L35 - Respiratory Failure Flashcards Preview

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Flashcards in L35 - Respiratory Failure Deck (51):

Define respiratory failure.

when lungs are unable to maintain arterial blood gases at normal levels when the subject breathes air at rest


What processes malfunction during respiratory failure?

1. Failure for oxygenation
2. Failure for CO2 removal
3. Failure for both


What are the general guide for arterial blood gases in respiratory failure?

 PO2 <60 mm Hg and/or
 PCO2 >50 mm Hg


What are the 2 types of resp. failure?

A. Pump (Ventilatory) failure
B. Gas-exchange failure


In ventilatory failure, what 2 main groups of defects develop?

1) defect along respiratory control pathway from medulla through resp. muscles

2)Defect in ventilatory apparatus


What 3 pathology conditions cause ventilatory failure by neural failure?

1. Depressed central respiratory drive
2. Defect in nerves to respiratory muscles
3. Neuromuscular disease


Name some diseases that correspond to the different neural defect mechanisms leading to ventilatory failure.

1.Depressed central respiratory drive: Brain tumour or hemorrhage, Narcotic drugs (morphine)

2.Defect in nerves to resp. muscles: poliomyelitis

3.Neuromuscular disease: myasthenia gravis (transmitter deficiency)


What 4 ways can Defect in ventilatory apparatus lead to Ventilatory failure?

1. Thoracic cage deformities / disorder

2. Respiratory muscle weakness

3. Limitation of lung expansion

4. Airway obstruction


Give examples of defects of resp. apparatus leading to resp. failure.

1. Thoracic cage deformities / disorder, e.g.:
 Kyphoscoliosis
 Morbid obesity

2. Respiratory muscle weakness, e.g. trauma

3. Limitation of lung expansion, e.g. interstitial lung diseases - pulmonary fibrosis)

4. Airway obstruction, e.g. COPD - chronic bronchitis)


Apart from ventilatory failure, what leads to resp. failure?

Gas- exchange failure


What defects arise from gas-exchange failure?

(i) Defective alveolocapillary membrane (increase thickness, less SA)

(ii) Mismatch of ventilation and perfusion (V/Q mismatching)


Give examples of diseases causing defective alveolocapillary membrane?

 Interstitial lung diseases (e.g. fibrosis of membrane)

 Acute respiratory distress syndrome (ARDS): fluid filled lungs


Give examples of diseases causing V/Q mismatch?

Uneven distribution of ventilation:
 Interstitial lung diseases

Uneven distribution of blood flow: vascular diseases


Difference between type I and II of respiratory failure according to pO2 and pCO2 levels?

Type I = gas exchange failure
LOW pO2 < 60 mmHg
NORMAL OR LOW pCO2 (50mmHg or below)

Type II= pump (ventilatory) failure
LOW pO2 < 60mmHg
HIGH pCO2 >50mmHg


Explain how alveolar hypoventilation leads to one type of resp. failure?

Alveolar hypoventilation (either due to defect in ventilatory appartus or neural defect) > Pump (ventilatory) failure > Severe hypoxemia and hypercapnia > Type II resp. failure


Explain the compensation to hypoventilation?

Caused by either defect in ventilatory apparatus or nerves > NO vent. compensation > further worsen


Explain how COPD leads to one type of resp. failure? (remember types of resp. failure are different in CO2 levels)

COPD > obstructive airway = high Raw > ventilatory apparatus failure + V/Q mismatch (gas-exchange failure) > Severe hypoxemia and moderate hypercapnia > Type II resp. failure


Explain the compensation to COPD?

Some ventilatory compensation but LIMITED by high Raw


Explain how Interstitial lung disease leads to one type of resp. failure?

Interstitial lung disease e.g. severe fibrosis of alveolocapillary wall > diffusion impairment and V/Q mismatch > gas exchange failure > Severe hypoxemia, unchanged pCO2 > Type I resp. failure


Explain the compensation to interstitial lung disease?

Ventilatory compensation effective for pCO2 but not pO2 due to LOW O2 SOLUBILITY


Explain how ARDS leads to one type of resp. failure?

ARDS > rapid severe inflammation and fluid accumulation > gas exchange failure > Extreme hypoxemia and low arterial CO2 > Type I resp. failure


Explain the ventilatory compensation to ARDS?

ARDS > rapid severe inflammation and fluid accumulation in alveoli

VERY STRONG VENTILATORY COMPENSATION > cause fall in pCO2 (CO2 washed out) but cannot correct severe hypoxemia due to Low O2 Solubility


What are the 4 causes of hypoxemia?

 Hypoventilation
 Diffusion impairment
 Shunt
 V/Q mismatching


Signs of hypoxemia?

 Cyanosis (most common sign)
 Tachycardia (reflex by chemoreceptors)
 Mental clouding (CNS) = direct depressant action (on central chemoreceptors)
 Low PaO2 in blood sample


What organ systems are most susceptible to hypoxemia?



