# Maintenance fluids

Status: LIVE
Price: $0.005 USDC
`GET /api/calc/maintenance_fluids`
HTML: https://magentlab.com/docs/maintenance-fluids
Markdown: https://magentlab.com/docs/maintenance-fluids.md

Not a medical device. Not a diagnosis, dose, or listing recommendation.

## What it computes

Compute Holliday–Segar 1957 daily maintenance water from weight, plus the corresponding hourly milliliters.

## When to use

When an agent needs the 1957 100/50/20 mL/kg daily maintenance-water arithmetic and must not invent a volume or apply the later 4-2-1 rule.

## When not to use

- Not a treatment order or IV prescription. Does not choose fluid type, electrolyte additives, or infusion-rate safety limits.
- Uses the paper's daily 100/50/20 mL/kg volumes. The later bedside 4-2-1 mL/kg/h rule is an hourly approximation and is not applied here.
- Estimates typical pediatric parenteral maintenance water only. Does not add fever, ongoing losses, or renal impairment.

## Formula

```
daily_ml = 100*min(kg,10) + 50*max(0, min(kg,20)-10) + 20*max(0, kg-20); hourly_ml = daily_ml / 24
```

## Citation

The maintenance need for water in parenteral fluid therapy
Holliday MA, Segar WE
Pediatrics. 1957;19(5):823-832
DOI: [10.1542/peds.19.5.823](https://doi.org/10.1542/peds.19.5.823)

## Worked example

### 30 kg

Given: `weight_kg=30`

1. first 10 kg: 100 × 10 = 1000 mL
2. next 10 kg: 50 × 10 = 500 mL
3. remaining 10 kg: 20 × 10 = 200 mL
4. daily_ml = 1700 mL
5. hourly_ml = 1700 / 24 = 70.833… → 70.8


## Parameters

- `weight_kg` (number, optional): Weight in kilograms. Provide weight_kg or weight_lb.
- `weight_lb` (number, optional): Weight in pounds. Converted as kg = lb * 0.45359237.

## Bulk (POST)

POST the same path with a JSON items array. Price is n times the GET unit. Invalid items return HTTP 400 before settlement.

Method: `POST /api/calc/maintenance_fluids`
Max items: 25
Price: unit_amount * n (unit 5000 atomic)
Status: PREVIEW

- 1 to 25 items. Each item uses the same keys as the GET query parameters.
- The first invalid item fails the whole request (index in the 400 JSON). You are not charged.
- HTTP 200 is {count, path, items}. Each items[i] is the GET 200 body for that row.
- Catalog misses (empty matches, found=false) stay paid 200s inside that slot.
- x402 resource URL is this path plus n and body_sha256. Browsers that prefer text/html get the same paywall as GET; Pay retries POST with the same items.

Example request:

```json
{
  "items": [
    {
      "weight_kg": "30"
    },
    {
      "weight_kg": "30"
    }
  ]
}
```

Human paywall (two-item fixture): https://api.magentlab.com/paywall/bulk/maintenance-fluids

Example 200:

```json
{
  "count": 2,
  "path": "/api/calc/maintenance_fluids",
  "items": [
    {
      "disclaimer": "Not a medical device. Deterministic published-formula or published-code output for autonomous agents. A licensed clinician remains responsible for patient care and billing submissions.",
      "citation": {
        "authors": "Holliday MA, Segar WE",
        "doi": "10.1542/peds.19.5.823",
        "id": "holliday-segar-1957",
        "source": "Pediatrics. 1957;19(5):823-832",
        "title": "The maintenance need for water in parenteral fluid therapy"
      },
      "formula": "holliday_segar",
      "formula_expression": "daily_ml = 100*min(kg,10) + 50*max(0, min(kg,20)-10) + 20*max(0, kg-20); hourly_ml = daily_ml / 24",
      "weight_kg": 30.0,
      "daily_ml": 1700,
      "hourly_ml": 70.8
    },
    {
      "disclaimer": "Not a medical device. Deterministic published-formula or published-code output for autonomous agents. A licensed clinician remains responsible for patient care and billing submissions.",
      "citation": {
        "authors": "Holliday MA, Segar WE",
        "doi": "10.1542/peds.19.5.823",
        "id": "holliday-segar-1957",
        "source": "Pediatrics. 1957;19(5):823-832",
        "title": "The maintenance need for water in parenteral fluid therapy"
      },
      "formula": "holliday_segar",
      "formula_expression": "daily_ml = 100*min(kg,10) + 50*max(0, min(kg,20)-10) + 20*max(0, kg-20); hourly_ml = daily_ml / 24",
      "weight_kg": 30.0,
      "daily_ml": 1700,
      "hourly_ml": 70.8
    }
  ]
}
```

## Response fields

- `formula` (string): holliday_segar
- `formula_expression` (string): Exact expression used
- `weight_kg` (number): Normalized weight in kg
- `daily_ml` (number): Holliday–Segar daily maintenance water in mL (integer if whole, else 1 decimal)
- `hourly_ml` (number): daily_ml / 24, 1 decimal. Not the later 4-2-1 bedside rule.
- `citation` (object): Holliday and Segar Pediatrics 1957 citation
- `disclaimer` (string): Not-a-device notice

