{"id":1145,"date":"2016-07-17T21:11:16","date_gmt":"2016-07-18T02:11:16","guid":{"rendered":"http:\/\/www.henrydelrosario.com\/?p=1145"},"modified":"2016-08-28T16:19:30","modified_gmt":"2016-08-28T21:19:30","slug":"vq-mismatch","status":"publish","type":"post","link":"http:\/\/www.henrydelrosario.com\/?p=1145","title":{"rendered":"V\/Q Mismatch &#038; Hypoxemia"},"content":{"rendered":"<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter size-full wp-image-1146\" src=\"http:\/\/www.henrydelrosario.com\/wp-content\/uploads\/2016\/07\/VQmismatch.jpg\" alt=\"VQmismatch\" width=\"879\" height=\"640\" srcset=\"http:\/\/www.henrydelrosario.com\/wp-content\/uploads\/2016\/07\/VQmismatch.jpg 879w, http:\/\/www.henrydelrosario.com\/wp-content\/uploads\/2016\/07\/VQmismatch-300x218.jpg 300w, http:\/\/www.henrydelrosario.com\/wp-content\/uploads\/2016\/07\/VQmismatch-768x559.jpg 768w, http:\/\/www.henrydelrosario.com\/wp-content\/uploads\/2016\/07\/VQmismatch-700x510.jpg 700w\" sizes=\"auto, (max-width: 879px) 100vw, 879px\" \/><\/p>\n<h2>V\/Q Mismatch Confusion<\/h2>\n<p>V\/Q mismatch is a confusing subject because the terms &#8220;dead space&#8221; and &#8220;shunt&#8221; are not very intuitive definitions. Moreover, there is a lot of confusion in textbooks and online from what I&#8217;ve seen. I read Marino&#8217;s The ICU Book and several articles on Up-to-date and came up with this outline that I think will be helpful for residents like myself.<\/p>\n<p>In essence, V\/Q mismatch is a spectrum: with dead space (no perfusion) and shunt (no ventilation) on either end. Some other people tell a narrative of V\/Q mismatch vs. shunt (but that to me seems imprecise). Some pathologies have a primarily dead space defect problem, and therefore oxygen can help; other pathologies have a\u00a0primarily shunt defect problem and therefore oxygen cannot help.<\/p>\n<p>My hypoxemia pdf has the full version of these notes:\u00a0<a href=\"http:\/\/www.henrydelrosario.com\/wp-content\/uploads\/2016\/07\/Hypoxemia.pdf\">http:\/\/www.henrydelrosario.com\/wp-content\/uploads\/2016\/07\/Hypoxemia.pdf<\/a><\/p>\n<hr \/>\n<h2>Definitions<\/h2>\n<ul>\n<li><span style=\"text-decoration: underline;\"><b>Hypoxemia<\/b><\/span>\n<ul>\n<li>Definition\n<ul>\n<li>Low partial pressure of oxygen (PaO2) in the blood (low level of oxygen in the blood)<\/li>\n<li>It does not always cause tissue hypoxia<\/li>\n<\/ul>\n<\/li>\n<li>Causes\n<ul>\n<li><span style=\"color: #ff00ff;\"><b>Hypoventilation<\/b><\/span><\/li>\n<li><span style=\"color: #ff00ff;\"><b>V\/Q mismatch<\/b><\/span>\n<ul>\n<li><span style=\"color: #ff00ff;\"><b>Primarily dead space defect <\/b>**(often called V\/Q mismatch)**<\/span><\/li>\n<li><span style=\"color: #ff00ff;\"><b>Primarily shunt defect<\/b><\/span><\/li>\n<\/ul>\n<\/li>\n<li><span style=\"color: #ff00ff;\"><b>Diffusion limitation<\/b><\/span><\/li>\n<li><span style=\"color: #ff00ff;\"><b>Reduced inspired O2 tension<\/b><\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<li><span style=\"text-decoration: underline;\"><b>Hypoxia<\/b><\/span>\n<ul>\n<li>Definition\n<ul>\n<li>Insufficient oxygen to meet a tissue\u2019s metabolic demand (low level of oxygen in a