De La Peña Silva, Ancizar Joaquín, et al. “Is Visual Estimation Useful in Determining the Extent of Perioperative Haemorrhage? A Study of Correlation Among Anaesthetists of Intermediate and High Complexity Hospitals in Cartagena, Colombia”. Colombian Journal of Anesthesiology, vol. 42, no. 4, Oct. 2014, pp. 247-54, https://www.revcolanest.com.co/index.php/rca/article/view/234.