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Respiratory Failure and Indications of Mechanical Ventilation

Respiratory Failure and Indications of Mechanical Ventilation. Outline. Respiratory Failure due to ↑ Resistance Respiratory Failure due to ↓ Compliance Respiratory Failure due to ↑ VE Respiratory Failure due to ↓ Neuromuscular competence. Gas Exchange. Lung Mechanics. transairway

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Respiratory Failure and Indications of Mechanical Ventilation

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  1. Respiratory Failure and Indications of Mechanical Ventilation

  2. Outline • Respiratory Failure due to ↑ Resistance • Respiratory Failure due to ↓ Compliance • Respiratory Failure due to ↑ VE • Respiratory Failure due to ↓ Neuromuscular competence

  3. Gas Exchange

  4. Lung Mechanics transairway pressure transrespiratory pressure transthoracic pressure volume elastance = Dpressure / Dvolume resistance = Dpressure / Dflow flow

  5. Expiratory Time Constant 900 600 Volume (mL) 300 RCexp 0 4 3 2 1 0 Time (sec)

  6. Variable Expiratory Time Constant 900 600 Volume (mL) Longer RCexp 300 Shorter RCexp 0 4 3 2 1 0 Time (sec)

  7. WOB Measurements WOB =∫0ti P x Vdt Elasic work: ABCA Resistive work Inspiratory: ADCA Expiratory: ACEA V B C E D P A

  8. Work of Breathing WEL = elastic work WR = resistive work Volume Volume Volume VT Pressure Pressure Pressure The total work of breathing can be partitioned between an elastic and resistive work. By analogy, the pressure needed to inflate a balloon through a straw varies; one needs to overcome the resistance of the straw and the elasticity of the balloon. • Work per breath is depicted as a pressure-volume area • Work per breath (Wbreath)= P x tidal volume(VT) • Wmin = wbreath x respiratory rate

  9. Work of Breathing Total Work Elastic Work Work of Breathing Frictional Work RV FRC TLC

  10. The balance between load neuromuscular competence strength

  11. Sustaining Oxygenation and Alveolar Ventilation Load Neuromuscular Competence The balance between load (resistive, elastic, and minute ventilation) and neuromuscular competence (drive, transmission, and muscle strength)

  12. Sustaining Oxygenation and Alveolar Ventilation Resistive Load AW Elastance Load L,CW ∆ V/Q Transmission Drive (RR) Work of Breath Muscle Strength (NIF) Minute Ventilation (VE) Load PaO2 PaCO2

  13. Respiratory Failure Resistive Load AW Elastance Load L,CW ∆ V/Q Transmission Drive (RR) Work of Breath Muscle Strength (NIF) Minute Ventilation (VE) Load ↓ ↑ PaO2 PaCO2

  14. Sustaining Oxygenation and Alveolar Ventilation Resistive Load AW Elastance Load L,CW ∆ V/Q ↑ Transmission Drive (RR) ↑ Work of Breath ↑ Muscle Strength (NIF) Minute Ventilation (VE) Load PaO2 PaCO2

  15. Case Presentation • 6 year old male with asthma who was brought to ER after riding on the school bus with severe respiratory distress • RR: 32/min, tachycardic 130/min, diaphoretic, wheezes, using accessory muscles • ABG’s: 7.47, PCO2: 30, PO2 88 O2 Sat: 95%

  16. Respiratory Failure due to ↑ Resistance Load ↑ ↑RCExp Wheezes Prolonged expiration Inflated chest Resistive Load AW Elastance Load L,CW ∆ V/Q ↑ Transmission Drive (RR) Deep rapid tachypnea Use of accessory muscles Signs of strain ↑ Work of Breath ↑ Muscle Strength (NIF) Minute Ventilation (VE) Load PaO2 PaCO2 Bronchospam: asthma, COPD or bronchiolitis Obstruction: croup, epiglotitis or OSA Edema, Secretion or scarring

  17. ↑ Work of Breath

  18. Balanced Load and Competence ↑ ↑ Resistive Load Neuromuscular Competence ABG’s: 7.47, PCO2: 30, PO2 88 O2 , HCO3: 22, Sat: 95%

  19. Imbalanced Load and Competence ↑ Resistive Load Neuromuscular Competence ↑ ABG’s: 7.39, PCO2: 44, PO2 72 O2 , HCO3: 22, Sat: 91%

  20. Case Presentation • A 23-year-old man is being evaluated in the emergency room for severe pneumonia • His respiratory rate is 38/min and he is using accessory breathing muscles, SBP 70 and HR 135/min • FiO2: 0.9, pH 7.19, PaCO2 49 mm Hg PaO2 57 mm Hg, SaO2 86% HCO3- 23 mEq/L • Na+ 149 mEq/L, K+ 4.1 mEq/L, Cl- 100 mEq/L, CO2 24 mEq/L, %COHb 2.1% Hb13 gm%.

