Respiratory failure Flashcards
Define respiratory failure
Acute or chronic impairment of gas exchange between the lungs and blood - causes hypoxia with/without hypercapnia
Type 1 respiratory failure
Hypoxic respiratory failure
- no hypercapniea
- Arterial PaO2 <60mmHg
Type 2 respiratory failure
Hypercapnic respiratory failure
- Arterial PaO2 <60mmHg
- Arterial PaCO2 >50mmHg
Normal PaO2
75-100mmHg
Normal PaCO2
38-42mmHg
Mortality from respiratory failure
20-40%
Gender differences in respiratory failure
M=F
What pulmonary infection is most often associated with respiratory failiure
Pneumonia
3 main causes of respiratory failure
- Respiratory causes
- Non-respiratory causes
- Traumatic causes
Respiratory causes of respiratory failure
- Acute exacerbation of asthma
- Pulmonary embolism
- Pulmonary oedema
- Acute respiratory distress syndrome (ARDS)
- Pneumonia
- Acute epiglotitis
Non-respiratory causes of respiratory failure
- Hypovolaemia
- Shock
- Severe anaemia
- Drug overdose
- Neuromuscular disorder
Traumatic causes of respiratory failure
- Blood loss
- Direct thoracic injury
- Pulmonary contusion
3 broad reasons for hypercapnic respiratory failure
- Increased dead space - anatomical
- Reduced minute ventilation
- Increased CO2 production
Causes for increased dead space in respiratory failure
- PE
- Vascular disease
- Hyperinflation
2 causes of reduced minute ventilation
- Decreased central respiratory drive
- Decreased respiratory neuromuscular/thoracic cage function
Reasons for decreased central respiratory drive
- Sedatives
- Encephalitis
- Stroke
- Sleep apnoea
- Alkalosis
- Hypothyroidism
- Hypothermia
- Starvation
Reasons for decreased respiratory neuromuscular/thoracic cage function
- MND
- Muscular disorders
- Toxins
Difference between hypoxia and hypoxaemia
- Hypoxaemia - PaO2 low
- Hypoxia - low O2 at tissue level
Pathophysiology of respiratory failure
- CO2/O2 exchange fails
- Metabolic demands for O2 and body system acid base stabilisation are not maintained
Type 1 and 2 respiratory failure have what in common?
- Hypoxemia
- Causes cellular anoxia and tissue asphyxia
Consequence of chronic hypoxia
Stimulates increases int he number of circulating RBC (erythrocytosis)
What does hypercapnia cause
- Carbonic acid accumulation
- Respiratory acidosis
Causes of hypercapnia
- Poor ventilatory muscle function
- Obstructed airways and alveoli
- Secretions in small airways
- Chest wall abnormalities
Classification of acute respiratory failure
- Acute lack of O2 transfer to the blood by the respiratory systems OR acute failure of the respiratory system to remove CO2
Classification of chronic respiratory failure
- Long-term lack of O2 delivery to the blood by the respiratory system
- Worsening respiratory acidosis
- Chronically low PaO2 or high PaCO2
- High carbonic acid with renal compensation (increased reabsorption of bicarbonate)
- Increased RBC count
Classification of type 1 hypoxic respiratory failure
PaO2 <60mmHg or 10% decrease in baseline
chronic lung disease may have PaO2 50mmHg already
Classification of type 2 hypercapnic respiratory failure
PaO2 <60mmHg and PaCO2 >50mmHg
Clinical presentation of type 1 respiratory failure
- Dyspnoea
- Agitation
- Anxiety
- Headache
- Confusion
- Somnolence
- Seizure
- Tachypnoea - fatigues - decreased RR
Clinical presentation of type 2 respiratory failure
- ** Generally tolerate symptoms better
- ** Respiratory failure develops more slowly
- Headache
- Confusion
- Disorientated
- Coma
- Seizure
- Hypoventilate - respiratory acidosis
- Agitation
- Slurred speech
- Tremour
Symptoms of SEVERE hypercapnia
- Asterixis
- Myoclonus (jerky movements)
- Seizures
- Papilloedema (optic nerve swelling)
- Dilated superficial veins
At what PaCO2 is there a decreased level of consciousness
PaCO2 >75mmHg
if chronic - may only develop symptoms >90mmHg
Risk factors for respiratory failure
- Smoking
- Young or old
- Pulmonary infection
- Chronic lung disease
- Upper and lower airway obstruction
- Alveolar abnormalities
- Perfusion abnormalities
- Cardiac failure
- Peripheral nerve abnormalities
- Muscle system abnormalities
- Opiates + sedatives
- Toxic fumes/gases
- Traumatic spinal injury
Investigations for respiratory failure
- Pulse oximetry
- Blood gas analysis
- FBC
- ECG
- CXR
- Capnometry (measures CO2 in expired gases)
- Pulmonary function test
- Toxicology testing
- Chest CT
- CTPA
- V/Q lung scanning
- Cardiothoracic US
DDX for respiratory failure
- Hyperventilation secondary to metabolic acidosis
- Hyperventilation secondary to anxiety
- Sleep apnoea
- Obesity
Acute management of respiratory failure
- Airway clearance
- Supplemental O2
- Treat underlying cause
If unconscious - endotracheal intubation and mechanical ventilation
Complications of respiratory failure
- Pneumothorax
- Endotracheal tube misplacement/dislodgement
- Nosocomial infection
- Throat pain with intubation
Describe chronic type 2 respiratory failure
High PaCO2 but normal pH due to renal compensation
