Transcranial Doppler Changes in Patients Treated with Extracorporeal Membrane Oxygenation

Transcranial Doppler (TCD) has significant implications for neurovascular assessment in patients being treated with venoarterial-extracorporeal membrane oxygenation (VA-ECMO). However, there have been no studies demonstrating the changes in pulsatility indices (PIs) seen in these patients. Nonpulsatile waveforms are seen during on-pump coronary artery bypass graft, but low or low-normal PIs have never been reported. It is important to be aware of these changes, as they can be misinterpreted as cerebral vasodilation, vasoconstriction, increased intracranial pressures (ICPs), or cerebral circulatory arrest.

Data from 11 TCDs from 8 patients on VA-ECMO in the Cedars Sinai Medical Center Cardiac Surgical Intensive Care Unit were reviewed. Mean pulsatility indices were calculated for each patient using Gosling's PI formula. The values obtained were correlated with ejection fraction (EF) values obtained from a transthoracic or transesophageal echocardiogram.

PIs were globally low or absent in all 11 TCDs. In 3 patients, TCDs were performed at the initiation and conclusion of the VA-ECMO cannulation. The PI values for these TCDs correlated directly with changes in EFs. Also, an abrupt rise in PI to normal value was seen with the placement of a total artificial heart and the return of pulsatile circulation.

We demonstrate that PIs on TCDs in patients treated with VA-ECMO are either low or cannot be calculated depending on the severity of myocardial suppression, and should not be mistaken for cerebral vasodilation or cerebral circulatory arrest. Moreover, rising PIs in these patients can represent improving cardiac function and should not be confused with elevated ICPs.