_id
683a15f1c782e11e38d1b0af
id
243
title
A-a O₂ Gradient
full_title
A-a O₂ Gradient
short_title
A-a O₂ Gradient
med_description
Assesses for degree of shunting and V/Q mismatch.
short_description
Shunting and V/Q Mismatch.
slug
a-a-o2-gradient
description
The A-a O₂ Gradient assesses for degree of shunting and V/Q mismatch.
keywords
A-a O2 Gradient, shunting, V/q mismatch, shunting v/q, shunting v/q mismatch, A-a o2, o2 gradient, a-a o2 calc, a-a o2 score, a-a shunting, a-a v/q, a-a gradient score, a-a gradient calc, a-a gradient mdcalc, a-a o2 gradient online, o2 gradient online, oxygen gradient calc, oxygen gradient online, A-a oxygen gradient, a-a gradient, elevated a-a gradient, elevated o2 gradient, alveolar gas, alveolar
complaint
[ "Cough", "Shortness of Breath" ]
formula
A-a O₂ Gradient = [ (FiO₂) × (Atmospheric Pressure - H₂O Pressure) - (PaCO₂/0.8) ] – PaO₂ from ABG H₂O pressure = 47 mmHg Normal Gradient Estimate = (Age/4) + 4
evidence
measurements
[ { "name": "Age", "unit": "age", "error_min": "0.001", "error_max": "120", "warn_min": "0.1", "warn_max": "100", "conversion": "1", "normal_max_si": "0", "normal_max_us": "0", "normal_min_si": "0", "normal_min_us": "0", "units_si": "years", "units_us": "years" }, { "name": "Atmospheric Pressure", "unit": "atm", "error_min": "250", "error_max": "800", "warn_min": "500", "warn_max": "762", "conversion": "0.133", "normal_max_si": "0", "normal_max_us": "0", "normal_min_si": "0", "normal_min_us": "0", "units_si": "kPa", "units_us": "mm Hg" }, { "name": "Partial Pressure of CO2", "unit": "paco2", "error_min": "1", "error_max": "150", "warn_min": "10", "warn_max": "60", "conversion": "0.133", "normal_max_si": "5.586", "normal_max_us": "42", "normal_min_si": "5.054", "normal_min_us": "38", "units_si": "kPa", "units_us": "mm Hg" }, { "name": "Partial Pressure of Oxygen", "unit": "pao2", "error_min": "1", "error_max": "650", "warn_min": "10", "warn_max": "600", "conversion": "0.133", "normal_max_si": "13.3", "normal_max_us": "100", "normal_min_si": "10", "normal_min_us": "75", "units_si": "kPa", "units_us": "mm Hg" }, { "name": "Fraction of Inhaled O2", "unit": "fio2", "error_min": "10", "error_max": "100.01", "warn_min": "20", "warn_max": "100.001", "conversion": "1", "normal_max_si": "NaN", "normal_max_us": "NaN", "normal_min_si": "NaN", "normal_min_us": "NaN", "units_si": "%", "units_us": "%" } ]
information
The 5 Causes of Hypoxemia
| Causes of Hypoxemia | A-a O₂ Gradient Shift | |
|---|---|---|
| 1 | V/Q Mismatch (ex: PNA, CHF, PE, ARDS, atelectasis, etc) | Elevation |
| 2 | Shunt (ex: PFO, ASD, pulmonary AVMs) | Elevation |
| 3 | Alveolar Hypoventilation (ex: interstitial lung dz, environmental lung dz, PCP PNA) | Elevation |
| 4 | Hypoventilation (ex: COPD, CNS d/o, neuromuscular dz, etc) | Depression |
| 5 | High altitude | Depression |
refrences
{ "Clinical Practice Guidelines": [], "Manufacturer Website": [], "Original/Primary Reference": [ { "href": "https://www.ncbi.nlm.nih.gov/pubmed/436542", "text": "Helmholz HF Jr. The abbreviated alveolar air equation. Chest. 1979 Jun;75(6):748" } ], "Other References": [], "Outcomes": [], "Validation": [ { "href": "https://www.ncbi.nlm.nih.gov/pubmed/8304364", "text": "McFarlane MJ, Imperiale TF. Use of the alveolar-arterial oxygen gradient in the diagnosis of pulmonary embolism. Am J Med. 1994 Jan;96(1):57-62." } ], "Validations": [] }
pearls
usecase
- Patients with unexplained hypoxia.
