Case 9

The most likely mechanism is cerebral ischemia from rapid changes in cerebral blood flow related to the precipitous drop in PaCO₂. The patient’s PaCO₂ dropped from 88 to 32 mmHg within 30 minutes of ECMO initiation—a decrease of 56 mmHg. CO₂ is a potent cerebral vasodilator; with chronically elevated CO₂, cerebral vasculature is maximally dilated. Rapid normalization of CO₂ causes abrupt cerebral vasoconstriction, reducing cerebral blood flow and potentially causing ischemic injury. The specific pre-ECMO vulnerability was the severely elevated PaCO₂ of 88 mmHg. Patients with high partial pressures of CO₂ prior to ECMO cannulation are at particular risk because rapid drops have been associated with various CNS injuries likely related to alterations in cerebral blood flow. An alternative or coexisting mechanism is thromboembolism from the ECMO circuit to a cerebral artery.

Answer: D. High pre-ECMO PaCO₂ with rapid correction after ECMO initiation is the most significant risk factor highlighted in this scenario. Rapid drops in PaCO₂ cause cerebral vasoconstriction and have been associated with CNS injury. Other pre-ECMO risk factors include hypoxemia, acidemia (metabolic and respiratory), and hypotension. 

Young age (A) is not specifically a risk factor. While large dual-lumen cannulas in the neck (C) can be associated with neurological issues, they are not the most prominent risk factor. High pre-ECMO PaO₂ (B) is not a recognized risk factor—the concern is hypoxemia, not hyperoxia.

A multidisciplinary discussion is required, including: 

(1) Neurology consultation to determine the degree of injury, provide prognostication, and guide acute stroke management. 

(2) Discussion with the patient’s family regarding the diagnosis, prognosis, and goals of care. 

(3) A team decision about whether to continue ECMO support—this depends on the extent of neurological injury and the patient’s overall trajectory. 

(4) If the decision is to continue ECMO, the circuit should be evaluated for clots and circuit-associated coagulopathy, with consideration for circuit exchange. A decision regarding anticoagulation intensity should be made. 

(5) Implement standard post-ischemic stroke management including serial neurologic examinations, blood pressure management, and seizure monitoring. 

(6) Minimize sedation to allow for accurate serial neurologic assessments.

Preventive strategies: 

(1) Most importantly, avoid rapid correction of PaCO₂. When initiating ECMO in patients with severe hypercapnia, the sweep gas flow should be started low and titrated slowly, allowing PaCO₂ to normalize gradually over hours rather than minutes. A commonly used approach is to target a PaCO₂ decrease of no more than 10–15 mmHg per hour. 

(2) Minimize sedation and perform serial neurologic examinations, especially in the first 24–48 hours after cannulation. 

(3) Maintain adequate blood pressure to ensure cerebral perfusion. 

(4) Optimize anticoagulation to prevent thromboembolism while monitoring for signs of circuit clot formation.

For hemorrhagic stroke on ECMO, anticoagulation management is the opposite of ischemic stroke: 

(1) Anticoagulation must be held and possibly reversed to prevent hematoma expansion. 

(2) Factor replacement should be considered to reduce the risk of clot extension—this may include platelets, fresh frozen plasma, cryoprecipitate, or specific factor concentrates depending on the coagulation profile. 

(3) A neurosurgery consultation is needed in addition to neurology, as surgical evacuation may be required depending on the size and location of the hemorrhage. 

(4) A multidisciplinary discussion with the patient’s family should determine the degree of injury and whether to continue ECMO support. 

(5) If the decision is to continue ECMO, the team must accept the increased risk of circuit thrombosis while anticoagulation is held, with close monitoring of the circuit. This creates an extremely challenging management dilemma.