Tavistock Neurosurgical Intensive Care Unit, Box 30, The National Hospital for Neurology and Neurosurgery, University College London Hospitals, Queen Square, London WC1N 3BG, UK E-mail: martin.smith{at}uclh.org
Neurocritical care is an evolving subspeciality of intensive care medicine that is just beginning to reach maturity.1 It focuses on the care of critically ill patients with primary or secondary neurosurgical and neurological problems and was initially developed to manage postoperative neurosurgical patients. It expanded thereafter to the management of patients with traumatic brain injury (TBI), intracranial haemorrhage and complications of subarachnoid haemorrhage, including vasospasm, elevated intracranial pressure (ICP) and the cardiopulmonary complications of brain injury. More recently, the concept of neurocritical care has further developed to coordinate the management of critically ill neurosurgical and neurological patients within a single specialist unit and to include clinical areas, such as acute ischaemic stroke, that were not traditionally seen as part of its role. Whilst it has been suggested that care in specialized intensive care units (ICUs) is of higher quality than in general units because it focuses on the special needs of a specific patient population and is provided by a multidisciplinary team whose training emphasizes the unique aspects of the disease processes in that patient population, the evidence that specialized neurocritical care improves outcome remains elusive.
The importance of the early identification and treatment of secondary insults after acute brain injury is well established,2 and the aim of the intensive care management of TBI is to anticipate, prevent and treat secondary physiological insults. Although the vast majority of recommendations for the management of severe TBI are not at the level of guidelines or options (based on class II or III data, respectively), consensus guidance for management of head injury has been issued3 4 and has contributed to changes in practice.5 Although the cerebral perfusion pressure (CPP) target remains the subject of much debate,6 optimal CPP should be determined for each patient and made part of an individualized treatment strategy.7 Therefore there has been a shift of emphasis from primary control of ICP to a multifaceted approach of maintenance of CPP and brain protection during the management of TBI. The importance of maintaining cerebral oxygenation and perfusion throughout the entire management period is now accepted.8
Intuitively, therefore, specialist neurocritical care with ICP- and CPP-guided therapy should improve outcome after TBI. However, we must ask whether there is any evidence that this is the case. Many studies over the last decade confirm the efficacy of protocol-driven neurocritical care in reducing mortality and improving outcome in patients with severe neurosurgical and neurological disease. Early work suggested that outcome is improved in stroke patients cared for by dedicated stroke teams in stroke units, and integrated multidisciplinary services for stroke patients are now commonplace.9 In a study investigating outcome after intracerebral haematoma, treatment in specialist neurocritical care units was associated with a 3.4-fold reduction in hospital mortality rate compared with treatment in general ICUs.10 Patel and colleagues11 demonstrated that establishment of an evidence-based protocol for head injury management resulted in a significant increase in favourable outcome after severe TBI (from 40.4% to 59.6%) compared with historical controls, including a high proportion with a favourable outcome in those presenting with evidence of raised ICP in the absence of intracranial mass lesions. In a similar study which included all categories of head injury admissions, the proportion of patients who experienced a favourable outcome increased from 40% to 84% following the introduction of a standardized treatment protocol system, and this was associated with a substantial reduction in mortality.12 The striking improvements noted in these studies suggest that high-quality neurocritical care with the delivery of targeted therapeutic interventions does have an impact, not only on survival, but importantly also on the quality of survival. In this issue, Clayton and colleagues13 add further evidence by reporting a reduction in ICU mortality from around 20% to 13.5%, and a reduction in hospital mortality from 24.5% to 20.8%, following introduction of an evidence-based management protocol for patients with TBI. The improvement in mortality occurred despite an increase in the median age and APACHE II score of the patient population after implementation of the protocol. This study used mortality as the only outcome measure, but decreased mortality does not always imply improved outcome, particular in the neurosciences. The Clayton study,13 like many others, used a historical control group and the authors accept that factors other than the introduction of protocol-guided management might have been responsible for their findings. However, the ICU in which the patients were managed in this study also admitted other patient groups, and the ICU mortality for those without head injury did not change significantly over the same period. This feature of the study lends considerable support to the claim that the benefits to the head-injured patients derived directly from introduction of a protocol-driven management paradigm.
