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Medical Studies 1 > 6.2 Understanding Respiratory Failure > Flashcards

6.2 Understanding Respiratory Failure Flashcards

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USMLE® Step 1 flashcards
1
Q

What is pulmonary ventilation?

A

The physical movement of air in and out of the lungs

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2
Q

What structures are in the respiratory zone of the airways?

A

-Respiratory bronchioles
- Alveolar Ducts
- Alveoli

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3
Q

Can gas exchange occur in the terminal bronchioles?

A

No; they aren’t the last bronchioles, they’re the last bronchioles that don’t exchange air.

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4
Q

What is respiratory failure?

A

Not enough O2 or too much CO2 in the blood due to a failure of the respiratory system

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5
Q

Describe type 1 vs type 2 respiratory failure

A

Type 1: Cannot move enough O2 into blood (1: primary job) -> hypoxaemia
Type 2: Cannot remove enough CO2 from blood ->hypercapnia

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6
Q

What is the role of Arterial Blood Gas (ABG) in diagnosis of hypoxaemia and hypercapnia

A
  • It provides an accurate assessment of hypoxaemia and hypercapnia; pulse oximetry cannot replace this.
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7
Q

List some causes of hypoxia

A
  • High altitude
  • Respiratory failure
  • Anaemia
  • Shock
  • Ischaemia
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8
Q

Describe failure of pulmonary ventilation, including causes and consequences

A
  • Failure to physically move air into and out of lungs
  • Causes: CNS depression, respiratory pump failure
  • Consequences: Hypoxaemia, hypercapnia
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9
Q

Pulmonary ventilatory failure can be caused by CNS depression. What can cause this?

A
  • Drugs (benzodiazepines)
  • Structural abnormalities (stroke, head injury)
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10
Q

Pulmonary ventilatory failure can be caused by failure of the respiratory pump. What can cause this?

A
  • Phrenic nerve dysfunction
  • Neuromuscular weakness
  • Chest cage restriction
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11
Q

Describe failure of pulmonary gas exchange (“lung failure”). What are the two categories of factors that can cause this?

A

Reduced O2 delivery from lung to blood, caused by:
- Lung (alveolar compartment and/or interface with capillary)
- Blood vessel (capillary compartment)

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12
Q

Pulmonary gas exchange failure can be caused by diffusion limitation. Provide an example of how this may occur

A

Thickened interstitium and thickened alveolar capillary membrane

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13
Q

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

A
  • Fluid in alveoli
  • Alveolar collapse
  • Alveolar damage
  • Obstruction/airway narrowing
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14
Q

Pulmonary gas exchange failure can be caused by perfusion defects. Provide an intuitive example of how this may occur

A

Pulmonary vascular narrowing or obstruction

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15
Q

How can a right-to-left anatomic shunt cause pulmonary gas exchange failure?

A

Deoxygenated blood bypasses pulmonary circulation, leading to hypoxaemia

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16
Q

Hypoxaemia and hypercapnia will both cause the same initial symptoms. List them.

A
  • Use of accessory muscles in breathing
  • Tachypnoea
  • Dyspnoea
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17
Q

List some organs that can be damaged via cellular hypoxia

A
  • Brain
  • Lungs
  • Heart
  • Liver
  • GIT
  • Kidneys
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18
Q

Chronic effects of hypoxaemia

A
  • Reduced asthma symptoms perception
  • Impaired cough reflex
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19
Q

Effect of hypoxaemia on sympathetic discharge. What are the two consequences of this?

A
  • Increased sympathetic discharge
  • Leads to tachycardia and hypertension
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20
Q

What is CO2 narcosis

A

Depressed level of consciousness caused by increased CO2

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21
Q

How can hypercapnia lead to seizure, coma, and death?

A
  • Central chemoreceptors detect CO2 in CSF
  • Increase blood flow to area
  • CO2 narcosis; coma, seizure, and death
22
Q

PaCO2 threshold for CO2 narcosis in normals vs people with chronic hypercapnia

A

Normal: 75mmHg
Chronic hypercapnia: 90mmHg (because of renal HCO3- buffering)

23
Q

Considering the Bohr effect, suggest how changes in oxygen transport may occur during hypercapnia

A

increased O2 offloading into tissues

24
Q

In terms of hypoxic ventilatory drive, how can oxygen therapy cause hypercapnia in COPD patients?

