ISRCTN 42061860.

The present review of fluid therapy studies using balanced solutions versus isotonic saline fluids (both crystalloids and colloids) aims to address recent controversy in this topic. The change to the acid-base equilibrium based on fluid selection is described. Key terms such as dilutional-hyperchloraemic acidosis (correctly used instead of dilutional acidosis or hyperchloraemic metabolic acidosis to account for both the Henderson-Hasselbalch and Stewart equations), isotonic saline and balanced solutions are defined. The review concludes that dilutional-hyperchloraemic acidosis is a side effect, mainly observed after the administration of large volumes of isotonic saline as a crystalloid. Its effect is moderate and relatively transient, and is minimised by limiting crystalloid administration through the use of colloids (in any carrier). Convincing evidence for clinically relevant adverse effects of dilutional-hyperchloraemic acidosis on renal function, coagulation, blood loss, the need for transfusion, gastrointestinal function or mortality cannot be found. In view of the long-term use of isotonic saline either as a crystalloid or as a colloid carrier, the paucity of data documenting detrimental effects of dilutional-hyperchloraemic acidosis and the limited published information on the effects of balanced solutions on outcome, we cannot currently recommend changing fluid therapy to the use of a balanced colloid preparation.

The porphyrins play a critical role in biology, being involved in a wide range of reactions related to oxygen utilization, transport, storage or formation. The synthetic pathway involved in the production of the porphyrins is complex and is governed by a sequence of enzymes. A defect in any of these enzymes results in accumulation of the preceding intermediaries and produces one form or another of the diseases known as the porphyrias. This review briefly outlines porphyrin synthesis, the diseases that arise from errors in porphyrin metabolism and the anaesthetic implications of these disorders. Control of haem biosynthesisThe control of the production of haem is effected primarily through ALA synthetase. This enzyme has a low endogenous activity and also has a very short half-life, making it ideally suited to a regulatory role. The formation of ALA