tissue or organ)<\/li>\n<li>Hypoxemia can lead to tissue hypoxia, but not always<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<li><span style=\"text-decoration: underline;\"><b>Oxygenation<\/b><\/span>\n<ul>\n<li>Definition\n<ul>\n<li>Process of oxygen diffusing from alveolus to pulmonary capillary to bind to hemoglobin or dissolve in plasma<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<hr \/>\n<h2>Causes of hypoxemia<\/h2>\n<ul>\n<li><span style=\"text-decoration: underline; color: #ff00ff;\">Hypoventilation<\/span>\n<ul>\n<li>Mechanism\n<ul>\n<li>Lung alveolus is a space of 100% gas \u2192 if the partial pressure of one gas increases the partial pressure of another gas must decrease<\/li>\n<li>In hypoventilation there is decrease air movement \u2192 alveolar increase of carbon dioxide (PACO2) \u2192 alveolar decrease of oxygen (PAO2)<\/li>\n<li><span style=\"color: #008000;\">A-a gradient is normal<\/span><\/li>\n<\/ul>\n<\/li>\n<li>Causes\n<ul>\n<li><span style=\"color: #0000ff;\">CNS depression (drug overdose, opiates, CNS lesions)<\/span><\/li>\n<li><span style=\"color: #0000ff;\">Obesity hypoventilation (Pickwickian) syndrome<\/span><\/li>\n<li><span style=\"color: #0000ff;\">Impaired neural conduction (ALS, GB)<\/span><\/li>\n<li><span style=\"color: #0000ff;\">Muscular weakness (myasthenia gravis, hypothyroidism, critical illness myopathy)<\/span><\/li>\n<li><span style=\"color: #0000ff;\">Poor chest wall mechanics (kyphoscoliosis)<\/span><\/li>\n<\/ul>\n<\/li>\n<li>Tx\n<ul>\n<li><span style=\"color: #ff0000;\">Responds to supplemental oxygen<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<li><span style=\"text-decoration: underline; color: #ff00ff;\">V\/Q mismatch<\/span>\n<ul>\n<li>Definition\n<ul>\n<li>Imbalance of ventilation and perfusion<\/li>\n<li><span style=\"color: #339966;\">A-a gradient is almost always elevated<\/span><\/li>\n<\/ul>\n<\/li>\n<li>Causes (two opposing forms; per Marino and UpToDate: Mechanical ventilation article)\n<ul>\n<li><span style=\"text-decoration: underline;\"><b>Primarily dead space defect<\/b><\/span>\n<ul>\n<li><span style=\"color: #0000ff;\">COPD, asthma, PE<\/span><\/li>\n<\/ul>\n<\/li>\n<li><span style=\"text-decoration: underline;\"><b>Primarily shunt defect<\/b><\/span>\n<ul>\n<li><span style=\"color: #0000ff;\">PNA, pulm edema, ARDS<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<li>Normal lung\n<ul>\n<li>A normal lung has V\/Q mismatch: V\/Q ratio is higher in the apices and lower at the bases (higher ventilation in the apices, more perfusion in the bases)<\/li>\n<\/ul>\n<\/li>\n<li><span style=\"text-decoration: underline; color: #ff00ff;\">Dead space<\/span>\n<ul>\n<li>Definition\n<ul>\n<li>Ventilation is excessive to perfusion (V\/Q &gt;1)<\/li>\n<li>Ventilated lung but no blood flow \u2192 no gas exchange<\/li>\n<li>***(when the pathology is of\u00a0mostly dead space defects = people tend to call this simply a V\/Q mismatch)***<\/li>\n<li><i>Memory cue: When I see DEAD, I think NO BLOOD = DEAD LUNG. There is SPACE, because alveoli are ventilated and open.