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Lisa T. Hannegan, MS, CNS, ACNPDepartment of Neurological Surgery
University of California, San Francisco
Era of Clinical Neuro Monitoring◦ Clinical Examination
◦ Heart rate
◦ Blood Pressure
◦ Body temperature
◦ Respiratory Rate
◦ Oxygen saturation
◦ Central venous Pressure
◦ Occasional use of intracranial pressure (ICP) monitoring
Era of Physiologic Monitoring◦ Intracranial Pressure Monitoring
◦ Occasional use of jugular bulb venous oxygen saturation (SjvO2) monitoring
Era of Multimodality Monitoring and Neurophysiologic Decision Support
Goal-directed therapy
Wartenburg et al. , Critical Care Clinics, 23 (2007)
Primary Brain Injury◦ Due to an illness or condition
Secondary Brain Injury◦ Follows the initial neurologic insult
Primary Brain Injury◦ Due to an illness or condition
Secondary Brain Injury◦ Follows the initial neurologic insult
The primary focus of Neurocritical Care for CNS problems is the prevention, identification, and treatment of secondary brain injury.
Claude Hemphill
WHY MONITOR?◦ Detect neurological worsening before irreversible
damage occurs
◦ Individualize patient care
◦ Guide management
◦ Monitor response to interventions
◦ Understand pathophysiology
◦ Design protocols
◦ Improve outcome
WHAT PROCESSES TO MONITOR?◦ Substrate delivery
Blood flow
Perfusion
◦ Energy failure and cellular stress
Intracranial pressure
Metabolic byproducts of ischemia
WHICH MONITORS?◦ Cardiac and respiratory physiology
Heart rate and rhythm, EF etc.
FiO2, TV, PEEP, etc.
◦ Intracranial pressure
Cerebral perfusion pressure
◦ Cerebral Blood Flow
Transcranial Doppler, thermal diffusion, laser Doppler flowmetry
WHICH MONITORS?◦ Brain oximetry
Jugular bulb venous oxygen saturation (SjO2)
Brain tissue oxygen tension (PbtO2, NIRS)
◦ Oxidative metabolism
Cerebral microdialysis (lactate, LPR)
◦ Cellular stress
Cerebral microdialysis (glutamate, glycerol)
Continuous EEG (cEEG)
Monro-Kellie ◦ 80% brain
◦ 10% circulating blood
◦ 10% CSF
P1—Percussive peak
P2—Tidal peak
P3—Dichrotic notch
P1—Percussive peak
P2—Tidal peak
P3—Dichrotic notch
C waves
B waves
A (plateau) waves
Normal pressure 0-10
Threshold to treat >20-25
CPP = MAP - ICP
CPP = MAP - ICP
CPP = MAP – JVP (if JVP > ICP)
CPP = MAP - ICP
CPP = MAP – JVP (if JVP > ICP)
Must be maintained within normal limitsOptimal pressure is 60-110 mm HG
◦ Too low ischemia
◦ Too high increased ICP
Flow remains constant over a range of CPP
Flow is constant from MAP of about 50-150
This relationship does not hold true with very low CPP, very high CPP and in injured brain.
Therefore, DIRECT MEASUREMENT is valuable in injured brain.
Kety-Schmidt technique
Xenon or krypton nuclear medicine studies
SPECT, Xenon CT
O15 PET
Perfusion CT or MRI
Transcranial Doppler (TCD)◦ These are all static techniques
Commonly used as a non-invasive test of cerebral blood flow in vasospasm related to subarachnoid hemorrhage
Uses flow velocity to infer vessel diameter
Use of Lindegaard Index to predict vasospasm eliminates elevated velocities related to hyperemia and loss of autoregulation
Results are operator-dependent
Continuous measurement techniques◦ Laser Doppler Flowmetry
Assesses the volume or concentration and flow velocity of red blood cells in a small volume (mm3) and generates a flow signal
◦ Thermal Diffusion
Quantitative estimation of flow in ml/100g per minute based on the tissue’s ability to dissipate heat
Real-time measurement of microvascular RBC perfusion in tissue
Measured in BPUs
Advantages◦ Directly measures
flow velocity in a region of interest
◦ Many of the probes are MRI compatible
◦ Does not need regular calibration
Advantages◦ Directly measures
flow velocity in a region of interest
◦ Many of the probes are MRI compatible
◦ Does not need regular calibration
Disadvantages◦ Probes are
susceptible to artifact◦ Area of flow studied
is tiny at 1mm3
◦ BPUs not directly translatable to physiological data
◦ Results vary depending on various blood parameters such as hematocrit
Two thermistors at the tip of a flexible catheter embedded in the white matter.
