Non-invasive, pre-operative detection
- Determination of cerebral vasomotor reserve (CO2-reactivity) with the CO2 test
- Determination of the proportion of blood flow from the contralateral side in patients with unilateral occlusion of the ICA
- Investigation of the potential of TCD with CO2-reactivity to identify patients expected to improve after ECA
- Identification of the TCD variables that can be utilised to predict patients who are at risk of cerebral ischaemia (during clamping of the CCA)
Non-invasive, peri-operative monitoring
One possible application of TCD is to monitor intracerebral hemodynamic during interventions with or without anesthesia. This fulfils the desire for a non-invasive, continuously-recording procedure for measuring cerebral blood flow during anesthesia. The user may be provided with valuable information by both, the flow rate (or changes in flow rate) and the characteristic profile of the intrinsic curve (pulsatility).
Many potential applications are conceivable during an intervention, especially in patients with increased risk of cerebral ischemia.
Endarterectomy of the carotid arteries
Recognition of cerebral ischemia during cross-clamping of the carotid artery is an indication in which TCD sonography is already an established and important procedure. It fulfils the majority of requirements for an ideal monitor, since TCD enables continuous, non-invasive monitoring of the changes occurring in cerebral hemodynamic during surgical occlusion of the carotid artery. With TCD it is possible to observe the typical changes in flow rate when the artery is clamped and released again.
Diagnosis and application in stroke units
Continuous recording of cerebral blood flow during recanalisation enables an optimized treatment.
Doppler can indicate the effectiveness of a thrombolytic treatment.
Surgery of cerebral aneurysms
Systemic hypotension reduces transmural pressure in the sacculated aneurysm and hence the risk of a tear during surgical dissection and clamping of a cerebral aneurysm.
Hypotension also reduces haemorrhaging from the small adjacent blood vessels, improving the visibility of the anatomy of the aneurysm and the perforating vessels.
Thanks to continuous TCD monitoring it is possible for the anaesthetist to decide whether the patient will tolerate induced hypotension. Moreover, the effect of hyperventilation on cerebral blood flow during this critical period may be seen.
Detection of emboli and its differentiation
Recognition of microemboli during a carotid endarterectomy
Microemboli frequently arises during a carotid endarterectomy. Both, gaseous and solid emboli can be detected by TCD. During carotid endarterectomy, emboli are probably more responsible than hemodynamic causes for peri-operative strokes.
Diagnosis and treatment of post-operative intimal flaps or thromboses
Using TCD it is possible to recognise the formation of a thrombus or a nidus of emboli at the end of surgery or in the recovery room. This enables rapid treatment to prevent an impending stroke. If symptoms suddenly develop in the recovery room a TCD investigation should be carried out immediately, thereby preventing invasive angiography having to be performed.
Emboli commonly occur during heart surgery. Emboli detection is one way of improving surgical technique, especially during cardiopulmonary bypass and during open-heart surgery.
Emboli due to right-left shunts e.g. Patent Foramen Ovale (PFO/OFO) are considered by the majority of specialists to be the possible cause of cerebral ischemia and subsequent stroke. Application of transcranial Doppler sonography while injecting an ultrasound contrast agent that does not penetrate the lung capillaries has been proposed as an alternative method for detecting of such right-left shunts.