<\/i><\/li>\n<\/ul>\n<\/li>\n<li>Anatomic dead space\n<ul>\n<li>Large conducting airways have no contact with capillary blood<\/li>\n<li><span style=\"color: #0000ff;\">Pharynx, trachea<\/span><\/li>\n<li><span style=\"color: #0000ff;\">Using a snorkel :)<\/span><\/li>\n<\/ul>\n<\/li>\n<li>Physiologic dead space\n<ul>\n<li>Poor perfusion<\/li>\n<li><span style=\"color: #0000ff;\">PE<\/span><\/li>\n<li><span style=\"color: #0000ff;\">Reduced blood flow (low CO)<\/span><\/li>\n<li><span style=\"color: #0000ff;\">COPD (emphysema destroys alveolar septae and pulm capillary bed \u2192 limited blood flow to a fairly well oxygenated lung)<\/span><\/li>\n<li><span style=\"color: #0000ff;\">Positive pressure ventilation (can inc ventilation to alveoli that do not have corresponding inc in perfusion \u2192 worsens dead space)<\/span><\/li>\n<\/ul>\n<\/li>\n<li>Tx\n<ul>\n<li><span style=\"color: #ff0000;\">Responds to supplemental oxygen<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<li><span style=\"text-decoration: underline; color: #ff00ff;\">Shunt<\/span>\n<ul>\n<li>Definition\n<ul>\n<li>Ventilation is inadequate to perfusion (V\/Q &lt;1)<\/li>\n<li>When blood passes from the right to the left side of the heart without being oxygenated<\/li>\n<\/ul>\n<\/li>\n<li>Anatomic shunts\n<ul>\n<li>When blood bypasses alveoli<\/li>\n<li>Can cause extreme V\/Q mismatch (V\/Q=0)<\/li>\n<li><span style=\"color: #0000ff;\">Intracardiac shunts (ASD, VSD), AVMs<\/span><\/li>\n<\/ul>\n<\/li>\n<li>Physiologic shunts\n<ul>\n<li>When non-ventilated alveoli are perfused<\/li>\n<li><span style=\"color: #0000ff;\">Atelectasis<\/span><\/li>\n<li><span style=\"color: #0000ff;\">Disease with alveolar filling (PNA, pulm edema, ARDS)<\/span><\/li>\n<li><span style=\"color: #0000ff;\">Obesity<\/span><\/li>\n<\/ul>\n<\/li>\n<li>Tx\n<ul>\n<li><span style=\"color: #ff0000;\">DOES NOT respond to supplemental oxygen<\/span>\n<ul>\n<li><span style=\"color: #ff0000;\">Blood is not in contact with an alveolar membrane that can exchange oxygen \u2192 so breathing 100% will not correct hypoxemia<\/span><\/li>\n<\/ul>\n<\/li>\n<li><span style=\"color: #ff0000;\">ICU<\/span>\n<ul>\n<li><span style=\"color: #ff0000;\">Particularly in the ICU, for ARDS, a shunt is created where lungs are perfused but ventilation is limited due to alveoli filling \u2192 thus, increasing FiO2 has limited benefit \u2192 thus, you can decrease FiO2 without causing more hypoxia<\/span><\/li>\n<li><span style=\"color: #ff0000;\">Positive pressure ventilation, esp with PEEP, can tx shunt caused by atelectasis, by opening more alveoli (presumably perfused)<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<li><span style=\"text-decoration: underline; color: #ff00ff;\">Diffusion limitation<\/span>\n<ul>\n<li>Definition\n<ul>\n<li>Impaired movement of oxygen from the alveolus to the pulmonary capillary due to problem with diffusion through the alveolar membrane<\/li>\n<li>Exercise induced-hypoxemia<\/li>\n<li><span style=\"color: #339966;\">A-a gradient is elevated<\/span><\/li>\n<\/ul>\n<\/li>\n<li>Mechanism\n<ul>\n<li>During rest, oxygen diffuses slowly, allowing even impaired diffusion to oxygenate sufficiently<\/li>\n<li>During exercise, there is less time for oxygenation \u2192 oxygenation is impaired<\/li>\n<\/ul>\n<\/li>\n<li>Causes\n<ul>\n<li><span