{"id":59530,"date":"2016-03-25T15:58:07","date_gmt":"2016-03-25T13:58:07","guid":{"rendered":"http:\/\/wpcalc.com\/?p=59530"},"modified":"2026-10-23T17:11:03","modified_gmt":"2026-10-23T14:11:03","slug":"arterial-blood-gas","status":"publish","type":"post","link":"https:\/\/wpcalc.com\/en\/medical\/arterial-blood-gas\/","title":{"rendered":"ABG Calculator \u2013 Arterial Blood Gas Interpretation"},"content":{"rendered":"<section class=\"not-prose calculator-box\" aria-labelledby=\"calculator-title\"><div class=\"flex items-baseline sm:items-center justify-between gap-2 sm:gap-3\"><div class=\"flex flex-col sm:flex-row sm:items-center gap-2\"><span class=\"icon icon-calculator text-primary-700! text-base! dark:text-primary-300!\" aria-hidden=\"true\"><\/span><h2 id=\"calculator-title\" class=\"text-lg font-display font-bold\">ABG Analysis and Acid-Base Imbalance Checker<\/h2><\/div><div class=\"calcdash-favorite group\">\n  <button type=\"button\" class=\"favorite\" id=\"favorite\" data-favorite-id=\"59530\" data-favorite-title=\"Arterial Blood Gas \" data-favorite-url=\"https:\/\/wpcalc.com\/en\/medical\/arterial-blood-gas\/\" data-favorite-excerpt=\"Enter pH, PaCO\u2082 and HCO\u2083\u207b from an arterial blood gas sample to classify the acid\u2013base disturbance: respiratory or metabolic acidosis or alkalosis, and whether it is acute, partly compensated or fully compensated.\" aria-label=\"Add to Favorites\" data-favorite-icon=\"icon icon-flask\">\n    <span class=\"icon icon-shape-star-empty\" aria-hidden=\"true\"><\/span>\n  <\/button>\n  <div class=\"calcdash-favorite__tip\" aria-hidden=\"true\">\n   <span class=\"favorite-tooltip\" id=\"favorite-tooltip\"><\/span>\n  <\/div>\n  <span class=\"sr-only\" role=\"status\" id=\"favorite-status\"><\/span>\n<\/div><\/div><form action=\"https:\/\/wpcalc.com\/en\/medical\/arterial-blood-gas\/\" method=\"POST\" class=\"calculator\" id=\"calculator-59530\" data-post=\"59530\"><fieldset class=\"fieldset-input\"><legend class=\"sr-only\">Input Fields<\/legend><div class=\"field\" id=\"input-1\"><label for=\"field-1\">pH<\/label><input type=\"text\" name=\"ph\" id=\"field-1\" data-number inputmode=\"decimal\" autocomplete=\"off\" spellcheck=\"false\" min=\"0\" max=\"14\" value=\"7.4\"\/><\/div><div class=\"field\" id=\"input-2\"><label for=\"field-2\">paCO\u2082<\/label><input type=\"text\" name=\"paco\" id=\"field-2\" aria-describedby=\"calc-unit-2\" data-number inputmode=\"decimal\" autocomplete=\"off\" spellcheck=\"false\" min=\"0\" value=\"40\"\/><div class=\"unit\" id=\"calc-unit-2\">mmHg<\/div><\/div><div class=\"field\" id=\"input-3\"><label for=\"field-3\">HCO\u2083\u207b<\/label><input type=\"text\" name=\"hco\" id=\"field-3\" aria-describedby=\"calc-unit-3\" data-number inputmode=\"decimal\" autocomplete=\"off\" spellcheck=\"false\" min=\"0\" value=\"24\"\/><div class=\"unit\" id=\"calc-unit-3\">mEq\/L<\/div><\/div><\/fieldset><div class=\"buttons\"><button type=\"submit\" data-text=\"Re-Calculate\" id=\"calculate-button\" data-post=\"59530\">Calculate<\/button><button type=\"reset\">Reset<\/button><\/div><div class=\"field is-checkbox hidden!\" id=\"field-auto-calc\"><input type=\"checkbox\" id=\"auto-calc\"><label for=\"auto-calc\">Calculate automatically<\/label><small>If enabled, the result will update automatically when you change any value.