CPPopt · DERIVED

Optimal CPP (CPPopt)

The CPP at which the brain's pressure reactivity is most negative, derived from a 4-hour parabolic fit of PRx versus CPP. The individualised perfusion target.

ReactivityBedside + researchPeds + adultInvasiveEmerging

BLast reviewed 2026-05-1714-min read

5-minute summary

CPPopt is the CPP at which this patient's PRx is most negative, found by fitting a parabola to (CPP, PRx) data over the past 4 hours.

Target: The shaded ±5 mmHg band around the vertex is the operational target.
Evidence: The framework (Aries 2012, Beqiri 2024 COGiTATE) is the most evidence-supported individualised CPP strategy in severe TBI; pediatric data (Tas 2022, 2024) confirm the same physiology with lower CPPopt in younger children.
Dose-response is real: time spent outside CPPopt correlates with 6-month outcome independent of mean CPP or peak ICP.
The five-step workflow is mechanical (accumulate 4 hours, compute PRx, bin by CPP, fit a parabola, re-target MAP); the bedside skill is recognising when CPPopt is fittable and when it is not.
When to trust it: A flat curve means revert to age-based default; a clear vertex means trust the number.

1. Bedside vignettes: why this matters in the PICU

Vignette A. The 8-hour COGiTATE loop in a 12-year-old severe TBI

A 12-year-old severe TBI day 3. ICP 14 mmHg, MAP 80, CPP 66. Default age-based CPP floor is 60. The bedside team runs a CPPopt loop using the unit's ICM+ workstation:

Hour 0–4: accumulate data, PRx oscillating between 0 and +0.3. CPPopt fit gives vertex at CPP 72 mmHg with a clear parabola. Lift MAP with noradrenaline, CPP rises to 71.
Hour 4–8: PRx falls to 0.05 within the new operating range. CPPopt vertex shifts to CPP 73, stable. Continue.
Hour 8–12: a small subdural extension on the right (re-CT for sudden pupil change) raises ICP to 22. CPPopt recalculates to 78 because the brain is now less compliant; team raises MAP further.

The loop followed the patient through a physiological change rather than holding a static number. Over the 24-hour window the ICP-dose accumulated was lower than the matched-protocol cohort, and the family reported sustained improvement in the patient's GOS at 6 months.

Vignette B. CPPopt unobtainable after 4 hours

A 6-year-old severe TBI day 1. After 4 hours of clean recordings the (CPP, PRx) plot is flat: PRx hovers near +0.15 across every CPP bin from 50 to 90. No vertex, no parabola. What to do?

First check: signal quality. Re-zero the arterial line; confirm ICP transducer is reading a clean three-peak waveform. Both pass.
Second check: did the patient experience MAP variation across the 4-hour window? If MAP was tightly controlled around a narrow range (say 65–72), the algorithm has no data outside that band and cannot fit a U-curve.
Third check: is the patient on a high-dose vasopressor that pegs MAP within ±5 mmHg of a fixed target? Consider a deliberate small MAP excursion (lower noradrenaline slightly for 30 minutes, then raise) to give the fit data.
Fallback: revert to age-based CPP floor (CPP > 50 for a 6-year-old) until a fittable CPPopt is available.

CPPopt is a fitted parameter; it is not always fittable. Do not invent a CPPopt.

Vignette C. Pediatric difference: CPPopt 50 in a 3-year-old vs default 60

A 3-year-old severe TBI day 2. ICP 11 mmHg, MAP 65, CPP 54. Default team protocol says "CPP < 60 means action": team starts a noradrenaline infusion to lift MAP. The PRx, computed over the past 4 hours, shows a clean U-curve with CPPopt at CPP 48 mmHg. The team's noradrenaline took CPP to 64, where PRx rose to +0.30. The intervention pushed the patient above CPPopt. They wean noradrenaline back to baseline; CPP returns to 54; PRx falls to −0.10.

