Introduction
Critical care medicine has evolved rapidly over the last two decades, with therapeutic and technological advances leading to improved outcome in a wide variety of life-threatening conditions. his is particularly the case for neurological disorders where improved understanding of the pathophysiology of neurological injury, in association with advances in monitoring and imaging techniques, has led to the introduction of more effective and individualized treatment strategies that have translated into improved outcomes. In parallel, neurointensive care has developed as a subspecialty of intensive care medicine dedicated to the treatment of critically ill patients with primary and secondary neurological disease. his topic will review the history, evolution and organization of neurointensive care units and emphasize the key role that neurointensive care teams play in delivering improved outcomes for patients.
History of neurointensive care
The origins of neurointensive care date back to the poliomyelitis epidemics of the 1940s and 1950s when specialized teams established the principles of prolonged mechanical ventilation and high-intensity nursing support in dedicated wards. In the 1970s and 1980s, advances in neurosurgery and neuroan-aesthesia allowed more complex interventions that brought the need for close monitoring and management in the post-operative period. Areas of neurosurgical wards, staffed by neurosurgical teams, became the early neurosurgical intensive care units (ICUs). hereafter, neurointensive care expanded to include the management of patients with a broader range of neurological disorders such as traumatic brain injury (TBI), subarachnoid haemorrhage (SAH), intracranial haemorrhage, elevated intracranial pressure (ICP), neuromuscular respiratory failure, status epilepticus and the medical complications of brain injury. he management of critically ill patients with neurosurgical and neurological disease were thus combined into a single specialist unit where neurointensivists, neurologists, neurosurgeons and their teams provide comprehensive management for complex and life-threatening disorders of the central nervous system (CNS). More recently, neurointensive care has embraced the management of conditions, such as acute ischaemic stroke, that were not traditionally seen as part of its role. Its primary challenge now is the resuscitation and treatment of patients with massive traumatic and vascular brain injuries that were previously assumed to be unsalvageable.
Key to the success of neurointensive care is an appreciation that not only is the CNS, and particularly the injured brain, greatly influenced by systemic physiological perturbations but that brain injury itself can adversely affect non-neurological organ systems. Neurointensive care has therefore evolved from its original single-system focus on the CNS to a multisystem speciality providing all aspects of a patient’s care.
Neuromonitoring
The monitoring of critically ill neurological patients has become increasingly complex. Besides the close monitoring and assessment of cardiac and respiratory functions common to all critically ill patients, modern neurointensive care utilizes a host of neurological monitoring techniques to identify or predict the occurrence of secondary insults and guide therapeutic interventions. he benefits of neuromonitoring can be summarized as follows:
1. Monitoring temporal changes in the pathophysiology of brain injury and its response to treatment.
2. Early detection of secondary adverse events.
3. Guiding individualized, patient-specific therapy.
4. Avoiding unnecessary, and potentially harmful, treatment interventions.
The role of the clinical examination in the assessment of neurological status should not be underestimated. Te Glasgow Coma Scale (GCS) provides a standardized, internationally recognized method for evaluating a patient’s global neurological status by recording their best eye opening, motor and verbal responses to physical and verbal stimuli.As the GCS is a global assessment of neurological function, it provides no information about focal deficits. Localizing signs such as pupil responses and limb weaknesses provide useful additional information and should be recorded alongside the GCS. T e Medical Research Council (MRC) grading scale is widely used to assess motor response.
Although serial clinical assessment performed by an experienced nurse is the simplest and most effective neurological monitor, clinical evaluation has several limitations. It is unable to detect changes in patients who are receiving sedative drugs and provides a qualitative rather than quantitative assessment of neurological function. Various cerebral m onitoring techniques have been developed in an attempt to overcome these disadvantages and are discussed elsewhere in this topic.
Developments in multimodality monitoring have allowed a move away from rigid physiological target setting towards an individually tailored, patient-specific approach to management. Multimodal monitoring also allows cross-validation between different monitoring variables, improved artefact rejection and greater confidence in making treatment decisions. In addition, it gives clinicians confidence to withhold potentially dangerous therapy in those without evidence of brain ischaemia/hypoxia or metabolic disturbance. Te wealth of data generated by multimodal monitoring provides a challenge in terms of data integration, analysis and accessibility, but software applications that provide clinically relevant information at the bedside have recently become available.
Variations in monitoring practice
Despite the widespread availability and relative simplicity of many neuromonitoring techniques, there is considerable variation in their placement and in the application of monitoring-guided therapeutic strategies. Tis is the case even for ICP monitoring, the indications for which are the subject of expert consensus guidance. In a 2002 study from the USA, ICP monitors were placed in only 58% of patients who fulfilled the established criteria for monitoring, but therapies to reduce raised ICP were routinely applied in patients who were not monitored. Recent audits suggest that around 75% of neurointensive care units in developed countries now use ICP monitoring after TBI, compared with 9-28% of non-specialist units that care for head-injured patients. Although a recent systematic review conducted by the Cochrane collaboration concluded that there is no evidence that ICP monitoring improves outcome in comatose brain-injured patients, there is a large body of clinical evidence supporting its use to detect expanding intracranial mass lesions, guide therapeutic interventions and assess prognosis after TBI. It is now widely accepted as a relatively low-risk, high-yield and value-for-money intervention in severe head injury and is being increasingly used in other conditions.
