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Aneasthesia > Intraoperative Support and Care > Flashcards

Intraoperative Support and Care Flashcards

17.2.14

0
Q

What are the two main forms of side effects associated with anaesthesia? Give examples of the latter.

A
  1. Cardiovascular and respiratory depression

2. Obtunded homeostatic mechanisms: baroreceptor reflex, hypoxic pulmonary vasoconstriction, thermal regulation

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1
Q

Define Homeostasis

A

The ability of an animal to maintain physiological stability in the face of constantly changing environmental factors which may be internal or external

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2
Q

In which species is cardiovascular and respiratory depression most marked?

A

Horses

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3
Q

What factors influence the extent to which homeostatic mechanisms are Obtunded during anaesthesia?

A

Depth, drugs used, underlying health status

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4
Q

What is the hypoxic pulmonary vasoconstriction reflex?

A

Blood diverted to oxygenated areas of the lungs (cf. all other organs in the body.)

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5
Q

Outline three things to be aware of regarding the general care of an anaesthetised animal.

A
  1. Positioning - especially thin and arthritic animals. Minimise ischemia to extremities.
  2. Nursing care - moving the animal carefully etc.
  3. Eye and tongue moistening
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6
Q

What physiological variables can be measured during anaesthesia?

A
  • breathing: rate, depth, character
  • heart: rate and rhythm
  • pulse: rate, rhythm, sync with heart beat?
  • blood pressure: arterial and central venous
  • haemoglobin oxygen saturation (pulse oximetry)
  • inspired/expired gas concentrations.
  • temperature: core and periphery
  • urine output and specific gravity *
  • blood: haematology (PCV, Hb, TB, platelets, coag times) biochem, electrolytes, blood gases (arterial and venous) *
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7
Q
  • why is urine output an unreliable variable to measure during surgery?
A

^ADH leads to vUrine output (something to do with drugs?)

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8
Q

*In which type of surgeries are blood has analyses particularly useful?

A

Chest surgeries

Equine surgery

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9
Q

In blood transfusions, why may electrolyte imbalances occur?

A

Citrate anticoagulant is also transfused - this binds with Ca2+ -> v[Ca2+]

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10
Q

What is the main aim of anaesthesia? How is this calculated?

A

Maintain tissue oxygen delivery.

Oxygen delivery = arterial oxygen content x cardiac output

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11
Q

What basic parameters should you check if experiencing difficulties?

A

A airway
B breathing
C circulation

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12
Q

When may respiratory support be required?

A

Maintain blood oxygen content by avoiding

  • hypoventilation
  • hypoxeamia
  • hypercapnia
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13
Q

Define hypoxeamia.

A

Arterial PO2 < 60mmHg

SpO2 < 90%

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14
Q

What may cause hypoxeamia?

A 
vFiO2
Hypoventilation 
V/Q mismatch 
CV depression 
Anaemia (does NOT affect PO2/SpO2, therefore hypoxia NOT hypoxeamia) 
Increased O2 demand eg. Pyrexia or ^BMR
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15
Q

Define hypercapnia.

A

Blood CO2 should be 35-45mmHg

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16
Q

What may cause hypercapnia?

A

Hypoventilation
Rebreathing exhaled gas
^BMR
V/Q mismatch(?)

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17
Q

What does hypercapnia lead to?

A 
Tachycardia
Hypertension
Cardiac arrythmias
Increased intracranial pressure 
CV depression at very high levels 
Respiratory acidosis
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18
Q

How can cases of hypercapnia and hypoxeamia be treated?

A 
Check anaesthetic depth isn't too deep 
Check airway 
Increase FiO2 if possible 
Ensure no rebreathing 
Ventilate using IPPV *
Consider using albuterol (Ventolin) in horses (bronchodilator)
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19
Q

What is IPPV?

A

Intermittent positive pressure ventilation

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20
Q

What causes inspiration and expiration?

