Clinical Monitoring II - Exam 1 (Ericksen) Flashcards
Side-stream (diverting) gas analyzer
- gas taken away from pts airway to the analyzer
Mainstream (non-diverting) gas analyzer
- gas is analyzed at the airway
Gas Analysis
What is the transit time?
- time lag for gas sample to reach analyzer
- not instantaneous
Gas analysis
What is the rise time?
time taken by the analyzer to react to the change in gas concentration
- ex: ETCO2 fluctuating when pt is getting sleepier - rises and then it levels out
Mainstream sampling
Sampling Challenges
- Water vapor (condense in airway tubing)
- Secretions & blood - clog ETCO2 sample line
- more interfaces for disconnections w/ mainstream
Side-stream Sampling
Sampling Challenges
- Kinking of sampling tubing
- water vapor
- failure of sampling pump
- leaks in line
- slow response time
Dalton’s Law states that –
the total pressure exerted by a mix of gases is equal to the sum of the partial pressures of each gas
How are gases expressed?
partial pressures (mmHg)
Volumes % (PP/Ptot x 100)
What is mass spectrometry?
- looking @ how many gas molecules are present in a expired sample
- the concenctration deterimined according to mass/charge ratio
What can mass spectrometry tell us?
- what portions of the gas are Sevo, O2, Nitrous, etc.
- can calculate 8 diff. gases
What is Raman Spectroscopy?
- argon laser produces photons that collide w/ gas molecules in a sample
- measured in a spectrum that identifies each gas & concentration
What is infrared analysis?
the measurement of energy absorbed from narrow band of wavelengths of IR radiation as it passes through a gas sample
What does infrared analysis measure?
the concentration of gases - they all have a different fingerprint/band length
CO2, nitrous oxide, water, volatile gases
What type of infrared analyzer is most common?
Non-dispersive (keeps it from going everywhere)
Why can infrared analysis not measure O2?
O2 does not absorb IR radiation
IR analyzer
Less light getting through =
higher concentration of the gas being measured
IR analyzer
more light getting through to detector =
Less concentration of the gas being measured
Side-stream analyzers report ________ temperature and ________ ____ dry values.
Ambient and Pressure dry
analyzers should report results at ____ temperature and pressure ________ values.
Body temp & pressure saturated (BTPS)
Example - calculating PP of a gas
- Ptot - PH2O (FiO2) = PP
- 30% O2 PP =
- 760mmHg - 47mmHg (0.30) = 214mmHg
if she does not say anything about H2O vapor, don’t account for H2O vapor
O2 analyzer
What is a fuel cell/galvanic cell?
- located in breathing tube (mainstream)
- oxygen battery - measure current produced when O2 diffuses across a membrane
Fuel Cell
The current measured by the oxygen battery is proportional to ——?
The PP of O2 in the fuel cell
O2 analyzers - Paramagnetic
Why is O2 a highly paramagnetic gas?
- d/t the magnetic energy of unparied electrons in their outer shell orbits
Fuel Cell
Where is it best to monitor the O2 concentration at?
In the inspiratory limb - so we know how much O2 the pt is actually getting
O2 analyzers
What does a paramagnetic analyzer detect?
the change in sample line pressure from the attraction of O2 by switched magnetic fields
signal changes that happen during the switching of magnetic fields correlate w/ O2 concentration
O2 analyzers
Where is the paramagnetic O2 analyzer mostly used?
In side-stream sampling multi-gas analyzers
O2 analyzers
What is the main advantage of the paramagnetic O2 analyzer over the fuel cell?
- rapid-response, breath-by-breath monitoring
- informs us w/ every breath what we need to do for the pt
O2 sampling inside the inspiratory limb –
- ensures O2 delivery to pt
- analyzes hypoxic mixtures
O2 sampling inside the expiratory limb –
- ensures complete PREOXYGENATION/denitrogenation
- ET O2 > 90% adequate - will never be 1.0 (100%)
what does an ET O2 <90% tell us?
The pt has lung comorbidities
Low O2 alarm reasons
- pipeline crossover
- incorrectly filled tanks
- failure of proportioning system - nitrous on and only so much can go through
Why is a High O2 alarm important?
- important to notify us of high O2 concentration in pts in can be harmful to (free O2 radicals)
– premature infants
– pts on chemotherapeutic drugs (bleomycin)
Airway pressure monitoring is a key component in measuring ________.
