Question about Cushing's

Specialties Neuro


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A cerebral SVO2 monitor (we used pediatric SVO2 swan ganz caths) is placed in the external jugular vein at the jugular bulb and you simply use it to monitor the mixed venous oxygen saturation as it leaves the cerebral circulation thereby giving you a measurement that reflexes cerebral oxygen utilization. When the cerebral SVO2 dropped below 75%(it may have been 70, it's been a while since I left neuro) an intervention was needed to either increase O2 delivery, or decrease O2 consumption. Regarding CSF drainage we would only drain for sustained increases in ICP>25mmHg, except where the ICP waveform showed decreased compliance in which case we would diurese and drain.

Hope this helps, as I said it's been a while since I did neuro:)


554 Posts

wow...neat use of a swan ganz cath.So you just utilize it like you would a swan only the placement site is different.Kinda neat idea....thanks for sharing!!!!


1 Post

I was actually looking this up for a different reason on Google and stumbled across this forum - thought I would throw in my 2cents.

The increased pulse pressure (due to the lower diastolic blood pressure) could be a result of the decreased HR found in the Cushing response.

DBP is generally affected by two things, HR and total peripheral resistance.

As HR decreases there is more time for "run off" (transfer of blood from the arterial to the venous circulation) and therefore less arterial volume at the end of diastole.

The lower arterial volume gives you the lower DBP, which would indeed widen the pulse pressure.

Specializes in NICU, DC planning, Neurosurgery, Inf Dis.

I'm reading this out of Barker 2nd edition Neuroscience Nursing A Spectrum of Care

"Cushing's reflex is helpful in explaining the late signs of increased ICP. This response is seen with sudden increases in pressure that result from distortion of a pressure area in the medulla beneath the floor of the fourth ventricle. When the CSF pressure rises to equal arterial pressure, the arteries become compressed and blood supply to the brain is decreased. The vasomotor center becomes ischemic and triggers the arterial pressure to rise in compensation for low perfusion. A sympathetically mediated response causes the systolic blood pressure to increase, and there is a widening pulse pressure, slowing of the pulse, and irregular respirations. Patients presenting with Cushing's reflex have recovered after rapid treatment."

I also asked a Neurosurgeon who explained it this the systolic rises but the pulse drops, it's like there is more time for the diastolic pressure to fall since the pulse is slower..not a lot of pressure built up between beats., therefore the diastolic pressure is lower...does that make sense???

hope that helps....and it really was an excellent question...:idea: topkat

Ras Twaka

1 Post

The Cushing Reaction is a combination of two events in response to cerebral ischemia:

1) Central chemoreceptors--in the brain--register an increase in PCO2 (increased pH) and stimulate vasoconstriction throughout the body to increase systolic pressure. Remember that the cerebral vessels do not have a great amount of muscle and therefore are not as succeptible to vasoconstriction.

2) The rise in peripheral BP (sensed by baroceptors in the carotid sinus and aortic arch) increases the rate of afferent (to the brain) firing of the nerves running to the brainstem (CN 9 and CN 10). This causes a reflex DECREASE in the firing of efferent SYMPATHETIC (and INCREASE in firing of efferent PARASYMPATHETIC) nerves to the heart resulting in BRADYCARDIA.

In short, Hypertension is the sympathetic response, and bradycardia is the parasympathetic response.

Hope this helps.


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