style=\"color: #0000ff;\">ILD, pulmonary fibrosis<\/span><\/li>\n<\/ul>\n<\/li>\n<li>Tx\n<ul>\n<li><span style=\"color: #ff0000;\">Responds to supplemental oxygen<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<li><span style=\"text-decoration: underline; color: #ff00ff;\">Reduced inspired O2 tension<\/span>\n<ul>\n<li>Definition\n<ul>\n<li>Decreased FiO2 or atmospheric pressure will decrease PiO2<\/li>\n<li>PiO2 = FiO2 x (Patm &#8211; PH2O)<\/li>\n<li><span style=\"color: #339966;\">A-a gradient is normal<\/span><\/li>\n<\/ul>\n<\/li>\n<li>Mechanism\n<ul>\n<li>Body naturally hyperventilates \u2192 PaO2 inc but PCO2 dec<\/li>\n<\/ul>\n<\/li>\n<li>Causes\n<ul>\n<li><span style=\"color: #0000ff;\">High altitude<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<hr \/>\n<h2>Sources<\/h2>\n<ul>\n<li><b>Good<\/b> (stating V\/Q mismatch consists of two opposing forms: dead space and shunt)\n<ul>\n<li>Marino\u2019s ICU Book<\/li>\n<li><a href=\"http:\/\/www.uptodate.com\/contents\/physiologic-and-pathophysiologic-consequences-of-mechanical-ventilation\">http:\/\/www.uptodate.com\/contents\/physiologic-and-pathophysiologic-consequences-of-mechanical-ventilation<\/a><\/li>\n<li><a href=\"https:\/\/www.openanesthesia.org\/pulmonary_physiology_and_respiratory_failure\/\">https:\/\/www.openanesthesia.org\/pulmonary_physiology_and_respiratory_failure\/<\/a><\/li>\n<\/ul>\n<\/li>\n<li><b>Okay<\/b> (really good explanations, but sometimes confusing)\n<ul>\n<li><a href=\"https:\/\/www.youtube.com\/watch?v=RJ-H8_0-8wk\">https:\/\/www.youtube.com\/watch?v=RJ-H8_0-8wk<\/a><\/li>\n<li><a href=\"https:\/\/www.youtube.com\/watch?v=pRIkwjlFRgo\">https:\/\/www.youtube.com\/watch?v=pRIkwjlFRgo<\/a><\/li>\n<\/ul>\n<\/li>\n<li><b>Hella confusing<\/b>, read with caution\n<ul>\n<li><a href=\"https:\/\/www.uptodate.com\/contents\/oxygenation-and-mechanisms-of-hypoxemia?source=machineLearning&amp;search=v%2Fq+mismatch&amp;selectedTitle=1%7E95&amp;sectionRank=2&amp;anchor=H15#H1\">https:\/\/www.uptodate.com\/contents\/oxygenation-and-mechanisms-of-hypoxemia<\/a><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"<p>V\/Q Mismatch Confusion V\/Q mismatch is a confusing subject because the terms &#8220;dead space&#8221; and &#8220;shunt&#8221; are not very intuitive definitions. Moreover, there is a lot of confusion in textbooks and online from what I&#8217;ve seen. I read Marino&#8217;s The ICU Book and several articles on Up-to-date and came up &#8230;<\/p>\n","protected":false},"author":1,"featured_media":1146,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_uag_custom_page_level_css":"","_exactmetrics_skip_tracking":false,"_exactmetrics_sitenote_active":false,"_exactmetrics_sitenote_note":"","_exactmetrics_sitenote_category":0,"ngg_post_thumbnail":0,"footnotes":""},"categories":[19],"tags":[28,31],"class_list":["post-1145","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-verbal","tag-health-care","tag-medical-school","column","threecol","has-thumbnail"],"uagb_featured_image_src":{"full":["http:\/\/www.henrydelrosario.com\/wp-content\/uploads\/2016\/07\/VQmismatch.jpg",879,640,false],"thumbnail":["http:\/\/www.henrydelrosario.com\/wp-content\/uploads\/2016\/07\/VQmismatch-150x150.jpg",150,150,true],"medium":["http:\/\/www.henrydelrosario.com\/wp-content\/uploads\/2016\/07\/VQmismatch-300x218.jpg",300,218,true],"medium_large":["http:\/\/www.henrydelrosario.com\/wp-content\/uploads\/2016\/07\/VQmismatch-768x559.jpg",660,480,true],"large":["http:\/\/www.henrydelrosario.com\/wp-content\/uploads\/2016\/07\/VQmismatch.jpg",660,481,false],"1536x1536":["http:\/\/www.henrydelrosario.com\/wp-content\/uploads\/2016\/07\/VQmismatch.jpg",879,640,false],"2048x2048":["http:\/\/www.henrydelrosario.com\/wp-content\/uploads\/2016\/07\/VQmismatch.jpg",879,640,false],"slider-thumb":["http:\/\/www.henrydelrosario.com\/wp-content\/uploads\/2016\/07\/VQmismatch-879x395.jpg",879,395,true],"blog-thumb":["http:\/\/www.henrydelrosario.com\/wp-content\/uploads\/2016\/07\/VQmismatch-700x300.jpg",700,300,true],"teaser-thumb":["http:\/\/www.henrydelrosario.com\/wp-content\/uploads\/2016\/07\/VQmismatch-332x205.jpg",332,205,true],"gallery-1-thumb":["http:\/\/www.henrydelrosario.com\/wp-content\/uploads\/2016\/07\/VQmismatch-432x432.jpg",432,432,true],"gallery-2-thumb":["http:\/\/www.henrydelrosario.com\/wp-content\/uploads\/2016\/07\/VQmismatch-268x268.jpg",268,268,true],"gallery-3-thumb":["http:\/\/www.henrydelrosario.com\/wp-content\/uploads\/2016\/07\/VQmismatch-268x164.jpg",268,164,true],"image-thumb":["http:\/\/www.henrydelrosario.com\/wp-content\/uploads\/2016\/07\/VQmismatch-700x510.jpg",700,510,true],"video-thumb":["http:\/\/www.henrydelrosario.com\/wp-content\/uploads\/2016\/07\/VQmismatch-700x393.jpg",700,393,true]},"uagb_author_info":{"display_name":"Del Rosario Henry","author_link":"http:\/\/www.henrydelrosario.com\/?author=1"},"uagb_comment_info":1,"uagb_excerpt":"V\/Q Mismatch Confusion V\/Q mismatch is a confusing subject because the terms &#8220;dead space&#8221; and &#8220;shunt&#8221; are not very intuitive definitions. Moreover, &#8230;","_links":{"self":[{"href":"http:\/\/www.henrydelrosario.com\/index.php?rest_route=\/wp\/v2\/posts\/1145","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/www.henrydelrosario.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.henrydelrosario.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.henrydelrosario.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/www.henrydelrosario.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=1145"}],"version-history":[{"count":10,"href":"http:\/\/www.henrydelrosario.com\/index.php?rest_route=\/wp\/v2\/posts\/1145\/revisions"}],"predecessor-version":[{"id":1222,"href":"http:\/\/www.henrydelrosario.com\/index.php?rest_route=\/wp\/v2\/posts\/1145\/revisions\/1222"}],"wp:featuredmedia":[{"embeddable":true,"href":"http:\/\/www.henrydelrosario.com\/index.php?rest_route=\/wp\/v2\/media\/1146"}],"wp:attachment":[{"href":"http:\/\/www.henrydelrosario.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=1145"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.henrydelrosario.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=1145"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.henrydelrosario.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=1145"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}