A
  • 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
25
Q

How can oxygen therapy cause hypercapnia in terms of hypoxic vasoconstriction?

A
  • Oxygen is delivered to dead space, causing blood to flow back to it
  • Increased CO2 retention
26
Q

Describe, in terms of the haldane effect, how supplemental oxygen can cause excess CO2

A

Increases offloading of CO2 from Hb, raising CO2 pressure

27
Q

Is O2 therapy the most effective long-term course of action for patients with type 1 respiratory failure?

A
  • No
  • Treat the underlying cause wherever possible
28
Q

What is the most common piece of equipment used in oxygen therapy?

A

Nasal cannula

29
Q

Can CIG masks take on higher or lower flow rates than nasal cannula?

A

Higher

30
Q

Describe high flow oxygen therapy. What are some advantages?

A

Blender of 100% O2 and medical air from wall

Advantages:
- Humidified and heated air
- Accurate delivery of FiO2 (no extra dilution)

31
Q

What is FiO2?

A

Fraction of inspired oxygen

32
Q

How can BiPAP be used in pulmonary oedema?

A

Dries out airways

33
Q

What is non-invasive ventilation AKA?

A

BiPAP

34
Q

How does BiPAP differ from CPAP?

A

BiPAP has lower pressure on expiration, whereas CPAP is constant

35
Q

What kind of conditions may warrant Bipap?

A
  • Neuromuscular disease
  • Chest wall respiratory disorder
  • Severe COPD with chronic hypercapnia
36
Q

List some major indications for intubation and mechanical ventilation

A
  • Loss of airway
  • Failure of non-invasive techniques
  • Sudden crash following organ failure
37
Q

What does ECMO stand for?

A

Extracorporeal membrane oxygenation

38
Q

Describe ECMO

A
  • Temporarily, oxygenation of blood is achieved outside the body
  • Returned to the body via arterial (VA ECMO) or venous (VV ECMO)
39
Q

Indications for ECMO

A
  • All other treatments have failed
  • Bridging to transplant
40
Q

Describe the respiratory response to lactic acidosis in severe hypoxaemia

A
  • Increased anaerobic metabolism -> increased lactic acid -> decreased pH
  • Respiratory system begins hyperventilating in an attempt to blow off CO2 and normalise pH
41
Q

Describe the renal response to respiratory acidosis in T2RF

A
  • Kidneys retain Bicarbonate in an attempt to buffer pH and decrease acidity
  • May take 24 hours or more to kick in
42
Q

Acute acid-base patterns of hypercapnia: PaCO2, pH, HCO3-

A

PaCO2: High
pH: Low
HCO3-: Stable

43
Q

Chronic acid-base patterns of hypercapnia: PaCO2, pH, HCO3-

A

PaCO2: High
pH: Stable
HCO3-: High

44
Q

Acute on chronic acid-base patterns of hypercapnia: PaCO2, pH, HCO3-

A

PaCO2: High
pH: low
HCO3-: High

45
Q

PaCO2 criteria for T2RF

A

> 45mmHg

46
Q

List the five parameters of ABG testing

A
  • PaO2
  • PaCO2
  • pH
  • Lactate
  • HCO3-
47
Q

Three questions to ask when assessing ABG

A
  1. Is there pulmonary gas exchange abnormality?
  2. Is there acid-base disturbance?
  3. Is there lactic acidosis?
48
Q

What O2 and CO2 levels in arterial blood would indicate pulmonary gas exchange abnormality in ABG?

A
  • Low O2 (T1RF) [PaO2 < 60mmHg)
  • High CO2 (T2RF) [PaCO2 > 45mmHg]
49
Q

What would indicate acid-base disturbance in ABG?

A
  • 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
50
Q

Hyperlactatemia vs lactic acidosis

A

Hyperlactatemia: >2mmol/L
Lactic acidosis: >4mmol/L

51
Q

What are the two types of lactic acidosis?

A

Type A: Tissue hypoxia/hypoperfusion
Type B: No hypoxia/hypoperfusion

52
Q

How do restrictive lung conditions such as pulmonary fibrosis influence work of breathing?

A

Increase

Medical Studies 1 (90 decks)

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