# Situation: A 30-year-old man is in the intensive care unit after a motorcycle crash caused a severe traumatic brain injury (TBI) and a spinal cord injury at the level of the sixth cervical vertebra (C6). He is intubated and sedated, his cervical spine is immobilized, and an intraventricular catheter monitors his intracranial pressure (ICP). The unit's targets are ICP 22 mmHg or lower and cerebral perfusion pressure (CPP) 60–70 mmHg. At 02:00 his blood pressure is 112/62 mmHg and his ICP is 26 mmHg. Mean arterial pressure (MAP) = (systolic + 2 × diastolic) ÷ 3. Rounding MAP to the nearest whole number, what is his CPP, and how does it compare with the unit target?

> source: MyMerci (mymerci.kr)  
> url: https://mymerci.kr/pages/nclex_q.php?qn_id=630034  
> language: ko  
> subject: Nursing Practice V — Care of Clients with Maladaptive Patterns of Behavior; Care of Clients with Life-Threatening Conditions, Acute Multi-Organ Problems, High Acuity and Emergency Situations

## 문제

Situation: A 30-year-old man is in the intensive care unit after a motorcycle crash caused a severe traumatic brain injury (TBI) and a spinal cord injury at the level of the sixth cervical vertebra (C6). He is intubated and sedated, his cervical spine is immobilized, and an intraventricular catheter monitors his intracranial pressure (ICP). The unit's targets are ICP 22 mmHg or lower and cerebral perfusion pressure (CPP) 60–70 mmHg.

At 02:00 his blood pressure is 112/62 mmHg and his ICP is 26 mmHg. Mean arterial pressure (MAP) = (systolic + 2 × diastolic) ÷ 3. Rounding MAP to the nearest whole number, what is his CPP, and how does it compare with the unit target?

## 보기

1. 86 mmHg, above the target range
2. 105 mmHg, above the target range
3. 53 mmHg, below the target range **✔ 정답**
4. 36 mmHg, below the target range

**정답: 3**

## 해설

MAP = (112 + 2 × 62) ÷ 3 = 236 ÷ 3 = 78.7, rounded to 79 mmHg. CPP = MAP − ICP = 79 − 26 = 53 mmHg, which is below the 60–70 mmHg target, so brain perfusion is inadequate and must be reported.

## 심화 해설

Step 1: Calculate the MAP

The formula given is MAP = (systolic + 2 × diastolic) ÷ 3. With a blood pressure of 112/62 mmHg, the calculation is:

MAP = (112 + 2 × 62) ÷ 3 = (112 + 124) ÷ 3 = 236 ÷ 3 = 78.7 mmHg, which rounds to 79 mmHg.

Step 2: Calculate the CPP

Cerebral perfusion pressure is the pressure gradient driving blood flow through the brain. It is defined as the difference between mean arterial pressure and intracranial pressure:

CPP = MAP − ICP = 79 − 26 = 53 mmHg.

Step 3: Compare with the unit target

The unit target is 60–70 mmHg. A CPP of 53 mmHg falls below the lower limit of the target range, indicating that cerebral perfusion is currently inadequate.

Why this matters in severe TBI

In severe traumatic brain injury, the brain’s autoregulatory capacity is often impaired. Cerebral perfusion pressure becomes a critical clinical variable because it reflects the net pressure available to deliver oxygen and glucose to injured but still viable brain tissue. When CPP drops too low, the risk of secondary ischemic injury rises, which can worsen neurologic outcome.

The meta-analysis by Karagianni et al. emphasizes that CPP is the arithmetic difference between MAP and ICP and is central to maintaining cerebral blood flow after sTBI, although the exact optimal threshold remains debated [1]. This case illustrates why continuous calculation—not just watching ICP in isolation—is essential: the ICP of 26 mmHg is above the stated ICP target of 22 mmHg or lower, and the resulting CPP of 53 mmHg confirms that both intracranial hypertension and systemic hypotension are combining to threaten brain perfusion.

The second source reinforces that optimal cerebral perfusion pressure is an emerging individualized target, but even standard fixed targets such as 60–70 mmHg serve as a practical floor below which perfusion is generally considered unsafe in severe brain injury [2].

Clinical priority

Watch out! A CPP below target is a reportable finding. The nurse should immediately notify the provider and anticipate interventions such as lowering ICP (e.g., ensuring sedation, head-of-bed positioning, cerebrospinal fluid drainage via the intraventricular catheter) or raising MAP (e.g., vasopressors or fluids) to restore CPP into the 60–70 mmHg range.

Key point! CPP is calculated as MAP minus ICP, not as systolic blood pressure minus ICP. Using the raw systolic value of 112 mmHg would incorrectly suggest a CPP of 86 mmHg, which is why the MAP must be computed first.References (research sources)

- [1]Cerebral Perfusion Pressure in Severe Traumatic Brain Injury Survivors and Non-Survivors: A Meta-Analysis.Meta-analysis/systematic reviewKaragianni M, Brotis AG, Vrettou CS, Goupou K, Stranjalis G, Fountas KN (2025) · DOI: 10.3390/brainsci15111161

- [2]Optimal Cerebral Perfusion Pressure in Brain Injury: Physiological Relationships and Outcome.Research articlePelah AI, Kazimierska A, Czosnyka M, Hawryluk GWJ (2025) · DOI: 10.1227/neu.0000000000003411

## 임상 시나리오

CPP Calculation in Severe TBIMAP minus ICP guides perfusion management
Calculate MAP first: (112 + 2 × 62) ÷ 3 = 78.7, rounded to 79 mmHg. Then CPP = MAP − ICP = 79 − 26 = 53 mmHg.

A CPP of 53 mmHg is below the unit target of 60–70 mmHg, indicating inadequate cerebral perfusion that requires prompt reporting and intervention.

CautionDo not monitor ICP in isolation; a falling CPP can cause secondary ischemic injury even when ICP changes appear modest.

## 핵심 개념

- **Cerebral perfusion pressure (CPP)** — The net pressure gradient driving blood flow to the brain, calculated as MAP minus ICP.
- **Mean arterial pressure (MAP)** — Average arterial pressure during one cardiac cycle, estimated as (systolic + 2 × diastolic) ÷ 3.
- **Intracranial pressure (ICP)** — Pressure inside the skull, normally 5–15 mmHg in adults; elevated ICP can reduce cerebral perfusion.
- **Traumatic brain injury (TBI)** — Brain injury from external force; severe TBI often impairs cerebral autoregulation and requires CPP monitoring.
- **Secondary ischemic injury** — Additional brain damage caused by inadequate perfusion or oxygenation after the primary injury.

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