<\/small><\/div><div class=\"fieldset-result is-hidden\" aria-labelledby=\"result-title\" aria-live=\"polite\" role=\"region\"> <h3 class=\"result-title bg-gradient-to-r from-primary-50 to-gray-50 dark:from-primary-900 dark:to-gray-800\" id=\"result-title\"><span class=\"icon icon-s-pulse\" aria-hidden=\"true\"><\/span> Your Results<\/h3><div class=\"result-box\"><div class=\"field-result\" id=\"output-1\"><span class=\"field-title\"><span>ABG Analysis<\/span><span class=\"result-term\">abg-result<\/span><\/span><span class=\"field-value\" id=\"result-1\"><\/span><button type=\"button\" class=\"copy-result\" data-tooltip=\"Copy Result\" aria-label=\"Copy Result\"><span class=\"copy-icon icon icon-document-copy\" aria-hidden=\"true\"><\/span><\/button><\/div><\/div><div class=\"result-actions\"><button type=\"button\" class=\"copy-link\"><svg viewBox=\"0 0 20 20\" fill=\"currentColor\" aria-hidden=\"true\"><path d=\"M12.232 4.232a2.5 2.5 0 0 1 3.536 3.536l-1.225 1.224a.75.75 0 0 0 1.061 1.06l1.224-1.224a4 4 0 0 0-5.656-5.656l-3 3a4 4 0 0 0 .225 5.865.75.75 0 0 0 .977-1.138 2.5 2.5 0 0 1-.142-3.667l3-3Z\"\/><path d=\"M11.603 7.963a.75.75 0 0 0-.977 1.138 2.5 2.5 0 0 1 .142 3.667l-3 3a2.5 2.5 0 0 1-3.536-3.536l1.225-1.224a.75.75 0 0 0-1.061-1.06l-1.224 1.224a4 4 0 1 0 5.656 5.656l3-3a4 4 0 0 0-.225-5.865Z\"\/><\/svg><span class=\"copy-link__text\">Copy link to this calculation<\/span><\/button><span class=\"sr-only\" role=\"status\" id=\"copy-link-status\"><\/span><\/div><\/div><a href=\"#respond\" class=\"hidden transition-opacity duration-300 opacity-0 w-50 text-sm justify-center items-center gap-2 px-4 py-2 rounded bg-gray-200 text-gray-700 hover:bg-gray-300\" id=\"leave-comment\"><span class=\"icon icon-comments\" aria-hidden=\"true\"><\/span>Leave a Comment<\/a><\/form><\/section><section id=\"calc-reactions\" class=\"not-prose hidden my-12 bg-gradient-to-r from-primary-50 to-gray-50 border border-indigo-100 rounded-xl px-6 py-4 shadow-sm\" data-post=\"59530\" aria-live=\"polite\" aria-labelledby=\"calc-reactions-title\"><p id=\"calc-reactions-title\" class=\"text-sm text-gray-500 text-center mb-2\">How did this result make you feel?<\/p><div role=\"group\" aria-labelledby=\"calc-reactions-title\" class=\"grid grid-cols-3 sm:flex sm:flex-row sm:justify-around gap-4 sm:items-center sm:flex-wrap\"><button type=\"button\" aria-pressed=\"false\" class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"like\"><span class=\"reaction-count\" data-reaction-count=\"like\">2<\/span><span class=\"reaction text-3xl\" aria-hidden=\"true\">\ud83d\ude00 <\/span><span class=\"reaction-description font-medium\">Like <\/span><\/button><button type=\"button\" aria-pressed=\"false\" class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"helpful\"><span class=\"reaction-count\" data-reaction-count=\"helpful\">6<\/span><span class=\"reaction text-3xl\" aria-hidden=\"true\">\ud83d\udca1 <\/span><span class=\"reaction-description font-medium\">Helpful <\/span><\/button><button type=\"button\" aria-pressed=\"false\" class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"confused\"><span class=\"reaction-count\" data-reaction-count=\"confused\">1<\/span><span class=\"reaction text-3xl\" aria-hidden=\"true\">\ud83d\ude15 <\/span><span class=\"reaction-description font-medium\">Confused <\/span><\/button><button type=\"button\" aria-pressed=\"false\" class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"disappointed\"><span class=\"reaction-count\" data-reaction-count=\"disappointed\">1<\/span><span class=\"reaction text-3xl\" aria-hidden=\"true\">\ud83d\ude1e <\/span><span class=\"reaction-description font-medium\">Disappointed <\/span><\/button><button type=\"button\" aria-pressed=\"false\" class=\"reaction-btn flex flex-col items-center gap-1 text-sm text-gray-700 hover:text-primary-600 