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

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elastance =  pressure /  volume volume transairway pressure transthoracic pressure transrespiratory pressure Lung Mechanics resistance =  pressure /  flow flow

Volume (mL) Time (sec) RCexp Expiratory Time Constant

Volume (mL) Time (sec) Shorter RCexp Variable Expiratory Time Constant Longer RCexp

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

Work per breath is depicted as a pressure-volume area Work per breath (W breath ) = P x tidal volume (V T ) W min = w breath x respiratory rate Pressure Volume VTVT W R = resistive work W EL = 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

RVFRCTLC Total Work Elastic Work Frictional Work

11 The balance between load neuromuscular competence strength

Sustaining Oxygenation and Alveolar Ventilation 12 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 13 Resistive Load AW Elastance Load L,CW Minute Ventilation (VE) Load Work of Breath Transmission Drive (RR) Muscle Strength (NIF) ∆ V/Q PaCO 2 PaO 2

Respiratory Failure 14 Resistive Load AW Elastance Load L,CW Minute Ventilation (VE) Load Work of Breath Transmission Drive (RR) Muscle Strength (NIF) ∆ V/Q PaCO 2 PaO 2 ↓↑

Sustaining Oxygenation and Alveolar Ventilation 15 Resistive Load AW Elastance Load L,CW Minute Ventilation (VE) Load Work of Breath Transmission Drive (RR) Muscle Strength (NIF) ∆ V/Q PaCO 2 PaO 2 ↑ ↑ ↑

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, PCO 2 : 30, PO 2 88 O 2 Sat: 95% 16

Respiratory Failure due to ↑ Resistance Load 17 Resistive Load AW Elastance Load L,CW Minute Ventilation (VE) Load Work of Breath Transmission Drive (RR) Muscle Strength (NIF) ∆ V/Q PaCO 2 PaO 2 ↑ ↑ ↑ ↑ Deep rapid tachypnea Use of accessory muscles Signs of strain ↑RC Exp Wheezes Prolonged expiration Inflated chest Bronchospam: asthma, COPD or bronchiolitis Obstruction: croup, epiglotitis or OSA Edema, Secretion or scarring

↑ Work of Breath 18

Balanced Load and Competence 19 Resistive Load Neuromuscular Competence ABG’s: 7.47, PCO 2 : 30, PO 2 88 O 2, HCO 3 : 22, Sat: 95% ↑ ↑

Imbalanced Load and Competence 20 Resistive Load Neuromuscular Competence ↑ ↑ ABG’s: 7.39, PCO 2 : 44, PO 2 72 O 2, HCO 3 : 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, PaCO 2 49 mm Hg PaO 2 57 mm Hg, SaO 2 86% HCO mEq/L Na mEq/L, K mEq/L, Cl mEq/L, CO 2 24 mEq/L, %COHb2.1% Hb13 gm%. 21

Case Presentation Oxygenation: –The PaO 2 and SaO 2 are both markedly reduced on 90% inspired oxygen –PAO 2 = FIO 2 (P B – 47 mm Hg) (PaCO 2 ) –PAO 2 = 0.9 (760– 47 mm Hg) - (55)= 586 –A-a Gradient= PAO 2- PaO 2 = = 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 22 FiO2: 0.9, pH 7.19, PaCO 2 49 mmHg PaO 2 57 mmHg, SaO 2 86% HCO mEq/L Na + 149, K + 4.1, Cl - 100, CO 2 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 23 FiO2: 0.9, pH 7.19, PaCO 2 49 mmHg PaO 2 57 mmHg, SaO 2 86% HCO mEq/L Na + 149, K + 4.1, Cl - 100, CO 2 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 Breath Transmission Drive (RR) Muscle Strength (NIF) ∆ V/Q PaCO 2 PaO 2 ↓ ↑ ↑ ↑ Rapid shallow tachypnea Use of accessory muscles Signs of strain ↓RC Rapid shallow breathing Alveolar edema, atelectasis pneumonia, ARDS Intrinsic PEEP

Imbalanced Load and Competence 25 Elastance Load Neuromuscular Competence ↑ ↑ pH 7.29, PaCO 2 55 mm Hg PaO 2 77 mm Hg, SaO 2 87% HCO mEq/L

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 PaCO 2 20 mm Hg PaO 2 80 mm Hg SaO 2 95% Hb13.3 gm% HCO mEq/L Na mEq/L, Cl mEq/L, CO 2 13 mEq/L, Hb13 gm%.

