BJA Education, 19(2): 54e59 (2019)

doi: 10.1016/j.bjae.2018.12.001
Advance Access Publication Date: 15 December 2018

Matrix codes: 1A01,

2A04, 3F00

Monitoring the brain

M. Elwishi* and J. Dinsmore
St Georges Hospital, London, UK
*Corresponding author: a.elwishi@nhs.net

Learning objectives Key points

By reading this article, you should be able to:
For accurate cerebral perfusion pressure calcula-

Describe the methods for measuring intracranial tion, both intracranial pressure (ICP) and MAP
pressure (ICP) and identify the components of a transducers should be zeroed at the level of the
normal ICP trace. external auditory meatus.

Discuss the available methods and clinical ap-
Multiple invasive and non-invasive imaging
plications of cerebral tissue oxygenation techniques are available for cerebral blood flow
monitoring. measurements.

Explain the underlying physical principles and
The lactate/pyruvate ratio generated via micro-
indications for cerebral blood flow measurement. dialysis is a useful marker of cerebral ischaemia
in conjunction with ICP and tissue oxygenation
(PtiO2), which is itself a useful marker for tissue
Monitoring the brain after traumatic injury, subarachnoid hypoxia.
haemorrhage, and neurosurgery plays a crucial role in guiding
Multimodality cerebral monitoring can provide
management, optimising cerebral function, and prevention of individualised targets for management.
secondary brain injury. This article aims to outline some of
the scientific principles and clinical applications of different
monitoring modalities. trace is pulsatile, reflecting cardiac and respiratory cycles. The
cardiac component has three peaks: the P1 (percussion wave)
correlating with arterial pulsation, P2 (tidal wave) generated by
Monitoring intracranial pressure both arterial pulsation and resistance from intracranial pa-
Intracranial pressure renchyma, and P3 (dicrotic wave) reflecting closure of the aortic
valve. The respiratory component of the waveform is generated
The cerebrospinal fluid acts as a dynamic pressure system.
by the changes in intrathoracic pressure caused by respiration.
Pressure can be measured directly from the lateral ventricle via
As intracranial compliance decreases, pathological waves start
a lumbar puncture, lumbar drain, or an intra-parenchymal
to appear. Lundberg described three types of pressure waves: A,
sensor. Intracranial pressure (ICP) has physiological values of
B, and C (Table 1; Fig. 1). However, this classification is no longer
3e4 mm Hg up to 1 yr, and 10e15 mm Hg in adults. Higher
considered to be useful clinically. In modern clinical practice,
values correspond to intracranial hypertension. The normal ICP
the emphasis on recognition and treatment of increased ICP
means that plateau waves (Lundberg A waves: an ICP of 50e100
mm Hg for 5e20 min) are rarely seen.
Monitoring of ICP is useful in a range of pathologies,
Mazen Elwishi FRCA is a consultant anaesthetist at St George’s
including traumatic brain injury (TBI), hydrocephalus, stroke,
Hospital with an interest in neuroanaesthesia and anaesthesia for
and encephalopathy. It can be measured using devices
interventional radiology.
inserted into the ventricle, brain parenchyma, and subdural or
Judith Dinsmore FRCA is a consultant anaesthetist at St George’s sub-arachnoid spaces. An intraventricular catheter is the
Hospital with a special interest in neuroanaesthesia. She is an gold standard method. This provides a global measurement of
examiner for the final FRCA and Joint Committee of Intercollegiate ICP, but also allows in vivo calibration, therapeutic drainage of
Examiners. She is also the current President of the Neuro Anaes- CSF, and administration of intrathecal drugs. However,
thesia & Critical Care Society of Great Britain and Ireland.

Accepted: 2 November 2018

© 2018 British Journal of Anaesthesia. Published by Elsevier Ltd. All rights reserved.
For Permissions, please email: permissions@elsevier.com

54
 Monitoring the brain

Table 1 Lundberg waves: variations in the intracranial pressure waveform

Types of ICP wave

A waves: pathological, plateau shaped, amplitude 50e100 mm Hg, last 5e20 min, suggestive of low brain compliance
B waves: rhythmic oscillations, amplitude <50 mm Hg, occur every 1e2 min, seen in patients undergoing mechanical ventilation, less
useful clinically, suggestive of low brain compliance
C waves: rhythmic oscillations, amplitude <20 mm Hg, occur every 4e8 min, synchronous with spontaneous variations in arterial
blood pressure, non-pathological