cursor-pointer transition-transform hover:scale-105\" data-reaction=\"inaccurate\"><span class=\"reaction-count\" data-reaction-count=\"inaccurate\">6<\/span><span class=\"reaction text-3xl\" aria-hidden=\"true\">\u274c <\/span><span class=\"reaction-description font-medium\">Inaccurate <\/span><\/button><\/div><div id=\"reaction-message\" class=\"hidden mt-8 rounded-md border border-primary-100 bg-white\/50 backdrop-blur-sm px-4 py-2 text-sm text-center shadow-sm\"><\/div><\/section><div class=\"calcdash-ad not-prose calcdash-ad--calc_result calcdash-ad--in-article\"><ins class=\"adsbygoogle\" style=\"display:block\" data-ad-client=\"ca-pub-1721569815777345\" data-ad-slot=\"6317458308\" data-ad-layout=\"in-article\" data-ad-format=\"fluid\"><\/ins><script>(adsbygoogle = window.adsbygoogle || []).push({});<\/script><\/div>\n<style id=\"wpcoderpro-inline-1\">.formula-box {\r\n\tborder-bottom: none !important;\r\n}<\/style><section class=\"formula-box\" aria-labelledby=\"formula-title\">\r\n\t<div id=\"formula-title\" class=\"not-prose font-display mb-4\"><span class=\"icon icon-formula\" aria-hidden=\"true\"><\/span><h2>Arterial Blood Gas Interpretation Formula<\/h2><\/div>\r\n\t<figure class=\"not-prose formula\">\r\n\t\t<figcaption class=\"formula-title\">Formula<\/figcaption>\r\n\t\t<div class=\"text-base text-gray-800\" id=\"formula\">\n\\[ 7.35 \\le \\mathrm{pH} \\le 7.45, \\qquad 35 \\le \\mathrm{PaCO_2} \\le 45~\\mathrm{mmHg}, \\qquad 22 \\le \\mathrm{HCO_3^-} \\le 26~\\mathrm{mEq\/L} \\]\n<\/div>\r\n\t<\/figure>\r\n\t<\/p>\n<p><strong>Where:<\/strong><\/p>\n<ul>\n<li>\\( \\mathrm{pH} \\) \u2014 acidity of arterial blood; normal range 7.35\u20137.45<\/li>\n<li>\\( \\mathrm{PaCO_2} \\) \u2014 partial pressure of arterial carbon dioxide, the respiratory component; normal range 35\u201345 mmHg<\/li>\n<li>\\( \\mathrm{HCO_3^-} \\) \u2014 bicarbonate concentration, the metabolic component; normal range 22\u201326 mEq\/L<\/li>\n<\/ul>\n<p>The three values are not independent: they are linked by the Henderson\u2013Hasselbalch equation \\( \\mathrm{pH} = 6.1 + \\log_{10}\\left( \\frac{[\\mathrm{HCO_3^-}]}{0.03 \\times \\mathrm{PaCO_2}} \\right) \\). The calculator compares each measured value with its normal range and then checks whether the opposing system is compensating for the primary disturbance.<\/p>\n<p>\r\n<\/section>\n<style id=\"wpcoderpro-inline-459\">.calculation-box {\r\n\tborder-bottom: none !important;\r\n}<\/style><section id=\"calculation\" class=\"calculation-box\" aria-labelledby=\"calculation-title\">\r\n\t<div id=\"calculation-title\" class=\"not-prose font-display\"><span class=\"icon icon-unordered-list\" aria-hidden=\"true\"><\/span><h2>Arterial Blood Gas \u2013 Calculation Example<\/h2><\/div>\r\n\r\n<\/p>\n<p><strong>Example:<\/strong> an arterial sample from a healthy adult at rest returns the calculator's default values: pH 7.40, PaCO\u2082 40 mmHg and HCO\u2083\u207b 24 mEq\/L.<\/p>\n<p>\\[ \\mathrm{pH} = 7.40 \\in [7.35,\\ 7.45] \\\\ \\mathrm{PaCO_2} = 40\\ \\mathrm{mmHg} \\in [35,\\ 45] \\\\ \\mathrm{HCO_3^-} = 24\\ \\mathrm{mEq\/L} \\in [22,\\ 26] \\]<\/p>\n<p><strong>Result:<\/strong> Normal Arterial Blood Gas \u2014 all three values lie inside their reference ranges, so acid\u2013base balance is intact.<\/p>\n<p>For contrast, entering pH 7.30, PaCO\u2082 40 mmHg and HCO\u2083\u207b 15 mEq\/L gives <strong>Acute Metabolic Acidosis<\/strong>: the pH is low, the PaCO\u2082 is still normal (no respiratory compensation has started yet) and the bicarbonate is far below range.