On the face of it, therefore, there seems to be little doubt that good neurocritical care and protocol-guided therapy are able to reduce mortality and improve outcome after brain injury. However, this does not in itself equate to proof that neurocritical care units provide enhanced care compared with general ICUs. Treatment algorithms for maintenance of CPP require intensive clinical and neuromonitoring, and the interventions that are required to monitor and treat acute brain injury could well be provided in any large general ICU. Therefore it is important to ask whether dedicated neurocritical care facilities can offer anything special over and above the care that can be provided in a general ICU setting. The answer to this question is almost certainly yes, but the reasons for this may not be immediately obvious. The association between systemic hypotension and adverse outcome after TBI is well established, and careful blood pressure control throughout the entire management period is crucial.14 Members of a multidisciplinary team who care regularly for patients with acute brain injury are more likely to be aware of the adverse impact on the brain of secondary physiological insults and to be more obsessional about their prevention, recognition and treatment. It is likely that blood pressure control is more aggressive in neurocritical care units compared with general ICUs, resulting in a lower incidence of systemic, often iatrogenic, hypotension.15 The same is also likely to be the case for the management of tight arterial blood gas targets. Furthermore, other complications, such as fever, that are common in brain-injured patients and which adversely affect outcome might be managed differently by neurointensivists than by general intensivisits. It is also likely that neurocritical care physicians will have a clearer understanding of the pathophysiological basis of the systemic complications that are common after TBI, and that this will result in more rational treatment strategies that do not worsen the underlying brain injury.16 The provision of a dedicated cohort of medical, nursing and other health professionals, supervision of ICU care by a dedicated neurointensivist and involvement of senior neurosurgeons with rapid access to surgical therapy is also likely to have a positive impact on patient management and outcome.10 For example, reliability of patient assessment, such as measurement of the Glasgow coma score, might be considerably different for nursing staff in a neurocritical care unit compared with those in a general ICU, leading to earlier detection of neurological deterioration. Acute rehabilitation is also important in securing improved long-term neurological outcomes after TBI. Intervention from neurophysiotherapists, as part of the neurocritical care multiprofessional team, is likely to occur earlier and more reliably in a specialist unit than in a general ICU.
Larger units and higher caseload are also important factors in improving outcome after brain injury.17 Protocols that include ICP monitoring and CPP-directed therapy can be (and are) established in general ICUs in non-neurosurgical centres. However, such units might see only two or three cases of severe TBI each year. They are unlikely to maintain sufficient skills to use complex interventions to manage patients as well as specialist centres which may admit this number of cases each week. Any benefits that might accrue from management of TBI in a specialist unit clearly depend upon multiprofessional working within a highly integrated team of specialists, delivering individualized care based on consensus guidelines. Therefore it has been suggested that neurocritical care is not just a name but a way of life.18
Notwithstanding the potential benefits of specialist neurocritical care, there remain clear variations in practice between units and significant differences in the implementation of established management and monitoring strategies.5 19 For example, in 1996 only 50% of neurosurgical centres in the UK routinely monitored ICP in comatose patients and ICP monitoring was never used in 8% of centres.19 By 2001, 75% of UK neurosurgical centres were monitoring ICP in the majority of severe TBI patients, and it seems likely that this shift in practice occurred because of improved adherence to published guidelines.5 Bulger and colleagues20 examined the effect of variations in care on outcome in patients with severe head injury and found that centres that aggressively monitor, and therefore presumably manage, ICP have better outcomes. The unanswered question remains whether aggressive ICP monitoring and management per se improve outcome or whether they are simply a proxy marker for units that control ICP and manage CPP more vigorously. In another study, there was no difference in the incidence of intracranial hypertension between centres, but there was a difference in maintenance of mean arterial pressure and CPP above target values, as well as in other markers of more aggressive therapy, such as vasopressor use and placement of ventriculostomies, in aggressive management centres.21 Thus it might be inferred that the management of head-injured patients in aggressive units is more targeted, and therefore perhaps more sophisticated, providing an integrated approach to the maintenance of cerebral perfusion rather than focusing solely on reduction in ICP. It is this integrated approach to patient management that is likely to be paramount in any potential benefits that might be delivered by specialist neurocritical care.
The ability to identify patients at risk of needing complex specialist treatment early in their clinical course would allow more selective referral of suitable patients to specialist neurocritical care facilities, but such stratification does not appear to be feasible.10 Although there is a compelling argument for managing all severely head-injured patients in a specialist ICU, whether or not they require neurosurgical intervention, there is currently underprovision of neurocritical care beds in the UK.22
Research into neurocritical care has contributed to our understanding of the pathophysiology of brain injury and its management. It is likely that the improved knowledge and expertise that comes with specialization and increased caseload will deliver improved outcomes after acute brain injury. Data suggest that patients managed in specialist neurocritical care units are more likely to do better than those managed in general ICUs. However, it is important that we continue to strive to demonstrate this conclusively, and determine exactly why it might be the case.
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