Link to the by Nick Mark MD onepagericu.com HYPOXIA & HYPOXEMIA ONE most current @nickmmark version → DEFINITIONS: 100% 20 13 Hypoxia – insufficient oxygen delivered to tissues to meet demands OXYGEN DELIVERY: O2

a 80% 16 11 Tissue hypoxia occurs when DELIVERY OF OXYGEN (DO ) is inadequate to meet O2 Hypoxemia – low oxygen in the blood (most common type of hypoxia) S 2

PIO2 a

=140 C metabolic demands. DO2 depends on CARDIAC OUTPUT (CO) & the P O2 – atmospheric oxygen (how much O2 is inspired) 60% 12 8 I MIXED OXYGEN CONTENT OF BLOOD (CaO ) ARTERIAL 2 PAO2 – alveolar oxygen (how much O2 reaches the alveoli) VENOUS 40% 8 5 SATURATION BLOOD CONTENT P O2 – oxygen dissolved in arterial blood (measured on ABG) BLOOD 2 HB a O �� = �� × �� × �. �� × �� × ��� + (��� × �. ���) PAO2 20% 4 3 � � � =100 SaO2 – percent saturation of hemoglobin in arterial blood SvO2 = 70% SaO2 = 98% 0 20 40 60 80 100 1 CaO2 – oxygen content of art. blood (dissolved & Hb bound) CvO2 = 15 CaO2 = 20 DISSOLVED O2 PaO2 O2 bound to hemoglobin O2 dissolved in blood PaO2 = 95 CO @Hb= 15 @Hb= HYPOXEMIC HYPOXIA ISCHEMIC HYPOXIA ANEMIC HYPOXIA CYTOPATHIC HYPOXIA 06) Insufficient oxygen in the blood Insufficient blood flow to tissues, Insufficient O2 carrying capacity Cells cannot use oxygen - 12 (the most common type of hypoxia) also called stagnant hypoxia (e.g. severe blood loss) or abnormal (e.g. cyanide toxicity, maybe sepsis) - SA3.0 -

(e.g low cardiac output) hemoglobin (e.g. COHb, MetHb) 2020 Low PaO2 Low SvO2 ! Low PaO2 Low CaO2 ! Low SvO2 ! Low PaO2 High PaO2, High SvO2 v1.0 ( v1.0 BY CC

LOW INSPIRED OXYGEN (PIO2) ALVEOLAR HYPOVENTILATION V/Q MISMATCH SHUNT DIFFUSION LIMITATION

Fewer oxygen molecules enter the Fewer O2 molecules reach the alveoli Imbalance between regional lung Blood passes from the right side of Impaired O2 diffusion from alveoli to lungs with respiration (low PAO2) due to decreased ventilation (low ventilation and perfusion (low V/Q). the heart to the left side without RBC, causing hypoxemia particularly PAO2). Most common cause of hypoxemia. being oxygenated. in with increased cardiac outpu. · Normal Aa difference · Normal Aa difference · Increased Aa difference · Increased Aa difference · Increased Aa difference · PaO2 normalizes with supplemental · PaO2 normalizes with supplm. O2 · PaO2 normalizes with suppl. O2 · PaO2 does NOT normalize with · PaO2 normalizes with supplm. O2 oxygen · Increased PaCO2 supplemental oxygen

· Causes: low atmospheric pressure · Causes: decreased respiratory drive · Causes: obstructive lung diseases · Causes: anatomical (ASD, VSD, · Causes: pulmonary fibrosis, edema, (e.g. high altitude), or low partial (opioids, brainstem stroke, OHVS), (COPD), pulmonary vascular disease pulm AVMs) & physiological shunts & inflammation that impair gas pressure of oxygen (FiO2 < 0.21 e.g. neuromuscular weakness (GBS, ALS), (PE), alveolar filling processes (atelectasis, pneumonia, ARDS) exchange in the alveoli confined space, low O2 gas mixtures) chest wall problems (kyphoscoliosis, (pneumonia, pulmonary edema), where blood bypasses alveoli Borderline With increased blood flail chest) or airflow obstruction interstitial disease & atelectasis without effective gas exchange normoxemia at flow frank hypoxemia (COPD, asthma) Low PAO2 due to Low PAO2 due to ↓ No O2 exchange rest ensues globally reduced ventilation relative to occurs and blood is LOW MIXED VENOUS O2 (SVO2) ventilation perfusion in one area not oxygenated ↓↓PAO2 NL PAO2 ↓PAO2 (PAO2 & PaO2 will (PAO2 & P O2 will = 0 (PaO2 will not fully ↓PAO2 ↓PAO2 a Venous blood returning to the lungs normalize with normalize with normalize with SvO2 = 70% SaO2 = 95% SvO2 = 70% SaO2 = 85% CvO2 = 15 CaO2 = 19 CvO2 = 15 CaO2 = 17 (SvO2) has very low O2 due to supplemental O2) supplemental O2) supplemental O2) increased extraction. Aa DIFFERENCE (aka Aa GRADIENT): ��� ��� + �� ������ �� ���������� = · Normal Aa difference The Aa DIFFERENCE is the ALVEOLAR OXYGEN TENSION � Alveolar CO2 tension (assumed to be equal to · PaO2 normalizes with SvO2 = 50% (PAO2) minus the ARTERIAL OXYGEN TENSION (PaO2), �� ���������� = � � − � � SaO2 = 85% � � � � arterial CO2) supplemental oxygen CvO2 = 10 CaO2 = 17 reflecting the efficiency of oxygen exchange. It is ���� used to identify the etiology of hypoxemic hypoxia: � unable to fully ���� = ���� × ���� − ���� − Causes: severe anemia (low CaO2 oxygenate the pulmonary causes have ↑ Aa difference whereas � rarely a problem unless Hb <5), low Respiratory extremely extra-pulmonary etiologies (↓ PiO2, ↓SvO2, & Atmospheric pressure H O vapor pressure cardiac output, & extremely high deoxygenated 2 Quotient alveolar hypoventilation) have nl Aa difference. (760 mmHg @ sea level, 630 mmHg @ (47 mmHg in the lungs) oxygen consumption venous blood 1500m, 530 mmHg @ 3000m) (normally ~0.8)