- Patients with hypoxia exceeding the degree of their clinical illness.
reasons
The A-a Gradient can help determine the cause of hypoxia; it pinpoints the location of the hypoxia as intra- or extra-pulmonary.
next_advice
After calculating the A-a Gradient and determining if it is elevated or normal, one can rule out several causes of hypoxia.
next_actions
next_management
diseases
[ "CHF", "Coronavirus", "COVID-19", "Pneumonia", "Pulmonary Embolism", "Respiratory Distress", "Chronic Obstructive Pulmonary Disease" ]
input_schema
{ "conditionality": "", "default": null, "fhir_rules": null, "inct": null, "label_en": "<p>Atmospheric pressure</p>", "name": "atmospheric_pressure", "optional": false, "tips_en": "Use 760 mm Hg (101.33 kPa) at sea level", "type": "textbox", "unit": "atm" }
{ "conditionality": "", "default": null, "fhir_rules": null, "inct": null, "label_en": "<p>PaO₂</p>", "name": "pao2", "optional": false, "tips_en": "", "type": "textbox", "unit": "pao2" }
{ "conditionality": "", "default": 21, "fhir_rules": null, "inct": null, "label_en": "<p>FiO₂</p>", "name": "fio2", "optional": false, "tips_en": "Use 21% for room air", "type": "textbox", "unit": "fio2" }
{ "conditionality": "", "default": null, "fhir_rules": null, "inct": null, "label_en": "<p>PaCO₂</p>", "name": "paco2", "optional": false, "tips_en": "", "type": "textbox", "unit": "paco2" }
{ "conditionality": "", "default": null, "fhir_rules": null, "inct": null, "label_en": "<p>Age (for expected A-a gradient)</p>", "name": "age", "optional": true, "tips_en": "", "type": "textbox", "unit": "age" }
[ { "conditionality": "", "default": null, "fhir_rules": null, "inct": null, "label_en": "<p>Atmospheric pressure</p>", "name": "atmospheric_pressure", "optional": false, "tips_en": "Use 760 mm Hg (101.33 kPa) at sea level", "type": "textbox", "unit": "atm" }, { "conditionality": "", "default": null, "fhir_rules": null, "inct": null, "label_en": "<p>PaO₂</p>", "name": "pao2", "optional": false, "tips_en": "", "type": "textbox", "unit": "pao2" }, { "conditionality": "", "default": 21, "fhir_rules": null, "inct": null, "label_en": "<p>FiO₂</p>", "name": "fio2", "optional": false, "tips_en": "Use 21% for room air", "type": "textbox", "unit": "fio2" }, { "conditionality": "", "default": null, "fhir_rules": null, "inct": null, "label_en": "<p>PaCO₂</p>", "name": "paco2", "optional": false, "tips_en": "", "type": "textbox", "unit": "paco2" }, { "conditionality": "", "default": null, "fhir_rules": null, "inct": null, "label_en": "<p>Age (for expected A-a gradient)</p>", "name": "age", "optional": true, "tips_en": "", "type": "textbox", "unit": "age" } ]
instructions
published
2022-04-21T20:29:10.715Z
purpose
[ "Formula" ]
search_terms
[ "intubation", "abg", "aa", "aaa", "alveolar", "PO2", "PaO2", "FiO2", "alveolar gas", "covid", "covid-19", "coronavirus" ]
seo
{ "keywords_en": "A-a O2 Gradient, shunting, V/q mismatch, shunting v/q, shunting v/q mismatch, A-a o2, o2 gradient, a-a o2 calc, a-a o2 score, a-a shunting, a-a v/q, a-a gradient score, a-a gradient calc, a-a gradient mdcalc, a-a o2 gradient online, o2 gradient online, oxygen gradient calc, oxygen gradient online, A-a oxygen gradient, a-a gradient, elevated a-a gradient, elevated o2 gradient, alveolar gas, alveolar", "meta_description_en": "The A-a O₂ Gradient assesses for degree of shunting and V/Q mismatch." }
specialty
[ "Critical Care", "Emergency Medicine", "Endocrinology", "Hospitalist Medicine", "Internal Medicine", "OB-Gyn", "Pulmonology", "Surgery (General)" ]
departments
[ "Cardiac", "Renal", "Respiratory" ]
tags
[]
version_number
1
versions
[]
related
[ { "calcId": 797, "short_title_en": "Light's Criteria", "slug": "lights-criteria-exudative-effusions" }, { "calcId": 58, "short_title_en": "Pediatric ET Tube Size", "slug": "pediatric-endotracheal-tube-ett-size" }, { "calcId": 4050, "short_title_en": "DRIP Score", "slug": "drug-resistance-pneumonia-drip-score" } ]
ismed
false
section
[ "whenToUseViewed", "whyUseViewed", "nextStepsViewed", "evidenceViewed" ]
cleaned_departments
[ "cardiology", "urology", "pulmonology" ]
cleaned_use
[ "Patients with unexplained hypoxia.", "Patients with hypoxia exceeding the degree of their clinical illness." ]
pub
true