Changes in calcium fractions during cardiopulmonary bypass in infants and neonates

The changes in total blood calcium fractions were investigated in 20 infants and neonates undergoing open-heart surgery for correction of congenital heart defects. On initiation of cardiopulmonary bypass (CPB), total serum calcium fell from 2.29 ± 0.05 mmol/I to 1.8 ± 0.04 mmol/I and there was a profound fall in biologically active ionized calcium from 1.26 ± 0.02 mmol/I to 0.49 ± 0.04 mmol/l. Protein-bound calcium also fell from 1.03 ± 0.07 mmol/I to 0.09 ± 0.03 mmol/l. Complexed calcium increased from 0.08 ± 0.02 mmol/I to 1.1 ± 0.05 mmol/l. The large fall in ionized calcium and increase in complexed calcium could be accounted for by the corresponding large increases in serum citrate (162.2 ± 29.8 μmol/l to 1689.8 ± 163.1 μmol/l) and serum lactate (1.27 ± 0.18 mmol/I to 7.79 ± 0.72 mmol/l). All measured fractions of calcium returned towards their pre-operative levels by the end of bypass. However, 13 of the 20 patients had less than optimal levels of ionized calcium when being weaned from bypass despite the empirical use of intravenous calcium supplements. This study demonstrates that ionized calcium can be quickly and easily measured in the peri-operative period, that there can be extremely large changes in calcium fractions during CPB in infants and neonates, and that ionized calcium can be unexpectedly low in the critical period when weaning patients from bypass. Total calcium measurements gave an inaccurate estimate of the ionized calcium fraction.

Calcium measurements in serum and plasma--total and ionized

This article will review the methods currently employed for measuring the concentrations of total and ionized calcium in serum or plasma. As far as total calcium is concerned, various techniques such as atomic absorption spectrometry, spectrophotometry, fluorometry, complexometric titration, and flame photometry will be described and compared. Particular emphasis will be given to the accuracy and precision of each technique. Possible sources of error and interfering agents will be identified and the various procedures for the taking and handling of blood samples evaluated. Inter-laboratory variation in the measurement of calcium will be studied. An assessment will be made of a new reference method for measuring total calcium in serum using isotope-dilution mass spectrometry. The usefulness of the total calcium measurement in clinical medicine will be briefly discussed. Within the last decade the refinement of spectrophotometric techniques and the improvements in ion-selective electrode technology have revolutionized the measurement of ionized calcium in serum, such that it may now be possible to replace total calcium measurements with ionized calcium measurements on a routine basis. The various techniques currently in use for measuring ionized calcium will be described and evaluated. Particular attention will be paid to the preparation of standards, the procedures for taking blood samples, and the handling of the samples prior to and during measurement. An assessment of the relative value of measuring total and ionized calcium will be presented.

Hypercalcaemia in rheumatoid arthritis: investigation of its causes and implications

When correction was made for hypoalbuminaemia, 23 of 50 ambulant patients with definite or classical rheumatoid arthritis were found to have hypercalcaemia. When these 23 patients were studied 6 months later, 7 had hypercalcaemia as defined by the correction factor for a low serum albumin level, and 6 of these patients had raised serum ionised calcium concentrations. Biochemical studies in the 23 patients indicated evidence of hyperparathyroidism, namely, hypophosphataemia, increased serum alkaline phosphatase, hyperchloraemia, and reduced tubular reabsorption of calcium. However, serum immunoreactive parathyroid hormone concentrations were normal. Only one patient had an abnormally low serum 25-hydroxy-vitamin D result: this patient had a high level of urinary D-glucaric acid and was receiving phenobarbitone for treatment of epilepsy. The biochemical features suggestive of parathyroid overactivity were particularly found in patients with raised serum calcium levels. The cause of hypercalcaemia in rheumatoid arthritis remains to be explained.

Urinary inhibitors of calcium phosphate formation: the inhibitory activity of normal and artificial urines

Eelven urine samples from normal subjects inhibited the formation of calcium phosphate. In all cases the activity of the urine was identical with that of an artificial urine having the same concentration of urea, creatinine, sodium, potassium, magnesium, calcium, ammonia, sulphate, chloride, inorganic phosphate, citrate, isocitrate and pyrophosphate, and the same pH.

Plasma calcium and magnesium fractions in liver disease

Plasma calcium and magnesium fractions were measured in 51 patients with either hepatocellular or biliary disease. The fractions were found to be only minimally deranged. Plasma albumin correlated with total calcium and with the protein bound and ionized fractions. Abnormalities of plasma calcium or magnesium fractions are unlikely to play a role in the pathogenesis of the osteomalacia seen in chronic biliary disease.

Correction of hypocalcaemic symptoms during plasma exchange

The supplementation of replacement solutions used during plasma exchange with calcium gluconate prevents hypocalcaemic symptoms.

An apparatus for the anaerobic ultrafiltration of bile and other biological fluids

A simple apparatus is described for the anaerobic ultrafiltration of a few millilitres of bile or other biological fluids. The principle employed enables viscous liquids which would normally block the membrane to be ultrafiltered successfully.