Influence of general anaesthesia on slow waves of intracranial pressure.
OBJECTIVE
Slow vasogenic intracranial pressure (ICP) waves are spontaneous ICP oscillations with a low frequency bandwidth of 0.3-4 cycles/min (B-waves). B-waves reflect dynamic oscillations in cerebral blood volume associated with autoregulatory cerebral vasodilation and vasoconstriction. This study quantifies the effects of general anaesthesia (GA) on the magnitude of B-waves compared to natural sleep and conscious state.


METHODS
The magnitude of B-waves was assessed in 4 groups of 30 patients each with clinical indications for ICP monitoring. Normal pressure hydrocephalus patients undergoing Cerebrospinal Fluid (CSF) infusion studies in the conscious state (GROUP A) and under GA (GROUP B), and hydrocephalus patients undergoing overnight ICP monitoring during physiological sleep (GROUP C) were compared to deeply sedated traumatic brain injury (TBI) patients with well-controlled ICP during the first night of Intensive Care Unit (ICU) stay (GROUP D).


RESULTS
A total of 120 patients were included. During CSF infusion studies, the magnitude of slow waves was higher in conscious patients (
0.23+/-0.10 mm Hg) when compared to anaesthetised patients (
0.15+/-0.10 mm Hg; p = 0.011). Overnight magnitude of slow waves was higher in patients during natural sleep (GROUP C: 0.20+/-0.13 mm Hg) when compared to TBI patients under deep sedation (GROUP D: 0.11+/- 0.09 mm Hg; p = 0.002).


CONCLUSIONS
GA and deep sedation are associated with a reduced magnitude of B-waves. ICP monitoring carried out under GA is affected by iatrogenic suppression of slow vasogenic waves of ICP. Accounting for the effects of anaesthesia on vasogenic waves may prevent the misidentification of potential shunt-responders as non-responders.
a Division of Neurosurgery, Department of Clinical Neuroscience , University of Cambridge , Cambridge , UK.|b Division of Neurosurgery , Addenbrooke's Hospital , Cambridge , UK.|c National and Kapodistrian University of Athens Medical School , Athens , Greece.
Despina A
DA
Lalou
a Division of Neurosurgery, Department of Clinical Neuroscience , University of Cambridge , Cambridge , UK.|b Division of Neurosurgery , Addenbrooke's Hospital , Cambridge , UK.
Marek
M
Czosnyka
a Division of Neurosurgery, Department of Clinical Neuroscience , University of Cambridge , Cambridge , UK.|b Division of Neurosurgery , Addenbrooke's Hospital , Cambridge , UK.
Joseph
J
Donnelly
d Neurosciences Critical Care Unit, Department of Anesthesia , Cambridge University Hospitals NHS Foundation Trust , Cambridge , UK.
Andrea
A
Lavinio
a Division of Neurosurgery, Department of Clinical Neuroscience , University of Cambridge , Cambridge , UK.|b Division of Neurosurgery , Addenbrooke's Hospital , Cambridge , UK.
John D
JD
Pickard
a Division of Neurosurgery, Department of Clinical Neuroscience , University of Cambridge , Cambridge , UK.|b Division of Neurosurgery , Addenbrooke's Hospital , Cambridge , UK.
Matthew
M
Garnett
a Division of Neurosurgery, Department of Clinical Neuroscience , University of Cambridge , Cambridge , UK.|b Division of Neurosurgery , Addenbrooke's Hospital , Cambridge , UK.
Zofia
Z
Czosnyka
D000368:Aged; D000369:Aged, 80 and over; D000768:Anesthesia, General; D016022:Case-Control Studies; D002560:Cerebrovascular Circulation / Q000187:drug effects* / Q000502:physiology; D003072:Cognition Disorders / Q000209:etiology; D015331:Cohort Studies; D003243:Consciousness; D005260:Female; D006801:Humans; D006850:Hydrocephalus, Normal Pressure / Q000150:complications / Q000000981:diagnostic imaging / Q000503:physiopathology* / Q000601:surgery; D007427:Intracranial Pressure / Q000187:drug effects* / Q000502:physiology; D008297:Male; D010477:Perfusion; D010507:Periodicity
B-waves; Cerebrospinal fluid dynamics; General anaesthesia; Hydrocephalus