How is blood loss estimated in a trauma patient?

From the Guidelines

Blood loss in trauma patients is most accurately estimated by combining multiple assessment methods, including vital signs, laboratory values, physical examination findings, and imaging studies, as recommended by the most recent European guideline on management of major bleeding and coagulopathy following trauma (1).

Estimation of Blood Loss

The estimation of blood loss in trauma patients is crucial for determining the severity of hemorrhage and guiding treatment. The Advanced Trauma Life Support (ATLS) classification system is commonly used to categorize blood loss into four classes based on percentage of blood volume lost: Class I (<15%), Class II (15-30%), Class III (30-40%), and Class IV (>40%) (1).

Clinical Assessment

Initial assessment relies on vital signs, with tachycardia, hypotension, and narrowed pulse pressure indicating significant hemorrhage (1). The Shock Index (SI), which is the ratio of heart rate to systolic blood pressure, can also be used to predict massive transfusion (MT) and emergent surgery (1).

Laboratory Values and Imaging Studies

Laboratory values, including hemoglobin, hematocrit, base deficit, and lactate levels, help assess the severity of hemorrhage, though initial hemoglobin may not reflect acute blood loss due to delayed hemodilution (1). Imaging studies like FAST ultrasound, CT scans, or diagnostic peritoneal lavage may be necessary for internal bleeding (1).

Recommendations

The most recent European guideline on management of major bleeding and coagulopathy following trauma (1) recommends a combination of clinical assessment, laboratory values, and imaging studies to estimate blood loss and guide treatment. This approach allows for early identification of bleeding sources, prompt measures to minimize blood loss, and restoration of tissue perfusion and haemodynamic stability.

• Key factors to consider in estimating blood loss include:

• Mechanism of injury
• Patient physiology
• Anatomical injury pattern
• Response to initial resuscitation
• Vital signs, such as tachycardia, hypotension, and narrowed pulse pressure
• Laboratory values, including hemoglobin, hematocrit, base deficit, and lactate levels
• Imaging studies, such as FAST ultrasound, CT scans, or diagnostic peritoneal lavage

• The Shock Index (SI) can be used to predict massive transfusion (MT) and emergent surgery (1).

From the Research

Estimating Blood Loss in Trauma Patients

Estimating blood loss in trauma patients is crucial for providing appropriate treatment and improving patient outcomes. Several methods have been developed to estimate blood loss, including:

• Vital Sign Analysis: Studies have shown that vital signs, such as heart rate and systolic blood pressure, can be used to estimate blood loss 2, 3. For example, the Automated Processing of the Physiological Registry for Assessment of Injury Severity (APPRAISE) system uses vital signs to identify patients with substantial bleeding 2.
• Scoring Systems: Scoring systems, such as the Assessment of Blood Consumption (ABC) score, have been developed to predict which patients will require massive transfusion 4. The ABC score uses factors such as heart rate, systolic blood pressure, and focused assessment with sonography for trauma (FAST) exam results to estimate blood loss.
• Machine-Learning-Based Models: Machine-learning-based models have been proposed to estimate blood loss using continuously monitored vital signs, such as photoplethysmography (PPG) and invasive arterial blood pressure (ABP) 3.
• Blood Component Therapy: Blood component therapy, including the use of red blood cells, plasma, and platelets, is commonly used to treat trauma patients with significant blood loss 5.

Factors Affecting Blood Loss Estimation

Several factors can affect the accuracy of blood loss estimation, including:

• Hemodynamic Resuscitation: The goals of hemodynamic resuscitation in hypotensive trauma patients are to restore adequate intravascular volume, correct pathologic coagulopathy, and maintain organ perfusion 6.
• Vasopressor Use: The use of vasopressors in trauma patients is controversial, but may be useful in counteracting vasodilation in hemorrhage 6.
• Prehospital Care: Prehospital care, including the use of scoring systems and vital sign analysis, can help identify patients with significant blood loss and activate massive transfusion protocols 4.

Key Findings

Key findings from the studies include:

• The APPRAISE system was 76% sensitive for identifying patients with substantial bleeding 2.
• The ABC score was 51% sensitive and 85% specific for predicting massive transfusion when calculated using prehospital data 4.
• Machine-learning-based models using PPG and ABP features outperformed traditional hematocrit computation formulas for estimating blood loss 3.