Cortical arousal in critically ill patients: an evoked response study

Objective: Assessing the level of sedation in critically ill patients remains a challenge for the intensivist in order to avoid over or under-sedation. Clinical scoring systems may fail in patients with concomitant neurological disorders or requiring muscle relaxants. We evaluated auditory (AER) and median nerve somatosensory evoked responses (MnSSER) in critically ill patients sedated with sufentanil and propofol, in order to quantify the level of sedation during therapeutic interventions. Design: Prospective clinical study. Setting: Anaesthesiological intensive care unit (ICU) in a university hospital. Patients and participants: Thirty-two patients following major abdominal or thoracic surgery requiring sedation during their stay on the ICU. Interventions: During physiotherapy and following nursing care (tracheal suctioning) AER and MnSSER were recorded. The level of sedation was evaluated clinically in relation to vital parameters. Data were analysed by multivariate analyses of variance (Hotellings n), Friedman test. Measurements and results: In comparison to baseline levels the AER latency Nb decreased, while the amplitude NaPa increased during physiotherapy and after tracheal suctioning (p < 0.001). In contrast, the MnSSER latency P25 decreased and the amplitude P25N35 increased after tracheal suctioning only (p less than or equal to 0.001). Clinical sedation scores decreased and mean arterial blood pressure increased during physiotherapy and nursing care. Conclusions: Changes of AER or MnSSER waves indicated cortical arousal in ICU patients during nursing care and physiotherapy. Further studies with evoked responses are recommended to evaluate whether bolus injections of sedatives and/or analgesics reduce cortical arousal and thereby minimise the patient's stress during nursing care.