1	Introduction to Acute Respiratory Failure Bela Patel MD Pulmonary and Critical Care Medicine The University of Texas - Houston
2	Types of Acute Respiratory Failure .
3	Acute Respiratory Failure Hypoxemic Respiratory Failure TYPE I <90% SaO2 on FiO2 of 0.60 Elevated A-a gradient Hypercarbic Respiratory Failure TYPE II PaCO2 > 45 mmHg and pH< 7.4 Normal A-a gradient
4	ABG What PaO2 concentration is Hypoxemia?
5	Expected PaO2 (.43 x age) – 100.8 = expected PaO2 30 year old = 88 80 year old = 66
6	Causes of Hypoxemia .
7	Causes of Hypoxemia Alveolar Hypoventilation V/Q mismatch Shunt Diffusion Limitation Low inspired FiO2
8	Alveolar-arterial oxygen gradient Measure of lung’s ability to transfer oxygen to pulmonary capillary blood
9	A-a gradient PAO2 = (FI02 X (PB – PH20) – PaCO2/RQ RQ is the proportional exchange of O2 and CO2 across the alv-cap surface Ideal alveolar O2 tension = (.21 x (760 mmHg – 47 mmHg ) – PaCO2/0.8 150 – PaCO2/0.8 Subtract from PaO2
10	Normal A-a gradient ½ age up to 30 mmHg Increases 5-7 mm Hg for every 10% FiO2 increase Loss of hypoxic vasoconstriction
11	Evaluation of Hypoxemia Hypoxemia and Normal A-a gradient Hypoventilation Drugs, neuromuscular disease Hypoxemia and Increase A-a gradient V/Q mismatch Shunt Diffusion Limitation
12	Hypoxemia and the CXR Abnormal CXR Pneumonia Pulmonary edema Pulmonary hemorrhage ARDS Fibrosis CXR without infiltrates Pulmonary embolism Pneumothorax Hypoventilation Pulmonary hypertension
13	Additional Physical Exam Clinical History
14	Management of Hypoxemic Respiratory Failure Low Flow Oxygen Delivery System Nasal prongs Face masks Masks with reservoir bags Final concentration of inhaled FiO2 is determined by the size of the oxygen reservoir, the rate or reservoir filling and ventilatory demands of the patient
15	Nasal Prongs Reservoir capacity 50 ml Nasopharynx Oropharynx Oxygen Flow Fio2 1 L/m .24 2 .28 3 .34 4 .38 5 .42 6 .46 Rate 20
16	Rate: Fi02 6 L/min with Vt 500 mL Rate 10 FiO2 .60 Rate 20 .44 Rate 40 .32
17	Oxygen Masks Face masks 150 –250 mL reservoir 5 – 10 L/min oxygen flow FiO2 .40 - .60 Same drawbacks as the nasal prongs
18	Masks with reservoir bags Reservoir 750-1250 mL Partial rebreather 5-7 L/min .35-.75 FiO2 Nonrebreather 5-10 L/min .4 – 1.0 FiO2
19	High Flow Oxygen Masks Delivers a constant O2 regardless of VE. Low flow rates through a narrowed orifice Drag pulls room air into the mask (size of opening) FiO2 max of .50 Especially useful in chronic hypercapnia
20	Acute Hypercarbic Respiratory Failure – Type II PaCO2 > 46 mmHG No compensatory metabolic alkalosis 3 major causes Hypoventilation – VA Increased Production – Vco2 Fever, exercise, carbohydrates Increased Dead Space Ventilation - Vd/Vt
21	Next Step: Hypercarbic Respiratory Failure ?
22	Check A-a Gradient If normal or unchanged A-a gradient Alveolar hypoventilation If increased A-a gradient Increased dead space ventilation
23	Alveolar Hypoventilation Brainstem medullary depression Overdose with narcotics/sedatives Obesity hypoventilation Hypothyroidism Metabolic Alkalosis Rabies Normal PI max
24	Alveolar Hypoventilation Neuropathic disorder Motor: C3 spinal cord, Tetanus, ALS, Polio Peripheral Neuropathy Guillain-Barre, critical care polyneuropathy Neuromuscular Junction Myasthenia gravis, Eaton-Lambert, Organophosphates, Botulism, NM blockade Low PI max
25	Alveolar Hypoventilation Myopathic disorders Myopathy Muscular dystrophy Polymyositis Drugs – NM blocking agents, steroids Endocrinopathy – hyperthyroid, Cushing's Metabolic Hypo/hyper K, hypo/hyper Mg, hypophos, acidosis Hyperinflation Low PI max
26	Hypercapnia with O2 administration Increase V/Q mismatch Attenuation of Hypoxic Ventilatory Drive Haldane Effect Bound CO2 decrease à increase in PaCO2
27	Hypoxemia from Hypoventilation 1.25 mmHg fall in PAO2 for 1 mmHg increase in PCO2 7.30/50/78 (baseline PO2 90) Dec 12.5 : Inc 10
28	Intubation? BiPAP?
29	Indication for NIV COPD exacerbation Hypercarbic respiratory failure Pulmonary edema
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31	Endotracheal Intubation Indications Inability to oxygenate SpO2 < 90% / PaO2 < 55 Inability of ventilate Increasing PaCO2 Inability to protect airway
32	Contraindications Neck immobility Increased risk of neck trauma (RA) Inability to open mouth Trismus, scleroderma, wiring Fiberoptic or surgical airway
33	Airway Assessment Medical history Physical exam Mechanical factors Anatomical factors Mallampati evaluation
34	Mallampati Signs
35	Laryngoscopic View
36	Grade I Open
37	Grade I Closed
38	Laryngoscope Blades
39	Airway Equipment
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49	Refractory Hypoxemia Establish an Airway Bagging Assist – Control Mode : volume cycled Tidal Volume 6-8 mL/kg Rate FiO2 Peep Peak Flow
50	ARF: Asthma Low tidal volumes Long expiratory time Auto peep Peak and Plateau pressures Permissive Hypercapnia Paralysis
51	ARF: COPD Long expiratory time Maintain baseline PaCO2 Auto peep
52	Pulse Oximetry Spectrophotometry: measures light reflection properties of molecules Two wavelengths 660 nm – oxygenated Hg 940 nm – deoxygenated Hg % saturation: fraction of oxygenated Hgb Based on assumption that no other forms exist
53	Pulse Oximetry COHb – overestimates % sat MetHb – overestimates % sat Underestimates % sat Blue/black nail polish Very dark pigmentation Methylene blue - Hypoperfusion
54	Pulse Oximetry 3% error if SaO2 is above 70% Accurate to BP of 30 mmHg Accurate to a Hg of 3g/dl