Ventilation
T/F: Airway pressure monitoring can only assess mechanical ventilation.
False, it can also assess spontaneous ventilation
What can Airway Pressure Monitoring Detect?
- circuit disconnects
- ETT occlusions
- kinking of inspiratory limb
- fresh gas hose kink/disconnect
- circuit leak
- sustained high circuit pressure (collection of H2O vapor, kink)
- high & low scavenging system pressures
What are the 2 types of pressure gauges used for airway pressure monitoring?
Which is highly reliable?
- Mechanical - highly reliable
* requires monitoring - Electronic
* has alarm system integrated
What type of Airway Pressure Alarm is required by the AANA/ASA?
Breathing circuit low pressure alarm
What is the purpose of the breathing circuit low pressure alarm?
- ID circuit disconnects/leaks
Airway Pressure Monitoring
What should the low pressure limit be set at?
- just below the normal peak airway pressure (20-30cmH2O)
Where do 70% of the disconnections of the breathing circuit occur?
At the Y-piece
Airway Pressure Monitoring
What is the sub-atmospheric pressure alarm?
- a negative pressure alarm
- measures and alerts of negative circuit pressure & potential for reverse flow of gases
What 3 things can negative airway pressures cause?
- pulmonary edema
- atelectasis
- hypoxia
What are 5 causes of the sub-atmospheric pressure alarm going off?
- active (suction) scavenging system malfunctions
- pt inspiratory effort against a blocked circuit
- inadequate FGF
- suction to misplaced NGT/OGT
- moisture in CO2 absorbent - prevent suction
When is the high-pressure alarm activated? What pt population is it important in?
- activated if airway pressure exceeds a certain limit
- pediatrics
Causes of high-pressure alarm activation
- obstructions
- reduced compliance
- coughing/straining
- kinked ETT
- endobronchial intubation
Airway pressure monitoring
What triggers the continuous pressure alarms to be activated?
- circuit pressure > 10cmH2O for > 15 seconds
Causes of the continuous pressure alarm being activated
- turned off vent, flipped to APL valve & forgot to squeeze bag
- malfunctioning adjustable pressure relief valve
- scavenging system occlusion
- activation of oxygen flush system
- malfunctioning PEEP (comorbidities)
Peripheral nerve monitoring
Supramaximal Stimulation
- reaction of a single muscle fiber to a stimulus follows on all-or-none pattern
What are the different sites of nerve stimulation?
- Ulnar - adductor pollicis muscle gold standard
- Facial nerve - orbicularis oculi & corrugator supercili muscle where we usually monitor
- median nerve
- posterior tibial nerve
- common peroneal nerve
The diaphragm has a ________ onset than the adductor pollicis. But, recovers ________ than peripheral muscles.
- shorter
- faster
Does the corrugator supercilii or adductor pollicis reflect NMB of laryngeal & abdominal muscles better?
- Corrugator supercillii
What is single twitch stimulation?
What is it used for?
- 1Hz every second - 0.1Hz every 10 seconds
- used in labs to establish an ED95
What is TOF and when do we use it?
- 4 supramaximal stimuli every 0.5 seconds
- evaluate the TOF count/fade in muscle response
- reliable assessment of onset and moderate blockade
What happens w/ TOF and a partial non-depolarizing block (Roc)
- TOFR decreases (fade)
- is inversely proportional to degree of block
What happens to TOFR and a partial depolarizing block (succ)
- no fade, ratio is 1.0
- if fade present = phase II block
What is Double Burst Stimulation?
- 2-3 short bursts of 50Hz tetanic stimulation separated by 750ms w/ 0.2 ms duration of each square wave impulse in burst
- DB 3,3 mode
- DB 3,2 mode
What is DBS good for?
- detecting fade
- not used in clinical practice
What is tetanic stimulation?
non-depolarizers response:
depolarizer response:
- 50Hz for 5 seconds
- non-depolarizers: one strong sustained muscle contraction w/ fade
- depolarizers: strong sustained muscle contraction w/o fade
* not really used
What is post-tetanic stimulation?
- tetanic stimulation (50 Hz for 5 sec)
- followed by 10-15 single twtiches (1Hz after 3 second post-tetanic stimulation)
- 9th twitch - may start to see recovery from non-depolarizer
What is the post-tetanic response dependent on?