The proximal thermistor measures the brain temperature in degrees Celsius
Two thermistors at the tip of a flexible catheter embedded in the white matter.
The proximal thermistor measures the brain temperature in degrees Celsius
The distal thermistor is programmed to a temperature two degrees above the temperature at the proximal thermistor
The energy used by the distal thermistor to maintain the temperature 2 degrees higher reflects the tissue blood flow.
Advantages◦ Reflects cerebral blood flow to a region of interest
◦ Direct correlation between flow intra-operatively during and after temporary arterial occlusion for aneurysm clipping. (Thome et al., J Neurosurg , 2001)
◦ Correlation between thermal diffusion CBF results with PbrO2 in patients with SAH and TBI
Jaeger et al, Achta Neurochir, 2005
◦ Larger sampling area than laser Doppler flowmetry
Disadvantages◦ Small sample area reflects regional flow
◦ Temperature cutoff reduces sampling time in febrile patients
◦ Must use another invasive procedure to replace non-functioning catheter
Range of values for CBF
Normal CBF◦ 50mL/100g/min
Loss of normal neuronal function and threshold for tissue ischemia◦ <20mL/100g/min
Indications◦ Detection of non-convulsive seizures
◦ Characterization of spells such as posturing, eye movements, and unexplained changes in heart rate and blood pressure
Indications◦ Detection of non-convulsive seizures
◦ Characterization of spells such as posturing, eye movements, and unexplained changes in heart rate and blood pressure
◦ Assessment of LOC during sedation and paralysis
◦ Detection of ischemia after SAH and during procedures
◦ Prognostication
Up to 35% of Neuro Intensive Care patients have subclinical seizures
Claassen J, et al (2004) Detection of electrographic seizures with continuous EEG Monitoring in critically ill patients. Neurology 62:1743-8.
EEG showing focal right frontal ictal discharges in a patient with localization-related nonconvulsive status epilepticus
Elevated ICP
Disturbed cerebral metabolism◦ Glutamate elevations
Increased lesional mass effect and midline shift
Misdirected treatment and diagnostic evaluations
Increased mortality
Near Infrared spectroscopy
Jugular bulb venous oxygenation
Direct brain tissue oxygen tension
Tissue oxygen pressure versus oxygen saturation◦ SO2 is a measure of the oxygen carried bound to
hemoglobin with 4 oxygen molecules per hemoglobin molecule.
◦ PO2 is related to the amount of oxygen dissolved in the plasma or tissue
Near infrared spectroscopy (NIRS) ◦ Measures regional oxygen saturation (rSO2) non-
invasively
Near infrared spectroscopy (NIRS) ◦ Measures regional oxygen saturation (rSO2) non-
invasively
◦ Works by by analyzing the differences between absorption spectra of oxygenated and de-oxygenated hemoglobin
Near infrared spectroscopy (NIRS) ◦ Measures regional oxygen saturation (rSO2) non-
invasively
◦ Works by by analyzing the differences between absorption spectra of oxygenated and de-oxygenated hemoglobin
◦ Normal value for rSO2 is 60-80%
Advantages◦ Non-invasive
◦ Simple to apply and change
◦ May be useful in operative monitoring for procedures such as carotid endarterectomy
Advantages◦ Non-invasive
◦ Simple to apply and change
◦ May be useful in operative monitoring for procedures such as carotid endarterectomy
Disadvantages◦ Limited and variable
penetration of infrared light through the skull
◦ Inconsistent reliability
SjvO2 is a result of the difference between the cerebral oxygen delivery (supply) and the cerebral metabolic rate of O2
(CMRO2)(demand).
