Respiratory · LIVE

SpO2/FiO2 ratio

Compute the SpO2/FiO2 (S/F) ratio as pulse-oximetry SpO2 percent divided by inspired oxygen fraction.

LIVE $0.005 USDC GET /api/calc/sf_ratio

Markdown: /docs/sf-ratio.md · Canonical: https://magentlab.com/docs/sf-ratio

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

What it computes

Compute the SpO2/FiO2 (S/F) ratio as pulse-oximetry SpO2 percent divided by inspired oxygen fraction.

When to use

When an agent needs SpO2 percent divided by FiO2 and must not invent a P/F ratio, ROX, or ARDS/Berlin bands.

When not to use

• Not a diagnosis.
• This is not the PaO2/FiO2 (P/F) ratio.
• Magent does not apply ARDS or Berlin severity bands.
• This is not the ROX index.
• FiO2 is required as a fraction (0.21–1.0), not a percent, and is not defaulted to room air.

Formula

sf_ratio = spo2_percent / fio2

Citation

Title

Comparison of the SpO2/FIO2 ratio and the PaO2/FIO2 ratio in patients with acute lung injury or ARDS

Authors

Rice TW, Wheeler AP, Bernard GR, Hayden DL, Schoenfeld DA, Ware LB

Source

Chest. 2007;132(2):410-417

DOI

10.1378/chest.07-0617

Worked example

Also searched as

• S/F ratio
• SpO2/FiO2
• SpO2 over FiO2
• SF ratio
• pulse ox FiO2 ratio
• Rice S/F
• SpO2 FiO2 ratio

Try

Opens the live endpoint. Unpaid browser requests show the paywall; agents should send Accept: application/json.

/api/calc/sf_ratio?spo2_percent=95&fio2=0.21

Full URL: https://api.magentlab.com/api/calc/sf_ratio?spo2_percent=95&fio2=0.21

Call

Expect HTTP 402 until you retry with PAYMENT-SIGNATURE. Incomplete query params return HTTP 400 before any quote or charge.

curl -i -H "Accept: application/json" "https://api.magentlab.com/api/calc/sf_ratio?spo2_percent=95&fio2=0.21"

Parameters

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.

POST /api/calc/sf_ratio Max 25 unit_amount + extra_item_amount * (n - 1) extra $0.002 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 (fixture)

{
  "items": [
    {
      "fio2": "0.21",
      "spo2_percent": "95"
    },
    {
      "fio2": "0.21",
      "spo2_percent": "95"
    }
  ]
}

Open bulk paywall →

Opens a two-item fixture on the API host. Unpaid browsers get the same MetaMask paywall as GET; Pay retries POST with those items.

Example 200 (fixture)

{
  "count": 2,
  "path": "/api/calc/sf_ratio",
  "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": "Rice TW, Wheeler AP, Bernard GR, Hayden DL, Schoenfeld DA, Ware LB",
        "doi": "10.1378/chest.07-0617",
        "id": "rice-2007",
        "source": "Chest. 2007;132(2):410-417",
        "title": "Comparison of the SpO2/FIO2 ratio and the PaO2/FIO2 ratio in patients with acute lung injury or ARDS"
      },
      "formula": "sf_ratio",
      "formula_expression": "sf_ratio = spo2_percent / fio2",
      "fio2": 0.21,
      "spo2_percent": 95.0,
      "sf_ratio": 452.4
    },
    {
      "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": "Rice TW, Wheeler AP, Bernard GR, Hayden DL, Schoenfeld DA, Ware LB",
        "doi": "10.1378/chest.07-0617",
        "id": "rice-2007",
        "source": "Chest. 2007;132(2):410-417",
        "title": "Comparison of the SpO2/FIO2 ratio and the PaO2/FIO2 ratio in patients with acute lung injury or ARDS"
      },
      "formula": "sf_ratio",
      "formula_expression": "sf_ratio = spo2_percent / fio2",
      "fio2": 0.21,
      "spo2_percent": 95.0,
      "sf_ratio": 452.4
    }
  ]
}

Response

Example JSON

Machine form of the same example. Frozen fixture. Not a live lookup.

{
  "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": "Rice TW, Wheeler AP, Bernard GR, Hayden DL, Schoenfeld DA, Ware LB",
    "doi": "10.1378/chest.07-0617",
    "id": "rice-2007",
    "source": "Chest. 2007;132(2):410-417",
    "title": "Comparison of the SpO2/FIO2 ratio and the PaO2/FIO2 ratio in patients with acute lung injury or ARDS"
  },
  "formula": "sf_ratio",
  "formula_expression": "sf_ratio = spo2_percent / fio2",
  "fio2": 0.21,
  "spo2_percent": 95.0,
  "sf_ratio": 452.4
}

Client errors (HTTP 400)

Invalid params return 400 without charge. Shared HTTP 402 and 503 meanings: Payments.

Related tools

• PaO2/FiO2 ratio — Compute the PaO2/FiO2 ratio as arterial PO2 in mm Hg divided by inspired oxygen fraction.
• ROX index — Compute the ROX index as pulse-oximetry SpO2 percent divided by inspired oxygen fraction, then divided by respiratory rate.

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. Unpaid valid requests return HTTP 402 with a base64 PAYMENT-REQUIRED header. HTTP 503 is not a new quote: retry the same PAYMENT-SIGNATURE. Full handshake and shared payment errors: Payments. Stdio MCP: /docs/mcp.

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.