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Author Topic: a question on dosing a spinal anesthetic  (Read 19927 times)

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nma

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a question on dosing a spinal anesthetic
« on: May 03, 2007, 07:18:11 AM »
At my institution, spinal anesthesia for C-sections are done with 1.4ml of 0.75% bupivicane, 200 ug intrathecal morphine, and 25ug Fentanyl for the average female. But I have seen different attendings (I'm a resident) change the 0.75% Bupivicane amount from 1.2 to 2.0 ml based on the patient's height. But none of my attendings can refer me to a chart or published document as to how to dose based on height (although they all seem to feel very strongly about how much to give to a particular patient). Where is it published how many milligrams of bupivicane you should give to a  patient of a particular height to get a particular level with your spinal? Similarly, how about for non -Ob spinals like a bilateral knee replacement?

I'd greatly appreciate your input.
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jafo1964

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Re: a question on dosing a spinal anesthetic
« Reply #1 on: May 05, 2007, 11:49:00 PM »
We use 0.5% hyperbaric bupivacaine 10 to 12.5 mg +/_ Fentanyl 25 mcg. This is the standard recommended dose in most literature. If your patient is short statured you may reduce the dose to 8 to 10 mg or stay with the same dose but concentrate on proper positoning of patient after block to limit its cephalad spread and also tackle the ensuing hypotension rapidly and aggressively. Some consultants get away with leeser amount of bupivacaine. I much rather would have a slightly higher block than a block that wears off requiring some form of IV supplementation. Since these pateints are potentially full stomach, supplementation takes the safety of RA technique away
With regard to B/L knee replacement its not the height of block that matters but the duration for which the block lasts in the operated site. A block upto L1 wears off faster than a block that starts from say T6. Keeping this in mind I would give about 17.5 mg of bupivacaine with 50 mcg of fentanyl. This should cover operations on the knee for a duration of almost 3 to 4 hours. But the problems are uncomfortable position  for the patient, shivering due to hypothermia, pain in unblocked upper back etc. I would much rather do a continuous epidural supplemented by a light GA. That should provide good analgesia extending into post-op as well as keep the patient quiet and comfortable.

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lovebailey2000

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Re: a question on dosing a spinal anesthetic
« Reply #2 on: May 12, 2007, 08:57:36 PM »
Hi

We dont use 0.75% bupivacaine in Obstetric patients as it is not favourite according to ASA! We use 0.5% Bupi. instead. The dose chart according to length for obs. patients is following-
             for pts. up to 150 cms. height- 8 mg 0.5 % Bupi. (Heavy)
            for pts. 150 to 170 cms. height- 10 mg 0.5 % Bupi.( Heavy)
             for pts. >170 cms. height       - 12 mg 0.5 % Bupi. (Heavy)

This dose schdule is given in an old edition of Wylie, which one I dont remember (as I read it in my residency). But I dont understand the use of both morphine and fentanyl in the same patient? Am I understood correct!

 Best of luck.
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rain

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Re: a question on dosing a spinal anesthetic
« Reply #3 on: May 21, 2007, 04:13:37 AM »
At first -  http://www.medana.unibas.ch/eng/amnesix1/obst_5a.htm (only for SC).
Second - based on the patient's height?  But what about patientís weight?
The dosage may be change very much. Especially in obstetrics.
What are thoughts about it?
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yogenbhatt1

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Re: a question on dosing a spinal anesthetic
« Reply #4 on: May 25, 2007, 12:09:22 PM »
Hi,
It is right to adjust the dose of spinal as per the height of the patient. But weight? Does it really matter? The nerve roots of a pt of 50 kg and other of 100 kg will be of the same size, logically needing the same amount of the Spinal drug. Can more ppl throw light on the same?
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yogenbhatt1

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Re: a question on dosing a spinal anesthetic
« Reply #5 on: May 25, 2007, 12:13:52 PM »
Hi,
IN India we do not get 0.75 % Bupivacain. Only choice is 0.5 %. Our group uses only 2.2 ml of 0.5% as a protocol Only variation is allowed if a patient is very short or very tall. That is 1.8 to 2.5 ml as justified.
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marivic orellan

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Re: a question on dosing a spinal anesthetic
« Reply #6 on: July 05, 2007, 12:12:12 AM »
hi! in my experience, i have used as much as 15mg or 3cc of 0.5% bupivacaine +/- morphine in c-section. though, i've experienced a high spinal, it was manageable and it doesn't happen at all times. I usually give it for 30 sec. Also, loading is very important to avoid hypotension. I also have a good experience with tetracaine in 2cc D10 water. I experience less high spinal and less hypotension. I usually give 12mg or 1.2ml. but if the fundic height is bigger, i give only 10mg or 1cc.

i hope this will help you...
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buthayna

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Re: a question on dosing a spinal anesthetic
« Reply #7 on: July 08, 2007, 06:40:39 AM »
hello,

I think many factors are contributing to dosing of local anesthetic in c-section. the patient first of all should be comfortable with a block reaching T4. At the same time measures to prevent high spinal should be attempted; patient positioning, crystalloids preloading or/and prophylactic dose of ephedrine.

I personally found that there is alot of patient to patient response variation. the standard dosing of 8-12 mg of bupivacain seems to be associated with higher incidence of high spinal in our population "Bahrain". Parturents here seem to be more sensitive. I am not sure if it is related to hight, because most of patients hights range from 150-170 cm.

I've never had to use more than 10mg bupivacaine even for the tallest.

good luck

buthayna 
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Alireza

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Re: a question on dosing a spinal anesthetic
« Reply #8 on: July 14, 2007, 06:10:28 AM »
Hi every one,we do spinal anesthesia for c/s with 10-12mg hyper bar bupivacain in all of height &weight!
Yes,dose modification in relation with height& weight, not recommended. Although increasing the dose of spinal anesthetic increases block height, doses above 15 mg significantly increase the risk of complications and not recommended.
About drug concentration: blockade extent does not greatly affected by concentration,but the density of sensory block may be better with the 0.75% than the 0.5%.
Miller, page:2324
But we use 0.5%  probably because this form of drug  is available easily. ;)
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