SjvO2 reflects global oxygenation (hemispheric)
Dominant internal jugular
Position verified by X-Ray
Calibration on insertion and every 8 hours
Advantages◦ Best use in TBI with
global injury associated with hypoperfusion, hypercapnia and elevated ICP
◦ Beneficial in SAH and intraoperative use
Advantages◦ Best use in TBI with
global injury associated with hypoperfusion, hypercapnia and elevated ICP
◦ Beneficial in SAH and intraoperative monitoring
Disadvantages◦ Limited by changes in
PaO2 and hemodilution◦ Frequent calibration◦ No information about
smaller regions of interest
◦ Complications Infection
jugular thrombosis
Pneumothorax
increased ICP
Range of SjvO2 Values◦ 50-75% Normal
◦ SjvO2 <50% indicates increased oxygen extraction fraction (OEF)
◦ SjvO2 >75% indicates reduced OEF and hyperemia
◦ In comatose patients, even a single desaturation to SjvO2 less than 50% was correlated with increased mortality
Feldman and Robertson, Critical Care Clinics, 1997, 13:51-77
Measures regional tissue oxygen pressure in a small area of the brain (PbO2, PbrO2, PtiO2, PbtO2)
Uses a microcatheter inserted into the brain parenchyma in a region of interest in the white matter
Depending on the device, one can also monitor temperature, PCO2 and pH.
Can be tunneled after craniotomy or placed through a multi-lumen bolt
Measured tissue volume is ~17mm3
Range of PbtO2 values◦ Normal PbtO2 is 20 in white matter and 35-40 in
gray matter
◦ Levels consistently >35mmHg correlate with good recovery
◦ Levels <20 indicate cerebral hypoxia
◦ Levels < 8 mmHg predict poor outcome
Normal values for additional modalities◦ PbtCO2 is 43-55mm Hg
◦ Brain tissue pH is 7.2
◦ Brain temperature correlates with core body temperature with a normal of 37° C
Advantages◦ Real-time
information about autoregulation
◦ Proven impact on patient management and outcome
Advantages◦ Real-time
information regarding autoregulation
◦ Proven impact on patient management and outcome
Disadvantages◦ Creates artifact on
MRI
◦ Invasive therapy
◦ Difficult to replace non-functioning probes
◦ Regional, not global information
A technique used to monitor the chemistry of the extracellular space
A thin dialysis probe, infused with saline or artificial CSF mimics a cerebral capillary
Measures◦ Glucose (substrate)
◦ Lactate (reflects anaerobic metabolism)
◦ Pyruvate (reflects carbohydrate metabolism)
Lactate to pyruvate ratio (LPR)
◦ Glutamate (reflects cell injury)
◦ Glycerol (reflects cell membrane breakdown)
Reduced glucose and increased lactate correlate with cerebral hypoxia and with death
Temporary arterial occlusion results in lowered glucose and pyruvate and also in elevated lactate and glutamate
Advantages◦ Probes are MRI safe
◦ Microdialysis can be done at the bedside at a regular interval
◦ Changes in values are early indications of ischemia
Advantages◦ Probes are MRI safe
◦ Microdialysis can be done at the bedside at a regular interval
◦ Changes in values are early indications of ischemia
Disadvantages◦ Focal information
◦ Current technology is limited to observation of trends
DIALYSIS CONCENTRATION
REINSTRUP et al SCHULZ et al CLINICAL USE
Glucose (mmol/L 1.7 (+/- 0.9) 2.1 (+/- 0.2) < 2.0
LPR 23 (+/- 4) 19 (+/- 2) > 25
Glycerol (µmol/L) 82 (+/- 44) 82 (+/- 12) > 100
Glutamate (µmol/L) 16 (+/- 16) 14 (+/- 3.3) >15
Reinstrup et al,, Neurosurgery 2000; 47:701-10Schulz et al, J Neurosurg 2000; 93: 233-8
Table adapted from a presentation by Peter LeRoux, MD, FACS
Provide an optimal cellular environment in order to preserve neurologic function and allow the best chance for recovery to occur
DeGeorgia and Deogaonkar, The Neurologist, 2005
Multimodality monitoring for neurophysiologic decision support
Goal-directed therapy
Proactive patient care management
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