  21. Case Presentation • Oxygenation: • The PaO2 and SaO2 are both markedly reduced on 90% inspired oxygen • PAO2 = FIO2 (PB – 47 mm Hg) - 1.2 (PaCO2) • PAO2 = 0.9 (760– 47 mm Hg) - (55)= 586 • A-a Gradient= PAO2-PaO2= 586-57= 529 • Indicating shunting process • Ventilation: • The patient is hypoventilating despite the presence of tachypnea, most likely indicating significant dead-pace ventilation • Acid Base: • Combined acute respiratory acidosis, combined metabolic acidosis and metabolic alkalosis FiO2: 0.9, pH 7.19, PaCO2 49 mmHg PaO2 57 mmHg, SaO2 86% HCO3- 23 mEq/L Na+ 149, K+ 4.1, Cl- 100, CO2 24 (mEq/L), %COHb 2.1% Hb13 gm%, LA: 12 mEq/L

  22. Case Presentation • Acid Base: • Acidosis • Acute respiratory acidosis: decrease in pH of 0.07 for each 10 PCO2: expected pH of 7.33 • Actual pH 7.19 indicating combined metabolic acidosis • Metabolic acidosis of high anion gap: 149- (100+24)= 25 • ∆ AG= 25-12= 13 indicatingan added acid of 13 mEql/L • Lactic acid level was 12 mEq/L • ∆HCO3 = 24-23=1 • ∆ AG > ∆ HCO3 indicating combined metabolic alkalosis FiO2: 0.9, pH 7.19, PaCO2 49 mmHg PaO2 57 mmHg, SaO2 86% HCO3- 23 mEq/L Na+ 149, K+ 4.1, Cl- 100, CO2 24 (mEq/L), %COHb 2.1% Hb13 gm%, LA: 12 mEq/L

  23. Respiratory Failure due to ↓ Compliance Load ↓RC Rapid shallow breathing Resistive Load AW Elastance Load L ↓ ∆ V/Q ↑ Transmission Drive (RR) Rapid shallow tachypnea Use of accessory muscles Signs of strain ↑ Work of Breath ↑ Muscle Strength (NIF) Minute Ventilation (VE) Load PaO2 PaCO2 Alveolar edema, atelectasis pneumonia, ARDS Intrinsic PEEP

  24. Imbalanced Load and Competence ↑ Elastance Load Neuromuscular Competence ↑ pH 7.29, PaCO2 55 mm Hg PaO2 77 mm Hg, SaO2 87% HCO3- 23 mEq/L

  25. Case Presentation A 46-year-old man has been in the hospital two days with urinary tract infection. He was recovering but has just become diaphoretic, dyspneic, and hypotensive. He is breathing oxygen through a nasal cannula at 3 l/min, RR 42/min, SBP 65 and HR 150/min pH 7.40 PaCO2 20 mm Hg PaO2 80 mm Hg SaO2 95% Hb 13.3 gm% HCO3- 12 mEq/L • Na+ 141 mEq/L, Cl- 103 mEq/L, CO2 13 mEq/L, Hb13 gm%.

  26. Case Presentation • Oxygenation: • The PaO2 is reduced on 32% inspired oxygen • PAO2 = FIO2 (PB – 47 mm Hg) - 1.2 (PaCO2) • PAO2 = 0.32 (760– 47 mm Hg) – 1.2 (20)= 204 • A-a Gradient= PAO2-PaO2= 204-80= 124 • Indicating V/Q mismatch process • Ventilation: • The patient is hyperventilating with low PCO2 • Indicating significant high minute ventilation secondary to high metabolism • Acid Base: • Metabolic acidosis with reparatory alkalosis indicating increased demand FiO2: 0.32, pH 7.40, PaCO2 20 mm Hg PaO2 80 mm Hg, SaO2 95% HCO3- 12 mEq/L Na+ 141 mEq/L, Cl- 103 mEq/L, CO2 13 mEq/L, Hb13 gm%.

  27. Respiratory Failure due to ↑ Minute Ventilation Load Resistive Load AW Elastance Load L ∆ V/Q ↑ Transmission Drive (RR) Rapid Deep tachypnea Use of accessory muscles Signs of strain ↑ Work of Breath ↑ Muscle Strength (NIF) Minute Ventilation (VE) Load ↑ PaO2 PaCO2 ↓ Excessive calories , sepsis, hypovolemia, PE VO2, VCO2, pH

  28. Balanced Load and Competence ↑ ↑ VE Load Neuromuscular Competence pH 7.40, PaCO2 20 mm Hg PaO2 80 mm Hg, SaO2 95% HCO3- 12 mEq/L

  29. Imbalanced Load and Competence ↑ VE Load Neuromuscular Competence ↑ pH 7.29, PaCO2 35 mm Hg PaO2 67 mm Hg, SaO2 86% HCO3- 13 mEq/L

  30. Case Presentation A 27-year-old man is being evaluated in the emergency department for acute dyspnea. FIO2 .21, pH, 7.19, PaCO2, 65 mm Hg, PaO2 65 mm Hg, HCO3-24 mEq/L, SaO2 90%

  31. Case Presentation • Oxygenation: • The PaO2 and SaO2 are reduced on 21% inspired oxygen • PAO2 = FIO2 (PB – 47 mm Hg) - 1.2 (PaCO2) • PAO2 = 0.21 (760– 47 mm Hg) – 1.2 (55)= 84 • A-a Gradient= PAO2-PaO2= 84-65= 19 • Indicatinghypoventilating process • Ventilation: • The patient is hypoventilating with high PCO2 • Acid Base: • Acute respiratory and metabolic acidosis FIO2 .21, pH, 7.19, PaCO2, 65 mm Hg, PaO2 65 mm Hg, HCO3- 24 mEq/L, SaO2 90%

  32. Respiratory Failure due to ↓ Neuromuscular Competence Resistive Load AW Elastance Load L ∆ V/Q ↓ Transmission Drive (RR) Low RR Low vital capacity < 15 mL/kg Low NIF < -15 cm H2O ↓ Work of Breath ↓ Muscle Strengh (NIF) Minute Ventilation (VE) Load ↑ PaO2 PaCO2 Brain stem lesion Drugs Hypothyroidism ALS, AG , GB, SMG Botulism Electrolytes, Fatigue Myopathy, Malnutrition

  33. Imbalanced Load and Competence ↓ Load Neuromuscular Competence pH, 7.19, PaCO2, 65, PaO2 65, HCO3- 24, SaO2 90%

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