How can hypoxemia cause metabolic acidosis?

Low O2 > cessation of aerobic respiration > anaerobic glycolysis > lactic acid accumulation > metabolic acidosis


Classify the SEVERITY (not type) of hypoxemia based on PaO2 values.

Mild = 60mmHg
Severe <40 mmHg
Very severe <20mmHg


List the 3 physiological changes under mild hypoxemia.

Impair mental performance
Impair vision
Mild hyperventilation (induced by peripheral chemoreceptors)


List the physiological changes under severe hypoxemia. (divide into CVS and CNS)

CNS: Depressive effects, headache, sleepiness, confusion

CVS: Tachycardia, mild hypertension + pulmonary hypertension (hypoxic global vasoconstriction)


List the physiological changes under Very severe hypoxemia.

CNS: permanent damage

CVS: direct depressant action on heart: bradycardia, hypotension + Severe pulmonary hypertension

Retinal hemorrhages

Renal: Proteinuria



What are some causes of hypercapnia?

V/Q mismatch
Misguided use of O2 therapy


How can misguided use of O2 therapy for COPD patient cause hypercapnia?

COPD patient: low O2 = more important drive than high CO2

Drastic increase in O2 > Abolish ventilatory drive > decrease Ventilation > Hypercapnia

Abolish hypoxic vasoconstriction > worsen V/Q mismatch


What are the effects of moderate hypercapnia?

Control of blood flow to brain by CO2, not neural

Moderate hypercapnia > cerebral vasodilatation > increase cerebral blood flow> increase intracranial pressure> headache


What are the effects of severe hypercapnia?

Severe hypercapnia = direct depressant action:
 Narcotic (催眠)
 Clouding of consciousness


What are the two types of acidosis caused by?

Respiratory acidosis = rise in volatile acid level (e.g. CO2)

Metabolic acidosis = rise in non-volatile acid level (e.g. lactate)


What are the 4 types of hypoxemia? (HASH)



Compare the PaO2 between types of hypoxemia.

Hypoxemic = low PaO2
Anemic = normal
Stagnant = normal
Histotoxic = normal


What are the 4 types of hypoxemia effect?

1) Hypoxemic: Insufficient O2
reaching blood

2) Anemic: Reduced O2
carrying capacity of blood

3) Stagnant: Impaired blood
flow = fail to transport O2

4) Histotoxic: Impaired
utilization of O2 by the cell


Causes of hypoxemic hypoxia?

 Low atmospheric PO2 (e.g. high altitude)
 Respiratory failure


Causes of Stagnant hypoxia?

 Heart failure
 Circulatory shock
 Local disruption of blood flow


Causes of Anemic hypoxia?

 decrease RBC
 Abnormal hemoglobin
 Carbon monoxide poisoning


Causes of Histotoxic hypoxia?

` Cellular poisoning by cyanide
 Tissue edema


Give examples for treating underlying disease for resp. failure e.g. infection or neuromuscular disorder

 Infection > antibiotic therapy
 Neuromuscular disorder > specific treatment


What are the two ways to treat airway obstruction?

 Remove secretion > cough, bronchoscopy, hydration and drugs to thin sputum

 Bronchoconstriction > use bronchodilators


What are the 3 treatment options for hypoxemia?

O2 therapy for COPD or shock lungs

Mechanical ventilation for neuromuscular disorder/ hypercapnia

Mechanical ventilator with PEEP (positive end-expiratory pressure) for shock lung


How does O2 therapy differ between COPD and SHOCK patients?

COPD = 25-30% O2
Shock = 60% O2


What treatments for cardiac failure leading to resp. failure?

1) Diuretics for edema, fluid retention (increase urine output)
2) Digitalis drug for heart failure (increase contractility)


What are the three causes of cardiac failure relating to resp. failure?

- Hypoxic pulmonary vasoconstriction
- Polycythemia
- Water retention


What are some other hazards of O2 therapy?

Removal of hypoxic ventilatory drive > hypercapnia, O2 toxicity & oxidative damage :

- edema,
-absorption acelectasis (form of alveolar collapse)


How is Retrolental fibroplasia caused by misused O2 therapy on infants with respiratory distress syndrome at birth?

Infant RDS > loss of surfactant > apply O2 therapy > body acclimatize to new O2 level > removal of therapy cause hypoxia > fibrous tissue grows into viscous humour > blinds baby


Why does O2 therapy of too high O2 conc cause absorption atelectasis?

atelectasis = collapsed lungs

Normally lung has 78% nitrogen that remains in alveolar space and maintain pressure to keep lungs inflated

100% oxygen therapy displaces nitrogen > loss of intra-alveolar pressure > all gas quickly absorbed into capillary > collapse lungs

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