Respiratory Failure

Question 1

What is a pulmonary shunt?

Answer 1

A condition where blood bypasses the lungs and re-enters the heart through the pulmonary vein, resulting in hypoxaemia That cannot corrected by O2 therapy.

Question 2

What are the two types of pulmonary shunts?

Answer 2

Anatomic shunts and physiological shunts.

Question 3

What is the normal V/Q ratio?

Answer 3

0.8

Question 4

What does a V/Q ratio of zero indicate?

Answer 4

Little perfusion compared to ventilation, leading to a pulmonary shunt where it bypasses pulmonary circulation, therefore supplementation of oxygen will not correct hypoxaemia due to no contact with alveoli.

Question 5

What physiological process contributes to pulmonary shunts?

Answer 5

Blood supplying and leaving the myocardium via Thebesian veins.
Bronchial circulation empties venous deoxygenated blood into pulmonary veins entering the left atria

Question 6

How does bronchial circulation contribute to pulmonary shunts?

Answer 6

It empties venous deoxygenated blood into pulmonary veins entering the left atria.

Question 7

What are the causes of anatomical shunts?

Answer 7

• Ventricular septal defect
• Atrial septal defect
• Patent ductus arteriosus

Question 8

What is the cause of left to right shunts?

Answer 8

patent ductus arteriosus and atrial septal defect, resulting in right ventircle hypertrophy

Question 9

What is the cause of right to left shunt?

Answer 9

Right to left is against the gradient: tetralogy of the fallot where ventricular septal
defect causes narrowing of ventricular outflow tract and disrupts pressure gradient, causing right side to be greater than left.

It also includes arteriovenous malformation, severe pneumonia and severe pulmonary oedema.

Question 10

What is Eisenmenger’s syndrome?

Answer 10

A condition where congenital heart disease leads to increased pressure in the right heart, causing a shift from left-to-right to right-to-left shunting.

Question 11

What characterizes the pathophysiology of Eisenmenger’s syndrome?

Answer 11

A triad of:
* Vasoconstriction of pulmonary arteries
* Remodeling of smooth muscle in pulmonary arteries
* Thrombosis due to increased vascular resistance

Question 12

What are common symptoms of Eisenmenger’s syndrome?

Answer 12

• Worsening exertional dyspnoea
• Cyanosis
• Syncope
• Swelling with volume retention

On examination, there may be cubbing, ascites and hepatomegaly dye to fluid congestion
O2 level can indicate the blood flow through the shunt in litres per minute

Question 13

Which conditions is Eismenger’s syndrome commonly seen?

Answer 13

This is commonly seeen in atrial septal defect, ventiruclar septal defect, patent ductus arteriosus and tetralogy of the fallout.

Question 14

What is the shunt fraction equation?

Answer 14

Qt = Qs + Qc or Qs/Qt = Qc

Question 15

What is the typical management for pulmonary shunts?

Answer 15

*Cardiopulmonary transplantation *management of hypoxia and respiratory acidosis with ventilatory support.

Question 16

What does ABG stand for?

Answer 16

Arterial blood gas: ABG is typically used for patient deterioration, acute exacerbation of chest discomfort, impaired consciousness, signs of CO2 retention with bounding pulse, drowsy and flapping tremor or headache
Cyanosis, confusion and visual hallucinations
Validate pulse oximetry measurements

Question 17

What is SpO2?

Answer 17

The oxygen saturation detected by pulse oximetry.

Question 18

What SpO2 level indicates a problem?

Answer 18

Less than 90%

Question 19

What is SaO2?

Answer 19

oxygen saturation of arterial blood.

Question 20

What causes differences in SpO2 and SaO2?

Answer 20

Carbon monoxide poisoning
hyperbilirubinaemia
* methaeminoglobinaemia
* Severe anaemia results in falsely low readings

Question 21

What is methaeminoglobinaemia?

Answer 21

Methaeminoglobinaemia is where Iron in the haem group is in the Fe3+ form rather than Fe2.

It commonly occurs due to the exposure with benzocaine (typically for local anaesthesia prior to upper endoscopy) or prelicaine (an anaesthetic) or exposure to nitrites, which infants are at higher risk for with well water

Question 22

What is the significance of PaO2?

Answer 22

The partial pressure of oxygen in arterial blood; less than 8kPa indicates severe hypoxaemia.

Question 23

What characterizes Type 1 respiratory failure?

Answer 23

Hypoxia with normal or slightly low CO2.

Question 24

What are some causes of Type 1 respiratory failure?

Answer 24

• Low atmospheric pressure of oxygen
• V/Q mismatch due to conditions like pneumonia and pulmonary oedema
• Diffusion defects
• Extrapulmonary shunts

Question 25

What causes a V/Q mismatch?

Answer 25

low ventilation compared to perfusion due to Pus or fluid, with *pneumonia
*Pulmonary embolism
*congestive heart failure
* acute respiratory distress syndrome
* COPD
* pulmonary oedema
*blood in pulmonary haemorrhage,
*atelactasis.
Patients tend to have an increased ventilation rate

Question 26

What causes an extreme V/Q mismatch?

