Anesthesia Monitoring Flashcards
Why do we monitor patients?
- one of the standards of care
- assess data indicating - patient status, patient’s response to therapeutic interventions, anesthesia equipment functionality
Standard 9
- monitor, evaluate, and document
- alarms on and audible
documentation requirements
- at least every 5 min
- BP
- HR
- RR
alarms in anesthesia
- reflect changes in patient or equipment status
- variable pitch
- threshold alarms on and audible
vigilance
state of clinical awareness whereby dangerous conditions are anticipated or recognized and promptly corrected
Standard 9 Required Monitors
- oxygenation
- ventilation
- cardiovascular
- thermoregulation
- neuromuscular function
Standard 9 oxygenation
continuously monitor oxygenation by clinical observation and pulse oximetry; team communicates and collaborates to mitigate risk of fire
Standard 9 ventilation
- continuously monitor ventilation by clinical observation and confirmation of continuous ETCO2 during moderate sedation, deep sedation, or general anesthesia
- verify intubation of trachea or placement of other artificial airway device by auscultation, chest excursion, and confirmation of expired CO2
oxygenation measurement tools
- oxygen analyzer
- pulse oximetry
- skin color
- color of blood
- ABG (when indicated)
oxygen analyzer facts
- measures FiO2 - inspired gas from inspiratory limb
- low concentration alarm if <30% from pipeline
- calibrate to RA and 100%
- required for any general anesthetic
- useful for calculating PaO2 with alveolar gas equation
oxygen analyzer
electrochemical sensor, cathode and anode embedded in electrolyte gel separated from oxygen gas by oxygen permeable membrane; O2 reacts with electrodes, generates electrical signal proportional to O2 pressure (mmHg) in sample gas
pulse oximetry
- standard of care for continuous oxygen monitoring
- early warning for hypoxemia
- requires pulsatile arterial bed
- finger, toe, ear lobe, bridge of nose, palm and foot in children
- continuous measurement of pulse rate and oxygen saturation of peripheral Hgb (SpO2)
mechanism of pulse oximetry
- beer-lambert law
- oxygenated Hgb absorbs more infrared light (960 nm)
- deoxygenated Hgb absorbs more red light (660 nm)
- oximeter calculates O2 saturation –> ratio of infrared and red transmitted to a photodetector; comparison of absorbances of these wavelengths
- basis of oximetry is change in light absorption during arterial pulsation (pulsation –> increased path length)
factors affecting pulse oximetry accuracy
- high intensity light
- patient movement
- electrocautery
- peripheral vasoconstriction
- hypothermia
- cardiopulmonary bypass
- presence of other Hgb (COHgb –> false high reading; MetHgb –> false low or high)
- IV injected dyes (methylene blue)
- hemoglobin < 5 (will not register)
Hypoxia
SaO2 less than 90%
what is ventilation
- movement of volume, inhalation/exhalation
- elimination of CO2
ventilation monitors
- continuous auscultation
- chest excursion (observation)
- end-tidal capnography
- spirometry
precordial stethoscope
- position at suprasternal notch or apex of left lung (where heart/lung sounds audible)
- easily detect changes in breath or heart sounds
- airway/circuit disconnect
- endobronchial intubation
- anesthetic depth/increase HR or contractility
esophageal stethoscope
- soft plastic catheter
- balloon covered distal openings
- limited to intubated patients
- better quality heart and breath sounds
- incorporated temperature probe
- place through mouth or nose into esophagus (distal 1/3), to provide core temperature
esophageal stethoscope contraindications
esophageal varices or strictures
respiratory gas analysis
- gas sampling line (CO2, O2, volatile anesthetics)
- allows measurement of volatile anesthetics
- non-dispersive infrared (NDIR) most common
NDIR
- side stream sampling (continuous gas aspiration)
- gas absorbs infrared energy at specific wavelength (sp to each gas)
- complex algorithm and microprocessor
- multiple narrow band optical filters through which infrared emission passed to determine which gas is present in that mixture
dispersive infrared gas analysis
prism or diffraction grading mechanism to separate component wavelengths for each of our agents
how much CO2 does the average adult produce
250 mL/min
how can CO2 production change
- patient condition
- anesthetic depth
- temperature
side stream sampling
- airway gas aspirated and pumped to measuring device
- sampling flow rates of 50-250 mL/min
- limitations –> H2O condensation can contaminate the system and create falsely high readings; lag time between sample aspiration and reading
normal PACO2 and PaCO2 gradient
2-10 mmHg
abnormal PACO2-PaCO2 gradient
- gas sampling errors
- prolonged expiratory phase
- V/Q mismatch
- airway obstruction
- embolic states
- COPD
- hypoperfusion
normal ETCO2
40 mmHg
indicative of adequate circulation, ventilation, and CO2 production
phase I of capnograph
- corresponds to inspiration
- anatomic/apparatus dead space devoid of CO2
- level should be zero unless rebreathing
- baseline elevated if –> CO2 absorbent exhausted, expiratory valve is missing/incompetent, Bain circuit
phase II of capnograph
- early exhalation/steep upstroke
- mixing of dead-space with alveolar gas
- prolonged upstroke associated with –> mechanical obstruction (kinked ETT), slow emptying of lungs (COPD, bronchospasm, asthma)
phase III of capnograph
- CO2 rich alveolar air
- horizontal with mild upslope
- steepness is function fo expiratory resistance (COPD, bronchospasm)
beta angle
-where the PETCO2 reads, what shows up on the monitor
phase IV of capnograph
- inspiration of fresh gas
- return to baseline
what do we observe in capnograph waveform?
