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