Fig 1 Lundberg CSF pressure waves A, B, and C. Note the different timescales for each.

intraventricular catheters can be a source of infection, and guidelines, for survival and favourable outcomes, target a CPP
placement may be difficult in patients with small ventricles or between 60 and 70 mm Hg. However, the minimum optimal
cerebral oedema. Intra-parenchymal catheters are used more CPP threshold is unclear and may depend upon the patient’s
commonly. These micro-transducer or fibreoptic tipped sys- capacity for cerebral autoregulation. An individualised target
tems are placed via a cranial access device or via a small burr CPP for each patient has been proposed.
hole into the subdural space. Although less invasive and
considered accurate, they tend to measure local pressure and
may show drift with time. Cerebrovascular pressure reactivity
Intracranial pressure monitoring allows the early detection Cerebrovascular pressure reactivity is a key component of
of an expanding lesion and the calculation of cerebral perfusion cerebral autoregulation and is frequently impaired in brain
pressure (CPP). It has become standard of care in the manage- injury. A pressure reactivity index (PRx) can be calculated as a
ment of TBI. The Brain Trauma Foundation (BTF) recommends moving correlation coefficient between consecutive values for
continuous ICP monitoring in the management of all patients ICP and arterial blood pressure (ABP) averaged over a defined
with severe TBI to reduce the in-hospital and 2 week mortality time. A positive PRx suggests disturbed reactivity of cerebral
after injury. Treatment of an ICP >22 mm Hg is also recom- vasculature or impaired autoregulation. A negative value,
mended, as values above this level are associated with where ABP is negatively correlated with ICP, reflects normal
increased mortality.1 However, there remains a lack of Class 1 autoregulation. It has been suggested that PRx be used to
evidence that ICP-guided therapy improves outcomes. A trial define individual CPP targets in TBI. However, although PRx
performed in South America found no difference in 3e6 month has been shown to correlate with outcome in some studies,
outcomes in patients with severe TBI whose care was guided by there is currently not enough prospective evidence for its
ICP monitoring compared with those whose care was based on routine use in clinical practice.4
imaging and clinical examination.2 However, this study had a
number of limitations. Differences in patient care, both before
hospital admission and after hospital discharge, were not re- Monitoring cerebral oxygenation
ported, and its applicability to routine practice in developed
Jugular venous oxygen saturation
countries has been questioned. The consensus opinion re-
mains that ICP monitoring remains the standard of care in TBI, Jugular venous oxygen saturation (SjvO2) gives an assessment
as a prospective randomised trial will be impossible. of global oxygenation and the adequacy of CBF. A catheter is
inserted by retrograde cannulation of the internal jugular vein
and advanced into the jugular bulb. It should be placed on the
Cerebral perfusion pressure
side of worst pathology or on the dominant side for venous
Cerebral perfusion pressure is calculated by the following drainage. Dominance is determined by compression of each
equation: CPP¼MAPeICP. For accurate calculation of CPP, the internal jugular vein separately and observing for the greatest
transducers measuring both MAP and ICP should be zeroed at change in ICP. If no dominance is seen, the right side tends to
the level of the foramen of Monro (external auditory meatus).3 be used. The catheter tip should lie level with the C1/C2 disc
The primary goal of an adequate CPP is to maintain cerebral and the position confirmed on a lateral cervical spine X-ray. If
blood flow (CBF) and tissue oxygenation, and its manipulation the tip is in the wrong position, significant error may result
has become central to the management of TBI. Current from admixture with extracranial blood. Additional

