Visual estimation of blood loss (VEBL) involves assessing the amount of blood a patient has lost simply by looking at it. This method is widely used in various medical settings, including emergency rooms, surgical suites, and childbirth. VEBL is a traditional approach for assessing blood loss, particularly in postpartum hemorrhage (PPH).
Common Techniques for Visual Estimation
Visual estimation of blood loss involves evaluating the size of blood pools on surfaces like floors or operating tables. It also includes assessing the saturation of absorbent materials such as gauze, towels, bed linens, or clothing. For example, a small 10×10 cm saturated swab might indicate 60 ml of blood loss, while a large 45×45 cm swab could represent 350 ml. A 100 cm diameter floor spill might be estimated as 1500 ml, and blood loss limited to the bed could indicate 1,000 ml.
Why Visual Estimation is Prone to Error
Visual estimation of blood loss is widely considered inaccurate and unreliable. The absorption differences of various materials significantly affect perceived volume. For example, a liter of blood on carpet might be underestimated as 347 ml, while 1,500 ml on concrete could be estimated as 885 ml. Conversely, 500 ml of blood on clothing has been overestimated by two to three times. Blood mixed with other fluids like water, amniotic fluid, urine, or saline can dilute its appearance, leading to underestimation of the actual volume.
Poor lighting conditions or individual differences in color perception can also affect judgment. Observer bias is another factor, as individual experience, training, and subjective judgment vary widely among healthcare providers. Studies show no association between a healthcare professional’s specialty, years of experience, or confidence level and the accuracy of their blood loss estimations. Additionally, clotted blood may appear as a smaller volume than its true liquid equivalent, and internal bleeding or blood loss into body cavities cannot be visually estimated.
More Accurate Methods for Blood Loss Measurement
Objective and precise methods are used to measure blood loss. The gravimetric method involves weighing blood-soaked materials, such as pads or sponges, and then subtracting their known dry weight. For instance, 1 gram of a soaked swab or pad is generally considered equivalent to 1 ml of blood loss. Volumetric measurement is another technique, where blood is collected directly in calibrated containers, such as suction canisters used during surgery.
Spectrophotometry is a laboratory method that quantifies hemoglobin concentration in collected fluids, offering high precision but typically being more expensive and complex to use. Quantitative Blood Loss (QBL) refers to more precise measurements, often combining gravimetric and volumetric techniques. Clinical indicators like changes in heart rate, blood pressure, and patient appearance, along with laboratory tests such as hemoglobin and hematocrit levels, also help assess a patient’s overall status and potential for shock.
Impact of Misjudging Blood Loss
Misjudging blood loss can have serious consequences. Underestimation can lead to delayed medical intervention, insufficient fluid resuscitation, and postponed blood transfusions. This delay can result in severe complications, including hypovolemic shock, where the body lacks enough blood or fluid to pump effectively, potentially causing organ damage or even death. For example, losing 20% or more of total blood volume can lead to hemorrhagic shock, characterized by rapid breathing, weakness, confusion, and cool, pale skin.
Conversely, overestimation of blood loss can lead to unnecessary interventions, excessive fluid administration, or inappropriate blood transfusions. These actions carry risks, such as fluid overload or transfusion reactions. Accurate assessment of blood loss is essential for timely and appropriate medical interventions, ensuring patient safety and optimal recovery.