What is widening pulse pressure?

purplekath · Mar 18, 2005

Hi, I hope I'm thinking of the same thing you are - disregard if I've misread!

It sounds like what you are talking about is "coning" - where the brain becomes so swollen and intracranial pressure so great that the brain is forced through the skull's foramen (foramen of munro) because it has nowhere else to go. In that circumstance you'd see what I call "fishtailing" of the BP and pulse rate all of a sudden, where the BP suddenly increases and the pulse suddenly decreases.

I"m not exactly sure why this is so, but it stands to reason that if the lower portion of the brain is squeezed through the foramen it may place pressure on the centres that regulate BP. If a pt came into the ER with a head injury it would probably depend upon the extent of injury and the degree of swelling as to how quicking coning would occur.

jaimealmostRN · Mar 18, 2005

It's part of Cushing's Triad: Increasing systolic and decreasing diastolic (widening pulse pressure), Bradycardia, irregular respirations (cheyne-stokes for ex.). This is a LATE sign of high ICP and usually occurs close to herniation. The first sign of rising ICP is change in LOC (if I remember my neuro right!). Hope this helps! :)

NurseyBaby'05, BSN, RN · Mar 18, 2005

Systolic goes up and diastolic goes down with widening pulse pressure. With increased ICP it's an ominous sign. Earliest sign is changes in LOC. There is a triad (Cushing's?) of signs of increased ICP: widening pulse pressure, rise in systolic BP, bradycardia. With these manifestations, the pressure increases on the brain stem. One of the functions in the brainstem is cerebral auto-regulation. When this malfunctions and BP goes up this increases the cerebral blood volume which leads to increased estravassation edema in the brain. Your result is increased ICP. If the opposite occurs with a decrease in BP, you can still wind up with the same result. If BP decreases so does the cerebral blood volume. This leads to hypoxia and hypercarbia and they also increase ICP.

Now as far as time goes, I don't remember there being a timetable as what to expect. What they did tell us was about a volume pressure curve. Will try to cut and paste: no soap! Will try later. Anyway, the gist of this curve was measuring the units of volume against ICP. You want to keep the ICP low (about 15?) With there being 1-2 mL too much of volume the patient's ICP stays low (around 10), but when you're getting to 3 the compensation is beginning to fail and it jumps to 15 with just one more mL. When it gets to 4mL it jumps to 25 mmHg. One thing they really emphasized with us is that as a nurse you don't know where the patient is on this curve and to do NOTHING that would increase ICP.

The other thing I found was on ICP monitoring. This measurement has a time factor. If there are waves measuring 50 mmHg, but they last just a short time (a minute or two), they are considered a warning sign. When they get between 50-100 mmHg and stay there: the pts ICP is up. I think the other reason there are no hard and fast time standards post-injury, is that ICP can increase a few days after the injury related to what they call "secondary insult" from the edema caused by the injury rather than the injury itself.

Hope this helps and sorry it was so long. Can you tell we were just tested on this. Repost this in a few weeks and I'll be a lot more fuzzy. Have a good night!

unknown99, BSN, RN · Mar 18, 2005

A pulse pressure is the difference between the systolic and the diastolic blood pressures. It is normally between 30 to 40 mm/hg, and indicates how well a patient maintains cardiac output.. It is a reflection of stroke volume, ejection velocity, and systemic vascular resistance.

An increase in pressure can be indicative of things that elevate the stroke volume such as anxiety, exercise, and bradycardia; fever;and atherosclerosis, aging, and hypertension.

A decrease in pressure reflects reduced stroke volume and ejection velocity such as shock, heart failure, and hypovolemia; or obstruction to blood flow during systole as in mitral or aortic stenosis.

A pulse pressure of less than 30mm/hg signifies a serious reduction of cardiac output.

Fraggle · Mar 18, 2005

DutchgirlRN said:
Can anyone explain widening pulse pressure? How does it play a part in diagnosing intracranial pressure? If a head injury came into the ER how quickly would the pressure change from the baseline? Thanks!

Also, Cerebral Perfusion Pressure (CPP) is a way of gauging how well the brain tissue is perfused. CPP is equal to MAP-ICP. If your pulse pressure widens, either your Sys is going up or your Dias is going down. Which will through off your MAP calculation too. So then your brain tissue isn't being perfused as well (too much or too little).

Also, the increased ICP causes the brain to herniate down through the foramen magnus (where else can the swollen brain go?), put pressure on the pons and medulla, which suppresses your vegitative functions. So now you're pulse and respirations decrease. I'm not sure how that effects pulse pressure, b/c I can't think this early. :chuckle