Acute Respiratory Problems / Respiratory Failure

Question 1

What is respiratory failure?

Answer 1

When the lungs aren’t working correctly, resulting in hypoxia

there may or may not be raised levels of carbon dioxide in the blood

Question 2

What are the main differences between type 1 and type 2 respiratory failure?

Answer 2

Type 1:

• there is hypoxia only
• this is focal - only one lobe / part of the lung is malfunctioning
• there is V/Q mismatch

Type 2:

• there is hypoxia and hypercapnia
• this is global - affects large areas of the lungs
• there is no global gas exchange

Question 3

What abnormalities are shown on ABG for type 2 respiratory failure?

Answer 3

• elevated PaCO₂
• reduced PaO₂
• elevated HCO₃^-

Question 4

What condition is very frequently associated with type 2 respiratory failure?

Answer 4

COPD

look for a history of heavy smoking

Question 5

What is represented by the boats and lorries in this diagram?

Answer 5

boats are ventilation (V) and lorries are perfusion (Q)

in order for adequate lung function, both ventilation and perfusion need to be functioning

ventilation involves getting air into the alveoli

perfusion involves getting the oxygen from the alveoli to the rest of the body

Question 7

What is meant by ventilation (V)?

Answer 7

the volume of gas inhaled and exhaled from the lungs in a given time period, usually one minute

this involves air entering the alveoli

Question 8

What is meant by perfusion?

Answer 8

perfusion is the total volume of blood reaching the pulmonary capillaries in a given time period

this involves getting oxygen from the alveoli to the rest of the body

Question 9

What would the ideal V/Q ratio be?

How does V/Q ratio differ in different parts of the lung and what does this mean?

Answer 9

the ideal V/Q ratio would be 1 for maximally efficient pulmonary function

the ratio varies depending on the part of the lung concerned

when standing up straight, the ratio is roughly 3.3 in the apex of the lung and 0.63 in the base

ventilation exceeds perfusion towards the apex

perfusion exceeds ventilation towards the base

Question 10

What is meant by V/Q mismatch?

Answer 10

a mismatch between the alveolar ventilation and the alveolar blood flow

this can arise due to either reduced ventilation of part of the lung or reduced perfusion

gas exchange in the affected alveoli is impaired, resulting in a fall in pO₂ and a rise in pCO₂

Question 11

Why does pCO₂ in the blood not usually rise despite V/Q mismatch?

What physiological mechanisms are in place to prevent this?

Answer 11

• hypoxic vasoconstriction causes blood to be diverted to better ventilated parts of the lung
• the haemoglobin in these well ventilated alveolar capillaries will already be saturated
• RBCs will be unable to bind additional oxygen to increase the pO₂
• the pO₂ of the blood remains low, which acts as a stimulus to cause hyperventilation, resulting in either normal or low CO₂ levels

Question 12

What is involved in the principles of type 1 respiratory failure relating to solubility of CO₂ and O₂ and compensation?

Answer 12

CO₂ is much more soluble than O₂

(this is why O₂ needs Hb to carry it)

• a good lung cannot hyper-oxygenate (>100% saturation)
• a good lung can hyperventilate to remove CO₂

Question 13

What is shown in this image of Type 1 respiratory failure?

Answer 13

• there is reduced ventilation in a part of the lung
  
  • oxygen is not getting into the alveoli, but perfusion is normal
• the rest of the lung has increased ventilation to compensate
  
  • ​perfusion to the rest of the lung is still normal and not increased
• the rest of the lung is at 100% capacity as it is fully oxygenating the blood
• due to the blue region, despite compensation, there is still hypoxia as you cannot go above 100% saturation

Question 14

How can pneumonia lead to type 1 respiratory failure?

Answer 14

in pneumonia the alveoli are filled with exudate

this impairs the delivery of air to the alveoli and lengthens the diffusion pathway for respiratory gases

Question 15

When does type 2 respiratory failure result from V/Q mismatch?

Answer 15

• the result of reduced ventilation / perfusion intially is hypoxia
• the lung is still able to remove CO₂, so hypercapnia does not occur unless ventilation is severely limited
• in T2RF there is a global problem leading to complete loss of gas exchange due to malfunctioning alveoli

Question 16

What are common causes of Type 1 respiratory failure?

