Neurological consultations in the medical intensive care unit
Journal of Neurology, Neurosurgery and Psychiatry
C ritical care therapy has advanced over the past two decades, treating more patients and providing more complex care. However, the improved survival from septic shock, adult respiratory distress syndrome (ARDS), and multiple organ system failure results in critically ill patients facing a spectrum of new complications secondary to both illness and treatment. A third of intensive care unit (ICU) admissions have a neurological complication detrimental to outcome. 1 Neurological status (mainly
... ressed consciousness) is the major contributor to prolonged ventilation in a third of those who need it and is a significant factor in an additional 40%. Neurological complications double both the length of stay in hospital and the likelihood of death; the mortality rate for patients with neurological complications is 55% compared to 29% for those without. It is therefore unsurprising that neurologists are being increasingly called upon to review patients on the medical intensive care unit (MICU). A neurological opinion is usually requested: c to assess neurological manifestations of the primary disease process c to evaluate the consequences of critical care therapy c to offer a prognosis, or c determine brain death. The neurologist must approach these complex patients in a logical, meticulous, and sensitive manner. There are obvious inherent difficulties in reviewing on the MICU: c difficulties in communication (sedation/endotracheal tube) c bulky case records and numerous investigation results (scans often "off-site") c a "Pandora's box" of ICU terminology (ARDS, SIRS, MODS, etc) c unfamiliarity with types and levels of respiratory support, anaesthetic agents, and neuromuscular blockade c limitations of the clinical examination caused by sedation or neuromuscular blockade c constraints in arranging further investigations (for example, availability of neurophysiology or ventilator/magnetic resonance imaging (MRI) compatibility) c TERMINOLOGIES The terminologies used on the ICU are formidable and often ill understood by the consulting clinician. Knowledge of the taxonomy of sepsis and allied syndromes is essential in appreciating their neurological implications. We define here the most important terms with their significance. Septic shock is the most common cause of death on the ICU, though the specific infection is identified on culture in only 30-50% of cases. The sepsis syndromes (table 1) represent a spectrum of clinical illness from systemic inflammatory response syndrome (SIRS) through organ dysfunction to multiple organ failure to death caused by immune responses to infection, and characterised by systemic inflammation. SIRS consists of alterations in physiological variables induced by infection. Sepsis is SIRS in the presence of documented infection. Severe sepsis is defined as sepsis with end organ dysfunction or hypoperfusion. Septic shock is sepsis associated with hypotension despite adequate resuscitation (intravenous fluids, inotropes, vasoactive agents, and specific treatment), together with perfusion abnormalities (lactic acidosis, oliguria, acute alteration in mental status). Organ dysfunction refers to inadequate function of kidneys, lungs, gut, liver, skin, heart or central nervous system. The multiple organ dysfunction syndrome (MODS) or multiple organ system failure is defined as the presence of altered organ function in an acutely ill patient such that homeostasis cannot be maintained without intervention. The inflammatory mediators released in the sepsis syndromes make them the most likely cause of acute lung injury (ALI) and the acute respiratory distress syndrome (ARDS). Altered integrity of the alveolar-capillary membranes leads to non-cardiogenic pulmonary oedema, resulting in hypoxaemic respiratory failure and ALI, the severe form of which is ARDS. The mortality rate in SIRS is approximately 7%, in sepsis 16-20%, and in septic shock 45%.