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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 - PowerPoint PPT Presentation
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Respiratory Failure and Indications of Mechanical
Ventilation
1
Outline• Respiratory Failure due to ↑ Resistance• Respiratory Failure due to ↓ Compliance• Respiratory Failure due to ↑ VE • Respiratory Failure due to ↓ Neuromuscular
competence
2
Gas Exchange
3
4
elastance = Dpressure / Dvolume
volume
transairwaypressure
transthoracicpressure
transrespiratorypressure
Lung Mechanics resistance = Dpressure / Dflow
flow
900
600
300
00 1 2 3 4
Volu
me
(mL)
Time (sec)
RCexp
Expiratory Time Constant
900
600
300
00 1 2 3 4
Volu
me
(mL)
Time (sec)
Shorter RCexp
Variable Expiratory Time Constant
Longer RCexp
WOB Measurements
PA
B C
D
E
VWOB = ∫0
ti P x Vdt• Elasic work: ABCA• Resistive work
– Inspiratory: ADCA– Expiratory: ACEA
Work per breath is depicted as a pressure-volume areaWork per breath (Wbreath) = P x tidal volume (VT)Wmin = wbreath x respiratory rate
Pressure Pressure Pressure
Volu
me
Volu
me
Volu
me
V T
WR = resistive work
WEL = elastic work
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 of Breathing
Work of BreathingW
ork
of B
reat
hing
RV FRC TLC
Total Work
Elastic Work
Frictional Work
11The balance between load neuromuscular
competence strength
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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)
Sustaining Oxygenation and Alveolar Ventilation
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Resistive Load AW Elastance Load L,CW
Minute Ventilation (VE) Load
Work of BreathTransmission Drive
(RR)
Muscle Strength (NIF)
∆V/Q
PaCO2PaO2
Respiratory Failure
14
Resistive Load AW Elastance Load L,CW
Minute Ventilation (VE) Load
Work of BreathTransmission Drive
(RR)
Muscle Strength (NIF)
∆V/Q
PaCO2PaO2↓ ↑
Sustaining Oxygenation and Alveolar Ventilation
15
Resistive Load AW Elastance Load L,CW
Minute Ventilation (VE) Load
Work of BreathTransmission Drive
(RR)
Muscle Strength (NIF)
∆V/Q
PaCO2PaO2
↑↑↑
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
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Resistive Load AW Elastance Load L,CW
Minute Ventilation (VE) Load
Work of BreathTransmission Drive
(RR)
Muscle Strength (NIF)
∆V/Q
PaCO2PaO2
↑
↑↑
↑ Deep rapid tachypneaUse of accessory muscles
Signs of strain
↑RCExpWheezes
Prolonged expirationInflated chest
Bronchospam: asthma, COPD or bronchiolitisObstruction: croup, epiglotitis or OSA
Edema, Secretion or scarring
↑ Work of Breath
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Balanced Load and Competence
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Resistive Load
Neuromuscular Competence
ABG’s: 7.47, PCO2: 30, PO2 88 O2 , HCO3: 22, Sat: 95%
↑↑
Imbalanced Load and Competence
20
Resistive Load
Neuromuscular Competence
↑
↑
ABG’s: 7.39, PCO2: 44, PO2 72 O2 , HCO3: 22, Sat: 91%
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
22FiO2: 0.9, pH 7.19, PaCO2 49 mmHg PaO2 57 mmHg, SaO2 86% HCO3
- 23 mEq/LNa+ 149, K+ 4.1, Cl- 100, CO2 24 (mEq/L), %COHb 2.1% Hb13 gm%, LA: 12 mEq/L
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 indicating an added acid of 13 mEql/L– Lactic acid level was 12 mEq/L– ∆HCO3 = 24-23=1– ∆ AG > ∆ HCO3 indicating combined metabolic alkalosis
23FiO2: 0.9, pH 7.19, PaCO2 49 mmHg PaO2 57 mmHg, SaO2 86% HCO3
- 23 mEq/LNa+ 149, K+ 4.1, Cl- 100, CO2 24 (mEq/L), %COHb 2.1% Hb13 gm%, LA: 12 mEq/L
Respiratory Failure due to ↓ Compliance Load
24
Resistive Load AW Elastance Load L
Minute Ventilation (VE) Load
Work of BreathTransmission Drive
(RR)
Muscle Strength (NIF)
∆V/Q
PaCO2PaO2
↓
↑↑↑
Rapid shallow tachypneaUse of accessory muscles
Signs of strain
↓RC Rapid shallow breathing
Alveolar edema, atelectasispneumonia, ARDS
Intrinsic PEEP
Imbalanced Load and Competence
25
Elastance Load
Neuromuscular Competence
↑
↑
pH 7.29, PaCO2 55 mm Hg PaO2 77 mm Hg, SaO2 87% HCO3
- 23 mEq/L
Case PresentationA 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 7.40PaCO2 20 mm HgPaO2 80 mm HgSaO2 95% Hb 13.3 gm%HCO3
- 12 mEq/LNa+ 141 mEq/L, Cl- 103 mEq/L, CO2 13 mEq/L, Hb13 gm%.
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
27FiO2: 0.32, pH 7.40, PaCO2 20 mm Hg PaO2 80 mm Hg, SaO2 95% HCO3
- 12 mEq/LNa+ 141 mEq/L, Cl- 103 mEq/L, CO2 13 mEq/L, Hb13 gm%.
Respiratory Failure due to ↑ Minute Ventilation Load
29
Resistive Load AW Elastance Load L
Minute Ventilation (VE) Load
Work of BreathTransmission Drive
(RR)
Muscle Strength (NIF)
∆V/Q
PaCO2PaO2
↑↑↑
Rapid Deep tachypneaUse of accessory muscles
Signs of strain
↑
Excessive calories, sepsis, hypovolemia, PE
VO2, VCO2, pH
↓
Balanced Load and Competence
30
VE LoadNeuromuscular
Competence
pH 7.40, PaCO2 20 mm Hg PaO2 80 mm Hg, SaO2 95% HCO3
- 12 mEq/L
↑↑
Imbalanced Load and Competence
31
VE Load
Neuromuscular Competence
↑
↑
pH 7.29, PaCO2 35 mm Hg PaO2 67 mm Hg, SaO2 86% HCO3
- 13 mEq/L
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%
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– Indicating hypoventilating process
• Ventilation:– The patient is hypoventilating with high PCO2
• Acid Base:– Acute respiratory and metabolic acidosis
33FIO2 .21, pH, 7.19, PaCO2, 65 mm Hg, PaO2 65 mm Hg,
HCO3- 24 mEq/L, SaO2 90%
Respiratory Failure due to ↓ Neuromuscular Competence
35
Resistive Load AW Elastance Load L
Minute Ventilation (VE) Load
Work of BreathTransmission Drive
(RR)
Muscle Strengh )NIF(
∆V/Q
PaCO2PaO2
↓↓↓
Low RR Low vital capacity < 15 mL/kg
Low NIF < -15 cm H2O
↑
Brain stem lesionDrugs
Hypothyroidism
Electrolytes, FatigueMyopathy, Malnutrition
ALS, AG , GB, SMGBotulism
Imbalanced Load and Competence
36
Load
Neuromuscular Competence↓
pH, 7.19, PaCO2, 65, PaO2 65, HCO3- 24,
SaO2 90%
37
38