RISK FACTORS IN THE CRITICAL BURN PATIENT

Santos Heredero F.X., Garcia Torres V.*, Herruzo R.*, Fernàndez Delgado J.*

Burn Unit, Hospital del Aire
* Burn Unit, Hospital "La Paz", Madrid, Spain

SUMMARY. 194 burned patients were studied to find out the influence of three risk factors, previous pathology (PP), inhalation syndrome (IS) and ventilatory support (VS), on their evolution. The mean mortality rate in patients with PP was 58.7%, more than twice the overall rate (25.2%). The higher mortality appeared in neurological (83%) and epileptic (80%) patients. Patients with PP developed twice as many complications as those without pre-existing disease. A history of toxic or hot fumes inhalation (with or without clinical correlation) was recorded in 42.5% of cases. This increased mortality to 50% (7% without IS). In this group of patients, complications were three times as frequent as in IS-free cases [ARDS (95%), sepsis (81%) and respiratory infections (80%)]. A total of 73 patients (37.6%) required VS. This therapy exponentially increased infective complications as long as the mechanical ventilation was maintained. It is concluded that an exhaustive exploration and anamnesis is mandatory to discover previous diseases and inhalation of fumes during the accident. Once the presence of PP or IS is confirmed a number of therapeutic steps should be taken to prevent the expected high number of complications and to reduce the death risk.

Usually the evaluation of the critical bum patient is based upon the age, burned surface area and depth of the wounds. According to all or some of these parameters, the "probit" scales are elaborated in an attempt to predict the mortality rate of these patients (1). Nevertheless, there are other risk factors directly related to the evolution of the bum disease. In an attempt to find out which are the most expressive factors, we considered a list of them (Table 1) (2).

In this first interpretation of the results obtained, we present the following risk factors:

• previous pathology
• inhalation syndrome
• ventilatory support.

During the period from January 1986 to December 1987, 194 patients were included in the study. The mean age was 39.9 (+/- 1.5) years. The sex distribution was 139 (71.6%) males and 55 (28.4%) females.
The mean burned surface area was 39.6%
1.5). 41.7% of the wounds were subdermal and 58.3% dermal.
Table 2 shows the distribution according to the bum mechanism. It should be pointed that almost 75% of the bums were caused by flame. This fact could explain the great incidence of inhalation injuries that will later be considered.
The frequency of each risk factor was studied in the group and then a statistic analysis was accomplished using chi-square and Fisher tests.

A total of 86 patients (44.3%) were found to suffer from one of the following types of disorders: alcoholism, cardiological, neurological, psychiatric, parenteral drug-addiction, pneumological, metabolic, epileptic, others. The distribution rates are shown in Table 3.
With regard to the influence of pre-existing disease on the mortality rate, Table 4 shows the significant elevation of the death rate in patients with some particular previous pathologies. The mean mortality rate in patients with previous pathology is 58.7%, compared to an overall mortality of 25.3%.
5 out of the 6 patients with neurologic previous disease died, i.e. 83%. These five patients were more than 65 years old: age was thus an added risk factor in th , eir neurological disease. Almost the same rate occurred in the epileptic patients. In contrast to the neurological patients, three out of the four deaths occurred in patients aged between 25 and 45 years old. In these cases age was therefore not an added risk factor.
Another more and more frequent event in our Bum Units is the presence of burned patients with a history of addiction to parenteral drugs. This factor should alert us when receiving this kind of patient. They are likely to have a worse evolution than average cases.
The presence of a previous pathology not only increases the mortality rate but also obscures the general evolution of the patient and causes a higher rate of complications. Out of a total number of 86 patients with previous diseases, 60 (70%) developed some kind of complication during their hospitalization. This contrasts with only 35% of complications in patients without any previous disease. In other words, the patients with previous pathology develop twice as many complications as those without pre-existing disease. Table 5 shows the complication rates with each type of previous disease. We can find some kind of complication in almost all the patients (90%) with psychiatric disorders. As in relation to the death rate, drug addicts show a very high rate of complications (83%). The complications considered in this study are: general infection (with or without sepsis), respiratory infection, cardiac disorders and adult respiratory distress syndrome (ARDS). In all groups of patients with previous pathology, the most frequent complication was ARDS, except for patients with pre-existing cardiac disease, who most frequently developed some kind of cardiac complication.