This is the most important pediatric lesson from Tas 2022 and 2024: younger children have lower CPPopt and the adult-style default of 60–70 mmHg can be harmful by causing over-perfusion. Trust the data, not the default.

2. What CPPopt is, and what it is not

CPPopt is the CPP coordinate at the vertex of a parabolic fit through (CPP, PRx) data over the past 4 hours.

\mathrm{CPPopt} = \arg\min_{CPP} \left[ \mathrm{PRx}(CPP) \right]

where PRx(CPP) is the binned mean of PRx values in each 5-mmHg CPP bucket.

The logic. PRx is minimised when autoregulation is most efficient: small CPP changes do not drive ICP changes. Below CPPopt the brain is under-perfused and autoregulation fails by passive collapse (vessels dilate but cannot maintain flow); above CPPopt the brain is over-perfused and autoregulation fails by hyperaemia (vessels saturated at maximum constriction). The shape of PRx-vs-CPP is therefore a U-curve, and the vertex is the patient's biological sweet spot.

Two things follow.

CPPopt requires PRx as the input. Without continuous high-quality ICP and MAP signals, CPPopt cannot be derived. Non-invasive surrogates (Mx with TCD, COx with NIRS) can substitute as input, with differing sample volumes and noise profiles.

CPPopt is dynamic. A patient's CPPopt drifts over hours-to-days. The 4-hour moving window is a compromise between responsiveness and noise suppression. Tas 2024 showed that within-patient CPPopt variation can exceed 15 mmHg over 48 hours.

Clinical pearl

CPPopt is not a number to set and forget. It is a moving target that responds to the brain's state. Re-fit every hour and update the operational target accordingly.

In children

Pediatric CPPopt is age-dependent and often below the adult-style default. The 3-year-old in Vignette C is the canonical example: CPPopt 48 vs default 60 means a 12 mmHg over-perfusion if the default is held rigidly. Younger brains have lower baseline cerebral metabolic rate and lower autoregulatory floor; trust the data.

3. The five-step workflow

Fig. 1

The CPPopt workflow. Step 1: accumulate 4 hours of synchronous ICP and MAP recordings at 100–200 Hz. Step 2: compute PRx in 5-minute moving windows updating every minute (288 windows over 4 hours, after artefact rejection typically 200+ remain). Step 3: bin the (CPP, PRx) points into 5-mmHg CPP buckets, take the mean PRx in each bucket. Step 4: fit a parabola (or smoothed U-curve) to the binned means; the vertex is CPPopt. Step 5: re-target MAP so CPP sits within ±5 mmHg of CPPopt. Repeat the loop every 30–60 minutes.

MNM-Edu, original schematic adapted from Aries 2012.

Step 1: Accumulate

Continuous ICP and MAP at 100–200 Hz from the patient monitor, synchronised to a common clock. ICM+ or equivalent software handles this. Four hours of data is the conventional window for first-fit; longer windows reduce noise but slow responsiveness.

Step 2: Compute PRx

5-minute moving windows of 30 paired 10-second averages. Update every 60 seconds. Reject windows containing flagged artefacts (motion, suction, transducer flush, low MAP variance). See PRx page for the math.

Step 3: Bin

Place each 5-minute (CPP, PRx) point into a 5-mmHg CPP bucket (e.g., CPP 60–64 mmHg, CPP 65–69 mmHg, …). Compute the mean PRx in each bucket. Buckets with fewer than ~5 points are excluded as undersampled.

Step 4: Fit

Fit a parabola (least-squares) through the bucket means. The vertex of the parabola is CPPopt. A clean U-curve has a clear vertex; a flat curve has no fittable vertex and CPPopt is "not available".

Step 5: Re-target

Set the operational CPP target as CPPopt ± 5 mmHg. Adjust MAP (via fluid, vasopressor, or sedation lightening) to bring CPP into this band. Re-evaluate the loop every 30–60 minutes.

Caveat

A flat curve is not a "wide CPPopt", it is "CPPopt unobtainable". Setting the target at the midpoint of a flat curve is inventing a number. Revert to age-based default and try again next hour.