6.2 Understanding Respiratory Failure Flashcards
What is pulmonary ventilation?
The physical movement of air in and out of the lungs
What structures are in the respiratory zone of the airways?
-Respiratory bronchioles
- Alveolar Ducts
- Alveoli
Can gas exchange occur in the terminal bronchioles?
No; they aren’t the last bronchioles, they’re the last bronchioles that don’t exchange air.
What is respiratory failure?
Not enough O2 or too much CO2 in the blood due to a failure of the respiratory system
Describe type 1 vs type 2 respiratory failure
Type 1: Cannot move enough O2 into blood (1: primary job) -> hypoxaemia
Type 2: Cannot remove enough CO2 from blood ->hypercapnia
What is the role of Arterial Blood Gas (ABG) in diagnosis of hypoxaemia and hypercapnia
- It provides an accurate assessment of hypoxaemia and hypercapnia; pulse oximetry cannot replace this.
List some causes of hypoxia
- High altitude
- Respiratory failure
- Anaemia
- Shock
- Ischaemia
Describe failure of pulmonary ventilation, including causes and consequences
- Failure to physically move air into and out of lungs
- Causes: CNS depression, respiratory pump failure
- Consequences: Hypoxaemia, hypercapnia
Pulmonary ventilatory failure can be caused by CNS depression. What can cause this?
- Drugs (benzodiazepines)
- Structural abnormalities (stroke, head injury)
Pulmonary ventilatory failure can be caused by failure of the respiratory pump. What can cause this?
- Phrenic nerve dysfunction
- Neuromuscular weakness
- Chest cage restriction
Describe failure of pulmonary gas exchange (“lung failure”). What are the two categories of factors that can cause this?
Reduced O2 delivery from lung to blood, caused by:
- Lung (alveolar compartment and/or interface with capillary)
- Blood vessel (capillary compartment)
Pulmonary gas exchange failure can be caused by diffusion limitation. Provide an example of how this may occur
Thickened interstitium and thickened alveolar capillary membrane
Pulmonary gas exchange failure can be caused by ventilatory defect (i.e. air can move, but is impeded/blocked in some way). Provide an example of how this may occur
- Fluid in alveoli
- Alveolar collapse
- Alveolar damage
- Obstruction/airway narrowing
Pulmonary gas exchange failure can be caused by perfusion defects. Provide an intuitive example of how this may occur
Pulmonary vascular narrowing or obstruction
How can a right-to-left anatomic shunt cause pulmonary gas exchange failure?
Deoxygenated blood bypasses pulmonary circulation, leading to hypoxaemia
Hypoxaemia and hypercapnia will both cause the same initial symptoms. List them.
- Use of accessory muscles in breathing
- Tachypnoea
- Dyspnoea
List some organs that can be damaged via cellular hypoxia
- Brain
- Lungs
- Heart
- Liver
- GIT
- Kidneys
Chronic effects of hypoxaemia
- Reduced asthma symptoms perception
- Impaired cough reflex
Effect of hypoxaemia on sympathetic discharge. What are the two consequences of this?
- Increased sympathetic discharge
- Leads to tachycardia and hypertension
What is CO2 narcosis
Depressed level of consciousness caused by increased CO2
How can hypercapnia lead to seizure, coma, and death?
- Central chemoreceptors detect CO2 in CSF
- Increase blood flow to area
- CO2 narcosis; coma, seizure, and death
PaCO2 threshold for CO2 narcosis in normals vs people with chronic hypercapnia
Normal: 75mmHg
Chronic hypercapnia: 90mmHg (because of renal HCO3- buffering)
Considering the Bohr effect, suggest how changes in oxygen transport may occur during hypercapnia
increased O2 offloading into tissues
In terms of hypoxic ventilatory drive, how can oxygen therapy cause hypercapnia in COPD patients?
- In patients with chronically low PO2, they depend on the body’s increased ventilatory drive
- If given excess oxygen, this drive may decrease, leading to CO2 retention and hence hypercapnia
How can oxygen therapy cause hypercapnia in terms of hypoxic vasoconstriction?
- Oxygen is delivered to dead space, causing blood to flow back to it
- Increased CO2 retention
Describe, in terms of the haldane effect, how supplemental oxygen can cause excess CO2
Increases offloading of CO2 from Hb, raising CO2 pressure
Is O2 therapy the most effective long-term course of action for patients with type 1 respiratory failure?
- No
- Treat the underlying cause wherever possible
What is the most common piece of equipment used in oxygen therapy?
Nasal cannula
Can CIG masks take on higher or lower flow rates than nasal cannula?
Higher
Describe high flow oxygen therapy. What are some advantages?
Blender of 100% O2 and medical air from wall
Advantages:
- Humidified and heated air
- Accurate delivery of FiO2 (no extra dilution)
What is FiO2?
Fraction of inspired oxygen
How can BiPAP be used in pulmonary oedema?
Dries out airways
What is non-invasive ventilation AKA?
BiPAP
How does BiPAP differ from CPAP?
BiPAP has lower pressure on expiration, whereas CPAP is constant
What kind of conditions may warrant Bipap?
- Neuromuscular disease
- Chest wall respiratory disorder
- Severe COPD with chronic hypercapnia
List some major indications for intubation and mechanical ventilation
- Loss of airway
- Failure of non-invasive techniques
- Sudden crash following organ failure
What does ECMO stand for?
Extracorporeal membrane oxygenation
Describe ECMO
- Temporarily, oxygenation of blood is achieved outside the body
- Returned to the body via arterial (VA ECMO) or venous (VV ECMO)
Indications for ECMO
- All other treatments have failed
- Bridging to transplant
Describe the respiratory response to lactic acidosis in severe hypoxaemia
- Increased anaerobic metabolism -> increased lactic acid -> decreased pH
- Respiratory system begins hyperventilating in an attempt to blow off CO2 and normalise pH
Describe the renal response to respiratory acidosis in T2RF
- Kidneys retain Bicarbonate in an attempt to buffer pH and decrease acidity
- May take 24 hours or more to kick in
Acute acid-base patterns of hypercapnia: PaCO2, pH, HCO3-
PaCO2: High
pH: Low
HCO3-: Stable
Chronic acid-base patterns of hypercapnia: PaCO2, pH, HCO3-
PaCO2: High
pH: Stable
HCO3-: High
Acute on chronic acid-base patterns of hypercapnia: PaCO2, pH, HCO3-
PaCO2: High
pH: low
HCO3-: High
PaCO2 criteria for T2RF
> 45mmHg
List the five parameters of ABG testing
- PaO2
- PaCO2
- pH
- Lactate
- HCO3-
Three questions to ask when assessing ABG
- Is there pulmonary gas exchange abnormality?
- Is there acid-base disturbance?
- Is there lactic acidosis?
What O2 and CO2 levels in arterial blood would indicate pulmonary gas exchange abnormality in ABG?
- Low O2 (T1RF) [PaO2 < 60mmHg)
- High CO2 (T2RF) [PaCO2 > 45mmHg]
What would indicate acid-base disturbance in ABG?
- Look at pH
- Whichever parameter (PaCO2 or HCO3-) agrees with pH is the cause; other is compensation
- If both parameters agree: mixed resp. and metabolic compensation
Hyperlactatemia vs lactic acidosis
Hyperlactatemia: >2mmol/L
Lactic acidosis: >4mmol/L
What are the two types of lactic acidosis?
Type A: Tissue hypoxia/hypoperfusion
Type B: No hypoxia/hypoperfusion
How do restrictive lung conditions such as pulmonary fibrosis influence work of breathing?
Increase
