Annals of the M.B.C. - vol. 1° - n° 2 - September 1988

PREVENTION AND THERAPY OF ACUTE RENAL FAILURE IN SEVERELY BURNED PATIENTS

SUMMARY. In burn casualties, renal function is severely affected. In the treatment of these cases prevention of renal failure is fundamental in preventing complications and death.
Maintenance of the efficiency of renal function is based on water and salts administration, control of cardiac, vascular and respiratory functions and prevention of infections.
In the treatment of impending or actual renal failure the following points must be considered:
- Evaluation of kidney function by assessing the variations of different parameters of renal performance.
- Conduct of proper therapeutic intervention to substitute the efFects of renal failure (dialysis), to minimize their damage to the total organism, and to facilitate clinical recovery (nutrition).

In patients with severe and extensive burns, the renal function can rapidly be endangered by shock, by hypovolaemia, by the loss of the trauma plasma proteins, by hydroelectrolyte imbalances and by the neuroendocrine response to stress.
Taking into consideration the high mortality rate caused by acute renal failure, every etTort must be made to spot the first signs of functional failure which always precede anatomical damage. The aim is to adopt at this stage all the efficacious prophylactic measures available.
To reach this primary objective it is indispensable to adopt a system of multi-parametric monitoring which uses a large range of date, some measured directly, others calculated.
When we decided to begin this type of monitoring we found there were difficulties linked to the value and the meaning to be attributed to the numerous parameters proposed by different authors; we thus had to make a preliminary selection.
Besides having to operate in emergency we had to overcome the difficulties linked to the time needed for the calculation of certain values. Fortunately, the use of the computer, with "ad hoc" programs, now enables us to carry out this type of multi-parametric evaluation in real time.
These programs, besides indicating the degree. of alteration of the function, also facilitate the differential diagnosis among the various possible causes of renal damage.
A preliminary analysis of this problem was necessary in order to realize a program of diagnostic and therapeutic aid. This could be schematized by the algorithms relative to the typical situations which are characteristic of certain types of renal failure: oliguria and anuria.
The appearance of anuria, once the presence of postrenal causes has been excluded, demands the prompt adoption of specific therapeutic measures. It must be kept in mind, in this case, that when there is no urine it is impossible to carry out a whole series of fundamental analyses. It is therefore necessary to base our handling of the case on haemodynamic and serum parameters as well as on the modifications we observe in response to those therapeutic measures which we gradually adopt. If hypovolaemia is present (Central Venous Pressure (CVP) less than 10 cm H 20 or Pulmonary Capillary Wedge Pressure (PCWP) less than 18 mmHg) it can be corrected by the infusion of a suitable quantity of colloids and crystalloids. At a later stage an attempt can be made to restore diuresis by means of the infusion of mannitol. At the same time the administration of 3-5 gamma/Kg/min of doparnine, which increases the renal blood flow, can be begun without -causing other unwanted haemodynamic effects.
If the volaemia is normal or increased (CPV higher than 10 cm H 2 0 or PCWP higher than 18 mmHg) the infusion of dopamine can be begun immediately with the same dosage, and that of fusemide with a high dosage (Img/Kg/hour). In normovolaemic and anuric patients, the administration of mannitol, even in small doses, should be avoided because of the risk of causing congestion or pulmonary oedema. The lack of response to these interventions is a signal to begin dialysis therapy.
In the presence of oliguria our behaviour will be different from that in the case of anuria since in these patients we are able to distinguish directly functional failures from organic ones.
In this sense, as we have already stated, the computer can help us especially in determining the parameters which will tell us the type of failure which is present.
The difterential diagnosis (Fig. 1) derives from the relative modifications of the following parameters: specific weight of the urine; urinary osmolality; the clearance of free water; the concentration of sodium in the urine; the excretion fraction of sodium (Na E17); the index of renal failure; the urinary serum ratios of creatinine and ureic nitrogen.

It is important to stress that these parameters, if taken individually, have a varying degree of reliability.
Recent evaluations have enabled us to establish thar the most reliable are the excretion fraction of sodium and the index of renal failure.
However, the evaluation of all the parameters selected enables us to make a surer judgement for the differential diagnosis between functional and organic forms.
Finally, we can take this opportunity to recall that ARF is not always associated with oligoanuria: in fact, forms in which diuresis is maintained are very frequent. In high risk patients it is therefore indispensable always to monitor the renal function even in the absence of oliguria.
With this in mind, we would like to give an example of the use of computerized monitoring adopted by us.
In the first place, the data for the identification of the patient and the values of the parameters measured are fed into the computer (Fig. 2). Then the computer proceeds to the calculation of the derived parameters (Fig. 3).

