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The first post-operative death presumed to be due to adrenocortical suppression following corticosteroid therapy occurred in 1952 1. Similar reports followed2-5, but it was not until 1961 that Sampson, Brooke & Winstone 6 demonstrated an abnormally low level of plasma cortisol (hydrocortisone) in a steroid-treated patient who had suffered a severe fall in blood pressure during operation. They reported a similar case the following year7 and recently a third has been recorded8, but these appear to be the only instances in the literature of post-operative collapse unequivocably due to adrenocortical failure. Other conditions, such as unrecognized blood loss, myocardial infarction and septicaemia, can produce a similar clinical picture and in these situations large doses of hydrocortisone will often raise the blood pressure by a direct inotropic action on the heart and other non-specific effectsg~lo. Many reported cases of collapse have undoubtedly been due to causes other than adrenocortical insufficiency and, as Copell has pointed out, 'the vast majority of such incidents seem to be associated with medical diagnostic, and not adrenal failure'.Nevertheless, it has been the usual practice to give large quantities of steroids to 'cover' operations in all patients who have received these drugs within the previous two years59 12. This is obviously undesirable in those with normal adrenal function, since corticosteroids may increase susceptibility to infection 1 3-15, retard healing161 1 5 , precipitate gastro-intestinal haemorrhage 1 7 , 1 8 and impair electrolyte balance 1 99 1 8. In this and the following paper an attempt is made to clarify the use of steroid cover, and to answer two questions :1 Which patients treated with corticosteroid drugs require cover for surgery ?2 What form should that cover take?

Location of Placenta-Thompson et al. BMTM 391At the end of the scan the individual counting rates from each detector viewing the " hot" region indicate whether the placenta was anterior or posterior. ResultsThe indications for placentography were a suspicion of placenta praevia in 58 patients who presented with antepartum haemorrhage (52) or a persistent unstable lie at 37 weeks (6) (see Table), and the need to define the placenta before amniocentesis in four. The usual gestation period at which the test was performed was 32-33 weeks, but satisfactory results were obtained as early as 30 weeks. In four patients placenta praevia diagnosed on scanning was not confirmed clinically. These false-positive results were due mainly to overcautious assessment of the scans early in the series, and with experience it has been possible to increase the accuracy of prediction. Of 42 patients with antepartum haemorrhage 32 were allowed home for intervals of two to six weeks after placentography had indicated that the placenta was in the upper uterine segment; no foetal loss resulted. Summary of Results Placental DiscussionClinical Applications.-The accuracy of the method described is 93%, and is comparable to that of other reported isotope techniques; its main clinical value is the exclusion of placenta praevia before allowing the patient home for part or all of the remainder of the antenatal period, and it is -important in this connexion to note that in no patient was a placenta praevia missed. In this way we calculate that the equivalent of three out of 100 hospital beds a year are released for other purposes. No attempt was made to estimate the degree of placenta praevia, as all cases carrv the risk of further possible severe haemorrhage, and are therefore kept in hospital until after delivery.The other application of the procedure is before amniocentesis, when there is clinical evidence of an anteriorly placed placenta. Here the scan is useful in the selection of a suitable puncture site.Choice of Isotope.-Albumin tagged with 181I was chosen as the most suitable tracer material, because it has been successfully used elsewhere for placental location (Weinberg et al., 1957; Heagy and Swartz, 1961 ; Durfee and Howieson, 1962), its biological characteristics are fully known, its production is reliable, it is relatively cheap, and it is readily obtained commercially. Isotopes such as 1321 and technetium 99m have the advantage of a much shorter half-life, so that larger quantities of radioactive material can be used, resulting in higher counting rates and better discrimination. If, however, the facilities required for routine production of albumin, tagged with these isotopes are not available 1811 albumin has been shown to give satisfactory results. SummaryA technique of isotope placental location is described which uses 1311 and a colour autoscan apparatus. The use of a twocollimator modification has been found to increase the definition of this method, so that the readily available albumin-tagged 1811 gave satisfactory re...

In the preceding paper 1 criteria have been suggested for deciding which patients treated with steroid drugs required cover for surgery. The investigation presented here was designed to determine what form this cover should take.Patients already receiving synthetic steroids were given operative cover according to one of three different regimes, in an attempt to simulate the plasma cortisol (hydrocortisone) levels seen during and after surgery in normal subjects.

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