- degree of block
- frequency & duration of tetanic stimulation
- lengtho f time b/w end of tetanic & first post-tetanic
- frequency of single twitch stimulation
- Duration of single twitch stimulation before tetanic stimulation
Can only perform every 6 min
What situation is post-tetanic stimulation good for monitoring?
- deep & surgical blockade - if pt is paralyzed very deep
Non-depolarizing intense blockade
Reversal??
- period of no response (3-6 min after intubating dose of NDMB)
- high dose sugammadex (16mg/kg) reversal
Non-depolarizing deep blockade
Reversal??
- absence of TOF, presence of at least 1 response to post-tetanic stimulation
- reversal - Neostigmine usually impossible, sugammadex (4mg/kg)
Non-depolarizing moderate block
Reversal??
- gradual return of 4 responses to TOF
- reversal: Neostigmine after 4/4 responses, Sugammadex (2mg/kg)
What happens in a depolarizing phase I block?
- no fade/tetanic stimulation
- no post-tetanic facilitation
- all 4 responses reduced - equal - disappear - come back
What happens in a phase II Depolarizing block?
- fade present in TOF and tetanic stimulation
- occurrence of post-tetanic facilitation
clinical tips for NMB & monitoring
- keep pt warm to prevent delaying nerve conduction
- moderate level block is sufficient for surgery w/ 1-2 responses to TOF
- reverse when all 4 responses to TOF present
- check for NM recovery prior to extubation post-reversal
Reliable clinical signs for extubation
- sustained head lift for 5 sec
- sustained leg lift for 5 sec
- sustained handgrip for 5 sec
- sustained tongue depressor test = can they bite down on the depressor around their ETT?
- max inspiratory pressure - take deep breath and hold it
EEG is a summation of –
excitatory & inhibitory postsynaptic potentials in the cerebral cortex
* 16 channels of info
What does an EEG identify?
- consciousness/unconsciousness
- seizures
- stages of sleep/coma
- hypoxemia/ischemia
EEG
Amplitude
- size/voltage of recorded signal
EEG
Frequency
- # of times per second the signal oscillates/crosses the 0-voltage line
EEG
Time
duration of sampling signal
Peri-op uses for EEG
- indentifies inadequate flow to cerebral cortex
- guides an anesthetic-induced reduction of cerebral metabolism
- predicts neuro outcome after brain insult
- Gauges depth of hypnotic state of pts under GA
EEG beta waves
> 13Hz
* awake, alert/attentive brain
EEG alpha waves
8-13Hz
* eyes closed
* anesthetic effects
EEG Theta & Delta Waves
- theta (4-7Hz)
- delta (<4Hz)
- depressed, slower frequency
How many channels does a processed EEG use?
What do we use it for?
< 4 channels (2 for each hemisphere)
* delineates unilateral from bilateral changes
– unilateral: regional ischemia d/t carotid clamping
– bilateral: depression from anesthetic drug bolus
When do we use a BIS monitor?
- cases where there is concern for neuro deficits
- estimates anesthetic depth
- can help prevent intra-op awareness
BIS ranges
100:
80:
60:
40:
20:
0:
- 100: Awake - responds to voice
- 80: responds to loud commands, mild prodding
- 60: GA - low chance of recall, no response to verbal
- 40: deep hypnotic state
- 20: burst suppression
- 0: flat line
What is the most common type of evoked potentials monitored intra-op?
Sensory-evoked Responses
* electric most common
* can also have auditory, or visual
How do sensory evoked potentials work?
- stimulate sensory pathway and record responses along the path to the cerebral cortex
Evoked potentials
Latency
- time measured from application of stimulus to onset/peak of response
Evoked potentials
amplitude
- size/voltage of recorded signal
Evoked potentials
What is one of the most important things for anesthesia?
- let the tech get their baseline tracing while we are pre-oxygenating
What are somatosensory evoked potentials (SSEPs)?
- stimulation to peripheral mixed nerves
- responses measured in sensorimotor cortex
SSEPs
short latency vs. long-latency waveforms
- short latency - more commonly recorded intra-op
– less affected by anesthetics - long-latency: changed by anesthesia
SSEPs
What things may alter the appearance of SSEPs?
- induction
- neuro disease
- age
What are Brainstem Auditory Evoked Potentials (BAEPs)?