A

INTRAPLEURAL PRESSURE REMAINS NEGATIVE THROUGHOUT THE CYCLE# *

Inspiration: expansion of the thorax generates negative intrapleural pressure
Expiration: intrapleural pressure rises as thorax contracts

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21
Q
  • why is negative thoracic pressure necessary?
A

Thoracic pump and cardiac output normal function

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22
Q

What are the negative effects of IPPV?

A

Intrapleural pressure remains > 0 throughout cycle

Decreased venous return through thoracic pump -> vCO *

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23
Q
  • In which scenarios are the negative effects of IPPV worst?
A

High pressures/long inspiratory times
Hypovoleamia
Heart failure

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24
Q

What are the guideline values for IPPV?

A

Tidal volume: 10-15ml/kg
Rate: 10-12 breaths/min
Inspiratory:expiratory ratio (I:E) 1:2 or 1:3
End tidal CO2 35-45mmHg
Peak inspiratory pressure (PIP): <5cmH2O*

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25
Q
  • when is PEEP used?
A

During thoracotomy

To prevent atelectasis

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26
Q

What measure is used in lieu of CO?

A

Blood pressure

27
Q

What factors may reduce CO?

A

Extremes of HR
Disturbance of rhythm
Poor SV: Low preload (poor ventricular filling)/poor myocardial contractility/High after load (high vascular resistance)

28
Q

What order should CV support be administered?

A
  1. Attend problems with HR/rhythm
  2. Treat underlying hypovoleamia/hypotension
    - reduce depth of anaesthesia
    - give IV fluids (bolus if necessary)
    - inotropes/vasopressors
29
Q

What effect do most anaesthetic agents have on vascular tone?

A

Vasodilators

30
Q

Define bradycardia

A

SA: <26bpm

31
Q

Which heart rate irregularity is most common during anaesthesia?

A

Bradycardia

33
Q

What may cause bradycardia?

A

High vagal tone (esp. If pulling something in abdomen)
Electrolyte and acid/base disturbance esp ^K+
Hypothermia -> vBMR
Drugs (opioids - mu ag; a2 ag)
Response to hypertension
Bradyarrythmias

34
Q

How can bradycardia and bradyarrythmias be treated?

A

Check monitored parameters and anaesthetic depth
Decrease a2 age as they cause bradycardia
Raised intracranial pressure can be a cause - BEWARE!
Anticholinergics to ^HR
eg. atropine 0.02-0.04mg/kg IV
eg. glycopyrrolate 0.005-0.01mg/kg IV

35
Q

Define tachycardia

A

Smallies HR>180

Equine HR>50bpm

36
Q

Outline causes of tachycardia during anaesthesia.

A 
^catecholamines*
hyperthermia (rare)
aneamia
drugs (sympathomimetics/parasympatholytics)
tachyarrhythmias
37
Q

*What may cause an increase in levels of circulating catecholamines? Which is most common and how may it be rectified?

A

Pain
Hypoxia, hypercapnia
Hypotension, hypovoleamia - most common eg. due to dehydration, give fluids, as a bolus if necessary

38
Q

How are tachycardia or tachyarrythmias treated?

A

Check monitored parameters
Check anaesthetic depth
Rule out/treat underlying cause

39
Q

What are the two types of SV arrythmias?

A
  1. AV block - usually secondary, especially seen with a2 ags (^BP->vHR, baroreceptor response) define cause if possible, give atropine or glycopyrrolate.
  2. Atrial fibrillation (unusual)
40
Q

What will be seen on the capnograph if the heart stops?

A

Decreases due to lack of CO2 to remove.

41
Q

In what two ways may ventricular arrythmias occur?

A

Singly or in runs

Ventricular tachycardia - may be paroxysmal

42
Q

When would ventricular arrhythmias be treated?

A

Determine cause and treat it (eg. Hypercapnia/hypoxia/electrolyte imbalance)
Treat if heamodynamically significant *

43
Q

*How can heamodynamic problems during anaesthesia be diagnosed?

