Question regarding fluid resuscitation

[Guest guest]

For the last few years, fluid resuscitation of trauma patients has been aimed at

maintaining a systolic BP of 80-90 mm Hg. The concept is that of " permissive

hypotension " based upon hydrostatic concerns about the effects of heightened

hydrostatic pressures in the fact of internal bleeding. It has been postulated

that increased hydrostatic pressures will dislodge clots that have been formed

as a natural response to injury, and that increased fluid volumes will dilute

clotting factors and lead to increased bleeding. These concepts are valid.

However, I propose that this concept fails to take into consideration one vital

aspect of trauma care, that of adequate perfusion of the brain. Cerebral

perfusion pressure (CPP) is the measure of brain perfusion, and it must be

maintained at a level of 80 mm Hg or better. Studies show that when a patient's

CPP is maintained at that level, there is a 35% improvement in outcomes, whereas

lower CPPs result in poorer outcomes.

There are two components of blood pressure: the systolic and diastolic

readings. Systolic pressure represents hydrostatic pressure, and diastolic

pressure represents the degree of vasoconstriction. This is an

oversimplification, but it is

basically accurate. Simply maintaining a systolic pressure of 80-90 mm Hg does

not insure adequate CPP.

In order to figure CPP, one must first determine mean arterial pressure (MAP)

and estimate the intracranial pressure (ICP). Intracranial pressure cannot be

monitored in the field, but can be estimated based upon clinical observations.

The formula for CPP is this: CPP = MAP - ICP.

MAP can easily be computed by this formula: (1/3 pulse pressure) + diastolic

pressure. Thus, a patient with a BP of 140/80 will have a pulse pressure of 60.

One-third of 60 is 20, and added to the diastolic pressure of 80, results in a

MAP of 100.

Normal patients without head injuries, at rest, have an ICP of from around 5 to

15 mm Hg. This can vary depending upon posture. For example, if a patient who

is supine suddenly stands up, his ICP will fall, and if he is dehydrated or

taking antihypertensives that antagonize alpha-1 vasoconstriction, he can become

dizzy or even faint. Conversely, when one coughs or sneezes, ICP spikes, but

only for a few seconds.

With a MAP of 100, and an estimated ICP of 15, the CPP would be 85, which is

fine. But if the BP is, for example, 90/50, then the MAP is only 63. [1/3

pulse pressure (40) = 13. Diastolic pressure of 50 + 13 = 63, the MAP.

Using the formula CPP = MAP - ICP, if one assumes a normal ICP of 10 mm Hg, then

MAP (63) - estimated ICP (10) = 53, far below the target CPP of 80. In fact, a

CPP of 53 is close to the limit for survival.

And this is in a patient without a head injury. Given a patient with rising

intracranial pressure, it becomes obvious that a higher MAP is needed to

adequately perfuse the brain.

These concepts are taught in the traumatic brain injury courses, but not

emphasized, I fear, in paramedic training.

So my question is this: How many of you who are EMS educators use this in your

teaching? How many of you who are Paramedics have had this training and

understand these concepts?

Are we doing enough to educate our medics to the basics of brain perfusion with

the current guidelines about fluid resuscitation?

Gene Gandy, JD, LP, NREMTP

PERCOMONLINE.COM

Tucson, AZ

..