- monitors responses to click stimuli
- delivered via foam inserts along auditory path from ear to auditory cortex
What are Visual Evoked Potentials (VEP)?
- monitors response to flash stimulation of retina
- uses light-emitting diodes in soft plastic goggles through closed eyelids or contacts
- least common technique intra-op
What are motor evoked potentials?
MEP
* monitors integrity of motor tract along spinal column, peripheral nerves, and innervated muscle
What is the most common MEP used?
Transcranial motor evoked potential
* via transcranial electrical stimulation overlying motor cortex
MEPs
What is electromyography?
- monitors responses generated by cranial and peripheral motor nerves
- allows early detection of surgically induced nerve damage & assessment of the level of nerve function intra-op
What is the primary thermoregulatory control center?
Hypothalamus
What nerve fibers are the heat/warmth receptors?
Unmyelinated C fibers
What nerve fibers are the cold receptors?
Alpha & delta fibers
Thermoregulatory - threshold:
the temp at which a response will occur
Thermoregulatory - Gain:
the intensity of the response
Thermoregulatory - Response
- sweating - decreases body temp
- vasodilation - more heat loss
- vasoconstriction - less heat loss
- shivering - increases body temp
What 6 things can alter temperature control?
- anesthesia
- age
- menstrual cycle
- drugs
- alcohol
- circadian rhythm
Hypothermia in GA
initial response
- rapid decrease of 0.5-1.0 degree C
- c/b anesthesia induced vasodilation (redistribution of body heat)
- happens over 30min
Hypothermia in GA
Slow linear reduction
- 0.3 degree C/hr
- c/b GA reducing metabolic rate by 20-30%
- heat loss exceeds production
- 1-2hrs after anesthesia induction
Hypothermia in GA
Plateau phase
- thermal steady state
- heat loss = production
- 3-4hrs after anesthesia
- pt is still losing peripheral heat - but not core (vasoconstriction)
Neuraxial Hypothermia
Central thermoregulatory control is inhibited, which means —
the threshold (temp) at that triggers peripheral vasoconstriction & shivering is lower
so more heat is lost
Neuraxial Hypothermia
What autonomic thermoregulatory defenses are impaired?
- vasodilation
- sweating
- vasoconstriction
- shivering
Neuraxial Hypothermia
What causes the initial decrease in core temp?
- neuraxial blockade induced vasodilation
Neuraxial Hypothermia
Will there be a plateau in temp?
NO, b/c inhibition of peripheral vasoconstriction
Heat Transfer
Radiation
Heat loss to the environment (30-40%)
main form of heat loss
* infants vulnerable b/c low BSA
Heat Transfer
Convection
- loss of heat to air immediately surrounding the body (30%)
- greater in rooms w/ laminar flow
Heat Transfer
Evaporation
- loss of heat through vaporization of water from open body cavities & resp. tract
- sweating (DM - blood sugar)
- ex-lap - pack abd w/ soaked gauze to prevent heat loss
Heat Transfer
Conduction
- heat loss d/t direct contact of body tissue or fluids w/ colder material
- ex: skin and OR table, IV fluids
electricity conduction - touching
Hypothermia complications (7 things)
- Coagulopathy
- increases transfusions (22%) and bleeding (16%)
- decreases O2 delivery to tissues (vasoconstriction)
- 3x rate of morbid cardiac outcomes (BP, HR and catecholamine levels increased)
- shivering (increased O2 demand)
- decreased drug metabolism - longer DOA NMB
- post-op thermal discomfort
5 benefits of hypothermia
- protects against cerebral ischemia
- reduces metabolism (8%/degree C)
- improved outcomes in cardiac arrest recovery
- use in neurosurgery when brain ischemia is unexpected
- more difficult to trigger MH
Peri-op temp management (4)
- airway heating & humidification (peds)
- warm IV fluids/blood
- cutaneous warming
– increase room temp, insulation, hot water mattress - forced air warming - prevents loss from radiation (uses convection)
4 temp monitoring sites
- pulmonary artery - gold standard
– correlates w/ other 3 - tympanic - approximates hypothalamus temp
- nasopharyngeal - brain temp (more error, epistaxis)
- distal esophagus - lower 1/3 - 1/4
OR temps
Children: 70 degrees F/21 C
Adults: 65 degrees F/18 C