Answer 16

• acute asthma
• atelectasis
• pulmonary oedema
• pneumonia
• pneumothorax
• pulmonary embolism
• ARDS

Question 17

What are common causes of type 2 respiratory failure?

Answer 17

• acute severe asthma
• COPD
• upper airway obstruction
• neuropathies (GBS, MND)
• drugs - opiates

Question 18

What is involved in the management of type 1 respiratory failure?

Answer 18

CPAP - continunous positive airway pressure

• air (above atmospheric pressure) is pumped into the lungs continuously, which opens deep distal airways
• this increases ventilation (V) so helps when there is a reduced V to an area of the lungs

Question 19

What is involved in the management of type 2 respiratory failure?

Answer 19

BIPAP - bilevel positive airway pressure

• there is increased airway recruitment, which increases ventilation (V)
• in BIPAP, you receive positive air pressure on inspiration and expiration, but the air pressure is higher on inspiration
  
  • CPAP involves the same amount of pressure being delivered on inspiration and expiration
• air is pumped in on inspiration, but CO₂ is also sucked out on expiration

Question 20

What is normal intrapleural pressure?

What happens if this is changed?

Answer 20

normal intrapleural pressure is from -5 to -8 cm H₂O

this is a negative pressure that holds open the lungs

if it is changed (i.e. through pneumothorax) then ventilation cannot occur as effectively

Question 21

What is a pneumothorax?

Answer 21

air within the pleural space

this air pushes on the outside of lung and makes it collapse

this could involve the collapse of entire lung or only a portion of the lung

Question 22

What is the difference between a primary and a secondary pneumothorax?

Answer 22

Primary pneumothorax:

• this occurs spontaneously without an apparent cause and in the absence of significant lung disease

Secondary pneumothorax:

• this occurs in the presence of existing lung disease

Question 23

What type of person is more likely to get a primary spontaneous pneumothorax?

How does it develop?

Answer 23

this is more likely to occur in a young, healthy person who does not have any significant lung disease

a bleb (lump in the pleura) bursts open, leading to air entering the pleural space

this is random and spontaneous

Question 24

What are the risk factors that increase the likelihood of primary pneumothorax?

Answer 24

• men are more likely to get pneumothoraces than women
• smoking
• Marfanoid habitus
  
  • really tall individuals with elongated limbs & hypermobility of joints

Question 25

Who is more likely to get a secondary pneumothorax?

Answer 25

* patients with a **smoking history** * patients are usually **_over 50_** with **_lung disease already diagnosed_** * this would include **younger patients with cystic fibrosis**

Question 26

How does secondary pneumothorax occur in someone with emphysema?

Answer 26

the alveolar bullae in emphysema can burst, allowing air to rush into the pleural space

Question 27

What happens in a tension pneumothorax?

Answer 27

a **_one-way valve_** is formed * with each **inspiration**, some air is pumped **into the pleural space** * upon **expiration**, the **_air cannot leave_** the pleural space * with every breath, **more air enters the pleural space** and the **_pneumothorax gets bigger_**

Question 28

What are the signs and symptoms of tension pneumothorax?

Answer 28

***_Due to lung compression:_*** * severe **dyspnoea** * **tracheal deviation** (away from the lesion) * **_silent_ chest** with **_hyperresonance_** and **_reduced expansion_** on lesioned side ***_Due to mediastinal shift:_*** * hypotension * tachycardia

Question 29

How does someone die from a tension pneumothorax?

Answer 29

death from tension pneumothorax is **cardiac**, rather than respiratory * the pneumothorax becomes so large that it presses against the **_vena cava_** in the mediastinum * this leads to a **loss of venous return** and **_circulatory collapse_** * **_tachycardia_** is present to try and **compensate for the hypotension**

Question 30

Which direction does the trachea deviate in tension pneumothorax?

Answer 30

as the tension pneumothorax balloons, it will **push the trachea away from itself** the trachea **_deviates AWAY_** from the side of the pneumothorax

Question 31

What does the chest sound like in a tension pneumothorax?

Answer 31

the chest sounds **_silent_** it is **_hyperresonant_** due it just being **air** present in this region and **no lung tissue**

Question 32

What is the management for tension pneumothorax?

Answer 32

**_large bore cannula_** in the **_2^nd intercostal space_** **_midclavicular line_** this is an **orange** or **grey** cannula this needs to be inserted **just above the 3^rd rib** to avoid the neurovascular bundle resting underneath the ribs

Question 33

How are other pneumothoraces (not tension pneumothoraces) managed?

