We are interested in estimating blood volume in healthy individuals. Since 1962 the "standard" formula used to predict blood volume is that presented by Nadler (Surgery 1962;51:224-32). This formula, however, has been criticized as being inaccurate for current estimates since today's populations have far more adiposity. and fat tissue requires less vascularization. Thus , the argument is that for heavy, short people particularly their blood volumes are over estimated. This is important when trying to determine what the appropriate volumes should be for say donating blood or blood products. Has anyone seen new formulas or modifications to the Nadler formula to deal with this problem?
Thanks.
Blood volume (BV) can be estimated by calculating its volume provided the hematocrit (HC) and the plasma volume (PV) as follows
BV = PV
1-HC
Alternatively it can be done using commercial available diagnostic machine BVA – 100 and it is said to be 98% accurate in measuring RED Blood cell and Plasma
1. I am not convinced that "accurately" and "estimate" should be used in the same sentence.
2. No, I haven't seen any new formulas for this particular problem, but it is an issue similar to predicting plasma concentrations of drugs when using exponential-based algorithms in syringe pumps. It relates to the ratio of fat to total body weight. There have been a number of ways of dealing with this that are accessible to internet search.
However, it boils down to how "accurate" you want your "estimate" to be. Bearing in mind that your lab blood Hb can be as much as 10 to 15% inaccurate, there doesn't seem to be a lot of point in obsessing about more accurate estimates of blood volume.
If you're stuck in a rural clinic and you can only measure height and weight, and the latter is going to give you a misleading answer, you're really only left with height.
What you are sort of saying is that blood volume does not relate to weight when the body weight is outside the "ideal" range of body weight, which varies with height. What you need to use to calculate blood volume outside this range is not the patient's actual weight, but what it should be.
Just roughly eyeballing the ideal body weight charts based on the Quetelet formula, and extracting the weight ranges associated with "normal" BMIs in the range of 18.5 to 25 (heights 1.5 to 2 m) also gives you an average weight within that range. Using these average weights with the Nadler formula gives you the average blood volume for each height. Linear regression on the data (R2 0.9996) gives you an approximate relationship of (6100 x body height in metres) - 5500.
Applying the process to the outer ranges of normality for weight suggests that using the average weight for each height will be =/- 15% accurate for the range.
Is that an "accurate" enough "estimate" for you?.
Obes Surg. 2006 Jun;16(6):773-6.
Estimating blood volume in obese and morbidly obese patients.
Here is a paper I wrote that is relevant to this question:
Friesen JHP. Lean-scaled weight can be used to estimate blood volume for obese patients. Can J Anesth. 2014 Nov;61(11):1059–60.
http://www.ncbi.nlm.nih.gov/pubmed/25091297
I don't think a really accurate estimation is possible in the clinical situation. but here is an app that takes into account both obesity and age:
Download BigSleep for iPhone and iPad from the App Store
Download BigSleep for Android from the Google Play Store
Online app and updates: www.bigsleep.altervista.org
This is limited by the large variability of individuals in medicine. Blood volume is ~7-8% of body weight or according to the Nadler formula. However, this should be corrected by clinical judgement e.g. for sex, obese, or athletic subjects.
Corrections of blood volume calculations for athletic subjects are available in: Apheresis: Basic Principles, Practical Conciderations and Clinical Applications,slides 54-58/77, by Schwartz J & Padmanabhan A, presented at the Review Session, ASFA Annual meeting, Scottsdale, Arizona, June 2011.
According to the well-presented information in the BigSleep app mentioned by Dr. Friesen, the Lemmens et al. equation is
Blood volume index (mL/kg body weight) = 70 / SQRT(BMI / 22) for adult males and
65 / SQRT(BMI / 22) for adult females. These are from the paper cited by Dr. Strauss.
Since muscle apparently contains 4 to 8 times more blood per kg than adipose (slide 58 of the presentation cited by Dr. Evers), these formulas seem to assume that all increases in BMI are due to fat. Has anyone used body composition data from DEXA to estimate blood volume?
In fact this formula is consistent with blood volume being proportional to lean body weight. See: Friesen JHP. Lean-scaled weight can be used to estimate blood volume for obese patients. Can J Anaesth. 2014 Nov;61(11):1059–60.
It corresponds to clinical experience, that there may be problems in obese plasma donors if the volume of separated plasma (including anticoagulant) is programmed at 860 ml. Then we have to reduce it to 760 ml. In Germany we use in routine no formulas or nomograms for calculating the volume of separated plasma, but the body weight and the medical presciption.
also, can calculate FFM and TBW from BMI and weight
! see Janmahasatian et al Quantification of Lean Bodyweight
! Clin Pharmacokinet 2005; 44 (10): 1051-1065
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