# Net fluid balance (I/O)

Net fluid balance (I/O)

Status: LIVE
Price: $0.005 USDC
`GET /api/calc/fluid_io`
HTML: https://magentlab.com/docs/fluid-io
Markdown: https://magentlab.com/docs/fluid-io.md

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

## What it computes

Compute net fluid balance in mL as caller-assigned total intake minus total output over the same interval, with a positive, negative, or zero label from the sign of that difference.

## When to use

When an agent needs Acheampong 2015 net fluid balance (total intake minus total output) from caller-assigned volumes and must not invent insensible-loss estimates, a resuscitation bolus, or a diuretic order.

## When not to use

- Not a medical device. Not a resuscitation or diuretic order. Not a fluid prescription.
- magent does not measure intake or output. Caller assigns volumes over the same interval.
- Does not estimate insensible losses (Acheampong 2015 excluded them as unreliable). Does not apply third-space coefficients or weight-based TBW.

## Formula

```
net_balance_ml = total_intake_ml - total_output_ml
```

## Citation

[A positive fluid balance is an independent prognostic factor in patients with sepsis](https://doi.org/10.1186/s13054-015-0970-1)
Acheampong A, Vincent JL
Crit Care. 2015;19(1):251
DOI: [10.1186/s13054-015-0970-1](https://doi.org/10.1186/s13054-015-0970-1)

## Worked example

### Intake 2500 mL, output 1800 mL

Given: `total_intake_ml=2500, total_output_ml=1800`

1. net_balance_ml = 2500 − 1800 = 700 mL
2. balance_label = positive (net_balance_ml > 0)


### Intake 1800 mL, output 2500 mL

Given: `total_intake_ml=1800, total_output_ml=2500`

1. net_balance_ml = 1800 − 2500 = −700 mL
2. balance_label = negative (net_balance_ml < 0)


## Also searched as

- net fluid balance
- I/O balance
- fluid intake output
- cumulative fluid balance
- Acheampong fluid balance
- daily fluid balance
- intake minus output

## Parameters

- `total_intake_ml` (number, required): Caller-assigned total fluid intake in mL over the interval (0-100000). Acheampong 2015: sum of intravenous and oral fluids. magent does not measure intake.
- `total_output_ml` (number, required): Caller-assigned total fluid output in mL over the same interval (0-100000). Acheampong 2015: urine, ultrafiltration, drain fluid, and estimated gastrointestinal losses. magent does not measure output.
- `oral_intake_ml` (number, optional): Optional oral intake in mL (0-100000). When any intake addend is sent, oral_intake_ml + iv_intake_ml (missing as 0) must equal total_intake_ml.
- `iv_intake_ml` (number, optional): Optional intravenous intake in mL (0-100000). When any intake addend is sent, oral_intake_ml + iv_intake_ml (missing as 0) must equal total_intake_ml.
- `urine_output_ml` (number, optional): Optional urine output in mL (0-100000). When any output addend is sent, urine + ultrafiltration + drain + GI (missing as 0) must equal total_output_ml.
- `ultrafiltration_ml` (number, optional): Optional ultrafiltration volume in mL (0-100000). When any output addend is sent, the output addends (missing as 0) must equal total_output_ml.
- `drain_output_ml` (number, optional): Optional drain fluid in mL (0-100000). When any output addend is sent, the output addends (missing as 0) must equal total_output_ml.
- `gi_output_ml` (number, optional): Optional estimated gastrointestinal losses in mL (0-100000). Acheampong 2015 counted stool only with profound diarrhea. When any output addend is sent, the output addends (missing as 0) must equal total_output_ml. magent does not estimate insensible loss.

## Bulk (POST)

POST the same path with a JSON items array. The first item is the GET unit; each additional item is $0.002. Invalid items return HTTP 400 before settlement.

Method: `POST /api/calc/fluid_io`
Max items: 25
Price: unit_amount + extra_item_amount * (n - 1) (unit 5000 atomic, extra 2000 atomic)
Status: PREVIEW

- 1 to 25 items. Each item uses the same keys as the GET query parameters.
- POST of 1 item costs the same as GET. Lists longer than 25: chunk into multiple POSTs. Extra items still execute; do not pad dummy rows.
- 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": [
    {
      "total_intake_ml": "2500",
      "total_output_ml": "1800"
    },
    {
      "total_intake_ml": "2500",
      "total_output_ml": "1800"
    }
  ]
}
```

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

Example 200:

