A.R. Michell

Comparison of cortisol concentrations in saliva and plasma of dogs

It is increasingly important to have simple, non-invasive indicators of stress in animals. Studies in various species have shown that concentrations of cortisol in saliva relate closely to plasma levels of the free hormone; the aim of the present procedure was to show a similar correlation in the dog. Baseline blood and saliva samples were collected concurrently from six male beagles. Synthetic adrenocorticotrophic hormone was given and further samples were collected at 0.25, 0.5, one, two and 2.5 hours later. The results indicated a statistically significant correlation between the levels of cortisol in blood and saliva. Concentrations in saliva were between 5 and 10 per cent of those in plasma at each collection time. To demonstrate a response to a more natural stimulus, saliva samples were taken from a dog during exposure to a known stressor for that individual. The results showed a marked, delayed increase from baseline which was maintained for at least 0.5 hours after stressing.

Comparison of direct and indirect (oscillometric) measurements of arterial blood pressure in conscious dogs.

Oscillometric measurements of arterial blood pressure were compared with direct measurements made on seven dogs fitted with catheters. Tail and limb cuff sites were used while the dogs were gently restrained either standing or in lateral recumbency. The accuracy of the readings for the various cuff sites was compared with the direct (gold standard) readings. The accuracy of the indirect readings was improved by using mean values from a series of readings rather than individual values and when the dogs were in lateral recumbency rather than standing. The differences between the direct and indirect values were greatest with high pressures, and with systolic rather than diastolic values. In standing dogs, the proximal forelimb readings (when obtainable) correlated most closely with the direct readings. The tail cuff readings correlated significantly with the direct readings, though less closely. The tail cuff readings were the most easily recorded in the standing dogs. In the laterally recumbent dogs, the readings from all the cuff sites correlated closely with the direct values except for diastolic readings from the distal hindlimb.

A comparison of direct and indirect (oscillometric) measurements of arterial blood pressure in anaesthetised dogs, using tail and limb cuffs.

Oscillometric measurements of arterial blood pressure were compared with direct measurements in anaesthetised dogs being monitored during routine surgery. Readings were obtained with tail cuffs and limb cuffs and the reproducibility (precision) of the readings from various cuff sites was also compared in conscious dogs. Tail cuffs gave the best precision in conscious dogs and the closest correlation with direct measurements in anaesthetised dogs, especially for systolic pressure. The proximal hindlimb site gave results with a slightly lower precision.

Evaluation of iohexol as a marker for the clinical measurement of glomerular filtration rate in dogs

The contrast medium iohexol can be used as a marker for the measurement of glomerular filtration rate. It has the advantages of sample stability and the availability of a simple, automated (though expensive) analyser. The clearance of iohexol was compared with the clearance of Tc-DTPA in 24 dogs with known or suspected renal impairment. The results were comparable but fractionally lower with iohexol. The correction factors developed for human beings were found to be satisfactory in the dogs, thus validating the software routines used in the automated analyser with the canine samples.

Changes in plasma composition in calves surviving or dying from diarrhoea.

With the growing variety of solutions available for oral and parenteral fluid therapy it is increasingly important to define the adverse changes in plasma associated with diarrhoea, particularly those associated with a fatal outcome. The effects of E. coli-induced diarrhoea in week-old Jersey calves were measured, comparing survivors with those that died. The main effects of diarrhoea were dehydration, metabolic acidosis, pre-renal uraemia and hyponatraemia. Hypernatraemia was unusual and mild. Calves which survived tended to be hypokalaemic whereas those which died showed intensifying metabolic acidosis and hyperkalaemia. Hypoglycaemia developed, but it was not generally worse in calves which failed to survive, though there were exceptions.

A SIMPLE METHOD FOR MEASURING GLOMERULAR FILTRATION RATE IN DOGS

A technique for measuring glomerular filtration rate (by six-sample plasma clearance) and extracellular fluid volume is described. The results obtained for glomerular filtration rat per extracellular fluid volume with a three blood sample technique are also presented. Concurrently with the blood sample techniques measuring plasma clearance, glomerular filtration rate per extracellular fluid volume was also measured using an external radiation detector and no blood samples. The validity of expressing glomerular filtration rate per extracellular fluid volume (rather than per body weight or surface area) and the clinical utility of the results obtained with the external radiation detector are discussed.

