Editing Cushing reflex (section)

==Differential diagnosis==
[[File:SubarachnoidP.png|thumb|Subarachnoid hemorrhage as shown on a CT scan. It is denoted by the arrow. This type of injury may result in damage to the brainstem, which could initiate or worsen the symptoms of the Cushing reflex]]
Whenever a Cushing reflex occurs, there is a high probability of death in seconds to minutes. As a result, a Cushing reflex indicates a need for immediate care. Since its presence is a good detector of high ICP, it is often useful in the medical field, particularly during surgery.<ref name="ayling"/> During any neurosurgery being performed on the brain, there is always a likelihood that raised intracranial pressure may occur. Early recognition of this is crucial to the well being of the patient. Although direct measurement of ICP is possible, it is not always accurate. In the past, physicians and nurses have relied on [[hemodynamics|hemodynamic changes]] or bradycardia, the late phase of the reflex, to identify the ICP increase. Once the initial stage of the Cushing reflex (bradycardia combined with hypertension) was discovered, it offered a much more reliable and swift warning sign of high ICP.<ref name=Wan /> It was found that hypertension and bradycardia occurred 93% of the time when [[cerebral perfusion pressure]] (CPP) dropped below 15 mmHg due to raised ICP. Also, the Cushing reflex is known to arise only from acute prolonged raises in ICP. Thus, it can be used as a tool by physicians to differentiate [[Acute (medicine)|acute]] and [[Chronic (medicine)|chronic]] rises in ICP.<ref name=JonesJV>{{cite journal | last = Jones| first = JV| title = Differentiation and investigation of primary versus secondary hypertension (Cushing reflex)| journal = Am. J. Cardiol.| volume = 63| issue = 6| pages = 10C–13C| date = 1989-02-02| doi = 10.1016/0002-9149(89)90398-6 | pmid =2643847}}</ref>

It has also been reported that the presence of a Cushing reflex due to an ICP increase could allow one to conclude that ischemia has occurred in the [[posterior cranial fossa]].<ref name=Wan /> Finally, the Cushing reflex may be one of many ways to identify if a patient has rejected a [[Organ transplantation|transplanted organ]]. Aside from the innate [[autoimmune]] response, ischemia in the cranial region has been detected with a transplanted organ that is being [[Transplant rejection|rejected]].<ref name=Kosieradzki>{{cite journal |last = Kosieradzki|first = M|author2=W Rowinski|title = Ischemia/reperfusion injury in kidney transplantation: mechanisms and prevention.|journal = Transplant. Proc.|volume = 40|issue = 10|pages = 3279–88|date = December 2008|doi = 10.1016/j.transproceed.2008.10.004|pmid = 19100373}}</ref> As such, the presence of a Cushing reflex due to ICP can indicate that ischemia may be occurring due to foreign organ rejection.{{cn|date=March 2021}}

As first postulated by Harvey Cushing, raised intracranial pressure is the primary cause of the Cushing reflex.<ref name="Cushing"/> Furthermore, continued moderate increases in cranial pressure allows for the Cushing reflex to occur. In contrast, rapid and dramatic pressure rises do not allow for the mechanism of the reflex to sufficiently take place.<ref name=Marshman>{{cite journal | last = Marshman| first = LA| title = Cushing's 'variant' response (acute hypotension) after subarachnoid hemorrhage. Association with moderate intracra- nial tension and subacute cardiovascular collapse.| journal = Stroke| volume = 28| issue = 7| pages = 1445–50| year = 1997| doi = 10.1161/01.str.28.7.1445| pmid = 9227698}}</ref> Elevated intracranial pressure can result from numerous pathways of brain impairment, including: [[subarachnoid hemorrhage]]s, ischemia, meningitis, [[Trauma (medicine)|trauma]], including [[concussion]]s, [[Hypoxia (medical)|hypoxia]], [[tumors]], and [[stroke]]. In one study, it was confirmed that raised ICP due to subarachnoid hemorrhaging causes mechanical distortion of the brainstem, specifically the medulla. Due to the mechanism of the Cushing reflex, brainstem distortion is then swiftly followed by sympathetic nervous system over activity.<ref name=Pasztor>{{cite journal | last = Pasztor| first = E|author2=Fedina L |author3=Kocsis B | title = Activity of peripheral sympathetic efferent nerves in experimental subarachnoid haemorrhage. Part 1: Observations at the time of intracranial hypertension. | journal = Acta Neurochir | volume = 79| issue = 2–4| pages = 125–31| doi = 10.1007/bf01407456| pmid = 3962742 | year=1986| s2cid = 1449385|display-authors=etal}}</ref> In addition, during typical neurosurgical procedures on patients, especially those involving neuroendoscopic techniques, frequent washing of the [[Ventricular system|ventricles]] have been known to cause high intracranial pressure.<ref name=Dickinson /> The Cushing reflex can also result from low CPP, specifically below 15 mmHg.<ref name=Kalmar>{{cite journal | last = Kalmar| first = AF|author2=JV Aken |author3=J Caemaert | title = Value of Cushing Reflex as warning sign for brain ischemia during neuroendoscopy | journal = Br J Anaesth | volume = 94| issue = 6| pages = 791–9| year = 2005| doi = 10.1093/bja/aei121| pmid = 15805143|display-authors=etal| citeseerx = 10.1.1.507.1734}}</ref> CPP normally falls between 70-90 mmHg in an adult human, and 60-90 mmHg in children.{{cn|date=March 2021}}

Brain plateau wave changes are also associated with the Cushing reflex. These waves are characterized by acute rises of the ICP, and are accompanied by a decrease of the cerebral perfusion pressure. It has been found that if a Cushing reflex occurs, brain plateau wave changes can be erased due to disappearance of high ICP.<ref name=Wan />