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MD2 Respiratory > Respiratory Failure > Flashcards

Respiratory Failure Flashcards

1
Q

List 4 conditions which may increase the drive to breathe

A

Anxiety
Exercise
Metabolic acidosis
Hypoxaemia

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2
Q

List 4 conditions which may reduce the drive to breathe

A

Breath holding
Narcotic overdose
Sedatives

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3
Q

What are the 3 main functions of the upper airway?

A

Humidifies, filters and warms the incoming air
First line of defence
Prevents aspiration

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4
Q

What pathological processes may cause obstruction or narrowing of the airways?

A

Bronchospasm
Increased secretions/sputum
Collapse

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5
Q

What pathological processes may result in collapse of the airways?

A

Lack of elastic support (e.g. in emphysema)

Endoluminal (carcinoma, sputum)

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6
Q

What is the role of surfactant?

A

Improves lung compliance by reducing surface tension of fluid lining alveoli and thereby preventing alveoli collapse

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7
Q

How does inspiration occur?

A

Diaphragm and intercostals contract, greater space produces negative pressure gradient and air moves in

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8
Q

How does expiration occur? Is it a passive or active process?

A

Relaxation of muscles reduces intrathoracic volume which forces air out
Usually a passive process caused by recoil tendency of lungs (due to elastic tissue fibres and alveolar surface tension)

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9
Q

When is expiration active?

A

During periods of high activity

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10
Q

How does gas exchange occur?

A

Difference between partial pressures of O2 and CO2 in alveoli and pulmonary capillaries promotes diffusion across alveolar-capillary membrane
This is normally very efficient (occurs passively via concentration gradients)

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11
Q

Normal ABG values (pH, PaCO2, PaO2, HCO3-, SaO2)

A 
pH: 7.35-7.45 (2 SDs)
PaCO2: 40 (35-45) mmHge
PaO2: 100 (>85) mmHg
HCO3-: 24 (22-30)
SaO2: 95-100%
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12
Q

What is the A-a gradient?

A

Difference between the arterial (a) and Alveolar (A) concentration of O2

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13
Q

What does an elevated A-a gradient suggest?

A

A problem with diffusion or a V/Q mismatch (less commonly a shunt)

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14
Q

What is the equation to calculate A-a gradient on room air at sea level?

A

A-a = (150 - (1.25 x PaCO2)) - PaO2

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15
Q

What is the normal range for the A-a gradient on room air at sea level for young adults? What is it for the elderly?

A

7-14 in young adults

Higher in the elderly

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16
Q

Define respiratory failure

A

Impairment of gas exchange between ambient air and circulating blood, occurring in intrapulmonary gas exchange or in the movement of gases in and out of the lungs

17
Q

Describe the pathophysiology of respiratory failure and distinguish between the 2 types

A

Impaired gas exchange usually results in hypoxaemia (PaO2 50 mmHg, type 2)
Type 1 will eventually progress to type 2 if no intervention, due to fatigue of muscles of respiration

18
Q

List 2 causes of reduced inspired O2

A

Altitudes

Fires

19
Q

List 2 causes of ventilation-perfusion mismatch

A

Pneumonia

PE

20
Q

List 2 causes of impaired diffusion

A

Pulmonary fibrosis

COPD

21
Q

List 5 causes of hypoxaemia

A 
Reduced inspired O2
Ventilation-perfusion mismatch
Impaired diffusion
Shunt
Hypoventilation (as pCO2 increases, pO2 must fall)
22
Q

List 6 causes of hypercapnia

A 
Central depression
Completely blocked upper airway
Primary "pump" failure
Muscle fatigue
Intrinsic lung disease (e.g. severe COPD; most common)
Chest wall abnormalities
23
Q

List 2 causes of central depression

A

Narcotics

Sedation

24
Q

List 2 causes of primary “pump” failure

A

NMD e.g. Guillain Barre syndrome, MND

25
Q

List 2 chest wall abnormalities which may contribute to hypercapnia

A

Obesity

Kyphosis

26
Q

List 4 symptoms of respiratory failure

A

Usually non-specific: SOB, drowsiness, confusion, headache

27
Q

List 4 additional signs of respiratory failure

A

Use of accessory muscles
Increased RR or irregular breathing
Low O2 saturation (does not provide an indication of PaCO2)
Signs of the cause e.g. HF

28
Q

Set of Ix for patient presenting with suspected respiratory failure

A

Basic bloods: FBE, UEC, LFT, CRP, ABG
Imaging: CXR, CT chest (CTPA, HRCT), VQ
Others: lung function (e.g. spirometry, methacholine challenge), sleep study

29
Q

Outline the 5 basic management principles for any patient with respiratory failure

A 
Maintenance of adequate O2 delivery (remembering that too much O2 can be detrimental to CO2 retainers, mostly patients with chronic lung disease)
Reduce respiratory workload
Maximise ventilation
Maintain stable pH/electrolytes
Try and target cause
30
Q

What general treatments are used for a patient presenting with respiratory failure?