- time
- amplitude (how high does it go?) - should be 35-40 mmHg
- frequency
- slope
- baseline (how does it look in relation to normal baseline)
mechanical ventilator
- tidal volume - integrated spirometry
- airway pressure - in circuit pressure gauge, peak inspiratory pressure, sustained elevated pressure
- disconnect alarm - low airway pressure
Standard 9 cardiovascular
- monitor and evaluate circulation to maintain patient’s hemodynamic status
- continuously monitor HR and CV status
- use invasive monitoring as appropriate
electrocardiogram
- standard of care requires continuous display (HR with audible indicator)
- detects –> cardiac dysrhythmias, conduction abnormalities, myocardial ischemia/ST depression, electrolyte changes, pacemaker function/malfunction
Three-electrode EKG
- typically monitor lead II
- limited in detection of myocardial ischemia
five-electrode EKG
- allows recording of six standard limb leads (I, II, III, aVR, aVL, aVF) and one precordial lead (usually V5)
- better in detecting myocardial ischemia
- allows better differential diagnosis of atrial and ventricular dysrhythmias
lead II
- yields max P wave voltage
- superior detection of atrial dysrhythmias
- detects inferior wall ischemia/ST depression
V5
- 5th ICS/anterior axillary line
- detection of anterior and lateral wall ischemia
RA (white)
R 2nd ICS midclavicular line
LA (black)
L 2nd ICS midclavicular line
RL (green)
R 5th/6th ICS midclavicular line
LL (red)
L 5th/6th ICS midclavicular line
V (brown)
4th intercostal space R sternal border (or any of the V leads)
noninvasive arterial BP monitoring (NIBP)
- oscillometric device –> air pump inflates cuff –> microprocessor opens deflation valve –> oscillations sampled
- easy, accurate
NIBP errors
- surgeon leans on cuff
- inappropriate cuff size (large –> low reading; small –> high reading)
- shivering or excessive motion
- atherslcerosis and HTN –> systolic low, diastolic high compared with invasive arterial pressure
invasive arterial BP indications
- any patient requiring BP measurement > minute to minute
- critically ill
- anticipated rapid blood loss
- major procedures - CPB, aortic cross-clamp, intracranial surgery, carotid sinus manipulation
- frequent ABG
CVP monitor indications
- fluid management of hypovolemia and shock
- infusion of caustic drugs
- aspiration of air emboli
- insertion of pacing leads
- total parenteral nutrition (TPN)
- venous access in patients with poor peripheral access
Pulmonary Artery Catheterization
- poor LV function (EF <0.4, Cl <2 L/min/m2)
- evaluation of response to –> fluids, vasopressors, vasodilators, inotropes
PA cath indications
- valvular heart disease
- recent MI
- ARDs
- massive trauma
- major vascular surgery
Standard 9 thermoregulation
- monitor body temp if clinically significant changes in body temperature are intended, anticipated or suspected
- use active measures to maintain normothermia
- MH triggering agents used –> monitor for S/S
factors affecting temperature
- ambient room temperature
- scope or length of surgery
- hypothalamic depression
- intraoperative fluid replacement
- vigilance in maintaining core temperature
radiation
heat radiated from patient into room
convection
heat loss due to air velocity
conduction
contact with OR table, blanket
evaporation
heat loss to dry inspired gases
heat loss
radiation > convection > conduction > evaporation
General anesthesia and temperature regulation
body cannot compensate for hypothermia because anesthetics inhibit central thermal regulation by interfering with hypothalamus function (normally plays a role in body temp regulation)
hypothermia defintion
- <36 degrees C
- mild 33-36; reduced enzyme function, coagulopathy
- moderate = 32; fibrillatory threshold
S/S of hypothermia
- shivering
- dizziness
- feeling hungry
- nausea
- rapid breathing
- problems speaking
- confusion
- coordination difficulties
- fatigue
- rapid HR
- drowsiness
- weak pulse
- shallow breathing
hypothermia in anesthesia
- heat loss outpaces metabolic heat production
- anesthesia impairs normal response
- body temp may decrease 1-4 degrees
- may delay awakening
- may cause shivering
shivering increases O2 consumption by how much?
