Mannitol and Hypertonic Saline Dose Calculator

About This Mannitol and Hypertonic Saline Dose Calculator

This Mannitol and Hypertonic Saline Dose Calculator turns one adult weight into the osmotherapy doses used for raised intracranial pressure and cerebral edema, and prints beside each one the sodium it carries, the route its evidence used, and how far the dose sits from its own FDA label. It is built for the intensivist, neurosurgeon, emergency physician or pharmacist at the bedside of an adult with a swelling brain, where the arithmetic is simple but the label position, the sodium accounting and the route are the parts that get missed.

The scope is adults of at least 40 kg. It does not cover children, in whom the weight bands and concentrations differ, and it does not cover the correction of hyponatremia, which uses the same drugs for an entirely different target. It is a dosing reference, not a treatment algorithm: for the tiered protocol that decides when osmotherapy is the right move, see the ICP Management Guideline.

How to Use This Calculator

Step 1 — Enter the weight. Type it or use the digit pad. It is used by mannitol only; the three saline rows show fixed adult volumes and do not change.

Step 2 — Read the row you plan to use. Each row shows the dose, the sodium and osmoles it delivers, and two badges: one for the evidence grade of that dose, one for any product-level warning.

Step 3 — Select the agent to open its contraindications, its monitoring and its US label position. Selecting more than one is for the cumulative sodium panel — it is not a combination order.

Step 4 — Open “Show your work” to see the arithmetic, including how each volume converts to grams, milliequivalents and milliosmoles.

How the Numbers Are Derived

Mannitol: grams to millilitres

20% mannitol is 0.2 g per mL, so grams divided by 0.2 gives the volume: 1 g/kg is 5 mL/kg. A 70 kg adult at the top of the band receives 70 g, which is 350 mL and therefore a 500 mL bag — the label prohibits connecting containers in series, so two 250 mL bags is not a substitute. At the labelled 0.25 g/kg the same patient receives 17.5 g, or 87.5 mL, which fits a 250 mL bag with most of it unused. The 12.5 g vial some units stock is a different product: 50 mL of 25% mannitol.

Saline: millilitres to milliequivalents

The 3% label states 513 mEq/L of sodium and a calculated osmolarity of 1,027 mOsm/L. Every other concentration scales from mass: 7.5% is 2.5 times 3%, and 23.4% is 4 mEq/mL by its own label. That is why 100 mL of 7.5% and 250 mL of 3% both deliver 128 mEq, and why 30 mL of 23.4% delivers 120 mEq in a tenth of the volume.

The sodium rise this predicts

The cumulative panel divides total sodium by total body water, taken as 0.6 × weight in men and 0.5 × weight in women. It is a first approximation for planning, not the Adrogué–Madias formula, and it ignores ongoing losses, renal handling and the sodium already on board. Measure the sodium; do not order from this number.

Where Each Dose Comes From

Mannitol — the only labelled indication

The label indicates mannitol for the reduction of intracranial pressure and treatment of cerebral edema, at 0.25 g/kg every 6 to 8 hours as an infusion over at least 30 minutes. The ACS Best Practices algorithm gives it by intermittent bolus at 0.25 to 1.0 g/kg, so the upper part of that band is guideline practice rather than labelled use, and this page says so on the row. The 1.5 to 2 g/kg figure on the same label is for intraocular pressure and must never be carried across to the brain.

3% saline — a dose with no label and no established weight band

No US label carries an intracranial-pressure indication for 3% sodium chloride: it is indicated “as a source of water and electrolytes,” its dosage section reads in full “As directed by a physician,” and its contraindications section reads “None known.” The 150 to 250 mL bolus is adult practice. The adult randomized trials that dosed it by weight do not agree on a rate, and this page prints each of them rather than inventing an average: 2.5 mL/kg over 5 minutes, 3 mL/kg over 30 minutes, and a variable volume at 6 mL per minute titrated until the pressure fell. The widely quoted 2 to 5 mL/kg band comes from a pediatric paragraph and is not an adult recommendation.

7.5% saline — trials only, and not a US product

Two adult regimens exist and they disagree on the shape of the dose, not on the drug. The equimolar trial infused 100 mL of 7.45% saline through a central catheter over 20 minutes, against 231 mL of 20% mannitol; a 993-patient cohort used the same fixed 100 mL over 20 to 30 minutes with a minimum 4-hour interval. A separate trial dosed 2 mL/kg over 20 minutes. This page prints the fixed volume because it is the regimen the larger adult experience used, and because a fixed dose is what the concentration is stocked for where it is stocked at all. There is no US human 7.5% product — it is a pharmacy-compounded preparation. It can be made from the concentrate, and the sum needs nothing but label figures: 23.4% is 4 mEq/mL, 0.9% is 154 mEq/L, and 100 mL of 7.5% has to carry 128 mEq — so 29.3 mL of 23.4% made up to 100 mL with 0.9% sodium chloride is the same sodium in the same volume. The diluent is part of that sum: sterile water carries none, so it would take 32.1 mL of 23.4% instead, and the two are not interchangeable at the same volume. This is an aseptic pharmacy preparation under USP compounding standards, not a bedside mix. Do not work a recipe back from the published cohort — its own figures do not reproduce to 7.5% — and confirm the final concentration independently before it reaches the patient.

