80 - Physiological Consequences of Increased Fluid Movement across Pulmonary Membranes Flashcards

1
Q

Features of pulmonary circulation

A

Low pressure, low resistance

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2
Q

Why can the pulmonary circulation be low pressure?

A

Mostly at the level of the heart, so don’t need pressure to push fluid against gravity

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3
Q

Pulmonary artery pressure

A

25/8 (systolic/diastolic)

Mean is 15mmHg

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4
Q

Capillary pressure

A

12/8 mmHg

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5
Q

What would happen if pulmonary circulation were high pressure?

A

Fluid would leak from vessels into the alveoli.

This would impair gas exchange

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6
Q

Components of pulmonary circulation

A

Thin-walled vessels, thin right atrium, ventricle

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7
Q

Capillary volume in pulmonary circulation at rest

A

60-80mL

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8
Q

Effect of exercise on pulmonary circulation pressure

A

No effect.

Vasodilation prevents pressure rise with increased CO

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9
Q

Effect of inspiration on pulmonary circulation

A

Pooling of blood

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10
Q

Amount of deoxyhaemoglobin for cyanosis to be visible

A

4g/L

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11
Q

Signs of a metabolic acidosis

A
Acidosis without elevated blood CO2.
Low bicarbonate (EG: loss from diarrhoea, or acting as a buffer for elevated lactic acid)
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12
Q

Signs of a respiratory acidosis

A

Elevated CO2 with decreased pH

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13
Q

Anion gap

A

Difference in concentrations of commonly-measured anions and cations in the blood (Anions and cations won’t be different, just measuring the common ones, EG: K+, Na+, Cl-, HCO3-).

Used to measure electrolyte imbalance.

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14
Q

Sum of the commonly measured anions and cations

A

Difference in charge is normally under 15.

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15
Q

How does the anion gap appear with metabolic acidosis, from introduced acid

A
Bicarbonate decreases (neutralising acid).
Anion gap goes above 15.
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16
Q

How does the anion gap appear with metabolic acidosis from diarrhoea

A

Gap stays the same, as although HCO3- is being lost, the body tries to retain Cl-, to maintain anion gap

17
Q

Clinical features of pulmonary oedema
1
2
3

A

Impaired gas exchange
Metabolic acidosis
Tissue hypoxia

18
Q

Factors determining fluid movement across pulmonary capillaries
1
2
3

A

Hydrostatic pressure inside and outside the capillary (Pc, Pi)
Oncotic pressure inside and outside the capillaries (Oc, Oi)
Permeability of the capillary (sigma)

Net fluid out = K[(Pc-Pi)-sigma(Oc-Oi)]

19
Q

What drives alveolar oedema in pulmonary oedema?

A

Increased hydrostatic pressure within capillaries

20
Q

What causes respiratory alkalosis?

A

Decreased blood CO2.

Exhaling too much CO2

21
Q

How to distinguish between metabolic and respiratory alkalosis

A

Observe whether CO2 is too low, or normal

22
Q

ARDS

A

Adult respiratory distress syndrome.
Respiratory capillaries become hyper-permeable.
Often in response to inflammation of some sort

23
Q

Effects of adult respiratory distress syndrome

A

Decrease V/Q units, shunt, leading to decreased PaO2.

Stiff lungs increases elastic work, leading to increased O2 demand.

24
Q

Difference between cardiogenic pulmonary oedema and ARDS

A

Very similar in symptoms (flooded alveoli), but ARDS can be unilateral, doesn’t have cardiomegaly.
Cardiogenic is from elevated hydrostatic pressure, ARDS from increased capillary permeability

25
Q

Normal rate of lymph flow

A

~20mL/hour from lungs

26
Q

When does fluid begin to accumulate in interstitial spaces and alveoli?

A

When it overwhelms the rate of lymphatic drainage.

Alveoli begin flooding after the interstitium is flooded with fluid.

27
Q
Mechanical changes in pulmonary oedema.
1
2
3
4
A

Decreased lung compliance
Decreased lung volumes (collapse of alveoli)
Increased airway resistance
Increased work of breathing (can hear wheezing)

28
Q

Effect of pulmonary oedema on gas exchange

A

Hypoxaemia due to shunt, low V/Q, diffusion impairment.

29
Q
Effect of pulmonary oedema on blood gasses
1
2
3
4
A

Decreased PaO2
Decreased PaCO2
Increased pH
If very severe, increase in PaCO2, decrease pH (metabolic and respiratory acidosis)

30
Q

Effect of pulmonary oedema on pulmonary circulation

A

Increases resistance

31
Q

Permeability of capillary endothelium

A

Capillary endothelium is highly permeable to water, ions and small molecules (not protein)

32
Q

Permeability of alveolar epithelium

A

Alveolar epithelium is not and actively pumps water from the alveoli into the interstitial spaces

33
Q

Is interstitial oedema more or less severe than alveolar oedema?

A

Interstitial oedema causes little functional effect but alveolar oedema has a large effect on lung function

34
Q

Causes of pulmonary oedema
1
2

A
  1. Increased capillary hydrostatic pressure
    eg left ventricular dysfunction, mitral stenosis, fluid overload, pulmonary veno-occlusive disease
  2. Increased capillary permeability
    eg toxins, sepsis, multiple trauma, aspiration of gastric acid
    ? high altitude, ? heroin, ? neurogenic
35
Q

Does altered colloid pressure lead to pulmonary oedema?

A

In theory, but not in practise.