BSA, IBW, and CrCl in amputees...need help

[mamapharmd]

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What is the BSA, IBW, and CrCl for a 74 YOF who had double below-the-knee amputations 10 years ago? 62 in. tall before amputations, 49 in. post-amputation. Usual weight is 157 lbs but recently lost down to 148 lbs. Serum Cr 1.2. I've never done this before so I'm just throwing out guesses here, but I get 1.38 m2 for BSA using DuBois & DuBois equation and taking off 18% for the amputations. I calculated the IBW using the pre-amputation height and then taking off 18%...gave me 41 kg. Now I'm stuck on CrCl...do I use the pre or post-amputation IBW to calculate?
Thanks for the help.

 

[bigpharmD]

What is the BSA, IBW, and CrCl for a 74 YOF who had double below-the-knee amputations 10 years ago? 62 in. tall before amputations, 49 in. post-amputation. Usual weight is 157 lbs but recently lost down to 148 lbs. Serum Cr 1.2. I've never done this before so I'm just throwing out guesses here, but I get 1.38 m2 for BSA using DuBois & DuBois equation and taking off 18% for the amputations. I calculated the IBW using the pre-amputation height and then taking off 18%...gave me 41 kg. Now I'm stuck on CrCl...do I use the pre or post-amputation IBW to calculate?
Thanks for the help.

personally i think there is NO way to accurately calculate renal function in a patient such as this...

 

[Praziquantel86]

Have you tried the Jelliffe method? It gives you a creatinine clearance independent of body weight.

Using Cockcroft-Gault, I would think that using the post-amputation body weight would overestime renal function.

 

[mamapharmd]

Just tried the Jellife method. It asks for height in inches over 5 ft, so do I use the pre-amputation height of 5'2"? Won't this overestimate also?

 

[bigpharmD]

Just tried the Jellife method. It asks for height in inches over 5 ft, so do I use the pre-amputation height of 5'2"? Won't this overestimate also?

exactly

 

[njac]

personally i think there is NO way to accurately calculate renal function in a patient such as this...

agreed. This is one of the challenges of pharmacokinetics - one of the ASHP listservs was full of discussion about this for a couple weeks last year, with lots of variation.

I did work with one pharmacist who was a huuuuuge fan of the Sanaka equation, but when I researched it further I could find only like 3 papers for it. Not sure if that's really enough data to use it universally.

 

[bigpharmD]

you might have to actually lay eyes on a patient like this to see their nutritional status etc...god forbid we do that

 

[Praziquantel86]

Just tried the Jellife method. It asks for height in inches over 5 ft, so do I use the pre-amputation height of 5'2"? Won't this overestimate also?

That would be a problem. Brings you back to square one pretty much.

I'm surprised that there isn't more information out there on this. You'd think that with all the diabetics requiring amputation someone would have come up with a somewhat accurate method of estimating renal function.

 

[rphello]

Here's information a preceptor gave me a couple of years ago. I have NOT had a chance to verify this, so if you decide to use this method, please do so responsibly.


Calculate lean body weight (LBW) based on the patient's pre-amputation height.

LBW (male) = 50kg + 2.3 (inches over 5 ft)
LBW (female) = 45.5kg + 2.3(inches over 5 ft)


Start with the LBW calculated from the patient's pre-amputation height. Then deduct a percentage depending on the extent of the amputation:

• Hand - Decrease LBW by 0.7%
• Forearm and hand - Decrease LBW by 2.3%
• Total arm - Decrease LBW by 4.9%
• Foot - Decrease LBW by 1.5%
• Calf and foot - Decrease LBW by 5.8%
• Total leg - Decrease LBW by 16%

If the patient's actual weight is less than the Amputee-Adjusted LBW (AALBW), then the patient is underweight and you should use the patient's current weight to calculate CrCl.

If the patient weighs more than the AALBW, then you should calculate the CrCl using the AALBW.

 

[WVUPharm2007]

Here's information a preceptor gave me a couple of years ago. I have NOT had a chance to verify this, so if you decide to use this method, please do so responsibly.


Calculate lean body weight (LBW) based on the patient's pre-amputation height.

LBW (male) = 50kg + 2.3 (inches over 5 ft)
LBW (female) = 45.5kg + 2.3(inches over 5 ft)


Start with the LBW calculated from the patient's pre-amputation height. Then deduct a percentage depending on the extent of the amputation:

• Hand - Decrease LBW by 0.7%
• Forearm and hand - Decrease LBW by 2.3%
• Total arm - Decrease LBW by 4.9%
• Foot - Decrease LBW by 1.5%
• Calf and foot - Decrease LBW by 5.8%
• Total leg - Decrease LBW by 16%

If the patient's actual weight is less than the Amputee-Adjusted LBW (AALBW), then the patient is underweight and you should use the patient's current weight to calculate CrCl.

If the patient weighs more than the AALBW, then you should calculate the CrCl using the AALBW.

Huh. Never seen anything like that before. Interesting.

 

[Vitamin K]

Here's information a preceptor gave me a couple of years ago. I have NOT had a chance to verify this, so if you decide to use this method, please do so responsibly.


Calculate lean body weight (LBW) based on the patient's pre-amputation height.

LBW (male) = 50kg + 2.3 (inches over 5 ft)
LBW (female) = 45.5kg + 2.3(inches over 5 ft)


Start with the LBW calculated from the patient's pre-amputation height. Then deduct a percentage depending on the extent of the amputation:

• Hand - Decrease LBW by 0.7%
• Forearm and hand - Decrease LBW by 2.3%
• Total arm - Decrease LBW by 4.9%
• Foot - Decrease LBW by 1.5%
• Calf and foot - Decrease LBW by 5.8%
• Total leg - Decrease LBW by 16%

If the patient's actual weight is less than the Amputee-Adjusted LBW (AALBW), then the patient is underweight and you should use the patient's current weight to calculate CrCl.

If the patient weighs more than the AALBW, then you should calculate the CrCl using the AALBW.

That's the same information that I have.