23.4% saline — observational data against an explicit label prohibition

The supporting adult data are a retrospective cohort in which 30 to 60 mL reversed transtentorial herniation clinically in 75% of cases. The label is not neutral about this: 23.4% sodium chloride is indicated as an additive in parenteral fluid therapy, its dosage section describes withdrawing a volume for dilution, and the vial itself is marked “CONCENTRATE” and “CAUTION: MUST BE DILUTED FOR I.V. USE.” Hospira’s warning for this concentration names the consequences directly, and goes further than the Fresenius Kabi vial label does: sudden hypernatremia, cardiovascular shock, osmotic demyelination syndrome, extensive hemolysis, cortical necrosis of the kidneys and severe local tissue necrosis if it reaches the tissues. Undiluted bolus for herniation is established neurocritical care practice and is not an approved use. Give it only under institutional protocol, through a confirmed-patent central catheter, and withdraw it from the 30 mL single-dose vial — the 100 mL and 200 mL Pharmacy Bulk Package of the same 4 mEq/mL concentration is labelled “Not for Direct Infusion.”

Clinical Interpretation & Limitations

Choose by physiology, not by a claimed hierarchy

Randomized evidence does not establish either drug class as better for outcome. A systematic review of 10 randomized trials found no effect of hypertonic saline on the 6-month Glasgow Outcome Scale (RR 0.82, 95% CI 0.48–1.40; 406 patients in 2 of those trials) or on mortality (RR 0.96, 95% CI 0.60–1.55; 486 patients in 5). The guideline that suggests hypertonic saline first for traumatic brain injury grades that suggestion conditional, on low-quality evidence, and in the same document states that neither agent should be used with the expectation of improving neurological outcome. What separates them is physiology rather than rank, and the tables below set out where that actually changes the choice.

Which agent, and when

Every preference below is conditional and rests on low or very low quality evidence, and none is a claim about survival or function — the same guideline states that neither agent should be used with the expectation of improving neurological outcome. Where a row reads either, the guideline declined to rank them.

Table 1 — by diagnosis. Every row is a recommendation statement from the Neurocritical Care Society guideline on the initial management of cerebral edema (2020).

Diagnosis	Preferred	What the guideline says, and how strong it is
Traumatic brain injury	Hypertonic saline	Suggested over mannitol for initial management. The stated reason is the putative advantage for fluid resuscitation and cerebral perfusion, not a difference in outcome. ACS Best Practices lists both as adjacent Tier One options and does not rank them.Conditional · low quality
Intracerebral hemorrhage	Hypertonic saline	Suggested over mannitol, on the same reasoning and weaker evidence. Separately, the mannitol label contraindicates active intracranial bleeding except during craniotomy.Conditional · very low quality Label
Acute ischemic stroke	Either	Neither agent is preferred for initial management. Hypertonic saline is suggested for patients without an adequate response to mannitol, and prophylactic scheduled mannitol is suggested against because of a possible association with harm.Conditional · low quality
Subarachnoid hemorrhage	Hypertonic saline, symptom-based bolus	The recommendation here is about how, not which: symptom-based bolus dosing is suggested rather than dosing to a serum sodium target.Conditional · very low quality
Hepatic encephalopathy	Either	The literature was not judged compelling enough to rank the two, so patient-specific factors decide.Conditional · very low quality

Table 2 — by the state of the patient in front of you. These rows come from the product labels and from the safety recommendations, which is why several of them are firmer than anything in Table 1.