BJA Education - Volume 19, Number 2, 2019 55

Monitoring the brain

complications include subclinical thrombosis and those healthy volunteers. They conclude that further refinements are
associated with central venous cannulation. Measurements required before NIRS can be considered reliable.6
can be taken intermittently using serial sampling. Spectro-
photometric catheters enable continuous measurement.
Brain tissue oxygenation
SjvO2 reflects the balance between the oxygen supply (CBF,
SpO2) and demand (Table 2). Normal SjvO2 is between 55% and Directly monitoring brain tissue oxygen is possible by
75%. Values below this suggest hypoperfusion with oxygen introducing small flexible micro-catheters placed directly
demand exceeding supply. Cerebral ischaemia is present into the brain parenchyma in the area of interest. Different
when SjvO2 is <55%, but cannot be assumed to be absent at devices are available commercially. The most commonly
higher values. High SjvO2 values indicate hyperaemia or used is the Licox® sensor (Integra, Mielkendorf, Germany),
reduced metabolic demand. Most studies are in severe TBI which measures tissue oxygenation (PtiO2) via a polaro-
where it has been used to guide interventions, such as the use graphic technique based on the Clark electrode. This consists
of hyperventilation. However, SjvO2 provides limited infor- of a membrane covering an aqueous potassium hydroxide
mation in patients with focal ischaemia. Positioning prob- electrolyte solution and two metallic electrodes (a silver
lems, clot formation on the catheter, and poor sampling anode and a gold cathode). The greater the partial pressure of
technique also affect accuracy.5 oxygen is, the greater the diffusion of oxygen is through the
membrane, where it is electrochemically reduced at the
cathode. The number of oxygen molecules reduced at the
Near-infrared spectroscopy cathode is reflected by changes in voltage. As this process is
temperature dependent, a temperature probe corrects for
Near-infrared spectroscopy (NIRS) is a non-invasive bedside
variations in tissue temperature. Measurement is limited to
monitor of regional cerebral oxygenation. Light waves in the
the immediate area. Positioning in an area of ischaemia or
near-infrared range (700e1000 nm) are able to penetrate the
haematoma will give misleading results. The Neurotrend™
skin, bone, and brain tissues relatively easily. The main
device (Codman, Raynham/Massachusetts, USA) used optical
chromophores present in the brain are oxygenated haemo-
luminescence to measure PtiO2, PtiCO2, pH, and temperature,
globin (HbO2), deoxygenated haemoglobin (Hb), and cyto-
but is no longer available. A newer device (Raumedic Neu-
chrome aa3 (Cytox), all of which have different absorption
rovent-PTO™, RAUMEDIC, Helmbrechts, Germany), also us-
spectra. Infrared light is shone through the surface layers of
ing luminescence, is available, which measures PtiO2, ICP,
the brain. The light is reflected, redirected, scattered, and
and temperature. Compared with Licox®, higher PtiO2 values
absorbed by different tissues with absorption dependent upon
have been noted, which are thought to be a result of different
the oxygenation status, and the emergent light is sensed by
sampling sizes of the probes. Licox® has a larger sensing
detectors. Changes in the concentration of the near-infrared
surface area, which provides more consistent and repro-
light can be quantified using reflectance spectroscopy based
ducible measurements.
on the modified BeereLambert law.
PtiO2 varies with changes in oxygenation and CBF. Most
NIRS has been used clinically to monitor patients with TBI
clinical experience is in patients with severe TBI, and data from
and as an intraoperative monitor in patients undergoing cardiac
this population have allowed the identification of baseline
surgery and carotid endarterectomy. The normal range of cere-
values, including PtiO2 20e35 mm Hg, PtiCO2 40e70 mm Hg,
bral regional oxygen saturation (rSO2) is reported to be 60e75%,
and pH 7.05e7.25.7 A consensus opinion of thresholds for
but there is a marked variability between NIRS devices. Other
ischaemia has also been deemed as PtiO2 <15e20 mm Hg: a
factors that reduce reliability include extracranial contamina-
threshold at which intervention should be considered. How-
tion and interference by ambient light. Ultrasound-tagged NIRS,
ever, none of these values have yet been proven and are
combining NIRS and ultrasound, has been proposed as a po-
dependent on the underlying pathology. There have been
tential improvement, as it aims to selectively detect the signal
encouraging results from ICP/CPP and PtiO2-guided in-
originating from changes in light passing through the grey
terventions in patients with severe TBI. Although part of the
matter. Stocchetti and colleagues used two devices to detect the
BTF guidance, there is currently insufficient evidence to
absence of CBF in brain-dead patients. The devices tested both
mandate its use. The Brain Oxygen Optimization in Severe TBI,
showed higher values of CBF in brain-dead patients than in
Phase 3 trial is underway, which aims to address this question.

