Respiratory Flashcards
What is type 1 respiratory failure?
Type I (hypoxaemic) resp failure
PaO2< 60 mm Hg with a normal or low PaCO2
VQ mismatch (eg alveoli collapse/fluid filled)
eg pulmonary oedema, pneumonia
What is type 2 respiratory failure?
Hypercapnic
Ventilation failure
PaCO2>50mm Hg
eg drug overdose, neuromuscular disease, chest wall abnormalities
What is CPAP?
CPAP: continuous positive airway pressure
Prevents alveoli collapsing at end of respiration
Reduces shunting
Used in type 1 respiratory failure
What is BIPAP?
Bilevel positive airway pressure
Increases tidal volume by changing pressure
Helps blow off CO2
Reduces shunting and increases oxygenation
Used in type 2 resp failure
Explain the numbers in BIPAP
eg 12/4
Numbers show the changing pressure, eg inspiration 12cmH2O, expiration 4cmH2O
In compliant lungs, only small differences are needed
If pt is hypoxic at 12/4, what would you change on the BIPAP machine?
Increase bottom number but keep difference the same (eg 13/5)
If pt is hypercapnic at 12/4, what would you change on the BiPAP machine?
Increase difference between pressures
eg 14/4
What is PPV?
Positive pressure ventilation
On a ventilator in ITU
What is the most common food to be aspirated?
Peanuts
Where do things go when aspirated?
Right main bronchus or trachea if larger
What are the phases of aspiration?
- Initial phase - Choking and gasping, coughing, or airway obstruction at the time of aspiration
- Asymptomatic phase - Subsequent lodging of the object with relaxation of reflexes that often results in a reduction or cessation of symptoms, lasting hours to weeks
- Complications phase - Foreign body producing erosion or obstruction leading to pneumonia, atelectasis, or abscess
How can you work out where the aspirated item is lodged from clinical signs?
Hoarseness/aphonia, stridor: laryngeal
Wheezing: tracheal
Bronchial: coughing, unilateral wheezing, decreased breath sounds
Treatment of aspiration
Rigid bronchoscopy if witnessed/radiologically confirmed/classic triad
Heimlich manoeuvre if complete obstruction
Types of stridor and cause
- Inspiratory stridor suggests a laryngeal obstruction
- Expiratory stridor implies tracheobronchial obstruction
- Biphasic stridor suggests a subglottic or glottic anomaly
Name 8 causes of acute stridor
Laryngotracheobronchitis Aspiration of foreign body Bacterial tracheitis Retropharyngeal abscess Peritonsillar abscess Spasmodic croup Allergic reaction Epiglottitis
Name the categories used for classifying chronic causes of stridor
External
Internal
Name 6 internal causes of stridor
- Laryngomalacia
- Vocal cord dysfunction
- Laryngeal dyskinesia
- Laryngeal webs in neonates
- Laryngeal cysts
- Haemangiomas
Name 3 external causes of stridor
- Vascular rings
- Double aortic arch
- Tumour
What is the difference in pH in acute versus chronic hypercapnic respiratory failure?
Acute hypercapnic respiratory failure develops over minutes to hours; therefore, pH is less than 7.3. Chronic respiratory failure develops over several days or longer, allowing time for renal compensation and an increase in bicarbonate concentration. Therefore, the pH usually is only slightly decreased.
What is the alveolar gas equation?
PAO2 = FiO2 × (PB – PH2 O) – PACO2/R
where PA O2 is alveolar PO2, FiO2 is fractional concentration of oxygen in inspired gas, PB is barometric pressure, PH2O is water vapour pressure at 37°C, PACO2 is alveolar PCO2 (assumed to be equal to PaCO2), and R is respiratory exchange ratio. R depends on oxygen consumption and carbon dioxide production. At rest, the ratio of VCO2 to oxygen ventilation (VO2) is approximately 0.8.
What does an increase in the alveolar-arterial PO2 gradient above 15-20 mm Hg indicate?
An increase in the alveolar-arterial PO2 gradient above 15-20 mm Hg indicates pulmonary disease as the cause of hypoxemia.
Define shunt
Shunt is defined as the persistence of hypoxemia despite 100% oxygen inhalation. The deoxygenated blood (mixed venous blood) bypasses the ventilated alveoli and mixes with oxygenated blood that has flowed through the ventilated alveoli, consequently leading to a reduction in arterial blood content. ie. Ventilation fails.
Anatomic shunt exists in normal lungs because of the bronchial and thebesian circulations, which account for 2-3% of shunt.
Define dead space
Dead Space is when there is ventilation but no perfusion. This is seen physiologically as the trachea and bronchi have ventilation but no semi permeable membrane and perfusion to transfer oxygen.
Signs of respiratory failure?
- Asterixis may be observed with severe hypercapnia. Tachycardia and a variety of arrhythmias may result from hypoxemia and acidosis.
- Cyanosis, a bluish colour of skin and mucous membranes, indicates hypoxemia. Visible cyanosis typically is present when the concentration of deoxygenated haemoglobin in the capillaries or tissues is at least 5 g/dL.
- Dyspnoea, an uncomfortable sensation of breathing, often accompanies respiratory failure. Excessive respiratory effort, vagal receptors, and chemical stimuli (hypoxemia and/or hypercapnia) all may contribute to the sensation of dyspnoea.
Investigations needed in respiratory failure
- ABG
- FBC (polycythaemia versus anaemia)
- Electrolytes (may exacerbate pulmonary dysfunction)
- Troponin (MI?)
- Chest radiography is essential
- Echocardiography is not routinely done but is sometimes useful
- Pulmonary functions tests (PFTs), if feasible, may be helpful, although more useful in terms of defining recovery potential
- ECG should be performed to evaluate the possibility of a cardiovascular cause of respiratory failure; it also may detect dysrhythmias resulting from severe hypoxemia or acidosis
