ICU Care Calculators

All ICU Care calculators

Intensive care runs on numbers: pressures, ratios, scores and targets that must be calculated correctly under pressure. This library collects the bedside mathematics of the ICU, from mean arterial pressure and the P/F ratio to sepsis screening scores, electrolyte corrections, insulin infusion starters and nutrition targets, each built to give a reliable answer in seconds.

Medically reviewed by Dr. Taimoor Asghar, physician.

In short: ICU calculators: MAP, GCS, P/F ratio, qSOFA, shock index, insulin infusion and nutrition targets. Free bedside tools for critical care clinicians. Browse the calculators below, each with an interpretation guide.

What intensive care covers, and the clinical questions these tools answer

Intensive care is the management of single or multiple organ failure: the resuscitation and support of patients whose cardiovascular, respiratory, neurologic or metabolic systems can no longer sustain them. Its daily work is titration: of vasopressors against blood pressure, ventilators against oxygenation, sedation against consciousness, fluids and electrolytes against shifting physiology. The calculators here answer the quantitative questions that recur on every round.

Haemodynamics come first. The mean arterial pressure (MAP) calculator derives the average arterial pressure across the cardiac cycle, the number against which vasopressor targets are set; a commonly used minimum target is 65 mmHg, individualised to the patient. The shock index, heart rate divided by systolic blood pressure, is an early warning signal: values above roughly 0.9 suggest the circulation is under stress before overt hypotension appears. The cerebral perfusion pressure (CPP) calculator subtracts intracranial pressure from MAP, giving the pressure driving blood into the brain; typical targets lie between 60 and 70 mmHg in brain-injured patients with ICP monitoring.

Oxygenation is quantified two ways. The P/F ratio divides arterial oxygen tension by the inspired oxygen fraction and places ARDS into the Berlin definition bands: 200 to 300 mild, 100 to 200 moderate, and 100 or below severe, all on a minimum PEEP. The oxygenation index incorporates mean airway pressure as well, making it useful in ventilated patients, particularly children, where ventilator pressures are part of the severity picture. Together they track whether lung injury is improving or worsening day to day.

Screening and neurology tools structure rapid assessments. The qSOFA score and SIRS criteria screen for sepsis-related risk from vital signs and basic labs, with qSOFA's three bedside items designed for speed outside the ICU. The Glasgow Coma Scale grades eye, verbal and motor responses from 3 to 15 and remains the common language for consciousness in trauma, stroke and critical illness. Metabolic tools include the corrected sodium calculator for hyperglycaemia, which adjusts measured sodium for the diluting effect of glucose using the Katz and Hillier approach, and the delta-delta gap calculator, which detects mixed metabolic acid-base disorders hiding behind a single anion gap.

Finally, the practical calculators cover dosing and feeding. The body metrics tool derives BMI, body surface area, ideal body weight and adjusted body weight, the denominators for drug dosing and ventilator settings. The insulin infusion calculator gives a safe starter rate in units and mL per hour for hyperglycaemic emergencies, and the nutrition estimator sets daily calorie, protein and fluid targets for critically ill patients.

When clinicians and students use these calculators

On ICU rounds these tools are used continuously. MAP is checked against the vasopressor target with every observation set; the P/F ratio is recalculated after ventilator changes; the GCS is scored on admission, after sedation holds and whenever neurology changes. The shock index earns its place in the emergency department and on rapid response calls, flagging occult shock in patients whose blood pressure still looks acceptable. qSOFA is designed for exactly these moments: three items, no labs, an immediate sense of sepsis risk.

Electrolyte and acid-base tools cluster around specific problems. Corrected sodium is calculated whenever significant hyperglycaemia accompanies hyponatraemia, preventing the error of treating a number that glucose has distorted. The delta gap is worked through when the anion gap does not fully explain the bicarbonate, revealing a concurrent normal-anion-gap acidosis or metabolic alkalosis. Insulin infusion starters are used at the initiation of treatment for severe hyperglycaemia or diabetic ketoacidosis protocols, always as the beginning of a titrated protocol rather than a fixed prescription.

Nutrition and body metrics are calculated on admission and reviewed as weight and fluid balance shift: calorie and protein targets guide feeding prescriptions, and ideal versus adjusted body weight determines drug doses and tidal volumes. For students, the ICU is where physiology becomes arithmetic, and working through these calculators builds the habit of quantifying before acting.

Interpreting results: what the numbers change in practice

A MAP below the set target prompts vasopressor titration upward; a MAP well above it in a stable patient prompts weaning, since excessive vasoconstriction carries its own harms. A shock index persistently above 0.9 in a bleeding or septic patient argues for escalation even when the systolic pressure has not yet fallen. A CPP below target in a brain-injured patient triggers the standard cascade: optimise MAP, reduce ICP, reassess; a CPP far above target raises concern about hyperaemia and systemic hypertension.

P/F ratio bands directly inform ventilator strategy and expectations: mild ARDS may respond to standard lung-protective ventilation, while severe ARDS prompts consideration of prone positioning, neuromuscular blockade or referral for extracorporeal support, according to local protocols. A rising oxygenation index over days signals deteriorating lung function even when the P/F ratio is confounded by ventilator adjustments. GCS trends matter more than single values: a fall of two or more points demands urgent reassessment, and the motor component carries the most prognostic weight.

