We report abnormal maternal laboratory parameters in twin-to-twin transfusion syndrome (TTTS) at mid-pregnancy. A retrospective chart review was undertaken of 109 patients with TTTS evaluated for placental laser surgery. Complete blood count (CBC), blood type and Rh factor, urine analysis and serum chemistry panel were obtained preoperatively, with the CBC and serum albumin repeated on the first postoperative day. The mean gestational age was 21.2 ± 1.7 weeks. Initial abnormal values included hematocrit (32.1 ± 3.0%), hemoglobin (11.0 ± 1.03 g/dl), serum magnesium (1.71 ± 0.17 mg/dl), total protein (6.08 ± 0.55 g/dl) and albumin (3.06 ± 0.34 g/dl). Despite minimal blood loss and conservative fluid replacement mean hematocrit, hemoglobin, and albumin were 27.3 ± 2.74%, 9.3 ± 0.94 g/dl and 2.56 ± 0.23 g/dl, respectively on postoperative day one. Weight gain (8.0 ± 5.5 lb.) and low urinary output were characteristic peri-operative events. Maternal hypoproteinemia and anemia occur in TTTS at mid-pregnancy. This may contribute independently to amniotic fluid production rates in the fetuses, and explain in part the maternal sensitivity to intravenous fluids in multiple pregnancy. Twin Research (2000) 3, 113–117.

The exchange of water between plasma and interstitial fluid (ISF) along the length of a capillary is attributed to a balancing of the Starling forces, site-specific differences in hydrostatic and osmotic pressures that theoretically determine directional fluid movement. The osmotic forces for water movement are attributed to the osmotic effects of proteins, colloid osmotic pressure (COP). Several physiological inconsistencies question the role of proteins and COP in fluid flux. A reconsideration of Hulett's insights concerning the osmosis of water provides substantial evidence that the effect of COP does not cause osmosis, and therefore another force is needed to explain plasma–ISF exchange. Review of whole-body tissue and blood ion concentrations and/or ion differences across isolated tissue or secretory epithelia from a variety of species indicates that the diffusion of bicarbonate and strong ions within plasma is the dominant osmotic effect returning ISF to the capillary. Conceptually, as these ions diffuse along physiological gradients, they alter the chemical potential of water through which they are diffusing (solute–solvent drag), creating an osmotic effect on plasma water, and explain plasma–ISF exchange. Considering venous–arterial differences, diffusing and strong ions give rise to a net osmotic force (~35 Torr) in venous end capillary plasma water that is coupled to ISF through pores in the endothelium. More importantly, diffusing and strong ions provide an incremental osmotic force (~150 Torr) that is essentially matched to any change in metabolic rate (e.g. muscular work) when CO2 output and water production are increased. The proposed diffusing ion osmotic force does not negate the necessity for colloidal proteins in volume regulation. Proteins can have an essential effect on fluid exchange in plasma when blood flow is intermittent or changes in protein concentration in the ISF such that proteins exert a force against a distensible boundary (i.e. the endothelium and basement membrane) as they are reflected by it or diffuse through the membrane due to changes in permeability.

Summary

Background and objective: The exact change in circulating blood volume (BV) during general anaesthesia is still unknown because there is no standard method of evaluating BV. We evaluated the changes in BV by general anaesthesia using simple and easy estimation methods.

Methods: Fourteen patients scheduled for minor surgery under general anaesthesia were enrolled. Propofol and vecuronium bromide were used for the induction of anaesthesia, and anaesthesia was maintained with sevoflurane and nitrous oxide. Haematocrit (Hct), total protein concentration (TP), as well as colloid osmotic pressure (COP) measured using a colloid osmometer, were determined before anaesthesia, and 30, 60 and 90 min after the induction of general anaesthesia. BV was calculated using Allen's formula and the changes in Hct, TP and COP. The estimated BV was compared with directly measured BV using indocyanine green dilution method (BVICG).

Results: Hct, TP and COP significantly decreased after the induction of anaesthesia (Hct: 42.1–39.4%; TP: 7.3–6.9 g dL−1; COP: 23–19 mmHg). The calculated BV as well as BVICG significantly increased after induction of anaesthesia (calculated by COP: 4.13–5.03 L; BVICG: 4.54–5.56 L). The change rate in BV calculated by the change of COP was larger than other calculated BVs, and was approximated to the change rate in BVICG. After emergence from anaesthesia, all values tended to return to baseline.

Conclusions: General anaesthesia increases BV. The value of BV calculated from the change in COP was most changeable.