Respiratory Failure_ Dr. Patel
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Transcript of Respiratory Failure_ Dr. Patel
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Introduction toAcute Respiratory Failure
Bela Patel MD
Pulmonary and Critical Care MedicineThe University of Texas - Houston
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Types of AcuteRespiratory Failure
.
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Acute Respiratory Failure
Hypoxemic Respiratory Failure TYPE I 45 mmHg and pH< 7.4
Normal A-a gradient
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ABG
What PaO2 concentration is Hypoxemia?
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Expected PaO2
(.43 x age) 100.8 = expected PaO2
30 year old = 8880 year old = 66
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Causes of Hypoxemia
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Causes of Hypoxemia
Alveolar Hypoventilation V/Q mismatch
Shunt Diffusion Limitation
Low inspired FiO2
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Alveolar-arterial oxygen gradient
Measure of lungs ability to transfer oxygento pulmonary capillary blood
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A-a gradient
PAO2 = (FI0 2 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 ) PaCO 2 /0.8 150 PaCO2/0.8 Subtract from PaO 2
What is normal A-a gradient
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Normal A-a gradient
age up to 30 mmHg
Increases 5-7 mm Hg for every10% FiO2 increase
Loss of hypoxic vasoconstriction
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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
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Hypoxemia and the CXR
Abnormal CXR Pneumonia Pulmonary edema
Pulmonary hemorrhage ARDS Fibrosis
CXR withoutinfiltrates Pulmonary embolism
Pneumothorax Hypoventilation Pulmonary
hypertension
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Additional
Physical Exam Clinical History
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Management of HypoxemicRespiratory Failure
Low Flow Oxygen Delivery System Nasal prongs Face masks
Masks with reservoir bags
Final concentration of inhaled FiO2 isdetermined by the size of the oxygen reservoir,the rate or reservoir filling and ventilatorydemands of the patient
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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
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Rate: Fi02
6 L/min with Vt 500 mL
Rate 10 FiO2 .60 Rate 20 .44 Rate 40 .32
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Oxygen Masks
Face masks 150 250 mL reservoir 5 10 L/min oxygen flow FiO2 .40 - .60 Same drawbacks as the nasal prongs
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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
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High Flow Oxygen Masks
Delivers a constant O2 regardless of V E. 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
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Acute Hypercarbic RespiratoryFailure Type II
PaCO2 > 46 mmHG No compensatory metabolic alkalosis
3 major causes Hypoventilation V A Increased Production Vco 2
Fever, exercise, carbohydrates
Increased Dead Space Ventilation - Vd/Vt
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Next Step: HypercarbicRespiratory Failure
?
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Check A-a Gradient
If normal or unchanged A-a gradient Alveolar hypoventilation If increased A-a gradient
Increased dead space ventilation
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Alveolar Hypoventilation
Brainstem medullary depression Overdose with narcotics/sedatives Obesity hypoventilation Hypothyroidism Metabolic Alkalosis
Rabies
Normal P I max
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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 P I max
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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 P I max
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Hypercapnia with O2administration
Increase V/Q mismatch Attenuation of Hypoxic Ventilatory Drive Haldane Effect
Bound CO 2 decrease increase in PaCO 2
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Hypoxemia fromHypoventilation
1.25 mmHg fall in PAO 2 for 1 mmHgincrease in PCO 2
7.30/50/78 (baseline PO2 90) Dec 12.5 : Inc 10
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Intubation?
BiPAP?
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Indication for NIV
COPD exacerbation Hypercarbic respiratory failure Pulmonary edema
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Endotracheal Intubation
Indications Inability to oxygenate SpO2 < 90% / PaO2 < 55
Inability of ventilate Increasing PaCO2
Inability to protect airway
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Contraindications
Neck immobility Increased risk of neck trauma (RA) Inability to open mouth
Trismus, scleroderma, wiring
Fiberoptic or surgical airway
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Airway Assessment
Medical history Physical exam Mechanical factors Anatomical factors Mallampati evaluation
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Mallampati Signs
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Laryngoscopic View
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Grade I Open
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Grade I Closed
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Laryngoscope Blades
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Airway Equipment
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Refractory Hypoxemia Establish an Airway Bagging Assist Control Mode : volume cycled
Tidal Volume 6-8 mL/kg Rate FiO2 Peep Peak Flow
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ARF: Asthma Low tidal volumes Long expiratory time
Auto peep
Peak and Plateau pressures Permissive Hypercapnia Paralysis
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ARF: COPD Long expiratory time Maintain baseline PaCO2 Auto peep
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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
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Pulse Oximetry CO Hb overestimates % sat MetHb overestimates % sat
Underestimates % sat Blue/black nail polish
Very dark pigmentation Methylene blue- Hypoperfusion
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Pulse Oximetry 3% error if SaO2 is above 70% Accurate to BP of 30 mmHg Accurate to a Hg of 3g/dl