From an overall evaluation of the tables supplied by the computer program, the state of renal functionality and of the specific hydro-electrolyte imbalances, which demand immediate correction, can be established with precision.
Once the diagnosis of "acute tubulonecrosis" has been made, it is clearly indispensable to begin immediately a therapy whose foundations are haemodialysis and clinical nutrition.
Much experience has in fact well documented the advantages of specific diets which improve the general conditions of the patient, prevent certain complications caused by uraemic intoxication and delay the beginning of dialysis or lessen its frequency.
Unfortunately, the appearance of anorexia, omiting, gastro-intestinal failure and respiratory failure often hinder adequate alimentation per os.
In this case, if parenteral nutrition is not promptly adopted, the lack of food intake and increased catabolism rapidly bring about a state of serious malnutrition whose effects have a significant influence on the evolution of the pathology.
Unfortunately, in these patients, a correct and efficacious parenteral nutrition meets numerous difficulties. For the most part, these are linked to the metabolic alterations which constantly occur in the course of renal failure. These metabolic alterations have not yet been sufficiently clarified, but they are closely correlated, complex and dynamically evolving; and they effect the carbohydrate, lipid and protein metabolism.
If one wants to assign a therapeutic role to nutrition, a sequential analysis of the evolutionary phases of the clinical situation is indispensable so that what should be done, and how and when, can be accurately programmed. The complete response to these questions does not in fact exist since precise and definitive criteria are not yet available. There do exist, however, principles which it is necessary to uphold, if only to respect the oldest, but still valid, commandment of medicine: "primum non nocere": first do no harm through actions or omissions.
For this reason, it is necessary to stress the need to evaluate attentively the single specific problems which can modify our nutritional strategy day by day. In particular we note sodium, potassium and water retention, the onset of metabolic acidosis, the high levels of ureic nitrogen, the increased demand for the essential aminoacids, the heightened susceptibility to infections, frequent plurisysternic failure and the altered utilization of the energy and plastic substrata.
Taking into consideration that these conditions are often present at the same time and are reciprocally damaging, one can form an idea of the operative difficulties one can meet in the indispensable application of an appropriate and safe parenteral nutrition.
It is possible to supply some indications on the quantitative and qualificative choices of the energyplastic supply which enable us to improve the nutritional state of these patients without causing a metabolic overload of the complications they carry with them.
With regard to the calorie supply, the choice of the energy substratum is fundamental for the realization of an efficacious and at the same time safe nutritional programme.
There are two possible alternatives: either to use glucose as the only calorie source (the Glucose System) or to use both glucose and lipids (the GlucoseLipids System). Both of these solutions have advantages and disadvantages and specific indications.
The Glucose System enables the physician to infuse a high quantity of calories in small volumes by using solutions of 50-70%. It is suggested that, in the case of all those patients with excess water, this be corrected first with appropriate dialysis therapy.
A counterindication for the use of glucose as the only calorie source is the well-documented intolerance associated with the uraemic syndrome, with a tendency to hyperglycaemia and the reduction of the hypoglycaemizing and anabolizing action of insulin.
Infusion with glucose only can also be associated with the inhibition of lipogenesis, an increase in the oxydization of the glucose and of the glycogen deposit, an increase of the catecholamines, increased consumption of O2 and increased production of CO2.
The use of glucose only is not advisable in the presence of respiratory failure and in the case of patients in mechanical ventilation.
On the other hand, the combined Glucose-Lipids System has numerous advantages: less metabolic overload compared to the infusion of a single substratum, the supply of the essential fatty acids, the diminished frequency of hyperglycaemia and hepatic steatosis and a reduced production of CO2 and consumption of O2.
With regard to the nitrogen supply, it is indispensable that it should be sufficient to supply the needs of the organism. For many years, in order to reduce the accumulation of the products of protein degradation which are potentially toxic and to favour the utilization of the urea as a source of nitrogen for the organism, hypoprotein-hypercalorie diets have been adopted. In fact, in the majority of cases, this method hindered the control of the toxic symptomatology and almost always worsened the condition of malnutrition.
Given the present state of knowledge, the hypothesis seems to emerge that with a timely and qualitative choice of alimentation and with appropriate dialysis it is possible to increase the quantity of the protein supply with the result of a rapid restoration and maintenance of a good nutritional equilibrium. The reaching of this objective is facilitated by the moderate use of proteins with a high biological value. The ratio essential aminoacids/total nitrogen must therefore always be greater than 3 to 1.
From what has been said (Fig. 4) it is possible to compile four different parenteral nutrition programmes.

The data are obviously indicative and must be considered exclusively as reference data. Personalization of the nutritional therapy, as far as possible, is always mandatory.
Programme 1 envisages the infusion of glucose as the single source of calories plus essential aminoacids, the latter being the only source of nitrogen. It is indicated for patients with a water overload, electrolyte imbalances, metabolic acidosis and high values of ureic serum nitrogen, to allow time for dialysis therapy to correct the above-mentioned alterations.
This programme can never be continued for a long period of time.
Programme 2 (Isocaloric-Hypoprotein) is indicated during those days when dialysis therapy is not carried out and in the period of resumption of renal function after acute renal failure until creatinine clearance rises above 20 ml/min.
Programmes 3 and 4 are indicated for patients in dialysis therapy. Only these are able to satisfy the high energy-plastic needs of patients with extensive burn. They should be adopted as soon as possible.
In conclusion we can safely affirm that we possess today sufficient diagnostic and therapeutic means to treat with good prospects of success acute renal failure even in patients suffering from severe burns and/or multiple parenchymal failures.

1. - Computerized multi-parametric monitoring facilitates early diagnosis.
2. - Aggressive dialysis technique permits a valid conrol of endotoxicosis.
3. - Parenteral nutrition favours the maintenance of a normal nutritional state and avoids the complications of malnutrition.

Respect for these three fundamental procedures in the treatment of acute renal failure in critical patients has enabled us (Fig. 5) to reduce progressively and significantly the mortality rate which is linked to these complications. From 1971 to 1986, it has progressively fallen from 79% to 42% in the cases we treated.

RÉSUMÉ. 11 est trés fréquent que la fonction rénale se trouve affectée chez les victims de brûlures graves. Dans le traitement de ces cas la prévention d'une crise rénale est fondamentale pour éiter les complications et la mort.
Pour maintenir en pleine efficacité la fenction rénale, it taut administrer de I'eau et des sets, contréIer la fonction cardiaque, vasculaire et respiratoire et prévenir les infections. Dans un tel traitement, it faut suivre différents points qui sont:
- évaluation de la fonction du rein en évaluant les variations des différents paramétres de fonctionnement rénal;
- méthode Wintervention thérapeutique proprement dite pour remplacer les effets de la crise rénale (dialyse), pour réduire leur ravage dans I'ensemble de I'organisme et pour faciliter la guérison clinique (nutrition).