From the Guidelines
Blood loss is determined through a combination of clinical assessment, laboratory tests, and quantitative estimates, with the severity classified into four classes based on the percentage of total blood volume lost, as outlined in the ATLS classification.
Clinical Assessment
Healthcare providers first evaluate visible bleeding, vital signs like blood pressure and heart rate, and symptoms such as dizziness or confusion.
- They assess the patient's physiology, anatomical injury pattern, and response to initial resuscitation, as recommended by the European guideline for the management of bleeding and coagulopathy following major trauma 1.
- The mechanism of injury is also an important factor in determining the extent of blood loss, with high-energy injuries producing greater damage to both the pelvis and organs 1.
Laboratory Tests
Laboratory tests, including complete blood count (CBC), are used to measure hemoglobin and hematocrit levels, which decrease with blood loss.
- For acute bleeding, serial measurements are taken to track changes over time 1.
- The hemoglobin level is an important factor in determining the need for blood transfusion, with most guidelines recommending a threshold of 7-8 g/dl for transfusion 1.
Quantitative Estimates
Quantitative estimates of blood loss are made by:
- Visual estimation of blood-soaked materials
- Weighing blood-soaked gauze (1 gram equals approximately 1 mL of blood)
- Measuring collected blood in suction containers
- In surgical settings, blood loss is calculated by weighing surgical sponges and measuring suction canister contents 1.
- For internal bleeding, imaging studies like ultrasound, CT scans, or MRI help locate and estimate blood volume 1.
Classification of Blood Loss
The severity of blood loss is classified into four classes based on the percentage of total blood volume lost, with:
- Class I being mild (<15%)
- Class II being moderate (15-30%)
- Class III being severe (30-40%)
- Class IV being life-threatening (>40%) 1. This comprehensive approach helps guide appropriate treatment decisions, including fluid resuscitation and blood transfusion requirements, with the goal of minimizing morbidity, mortality, and improving quality of life.
From the Research
Determining Blood Loss
To determine blood loss, several methods and factors can be considered, including:
- Mechanism of injury, base deficit, and blood lactate levels 2
- Central venous oxygen saturation and oxygen transport parameters 2
- Vital signs, although standard classifications and vital signs alone are inadequate for guiding therapy 2
- Continuously monitored photoplethysmography (PPG) and invasive arterial blood pressure (ABP) using machine-learning-based models 3
- Calculation of allowable blood loss using a programmable pocket calculator, taking into account blood volume, preoperative hemoglobin concentration, and hemodilution prior to surgery 4
Classification of Blood Loss
Blood loss can be classified into different categories, including:
- Acute blood loss, which is a common and challenging problem facing emergency physicians 2
- Massive transfusion, which requires the administration of crystalloids, colloids, and plasma-poor red cell concentrates to maintain normovolemia and oxygen supply 5
- Microvascular bleeding, which can be induced by impaired hemostasis and requires the timely administration of plasma and platelet concentrates 5
Estimating Blood Loss Volume
Estimating blood loss volume is crucial in clinical settings, and several methods can be used, including:
- Traditional hematocrit computation formulas, although these may have a high estimation error 3
- Machine-learning-based models using continuously monitored vital signs, such as PPG and ABP 3
- Calculation of allowable blood loss using a programmable pocket calculator 4
Considerations
When determining blood loss, it is essential to consider individual patient factors, such as: