Different strategies to initiate and maintain hyperventilation: their effect on continuous estimates of dynamic cerebral autoregulation.

Abstract

OBJECTIVE\nCapnography is a key monitoring intervention in several neurologically vulnerable clinical states. Cerebral autoregulation (CA) describes the ability of the cerebrovascular system to maintain a near constant cerebral blood flow throughout fluctuations in systemic arterial blood pressure, with the partial pressure of arterial carbon dioxide known to directly influence CA. Previous work has demonstrated dysautoregulation lasting around 30\u2009s prior to the anticipated augmentation of hyperventilation-associated hypocapnia. In order assess to potential benefit of hypocapnic interventions in an acute stroke setting, minimisation of dysregulation is paramount.\n\n\nAPPROACH\nHyperventilation strategies to induce and maintain hypocapnia were performed in 61 healthy participants, effects on temporal estimates of dynamic cerebral autoregulation (autoregulation index, ARI) were assessed to validate the most effective strategy for inducing and maintaining hypocapnia.\n\n\nMAIN RESULTS\nThe extent of initial decrease was significantly smaller in the continuous metronome strategy compared to the delayed metronome and voluntary strategies (▵ARI 0.33\u2009\u2009±\u2009\u20091.18, 2.80\u2009\u2009±\u2009\u20093.33 and 3.69\u2009\u2009±\u2009\u20092.79 respectively, p\u200a\u2009\u2009<\u2009\u20090.017).\n\n\nSIGNIFICANCE\nThe use of a continuous metronome to induce hypocapnia rather than the sudden inception of an auditory stimulus appears to reduce the initial decrease in autoregulatory capacity seen in previous studies. Dysautoregulation can be minimised by continuous metronome use during hyperventilation-induced hypocapnia. This advancement in understanding of the behaviour of CA during hypocapnia permits safer delivery of CA targeted interventions, particularly in neurologically vulnerable patient populations.