APEX: MISC MONITORS Flashcards
Best describes the CEREBRAL OXIMETRY
A greater than 25% change from baseline suggests a REDUCTION in CEREBRAL OXYGENATION
Cerebral oximetry is a
noninvasive technique that utilizes near infrared spectroscopy NIRS to measure regional (NOT GLOBAL) cerebral oxygenation
What is cerebral oximetry based on
The principle that decrease cerebral oxygen delivery lead to increase cerebral oxygen extraction and decrease venous hgb saturation
Cerebral oximetry sensor is placed where
Patient’s scale over the frontral lobe
Cerebral oximetry contains a light emiting
Diode and 2 light sensor: surface photodetector and a DEEP photodetector
The infrared light in cerebral oximetry follos
Elliptical pathway from the emitting diode –>scalp –> skull –> brain–> skull –> scalp–> Photodetectors
Cerebral oximetry relies on the facts that
Cerebral blood volume is 1 part arterial and 3 parts venous. 75% of the blood in the brain is on the venous side of circulation
Can NIRS detect pulsatile blood flow?
no
Since NIRS does not have ability to detect pulsatile BF, it is primarily a measure of what?
Venous oxyhemoglobin saturation and Oxygen extraction.
Can contaminate the signal of NIRS
Scalp hypoxia , may falsely interpret it as brain ischemia
EEG waves from high to low frequency (BAT-D)
Beta
Alpha
Theta
Delta
EEG measures the difference between
Electrical potentials in multiple regions of the brain.
EEG Provides information about electrical activity of the
Cerebral cortex
EEG provide little information about the
Subcortical structures, spinal cord and the cranial and peripheral nerves.
High Frequency low voltage waves
beta waves
Beta waves associated with
Awake mental stimulation and LIGHT ANESTHESIA
Beta frequencies
13-30 cycles/sec
Alpha waves associated with
Awake but RESTFUL STATE WITH EYES CLOSED.
Alpha frequencies
8-12 cycles/second
Theta waves frequencies
4-7 cycles/second
Theta wave associated with
GA
Waves associated with children during normal sleep
Theta waves
Delta waves associated with
GA, DEEP SLEEP, brain ischemia or injury
Burst suppression is associated with
GA, hypothermia, CBP, Cerebral ischemia (especially if its UNILATERAL burst suppression)
Isoelectricity is
absence of electrical activity
Associated with very deep anesthesia and death.
How brain waves change during anesthesia? Induction
Increased beta wave activity
How brain waves change during anesthesia? light anesthesia
Increased beta wave activity
Waves the predominate during GA
Theta and beta
Produces burst suppresion
Deep anesthesia
At what MAC does GA cause complete suppresion or isoelectricity?
1.5-2.0 MAC
Nitrous and EEG
When administered alone, Increases beta wave activity
Can increase EPILEPTIFORM EEG activity
Sevoflurane
Can cause myoclonus
Etomidate
Can cause myoclonus but this is not associated with epeleptiform EEG activity
Etomidate
Ketamine on EEG
Increase high frequency cortical activity and may confuse EEG interpretation - the patient may be deeper than the EEG SUGGESTS>
When does burst suppresion occur with temp
hypothermia, especially with CPB
This kind of burst suppresion suggest cerebral ischemia
Unilateral burst suppression .
EEG usefulness for infarction?
EEG provides a sensitive measure of brain tissue at risk of infarction
The brain requires an
Adequate perfusion pressure to provide a steady supply of oxygen and glucose.
In the absence of these substrates the brain is unable to maintain its electrical function
Oxygen
Glucose.
You are seeing the development of new delta waves during anesthetic maintenance may signify
that brain is at risk for ISCHEMIA
Circumstance that mimic cerebral ischemia:
Deep anesthesia
Hypothermia
Hypocarbia
EEG monitoring useful during the following neck procedure:
Carotid endarterctomy
EEG monitoring useful during these brain surgeries
AV malformations
Cerebral aneurysm
Epilepsy dx and tx
EEG monitoring useful for other procedures
ASsessment of barbiturate coma
Deliberate hypotension
CPB
Coma and death.
Bispectral index monitor with ketamine
Ketamine falsely elevates the BIS value
BIS and burst suppresion
Burst suppresion begins at a BIS value of 20
While most general anesthetics reduce HIGH FREQUENCY EEG activity , Ketamine
Increases them
There is a
20-30 secong lag between measuring the EEG and computing BIS value.
Patient safety index monitor is similar to BIS in what ways?
Measures EEG, runs the data through an algorithm and displays the number that indicates the level of anesthetic depth.
Unlike BIS, the patient safety monitor target for GA is
40-60
Unlike BIS, the patient safety monitor target for PSA is
25-50
BIS number are from
0-100
BIS number of 100
Fully awake
BIS NUMBER of 80
Light-moderate sedation
BIS 40-60
General Anesthesia
BIS number associated with low probability of explicit recall
40-60
BIS 40
Deep hypnotic state
BIS 20
Burst suppression
BIS 0
Absence of cerebral activity .