400%
greatest risk for hypothermia
- elderly
- burn patients
- neonates
- patients with spinal cord injuries
hyperthermia in anesthesia
- rarely develops under anesthesia
- late sign of MH
- other causes –> endogenous pyrogens, thyrotoxicosis or pheo; anitcholinergic blockade of sweating; excessive environmental warming
temperature monitoring sites
- esophagus (lower 1/3) accurately reflects blood temperatures
- nasopharynx
- rectum (not as reliable)
- bladder (integrated into foley)
- tympanic membrane
- blood (PA cath)
- skin
superficial active warming modalities
- forced air warmer (bair hugger) - most effective; decreases radiant and convective loss; decreases post op shivering and PACU stay
- warming blanket - water circulating; minimally effective
- radiant heat unit - no impact on mean body temp
- heated liquids - IV bags/bottles on patients (dangerous)
core active warming modalities
- IV fluid warmers - warmed liquid transfer of heat to infusate; delivers fluids at the highest temperature of any technology
- gastric lavage - warms body core, impractical intraoperatively
- peritoneal irrigation - encourage use of warm irrigation during intra-abd procedures
passive warming modalities
- ambient temperature - huge effect on maintaining body heat; ambient temp >24; most adults remain normothermic without requiring other measures
- insulation - extremities and head
- heat and moisture exchanger - artificial nose, retains moisture
- coaxial breathing circuit - warms/humidifies inspiratory gases
neuromuscular function standard 9
when NMB agents administered, monitor neuromuscular response to assess depth of blockade and degree of recovery
peripheral nerve stimulator
- monitors effect of NMB agents on NMJ - know and compare to baseline; quantify by feel
- delivers electrical stimulation to peripheral motor nerve
- evokes mechanical response
- permits titration of NMBD to optimal effect
- quantifies recovery from NMB
S/S residual paralysis
- hypoxia
- low TV
- stridor
- muscle weakness
- increased oxygen requirement
PNS monitoring sites
- ulnar nerve
- facial nerve
- posterior tibial nerve
- peroneal nerve
ulnar nerve PNS
- stimulates adductor pollicis
- thumb adduction
- electrodes placed at wrist or elbow (negative/black placed distally; positive/red proximally)
- most common monitoring site
- best for recovery
- not as good for onset because inaccurate reflection of degree of block of diaphragm or airway muscles
- only site for quantitative
facial nerve PNS
- lies within parotid gland
- electrodes placed in front of tragus of ear and below
- avoid direct muscle stimulation; negative electrode placed over nerve at tragus; positive at outer campus of eye
- be careful of facial hair intereference
- stimulates orbicularis occuli (close eyelid or corrugator supercilli (furrows brow)
- temporal or zygomatic branches
- best site for onset bc mimics paralysis of diaphragm
posterior tibial nerve PNS
- place electrodes behind medial malleolus of tibia
- stimulates flexor hallucis brevus muscle
- causes big toe flexion
- can also be used for recovery if no access to ulnar nerve
peroneal nerve PNS
- electrodes on lateral aspect of knee
- response - dorsiflexion of foot
single twitch
- single pulse delivered every 10 seconds
- 0.1 or 1 Hz
- increasing block results in diminished response
- twitch height depressed when 75% of receptors are blocked (twitch height will remain normal until 75% of nAChR are blocked)
- twitch height will disappear when 90-95% of receptors blocked
train of four (TOF)
- most commonly used
- 4 repetitive stimuli (2 Hz every 0.5 second)
- twitches progressively fade as relaxation increases
- ratio of responses to 1st and 4th twitches are sensitive indicator of NMB
T4/T1 ratio
- assessment of number of twitches ranging from 0 to 4
- compares the strength of the fourth twitch to that of the first
- seen as a percentage on the screen
loss of 4th twitch
75% receptors blocked
loss of 3rd twitch
80% receptors blocked
loss of 2nd twitch
90% receptors blocked
loss of 1st twitch
90-98% receptors blocked
what is clinical relaxation?
