Measurement of Blood Loss: Review of the Literature

Description of Existing Measures

Visual Estimation

Visual estimation is the most frequently practiced method of determining blood loss during childbirth in the United States, and the results are usually included in the documentation of events pertaining to the birth. This method is used despite repeated studies showing its inaccuracy. There were 23 publications reviewed that evaluated the accuracy of visual estimation of blood loss. Some found that underestimation was common, others overestimation, and still others found inconsistencies but without any particular pattern.

Prasertcharoensuk et al.^[7] compared visual estimation with direct measurement of blood loss during vaginal births. The incidence of PPH was underestimated in the visual estimation by 89%. Brant^[8] and Duthie et al.^[9] found that actual blood loss was higher than estimated blood loss during vaginal births; the underestimation increased as the quantity of blood loss increased. In contrast, Razvi et al.^[10] found that estimated blood loss was 20% greater than the measured blood loss in 57% of vaginal births. However, consistent with Prasertcharoensuk et al.,^[7] the tendency to underestimate increased when the loss was > 300 mL. In contrast, Larsson et al.^[11] reported significant overestimation by birth attendants in cesarean births; blood loss visual estimates were under- and overestimated in vaginal births without a consistent pattern.

Duthie et al.^[12] reported a significant underestimation of blood loss during cesarean births when compared against a laboratory method of measurement. Stafford et al.^[13] compared visual estimation to a calculated measurement based on maternal blood volume in vaginal and cesarean births. They found the estimated amount to be significantly lower in the visual method. The visual estimation was less than half the calculated measurement in operative vaginal births and about a third in vaginal births associated with third- and fourth-degree lacerations. The tendency to underestimate was greatest with a calculated loss of > 1000 mL.

There is evidence that midwives are relatively accurate in estimating blood loss. Kavle et al.^[14] reported nurse-midwives' ability to estimate blood loss during birth as accurate within 5 mL of a laboratory determination; however, the higher the blood loss, the greater the imprecision of the estimate by under- or overestimating the loss. When a loss was > 200 mL, the mean difference from the laboratory finding was 62 mL either under- or overestimation. Glover^[15] also reported accuracy in midwife estimation of blood loss during a simulated birth; however, error increased when the blood loss was > 600 mL. Similarly, Budny et al.^[16] reported a strong positive association between calculated blood loss and blood loss estimates by junior and senior surgeons and senior anesthetists following burn surgery.

Kolb et al.^[17] showed the unreliability of visual estimation in a controlled study. A selected, known quantity of human blood was distributed on laparotomy pads. A variety of types of professionals who worked in the surgery area of a hospital were evaluated on their ability to estimate the quantity of blood. There were no differences among the groups of professionals or by amount of experience in their ability to accurately estimate blood loss. Higgins^[18] conducted a similar study using a known amount of blood on sanitary pads to evaluate registered nurses' (from labor and delivery, emergency room, postpartum, and the operating room) ability to estimate blood loss. Contrary to the other studies, many of the nurses (71%) overestimated, while 25% underestimated the blood loss. Similarly, Buckland and Homer^[19] conducted simulated birth blood loss scenarios. Health care professionals were able to estimate small volumes of blood more accurately than large volumes, and blood in containers more accurately than blood on sanitary pads or linens. Tall et al.^[20] and Patton et al.^[21] conducted controlled simulation blood loss scenarios for emergency personnel. Estimations were so inaccurate that they suggested that emergency personnel not waste time trying to visually estimate blood loss when that time could be used attending to the patient. Patton et al.^[21] suggested that field and hospital treatment should be provided based on vital signs, symptoms of shock, mechanism of injury, and comorbidities rather than visual estimates of blood loss. Beer et al.^[22] conducted epistaxis simulations and found blood loss > 100 mL to be somewhat underestimated and > 500 mL to be grossly underestimated by medical and nonmedical personnel, with the nonmedical personnel being the most inaccurate.

When self-reporting menorrhagia, women have difficulty quantifying blood loss. Wyatt et al.^[23] devised a method to increase the accuracy of visual estimation of blood loss during menstruation by using a menstrual pictogram. Women used this pictogram to quantify their blood loss. Their estimates had a high level of agreement with a laboratory assessment with a sensitivity of 86% and specificity of 88%. The mean total blood loss for the group with menorrhagia was 109 mL (range, 15–836 mL).

Menstrual bleeding is relatively small and is lost over a longer time frame than bleeding in childbirth. However, by using the findings of the menstrual pictogram, Bose et al.^[24] developed a similar pictogram for use as a teaching tool in the labor ward. Twelve clinical stations of common obstetric scenarios involving blood loss were constructed. Six different types of health care providers significantly underestimated blood loss in 5 of the 12 stations. Most importantly, the large blood losses representing floor spillage, large surgical swab capacity, and a massive PPH were consistently underestimated. None of the stations was significantly overestimated. These stations were used to develop a pictogram for a potential teaching tool. The poor visual estimation results validated the need for education.

