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.:
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?
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
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
What are some causes of hypercapnia?
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:
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
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)
Causes of Stagnant hypoxia?
Local disruption of blood flow
Causes of Anemic hypoxia?
Carbon monoxide poisoning
Causes of Histotoxic hypoxia?
` Cellular poisoning by cyanide
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
- Water retention
What are some other hazards of O2 therapy?
Removal of hypoxic ventilatory drive > hypercapnia, O2 toxicity & oxidative damage :
-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