Inhalation injury appears in three basic forms, alone or in combination: carbon monoxide poisoning, direct heat injury, and chemical damage (8). In our series 82 patients '(42.5%) inhaled some kind of toxic or hot fumes during the thermal accident. This was more frequent in bums caused by flame (64 cases, 78%) occurring in a closed space. These data agree with the most reliable series (4, 5, 6, 7).
A relation was found between IS and the mortality rate. Out of the 82 patients who inhaled toxic fumes, 41 died, representing a mortality rate of 50%. Among the other 45 cases in whom smoke inhalation was not reported, there were only 8 deaths (mortality 17%). The death causes were distributed as follows; sepsis 16 cases (39%), ARDS 13 cases (36.5%), cardiac disorders 5 cases (12.1%), others 5 (12. 1 %). These rates are not far away from the 45 -78% reported by various authors (8, 9, 10).
The above data clearly indicate that the inhalation of toxic fumes is one of the most important risk factors preventing the survival of burned patients. Smoke inhalation has multiple clinical effects: upper airways oedema, tracheo-bronchitis, pulmonary insufficiency, atelectasis, bronchiolitis, ARDS, etc. In our series we consider a patient to have IS only on the basis of the accident history, independently of the clinical repercussion of the fact.
In an attempt to find out the influence of IS on the clinical evolution of the burned patient, the complications of such patients were recorded. Table 6 shows the most important complications and their relation with the presence or absence of IS. Among the 82 patients with IS, 70 of them (85%) developed some of the recorded complications. On the other hand, among the 112 patients without IS, only 28 of them (25%) had a complicated evolution. These data indicate that patients who inhaled smoke develop three times as many complications as those who are IS-free.

Table 1 Potential risk factors

• - Age
• - Burn mechanism
• - Sex
• - Inhalation of hot or toxic fumes
• - Burn surface area
• - Bum depth
• - Debridement date
• - Type of debridement
• - Ventilatory support
• - Previous pathology
• - etc.

Complications related to infection and, pulmonary function were most frequently recorded in patients with IS. As many as 95% of IS patients developed ARDS, and 80% some other kind of respiratory disease. This means that almost all the patients with a history of toxic inhalation will have their lung function compromised. But more serious than this is the finding of 89% of IS patients with ARDS, respiratory infection and sepsis, who developed a critical status that in the majority of cases needed intensive respiratory care.
Other complications occurred only in 32% of IS patients.
In conclusion, patients with a history of toxic inhalation, with or without clinical repercussion on admission, will develop pulmonary conditions and will be infected.

A total of 73 patients required mechanical ventilation, representing 37.6% of the series. This ventilatory support was maintained for I to 7 days in 31 patients, for 7 to 14 days in 29, and for more than 15 days in 13 patients.
Out of the 121 patients without ventilatory support, only I died (0.9%), but out of the 73 mechanically ventilated patients, 49 died (67%). This first finding directly associates mechanical ventilation with mortality (chi-square 42.273, p <0.001).
If we correlate the need of ventilatory support with the incidence of complications, the data are more significant. Table 7 shows the complication rate in patients with and without mechanical ventilation. The first conclusion obtained from these data is that complications are directly associated with mechanical ventilation (p<0.001). Infections are the most frequently reported complications (34%), including sepsis, wound infection and respiratory infections. ARDS, directly or indirectly related to respiratory infection, also has a high rate in patients under mechanical ventilation (50%).
If we draw a graph showing the evolution of infective complications in relation to the duration of mechanical ventilation, we obtain the result shown in Fig. 1. Infective complications are more frequent, in absolute figures, during the second week of mechanical ventilation. In relative terms, there is a progressive increase of complications as the number of days under mechanical ventilation increases. In the second week, 12 out of the 29 patients developed infection (41.4%). With ventilations longer than 15 days we recorded 10 infections out of 13 patients (77%). There is therefore an exponential increase of infective complications in relation to the duration of mechanical ventilation (Fig. 1).
Hansbrough et al. (11) notice that altered cell-mediated immunity accompanies hyperbaric oxygen exposure, and the immunosuppressive effect is exerted through inactivation of macrophages. This could be the origin of some of the infective complications observed in patients under mechanical ventilation with high oxygen concentrations.

Among the 86 patients with previous pathology, 49 (57%) inhaled toxic fumes during the accident. Only 33 patients among the 108 without previous; pathology inhaled smoke (30.5%). This means a double incidence of IS in patients with previous disease if compared with the rate obtained in the group without any pre-existing pathology.
Table 8 shows the incidence of IS among patients with previous pathology. It should be noticed that 100% of the epileptic patients inhaled fumes. Four of them sustained the accident in direct relation with an attack, losing consciousness and inhaling smoke for some time. The fifth epileptic patient was burned while sleeping and until he awoke and escaped he had been inhaling for several minutes.
Drug addiction is another previous pathology with a very high incidence of IS (83.3%). It is probably related to the poor level of self-control of these patients, who are not able to escape rapidly from the fire, and are thus exposed to toxic fumes for a long time.
The eight patients with neurological disease who inhaled smoke were all more than 65 years old. This explains the high incidence of IS in patients with ischaemic cerebral disease.

Alcoholism, a very frequent pathology among our patients, is present in 22% of the cases, and this group had a mortality rate of 58.4%. The altered liver function and associated disorders could be responsible for the poor response to the "general bum syndrome.
Probably age ( >65 years) is responsible for the high mortality (83%) of the patients with pre-existing

Table 5 Complications in patients with previous pathology Table 6 Complications in patients with IS

Table 7 Complications in patients under mechanical ventilation

PP PP / IS % Epileptic 5 / 5 100% Drug addiction 6 / 5 83.3% Neurol ogical 13/ 8 61.5% Psychiatric 10 / 6 60% Metabolic 5 / 3 60% Pneumological 16 / 3 50% Cardiac 15/ 7 46.7% Alcoholism 19/ 8 42% Others 6 / 4 67% Total 86 / 49 57% Table 8 IS in patients with previous pathology (PP)

 

Figure 1 Relation between days of ventilation and infective complications disease.