Childbirth in developing countries often occurs in remote areas and is attended by traditional birth attendants (TBAs). Transportation to a medical facility is often difficult for a variety of reasons, so estimation of blood loss is encouraged to determine when transport is necessary. Prata et al.^[25] described a unique approach to blood loss estimation used by TBAs in Kigoma, Tanzania. A kanga is a precut, standard sized piece of cloth that is commonly used as a skirt, shawl, head wrap, or to carry a baby. Traditionally, old kangas are used as postpartum blood collection towels. Following verification through repeated measurements, it was determined that two blood-soaked kangas represented slightly > 500 mL. With this knowledge, TBAs were educated to begin treatment for hemorrhage and transport at the 2-kanga threshold.

Providing education through simulation exercises improves the ability of health care providers to estimate a predetermined quantity of blood volume on materials simulating clinical scenarios;^[26–29] however, the estimates are still inaccurate, particularly with large volumes. Dildy et al.^[26] and Sukprasert et al.^[27] conducted similar educational programs for obstetric clinicians. Seven stations were created with premeasured whole blood of varied quantities on supplies common in vaginal and cesarean births, such as underbuttocks drapes, laparotomy sponges, sanitary pads, and 4 × 4 sponges. They compared visual estimation before and after an educational program that included mathematical formulas, demonstration of volumes of common objects, and some general rules to assist in estimating blood loss. Dildy et al.^[26] found a trend in overestimating quantities at the lower levels and underestimating higher quantities of blood before the education program; following the education, a reduction in over- and underestimation of blood loss in all but two stations was reported. Sukprasert et al.^[27] reported an improved percentage of accuracy following the education program. Neither study used quantities of blood > 500 mL at any of the stations.

Maslovitz et al.^[28] created simulated PPH scenarios for obstetric teams of residents and midwives to visually estimate blood loss. The residents underestimated blood loss by 49% and midwives by 40%. A repeat of the simulations was offered to a second group; however, at different points in the scenario, participants were asked to consider the amount of blood loss, and the total estimated loss was obtained at the end of the simulation. The participants still underestimated the loss, but their total estimates were more accurate. These results suggest that visually estimating the amount of blood loss periodically through an event may result in a more accurate total than attempting to estimate the total at the end of an event.

Moscati et al.^[29] evaluated emergency medical technicians' ability to visually estimate blood loss in six stations with various quantities of blood on different types of surfaces (absorbent versus nonabsorbent). Following the initial testing, one group received education through a slide show of blood loss scenarios, and both groups received education on common volumes to consider when estimating blood loss. A month later, they were retested. Both groups tended to underestimate volumes on all surfaces on the first test. Both groups improved on the second test with no significant difference between the groups.

Direct Measurement

Direct measurement is one of the oldest methods of accurately determining blood loss. Seven studies used a tool to collect blood for direct measurement, and these tools were all for use during childbirth in an attempt to quantify normal blood loss. Williams^[1] described collection of blood in a douche pan. Williams^[1] also referenced two studies from 1898 and 1904. One used a basin in front of the external genitalia to collect blood, and the other used a large copper funnel that passed through the mattress at the level of the buttocks and drained into a container placed beneath the bed. Strand et al.^[30] collected the blood directly into a bucket through an opening in a cholera bed (a bed with an opening designed to collect diarrhea). Several researchers used various drapes with built-in pouches to assist with direct collection.^[31–34] Hill et al.^[31] reported a recovery of 99% of the blood loss, but how the recovery rate was calculated was not presented.

Haswell^[32] described using an underbuttocks drape with a graduated pouch for measurement. A description of the separation of amniotic fluid and blood, which was visually apparent, was presented as improving the accuracy. Nelson et al.^[33] used the underbuttocks drape with a pouch to collect blood and foreign fluid at the time of birth and collected blood-soaked sponges. The blood in the sponges was calculated by direct weight, converting 1 g to 1 mL. A procedure was followed to improve the accuracy by removal of the foreign contaminant from the fluid captured in the pouch. This procedure took several steps and a few hours. The maximum blood loss was considered the total in the sponges plus the measured contents in the drape. When the lengthy procedure was conducted, the amount of contaminant in the pouch ranged between 4% and 81% of the total fluid collected. The wide variation in the amount of contaminant illustrates the major limitation of direct weighing or measuring blood loss.

