Little et al 1995 - Preventable deaths

Question 1

Outline the contents of Little et al 1995

Answer 1

Published in the ‘Journal of Accident and Emergency Medicine’

Attempt to recognise and diagnose occult bleeding

Questions the previously held belief that elevated heart rate and low blood pressure were the main hallmarks of hypovolaemic shock - historical papers from WW1 and 2 which had already identified this

Goes on to discuss:
- Reflexes in response to haemorrhage
- Cardiovascular response to injury
- Cardiovascular response to combined haemorrhage and injury
- Role of endogenous opioids
- 5-Hydroxytryptamine and its none use
- Effects of ethanol
- Use of shock index
- Use of stroke distance

Concludes that using SI And SD will provide a useful means of detecting changes in cardiac output and therefore lead to a reduction in preventable trauma deaths

Question 2

Discuss the reflexes involved in haemorrhage as per Little et al 1995

Answer 2

Three reflexes:
1. arterial baroreceptors
- medio-adventitial arterial wall
- aortic arch and carotid sinus
- slow adapting
- during haemorrhage cause vagal activity to be withdraw and enhanced sympathetic activity
- leads to tachycardia and vasoconstriction
- prioritises brain perfusion over skeletal muscle
- kicks in at 10-15% blood loss

2. Activated Cardiac C-fibres
   - located in mainly in left ventricle
   - cause profound reflex bradycardia and reduced muscular and renal vascular resistance
   - bradycardia mediated by vagal efferent activity
   - may be protective to reduce cardiac workload when coronary blood flow is compromised
3. Arterial chemoreceptor reflex
   - in carotid and aortic bodies
   - sensitive to fall in oxygen, increase in CO2 and decrease in pH
   - produce hyperventilation, bradycardia and vasoconstriction
   - can off set the c-fibre mediated bradycardia
   - during PHEA could result in bradycardia

Question 3

Describe the cardiovascular response to ‘injury’

Answer 3

• intense sympathetic vasoconstriction can cause reduced blood flow to vital organs
• tachycardia
• baroreceptor response is impaired

Question 4

Describe the cardiovascular response to combined haemorrhage and injury

Answer 4

• Cardiovascular response to haemorrhage is attenuated by presence of tissue injury
• May be protective against the hypotensive effects of severe haemorrhage

Question 5

What is the role of endogenous opioids in the response to severe hypovolaemia?

Answer 5

Make it worse, naloxone seems to help
No one knows why

Question 6

What effect does ethanol have on the cardiovascular response to injury?

Answer 6

Exacerbate the injury induced reduction in baroreflex sensitivity

Question 7

What does figure 1 of the Little et al 1995 paper show?

Answer 7

Controlled venesection of a human volunteer over time.

Showing initial baroreflex followed by depressor reflex.

Baroreflex - rising TPR, HR as BP falls slightly along with RAP and CO
Depressor reflex - precipitous fall in TPR, HR and BP leads to faint

Question 8

What does figure 2 of Little et al 1995 paper show?

Answer 8

Who knows

Question 9

What does figure 3 of Little et al 1995 show?

Answer 9

A: shows that injury decreases the sensitivity of the baroreflex and resets it to be less pronouced
B: Shows reflex is less sensitive in the presence of injury

Question 10

What does figure 4 of little et al 1995 show?

Answer 10

Pathways whereby depressor reflex is inhibited by response to injury - unable to interpret

Question 11

What does figure 5 of little et al 1995 show?

Answer 11

Who knows