Respiratory Failure Flashcards
Definition of respiratory failure
An arterial partial pressure of oxygen (at sea level, FiO2 0.21) at rest <8 kPa (60mmHg)
What is type 1 respiratory failure?
Hypoxemic respiratory failure. PaO2 < 8kPa, PCO2 normal
Causes of Type 1 respiratory failure
Right to left shunt or V/Q mismatch
Q: PE
V: chest infection, asthma, pulmonary oedema, ARDS, aspiration pneumonitis, airway obstruction, diffuse parenchymal lung disease
What is type 2 respiratory failure?
Hypercapnic respiratory failure.
Hypoxemia with arterial PaCO2 > 6.5 kPa (50mmHg)
Causes of type 2 respiratory failure
Reduced central drive: opioids, anasthetic agents, sleep apnea, stroke
Impaired peripheral respiratory system: airway obstruction, COPD, restriction due to pain/obesity/ascites, myopathy, chest wall abnormality)
Principles of management in patient’s with respiratory failure
- Primary aim: treat hypoxemia
- Secondary aim: control paCO2 and respiratory acidosis
- Identify and treat underlying cause
Indication for invasive ventilatory support
- Airway obstruction
- Airway protection
- Unconscious patient with impaired laryngeal reflexes
- Hypoxia or hypercapnea
- Anaesthesia (prolonged surgery, prone positioning, one lung ventilation)
What are the clinical indicators of failure of basic respiratory support
- RR>30
- Increasing oxygen requirement to maintain SaO2
- PaO2 < 8KPa
- PaCO2 > 8 kPa with respiratory acidosis (pH <7.35)
- Low GCS/exhaustion/dyspnea
How do we monitor respiratory function?
- Respiratory rate
- Oxygen saturation
- Oxygen requirement
- Conscious level
- End-tidal carbon dioxide
- Blood gas analysis
What are signs of respiratory distress?
Tachypnea, mouth opening during inspiration
Pursed lips, expiratory grunting
Use of accessory muscles
Central cyanosis
Tachycardia, dilated pupils, sweat (sympathetic overactivity)
Complications of mechanical ventilation
- Volume related
- Pressure related (barotrauma)
- tension pneumothorax
- pulmonary interstitial emphysema
- pneumopericardium/mediastinum
- Oxygen
- oxygen toxicity (lung endothelial injury)
- ventilatory depression
- absorption atelectasis
What are types of non-invasive mechanical ventilation?
CPAP (continuous positive airway pressure)
BIPAP (bi-level positive airway pressure)
What is CPAP?
Application of positive airway pressure through all phases of respiration.
Delivered gas flow must exceed peak inspiratory flow ( up to 60L/min)
What are the advantages of CPAP?
- increases functional residual capacity by recruiting areas of atelectasis → improves oxygenation, reduced work of breathing
- increase pulmonary lymphatic flow
- improves mechanical function of heart to prevent further buildup
Indications for CPAP
- Sleep apnea
- Pulmonary edema
- Hypoxemic respiratory failure
What is BIPAP
Different set pressures for inspiratory and expiratory phase of respiration
How to assess readiness to wean off ventilator
- Adequate cough
- Adequate mentation
- Resolution of underlying disease
- Stable cardiovascular status
- Adequate oxygenation (able to maintain with non-invasive measures)
Satisfactory parameters that signify “adequate lung function”
RR > 35/min
PaO2 > 11 kPA
Minute volume < 10L/min
Tidal volume > 5ml/kg
Max inspiratory force > 20cm H2O
How to adjust parameters to improve oxygenation?
increase FiO2
increase PEEP
increase I: E ratio
How to adjust parameters to improve ventilation?
Increase respiratory rate
Increase tidal volume
Increase peak pressure
What are the basic modes of ventilation?
- Pressure control
- Volume control
- Assisted modes
- Pressure support ventilation
- Synchronised Intermittent Mandatory Ventilation
What is pressure control ventilation? Advantages and disadvantages
Pre-set inspiratory pressure delivered
Pros: less barotrauma
Cons: hypoventilation
What is volume control ventilation? Advantages and disadvantages
Fixed tidal volume delivered and respiratory rate
Pros: ensures adequate minute ventilation to satisfy metabolic demand. Ideal for muscle rest
Cons: barotrauma
What is plateau pressure? How to measure?
The equilibrated alveolar pressure at full volume / alveolar distending pressure
What is the peak inspiratory pressure? How to measure
The dynamic pressure needed to fully inflate the lung. It is the peak of the wave form
What does increase PIP and PPlat signify?
Decreased compliance of lung
What does increased PIP and unchanged pPlat signify?
Airway obstruction: bronchospasm, ETT occlusion, secretions
What is the most common primary initial mode of ventilatory support?
Volume assist control. It is ideal for muscle recovery (can trigger full tidal volume on an attempted breath)
Draw the waveform that would appear on the monitor of a ventilator
What is the A-a gradient?
PAO2-PaO2
Alveolar partial pressure oxygen minus the arterial partial pressure of oxygen
What is a normal A-a gradient
5-10 mmHg
Causes of raised A-a gradient
V/Q mismatch
Right-to left shunt (intrapulmonary/cardiac
Increase O2 extraction
Diffusion defect (rare)
Possible causes of hypotension while on ventilator
- Underlying cause of shock
- Increases intrathoracic pressure
- Tension ptx
- PEEP and TV too high
- Sedatives
