MAP & Maintenance Fluids Calculator
Two calculators the neuro ICU runs on: mean arterial pressure — the number CPP targets are built from — and Holliday-Segar maintenance fluids, with the neuro-specific caveat that hypotonic maintenance fluid and the injured brain are a bad marriage.
Reviewed by Zaka Ahmed, MD Clinical reference · 3 min read
Mean Arterial Pressure & Maintenance Fluids
Enter blood pressure for MAP; enter weight for Holliday-Segar maintenance rate.
MAP, and maintenance rate if weight is entered, appear here.
Derived values
Educational tool only. The MAP formula assumes a normal heart rate and waveform (arterial lines compute true MAP by integration), and maintenance-fluid arithmetic never substitutes for volume assessment. It does not replace clinical judgment.
Clinical notes & interpretation Scoring guidance, pitfalls, FAQs, and references
MAP is the brain's blood pressure
The organ this site cares about autoregulates around MAP, not systolic — cerebral perfusion pressure is MAP minus ICP, and every neurocritical care target (CPP ≥60–70 in severe TBI, pressor thresholds in shock, augmentation targets in vasospasm) is written in MAP language. The cuff formula — diastolic plus a third of the pulse pressure — approximates the time-weighted mean at normal heart rates; arterial lines integrate the actual waveform, which is why the line and the cuff disagree in tachycardia, arrhythmia, and severe vasoconstriction. Chronic hypertension shifts the autoregulatory curve rightward, which is the physiologic argument behind cautious, proportional BP reduction in acute stroke rather than normalization — the acute targets themselves live on the Acute BP Targets page.
Maintenance fluids: the 4-2-1 rule and its neuro asterisk
Holliday and Segar's 1957 arithmetic — 4 mL/kg/h for the first 10 kg, 2 for the next 10, 1 thereafter — remains the universal maintenance estimate. The neuro asterisk matters more than the arithmetic: their original prescription implied hypotonic fluid, and hypotonic maintenance in acute brain injury promotes hyponatremia and cerebral edema. On a stroke or neuro-ICU service the defaults are isotonic (normal saline or balanced crystalloid), with sodium trends watched, and with the reminder that most stroke patients need a swallow evaluation and nutrition plan long before they need day three of "maintenance" fluids.
Frequently asked questions.
Why is MAP weighted toward diastole?
Because diastole occupies roughly two-thirds of the cardiac cycle at normal rates, the time-averaged pressure sits closer to diastolic. At high heart rates diastole shortens and the formula drifts from the true integrated mean.
What MAP should I target in acute stroke?
There is no single number — permissive hypertension pre-reperfusion, post-tPA and post-EVT caps, and ICH targets all differ by scenario. See the Acute BP Targets tool for the scenario-specific evidence.
Which maintenance fluid for a stroke patient?
Isotonic — hypotonic solutions risk hyponatremia and worsened cerebral edema in the injured brain. And reassess daily whether IV maintenance is needed at all once enteral intake is established.