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Horsey > Ventilation > Flashcards

Ventilation Flashcards

1
Q

Problems in equine ventilation

A
  • hypercapnia
  • hypoxaemia
  • hypotension
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2
Q

Hypercapnia definition

A

high arterial CO2 levels due to respiratory depression

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3
Q

What causes hypoventilation?

A
  • sedatives
  • opioids
  • IV anaesthetics
  • muscle relaxants
  • positioning (horse on side for a long time)
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4
Q

How do you asses hypercapnia?

A
  • take multiple blood samples

- monitor end tidal CO2 alveolar gas analysis (machine): less accaurate but less invasive

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5
Q

Benefits and adverse effects of hypercapnia

A

Benefits:
-improved sympathetic stimulation leads to increased myocardial contractility and improved tissue blood flow.

disadvantages:

  • increased incidence of cardiac arrhythmia’s
  • acidaemia (leads to enzyme dysfunction and reduced myocardial contractility)
  • narcosis
  • hypoxaemia
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6
Q

What is normal blood pH?

A

7.35-7.45

PaCO2 of 80mmHg will decrease it to less than 7.2

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7
Q

Treatment of hypercapnia

A
  • reduce anaesthetic depth

- IPPV

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8
Q

Hypoxaemia definition

A

low blood oxygen

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9
Q

SpO2 vs PaO2

A

SpO2: haemoglobin oxygen saturation as measured by a pulse oximeter

PaO2 partial pressure of oxygen in arterial blood

as PaO2 decreases, SpO2 will decrease.

at SpO2 of 90% an animal will have PaO2 of 60mmHg (below this they are hypoxaemic!)

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10
Q

Causes of hypoaxaemia?

A
  • low inspired O2 (check equipment!)
  • hypoventilation*
  • VQ mismatch*
  • diffusion impairment (e.g. pulmonary oedema thickens barrier)
  • shunt

*most common

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11
Q

What is a closing capacity and what does it have to do with hypoaemia?

A

when you breath out maximally and approach your residual volume and the small airways in lower part of lungs begin to close.

collapse of airways causes ventilation perfusion mismatching and may lead to hypoxaemia

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12
Q

Why do alveoli collapse in the horse?

A

-dorsal recumbency is not a natural position for the horse

the added weight of viscera causes FRC causing atelectasis and approaches closing capacity

it is a big problem in the horse as the have a large dorsal lung area due to them being athletes (this is where perfusion occurs and if these areas collapse O2 can not cross over the barrier)

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13
Q

why does perfusion (Q) change?

A
  • gravity influences
  • reduced cardiac output due to decreased contractility /HR
  • vasodialtion (due to anaesthesia)
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14
Q

How to avoid VQ mismatch?

A
  • positioning
  • IPPV
  • give O2 AND air (N2 and O2) will prevent absorption atelectasis
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15
Q

Treatment of VQ mismatch

A

IPPV improves V

drugs can help with Q

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16
Q

Treatment of Q

A

B2 agonists: clenbuterol/salbutamol
bronchodilators but more likely help by improving vasodialtion
given by inhalation

17
Q

Treatment of V

A

inflating lungs to a higher pressure than normal for prolonged periods of time (8-12 seconds) can recruit lost alveoli

18
Q

What are the consequences of hypoxaemia?

A
  • reduced O2 delivery to tissues: particularly muscles may result in myopathy upon recovery
  • CCN and spinal cord malacia
  • if sever and persistent may lead up myocardial and cerebral dysfunction
19
Q

Hypotension defintion

A

low blood pressure

20
Q

What causes hypotension?

A

CO=HRxSV

low HR or a low SV

21
Q

What causes a low SV?

A
  • decreased preload
  • decreased contractility
  • increased afterload
22
Q

What causes a reduced preload?

A
  • dehydration
  • haemorrhage
  • positioning
  • IPPV (positive pressure/enclosed thorax/squashed VC/decreased VR)
23
Q

what causes reduced contractility?

A
  • drugs
  • arrhythmias
  • volatile agents
  • acidaemia
24
Q

what causes an increased afterload?

A

-arteriolar vasoconstriction
-increased resistance to outflow from the heart
-increased cardiac work
reduced CO
-drugs

25
Q

Treatment of hypotension?

A
  • check depth and lighten if possible
  • give IVFT
  • give drugs
26
Q

What drugs could be used to treat hypotension and why?

A

-antihcholinergics: improves HR
-inotropes (B1 agonists): increase contractility
dobutmine is drug of choice in horses: has B2 effects causing vasodilation in muscles and increases perfusion
-pressors (a1 agonists): increase TPR
phenylephrine is commonly used in anaesthesised patients

Horsey (14 decks)

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