What is the cerebral perfusion pressure if blood pressure is 90/60 mm Hg and ICP is 18 mm Hg?

Appeared in: JIPMER Pondicherry NO - 2022

Explanation

Cerebral Perfusion Pressure (CPP) is calculated using the formula: CPP = Mean Arterial Pressure (MAP) - Intracranial Pressure (ICP).
First, the MAP must be calculated from the blood pressure. The formula is MAP = [Systolic BP + (2 × Diastolic BP)] / 3.
Substituting the given values: MAP = [90 + (2 × 60)] / 3 = (90 + 120) / 3 = 210 / 3 = 70 mm Hg.
Then, calculate the CPP: CPP = 70 mm Hg (MAP) - 18 mm Hg (ICP) = 52 mm Hg.
A normal CPP is 70-100 mm Hg. A value of 52 mm Hg is dangerously low and indicates cerebral hypoperfusion, putting the patient at risk for ischemic brain injury.

Option A: The value 70 is the calculated Mean Arterial Pressure (MAP), not the Cerebral Perfusion Pressure (CPP).
Option B: This is an incorrect calculation. It is close to the correct answer and falls within the critical range for ischemia, making it a plausible distractor.
Option D: The value 18 is the given Intracranial Pressure (ICP). It is not the CPP.

Clinical Relevance

Nursing practice connection: Knowing Calculation of Cerebral Perfusion Pressure (CPP) helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
Maintaining adequate CPP is a primary goal in managing patients with traumatic brain injury, stroke, or other conditions causing increased ICP to prevent secondary brain injury.
A CPP that falls below 50-60 mm Hg for a sustained period can lead to irreversible brain ischemia, infarction, and cell death.
Nurses in critical care settings must continuously monitor BP and ICP, calculate CPP, and report values outside the target range. Interventions may include administering vasopressors to increase MAP or using therapies like osmotic diuretics to lower ICP.

How to Approach the Question

First, identify the values provided in the question: Systolic BP = 90, Diastolic BP = 60, and ICP = 18.
Recall the two-step process required. You need the formula for Cerebral Perfusion Pressure (CPP), which is CPP = MAP - ICP.
Recognize that to use the CPP formula, you must first calculate the Mean Arterial Pressure (MAP).
Recall the formula for MAP: MAP = [Systolic BP + (2 × Diastolic BP)] / 3.
Step 1: Calculate MAP. Plug in the BP values: MAP = [90 + (2 * 60)] / 3 = 70 mm Hg.
Step 2: Calculate CPP. Now use the MAP you just calculated and the given ICP: CPP = 70 - 18 = 52 mm Hg.

Concept Tested & Keywords

Concept Tested: Calculation of Cerebral Perfusion Pressure (CPP)
Stem keywords: cerebral perfusion pressure, blood pressure, 90/60 mm Hg, ICP, 18 mm Hg
Lead-in keywords: What is
Clinical cues: BP 90/60 mm Hg indicates relative hypotension.
Clinical cues: ICP 18 mm Hg indicates elevated intracranial pressure.

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E6 Nursing Brunner Adult Health 3SA Vol 2 Part 2 p. 30-32

E6 Medicine Harrison 22e Part 2 p. 247-249

E6 Medicine Davidson Principles Practice 24e p. 228-230

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