Critical Patient Monitoring

Question 1

What does pulse oximetry measure?

Answer 1

• Displays percentage oxygen saturation of haemoglobin

Question 2

How useful is pulse oximetry in critical patients?

Answer 2

• In critical patients unfortunately the least useful monitors we have
• Gives us no idea of the total amount of haemoglobin or total oxygen saturation in the blood

Question 3

Accuracy of pulse oximetry is affected by?

Answer 3

• poor circulation (common in critical patients)
  
  • hypovolaemia
• ambient light
  
  • strip lights affect the accuracy
• movement of the probe
  
  • e.g. if the animal is being ventilated

Question 4

Tachycardia (sinus) may be the result of…?

Answer 4

• Nociception
• Hypercapnia
• Hypovolaemia
• Hypokalaemia
• etc.

Question 5

What does capnography measure?

Answer 5

• Carbon dioxide measurement
• Conveys information relating to both respiratory and cardiac function
• Probably the most useful monitoring tool - info about alveolar ventilation and cardiac function.

Question 6

How does hyper- and hypoventilation affect ETCO₂?

Answer 6

• Hyperventilation – Decreased ETCO₂
• Hypoventilation - Increased ETCO₂

Question 7

If you see a “shark fin” shape on the capnograph reading what does this mean?

Answer 7

• Endotracheal tube obstruction
• Replace tube

Question 8

Indirect methods of blood pressure measurement?

Answer 8

• Oscillometric (cuffs that inflate or deflate which give you mean diastolic and systolic)
• Doppler (gives you systolic in theory)

Question 9

Direct methods of blood pressure measurement?

Answer 9

• Direct arterial pressure via an arterial cannula “gold standard”
• Usually placed in the dorsal pedal artery

Question 10

How useful is blood pressure in determining organ perfusion?

Answer 10

• Although blood pressure monitoring is important it does not tell us directly about organ perfusion
• Assessing urine output may be of equal value in determining renal perfusion
  
  • Urinary catheter into critical patients to monitor this
  • Aim for 1-2ml/kg/hr intraoperatively
    
    • Showing that the kidneys are being perfused enough to function

Question 11

Causes of decreased blood pressure?

Answer 11

• Intravascular fluid loss (haemorrhage, third space losses)
• Failing myocardial function
• Sepsis
• Relative hypovolaemia (vasodilation – drugs/sepsis)

Question 12

How would you treat a hypothermic patient with bradycardia and low blood pressure?

Answer 12

Anticholinergic treatment (atropine or glycopyrrlate) and warming to raise heart rate and subsequently blood pressure

Question 13

How would you treat a septic patient with tachycardia but poor blood pressure?

Answer 13

• Intravenous fluid therapy to improve status
• Vasodilated and relatively hypovolaemic so if you gave atropine etc. to further increase the work of the heart it would probably arrest
• Patients with advanced sepsis require pressor support
  
  • Noradrenaline
  • Dopamine
  • Phenylephrine

Question 14

What is Central Venous Pressure (CVP) a measure of?

Answer 14

• Informs us about cardiac preload
• Used as an approximation of right atrial filling pressure (late guide)
• Acts as a guide to correct fluid therapy (late guide)
• Not used much in practice

Question 15

Ian Self’s preferential list of monitoring equipment?

Answer 15

• In order;
  
  • Dedicated anaesthetist
  • Capnograph
  • Direct blood pressure/dynamic indices
  • ECG
  • Central venous pressure (probably not now)
  • Pulse oximeter
  • Cardiac output