Case Presentation Oxygenation: –The PaO 2 is reduced on 32% inspired oxygen –PAO 2 = FIO 2 (P B – 47 mm Hg) (PaCO 2 ) –PAO 2 = 0.32 (760– 47 mm Hg) – 1.2 (20)= 204 –A-a Gradient= PAO 2- PaO 2 = = 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 27 FiO2: 0.32, pH 7.40, PaCO 2 20 mm Hg PaO 2 80 mm Hg, SaO 2 95% HCO mEq/L Na mEq/L, Cl mEq/L, CO 2 13 mEq/L, Hb13 gm%.

Case Presentation Acid Base: –pH: 7.40 with decreased HCO 3 indicating mixed disorder –Decreased HCO 3 indicating metabolic acidosis –Expected PaCO 2 : Predicted PCO2 (Respiratory compensation): PCO 2 = 1.5 X[HCO3]+8  2: therefore PCO 2 should have been 1.5X12+8= 26  2: –Actual PCO 2 =20 indicating combined respiratory alkalosis –AG= Na-(Cl+HCO3)= 141-(103+13)= 25 –∆ AG= 25-12= 13 indicating an added acid of 13 mEql/L –∆HCO3 = 24-13=11 –∆ AG ~ ∆ HCO3 indicating no combined metabolic disorder 28 FiO2: 0.32, pH 7.40, PaCO 2 20 mm Hg PaO 2 80 mm Hg, SaO 2 95% HCO mEq/L Na mEq/L, Cl mEq/L, CO 2 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 Breath Transmission Drive (RR) Muscle Strength (NIF) ∆ V/Q PaCO 2 PaO 2 ↑ ↑ ↑ Rapid Deep tachypnea Use of accessory muscles Signs of strain ↑ Excessive calories, sepsis, hypovolemia, PE VO 2, VCO 2, pH ↓

Balanced Load and Competence 30 VE Load Neuromuscular Competence pH 7.40, PaCO 2 20 mm Hg PaO 2 80 mm Hg, SaO 2 95% HCO mEq/L ↑ ↑

Imbalanced Load and Competence 31 VE Load Neuromuscular Competence ↑ ↑ pH 7.29, PaCO 2 35 mm Hg PaO 2 67 mm Hg, SaO 2 86% HCO mEq/L

Case Presentation A 27-year-old man is being evaluated in the emergency department for acute dyspnea. FIO 2.21, pH, 7.19, PaCO 2, 65 mm Hg, PaO 2 65 mm Hg, HCO mEq/L, SaO 2 90%

Case Presentation Oxygenation: –The PaO 2 and SaO 2 are reduced on 21% inspired oxygen –PAO 2 = FIO 2 (P B – 47 mm Hg) (PaCO 2 ) –PAO 2 = 0.21 (760– 47 mm Hg) – 1.2 (55)= 84 –A-a Gradient= PAO 2- PaO 2 = 84-65= 19 –Indicating hypoventilating process Ventilation: –The patient is hypoventilating with high PCO2 Acid Base: –Acute respiratory and metabolic acidosis 33 FIO 2.21, pH, 7.19, PaCO 2, 65 mm Hg, PaO 2 65 mm Hg, HCO mEq/L, SaO 2 90%

Case Presentation Acid Base: –pH: 7.19: acidosis –PaCO 2, 65: respiratory acidosis (acute) –For every 10-mm Hg rise in PaCO 2 pH falls about 0.07 units. –Expected fall in pH: 0.17 thus pH should be = 7.23 –Actual pH: 7.19 suggesting combined metabolic acidosis –HCO 3 - should be elevated 1 mEq/L for each 10 mm Hg= 2- 3 mEq/L thus expected HCO 3 - should be 26 –Actual HCO 3 - = 24 suggesting combined metabolic acidosis 34 FIO 2.21, pH, 7.19, PaCO 2, 65 mm Hg, PaO 2 65 mm Hg, HCO mEq/L, SaO 2 90%

Respiratory Failure due to ↓ Neuromuscular Competence 35 Resistive Load AW Elastance Load L Minute Ventilation (VE) Load Work of Breath Transmission Drive (RR) Muscle Strengh (NIF) ∆ V/Q PaCO 2 PaO 2 ↓ ↓ ↓ Low RR Low vital capacity < 15 mL/kg Low NIF < -15 cm H 2 O ↑ Brain stem lesion Drugs Hypothyroidism Electrolytes, Fatigue Myopathy, Malnutrition ALS, AG, GB, SMG Botulism

Imbalanced Load and Competence 36 Load Neuromuscular Competence ↓ pH, 7.19, PaCO 2, 65, PaO 2 65, HCO , SaO 2 90%

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