<\/p>\n<p>\n\r\n<\/section>\n<h2>How to Use the ABG Calculator<\/h2>\n<ol>\n<li>Enter the measured <strong>pH<\/strong> in the pH field (accepted values 0\u201314, e.g. 7.40).<\/li>\n<li>Enter the carbon dioxide value in the <strong>paCO\u2082<\/strong> field, in mmHg.<\/li>\n<li>Enter the bicarbonate value in the <strong>HCO\u2083\u207b<\/strong> field, in mEq\/L (many labs report mmol\/L, which is numerically identical).<\/li>\n<li>Read the classification in the <strong>ABG Analysis<\/strong> result \u2014 for example \"Acute Respiratory Acidosis\", \"Compensated Metabolic Acidosis\", \"Mixed Disorders\" or \"Normal Arterial Blood Gas\".<\/li>\n<\/ol>\n<h2>What Is Arterial Blood Gas Interpretation?<\/h2>\n<p>An arterial blood gas (ABG) is one of the most informative single tests in acute medicine. It shows how well the lungs oxygenate the blood and how well the lungs and kidneys together maintain acid\u2013base balance. Three of the reported values define the acid\u2013base status: pH (the overall acidity), PaCO\u2082 (the respiratory component, controlled by ventilation) and HCO\u2083\u207b (the metabolic component, controlled by the kidneys).<\/p>\n<p>Every acid\u2013base disorder is either respiratory or metabolic, and either acidosis or alkalosis \u2014 four primary patterns in total. The quickest bedside rule: if the pH moves in the opposite direction to PaCO\u2082 (low pH with high PaCO\u2082, or high pH with low PaCO\u2082), the primary problem is respiratory; if the pH moves together with HCO\u2083\u207b (both low or both high), the primary problem is metabolic.<\/p>\n<p>Because two systems control one variable, the healthy system always tries to correct the failing one. Lungs respond within minutes \u2014 hyperventilating to blow off CO\u2082 in metabolic acidosis \u2014 while kidneys need hours to days, for example retaining bicarbonate in chronic respiratory acidosis. The calculator's wording reflects this timeline: <em>Acute<\/em> means no compensation has begun, <em>Partly Compensated<\/em> means the second system is moving but the pH is still outside 7.35\u20137.45, and <em>Compensated<\/em> means the pH has been pulled back into the normal range. Physiological compensation never overcorrects, so a pH on the \"wrong\" side of 7.40, or a second value moving in an unexpected direction, should raise suspicion of a mixed disorder \u2014 which the calculator reports as <em>Mixed Disorders<\/em>, meaning both components are abnormal in a way a single primary process with compensation cannot explain.<\/p>\n<p>Because the kidneys maintain bicarbonate, metabolic acidosis is a hallmark of advanced renal failure. If the ABG shows a metabolic acidosis, it is worth estimating kidney function \u2014 for example with the <a href=\"https:\/\/wpcalc.com\/en\/medical\/cockcroft-gault\/\">Cockcroft-Gault creatinine calculator<\/a> or the <a href=\"https:\/\/wpcalc.com\/en\/medical\/bun-to-creatinine-ratio\/\">BUN to creatinine ratio calculator<\/a>. In diabetic ketoacidosis, the acidosis is compounded by hyperglycemia-driven sodium shifts, which you can assess with the <a href=\"https:\/\/wpcalc.com\/en\/medical\/hyperglycemia-sodium-correction\/\">corrected sodium calculator<\/a>.