Skip to Main Content

++

INTRODUCTION

++

Autoregulation is the maintenance of constant cerebral blood flow (CBF) over a range of cerebral perfusion pressure (CPP). Cerebral perfusion pressure is defined as mean arterial pressure (MAP)−central venous pressure (CVP) or intracranial pressure (ICP) or cerebral venous pressure (cVP), whichever is greatest. Because ICP, CVP, and cVP are usually less than 10 mm Hg in the healthy brain, MAP is the main driving force for CPP. In light of this, autoregulation is often depicted as maintenance of constant CBF over range of MAP usually 50-150 mm Hg (Figure 118-1).

++
FIGURE 118-1

Relationship between CBF and MAP. (Reproduced with permission from Butterworth JF, Mackey DC, Wasnick JD, Morgan and Mikhail’s Clinical Anesthesiology, 5th ed. McGraw-Hill; 2013.)

Graphic Jump Location
++

To keep CBF constant, compensatory changes in vasomotor tone are made in response to changes in CPP or MAP. When CPP increases, cerebral vascular resistance increases. Likewise, when CPP decreases, cerebral vascular resistance decreases. It may take up to a minute for these compensatory changes to initiate. Hence, for brief periods there may be changes in CBF with swings in blood pressure even within the limits where there is usually autoregulation.

++

For individuals who are chronically hypertensive, the autoregulatory curve is shifted to the right for both the upper and lower limits. These individuals are at risk of experiencing cerebral hypoperfusion and ischemia with blood pressures that would be considered acceptable for individuals without hypertension.

++

Autoregulation may be impaired or nonexistent in or around areas of the brain with relative ischemia, surrounding mass lesions, following brain injury, during the postictal state, or during periods of hypoxemia, or hypercarbia. Patients are susceptible to new or worsening injuries from swings in blood pressure.

++

EFFECTS OF ANESTHETIC AGENTS

++

The degree to which the cerebral vasculature tone can be altered to facilitate autoregulation while under anesthesia is influenced by background factors that also alter vascular tone. Such factors include hypercapnea, hypocapnea, temperature, cerebral metabolic rate, and neuronal activation. All of these factors must be taken into consideration when assessing the effect of anesthesia on cerebral autoregulation. For example, when administered alone, volatile anesthetics impair cerebral autoregulation in a dose-dependent manner such that as the dose of the anesthetic is increased the level of impairment increases. Autoregulation may be completely abolished at very high doses. The effect is different for each agent. Nitrous oxide causes significant cerebral vasodilation and increase in CBF. This effect can be attenuated by other anesthetic agents or by hyperventilation. Cerebral autoregulation is preserved with intravenous induction agents. Opioids generally do not affect cerebral autoregulation

Want remote access to your institution's subscription?

Sign in to your MyAccess profile while you are actively authenticated on this site via your institution (you will be able to verify this by looking at the top right corner of the screen - if you see your institution's name, you are authenticated). Once logged in to your MyAccess profile, you will be able to access your institution's subscription for 90 days from any location. You must be logged in while authenticated at least once every 90 days to maintain this remote access.

Ok

About MyAccess

If your institution subscribes to this resource, and you don't have a MyAccess profile, please contact your library's reference desk for information on how to gain access to this resource from off-campus.

Subscription Options

AccessAnesthesiology Full Site: One-Year Subscription

Connect to the full suite of AccessAnesthesiology content and resources including procedural videos, interactive self-assessment, real-life cases, 20+ textbooks, and more

$995 USD
Buy Now

Pay Per View: Timed Access to all of AccessAnesthesiology

24 Hour Subscription $34.95

Buy Now

48 Hour Subscription $54.95

Buy Now

Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.