A positive qSOFA (two or more points) should prompt a full sepsis workup and lactate measurement; SIRS criteria, more sensitive and less specific, cast a wider net that must be interpreted alongside the clinical picture. Corrected sodium reframes hyponatraemia management: much of the apparent abnormality may vanish once glucose is accounted for, changing the urgency of treatment. The delta gap reveals hidden disorders: a large positive gap suggests concurrent metabolic alkalosis, a large negative gap a concurrent normal-anion-gap acidosis, each pointing to additional causes to investigate. Insulin starter rates are exactly that, starters: the infusion is then titrated to glucose according to the unit's protocol, with potassium monitored throughout. Nutrition targets set the prescription, commonly around 25 to 30 kcal per kilogram and 1.2 to 2 grams of protein per kilogram per day, adjusted for the patient's phase of illness.

Limitations and pitfalls: what these tools cannot do

Targets are starting points, not laws. A MAP of 65 suits many patients but may be inadequate for someone with chronic hypertension whose organs are accustomed to higher pressures, or excessive for a young patient with no vascular disease; targets should be individualised and reassessed. CPP targets assume reliable ICP measurement, and the number is meaningless if the transducer is mislevelled or damped. The P/F ratio is profoundly affected by PEEP and FiO2, so ratios calculated under different ventilator settings are not comparable; always note the settings alongside the number.

qSOFA is specific but insensitive: a negative qSOFA does not exclude sepsis, and it was never designed as a sole screening test. SIRS criteria are sensitive but non-specific, positive in many non-infectious conditions from pancreatitis to trauma. The GCS cannot be scored reliably in intubated, sedated or aphasic patients without modification, and the verbal component is untestable with an endotracheal tube in place. Corrected sodium is an estimate: the Katz and Hillier correction is a useful approximation, not a measured truth, and treatment should follow the patient's actual tonicity and symptoms. The delta gap assumes a normal baseline anion gap and albumin, and hypoalbuminaemia distorts it.

Insulin infusion calculators provide starter rates only; they do not replace protocols, glucose monitoring or potassium management, and hypoglycaemia remains the chief danger of any insulin infusion. Body weight estimates falter in oedema, ascites and amputation, where measured weight misleads dosing. Nutrition targets are population averages applied to individuals: the hypermetabolic burn patient and the chronically starved patient need specialist dietetic input beyond any calculator.

How to use this library

Use these tools at the bedside, in the moment. Calculate the MAP before adjusting the noradrenaline, the P/F ratio after changing the ventilator, the corrected sodium before treating the hyponatraemia. Record the result with its context: the ventilator settings with the P/F ratio, the glucose with the corrected sodium, the sedation state with the GCS. Numbers without context mislead the next clinician as easily as they informed you. And when a calculated value conflicts with the patient's appearance, believe the patient first and recheck the inputs second.

Related specialities

These calculators are often used alongside tools from neighbouring fields:

Frequently asked questions

What MAP should I target in a critically ill patient?

A minimum MAP of 65 mmHg is the commonly used target in septic shock and many other critical illnesses, but it is a starting point rather than a universal law. Patients with chronic hypertension may need higher pressures to protect organ perfusion, while others tolerate lower values. The target should be individualised, guided by signs of perfusion such as urine output, mentation and lactate, and reviewed as the patient's condition changes.

What is the difference between qSOFA and SIRS?

SIRS criteria are sensitive and cast a wide net: two or more of fever or hypothermia, tachycardia, tachypnoea and leucocytosis suggest systemic inflammation, but many non-infectious conditions meet them. qSOFA uses three bedside items, low blood pressure, fast respiratory rate and altered mentation, and is more specific for poor outcomes in suspected infection but less sensitive. A positive qSOFA should prompt urgent sepsis assessment; a negative one does not exclude sepsis.

What P/F ratio indicates ARDS, and how is severity graded?

The Berlin definition classifies ARDS by P/F ratio on a minimum PEEP: 200 to 300 is mild, 100 to 200 moderate, and 100 or below severe. The ratio must be interpreted with its ventilator settings, since PEEP and FiO2 strongly affect it, and the clinical criteria of timing, imaging and cardiac origin must also be met before the label is applied.

Why correct sodium for hyperglycaemia?

High blood glucose draws water out of cells and dilutes serum sodium, producing an apparent hyponatraemia that does not reflect true tonicity. The Katz and Hillier correction estimates what the sodium would be at normal glucose, preventing unnecessary or dangerous treatment of a laboratory artefact. True hypo- or hypernatraemia should still be assessed from the clinical picture and, where needed, measured osmolality.

Do these calculators replace clinical judgement?

No. They are decision aids that structure clinical reasoning and make implicit judgements explicit. Scores are derived from specific study populations and cannot capture every factor in an individual patient, such as frailty, preferences or the trajectory of illness. An unstable patient needs urgent treatment regardless of what a score says, and every result should be interpreted by a qualified clinician in full clinical context.

How often are the calculators reviewed?

Each calculator implements a published scoring system and is reviewed periodically against the original criteria. If a scoring system is updated by its authors, the calculator is revised to match. The review date is shown on each calculator page, and the underlying clinical criteria have not changed for most of these long-established scores.

Medical disclaimer

These calculators are educational tools for clinicians, students and informed readers. They are not medical advice, and they do not create a doctor-patient relationship. Scores and results must be interpreted by a qualified healthcare professional in full clinical context. If you are unwell or concerned about your health, seek care from a doctor or other qualified professional promptly, or contact emergency services in an emergency.