<\/p>\n<h2>ABG Pattern Reference Table<\/h2>\n<table>\n<thead>\n<tr>\n<th>Primary disorder<\/th>\n<th>pH<\/th>\n<th>PaCO\u2082<\/th>\n<th>HCO\u2083\u207b<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Respiratory acidosis \u2014 acute<\/td>\n<td>\u2193<\/td>\n<td>\u2191<\/td>\n<td>Normal<\/td>\n<\/tr>\n<tr>\n<td>Respiratory acidosis \u2014 compensated<\/td>\n<td>Normal<\/td>\n<td>\u2191<\/td>\n<td>\u2191<\/td>\n<\/tr>\n<tr>\n<td>Respiratory alkalosis \u2014 acute<\/td>\n<td>\u2191<\/td>\n<td>\u2193<\/td>\n<td>Normal<\/td>\n<\/tr>\n<tr>\n<td>Respiratory alkalosis \u2014 compensated<\/td>\n<td>Normal<\/td>\n<td>\u2193<\/td>\n<td>\u2193<\/td>\n<\/tr>\n<tr>\n<td>Metabolic acidosis \u2014 acute<\/td>\n<td>\u2193<\/td>\n<td>Normal<\/td>\n<td>\u2193<\/td>\n<\/tr>\n<tr>\n<td>Metabolic acidosis \u2014 compensated<\/td>\n<td>Normal<\/td>\n<td>\u2193<\/td>\n<td>\u2193<\/td>\n<\/tr>\n<tr>\n<td>Metabolic alkalosis \u2014 acute<\/td>\n<td>\u2191<\/td>\n<td>Normal<\/td>\n<td>\u2191<\/td>\n<\/tr>\n<tr>\n<td>Metabolic alkalosis \u2014 compensated<\/td>\n<td>Normal<\/td>\n<td>\u2191<\/td>\n<td>\u2191<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p>Note that a normal pH with a low PaCO\u2082 and a low HCO\u2083\u207b fits both compensated metabolic acidosis and compensated respiratory alkalosis; the calculator reports both possibilities, and the patient's history decides which is the true primary disorder.<\/p>\n<h2>Limitations and Practical Tips<\/h2>\n<ul>\n<li><strong>No oxygenation assessment.<\/strong> The calculator uses only pH, PaCO\u2082 and HCO\u2083\u207b; it says nothing about PaO\u2082 or oxygen saturation, which are essential parts of a full ABG report.<\/li>\n<li><strong>No expected-compensation formulas.<\/strong> For borderline or mixed results, calculate the expected compensation yourself \u2014 for metabolic acidosis, Winter's formula \\( \\mathrm{PaCO_2}^{\\text{expected}} = 1.5 \\times [\\mathrm{HCO_3^-}] + 8 \\pm 2 \\) \u2014 and consider the anion gap, which this tool does not compute.<\/li>\n<li><strong>\"Mixed Disorders\" is a broad category.<\/strong> It covers many combinations; common causes include sepsis, cardiac arrest, renal failure combined with respiratory failure, and vomiting in a patient on diuretics.<\/li>\n<li><strong>Preanalytical errors matter.<\/strong> Air bubbles in the syringe, delayed analysis, excess heparin or an inadvertently venous sample can shift all three values and change the interpretation.<\/li>\n<li><strong>Educational tool only.<\/strong> Always interpret an ABG together with the history, examination and other laboratory results; never base treatment decisions on the calculator output alone.<\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"<p>Enter pH, PaCO\u2082 and HCO\u2083\u207b from an arterial blood gas sample to classify the acid\u2013base disturbance: respiratory or metabolic acidosis or alkalosis, and whether it is acute, partly compensated or fully compensated.<\/p>\n","protected":false},"author":70,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[8],"tags":[50],"class_list":["post-59530","post","type-post","status-publish","format-standard","hentry","category-medical","tag-diagnostics"],"acf":[],"_links":{"self":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/59530","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/users\/70"}],"replies":[{"embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/comments?post=59530"}],"version-history":[{"count":5,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/59530\/revisions"}],"predecessor-version":[{"id":67520,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/posts\/59530\/revisions\/67520"}],"wp:attachment":[{"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/media?parent=59530"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/categories?post=59530"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/wpcalc.com\/en\/wp-json\/wp\/v2\/tags?post=59530"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}