Evaluation of a nutritive oral rehydration solution for the treatment of calf diarrhoea.

The essential constituents of a conventional oral rehydration solution (ORS) are sodium, glucose and a bicarbonate precursor. The glucose promotes sodium uptake but because these solutions are isotonic, it is insufficient to sustain calorie requirements. This paper examines the performance of a novel ORS with over three times the conventional glucose concentration, by comparing it with two leading commercial ORSs in calves with induced Escherichia coli diarrhoea. This solution showed greater ability than the current market-leading ORS to repair extracellular fluid and plasma volume and to correct both hyponatraemia and metabolic acidosis, especially in more severely affected calves. In acidotic calves it was more effective in correcting hyperkalaemia, probably by supplying glucose to promote cellular potassium uptake as well as by correcting the acidosis. It therefore appears possible to depart from the traditional isotonic formulations for calf ORSs and gain significant nutritional support while retaining effective rehydration and correction of acid-base and electrolyte disturbances. This seems especially important in young animals where energy deprivation imposes a particular penalty; the use of hypertonic ORSs should not, however, be extended to other species without further research.

Fallibility of faecal consistency as a criterion of success in the evaluation of oral fluid therapy for calf diarrhoea

It is often said that the success of oral rehydration in humans depends on the adequacy of the improvement in the composition and volume of extracellular fluid, not reduction of faecal output. Indeed, the latter may increase initially. Such increases do not prevent the treatment from being effective but they may, falsely, undermine its acceptability to patients or those caring for them. This paper provides data to show that standard oral rehydration solutions used to treat experimentally induced calf diarrhoea procure identical improvements in plasma volume during the first 48 h, whether faeces improve or not, and those calves whose faecal consistency improved actually showed greater deterioration of extracellular fluid volume. While it is important for this to be appreciated by clinicians and explained to owners, it is absolutely imperative that those responsible for the approval of new therapeutic products for registration understand and accept that faecal consistency offers no reliable insight into the effectiveness of oral rehydration therapy for calf diarrhoea. It was, however, interesting that there was some relationship with correction of acidosis--perhaps because some of the contributing factors arise from colonic dysfunction.

Evaluation of a glutamine-containing oral rehydrationsolution for the treatment of calf diarrhoea using an Escherichia coli model

A high-calorie oral rehydration solution (ORS) with glutamine (n=11) was more effective in correcting plasma, extracellular fluid and blood volume than solutions without (one WHO-type solution, n=6, and two high-glucose but glutamine-free solutions, n=7, n=12). It was the only solution to improve plasma volume significantly within 48 h and sustain the improvement throughout treatment; similarly, it was the only solution to correct packed-cell volume within 48 h and sustain the benefit to the end of treatment. At the end of treatment, the glutamine-treated calves were the only ones to avoid a significant weight loss compared with their pre-diarrhoeic values. The crucial difference between this solution and those used with glutamine previously is that it gave significant nutritional support whereas WHO type solutions did not. It also had more favourable effects on hyponatraemia and metabolic acidosis than a standard ORS. Use of a high-calorie ORS for 4 days (rather than 2 days of 50:50 admixture with milk replacer) brought additional beneficial effects on blood glucose and body weight.

Plasma and extracellular volume in calves: comparison between isotopic and ‘cold’ techniques

While isotopic techniques have largely superseded traditional markers for the determination of the volume of fluid compartments in vivo, they are not always convenient, especially with diarrhoeic animals. A direct comparison was therefore made in week-old calves between Evans blue and radio-iodinated serum albumin as measures of plasma volume and thiocyanate or 24sodium as measures of extracellular fluid space. The correlation coefficients were excellent (1.00, 0.96; P < 0.001) and the calves had plasma and extracellular fluid volumes of 72 +/- 2 and 438 +/- 2 ml kg-1, respectively. The latter value is, though high, typical of young animals and comparable with other data in calves.