Hyperventilation versus cerebral perfusion pressure management: time to change the question

Monitoring the injured brain: ICP and CBF

Raised intracranial pressure (ICP) and low cerebral blood flow (CBF) are associated with ischaemia and poor outcome after brain injury. Therefore, many management protocols target these parameters. This overview summarizes the technical aspects of ICP and CBF monitoring, and their role in the clinical management of brain-injured patients. Furthermore, some applications of these methods in current research are highlighted. ICP is typically measured using probes that are inserted into one of the lateral ventricles or the brain parenchyma. Therapeutic measures used to control ICP have relevant side-effects and continuous monitoring is essential to guide such therapies. ICP is also required to calculate cerebral perfusion pressure which is one of the most important therapeutic targets in brain-injured patients. Several bedside CBF monitoring devices are available. However, most do not measure CBF but rather a parameter that is thought to be proportional to CBF. Frequently used methods include transcranial Doppler which measures blood flow velocity and may be helpful for the diagnosis and monitoring of cerebral vasospasm after subarachnoid haemorrhage or jugular bulb oximetry which gives information on adequacy of CBF in relation to the metabolic demand of the brain. However, there is no clear evidence that incorporating data from CBF monitors into our management strategies improves outcome in brain-injured patients.

Hyperventilation in head injury: a review

The aim of this review was to consider the effects of induced hypocapnia both on systemic physiology and on the physiology of the intracranial system. Hyperventilation lowers intracranial pressure (ICP) by the induction of cerebral vasoconstriction with a subsequent decrease in cerebral blood volume. The downside of hyperventilation, however, is that cerebral vasoconstriction may decrease cerebral blood flow to ischemic levels. Considering the risk-benefit relation, it would appear to be clear that hyperventilation should only be considered in patients with raised ICP, in a tailored way and under specific monitoring. Controversy exists, for instance, on specific indications, timing, depth of hypocapnia, and duration. This review has specific reference to traumatic brain injury, and is based on an extensive evaluation of the literature and on expert opinion.

Management of brain and spine injuries

For both SCI and TBI, physicians are unable to affect reversal of the cellular injuries suffered at the time of trauma directly. Unfortunately, understanding such processes is just on the horizon. Physicians do, however, have significant influence on recovery through the avoidance of secondary insults to the injured nervous system. In keeping with trauma in general, the mechanism for this is focused and coordinated multi-disciplinary care originating at the earliest contact and continuing through acute care. Aggressive and pre-emptive attention to the ABC(D)s with attention to the needs of the injured nervous system, appropriate monitoring in all patients, meticulous medical management, and prompt surgical intervention when indicated have made marked improvements in outcome, particularly in TBI. Focusing on the basics and strict attention to detail appear to be the major roles played in the care of CNS trauma.

Outcome of severe traumatic brain injury: comparison of three monitoring approaches

The determination of cerebral perfusion pressure (CPP) is regarded as vital in monitoring patients with severe traumatic brain injury. Besides indicating the status of cerebral blood flow (CBF), it also reveals the status of intracranial pressure (ICP). The abnormal or suboptimal level of CPP is commonly correlated with high values of ICP and therefore with poor patient outcomes. Eighty-two patients were divided into three groups of patients receiving treatment based on CPP and CBF, ICP alone, and conservative methods during two different observation periods. The characteristics of these three groups were compared based on age, sex, time between injury and hospital arrival, Glasgow Coma Scale score, pupillary reaction to light, surgical intervention, and computerized tomography scanning findings according to the Marshall classification system. Only time between injury and arrival (p = 0.001) was statistically significant. There was a statistically significant difference in the proportions of good outcomes between the multimodality group compared with the group of patients that underwent a single intracranial-based monitoring method and the group that received no monitoring (p = 0.003) based on a disability rating scale after a follow up of 12 months. Death was the focus of outcome in this study in which the multimodality approach to monitoring had superior results.

Renal replacement therapy in the patient with acute brain injury

The patient with an acute brain injury requiring renal replacement therapy presents a major problem in that conventional intermittent hemodialysis may exacerbate the injury by compromising cerebral perfusion pressure, either after a reduction in cerebral perfusion or because of increased cerebral edema. Compared with standard intermittent hemodialysis, the continuous forms of renal replacement therapy (CRRT) provide an effective therapy in terms of solute clearance, coupled with improved cardiovascular and intracranial stability. The disadvantage of CRRT is that anticoagulation may be required, and anticoagulants with systemic effects may provoke intracerebral hemorrhage, either at the site of damage or around the intracranial pressure monitoring device. Although peritoneal dialysis does not require anticoagulation, the clearances achieved are often less than those of CRRT, and sudden changes in intraperitoneal volume may provoke cardiovascular and thus intracranial instability.

[Management of severely head-injured patients during the first 24 hours. Which specific therapeutics?]

Intracranial and systemic mechanisms of the secondary brain lesion are the targets of specific therapy for the head-injured patient. Recommendations for good clinical practice have recently defined the role of the main therapeutic measures. There is no indication for corticosteroids in head injury. Mannitol is the first-choice therapy for increased intracranial pressure, and barbiturates are still considered as a rescue therapy in case of refractory intracranial hypertension. The place of hypothermia remains to be defined. Although controversial, optimized hyperventilation, induced systemic hypertension and vasoconstrictive therapy are optimally used under multimodal monitoring. New therapeutic perspectives, aimed at controlling biochemical disorders at a cellular level, are under investigation, but are still inconclusive at the present time.

Standardized management of intracranial pressure: a preliminary clinical trial

OBJECTIVE

To test a standardized protocol for management of intracranial pressure (ICP) after severe head injury (i.e., traumatic brain injury), consistent with published guidelines.

METHODS

We compared prospective use of a standardized protocol for ICP management in 12 patients with severe head injuries and retrospective ICP management using preprinted hospital orders in combination with ad hoc physician orders in 12 historical control patients with severe head injuries. With the standardized protocol, flow-chart decision logic diagrams were applied at patient bedside by critical care practitioners, with nursing shift review.

RESULTS

ICP and its variation during the first 6 intensive care unit days was less for the standardized protocol- than for the preprinted order-managed group (p <0.001), indicating better process control with the standardized protocol. ICP exceeded 25 mm Hg for less time for the standardized protocol group (182 hours; 15+/-23 hours/patient) than for prescribed order group (429 hours; 36+/-28 hours/patient) (p = 0.03). On average, ICP exceeded 20 mm Hg for 2.3 days for the standardized protocol-managed group and for 4.7 days for the prescribed order-managed group. Cerebral perfusion pressure was significantly greater and its variation less for the standardized protocol- than for the preprinted order-managed group. Fewer interventions were made for ICP management for the standardized protocol- than for the preprinted order-managed patients (601 vs. 876), suggesting more effective nursing time using the standardized protocol.

CONCLUSION

ICP management was more consistent, and intracranial hypertension was better controlled, in patients managed according to a standardized, data-driven protocol for escalation and weaning of therapies in response to immediate patient needs. We recommend computerized implementation and a randomized clinical trial to compare the protocol with prescribed orders.