The visually estimated blood volume in scaled canisters based on a simulation study

The most common technique used worldwide to quantify blood loss during an operation is the visual assessment by the attending intervention team. In every operating room you will find scaled suction canisters that collect fluids from the surgical field. This scaling is commonly used by clinicians for visual assessment of intraoperative blood loss. While many studies have been conducted to quantify and improve the inaccuracy of the visual estimation method, research has focused on the estimation of blood volume in surgical drapes. The question whether and how scaling of canisters correlates with actual blood loss and how accurately clinicians estimate blood loss in scaled canisters has not been the focus of research to date.

A simulation study with four "bleeding" scenarios was conducted using expired whole blood donations. After diluting the blood donations with full electrolyte solution, the sample blood loss volume (SBL) was transferred into suction canisters. The study participants then had to estimate the blood loss in all four scenarios. The difference to the reference blood loss (RBL) per scenario was analyzed.

Fifty-three anesthetists participated in the study. The median estimated blood loss was 500 ml (IQR 300/1150) compared to the RBL median of 281.5 ml (IQR 210.0/1022.0). Overestimations up to 1233 ml were detected. Underestimations were also observed in the range of 138 ml. The visual estimate for canisters correlated moderately with RBL (Spearman's rho: 0.818; p < 0.001). Results from univariate nonparametric confirmation statistics regarding visual estimation of canisters show that the deviation of the visual estimate of blood loss is significant (z = - 10.95, p < 0.001, n = 220). Participants' experience level had no significant influence on VEBL (p = 0.402).

The discrepancies between the visual estimate of canisters and the actual blood loss are enormous despite the given scales. Therefore, we do not recommend estimating the blood loss visually in scaled suction canisters. Colorimetric blood loss estimation could be a more accurate option.