Principles of neurointensive care
Critically ill neurological patients require meticulous general intensive care support as well as interventions targeted to their neurological disorder. Te overall goals of neurointensive care are to resuscitate and support the acutely ill patient, minimize secondary neurological injury, and prevent or treat systemic (non-neurological) complications.
Evolving practice
Many developments over the last decade have changed the way that acute disorders of the CNS are viewed and treated. For example, the intensive care management of brain injury has undergone extensive revision as evidence accumulates that long-standing and established practices are not as efficacious or innocuous as previously believed. Traditional therapies such as fluid restriction and hyperventilation have been called into question and are no longer recommended, and newer or reinvented therapies, such as therapeutic hypothermia and decompressive craniectomy, remain controversial. Te sole goal of identifying and treating intracranial hypertension has been superseded by a focus on the prevention of secondary cerebral ischaemic insults using a multifaceted physiological neuroprotective strategy. his usually incorporates a systematic, step-wise approach to maintenance of adequate cerebral perfusion and oxygenation, and control of raised ICP. As there is considerable pathophysiological heterogeneity after brain injury, some commonly used interventions may be ineffective, unnecessary or even harmful in some patients at certain times. he importance of individualized therapy, guided by multimodal monitoring, cannot therefore be overemphasized. he general principles of the intensive care management of brain injury are shown in Table 18.1.
Table 18.1 Summary of intensive care management of patients with brain injury
|
Respiratory |
PaO2 >13 kPaand PaCO2 4.5-5.0 kPa |
|
PEEP (<15 cmH2O)to maintain oxygenation |
|
|
Strategies to minimize risk of pneumonia |
|
|
Cardiovascular |
MAP >90 mmHg |
|
Normovolaemia |
|
|
Vasopressors/inotropes |
|
|
ICP and CPP management (after TBI) |
ICP <20 mmHg and CPP |
|
50-70 mmHg |
|
|
Sedation/analgesia |
|
|
20-30° head-up tilt |
|
|
Volume expansion plus norepinephrine to maintain CPP |
|
|
Treatment of intracranial hypertension |
Osmotic therapy (mannitol or hypertonic saline) |
|
Moderate hyperventilation |
|
|
Moderate hypothermia |
|
|
Cerebrospinal fluid drainage |
|
|
Barbiturates |
|
|
Decompressive craniectomy |
|
|
Miscellaneous |
Normoglycaemia |
|
Pyrexia treatment |
|
|
Enteral nutrition |
|
|
Thromboembolic prophylaxis |
|
|
Seizure control |
CPP, cerebral perfusion pressure; ICP, intracranial pressure; MAP, mean arterial pressure; PaCO2, arterial partial pressure of carbon dioxide; PaO2, arterial partial pressure of oxygen; PEEP, positive end-expiratory pressure.
The scope of practice
As neurointensive care has evolved, its case mix has broadened and, in parallel, the severity of cases admitted to neurointensive care units has increased.
Traumatic brain injury
Consensus guidance for the management of TBI has been available for many years and the most comprehensive, from the Brain Trauma Foundation, has recently been revised. Because of the lack of class 1 data from randomized controlled trials, the majority of the recommendations are at the level of options based on class 2 or 3 data, i.e. from small prospective or retrospective studies, observational studies or case series. Despite the paucity of high-quality evidence, there is a consensus that rigorous and continuous monitoring and management of TBI on the neurointensive care unit is associated with improved outcome.
The intensive care management of TBI is complex and requires a coordinated approach. In addition to brain-targeted therapy, general intensive care principles, including optimization of cardiorespiratory variables, glycaemic control, management of pyrexia and early enteral nutrition.
Cerebral ischaemia is the dominant factor determining secondary brain injury, and recent studies characterizing its incidence and mechanisms have demonstrated that the ischaemic burden is correlated with outcome after TBI. Prevention and treatment of cerebral ischaemia using ICP- and cerebral perfu-sion pressure (CPP)-guided treatment strategies is a major focus of the intensive care management of TBI. However, recent evidence suggests that brain resuscitation based on control of ICP and CPP alone does not prevent cerebral ischaemia/hypoxia in all patients. Measurement of ICP and CPP in association with monitors of the adequacy of cerebral perfusion, such as brain tissue oxygenation and biochemistry, provides a more complete picture of the injured brain and its response to treatment. here is preliminary evidence to suggest that treatment targeted towards maintenance of adequate brain tissue oxygen tension, in addition to ICP and CPP, might be associated with improved outcome after TBI.