A

Bed rest initially (may need to be seated)
Adequate sleep
Analgesia (avoid too much as you may cause sedation)
Fluid, calories
Humidification
Physiotherapy to help clear secretions and to recondition
Avoid aspiration (via correct positioning, etc) and fluid overload
NIV

31
Q

21 year old male admitted with multiple fractures after MVA
18 hours post-admission develops agitation and respiratory distress
O/E: RR 30, HR 130, BP 130/80, afebrile, a few bilateral basal crepitations
Initial tests?

A

Most importantly:
ABG: pH 7.48, PaO2 50, PaCO2 30, HCO3- 26
CXR: diffuse bilateral coalescent opacities

32
Q

21 year old male admitted with multiple fractures after MVA
18 hours post-admission develops agitation and respiratory distress
O/E: RR 30, HR 130, BP 130/80, afebrile, a few bilateral basal crepitations
What is the likely pathological process and how is it causing respiratory failure?

A

ARDS
Increased pulmonary capillary permeability causing gas exchange defect (low V/Q units, shunt) and mechanical defect (increased elastic work of breathing)

33
Q

21 year old male admitted with multiple fractures after MVA
18 hours post-admission develops agitation and respiratory distress
O/E: RR 30, HR 130, BP 130/80, afebrile, a few bilateral basal crepitations
What is the management?

A

High flow humidified O2
Careful monitoring (clinical, SpO2, ABG)
CPAP/BiPAP
Invasive ventilation if unable to sustain adequate PaO2 or if type II ventilatory failure develops

34
Q

25 year old asthmatic in ED with acute attack
Initially: generalised wheeze, RR 26, PEFR 30% pred, ABG pH 7.50, PaO2 68, PaCO2 28
2 hours later after standard Rx: sleepy, RR 22, quiet chest, ABG pH 7.32, PaO2 70, PaCO2 52 (40% O2)
What is the pathophysiology of the respiratory failure?

A

Abnormal gas exchange (due to low V/Q units) and increased O2 demand leads to increased ventilation (however abnormal mechanics of breathing lead to increased resistive WOB)
Results in development of respiratory muscle fatigue and ventilatory failures

35
Q

25 year old asthmatic in ED with acute attack
Initially: generalised wheeze, RR 26, PEFR 30% pred, ABG pH 7.50, PaO2 68, PaCO2 28
2 hours later after standard Rx: sleepy, RR 22, quiet chest, ABG pH 7.32, PaO2 70, PaCO2 52 (40% O2)
What is the management?

A

Assisted ventilation (invasive) for rest
O2
Bronchodilators (to reduce WOB)
Corticosteroids

36
Q

53 year old woman now day 3 post-laparotomy for Ca bowel
Some cough and fever, ongoing abdo pain
Crepitations in both lung bases
ABG on 40%: 7.48/pCO2 33/pO2 66/23
12 hours later after analgesia and Abx, looks more unwell
ABG on 60% now: 7.28/pCO2 46/pO2 50/16
What is going on?

A

Abnormal gas exchange (likely caused by infection, alveolar oedema or atelectasis) and increased O2 demand causes increased ventilation initially, but because of abnormal mechanics of breathing (and an already reduced respiratory effort due to pain, reduced drive due to possible narcotic OD) results in increased elastic WOB
Development of respiratory muscle fatigue and possible narcotic OD results in respiratory failure (and worsening gas exchange)

37
Q

53 year old woman now day 3 post-laparotomy for Ca bowel
Some cough and fever, ongoing abdo pain
Crepitations in both lung bases
ABG on 40%: 7.48/pCO2 33/pO2 66/23
12 hours later after analgesia and Abx, looks more unwell
ABG on 60% now: 7.28/pCO2 46/pO2 50/16
What is the management?

A

Adequate O2
Ensure not narcotised, suitable pain control
Reduce WOB with diuretics and physiotherapy
Assisted ventilation
Sleep

38
Q

45 year old man with known MND, presents with a number of weeks of morning headache, daytime sleepiness and poor memory
ABG on RA 7.4/pCO2 50/pO2 77/33
What could be happening?

A

Normal pH with evidence of compensation because this is a chronic process
Likely the result of hypoventilation due to “pump” failure

39
Q

45 year old man with known MND, presents with a number of weeks of morning headache, daytime sleepiness and poor memory
ABG on RA 7.4/pCO2 50/pO2 77/33
What is the management?

A 
Lung function
Diagnostic sleep study
Maximise ventilation (likely to need ventilatory support at night, may need to reduce weight)
Avoid aspiration (appropriate positioning etc)

MD2 Respiratory (9 decks)

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