Brain oxygenation

Pressures, Flow, and Brain Oxygenation During Plateau Waves of Intracranial Pressure

Authors: Dias C, Maia I, Cerejo A, Varsos G, Smielewski P, Paiva JA, Czosnyka M.

BACKGROUND: Plateau waves are common in traumatic brain injury. They constitute abrupt increases of intracranial pressure (ICP) above 40 mmHg associated with a decrease in cerebral perfusion pressure (CPP). The aim of this study was to describe plateau waves characteristics with multimodal brain monitoring in head injured patients admitted in neurocritical care.
METHODS: Prospective observational study in 18 multiple trauma patients with head injury admitted to Neurocritical Care Unit of Hospital Sao Joao in Porto. Multimodal systemic and brain monitoring of primary variables and secondary variables related to cerebral compensatory reserve and cerebrovascular reactivity were supported by dedicated software ICM+ ( www.neurosurg.cam.ac.uk/icmplus) . The compiled data were analyzed in patients who developed plateau waves.
RESULTS: In this study we identified 59 plateau waves that occurred in 44 % of the patients (8/18). During plateau waves CBF, cerebrovascular resistance, CO, and brain tissue oxygenation decreased. The duration and magnitude of plateau waves were greater in patients with working cerebrovascular reactivity. After the end of plateau wave, a hyperemic response was recorded in 64 % of cases with increase in CBF and brain oxygenation. The magnitude of hyperemia was associated with better autoregulation status and low oxygenation levels at baseline.
CONCLUSIONS: Multimodal brain monitoring facilitates identification and understanding of intrinsic vascular brain phenomenon, such as plateau waves, and may help the adequate management of acute head injury at bed side.

The Relationship Between Intracranial Pressure and Brain Oxygenation in Children with Severe Traumatic Brain Injury

Authors: Rohlwink UK, Zwane E, Fieggen AG, Argent AC, Leroux PD, Figaji AA.

BACKGROUND: Intracranial pressure (ICP) monitoring is a cornerstone of care for severe traumatic brain injury (TBI). Management of ICP can help ensure adequate cerebral blood flow and oxygenation. However, studies indicate that brain hypoxia may occur despite 'normal' ICP and the relationship between ICP and brain oxygenation is poorly defined. This is particularly important for children in whom less is known about intracranial dynamics.

OBJECTIVE: To examine the relationship between ICP and brain tissue oxygen (PbtO2) in children with severe TBI (Glasgow Comma Score ≤ 8) admitted to Red Cross War Memorial Children's Hospital, Cape Town.

METHODS: The relationship between time-linked hourly and high frequency ICP and PbtO2 data was examined using correlation, regression and generalized estimating equations. Thresholds for ICP were examined against reduced PbtO2 using age bands and receiver-operating curves.

RESULTS: Analysis using over 8300 hourly (N=75) and 1 million high frequency data points (N=30) demonstrated a weak relationship between ICP and PbtO2 (r = .05, r=.04). No critical ICP threshold for low PbtO2 was identified. Individual patients revealed a strong relationship between ICP and PbtO2 at specific times, but different relationships were evident over longer periods.

CONCLUSION: The relationship between ICP and PbtO2 appears complex and several factors likely influence both variables separately and in combination. Although very high ICP is associated with reduced PbtO2, in general, absolute ICP has a poor relationship with PbtO2. Since reduced PbtO2 is independently associated with poor outcome, a better understanding of ICP and PbtO2 management in pediatric TBI seems needed.

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