Estimating Blood Loss in a Trauma Patient Based on Vital Signs According to ATLS

Shock* in a trauma patient is almost always do to blood loss, either internal (hidden) bleeding or external (visible) bleeding.** And the treatment of shock due to blood loss is to stop the bleeding and give fluid (Ringer’s Lactate or Normal Saline) and/or blood products.

In the Advanced Trauma Life Support (ATLS) manual the following procedure is suggested***.

First estimate the patient’s normal blood volume before bleeding. For adults it is about 7% of body weight. You convert the person’s weight in pounds to weight in kilograms (kg) and then multiply that number by .07 (7). For obese patients use the ideal body weight formula to calculate the estimated blood volume.


150 lb man—150 lbs x 2.2 kg/lb = 70 kg (approx)

70 kg x .07 liters of blood/kg of body weight = 5 Liters (5 L or 5000 ml [milliliters]) of blood

So an average sized man has 5 liters (L) or 5000 milliliters (mL). These numbers are what we will use for our estimation of how much blood a person has lost based on his vital signs.

Based on the initial vital signs we estimate the amount of blood loss as Class I (up to 15% of blood volume lost), Class II (15% – 30% blood loss), Class III (30% – 40% blood loss), Class IV (more than 40% of blood loss.

For what follows, the volume of milliliters of blood loss estimate will be based on a patient weight of 70 kg.

Class I hemorrhage means up to 15% of blood volume lost (up to 750 mL).

Pulse rate less than 100, systolic blood pressure normal, pulse pressure**** normal, respiratory rate is 14 to 20, urine output is greater than 30 mL/hour, mental status is slightly anxious, and initial fluid replacement is crystalloid (Ringer’s Lactate or Normal Saline).

“For otherwise healthy patients, this amount of blood loss does not require replacement, because transcapillary refill and other compensatory mechanisms will restore blood volume within 24 hours, usually without the need for blood transfusion.”

Class II hemorrhage means from 15% to 30% blood volume lost (750 mL to 1500 mL).

Pulse rate is from 100 to 120, systolic blood pressure normal, pulse pressure decreased, respiratory rate is 20 to 30, urine output is 20 to 30 mL/hour, mental status is mildly anxious, and initial fluid replacementis crystalloid.

“Some patients in this category may eventually require blood transfusion, but most are stabalized initially with crystalloid solutions.”

Class III hemorrhage means from 30% to 40% blood volume loss (1500 mL to 2000 mL).

Pulse rate is from 120 to 140, systolic blood pressure is decreased, pulse pressure is decreased, respiratory rate is 30 to 40, urine output is 5 to 15 mL/hr, mental status is anxious and/or confused, fluid replacement is crystalloid and blood.

“Patients [with this amount of blood loss] will almost always present with the classic signs of inadequate perfusion, including marked tachycardia and tachypnea, significant change in mental status, and a measureable fall in systolic blood pressure”

Most of these patients will require blood and blood products with the decision to transfuse based on the patient’s response to the initial 1 to 2 liter crystalloid infusion.

It is urgent that the hemorrhage be stopped in these patients by emergency operation or by embolization.

Class IV hemorrhage means blood loss of greater than 40% (greater than 2000 mL).

The pulse rate is greater than 140, systolic blood pressure is decreased, pulse pressure is decreased, the respiratory rate is greater than 35, urine output is negligible, mental status is confused and/or lethargic, and these patients will require crystalloid and blood.

These patients are in immediate danger of death.

“Patients with class IV hemorrhage frequently require rapid transfusion and immediate surgical intervention.

In the next post, I’ll go over the ATLS recommendations for initial fluid therapy.

*The trauma patient in shock will have a number of signs including low blood pressure, rapid breathing, rapid heart rate and others as above. The term shock means that the body’s organs (brain, heart, muscle, etc.) are not getting enough blood and oxygen for normal function. If shock (inadequate blood flow and oxygen delivery) are not quickly reversed, the patient will suffer permanent damage or death.

**Although shock (usually manifested by low blood pressure) in trauma patients is by far most often caused by acute blood loss, there are other causes which must be looked for and treated if present: tension pneumothorax, cardiac tamponade, cardiogenic shock, neurogenic shock, and septic shock.

***Advanced Trauma Life Support Student Course Manual,9th ed, 2013, American College of Surgeons, pp. 68-70.

****Pulse pressure is the sytolic blood pressure (the higher blood pressure number) minus the diastolic blood pressure (the lower blood pressure number). If a person has a blood pressure of 120/80, then the pulse pressure is 40 (120 – 80).

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