Answer 33

**_chest drain_** or **_needle aspiration_** this needs to be inserted in the **safe triangle** this is in the **2^nd intercostal space**, **midclavicular line** using a **sterile** technique

Question 34

What are the stages involved in the pneumothorax treatment algorithm?

Answer 34

if the patient is **_symptomatic_** (**breathless**) or the pneumothorax is **_\>2cm_** then management is different large or symptomatic secondary pneumothorax - go straight for the chest drain regardless of the size of the pneumothorax, if the patient is **_symptomatic_** then **_different management_** needs to be taken

Question 35

Answer 35

**D - needle aspiration and give O₂** the pneumothorax is primary and less than 2cm however, the patient is symptomatic (breathless) so needle aspiration is performed if this is not successful, then a chest drain would be performed

Question 36

What is a pulmonary embolism? Where does it originate from?

Answer 36

PE tends to come from a **_VTE_** - a clot that forms elsewhere in the body these tend to be **_DVTs_** that occur in the **deep veins of the calves** this is because the **compliance is massive** and the **pressure is low** here

Question 37

What are the stages involved in a PE developing from a thrombus?

Answer 37

a small part of the thrombus breaks off and drains into the **inferior vena cava** this enters the **right side of the heart** and into the **pulmonary artery**, to become lodged in the lungs

Question 38

What are the 3 different types of PE?

Answer 38

* **acute massive PE** * **acute submassive** & **small PE** * **chronic PE**

Question 39

What is an acute massive PE and what are the typical symptoms?

Answer 39

this involves **_sudden complete occlusion_** of the pulmonary artery this results in: * ***collapse*** * ***central crushing chest pain*** * ***severe dyspnoea***

Question 40

What is an acute submassive & small PE? What are the typical symptoms?

Answer 40

**_sudden incomplete occlusion_** of pulmonary artery or distal artery this results in: * ***pleuritic chest pain*** * ***haemoptysis*** * ***dyspnoea***

Question 41

What is a chronic PE? What symptoms does this present with?

Answer 41

this involves chronic occlusion of **_pulmonary microvasculature_** this results in ***exertional dyspnoea***

Question 42

What might be seen on CXR for someone with PE?

Answer 42

* classical **S₁Q₃T₃ pattern** * right axis deviation * right bundle branch block * sinus tachycardia

Question 43

What is meant by S₁Q₃T₃ pattern on ECG?

Answer 43

* **big S wave** in lead 1 * **pathological Q wave** in lead 3 * **inverted T wave** in lead 3 * this is a sign of **_right heart strain_** * right side strain is increased to try and **overcome the obstruction** in the pulmonary vasculature

Question 44

What sign might be seen on CXR for pulmonary embolism?

Answer 44

CXR can show **_Westermark's sign_**, which has a high positive predictive value it is a finding of **oligaemia (increased translucency)** distal to a large vessel that is occluded by a PE

Question 45

What mnemonic is used to remember the risk factors for PE?

Answer 45

CT, s'il vous plait WHY - because you will be asking the radiologist for a CTPA

Question 46

What does C stand for in the mnemonic CT s'il vous plait?

Answer 46

* cancer * chemotherapy * cardiac failure * COPD * Factor C deficiency

Question 47

What does T stand for in the mnemonic CT s'il vous plait?

Answer 47

* trauma * time (age) * thrombocytosis

Question 48

What does S stand for in the mnemonic CT s'il vous plait?

Answer 48

* stasis * surgery * Factor S deficiency

Question 49

What does V stand for in the mnemonic CT s'il vous plait?

Answer 49

* **varicose veins** * **virchow's triad** (3 factors important in development of venous thrombosis) * stasis of blood flow * endothelial injury * hypercoagulability * **Factor V Leiden**

Question 50

What does P stand for in the mnemonic CT s'il vous plait?

Answer 50

* pill (OCP) * pregnancy * puerperium (period of 6 weeks after childbirth) * previous VTE * polycythaemia * paraprotein deposition

Question 51

What are the NICE guidelines for preventing VTE? How can the mechanisms for preventing VTE be remembered?