75-95% receptors blocked
non-depolarizing NMB
- fade will be seen
- ratio decreases and is inversely proportional to degree of block
depolarizing NMB
- succinylcholine
- amplitude of all 4 twitches will decrease but TOF will remain 1 because all four twitches have the same amplitude
- all or nothing –> no fade
tetanic stimulation (tetany)
- tetany at 50-100 Hz
- 5 seconds at 50 Hz evoked tension approximates tension developed during a maximal voluntary effort
- in presence of NMB fade occurs
- sustained response occurs when TOF >70%
- disadvantage = painful for patient
post-tetanic count
- useful when all twitches suppressed
- apply tetanus at 50 Hz for 5 seconds
- wait 3 seconds
- apply single twitches (or TOF) every second up to 20
- number of twitches inversely related to depth of block (so more twitches means less block)
double burst suppression
- less painful than tetany
- DBS3,3 - 3 short 50 Hz impulses, 750 msec pause, followed by 3 more bursts
- more sensitive than TOF for visual evaluation of fade
PNS Induction
- TOF
- single twitch
PNS maintenance
- TOF
- post tetanic count
PNS emergence
- TOF
- DBS
fast onset/tracheal intubation
- site = orbicularis oculi
- twitch modality = single twitch or TOF
- target response = 0 twitches
profound blockade
- site = adductor pollicis or orbicularis oculi
- twitch modality = TOF or post tetanic count
- target response = relaxant dependent
adequacy of relaxation (abdominal surgery)
- site = adductor pollicis
- twitch modality = TOF
- target response = 1-2 twitches present
predicting reversible block (when no TOF response present)
- site = adductor pollicis
- twitch modality = post tetanic count
- target response = relaxant dependent
detecting reversible block
- site = adductor pollicis
- twitch modality = TOF
- target response = at least 2 twitches present
detecting adequate neuromuscular function
- site = adductor pollicis
- twitch modality = double burst suppression
- target response = no fade present
sensitivity of muscle groups to non-depolarizing muscle relaxant from most to least sensitive
- extraocular
- pharyngeal
- masseter
- adductor pollicis
- abdominal rectus
- orbicularis oculi
- diaphragm
- vocal cords
why is diaphragm first muscle to recover from NMB?
it is rich in nAChR
Which nerve do you monitor for onset?
facial nerve
which nerve do you monitor for recovery?
ulnar nerve
1 of 4 twitches on TOF
reversal may take as long as 30 min
2-3 twitches on TOF
reversal may take 10-12 min following long-acting relaxants, 4-5 min after intermediate relaxants
4 of 4 twitches on TOF
adequate recovery within 5 minutes of neostigmine, within 2-3 minutes of edrophonium
unreliable clinical signs of NMB recovery
- sustained eye opening
- tongue protrusion
- arm life to opposite shoulder
- normal TV
- normal or near normal vital capacity
- max inspiratory pressure <40-50 cmH2O
reliable clinical signs of NMB recovery
- sustained head lift x 5 sec
- sustained leg lift x 5 sec
- sustained handgrip x 5 sec
- max inspiratory pressure 40-50 cmH2O or greater
quantitative nerve monitoring
- device that quantifies degree of NMB
- reliable, accurate and objective
- post stimulation, the muscle response is objectively quantified versus baseline (MUST GET A BASELINE)
Acceleromyography (AMG)
piezoelectric sensor measures muscle acceleration (voltage generated upon muscle contraction)
Electromyography (EMG)
muscle action potentials recorded; electrical activity proportional to the force of contraction
Kinemyography (KMG)
quantifies muscle movement with motion sensor strip containing piezoelectric sensors
Mechanomyography (MMG)
detects contraction force, converts to electrical signal, signal amplitude reflects contraction strength
Phonomyography (PMG)
muscle contraction produces low-frequency sounds, calculates muscle response
Bispectral Index Score (BIS)
- used to assess depth of anesthesia
- optional, not currently part of the standard of care
- EEG signal
reported BIS advantages
- reduced risk of awareness
- better management of responses to surgical stimulation
- faster wake up (controversial)
- more cost effective use of anesthetics
BIS numerical values
- ranges from 0-100
- 100 = awake CNS
- > 70 = greater recall risk
- 40-60 = general anesthesia
- 0 = isoelectric EEG
What affects BIS reading?
- electrocautery
- EMG
- pacer spikes
- EKG signal
- patient movement
cerebral oximetry
- assesses cerebral oxygen saturation using near infrared spectrophotometry (NIRS)
- normal = 60-80%
- 20% reduction in cerebral NIRS has been associated with regional and global ischemia
- noninvasive
- detects decreases in CBF in relation to CMRO2
- intensity difference between transmitted and received light, determines regional oxygen saturation (similar to pulse oximetry and beer-lambert)
- light source adheres to forehead, light transmits through tissue and cranium
