Observational study of haemoglobin trend during an elective caesarean section
Abstract Number: S-44
Abstract Type: Original Research
Many factors alter a parturient's haemoglobin (Hb) during a caesarean section (CS) including haemorrhage, haemodilution, autotransfusion from the uterus, physiological changes at delivery and effects of regional anaesthesia.(1,2) The Masimo rainbow® SET Radical-7 co-oximeter provides a continuous non-invasive measurement of total Hb (SpHb). Using this equipment, we aim to measure the trend of SpHb during CS and identify relationships between this and a number of variables.
Following written consent, 41 healthy women having elective CS under regional anaesthesia were recruited. SpHb measurements were taken every 5 minutes until end of surgery using the Masimo. Timings of specific events (e.g. spinal, knife to skin (KTS), knife to uterus (KTU) etc.) were recorded as well as amount of fluid and vasopressor used. Fixed effects were considered by comparing Akaike's Information Criterion.
We considered models with fixed effects for time, fluid and vasopressor dose. Time and vasopressor dose were not significant at the 5% level. Patient-specific plots of SpHb changes suggested a random effects structure for fluid, in which haemoglobin change is proportional to the square root of the volume of fluid administered.
The trend of SpHb during CS is influenced by multiple complex variables. The trends suggest an initial fall in mean SpHb following start of measurement until delivery when there is a slight increase followed by a steady fall until end of surgery. We also observed a SpHb rise following delivery in a number of cases which may represent auto-transfusion from the uterus. Statistical modelling identified a relationship between fluid given and SpHb change. In addition to haemodilution, the interplay between fluid requirement and a number of the factors outlined above may account for this relationship.
1. Hann GR. Volume kinetics for infusion of fluids. Anesthesiology 2010;113: 470 -81
2. Macknet MR, Allard M, Applegate RL, Rook J. The Accuracy of Noninvasive and Continuous Total Hemoglobin Measurement by Pulse Co-Oximetry in Human Subjects Undergoing Hemodilution. Anesth Analg. 2010 Dec;111(6):1424-6