# Allowable Blood Loss (ABL) Calculator

Uses patient weight, ABV and haematocrit to estimate the lost blood allowance during surgery.

In the text below the calculator there is more information about the blood loss compensation.

The allowable blood loss calculator estimates the ABL based on patient data in order to facilitate blood provision during surgery and other procedures.

It accounts for the type of patient (with a choice from premature neonate to adult man or woman), patient weight, initial and final haematocrit and average blood volume.

Please note that the ABV values used for each type of patient can be found in the text below the tool.

The first step in finding ABL is retrieving the estimated blood volume:

■ EBV in mL = Weight in kg x Average blood volume in mL/kg

EBV is then multiplied by hematocrit values, to determine the allowable blood loss:

■ ABL = (EBV x (Hi-Hf))/Hi

Where:

- Hi – initial hematocrit;

- Hf – final hematocrit.

Patient
Weight
Initial hematocrit
Final hematocrit
Average blood volume (ABV)
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## Send Us Your Feedback

Steps on how to print your input & results:

1. Fill in the calculator/tool with your values and/or your answer choices and press Calculate.

2. Then you can click on the Print button to open a PDF in a separate window with the inputs and results. You can further save the PDF or print it.

Please note that once you have closed the PDF you need to click on the Calculate button before you try opening it again, otherwise the input and/or results may not appear in the pdf.

## ABL variables and formula

This ABL calculator determines the allowance for blood loss during surgery and other invasive procedures. The variables used are explained in the table below:

 Variable Description Type of patient Premature neonates Full term neonate Infant Adult woman Adult man Weight Patient weight in either kg or lbs Initial hematocrit Percentage blood composition before surgery Final hematocrit Percentage blood composition expected after surgery Average blood volume Quantity of blood in mL per kg (per guidelines) Premature neonates (95) Full term neonate (85) Infant (80) Adult woman (65) Adult man (75)

Allowable blood loss is calculated after the Gross formula and can provide assistance in regard to haemorrhage management in both internal and external blood loss.

There are two steps to perform when calculating ABL:

■ First step is to establish the estimated blood volume:

EBV in mL = Weight in kg x Average blood volume in mL/kg

■ Second step is to use the EBV and haematocrit values to determine the allowable blood loss:

ABL = (EBV x (Hi-Hf))/Hi

Where:

- Hi – initial hematocrit;

- Hf – final hematocrit.

When the maximum ABL value is reached, haemorrhage complication become increasingly more likely.

## Blood loss compensation

Using an accutate recording of blood loss means that replacement therapy (crystalloid or colloid solutions) can be started in a timely manner to reobtain normovolemia (normal intravascular volumes).

A haemoglobin between 7 and 10 mg/dL (which corresponds to a haematocrit of 21-30%) marks the threshold from which IV solutions are replaced with blood transfusions.

However, it is also important to note that in acute haemorrhage, haematocrit changes do not reflect the true extent of blood loss, for example 1000 mL blood loss only marks a 3% drop in Ht during the first hour.

ABL comes to usage especially because in many clinical settings (e.g. obstetrics), blood loss is underestimated.

The following introduces the main stages of blood loss and the associated blood pressure changes:

 Stage Blood loss Blood pressure changes Compensation BL 500 – 1,000 mL No change in BP Mild BL 1,000 – 1,5000 mL Slight fall in BP (to 80-100 mmHg) Moderate BL 1,500 – 2,000 mL Marked fall in BP (to 70-80 mmHg) Severe BL More than 2,000 mL Profound fall in BP (to 50-70 mmHg)

## References

1. Hahn RG. Estimating allowable blood loss with correction for variations in blood volume. Acta Anaesthesiologica Scandinavica. 1989; 33(6), 508–512.

2. Iijima T, Brandstrup B, Rodhe P, Andrijauskas A, Svensencor CH. The maintenance and monitoring of perioperative blood volume. Perioper Med (Lond). 2013; 2(9).

3. Seigne R, Puri GD, Niraj G, Arun D, Chakravarty V, Aveek J, Chari P. Intraoperative blood transfusions. Oxford Journals, Medicine & Health BJA. 2004; 92(4).

Specialty: Hematology

System: Cardiovascular

Objective: Determination

Type: Calculator

No. Of Variables: 5

Abbreviation: ABL

Article By: Denise Nedea

Published On: May 16, 2017

Last Checked: May 16, 2017

Next Review: May 16, 2023