Paula cannot raise her respiratory rate at rest during illness; implications for the Cushing’s Reflex and Hypercapnia

Physiologic parameters of the Cushing reflex

P A Grady 1O R Blaumanis PMID: 3375974 DOI: 10.1016/0090-3019(88)90140-1


The effects of increased intracranial pressure and blood gas tensions on systemic blood pressure were examined in this study. Intracranial pressure was raised hydrostatically and blood gas tensions, blood pressure, and respiration were monitored in anesthetized dogs. Small gradual increments in intracranial pressure resulted in increased cerebral venous carbon dioxide tension, followed by increased respiration, a gradual rise in blood pressure, and finally an increase in heart rate. The results of this study indicate that blood pressure changes appear to be determined by alterations in carbon dioxide tension following increases in intracranial pressure; small increases in intracranial pressure elicit a cluster of physiologic responses, all directed toward stabilization of local cerebral carbon dioxide tension.

These are difficult studies to do in ambulatory patients.

Yet we know hypercapnia can occur in awake, ambulatory patients. Intracranial pressure is still impossible [we think] to measure in these patients so we do not know very much about the signs and symptoms. Rising ICO [Intracranial pressure] is associated with headache, vomiting and altered mental status. Before Paula got very sick, she did have vomiting,[she thought she had the stomach flu] headache [she was physical ill so..] and then she developed [quiet] altered mental and motor status.


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