Table 2 Factors affecting jugular venous oxygen saturation

Monitoring CBF
(SjvO2) Transcranial Doppler and transcranial colour-coded
duplex
Low SjvO2 High SjvO2
Transcranial Doppler (TCD) provides a non-invasive method for
Reduction in oxygen delivery Reduced cerebral oxygen indirect measurement of CBF. Using a 2 MHz probe and pulsed-
consumption wave Doppler, flow velocities (FVs) can be measured in the
Raised ICP Coma intracranial arteries via insonation windows. It uses the Doppler
Reduced CBF Hypothermia
effect, whereby the observed frequency of a signal increases as
Hypoxia Cerebral infarction
the source moves towards the observer. The velocity of blood
Profound hypocarbia
Increased cerebral oxygen Increased oxygen delivery flow is directly related to the change in transmitted frequency of a
demand sound wave, which is then incorporated in the Doppler equation:
Seizures Hypercapnia
Pyrexia Vasodilation V ¼ FD c=2Ft cosq

56 BJA Education - Volume 19, Number 2, 2019

 Monitoring the brain

where V¼velocity, c¼speed of wave, q¼angle of blood flow

relative to the probe, Ft¼frequency of transmitted wave,
and FD¼Doppler shift frequency.
The mean FV correlates to changes in CBF provided that
the diameter of the blood vessel and the angle of insonation
both remain constant. The middle cerebral artery (MCA) is the
most commonly insonated through the transtemporal win-
dow, which also allows insonation of anterior and posterior
cerebral arteries (see Table 3). The transorbital window allows
insonation of the ophthalmic artery and carotid circulation,
whereas the distal vertebral and basilar arteries are accessed
via the transforaminal window. Transcranial colour-coded
duplex (TCCD) combines the pulsed-wave Doppler with real-
time imaging to provide the capability for more accurate
measurements (Figs 2 and 3).
Transcranial Doppler is used primarily to monitor for
vasospasm after subarachnoid haemorrhage. It can predict
angiographic spasm with good sensitivity and specificity,
increased further by the use of TCCD and inclusion of the
Lindegaard index. Values of mean FV in the MCA values >120 Fig 3 MCA Doppler waveform, demonstrating a flow velocity (cm s1)
cm s1 coupled with a Lindegaard index 3e6 are highly waveform using the pulsed-wave Doppler mode.

indicative of vasospasm.8 The Lindegaard index is the ratio of

the mean FV in the MCA to the mean FV in the internal carotid
artery measured through the submandibular window.
(i) detection of microemboli
Other clinical applications of TCD include the following:
(ii) intraoperative monitoring during carotid surgery
(iii) estimation of ICP through monitoring changes in pulsa-
tility index (PI)
Table 3 Depth ranges and normal flow velocities (FV) (PI¼FV systoliceFV diastolic/FV mean)
An online educational video on the performance of TCD
Insonation Depth FV mean examination can be found at https://vimeo.com/176611066.
window range range
(mm) (cm s¡1)
Imaging methods
Middle cerebral artery Transtemporal 30e65 43e77
Anterior cerebral Transtemporal 65e75 39e61 CT perfusion
artery CT perfusion is widely used to assess CBF, particularly in
Posterior cerebral Transtemporal 55e80 29e49
patients presenting with acute stroke and subarachnoid
artery
Vertebral artery Transforaminal 60e95 27e47 haemorrhage, to identify potentially reversible cerebral
Basilar artery Transforaminal 90e120 31e51 hypoperfusion (ischaemic penumbra) and differentiate these
Ophthalmic artery Transorbital 35e55 16e26 areas with infarcted areas of the brain. It can be rapidly
Internal carotid artery Submandibular 35e80 28e45 performed using a spiral CT scanner with images analysed
(extracranial) by commercially available software to produce perfusion
maps. Iodinated contrast is injected intravenously and
multiple slices taken at the level of the basal ganglia to
visualise all vascular territories (anterior, middle, and pos-
terior cerebral arteries); however, this repetitive imaging of
the brain tissue produces high doses of radiation for the
patient. Calculations are made for mean transit time (MTT),
measured in seconds and representing the average length of
time a certain volume of blood spends in the cerebral arterial
circulation, and cerebral blood volume (CBV), measured in
millilitres of blood per 100 g of brain tissue and representing
the total volume of blood in the cerebral arterial and venous
systems per cerebral tissue volume. CBF is measured in
millilitres of blood per 100 g of brain tissue per minute, and is
related to CBV and MTT by the central volume principle,
whereby CBF¼CBV/MTT. CT perfusion maps are most
commonly interpreted by visual inspection; in the example
of acute stroke, the ischaemic penumbra is identified as the
area with increased MTT, reduced or diminished CBF, but
with preserved CBV because of blood supplied from the
Fig 2 TCCD image showing middle and posterior cerebral arteries [MCA
collateral circulation (Fig. 4).
and PCA] as insonated via the trans-temporal window at an approximate
Calculations are also made for time (in seconds) for
depth of 50e60 mm.
contrast to peak in brain tissue and to drain away, giving time-