Patel et al.^[34] compared measured estimates with a laboratory method for 10 women. The Pearson correlation coefficient for the two methods was .93, supporting the accuracy of the direct measurement method. Prasertcharoensuk et al.^[7] reported the inaccuracy of visual estimation when compared against measured blood loss in the third stage of vaginal births, but they did not report how the blood was measured.

Gravimetric

A variety of gravimetric (measurement by weight) methods to determine blood loss have been used. Five publications used gravimetric methods, and all the studies were conducted to determine blood loss intraoperatively. Comeau^[35] used a precision computerized scale system to weigh sponges and suction contents as they were placed on a scale. The patient's height and weight were entered into the computer, and the scale computed the acceptable blood loss (10% of the total blood volume). An alarm sounded when the 10% mark was reached, but the scale would continue to weigh. The machine could detect very large or very small quantities. Testing was reported to be within ± 2 g of error.

Lee et al.^[36] compared gravimetric and laboratory methods of quantifying blood loss during animal surgery. Intraoperative blood loss was quantified by measuring irrigation fluid and weight measurement of surgical sponges. Intraoperative blood loss was the weight difference between the sterile saline solution and gauze sponges preoperatively and postoperatively. The sponges went through a process to extract all traces of blood. The hemoglobin concentration in the solution was determined. A highly significant correlation was found between the laboratory and gravimetric method, supporting the use of weight measurement as accurate and less time consuming or costly when compared to the laboratory method. In contrast, Johar and Smith^[37] found no significant correlation between the blood loss estimated by the gravimetric method and blood loss as measured by the same laboratory method. Similarly, Budny et al.^[16] reported blood loss extrapolated from the weight of swabs saturated with blood. A mean value of 51% of the calculated blood loss was obtained suggesting poor reliability; however, there was a positive association between the weight and the calculated measurements (r = 0.88).^[16] Calculated blood loss was determined through a formula using pre- and postoperative hemoglobin levels. The validity of the calculated blood loss was not provided.

Rains^[38] compared multiple methods of determining blood loss; two involved weighing. Following various surgeries, all swabs and towels with blood contamination from the surgical procedure were weighed to determine the amount of blood loss, similar to the method of Lee et al.^[36] Alternatively, patients were weighed before and after surgery with corrections made for fluid given, tissues removed, dressings and ligatures added, water absorbed in the rebreather, and insensible skin loss. The swab weighing was very simple to carry out and results could be obtained periodically during the course of the surgery.

Photometry

Eleven publications using photometry for blood loss measurement were reviewed. These studies involved blood loss during birth, surgery, and simulation. A photometric technique was used to convert blood pigment to alkaline hematin in several studies. The alkaline hematin method is referred to as the gold standard for measuring blood; other methods are compared against it to determine accuracy. Chua et al.^[39] took known measured blood collected from gynecologic surgeries and simulated postpartum conditions by pouring this blood on sanitary pads and towels. These pads and towels were collected in a plastic bag and given to a laboratory technologist who was not informed of the original known quantity of blood. An automatic extractor (Stomacher Lab-Blender) provided quick extraction of blood into a 5% sodium hydroxide solution. The blended material was filtered and the optical density was read. The calculation included the measurement of hemoglobin obtained from a sample of the patient's blood before surgery. The blood loss measured in the laboratory demonstrated an error between 0% and 9.4%. The intraclass correlation coefficient was 0.99. Newton et al.^[40] reported that the mean blood recovered was 97.9%. Brant^[8] and Wallace^[41] reported a similar machine extraction method of blood loss at vaginal birth by measurement of oxyhemoglobin by spectrometer. Swabs, paper pads, and all blood collected were placed in a washing machine with a preset volume of water, ammonium hydroxide, and a surface-active agent used to accelerate release of hemoglobin. A sample of the resulting solution was centrifuged and filtered. The oxyhemoglobin concentration was measured in a photoelectric colorimeter and compared to a sample of the patient's venous blood taken on admission. Wallace^[41] explained that this method is based on the theory that "if any unknown quantity of blood is added to a known volume of hemolyzing solution the hemoglobin content of the resulting dilution will be proportional to the volume and original hemoglobin concentration of the blood added." Brant^[8] and Mainland^[42] reported the resultant calculated blood loss through the use of a formula.

Duthie et al.^[12] and Wilcox et al.^[43] used the photometric method to measure blood loss during cesarean births. Wilcox et al.^[43] validated the method through comparisons with a radioactive chromium tagged red blood cell technique and a sample photometry method (error of < 1%). Both studies reported a tendency to underestimate when the blood loss was greater. Larsson et al.^[11] used the photometric method to evaluate visual estimation of blood loss following vaginal and cesarean births and found a tendency to underestimate in cesarean births and no correlation in vaginal births. Duthie et al.^[9] used the photometric method to measure blood loss during vaginal births and found consistent underestimation in the estimation of blood loss.

