MedStudentt
Badges: 10
Rep:
?
#1
Report Thread starter 1 month ago
#1
Hi,

so I have the Prescribing exam coming up and I'm struggling to understand when K is given with NaCl as KCL 0.3% for example or when it's prescribed as mmol's e.g.
1000mls 0.9% NaCl with 10mmol of K over 4 hours, for example?

I really struggle with fluids so would appreciate anyone explaining this to me in dummy style :P
0
reply
macpatgh-Sheldon
Badges: 20
Rep:
?
#2
Report 1 month ago
#2
Hi,
Is this not mathematics in medicine? From an empirical viewpoint [you mentioned "dummy style"!], and apologies cos you probs know this like the back of your hand,
BUT:
If I remember right the mass number of K is 40 [Na is 23 isn't it? - sry too tired r n tyo google it], so taking your example of 10 mmoles of K would be equivalent to 10 X 40 mg per litre = 400 mg/L - as the density of water is unity [it is the standard] this equates to 400mg/kg [one litre of water weighs 1kg] which is 0.4g/kg OR 0.0004kg/kg i.e. 4/10000 w/w [weight in weight] so 4/10000 X 100 % w./w = 0.04% w/w.

I would think it will depend on the degree of dehydration of the patient, the serum K+ level and oc you want to administer a solution that is equi-osmolar to plasma to avoid either oedema or cytolysis.

I think we need help from current practising clinicians - calling ecolier OR Jpw1097??

Sorry if this confuses you more!
M
0
reply
Jpw1097
Badges: 18
Rep:
?
#3
Report 1 month ago
#3
(Original post by MedStudentt)
Hi,

so I have the Prescribing exam coming up and I'm struggling to understand when K is given with NaCl as KCL 0.3% for example or when it's prescribed as mmol's e.g.
1000mls 0.9% NaCl with 10mmol of K over 4 hours, for example?

I really struggle with fluids so would appreciate anyone explaining this to me in dummy style :P
As you are probably aware, replacement fluids should be 1 mmol/kg/day Na, K, Cl; 25-30 ml/kg/day water and 50-100 g/day glucose.
There are premade forms of 0.9% saline, 5% dextrose, etc. that have 20 mmol or 40 mmol already added. 0.3% KCl contains 40 mmol/L K, 0.15% contains 20 mmol/L, however, the bag is usually written as 20 or 40 mmol rather than 0.3%.

An average 70 kg man will need 1750-2100 ml water; 70 mmol Na, K, Cl; and 50-100 g glucose. Therefore, a fluid regimen may be 1 bag 1L 5% dextrose with 40 mmol K over 8 hours; 1 bag 500 ml 0.9% NaCl with 20 mmol K over 8 hours; 1 bag 500 ml 5% dextrose with 20 mmol K over 8 hours.
In total, the patient would have received 2L water, 77 mmol Na, 80 mmol K and 100g glucose, in line with the daily requirements. However, if the patient has a K deficit then they will need more. If a patient has low K, you may want to give 40 mmol K over 4 hours (10 mmol/hour is the maximum rate of K infusion without ECG monitoring). Realistically you will be checking U&Es regularly and adjusting accordingly.

By the way, I am also a medical student so don't take what I say as gospel, there are plenty of doctors on tsr who will have a better idea, but I think I have a relatively good grasp of fluids.
0
reply
MedStudentt
Badges: 10
Rep:
?
#4
Report Thread starter 1 month ago
#4
(Original post by Jpw1097)
As you are probably aware, replacement fluids should be 1 mmol/kg/day Na, K, Cl; 25-30 ml/kg/day water and 50-100 g/day glucose.
There are premade forms of 0.9% saline, 5% dextrose, etc. that have 20 mmol or 40 mmol already added. 0.3% KCl contains 40 mmol/L K, 0.15% contains 20 mmol/L, however, the bag is usually written as 20 or 40 mmol rather than 0.3%.

An average 70 kg man will need 1750-2100 ml water; 70 mmol Na, K, Cl; and 50-100 g glucose. Therefore, a fluid regimen may be 1 bag 1L 5% dextrose with 40 mmol K over 8 hours; 1 bag 500 ml 0.9% NaCl with 20 mmol K over 8 hours; 1 bag 500 ml 5% dextrose with 20 mmol K over 8 hours.
In total, the patient would have received 2L water, 77 mmol Na, 80 mmol K and 100g glucose, in line with the daily requirements. However, if the patient has a K deficit then they will need more. If a patient has low K, you may want to give 40 mmol K over 4 hours (10 mmol/hour is the maximum rate of K infusion without ECG monitoring). Realistically you will be checking U&Es regularly and adjusting accordingly.

By the way, I am also a medical student so don't take what I say as gospel, there are plenty of doctors on tsr who will have a better idea, but I think I have a relatively good grasp of fluids.
Incredibly helpful, thank you! Do u have any resources that you used to understand?
0
reply
Jpw1097
Badges: 18
Rep:
?
#5
Report 1 month ago
#5
(Original post by MedStudentt)
Incredibly helpful, thank you! Do u have any resources that you used to understand?
No worries. Try these:
https://geekymedics.com/intravenous-...ribing-adults/
https://teachmesurgery.com/periopera...id-management/
https://oscestop.com/Adult%20IV%20Fluids.pdf
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Back
to top
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

Which of these would you use to help with making uni decisions?

Webinars (62)
12.7%
Virtual campus tours/open days (114)
23.36%
Live streaming events (44)
9.02%
Online AMAs/guest lectures (47)
9.63%
A uni comparison tool (111)
22.75%
An in-person event when available (110)
22.54%

Watched Threads

View All
Latest
My Feed