Answer 51

* everyone must be VTE risk assessed **_within 24 hours_** of hospital admission * mechanical prevention involves **_anti-embolic stockings_** (TED stockings) * pharmacological prevention involves **_low-molecular-weight-heparin_** (**tinzaparin**) * this can be remembered as **_"TEDs & Tinz"_**

Question 52

What score is used to stratify PEs?

Answer 52

the **_Well's score_** * a **_score \<4_** is a **low-risk PE** and a **_D-dimer test_** is done * a score of **_4 or more_** is a **high-risk PE** and **_CTPA_** is done

Question 53

What factors are scored in the Well's score? What mnemonic is used to remember this?

Answer 53

can be remembered using "PE SCORE" * P - previous DVT / PE * E - evidence of DVT * S - stasis * C - cancer * O - opinion is PE * R - rate raised (\>100) * E - exsanguination (haemoptysis)

Question 54

What question must be asked before deciding how to manage a patient with PE?

Answer 54

are they **_haemodynamically stable_**? i. e. systolic blood pressure **_\< 90_** * if **YES** then this is a **submassive/small PE** * if **NO** then this is a **massive PE**

Question 55

What is the treatment for submassive/small PE?

Answer 55

* **respiratory support** * **anticoagulation** * the aim of the treatment is not to eradicate the PE that is already present, but to **_prevent further PEs_**

Question 56

What type of anticoagulation is used to treat a submassive / small PE?

Answer 56

* **_Fondaparinux / Heparin_** is given for **5 days** * this is "bridging warfarin" * warfarin takes a **few days to take effect** clinically and is a **procoagulant** in the acute phase, so heparin needs to be given to bridge this effect * **_Warfarin_** is then given for **3 months** * a **_DOAC (e.g. dobigatran)_** is also started

Question 57

What are the treatments for someone presenting with a massive PE (not haemodynamically stable)?

Answer 57

* respiratory support * 1st line treatment is **_thrombolysis_** with a clot-busting drug * 2nd line treatment is **_embolectomy_**

Question 58

What type of drugs are used for thrombolysis? Why are they not used to treat a submassive/small PE?

Answer 58

**_IV thrombolytics (fibrinolytics)_** such as **alteplase** and **streptokinase** these have risks associated with them, and the risks outweight the benefits for small/submassive PE

Question 59

What is the definition of ARDS?

Answer 59

ARDS is a form of **_hypoxaemic acute lung injury_** it is a **_non-cardiogenic pulmonary oedema_** (i.e. pulmonary oedema occurring due to an immune reaction) it is a type of **respiratory failure** characterised by **rapid onset** of **widespread inflammation** in the lungs

Question 60

What are the common causes of ARDS? In what type of patient is it particularly common?

Answer 60

* drugs * ventilation * nearly drowning * severe burns * sepsis * pneumonia * transfusion reactions it is particularly common in critically ill (ITU) patients

Question 61

How does ARDS lead to alveolar collapse and shunt?

Answer 61

* the body responds to the cause with a profound **inflammatory response** * this increases **vascular permeability** and allows fluid into the lungs, resulting in **_pulmonary oedema_** * **fluid in the alveoli** weighs on the alveoli and **ruins their _structure_ and _integrity_** * this leads to **_alveolar collapse_** and **_diffuse alveolar damage_** * fluid leaks into the **space between the capillary and the alveolus**, increasing this space * this leads to a **_shunt_** in **50%** of the alveoli

Question 62

What criteria is used to define ARDS?

Answer 62

the **_Berlin criteria_**, which can be simplified to: * **_A_** - alternative cause (i.e. not cardiogenic pulmonary oedema) * **_R_** - rapid onset (\< 1 week) * **_D_** - dyspnoea * **_S_** - similar on CXR

Question 63

What are the 3 main symptoms of ARDS?

Answer 63

* **dyspnoea** (shortness of breath) * bluish discolouration of the skin (**cyanosis**) * **tachypnoea** (rapid breathing)

Question 64

What are the investigations performed for ARDS?

Answer 64

* **arterial blood gas (ABG)** * **CXR / CT** * **Echocardiogram** * **Covid swab** - COVID-19 has been seen to cause ARDS it is important to treat the underlying cause and be aware that it exists

Question 65

Answer 65

**A - apixaban** * the patient is **haemodynamically stable** as **_SBP \> 90_** * alteplase should not be given as thrombolysis is not in the patient's best interest at this stage * a **DOAC**, such as **apixaban**, should be given