Razvi et al.^[10] reported the determination of blood loss through a colorimetric method. All blood lost during the third stage of labor and 2 hours later was collected by using absorbent paper. The blood loss was then quantified by colorimetric measurement of the hemoglobin content. The details of the colorimetric method were not provided, and the results were variable. Compared to estimated blood loss, the estimation was greater than the measured blood loss 64% of the time (range, 0.5%–500%), and 34% were underestimated (range, 3%–75%).

Freedman^[44] tested known volumes of blood spilled onto swabs with known hemoglobin concentrations and plasma potassium concentrations. The swabs were washed, the potassium concentration of the washings was measured by flame photometry, and the estimated spilled blood volume was derived through a formula. The estimates of blood loss using this technique generally came within 10% to 15% of the true volume.

Miscellaneous Methods

Ten publications were reviewed that evaluated other methods to measure blood loss. These were conducted in emergency rooms, vaginal births, and cesarean births. Stafford et al.^[13] compared visual estimation to a calculated blood loss. The calculated blood loss was derived by multiplying the calculated maternal blood volume (based on height and weight) by the percent of blood volume lost (based on pre- and postbirth hematocrit levels). As the authors noted, these calculations can be inaccurate based on the hydration status of the woman, especially with the intravenous loading conducted with regional anesthesia (> 90% had an epidural) or with pregnancy-induced hypertension (10% of the participants). They also acknowledged that maternal physiologic blood volume changes may alter the hematocrit values. The researchers only compared the calculated method to the unreliable visual estimation rather than with any of the more reliable methods, such as direct measurement, gravimetric, or photometry.

Lyon et al.^[45] and Sefidbakht et al.^[46] measured the diameter of the inferior vena cava by ultrasound in trauma patients in the emergency room to determine if there was a relationship between the diameter of the inferior vena cava and the amount of blood loss. The diameter of the inferior vena cava was significantly smaller in both studies with large blood loss and was present before other signs of shock. Lyon et al.^[45] noted this decreased size in the inferior vena cava when the blood loss was > 450 mL.

Palm^[47] compared hemoglobin drawn at the last prenatal visit before birth, the third day postpartum, and 10 weeks postpartum. The results were compared to estimated blood loss during and up to 4 hours postpartum by the attending midwife. No validation of the estimates was provided. There was a weak correlation between hemoglobin levels at 3 days postpartum and the estimated blood loss, and no correlation between hemoglobin levels at 10 weeks postpartum and estimated blood loss. The results supported the findings of Williams^[1] that hemoglobin did not significantly change by the third postpartum day. However, the findings were based on estimated blood loss, which has been repeatedly shown to be inaccurate.

Tagging red blood cells (RBCs) has been tried several ways. Read and Anderton^[48] used radioactive-tagged RBCs to determine a change in blood volume, thereby calculating blood loss during cesarean birth. Similarly, Holt et al.^[49] estimated blood loss through quantifying loss of radioactive-tagged cells. They found this method to have limited accuracy and reproducibility, particularly with small volumes. Rains^[38] estimated changes in blood volume following intravenous injection of a dye to mark RBCs, and an absorptiometer was used to estimate changes in blood volume. Errors occurred in the process, resulting in erroneous results. Quinlivan and Brock^[50] used radioactive-tagged RBCs and Evans blue dye techniques to quantify blood volume before and after vaginal birth. They compared these methods with direct collection and found that the volume was similar, supporting the concept that the blood volume change was related to blood loss rather than shunting away from circulation.

Conn et al.^[51] used serum-specific gravity to determine blood loss. Whole blood was collected periodically during labor and following birth. Blood loss was measured and calculated on the basis of percentage of body weight before birth. Values for hemoglobin, RBCs, and packed RBCs were also collected. Specific gravity of serum within 24 hours before birth was considered a rough index of the extent of blood loss in the third stage of labor. No comparison group was provided.

Scalea et al.^[52] demonstrated the high sensitivity of central venous blood saturation as an indicator of blood loss in animals. Desaturation occurred after a 3% or 6% blood loss in 90% of the cases. The application to pregnant women who have just given birth is limited because of the difference in body mass, increased blood volume in pregnancy, and the practicality of placing a central line in a woman who has just given birth in a variety of possible settings.

J Midwifery Womens Health. 2010;55(1):20-27. © 2010  Elsevier Science, Inc.

Cite this: Measurement of Blood Loss: Review of the Literature - Medscape - Jan 01, 2010.