Unclear mechanism of cardiopulmonary arrest following cervical epidural steroid injection.

We read with much interest the case report titled 'Cardiopulmonary Arrest Following Cervical Epidural Steroid Injection' by Stauber et al (1) in the March/April 2012 issue. The case report highlighted a cardiopulmonary arrest which occurred within 5 seconds after the injection of epidural steroid in 1% lidocaine. The quoted amount of betamethasone was 12 mg in a total volume of 4 mL. Assuming a standard concentration of 6 mg per milliliter, this would indicate two milliliters of 1% lidocaine were injected into the epidural space. The authors maintain that the cardiopulmonary arrest was caused from the blockade of sympathetic cardiac accelerator fibers immediately following the injection at C6-C7. It was also postulated that the pneumocephalus that was later found on CT scan was the result of a similar "pump" mechanism proposed by the Imanishi article (2) which describes the finding of air in intracranial veins after CPR. A more likely cause that would account for the case details is intrathecal administration of lidocaine as the culprit for subsequent cardiac arrest. The fact that the pneumocephalus found on CT was subarachnoid and that loss of resistance to air was the method used to locate the epidural space leads me to believe that it is more probable that the air entry site was also subarachnoid. Imanishi's article explains the rare finding of air in intracranial veins after external cardiac massage but does not adequately explain the finding of