## Example JSON

Frozen fixture. Not a live lookup.

```json
{
  "disclaimer": "Not a medical device. Deterministic published-formula or published-code output for autonomous agents. A licensed clinician remains responsible for patient care and billing submissions.",
  "citation": {
    "authors": "Holliday MA, Segar WE",
    "doi": "10.1542/peds.19.5.823",
    "id": "holliday-segar-1957",
    "source": "Pediatrics. 1957;19(5):823-832",
    "title": "The maintenance need for water in parenteral fluid therapy"
  },
  "formula": "holliday_segar",
  "formula_expression": "daily_ml = 100*min(kg,10) + 50*max(0, min(kg,20)-10) + 20*max(0, kg-20); hourly_ml = daily_ml / 24",
  "weight_kg": 30.0,
  "daily_ml": 1700,
  "hourly_ml": 70.8
}
```

## Errors

- HTTP 400 `invalid_weight`: weight_kg (1-500) or weight_lb (2-1100) is required Returned before settlement; you are not charged.
- HTTP 400 `invalid_items`: POST body must be a JSON object with only an items array Returned before settlement; you are not charged.
- HTTP 400 `invalid_item_count`: items must be an array of 1 to 25 objects Returned before settlement; you are not charged.
- HTTP 400 `invalid_item`: each items entry must be a JSON object Returned before settlement; you are not charged.
- HTTP 402 `payment_required`: Missing or invalid PAYMENT-SIGNATURE; decode the PAYMENT-REQUIRED header
- HTTP 409 `payment_in_progress`: The same authorization nonce is already being settled; retry shortly
- HTTP 429 `rate_limited`: Too many requests from this client
- HTTP 503 `settlement_uncertain`: Settlement is unconfirmed; retry with the same PAYMENT-SIGNATURE
- HTTP 503 `settle_failed`: Settlement failed; retry with the same PAYMENT-SIGNATURE shortly
- HTTP 503 `facilitator_unavailable`: Payment facilitator unavailable
- HTTP 503 `facilitator_misconfigured`: Payment facilitator is not configured
- HTTP 503 `facilitator_unauthorized`: Payment facilitator rejected credentials
- HTTP 503 `ledger_unavailable`: Payment ledger unavailable
- HTTP 503 `payment_unavailable`: Payment processing unavailable

## Related tools

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- [Devine IBW](https://magentlab.com/docs/ibw) — Compute Devine ideal body weight and 0.4 adjusted body weight from height, sex, and actual weight.
- [Harris-Benedict BEE](https://magentlab.com/docs/bee) — Compute Harris–Benedict 1919 basal energy expenditure in kcal/day from height, weight, age, and sex.

## Also searched as

- Holliday Segar
- maintenance fluids
- pediatric maintenance water
- 100 50 20 fluids
- Holliday-Segar water

## Payment

Required query parameters must be present and valid. Invalid params return HTTP 400 JSON before settlement. magent does not charge. Fix the params, then request a new 402 quote for that complete URL. Catalog misses (empty matches, found=false) are valid paid 200s.

- GET the tool with Accept: application/json (do not send Accept: text/html unless you want the human paywall).
- HTTP 402 means you have not paid. Decode the base64 PAYMENT-REQUIRED header. HTTP 503 is not a new quote.
- Sign EIP-3009 (scheme exact, assetTransferMethod eip3009) with validBefore = now + accepts[0].maxTimeoutSeconds (600 seconds). That window starts when you sign and must cover wallet confirmation plus CDP verify and settle. Magent retries transient facilitator 429/5xx before answering. Do not send upto or batch-settlement payloads; magent does not offer those schemes.
- Retry the same URL with PAYMENT-SIGNATURE (base64 JSON echoing accepted, payload, and extensions when present).
- Success is HTTP 200 JSON plus PAYMENT-RESPONSE. Settlement happens before the tool runs. HTTP 503 settlement_uncertain or settle_failed: retry the same PAYMENT-SIGNATURE. Mint a new nonce only after a new HTTP 402.

- offered `exact` on eip155:8453: Fixed-price USDC on Base. The buyer authorizes the advertised amount (EIP-3009). magent settles before the tool runs (paymentFlow upfront). extra.assetTransferMethod=eip3009 extra.paymentFlow=upfront.

- not offered `upto`: Not offered. Usage-based: buyer authorizes a ceiling, seller settles the actual amount after work. Reserved for a future metered tool. Not for current calculators or code search.
- not offered `batch-settlement`: Not offered. Payment-channel vouchers claimed later in batches. Not the same as POST {items} bulk (that is still exact).

Same-path POST {items} is still scheme exact: one EIP-3009 authorization for n times the GET unit. That is not x402 batch-settlement (payment channels / vouchers).

## Guarantees

- Invalid query parameters return HTTP 400 before settlement. You are not charged.
- Settlement finishes before the tool executes (paymentFlow upfront). Uncertain or failed settlement fails closed (HTTP 503). Retry the same PAYMENT-SIGNATURE.
- HTTP 402 is unpaid only. Do not sign a second authorization because of a 503.
- Execution is timeout-bounded and concurrency-capped.
- Calculator inputs are stored encrypted for allowlisted operators (Magent Console). They are not in public logs, SSH lookups, catalog, or rollups. Request logs store path without query.