littleeggy
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Hi everyone, currently on a vascular surgery placement for my SSU (just at the beginning of my second year). Chatting to one of the anaesthetists, he was talking about giving an epidural to a patient causing a 'sympathetic nerve block' and he noted that this would cause increased peripheral circulation to the legs. I'm not quite sure I understand why this is. I thought the sympathetic system would cause peripheral vasodilation so surely if you are suppressing it, then it wouldn't increase peripheral circulation? Hmmmm. Please someone help to explain this!

I've found some sites talking about sympathetic nerve block and that it can cause increased peripheral circulation but nothing seems to explain why. Would appreciate any physiology insights, as this subject has me confused now... Thank you.


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carcinoma
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(Original post by littleeggy)
Hi everyone, currently on a vascular surgery placement for my SSU (just at the beginning of my second year). Chatting to one of the anaesthetists, he was talking about giving an epidural to a patient causing a 'sympathetic nerve block' and he noted that this would cause increased peripheral circulation to the legs. I'm not quite sure I understand why this is. I thought the sympathetic system would cause peripheral vasodilation so surely if you are suppressing it, then it wouldn't increase peripheral circulation? Hmmmm. Please someone help to explain this!

I've found some sites talking about sympathetic nerve block and that it can cause increased peripheral circulation but nothing seems to explain why. Would appreciate any physiology insights, as this subject has me confused now... Thank you.


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Sympathetic activation leads to constriction of arteries and arterioles which acts to increase peripheral vascular resistance. Hence a reduction in blood flow.

An epidural anaesthetic leads to loss of sympathetic tone below the level of the epidural, this therefore leads to unopposed parasympathetic activity, which causes dilation of the arteries and arterioles, reducing peripheral vascular resistance and hence increasing blood flow.

http://cvphysiology.com/Blood%20Pressure/BP009.htm


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Spencer Wells
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Just to slightly correct things - the parasympathetic activation does not decrease systemic vascular resistance - there are no parasympathetic nerve fibres running to blood vessels. Blocking sympathetic signals just blocks the resting motor tone of arterioles which is directly sympathetically mediated.
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littleeggy
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(Original post by carcinoma)
Sympathetic activation leads to constriction of arteries and arterioles which acts to increase peripheral vascular resistance. Hence a reduction in blood flow.

An epidural anaesthetic leads to loss of sympathetic tone below the level of the epidural, this therefore leads to unopposed parasympathetic activity, which causes dilation of the arteries and arterioles, reducing peripheral vascular resistance and hence increasing blood flow.

http://cvphysiology.com/Blood%20Pressure/BP009.htm


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Thank you so much to both of you. Carcinoma, I would give you another rep but looks like I've given you too many already.


(Original post by Spencer Wells)
Just to slightly correct things - the parasympathetic activation does not decrease systemic vascular resistance - there are no parasympathetic nerve fibres running to blood vessels. Blocking sympathetic signals just blocks the resting motor tone of arterioles which is directly sympathetically mediated.
Thank you, this is really helpful Spencer Wells.
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