BJA Education - Volume 19, Number 2, 2019 57

Monitoring the brain

Fig 4 CT perfusion image in acute stroke demonstrating a left MCA territory mismatch with preserved CBV, but reduced CBF and increased MTT (note the colour-
coded key next to each slice), indicating the ischaemic penumbra marked in red.

to-peak (TTP) and time-to-drain derivations, which are highly Nuclear medicine methods
sensitive markers for cerebral ischaemia.9 (i) Positron emission tomography: This uses radioactive-
labelled water [15O] H2O injected intravenously then scanned
Xenon-enhanced CT on a tomograph for a 10 min session, with arterial blood
Xenon is a highly lipid soluble inert gas. It readily crosses the sampling to measure radioactivity. The injected [15O] H2O
bloodebrain barrier and is clearly visible on CT scans. After a rapidly distributes into the brain tissue proportional to CBF,
baseline CT scan, oxygen 100% is inhaled to wash out nitro- and then rapidly washes out. CBF is calculated by an analysis
gen, followed by inhalation of xenon until it equilibrates at a of time activity curves generated by the PET scanner.
predetermined percentage. Another CT scan is performed and (ii) Single photon emission computed tomography: This
xenon inhalation discontinued. Serial CT scans are then taken uses radioactive tracers, most commonly g-emitting techne-
and an analysis of xenon washout patterns allows the quan- tium 99. This is highly lipophilic, readily crosses the
tification of CBF through a modification of KetyeSchmidt bloodebrain barrier, and its distribution is proportional to
technique.10 CBF. It continues to emit g radiation for some hours, which
can be detected by g cameras to produce a 3D image repre-
senting CBF.
Perfusion-weighted MRI techniques

(i) Arterial spin labelling: This is a non-invasive technique,

as no contrast is injected. Protons in the arterial blood Monitoring cerebral metabolism
water are magnetically labelled by applying a radio-
Microdialysis
frequency pulse and rendering it an ‘endogenous tracer’.
After a time delay called transit time, the tracer will arrive Cerebral microdialysis allows the continuous bedside moni-
at its destination or region of interest, and at this point, toring of changes in local metabolites, which reflects cerebral
MRI imaging is performed. This is compared to baseline energy metabolism. It has been used in patients with TBI and
imaging, and cerebral flow maps are produced. subarachnoid haemorrhage, and after surgery. A thin (0.6
(ii) Dynamic susceptibility contrast-weighted imaging: mm) coaxial catheter is inserted into the chosen area. This has
When the i.v. contrast agent, gadolinium, passes through a dialysis membrane on its outer surface through which low
the cerebral arterial vasculature, it reduces the signal flow rates of perfusate are pumped. The catheter wall allows
intensity for MRI images. Using this principle, gadolinium free diffusion of water and solutes driven by the concentration
is injected, and repeated rapid MRI imaging is performed. gradient between the interstitial fluid and the perfusate. The
When the sequence is analysed, a signal intensity curve molecular weight of the molecules sampled is limited by the
is produced from which CBF can be calculated. pore size of the dialysis membrane. Micro-dialysate samples

