respiratory failure_ dr. patel

8/6/2019 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

respiratory failure_ dr. patel

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