As the anesthesia becomes deeper, the EEG waveforms exhibits a (FLAH)
Lower frequency
HIGHER AMPLITUDE
2 exceptions that can interfere with BIS value
Nitrous oxide
Limitations of BIS
There is a 20-30 second lag between measuring the EEG and computing BIS value.
Can impair the accuracy of the BIS
Hypothermia EMG interference (increase muscle tone)
BIS and children
less accurate with children.
Data to suggest that a BIS value < 40 for more than 5 minutes correlates with
INCREASED 5 year mortality
Patient safety index monitor target range of GA
25-50
Function of the LINE ISOLATION MONITOR
ALarm sounds when the OR power supply becomes grounded.
The electrical supply in the OR is
NOt grounded
Why is LIM alerting the OR staff that the power supply is grounded important?
Because a second electrical fault can lead to an electric shock
Does the line isolation monitor protect the patient from microshock?
no
Does the line isolation monitor Isolate the electrical equipment from the ground?
No
Does the line isolation monitor cut off the power supply to a piece of equipment that has become grounded?
no
Electricity obeys this law
Ohm’s => Voltage (driving pressure) = Current (flow) x Impedance (resistance)
To receive a shock, a person must be
part of and complete an electrical circuit.
For current to flow there has to be
voltage pressure across an impedance (resistance)
If a closed circuit exists,
then exposure to a live electricity source provides an elctromotive force (voltage) that pushes the current through an impedance (resistance). The impedance can be you or the patient.
An electric current that enters the body will exit the body
Along the path of least resistance.
Consequences of electrical injury?
Cardiac arrythmias
Nerve injury - muscle contraction and diaphragmatic paralysis
Thermal injury ( damage to internal organs)
Macroshock is a
Larger amount of current that is applied to the external surface of the body
The impedance of the skin offers a _____Resistance, so it takes a _____ current to induce vfib
HIGH ; larger
Microshock is a
Smaller amount of current that is applied DIRECTLY to the myocardium
With microshock to the myocardium, the high resistance of the skin is bypassed, therefore it takes a
Significantly smaller amount of current to induce vfib.
Things that increases the patient’s susceptibilty to microshock?
Central line
PAC
Pacing wires.
What is the MAXIMUM allowable current leak in the OR
10 MicroAmps (10mA)
What is the current that will lead to VFIB
100 microamps
Threshold for touch perception of electrical shock
1 milliAmp
Maximum current for a HARMLESS electrical shock
5 milliAmp
Let go current occuring before sustained contraction
10-20mA
Loss of consciousness current
50 mA
The electrical systems in the OR are designed to reduce the risk of electric shock because
The OR power supply is not grounded
The equipment is grounded.
The absence of grounding in the OR provides a
Second layer of protection against electrical shock
For an electrical shock to occur in the OR there must be faults in the system?
After the 1st fault, the OR power supply become grounded, there is NO COMPLETED CIRCUIT and there IS NO SHOCK
after the 2nd fault, the circuit is complete and an ELECTRIC SHOCK occurs
The line isolation monitor assesses the
integritiy of the ungrounded power system in the OR. It tells you when the OR becomes grounded and how much current could potentially flow through you or a patient if a second fault occurs.
The primary purpose of the LIM is to
Alert the OR staff of the first fault (this means that OR has become grounded)
Does LIM protect from macro or microshock?
no
IF the LIM alarm sounds, what should be done?
The LAST PIECE OF EQUIPMENT THAT WAS PLUGGED IN SHOULD BE UNPLUGGED>
The LIM will alarm when
2-5 milliAMps of leak current is detected.
All electrical devices
leak a small amount of current.
If the sum of all the currents exceeds 2-5 mA, what happens to the LIM ?
the alarm will sound, however, there is no risk of electric shock in this situatio and no corrective actiion is required
Electrocautery on PM function
Suppress
If the operative site is near a PM or ICD
The bipolar cautery is useful
Is a return pad required?
Because the current flows from one tip of the instrument to the other, no return pad is required.
On a monopolar electrocautery unit, what is needed?
Return pad
What is a return pad necessary for a monopolar electrocautery unit?
Because the return pad provides a location for the electrical current to exit the body . if the pad is too small or does not make good contact with the patient, the electrical current will find another way to exit the body such as EKG pads, jewelry, temp probes, or anything else with conductive properties.
The surgical electrocautery device delivers
HIGH FREQUENCY current (500000-1million hz) that is used to cut, coagulate, dissect or destroy tissue.
Risk with surgical electrocautery device?
Vfib
Energy pathway for monopolar electrocautery
Electrosurgical generator –> Active cable –> Active electrode –> Return pad –> return cable.
To prevent burn at the return pad site, the entire surface of the return electrode should
be in direct contact with the patient’s skin.
Return pad should NOT be placed where
bony prominences or metal implants.
The electrolyte gel on the return pad should be inspected for
Dryness.
If the gel of the electrolyte gel dries out what happens?
The Electrical current wont have a direct path to the return electrode and will find another way to exit the body.
