神仙、老虎、狗

Recognizing the degree of blood loss is critical in the trauma patient. The American College of Surgeons Advanced Trauma Life Support (ATLS) hemorrhagic shock classification links the amount of loss to expected physiologic responses in a healthy 70 kg patient. As total circulating volume accounts for approximately 7% of total body weight, this equals approximately five liters in the average 70 kg male patient.

Class : Volume loss up to 15% of total blood volume, approximately 750 mL. Heart rate is minimally elevated or normal. Typically, there is no change in blood pressure, pulse pressure, or respiratory rate.

Class : Volume loss from 15% to 30% of total blood volume, from 750 mL to 1500 mL. Heart rate and respiratory rate become elevated (100 BPM to 120 BPM, 20 RR to 24 RR). Pulse pressure begins to narrow, but systolic blood pressure may be unchanged to slightly decreased.

Class : Volume loss from 30% to 40% of total blood volume, from 1500 mL to 2000 mL. A significant drop in blood pressure and changes in mental status occurs. Heart rate and respiratory rate are significantly elevated (more than 120 BPM). Urine output declines. Capillary refill is delayed.

Class : Volume loss over 40% of total blood volume. Hypotension with narrow pulse pressure (less than 25 mmHg). Tachycardia becomes more pronounced (more than 120 BPM), and mental status becomes increasingly altered. Urine output is minimal or absent. Capillary refill is delayed.

While we'd all like it to be that easy, unfortunately, the classic stages of hemorrhagic shock are of limited clinical use because:

Like most medical/pharm calcs is based off a healthy 70kg male.

Differences in compensation for different types of injuries (blunt versus penetrating)

Age (blunted physiological responses in the elderly, rate dependant cardiac output in peds)

Comorbidities (patients with baseline hypertension may be functionally hypotensive with a systolic blood pressure of 110 mmHg!)

Medications (e.g. beta-blockade)

Therefore while the listed factors are important, like most things in medicine we need to take all the factors available into account and make a clinical call.