Patient state	Preferred	Why, and where it comes from
Hypovolemic, hypotensive, or a marginal perfusion pressure	Hypertonic saline	Severe hypovolemia is a mannitol contraindication in section 4 of its label, and the osmotic diuresis can lower the perfusion pressure the dose was given to protect. Saline expands the intravascular space instead.Label contraindication
Sodium already at or above 155 mEq/L, or volume overloaded	Mannitol	This is the situation the guideline names when it calls mannitol an effective alternative. For hypertonic sodium it suggests avoiding severe hypernatremia and hyperchloremia, offering 155–160 mEq/L sodium and 110–115 mEq/L chloride as a reasonable ceiling; ACS sets a sodium limit of 155 mEq/L for either agent.Conditional · very low quality
Anuric	Hypertonic saline	Anuria is a mannitol contraindication in section 4. A serum osmolality above 320 is not itself a reason to stop: the guideline records that this threshold does not affect the incidence of acute kidney injury, and found insufficient evidence to recommend any osmolar gap cutoff. (ACS, in its algorithm footnote, does recommend 320 as a limit for either agent — local protocol decides which document governs.)Label contraindication
Pulmonary edema or pulmonary vascular congestion	Neither is neutral	Pre-existing pulmonary vascular congestion or pulmonary edema is a mannitol contraindication in section 4; hypertonic saline expands the intravascular volume, which is the same problem approached from the other side. This row is a reason to involve the treating team, not to pick from a table.Label contraindication
Herniating, and the fluid has to be small and fast	23.4% saline, 30 mL	Retrospective adult data only: clinical reversal of transtentorial herniation in 75% of 68 episodes, with 32.4% surviving to discharge. It is given against an explicit label prohibition and needs a confirmed-patent central catheter.Observational Contra-label
No central venous access yet	Mannitol	No adult trial of 3% for raised ICP dosed it peripherally — those that reported a route used a central catheter — and 23.4% must never go peripherally. Mannitol is the least bad option rather than a safe one: its own label prefers a large central vein and warns of phlebitis, compartment syndrome and extravasation injury.Route is practice

The hypernatremia signal, and what dominates it

The same review found hypertonic saline associated with adverse hypernatremia: RR 2.13 (95% CI 1.09–4.17), I² = 0%, 386 participants in 2 trials, an absolute rise from 57 to 121 per 1,000 at GRADE Low certainty. That estimate is dominated by the multicentre COBI trial of 20% saline given as a continuous infusion for at least 48 hours, and the review says so explicitly, so it should not be read as the risk of a single bolus. It is a reason to count the sodium, not a reason to withhold a dose in herniation.

What this page does not do

It gives single doses on total body weight and does not adjust for age, renal function, heart failure or the sodium already on board, all of which change what is safe. It does not decide whether osmotherapy is indicated, does not cover continuous infusion targets beyond stating the starting rate and its titration step, and does not cover hyponatremia correction, where the same solutions are used with an entirely different ceiling on the rate of change. Contraindications are summarized, not exhaustive. Repeat dosing is symptom-driven in every source here; none of them supports a fixed clock. This tool does not replace clinical judgment, local protocol, or the pharmacist.

Frequently Asked Questions (FAQ)

1. How much mannitol is given for raised intracranial pressure?

ACS Best Practices gives mannitol by intermittent bolus at 0.25 to 1.0 g/kg. The US label authorizes only the bottom of that band: 0.25 g/kg over at least 30 minutes, every 6 to 8 hours. Anything above 0.25 g/kg is guideline practice, not labelled use. In 20% mannitol 1 g/kg is 5 mL/kg, so a 70 kg adult gets 350 mL and needs a 500 mL bag.

2. How much 3% hypertonic saline is one bolus dose?

Adult practice is a fixed bolus of 150 to 250 mL, and 250 mL is the common order. There is no established adult weight based dose: the randomized trials that dosed 3% by weight used 2.5 mL/kg over 5 minutes and 3 mL/kg over 30 minutes, and a third titrated a variable volume at 6 mL per minute. The widely quoted 2 to 5 mL/kg band is pediatric.

3. Why is 7.5% saline dosed as a fixed 100 mL rather than by weight?

Because that is how the adult evidence gave it. The equimolar trial infused 100 mL of 7.45% saline centrally over 20 minutes against 231 mL of 20% mannitol, and a 993 patient cohort used the same fixed 100 mL over 20 to 30 minutes with a minimum 4 hour interval. A separate trial used 2 mL/kg instead. There is no US human 7.5% product, so it is compounded.

4. Can hypertonic saline be given through a peripheral IV?

No adult randomized trial of 3% saline for raised intracranial pressure gave it peripherally, and every trial that reported the route used a central venous catheter; 23.4% must never be given peripherally. Peripheral 3% is a local policy decision rather than an evidence backed route, and the concentrated label warns of severe local tissue necrosis if it reaches the tissues.

5. Should mannitol be held when serum osmolality reaches 320 mOsm/kg?

It is a signal to reassess, not an absolute stop. The Neurocritical Care Society guideline notes that a threshold above 320 does not affect the incidence of acute kidney injury, and it found insufficient evidence to recommend any osmolar gap cutoff either. Withholding a life saving dose in herniation on this number alone is the error to avoid. ACS Best Practices does list 320 as a recommended limit alongside its 155 mEq/L sodium limit, so know which document your institutional protocol follows.

Related Calculators

• ICP Management Guideline
• Serum Osmolality & Osmolar Gap Calculator
• Status Epilepticus Drug Dose Calculator
• ICU Sedation Protocol