**3. Functional assessment of ANS in patients with SAE**

Assessment of the functional state of ANS is carried out by calculating the autonomic Kerdo index, assessing the severity of pain syndrome using BPS; BrainStem Scores (FOUR, PBSS); trends in the hemodynamic profile of a patient with invasive measurement of systemic hemodynamics, assessment of HRV (variational cardiointervalography), thermometry (peripheral and central), photoplethysmography assessment of perfusion index, quantitative assessment of muscle strength on the MRC scale and MAS; diagnostics the severity of the PSH syndrome in the case of its development with gross dysfunction of the oral parts of the brainstem [52].

### **3.1 Pupillometry**

In recent years, a quantitative evaluation of the pupillary light reflex (PLR) using portable pupillometers has become available in the ICU [53, 54].

Pupillary size is controlled by the balance between sympathetic and parasympathetic systems, integrated at the midbrain level, as well as by neuronal activity of the locus coeruleus, colliculi, and cingulate cortex. It is known that the cholinergic parasympathetic pathways of the brain play the important role in the recognition of infection and integrative response to systemic infection [55].

Various neurotransmitter systems are involved in the control of cortical activity, which may also affect pupillary size, in particular acetylcholine and norepinephrine [55]. *DOI: http://dx.doi.org/10.5772/intechopen.108392 Diagnostics of Central and Autonomic Nervous System Dysfunction in Patients…*

Several researchers have supposed that quantitative PLR (expressed as the percentage pupillary constriction to a calibrated light stimulus) may improve the prediction of neurological outcomes after cardiac arrest [56, 57].

Quantitative pupillometry is used for the assessment of pupillary function, in particular, the neurological pupil index (NPi). The NPi is a scalar value (between 0 and 5) that is calculated based on an algorithm that accounts for several measured pupillary variables, including size, percentage constriction, constriction velocity, dilation velocity, and latency [58]. The NPi is only minimally influenced by medications, in particular, opioids and ambient light, and it accounts for individual baseline pupil size [58, 59]. This is especially valuable due to the fact that patients with SAE in a coma require a therapeutic technique—neurovegetative blockade, implying the use of opioids, hypnotics, and a2-adrenoagonists.

The diagnostic value of the method for monitoring the function of the brainstem for making clinical decisions—withdrawal to the diagnostic window, cessation of neurovegetative blockade—is very high. Since the method is increasingly being used to predict outcomes after cardiac arrest [60], we believe that a dynamic assessment of the diameter and reactivity of the pupil—the most important autonomous PLR using the automated infrared pupillometry method will allow monitoring the functional state of the brainstem (midbrain) and identify the earliest changes in sepsis in the central nervous system. In one study, scientists observed only a weak correlation between NPI (i.e., one pupillometry-derived variable) and the Mxa, which is an index assessing cerebral AR. This correlation remained significant in the septic patients' group, while no correlation was observed in non-septic patients [61].

#### **3.2 Electroneuromyography**

Qualitative electromyography (EMG) reveals myopathic changes in the study of muscles: a decrease in the amplitude and a shortening of the duration of the action potential [62]. One study assessed the frequency and time of onset of neuromuscular disorders using electromyography in patients with systemic inflammatory response syndrome (SIRS) and/or sepsis [63]. Electromyography and conduction velocity measurements were performed on days 2–5 after admission to the intensive care unit. In patients, electromyography revealed signs of neuromuscular abnormality. The means of compound muscle action potential amplitudes of the median and ulnar nerves were decreased.

Special electrophysiological examination—nerve conduction studies (NCS) and EMG are used in critically ill patients from time to time because of the intensity of work in ICUs—heavy patient workload and high cost [64]. Usually, NCS registrate reduced compound muscle action potentials; in the case of (coexistent) critical illness polyneuropathy, reduced sensory nerve action potentials, and normal or slightly reduced nerve conduction velocity [65]. According to Stevens et al., EMG examination of patients in ICU with sepsis revealed primary distal axonal nerve degeneration involving both sensory and motor fibers without signs of demyelination or inflammation [66].

#### **4. Conclusion**

Despite significant advances in the treatment of sepsis, SAE is still associated with the development of acute cerebral insufficiency, severe autonomic dysfunction in the form of autonomic distress syndrome and high mortality due to dystrophic and necrobiotic changes in the autonomic nuclei of the ANS, as shown by studies of pathologists. The revealed changes prove that the septic process causes not only functionally reversible but also morphological pathological changes in the brain resulting from damage to structural and anatomical formations of the ANS, which can serve as an application point for the development of treatment methods for SAE.

The creation of a universal tool for assessing the severity of encephalopathy and determining the dynamics of the restoration of neurocognitive functions, in a particular patient will help the practitioner to evaluate the effectiveness of therapeutic measures, as well as complement specific neuroprotective or metabolotropic therapy. The sensitivity and specificity of each of the considered neuroimaging, neurophysiological research methods, and options for monitoring the functional state of the central and ANS in sepsis will be determined—the next important step in research. Obviously, the development of an algorithm for diagnosing, predicting the course and outcome, and intensive therapy of patients with SAE is ahead. We are convinced that only a multidisciplinary approach for solving such complex tasks will allow us to see results in the coming years.
