Respiratory Failure Flashcards
RESPIRATORY FAILURE
The inability of respiratory system to realize the gas
exchange between alveolar air and pulmonary
capillary at Rest and during Effort with the purpose
to maintain O2 and CO2 homeostasis in the arterial
blood determine RESPIRATORY FAILURE
External Respiration
- the process by which the gas exchange between the lungs and the atmosphere air at the level of the alveolo-capillary membrane is realized
- Any impairment led to respiratory failure
Internal Respiration
- the process by which gas exchange is performed and oxygen is used by the tissues
- Its impairment does not led to respiratory failure
Normal values- didactic
PaO2 = 96 mmHg (arterial blood)
– Varies with age, temperature, atmospheric pressure, O2 % in inspired air
– calculated by regression equation
– PaO2=100,1-0.323 x (age in years) ±5 mmHg
• SaO2 = 96% (hemoglobin saturation O2 in circulation)
• PaCO2 = 40-45 mmHg at an atmospheric pressure of 760 mmHg
– It does not depend on age, unaffected by environmental parameters
- HCO3 25 mEq/l
- pH blood 7.42
- mean PaP 15 mmHg (mean pulmonary artery pressure)
Respiratory failure: Pathophysiology
Isolated or combined dysregulation of
- Alveolar ventilation
- Capillary perfusion
- Alveolo-capillary diffusion
- Neuro-humoral control of respiration
Hypoxemia
• Alveolar ventilation ↓ • Diffusion abnormality • V/Q mismatch • intrapulmonary shunt RL • Oxygen consumption, (VO2 ) ↑: fever, chill, dyspnea, twitch
Hypercapnia
• CO2 production↑ fever, infection, epilepsy • Alveolar ventilation ↓ • neuromuscular diseases or fatigue of respiratory muscles • obstructive ventilation disorder
Hypoxemia: mechanisms
- Alteration of ventilation / perfusion ratio
(VA / Q) → VA / Q ratio = 0.8
Hypoxemia can be corrected by administering oxygen with a low concentration (24-40%) - Alveolar hypoventilation
Hypoxemia is associated with hypercapnia
If it acts as a single process → the number of mmHg with which PaO2 decreases = with no mmHg with which O2 increases. If not, other mechanisms are associated
Can be corrected by administering large amounts of oxygen (100%) - O2 diffusion capacity altered
If it is not severely altered → hypoxemia occurs only at exertion or altitude
Hypoxemia Correct easily with small amounts of O2 in the breathed air - Right to left intrapulmonary shunt
Pulmonary arterio-venous fistulas are present or Determined by perfusion of an
unventilated lung entities (atelectasis, pneumonia, pulmonary edema)
Hypoxemia cannot be corrected by O2
Lung diseases that cause respiratory failure by primitive impairment of
VA / Q, diffusion and by right-left intrapulmonary shunts
- Lower respiratory airways ->COPD, Bronchitis, Bronchiectasis
- Parenchyma ->
- Lung Abscess
- Lung Cancer
- Atelectasis
- Interstitial Fibrosis - Pulmonary Vessels -> Pulmonary Embolism , Heart failure
- Other pulmonary disorders ->
- Cystic Fibrosis
- Emphysema
- Respiratory distress syndromes
Respiratory failure: Classification
By pH
- Compensated with normal pH (7.4)
* Decompensated with pH < 7.35
Respiratory failure: Classification
According to Pathophysiology & arterial blood gas:
TYPE III &IV
Type III- results from lung atelectasis, also called perioperative respiratory failure, due to atelectasis that occurs so commonly in the Perioperative period
Type IV- This form results from hypoperfusion of
respiratory muscles in patients in shock (septic, hypovolemic,
cardiogenic)
Type I Respiratory failure
A failure of gas exchange
• Hypoxemia (PaO2 < 60 mmHg) • Main mechanism: ventilation / perfusion abnormalities • Other mechanisms: right to left intrapulmonary shunts (less often) Frequent Etiologies • Pneumonia • Pulmonary Edema • Fat tissue embolism • ARDS = a severe form of type-1 RF
Type II Respiratory failure
A failure of ventilation
Main mechanism: alveolar hypoventilation
Other mechanisms: VA / Q alteration may also be associated
Etiological categories
A. Normal lungs + hypoventilation
Respiratory center depression
Neuromuscular and medullary diseases (myasthenia, poliomyelitis)
Chest injuries
B. Lung disorders that cause disorders of ventilation and VA / Q
COPD, emphysema
Acute bronchitis, asthma, bronchiolitis
Syndrome component
Humoral component
Hypoxemia PaO2 < 60 mmHg associated or not with: Hypercapnia PaCO2 > 45 mmHg ± acid-base disturbances 1. Respiratory acidosis 2. Respiratory alkalosis 3. Metabolic acidosis
Syndrome Component
Clinical component
= tissue aspect - poorly correlated with laboratory data - not included in diagnosis definition - reflects tissue suffering = a set of clinical signs secondary to hypoxemia and / or Hypercapnia eg: • CNS • Cardiovascular