, or when arterial blood gas sampling is not feasible. 1, 2
When VBG is NOT Indicated
VBG should not be obtained in lower-risk patients with brief resolved seizures who have returned to baseline, as the benefits of reducing unnecessary testing, pain, and false-positive results outweigh the rare diagnostic opportunities for acid-base disturbances 1
In otherwise healthy adults with new-onset seizures who have returned to baseline, only serum glucose and sodium levels are recommended, not blood gas analysis 3, 4
Routine VBG testing in uncomplicated seizure presentations adds minimal diagnostic value and should be avoided to reduce costs, procedural pain, and patient anxiety 1
When VBG IS Indicated
Status Epilepticus
VBG (or ABG) should be performed in patients with status epilepticus who have respiratory compromise or suspected metabolic acidosis, as these patients require comprehensive metabolic assessment 2
In critically ill seizure patients, VBG can reliably detect metabolic acidosis, metabolic alkalosis, and respiratory acidosis with high sensitivity (100%), making it a reasonable alternative to arterial sampling 5
Specific Clinical Scenarios
VBG may help predict seizure recurrence when obtained within 1 hour of the last seizure episode, with threshold values including pH <7.245, bicarbonate <17.1 mmol/L, base excess <-11.1 mEq/L, and lactate >7.65 mmol/L showing 80% sensitivity and >96% negative predictive value 6
In patients with central venous access, VBG provides accurate acid-base diagnosis comparable to ABG, even in shock states, avoiding the risks of arterial puncture 5
Key Limitations and Caveats
VBG cannot reliably assess oxygenation status or accurately measure PCO2, with 95% limits of agreement for PCO2 of approximately 20 mmHg compared to ABG 7
However, a venous PCO2 ≤45 mmHg (6 kPa) reliably excludes clinically significant hypercarbia, making VBG useful for ruling out respiratory failure 7
pH and bicarbonate values from VBG are clinically interchangeable with ABG values, supporting its use for metabolic assessment 7, 5
Recommended Approach
For routine seizure evaluation: Check only serum glucose and sodium immediately; pregnancy test for women of childbearing age 3, 4
For status epilepticus: Obtain VBG if respiratory compromise is present or if comprehensive metabolic assessment is needed, particularly when arterial access is not available 2
For seizure recurrence risk stratification: Consider VBG within 1 hour of the last seizure if predicting recurrence risk will alter management 6