```json
{
  "count": 2,
  "path": "/api/calc/fluid_io",
  "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": "Acheampong A, Vincent JL",
        "doi": "10.1186/s13054-015-0970-1",
        "id": "acheampong-2015",
        "pmid": "26073560",
        "source": "Crit Care. 2015;19(1):251",
        "title": "A positive fluid balance is an independent prognostic factor in patients with sepsis"
      },
      "formula": "acheampong_2015",
      "formula_expression": "net_balance_ml = total_intake_ml - total_output_ml",
      "balance_label": "positive",
      "net_balance_ml": 700,
      "total_intake_ml": 2500,
      "total_output_ml": 1800
    },
    {
      "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": "Acheampong A, Vincent JL",
        "doi": "10.1186/s13054-015-0970-1",
        "id": "acheampong-2015",
        "pmid": "26073560",
        "source": "Crit Care. 2015;19(1):251",
        "title": "A positive fluid balance is an independent prognostic factor in patients with sepsis"
      },
      "formula": "acheampong_2015",
      "formula_expression": "net_balance_ml = total_intake_ml - total_output_ml",
      "balance_label": "positive",
      "net_balance_ml": 700,
      "total_intake_ml": 2500,
      "total_output_ml": 1800
    }
  ]
}
```

## Response fields

- `formula` (string): acheampong_2015
- `formula_expression` (string): Exact expression used
- `total_intake_ml` (number): Caller-assigned total intake in mL used in the subtraction
- `total_output_ml` (number): Caller-assigned total output in mL used in the subtraction
- `net_balance_ml` (number): total_intake_ml minus total_output_ml, 1 decimal then integer when whole
- `balance_label` (string): positive (net_balance_ml > 0), negative (net_balance_ml < 0), or zero (net_balance_ml = 0). A sign label, not a fluid order.
- `citation` (object): Acheampong and Vincent Crit Care 2015 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": "Acheampong A, Vincent JL",
    "doi": "10.1186/s13054-015-0970-1",
    "id": "acheampong-2015",
    "pmid": "26073560",
    "source": "Crit Care. 2015;19(1):251",
    "title": "A positive fluid balance is an independent prognostic factor in patients with sepsis"
  },
  "formula": "acheampong_2015",
  "formula_expression": "net_balance_ml = total_intake_ml - total_output_ml",
  "balance_label": "positive",
  "net_balance_ml": 700,
  "total_intake_ml": 2500,
  "total_output_ml": 1800
}
```

## Errors

- HTTP 400 `invalid_fluid_io`: Fluid-balance inputs must match caller-assigned intake and output volumes as published. 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.

Shared HTTP 402 and 503: https://magentlab.com/docs/payments

## Related tools

- [NICE adult IV maintenance](https://magentlab.com/docs/nice-iv-maintenance) — Compute NICE CG174 adult hospital routine maintenance water (20, 25, or 30 mL/kg/day), approximately 1 mmol/kg/day sodium, potassium, and chloride each, and the fixed 50–100 g/day glucose range.
- [Parkland formula](https://magentlab.com/docs/parkland) — Compute adult Parkland 24-hour crystalloid volume from weight and percent TBSA, with half allotted to the first 8 hours from the time of burn.
- [Maintenance fluids](https://magentlab.com/docs/maintenance-fluids) — Compute Holliday–Segar 1957 daily maintenance water from weight, plus the corresponding hourly milliliters.

## Payment

Unpaid requests return HTTP 402 even if query parameters or POST items are missing or invalid, so CDP and agents can index the path. After a PAYMENT-SIGNATURE, 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 accepts[0] (exact, EIP-3009) with validBefore = now + maxTimeoutSeconds (600 seconds), or accepts[1] (batch-settlement deposit/voucher) on product GET. Ping and POST {items} stay exact. Magent retries transient facilitator 429/5xx before answering.
- Retry the same URL with PAYMENT-SIGNATURE (base64 JSON of accepted and payload). Magent attaches canonical extensions.bazaar on CDP verify/settle; echoing 402 bazaar is optional.
- Success is HTTP 200 JSON plus PAYMENT-RESPONSE. exact settles before the tool. batch-settlement verifies (and deposit-settles) before the tool and commits the charge after HTTP 2xx. HTTP 503: retry the same PAYMENT-SIGNATURE. Mint a new exact 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.
- offered `batch-settlement` on eip155:8453: Payment-channel vouchers claimed later in batches. Exact stays accepts[0]. Same-path POST {items} is still exact. extra.assetTransferMethod=eip3009 extra.paymentFlow=authorization.

- 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.

Same-path POST {items} is still scheme exact: one EIP-3009 authorization for GET unit plus $0.002 per extra item. That is not x402 batch-settlement (payment channels / vouchers).

Shared HTTP 402 and 503 table: https://magentlab.com/docs/payments

Stdio MCP (one process per host): https://magentlab.com/docs/mcp

## Guarantees

- HTTP 402 is unpaid, including a missing query. After PAYMENT-SIGNATURE, invalid parameters return HTTP 400 before settlement. You are not charged. HTTP 402 never includes the tool JSON.
- exact: settlement finishes before the tool (paymentFlow upfront). batch-settlement: verify/deposit before the tool; chargedCumulativeAmount commits after HTTP 2xx. 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.