Drug addiction seems to be a more and more frequent problem in Bum Units. These patients, with or without AIDS antibodies, had 50% mortality and some kind of major complication in 83% of cases. Special attention should be paid to the high incidence of infection in these patients, which seriously obscures the general evolution of the bum syndrome.
Burns caused by flame provoke inhalation of toxic fumes in 78% of cases. This increases the mortality rate to seven times the expected rate for patients without inhalation. The cause of this increase is the presence of three times as many complications in these patients. Almost 100% of the overall IS cases develop either pulmonary or infective complications. Although IS in our series includes only a history of smoke inhalation, with or without clinical correlation, ARDS was developed by 95% of cases and respiratory infection by 80%. These data show the great influence of fumes inhalation on ventilatory function. It means that every patient should be checked for direct or indirect signs of smoke inhalation. These signs mainly are: singed nasal vibrissae, carbonaceous sputum, rales, rhonchi and, in particular, all facial bums caused by flame. The patient or accompanying persons should also be interrogated for details of the accident: mechanism, open or closed space, loss of consciousness, etc. Even if there are no signs of IS on admission, but suspicion of it is amply justified, all measures should be taken to prevent and treat the more than probable complications (10, 12). These measures include thorax X-ray control, ventilatory function monitoring, and blood gas analyses, together with the possibility of oxygenotherapy, intubation, and ventilatory support with PEEP (13) at the first sign of respiratory distress. We believe that the standardizing of an intestinal decontamination protocol helps in preventing a great number of autoinfections. If this is true for all kinds of critically burned patients, in those with IS it should be mandatory, considering their high risk of serious infective complications.
If IS is a demonstrable risk factor for burned patients, another factor is frequently present: the necessity of mechanical ventilatory support. This measure was needed in 89% of the IS patients. Mortality rates increased to almost 10 times those obtained in patients without ventilatory support. This spectacular increase in mortality is directly related to an exponential rise of complications in relation to the number of days under mechanical ventilation. The confirmation of this finding is one of the most evident results of our series. The longer the mechanical ventilation was maintained, the higher the risk of infective complications. This would seem to be due to the presence of a permanent new colonization pathway, restriction of mucociliar bronchial function, etc. Special attention should be focused on keeping the best lung function during respiratory support, in order to minimize areas of poor ventilation, which is a very frequent cause of respiratory infection. If I patient is not able to maintain an acceptable air flow spontaneously, he should be immediately sedated and the ventilator should be used to expand the lungs adequately. In such cases, frequent oropharyngeal cultures, as well as from the tubes system, should be performed, in order to identify possible colonizations
Three pre-existing diseases appeared to have the most important relationship with IS: epilepsy, drug addiction and neurological syndromes. This finding was easily explained by the actual characteristics of the first two pathologies and by the age ( 65 years) and partial disability of the neurological patients. Nevertheless, patients with decreased mentation, such as that produced by drug overdose, alcohol intoxication or neurological disease, frequently experience smoke inhalation injury because , f prolonged exposure to the offending gases. Prim respiratory disease and cigarette smoking compound the effects of inhalation injury and may transform a relatively insignificant injury into a fatal disease.

RÉSUMÉ. Les Auteurs ont étudié 194 patients brûlés pour établir l'influence sur leur évolution de trois facteurs de risque, C'est-à-dire la pathologie précédente (PP), la syndrome d'inhalation (SI) et le support ventilatoire (SV). Le taux moyen de mortalité chez les patients avec PP était 58,7%, plus de deux fois le taux complessif (25,3%). La mortalité majeure se vérifiait chez les patients neurologiques (83%) et épileptiques (80%). Les patients avec PP ont développé des complications deux fois plus fréquemment que les patients sans PP. Il y avait une histoire d'inhalation de fumées toxiques ou chaudes (avec ou sans corrélations cliniques) en 42,5% des cas, ce qui augmentait la mortalité à 50% (7% sans SI). Chez ce groupe de patients les complications étaient trois fois plus fréquentes que chez les cas sans SI [ARDS (95%) ' infection générale (81%), infections respiratoires (80%)]. 73 patients (37,6%) ont eu besoin de SV. Cette thérapie augmentait en manière exponentielle les complications infectieuses tant que durait la ventilation mécanique. Les Auteurs concluent qu'il faut absolument exécuter une exploration et une anamnèse exhaustive pour établir soit les maladies précédentes soit l'inhalation de fumées pendant l'accident. Une fois confirmée la présence de PP ou de SI, il faut prendre des mesures thérapeutiques pour prévenir les nombreuses complications prévisibles et pour réduire le risque de la mort.

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