58 BJA Education - Volume 19, Number 2, 2019

 Monitoring the brain

are collected about every 60 min to enable the measurement References

of substances in the cerebral extracellular fluid. The sub-
stances routinely analysed are the following: 1. Brain Trauma Foundation. Guidelines for the manage-
ment of severe TBI, 4th ed. Available from: https://
(i) energy-related metabolites (e.g. glucose, lactate, and braintrauma.org/guidelines/guidelines-for-the-
pyruvate) management-of-severe-tbi-4th-ed#/. [Accessed 25 May
(ii) neurotransmitters (e.g. glutamate and aspartate) 2018].
(iii) markers of cellular degradation (e.g. glycerol and 2. Chestnut RM, Temkin N, Carney N et al. A trial of intra-
potassium) cranial pressure monitoring in traumatic brain injury.
(iv) exogenous substances (e.g. drugs) N Eng J Med 2012; 367: 2471e81
The concentration of these substances measured is not the 3. Thomas E (on behalf of NACCS), Czosnyka M,
absolute concentration, but dependent on the degree of Hutchinson P (on behalf of SBNS). Calculation of cerebral
equilibration between the interstitial fluid and the perfusate. perfusion pressure in the management of traumatic brain
Microdialysis is considered useful in patients at risk of ce- injury: joint position statement by the councils of the
rebral ischaemia or hypoxia. Glucose, lactate, and pyruvate Neuroanaesthesia and Critical Care Society of Great Brit-
concentrations provide information on cerebral glucose de- ain and Ireland (NACCS) and the Society of British
livery, utilisation, and the contributions of aerobic vs anaerobic Neurological Surgeons (SBNS). Br J Anaesth 2015; 115:
metabolism. The metabolic derangements seen in severe brain 487e8
injury are associated with an elevation of the lactate/pyruvate 4. Nordstrom C-H, Koskinen L-O, Olivecrona M. Aspects on
ratio and reductions in brain glucose. Glycerol is produced from the physiological and biochemical foundations of neuro-
enzymatic degradation of phospholipid membranes after cell critical care. Front Neurol 2017; 8: 274
death, and increased levels have been found in microdialysis 5. Le Roux P, Menon DK, Citerio G et al. Consensus summary
samples after severe TBI. Variations in the concentrations of statement of the international multidisciplinary
glutamate and aspartate are also seen, with extremely high consensus conference on multimodality monitoring in
levels in secondary cerebral ischaemia and contusions. The neurocritical care. A statement for healthcare pro-
lactate/pyruvate ratio is considered a useful marker of fessionals from the Neurocritical Care Society and the
impaired cerebral metabolism and enables interventions to be European Society of Intensive Care Medicine. Neurocrit
tailored accordingly.7 However, microdialysis is not currently Care 2014; 21(Suppl. 2): 1e26
recommended for routine clinical use. As this technique only 6. Caccioppola A, Caarbonara M, Macri M et al. Ultrasound-
gives information regarding a small area surrounding the tagged near-infrared spectroscopy does not disclose ab-
catheter, results must be interpreted in the context of catheter sent cerebral circulation in brain-dead adults. Br J Anaesth
location, other monitors (e.g. ICP), and the clinical condition of 2018; 121: 588e94
the patient. As with any invasive technique, there is the pos- 7. Bhatia A, Gupta AK. Neuromonitoring in the intensive
sibility of complications, but these are rare. care unit. II. Cerebral oxygenation monitoring and
microdialysis. Intensive Care Med 2007; 33: 1322e8
8. Marshall SA, Nyquist P, Ziai WC. The role of trans-
Multimodality monitoring cranial Doppler ultrasonography in the diagnosis and
Primary brain injury is characterised by a host of pathophys- management of vasospasm after aneurysmal sub-
iological changes not all of which will be detected by indi- arachnoid hemorrhage. Neurosurg Clin N Am 2010; 21:
vidual neuromonitoring devices. Multimodality monitoring 291e303
involves data integration from various monitoring tools 9. Abels B, Klotz E, Tomandl BF, Kloska SP, Lell MM. Perfu-
assessing both local and global cerebral oxygenation, hae- sion CT in acute ischemic stroke: a qualitative and
modynamics, and metabolism.11,12 Multimodality monitoring quantitative comparison of deconvolution and maximum
provides a more comprehensive view of the patient’s status, slope approach. Am J Neuroradiol 2010; 31: 1690e8
and enables optimal intervention targets to be set and the best 10. Yonas H, Pindzola RR, Johnson DW. Xenon/computed
treatment choices made. tomography cerebral blood flow and its use in clinical
management. Neurosurg Clin N Am 1996; 7: 605
11. Kirkman MA, Smith M. Intracranial pressure monitoring,
Declaration of interest cerebral perfusion pressure estimation, and ICP/CPP-
The authors declare that they have no conflicts of interest. guided therapy: a standard of care or optional extra af-
ter brain injury? Br J Anaesth 2014; 1: 35e46
12. Kirkman MA, Smith M. Multimodal intracranial moni-
MCQs toring: implications for clinical practice. Anesthesiol Clin
The associated MCQs (to support CME/CPD activity) will be 2012; 30: 269e87
accessible at www.bjaed.org/cme/home by subscribers to BJA
Education.

BJA Education - Volume 19, Number 2, 2019 59