Amputee Calculator Info

It seems obvious special considerations should be made for dosing chemotherapy in amputees. However, there is a shortage of evidence based knowledge to help guide practitioners on how to best accomplish this. One previously popular solution was an unreferenced excel spreadsheet that has since been removed from the web.

Reviewing published data didn’t yield much. The reference that seems the most useful was published in 1984: AJHP 1984

BSA and body weight do not correspond directly, so calculating a BSA simply using amputated weight will be inaccurate. To most accurately determine an amputee’s BSA, one must first determine the patient’s unamputated BSA, then remove the amputated limbs from the total. To determine this unamputated BSA, the unamputated height and weight must be known, making it necessary to add back the missing limbs’ weight. There does not seem to be a consensus on what proportion of body weight limbs make up, and the extent of the amputation may not align with a simple definition. A summary of literature can be found here: Limb Proportions

How Dr. K’s Amputee BSA calculator works:

User enters pre-amputation height, amputated weight and chooses all missing limbs.

The calculator will determine the non-amputated weight based on the amputated weight and the extend of the amputations. The percentage of body mass is used as follows: Foot 1.35%, at the knee 6.2%, at the hip 18%, hand 0.6%, at elbow 2.25%, at shoulder 5%. These numbers are roughly interpolated from the information provided at the LimbProportions link above.

The calculator then determines a non-amputated BSA based on the Haycock formula, as the Haycock formula seems to be preferred in the Colangelo article.

Next, the amputated BSA is determined by removing the percentage of lost BSA based on Table 2 in the Colangelo article. This table offers a separate equation for each body part based on the linear regression analysis of the measured data. The calculator will use the complete equation as offered.

Finally, the user is offered the opportunity to determine a BSA based dose for the patient.

In sum, there is no standard solution. The Colangelo article seems to have the best data for estimating the BSA in amputees and in fact has an even bigger n (42) than the Dubois (33) and the Haycock (19) papers for determining BSA in non-amputees. While this calculator is based on the best evidence available, the information obtained is only an estimate and ultimately the clinician must decide what adjustments should be made to best meet the patient’s needs.