NIRS monitoring

An O3^® Regional Oximeter (Massimo, Irvine, CA), a 4-wavelength continuous-wave NIRS device with two light detectors, was used to continuously monitor the rSO₂ of the affected and unaffected hemispheres. ¹⁸ On arrival of the patient in the angiography suite, NIRS sensors were applied to the scalp bilaterally. Before sensor application, we extensively prepared the sites to ensure optimal sensor adherence and accurate sensor readings. The sites were first shaved, if applicable, and subsequently degreased, wiped clean and dried. In patients from the temporal cohort, adhesive NIRS sensor were applied bilaterally to the temporal scalp 2 cm above each ear, corresponding approximately to the T3/T4 positions on an EEG 10-20-system. ¹⁹ There were no recommendations for temporal NIRS monitoring in the operator’s manual. ²⁰ The sensor location was therefore determined by the authors and was based on previously published templates regarding the flow territories of the middle cerebral artery (the closest location to the ischaemic area of interest) ²¹ and practical considerations (a clear anatomical landmark that allowed the sensors to be applied at the same site in each patient). In the frontal cohort, NIRS sensors were applied bilaterally to the forehead, above the eyebrows as recommended by the operator’s manual. ²⁰

The intention was to start NIRS monitoring before induction of anaesthesia, but due to the emergency nature of the procedure this was not always feasible. In all cases it was possible to begin monitoring before the start of EVT (defined as groin puncture). NIRS monitoring ended after endotracheal extubation or shortly before departure from the angiography suite if extubation was not feasible or not performed.

After the completion of data collection, as part of a post hoc analysis, available CT perfusion images were re-assessed (RB) to investigate the plausibility that the NIRS sensors would have been able to measure the rSO₂ in the penumbra and ischaemic core (Supplemental Figure 1).