A

Pulse rate and quality
Blood pressure
SpO2, mucous membrane colour and CRT

44
Q

What are ventricular arrhythmias commonly associated with?

A

Splenic or liver masses

45
Q

Which drug is used to treat ventricular arrhythmias? Dosage?

A

Lidocaine IV
Dog and Horse: 2-4mg/kg slow bolus
Cat: 0.25-0.75mg/kg bolus
Followed by CRI at 10-100microg/kg/min

46
Q

What type of fluids are commonly given during anaesthesia? Why?

A

Crystalloid

Relative hypovoleamia

47
Q

What is the most common crystalloid fluid given during anaesthesia? Why? How is it given and what is the dosage?

A

CSL (Compound Sodium Lactate)
Because it is ‘balanced’
~5ml/kg/hr
In an emergency - rapid bolus of 5-10ml/kg

48
Q

When are colloids given?

A 
Total Protein (TP) <35g/l 
If better intravascular filling is required
49
Q

What are the 6 types of fluid potentially given during anaesthesia?

A 
CSL
Colloids
Plasma
Fresh Whole Blood
Packed Red Blood Cells (PRBC)
Human Serum Albumin (HSA)
50
Q

When would plasma be given?

A

Same reasons as colloids

If clotting factors are required

51
Q

What is the average blood volume of a dog? Cat?

A

Dog: 80-90ml/kg
Cat:60-70ml/kg

52
Q

What fluids should be given if >10% total blood volume has been lost?

A

Crystalloid

53
Q

What fluids should be given if 10-25% total blood volume has been lost?

54
Q

What fluids should be given if >25% total blood volume has been lost?

55
Q

When would blood or PRBCs be necessary?

A

PCV<10g/dl

56
Q

What are the two most common inotropic drugs used in a) SA and b) Equine anaesthesia?

A

SA: Dopamine
Eq: Dobutamine

57
Q

Why is dopamine not used in horses?

A

Causes tachycardia

58
Q

What receptors does dopamine act on?

A

DA receptors at LOW concentration
b1 receptors at MEDIUM concentration
a1 receptors at HIGH concentration

59
Q

What receptors does dobutamine act on?

A

Mainly b1

a1 and b1 in peripheral vasculature tend to cancel out -> + inotropic effect, with little effect on vascular resistance

60
Q

Why may dobutamine be better than dopamine?

A

Mild chronotropic effects

Less arrythmogenic than dopamine

61
Q

What dose is dobutamine given at?

A

0.5-10 microg/kg/min

62
Q

What are the secondary effects of hypothermia?

A 
Reduced requirement for anaesthetics* 
Pharmacokinetics and pharmacodynamics of drugs altered -> prolonged recovery 
^Clotting time -> ^blood loss 
Shivering -> ^O2 demand in recovery 
Risk of surgical wound infections
Unpleasant!
63
Q

*How much is MAC reduced for every degree C reduction in body temperature?

64
Q

How may hypothermia be prevented during anaesthesia?

A 
Rebreathing circuits 
Heat and moisture exchangers (HMEs) 
Warm IV fluids
Bubble wrap/foil blankets/leg wraps/heated water blankets/warm air blowers
Warm room
Warm lavage of body cavities
65
Q

What is the Cushing reflex?

A

Hypertensive
Bradycardic
Breathing changes if not ventilated
Indicative of impending DEATH - attempt to maintain perfusion.
Due to medullary compression with increased intracranial pressure (due to mass in head etc.)

66
Q

What can increased ICP (Intracranial Pressure) cause?

A

Cushing reflex - Bradycardia with hypertension, and respiratory changes if not ventilated.

67
Q

How can increased ICP be treated?

A

Hyperventilate as an emergency measure
Mannitol - osmotic effects reduce blood viscosity, improving flow and O2 delivery, and also remove fluid from brain tissue
Hypertonic saline
Furosemide (~synergistic with mannitol)

Aneasthesia (11 decks)

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