Answer 26

Extreme V/Q mismatch where low ventilation occurs due to a pulmonary shunt from acute respiratory distress syndrome, SEVERE pneumonia, pulmonary oedema from congestive heart failure, SEVERE alveolar haemorrage and atelactasis and mucus plug

Question 27

What causes a diffusion defect?

Answer 27

emphysema and interstitial lung disease -> CO2 remains normal as CO2 can diffuse more easily across alveoli than oxygen

Question 28

What characterizes Type 2 respiratory failure?

Answer 28

pH less than 7.35 and PaCO2 over 45 mmHg with normal or decreased oxygen.

Question 29

What can cause Type 2 respiratory failure?

Answer 29

Conditions affecting ventilation

• Airway obstruction
• Reduced compliance of lung or chest wall
• Opiates
• Neuromuscular dysfunction
  *CNS depression

Question 30

What causes reduced compliance of lung or chest wall?

Answer 30

pneumonia
diaphragmatic paralysis
obesity
rib fractures
kyphoscoliosi
flail chest

Question 31

what causes CNS depression?

Answer 31

opiates
neuromuscular dysfunction with Gullian-barre syndrome
myasthenia gravis
severe fatigue
spinal cord injury

Question 32

What are general clinical signs of respiratory failure?

Answer 32

Accessory muscle use
cachetic
conversational dyspnoea
central cyanosis
Horner’s syndrome
JVP distentio
Lymphadenoapthy
tracheal deviation

Question 33

What are the clinical signs of Type 1 respiratory failure?

Answer 33

dyspnoea, confusion, tachycardia, tachypnoea and cyanosis

Question 34

What are the clinical signs of Type 2 respiratory failure?

Answer 34

change of behaviour, headache, warm extremities, asterixis, papilloedema and coma.

Question 35

What investigations are used for respiratory failure?

Answer 35

• baseline observations for respiratory rate, oxygen saturation, pulse rate, HR and blood pressure
• Arterial blood gas
• FBC; U&Es, CRP
• Sputum and blood cultures
• Capnometry
• Radiography
• Pulse oximetry
• CT pulmonary angiogram
• Echocardiogram to assess for shunt, especially in cases where hypoxaemia does not correct with supplemental oxygen

Question 36

What is the general management of respiratory failure?

Answer 36

Correcting hypoxia to maintain adequate tissue oxygenation, but must be controlled to avoid oxygen toxicity and CO2 narcosis. Therefore, inspired oxygen concentration should be maintained at 90-94%.

Question 37

Which medications can improve respiration?

Answer 37

doxapram, a respiratory stimulant that acts on carotid chemoreceptors
Bronchodilators such as beta blockers and anti-muscarinic agents

Question 38

What is the goal of oxygen therapy in respiratory failure?

Answer 38

To maintain adequate tissue oxygenation without causing oxygen toxicity or CO2 narcosis.

Question 39

How is Type 1 respiratory failure managed?

Answer 39

Treat underlying cause and provide oxygen via face-mask unless there is a decreased diffusion capacity
-> progress to assisted ventilation if O2 remains below 6kPA despite 60% oxygen administration.

No change of hypoxaemia indicates cardiac shunt, therefore obtain echocardiogram.

Question 40

How is Type 2 respiratory failure managed?

Answer 40

Controlled oxygen therapy at 24%
Recheck ABG after 20 minutes. Stable or lowered O2, then increase O2 concentration. If CO2 has higher and patient is hypoxia, assisted ventilation should be considered
Non-invasive ventilation with high flow nasal cannulae
Patients with hypercapnic respitatory failure or cardiogenic pulmonary oedema will benefit from bi-level positive airway pressure

Question 41

Which patinets should mechanical ventilation be indicated for?

Answer 41

Mechanical ventilation is indicated for patinets with tachypnoea and an RR over 30, disturbed consciousness, haemodynamic insabtility, respiratory muscle fatigue, hypercapnia with pH less than 7.25 and failure of supplemental non-invasive oxygen to sufficiently raise oxygen

Question 42

What is the recommended oxygen concentration for Type 1 respiratory failure?

Answer 42

Oxygen via face-mask; progress to assisted ventilation if O2 remains below 6 kPa despite 60% oxygen administration.

Question 43

What is BiPAP used for?

Answer 43

Non-invasive ventilation which is ideal for hypercapnic respiratory failure and cardiogenic respiratory failure.

Question 44

What is positive end expiratory pressure?

Answer 44

Positive end expiratory pressure is the positive pressure that will remain in the alveoli at the end of the expiratory cycle to allow it to participate in diffusion- when this is high, it will increase PO2/when it is low, it will decrease PO2. is an indicator for airway resistance with bronchospasm or mucus plug

Question 45

What is the significance of Pplat in mechanical ventilation?

Answer 45

It indicates the pressure in the alveoli at the end of inspiration, reflecting elastic recoil or excessive tidal volume.

Question 46

What is a spontaneous breathing trial (SBT)?

Answer 46

An assessment of patient breathing independently or with minimal help from ventilation.

Question 47

What is the purpose of high-dose combination bronchodilators?

Answer 47

To improve ventilation.