Critical Care Registered Nurse (CCRN) Practice Exam

In what condition does autoregulation of cerebral blood flow typically fail?

1. 60-160 mmHg MAP

2. Above 160 mmHg MAP

3. Below 60 mmHg MAP

4. Both above and below these ranges

The correct answer is: Both above and below these ranges

Autoregulation of cerebral blood flow refers to the brain's ability to maintain a constant blood flow despite changes in perfusion pressure, typically effective in a mean arterial pressure (MAP) range of 60-160 mmHg. When MAP falls below 60 mmHg, there is inadequate perfusion pressure, leading to potential ischemia and inadequate blood supply to brain tissue. Conversely, when MAP exceeds 160 mmHg, the autoregulation mechanisms often fail, resulting in excessively high cerebral blood flow which can cause intracranial pressure increases and potential damage due to cerebral edema or hemorrhage. Thus, both scenarios—below 60 mmHg and above 160 mmHg—represent conditions where autoregulation is compromised. In these ranges, the brain cannot effectively self-regulate its blood supply, potentially leading to significant morbidity. Therefore, recognizing that autoregulation fails outside the physiological range is critical for the management of patients in critical care settings.