Critical Care Monitoring: Lesson 08
Bradycardia
Objective: To enable you to anticipate and recognise bradycardia.
What conditions / situations do you associate with bradycardia?
Answer H1
Play video 8.1, it will stop at 8:32.
http://custos.co.nz/videos/Video8_1.mp4
What would you do at this point?
Answer H2
Fig 8.1 the same situation at 8:34
What has happened?
Answer H3
Fig 8.2 The same EBMe Screen with 'diagnostics' turned on
HT = hypotension, CR = Cushing response, DT = damped trace
Play video 8.3 The video will stop at 8:51
http://custos.co.nz/videos/Video8_3.mp4
What is going on?
Answer H4
The repeated need for vasopressor suggests hypovolaemia (absolute or relative). This
diagnosis occurs around 8:58, see below.
Fig 8.3 Hypovolaemia (HA) at 8:58
Note the speed of the change in heart rate at 8.51....it can happen very quickly.
What is the difference between absolute and relative hypovolaemia?
Answer H5
Play video 8.4 to see what happens.
http://custos.co.nz/videos/Video8_4.mp4
A major fall in heart rate can cause a fall in cardiac output; so not only is there bradycardia
and hypotension but also a decrease in EtCO2.
If the patient is awake the hypotension associated with the bradycardia can cause the patient
to feel nauseated; they may vomit. Without close monitoring this may be the earliest sign.
Cardiac standstill is possible.
Name two drugs that can be used to treat severe bradycardia that might progress to cardiac
arrest.
Answer H6
Untreated severe bradycardia can cause harm and should be detected early. Only by constant
vigilance and appropriate alarm settings will it be detected.
Answer H1
1. Fainting
2. Drugs can cause bradycardia; bolus doses (or infusions) of vasoconstrictors - for example
the pure alpha agents like metaraminol.
3. The oculocardiac reflex - traction on the eye, the manipulation of the zygomatic arch after
a fracture or even a wisdom tooth extraction - all stimulate the Trigeminal nerve which can
set off the reflex.
4. The Cushing Reflex - this is where an acute increase in intracranial pressure causes a
bradycardia with hypertension
5. The Bezold Jarisch reflex - this can occur during spinal anaesthesia when the blood pools
in the legs - this cause a central hypovolaemia that sets off the reflex
References for bradycardia
Bezold Jarisch: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2842957/
Oculocardiac reflex: http://www.ncbi.nlm.nih.gov/pubmed/1914059
Cushing reflex: http://bja.oxfordjournals.org/content/94/6/791.full
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Answer H2
The BP has fallen to 101 mmHg.
a vasoconstrictor?
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Wait?
Give vasoconstrictor? What might occur if you give
Answer H3
BP up, HR down, PV down.
This is a Cushing type response – cause - vasoconstrictor.
Also at this time there is a very small pulse pressure (180/150) - this small pulse pressure
suggests damping but maybe not.
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Answer H4
The blood pressure has stabilised but started to fall again at 8:47.
At 8:50 the BP was low again and more vasoconstrictor was given.
On this occasion the physiological changes were insufficient to generate an alert. See next
figure.
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Answer H5
Relative hypovolaemia is where there is no loss of blood volume.
Absolute hypovolaemia is where there is loss of blood volume, this may be actual blood, it
may be loss of plasma (burns) or it may be due to dehydration.
The vascular capacity is the space available for the blood in the cardiovascular system. Even
without loss of blood, if the vessels dilate the capacity to hold blood will increase so the
blood pressure will fall.
Consider two jugs of the same height. Pour 500ml into the narrow one, measure the height
(pressure). Now pour the 500 ml into the larger, wider jug, measure the height (pressure)
again, it will be lower. No liquid has been lost. This is relative hypovolaemia.
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Answer H6
Atropine
Adrenaline
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