**3. Source of problems**

The best defense is an attack, and in our case, the best fight against delirium is to prevent the factors that lead to it. Many studies do not ignore these factors. Among them, one can single out those that are relevant for any surgical interventions, and

those that are found only in cardiac surgery. The first group of factors is very diverse, and it is interesting that they exist even before the start of the operation. Among them, there are obvious ones, such as the administration of anticholinergic drugs or benzodiazepines for the purpose of premedication, which has long become by no means a positive tradition for many medical institutions [28, 29]. A less obvious factor that is rarely paid attention to is the increased level of preoperative anxiety in the child, which significantly increases the risk of developing POD in the postoperative period [30, 31]. If we talk about the characteristic features of children in the older age group, then it makes sense to single out the social predictors of POD: this is the male gender and the low level of education. It is also known that belonging to the white race reduces the likelihood of AML [32]. Age plays an important role in the pathophysiology of POD development. It's all about the active transformation of the child's brain—the development of neurons and interneuronal connections at the age of up to 1 year. That is why most researchers consider this age to be the most dangerous for operations in terms of the development of cognitive impairment [1–3], although there are studies on the basis of which the FDA recommends extending this age interval to 3 years. According to the same recommendations, the duration of anesthesia over 3 h is associated with an increased risk of developing POD [33]. The frequency of anesthesia, of course, also has a negative impact [34]. Regarding the anesthetic management itself, it must be remembered that inadequate analgesia can lead to the appearance of delirium, and pain is important not only from the surgery itself but also from concomitant manipulations, such as tracheal intubation or placement of a central venous catheter [9, 35, 36]. Given that the brain is a finely organized structure with special needs, metabolic imbalances in the body, such as episodes of intraoperative hypoxia or hypoglycemia at any time of the operation, are also a risk factor for the development of POD [37]. Often, such hypoxia can occur due to blood loss and acute anemia (which is very typical for cardiac surgery), in which case transfusion of erythrocyte mass and fresh frozen plasma is used. But, as recent studies show, such correction may increase the risk of postoperative cognitive impairment. The reason for this is the systemic inflammatory response (SIR) [38, 39], and we will return to it later.

More narrowly specialized is a group of factors in cardiac surgery. Such interventions are often accompanied by hemodynamic changes and infusion of sympathomimetic drugs, which is especially typical for surgical interventions in children with CHD and adversely affects cerebral perfusion and, consequently, the child's cognitive status [40, 41]. However, the widest range of factors provoking the development of postoperative cognitive disorders is cardiopulmonary bypass [42]. This is the contact of the patient's blood with the surface of the circuit of the heart-lung machine, initiating SIR [43], hemolysis due to mechanical injury of erythrocytes from the operation of roller pumps, and contact of blood with the air [44], hemodilution, which causes a decrease in the patient's hematocrit and oncotic blood pressure [26, 45]. The consequence of hemodilution and hemolysis, and not only large blood loss, explains such a frequent need for transfusion during cardiac surgery. The components of donor blood, carrying foreign material for the body, always incline it to the progression of SIR, affecting the brain [38, 46]. In a recent study, it was found that children who received at least one transfusion were twice as likely to develop POD as compared to children without a history of transfusions. Moreover, the following relationship was observed: every 10 ml of RBC transfusion per kilogram of body weight increased the likelihood of developing delirium by 90% [39].

With the introduction of the latest devices for registering microemboli in the circuit of the heart-lung machine, the problem of their influence on the cerebral

## *Delirium in Children after Cardiac Surgery: Brain Resuscitation DOI: http://dx.doi.org/10.5772/intechopen.102130*

vessels and cerebral ischemia that occurs, in this case, has gained relevance [47, 48]. Changes in the patient's blood temperature during cardiopulmonary bypass are also directly related to it. The whole point is in mixing the venous blood flowing into the cardiotomy reservoir (the temperature of which is always lower) and the arterial blood flowing out of the oxygenator (most often having a temperature that is familiar to humans—about 37°C). With this mixing, air bubbles are formed from the liquid part of the blood, which can get to the patient, causing air microembolism [49]. Temperature control is also important to avoid cerebral hyperthermia, which can negatively affect the brain [50].

Of great importance is not only the fact of cardiopulmonary bypass but also its duration, as well as the time of clamping of the aorta (actually ischemia of the heart myocardium) [37]. All of these factors, in addition to their direct destructive effect on the brain, ultimately initiate and enhance the development of SIR [43, 51]. The combination of such a variety of factors determines the entire complex of the pathophysiology of brain damage.

However, the problem is also that the onset of delirium is influenced not only by intraoperative but also by many factors of the immediate postoperative period. For cardiac surgery (especially in children), this period is always difficult due to the volume of interventions. Often, a long stay in the intensive care unit is required, due to which patients experience stress caused by medical manipulations, noise and disturbance of circadian rhythms, pain syndrome, and many other factors [52, 53]. In an attempt to neutralize at least some of these factors, benzodiazepines are often used (especially in patients on mechanical ventilation). But such an aspiration does not always benefit the patient and, based on recent studies, increases not only the incidence of POD, but also the length of stay in the intensive care unit [54, 55]. It is also interesting that the harmful effect of benzodiazepines can be enhanced by the administration of anticholinergic drugs [56]. Often, patients require prolonged mechanical ventilation, which is directly related to the risk of delirium. A recent study shows that any form of respiratory support can lead to the development of delirium. Of course, invasive artificial ventilation of the lungs with the presence of an endotracheal tube in a child has the greatest effect on him; nevertheless, attention is drawn to the fact that even the use of nasal cannulas for oxygen therapy can increase the risk of developing AML [26].
