Respiratory Failure Flashcards
What is the most common input to the central and peripheral control system?
Hypoxia
- Chemoreceptors in carotids - look at O2
- Chemoreceptors in brainstem - detect acid-base
What happens when the chemoreceptors in the brainstem detect an increase in pH?
Decrease breathing to keep CO2
What happens when the chemoreceptors in the brainstem detect a decrease in pH?
Increase breathing to blow off CO2
What are other stimulants of respiratory drive?
Pain
Anxiety
Exercise
Hypoxaemia
What are the components of the respiratory pump?
Thoracic skeletal muscles
Diaphragm
What can cause the respiratory pump to fail?
Post-laparotomy, bowel tenses > pushes up against diaphragm > diaphragm can’t move
Phrenic nerve damage
Muscle relaxants paralyse diaphragm > don’t breathe
What is paradoxical breathing?
Chest moves inwards during inhalation > decreases O2 inhaled
What can affect the alveolar-capillary membrane, thus affecting respiration?
Inflammation > pus Emphysema Aspirated material Mucus Blood; eg: - Haematemesis - Bleeding Pulmonary oedema Atelectasis Septic shock > inflammatory peptides released > V-Q mismatch
What conditions can decrease respiratory drive?
Holding breath
Narcotic overdose
Sedatives
Against which forces does passive breathing occur?
Elastic and resistive forces
What are the roles of the upper airways?
Humidifies, filters, and warms incoming air
1st line of defence
Prevents aspiration
How can the upper airways contribute to respiratory failure?
Obstruction
How can the conductive airways contribute to respiratory failure?
Obstruction/narrowing
- Bronchospasm
- Secretions/sputum
- Collapse
- Lack of elastic support; eg: emphysema
- Endoluminal; eg: carcinoma, sputum
What does surfactant do?
Reduces surface tension and prevents alveolar collapse > improves lung compliance
What are the normal values of arterial blood gases?
pH = 7.4 (7.35-7.45) PaCO2 = 40 (35-45) mmHg PaO2 = 100 (>85) mmHg HCO3 = 24 (22-30) mmol/L SaO2 = 95-100%
What is the A-a gradient?
Difference between arterial (a) and alveolar (A) concentration of O2
What does an elevated A-a gradient suggest?
Problem with diffusion
V-Q mismatch
What is the A-a gradient on room air at sea level?
150 - 12.25 x PaCO2 - PaO2 = 7-14 in young adults - higher in elderly
What is respiratory failure?
Impairment of gas exchange between ambient air and circulating blood
Occurs in
- Intrapulmonary gas exchange
- Movement of gases in and out of lungs
What does impaired gas exchange usually result in?
Hypoxaemia > type 1 respiratory failure
PaO2 <60 mmHg
What does hypoventilation (inadequate movement of gases in and out of lungs) primarily result in?
Hypercapnia > type 2 respiratory failure
PaCO2 >50 mmHg
What can result in hypoxaemia?
Reduced inspired O2 - Altitude - Fires V-Q mismatch - Pneumonia - PE Impaired diffusion - Pulmonary fibrosis - COPD Shunt Hypoventilation
What can result in hypercapnia?
Central depression - Narcotic overdose - Sedation - Injury Completely blocked upper airway Primary pump failure - Neuromuscular disease Muscle fatigue - Usually due to increased WOB Intrinsic lung disease - Most common Chest wall abnormalities - Obesity - Kyphosis
What are the symptoms of respiratory failure?
May be non-specific SOB Drowsiness Confusion Headache
What are the signs of respiratory failure?
Use of accessory muscles Increased RR Irregular breathing Low O2 saturation Drowsiness Confusion Signs of cause
What immediate investigations are carried out for respiratory failure?
Arterial blood gases
What are the principles of management for respiratory failure?
Maintain adequate O2 delivery Reduce respiratory workload Maximise ventilation Maintain stable pH/electrolytes Try and target cause