A study from the Trauma Audit and Research Network confirmed that 33% of 22,216 patients presenting with severe TBI in the UK between 1989 and 2003 were not treated in a neurosurgical centre at any stage in their management. his was associated with a 26% increase in mortality and a 2.15-fold increase (95% confidence interval (CI) 1.77-2.60) in the case-mix adjusted odds of death compared with treatment in a neurosurgical centre. Underprovision of specialized neurointensive care beds is the reason why many head-injured patients continue to be managed in non-neurosurgical units in many parts of the world. As a consequence, referral practices are dominated in many areas by the need for operative neurosurgical intervention at presentation so that those requiring urgent intracranial surgery are prioritized for transfer to a neurointensive care unit. However, many patients with severe TBI have evidence of raised ICP in the absence of surgical lesions, and suffer morbidity and mortality equal to those with such lesions. Furthermore, patients with no surgically remedial lesion often require complex therapeutic interventions to control ICP and CPP, and outcome is improved when these are delivered within the context of specialist neurointensive care. It is therefore illogical that these are the patients who are still most likely to be managed in non-neuroscience units. It can also never be certain that a patient with severe TBI will not require urgent neurosurgical intervention at some stage, and delay in providing such treatment is a major preventable cause of mortality and morbidity.
Subarachnoid haemorrhage
Patients with aneurysmal SAH require complex treatment and extended monitoring. Management is targeted at securing the ruptured aneurysm, optimizing cardiovascular variables, detecting and treating cerebral vasospasm and managing medical complications. hese treatment strategies call for interdisciplinary collaboration between neurosurgeons, neuroradiolo-gists, neurointensivists and specialist nurses, and the neurointensive care unit is the focal point of these combined efforts. Multidisciplinary clinical collaborations, in association with technological advances, have reduced the overall mortality rate after aneurysmal SAH from around 50% to 20% over the last two decades. he advent of less invasive interventions for securing a ruptured aneurysm has allowed effective treatment of sicker patients and, as a result, many more World Federation of Neurological Surgeons (WFNS) grade 4 and 5 SAH patients are being admitted to neurointen-sive care units. Although such patients have substantial comorbidities and are at increased risk of developing intracranial and systemic complications, there is accumulating evidence that aggressive cardiopulmonary and neurological resuscitation, in association with early aneurysm control and advanced monitoring and management in a neurointensive care unit, offers the best potential for achieving good outcomes.
Intracerebral haemorrhage
Intracerebral haemorrhage is the most devastating form of stroke, with high rates of mortality and morbidity. Aggressive treatment, including monitoring and management of cardiorespiratory variables and ICP, in addition to meticulous blood pressure, fluid balance and glycaemic control, improves outcome after intracranial haemorrhage. here is substantial evidence that management of patients in a specialist neurointensive care unit is also associated with improved outcomes. One study analysed data collected prospectively by Project Impact (a data collection tool developed by the Society of Critical Care Medicine) from 42 participating ICUs over a 3-year period and found that not being in a neurointensive care unit was associated with an increased hospital mortality rate (odds ratio 3.4) after acute intracranial haemorrhage. In another study, mortality and hospital discharge status were significantly improved following treatment of intracranial haemorrhage in a neu-rointensive care unit compared with a similar cohort of patients treated 2 years earlier in a general ICU in the same institution. In this study, patients treated in the neurointensive care unit also had shorter hospital stays and lower total costs of care than a national benchmark.
Ischaemic stroke
Early studies confirmed that patients cared for by dedicated stroke teams in stroke units have better outcomes, and integrated multidisciplinary services for stroke patients are now commonplace. More recent studies have demonstrated that input from a specialized neurointensive care team can bring additional outcome benefits in critically ill stroke patients. In a retrospective case note review of 400 patients with acute ischaemic stroke admitted to a neurointensive care unit over a 3-year period, the introduction of a neurointensive care multidisciplinary team was associated with decreased ICU and hospital lengths of stay and a significantly greater proportion of patients being discharged home rather than to a long-term care facility (47 vs. 36%, respectively).
Recent advances in stroke management include intra-arterial thrombolysis, neurointerventional techniques for mechanical clot extraction or lysis, and decompressive craniectomy for malignant middle cerebral artery infarction. In most comprehensive stroke centres, the neurointensive care unit has become the focal point for coordinating these urgent, high-intensity and complex interventions, and for managing intracranial and systemic complications.
Hypoxic brain injury
Although overall survival rates following cardiac arrest remain low, approximately one-third of patients admitted to an ICU after cardiac arrest survive to hospital discharge. However, there is considerable variation in post-cardiac arrest treatment and patient outcome between institutions, despite good evidence that targeted interventions applied after the return of spontaneous circulation significantly increase the chances of survival with good neurological outcome. he neurointensive care unit is the optimal location for the management of comatose cardiac arrest survivors because many of the interventions that increase the chances of a good neurological recovery are identical to those that are widely applied in brain-injured patients generally.
Primary neurological disease
Specialist neurointensive care units are also concerned with the management of primary neurological illness and its consequences. hese include myasthenia gravis, Guillain-Barre syndrome, encephalopathies, CNS infections and status epilepticus. Management is directed towards specific treatments of the primary condition and also to the management of ensuing complications, such as profound neuromuscular weakness-related ventilatory failure, autonomic derangements and bulbar insufficiency.Many neurological patients remain dependent on intensive care support for very long periods of time, resulting in significant psychological demands on the patient, their carers and the neurointensive care unit multidisciplin-ary team.
