Hypercapnia Impact on Vascular and Neuronal Reactivity in Patients Before and After Carotid Endarterectomy

Abstract

Hypothesis: Regional cerebral blood flow (rCBF) and vascular reactivity strongly affect neuronal function. The restoration of blood flow values in the cerebral vascular system may be another benefit of carotid endarterectomy (CEA) in a specific group of patients. Animal experiments in dogs have provided evidence of neuronal reactivity depending on rCBF and vascular reactivity. However, as yet, there are no reports on neuronal reactivity changes related to altered perfusion parameters in humans.

Material and Methods: The cohort under study consisted of 41 patients after transient ischaemic attack (TIA) or reversible ischaemic neurological deficit (RIND) whose neurological findings were normal (group A) and 17 patients after minor stroke with a mild degree of hemiparesis or hemihypesthesia (mRS≤2) (group B). All patients were examined 0-2 days before CEA, on postoperative days 3-7 and at 3 months after CEA. The tests included median nerve somatosensory evoked potentials (SEPs) and transcranial Doppler (TCD) at rest, during hypercapnia (et-CO₂=7.0-7.5 kPa) and at rest after hypercapnia.

Results: Group A was found to have a significant increase in V_sys, V_mean and PI in response to hypercapnia in all periods (i.e., 0-2 days before CEA, on postoperative days 3-7 and at 3 months after CEA). N20/P25 amplitude decreased in response to hypercapnia before and early after CEA. Changes in other SEP parametres before and after hypercapnia were non-significant. Group B showed significant differences resulting from hypercapnia before and after CEA only in vasoreactivity (V_sys, V_mean, PI).

Conclusion: In the analysed group of patients high-grade carotid stenosis caused no haemodynamic impairment. Moreover, no evidence was found of artificially increased rCBF being accompanied by an equally significant change in somatosensory evoked scalp response.

Zusammenfassung

Hypothese: Die regionale cerebrale Blutzirkulation (cBZ) und die vaskuläre Reaktivität haben großen Einflussß auf die neuronale Funktion. Die Wiederherstellung des Blutflusses im cerebralen Gefäßsystem ist vermutlich ein weiterer Benefit der Karotisendarterektomie in einer selektiven Gruppe von Patienten. Tierexperimentelle Studien an Hunden lieferten den Beweis, dass die neuronale Aktivität vom cBZ und der vaskulären Reaktivität abhängig ist. Bis dato gibt es jedoch keine Berichte über Veränderungen der neuronalen Reaktivität in Zusammenhang mit der erhöhten Perfusion am Menschen.

Material und Methoden: In diese Studie wurden 41 Patienten nach einer transienten ischämischen Attacke oder prolongiertem reversiblem ischämischen Defizit (PRIND), deren neurologischer Status unauffällig war (Gruppe A), und 17 Patienten nach einem leichten Schlaganfall mit einer leichtgradigen Hemiparese oder Hemihypästhesie (mRS≤2) (Gruppe B), eingeschlossen. Alle Patienten wurden 0-2 Tage vor der CEA, am 3.-7. post-operativen Tag und 3 Monate nach CEA untersucht. Zu den Untersuchungsmethoden zählten somatosensibel evozierte Potentiale (SEPs) am N. medianus, eine transkranielle Doppleruntersuchung (TCD) in Ruhe, während Hyperkapnie (et-CO₂=7.0-7.5 kPa) und in der Ruhephase nach Hyperkapnie.

Ergebnisse: Gruppe A hatte einen signifikanten Anstieg in V_sys, V_mean und PI aufgrund der Hyperkapnie zu allen Zeitpunkten (d. h. 0-2 Tage vor der CEA, 3.-7. post-op Tag und 3 Monate nach CEA). Die N20/P25 Amplitude fiel in Folge der Hyperkapnie vor und unmittelbar nach der CEA ab. Die Veränderungen der anderen SEP Parameter zeigten keine Signifikanz. Gruppe B zeigte signifikante Unterschiede in Folge der Hyperkapnie vor und unmittelbar nach der CEA nur in Bezug auf die Vasoreaktivität (V_sys, V_mean, PI).

Schlussfolgerung: Die hochgradige Karotisstenose verursachte keinerlei hämodynamische Beeinträchtigung in der untersuchten Gruppe der Patienten. Darüber hinaus konnte kein artifizieller Anstieg des cBZ begleitet von einer ebenso signifikanten Veränderung der SEPs nachgewiesen werden.

Carotid endarterectomy - neuronal reactivity - somatosensory evoked potentials - cerebral vasoreactivity

Karotisendarterektomie - Neuronalreaktivität - somato-sensorisch evozierte Potentiale - Vascularreaktivität

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