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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

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Presentation Transcript
outline
Outline
  • Respiratory Failure due to ↑ Resistance
  • Respiratory Failure due to ↓ Compliance
  • Respiratory Failure due to ↑ VE
  • Respiratory Failure due to ↓ Neuromuscular competence
lung mechanics
Lung Mechanics

transairway

pressure

transrespiratory

pressure

transthoracic

pressure

volume

elastance = Dpressure / Dvolume

resistance = Dpressure / Dflow

flow

expiratory time constant
Expiratory Time Constant

900

600

Volume (mL)

300

RCexp

0

4

3

2

1

0

Time (sec)

variable expiratory time constant
Variable Expiratory Time Constant

900

600

Volume (mL)

Longer RCexp

300

Shorter RCexp

0

4

3

2

1

0

Time (sec)

wob measurements
WOB Measurements

WOB =∫0ti P x Vdt

Elasic work: ABCA

Resistive work

Inspiratory: ADCA

Expiratory: ACEA

V

B

C

E

D

P

A

work of breathing
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
work of breathing1
Work of Breathing

Total Work

Elastic Work

Work of Breathing

Frictional Work

RV

FRC

TLC

sustaining oxygenation and alveolar ventilation
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 ventilation1
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

respiratory failure
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

sustaining oxygenation and alveolar ventilation2
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

case presentation
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%
respiratory failure due to resistance load
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

balanced load and competence
Balanced Load and Competence

Resistive Load

Neuromuscular Competence

ABG’s: 7.47, PCO2: 30, PO2 88 O2 , HCO3: 22, Sat: 95%

imbalanced load and competence
Imbalanced Load and Competence

Resistive Load

Neuromuscular Competence

ABG’s: 7.39, PCO2: 44, PO2 72 O2 , HCO3: 22, Sat: 91%

case presentation1
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%.
case presentation2
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

case presentation3
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

respiratory failure due to compliance load
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

imbalanced load and competence1
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

case presentation4
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%.
case presentation5
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%.

respiratory failure due to minute ventilation load
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

balanced load and competence1
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

imbalanced load and competence2
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

case presentation6
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 presentation7
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%

respiratory failure due to neuromuscular competence
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

imbalanced load and competence3
Imbalanced Load and Competence

Load

Neuromuscular Competence

pH, 7.19, PaCO2, 65, PaO2 65, HCO3- 24, SaO2 90%