Anesthesia Monitoring Flashcards
Standard 9
Monitoring and alarms
- ventilation (etco2 and spo2)
- cv status
- thermoregulation
- neuromuscular function (NMBs)
- patient positioning
What must you do if you omit a standard monitor
DOCUMENT
standard 11
Transfer of care
How do we monitor oxygenation
O2 analyzer Pulse ox Skin color Color of blood ABG
O2 analyzer
Measures fio2 of inspired gas on the Inspirators limb
Low concentration alarm = <30%
Required for any general anesthetic
Electrochemical sensor - cathode and annode embedded in electrolyte gel, separated from oxygen gas by O2 permeable membrane
- O2 reacts with electrodes, generates electrical signal proportional to O2 pressure in sample gas in mmHg
PAO2 calculation
PAO2 = FiO2 * (Pb-47) - PaCO2
pulse ox
Standard of care to provide early warning sign of hypoxemia
Measures arterial o2 sat (oximetry and plethysmography)
Requires pulsatile arterial bed (finger, toe, earlobe, nose, palm and foot in kids)
Gives continuous measurement of pulse rate and oxygen saturation of peripheral Hgb
What law deals with pulse ox
Beer-lambert law of spetrophotometry
Wavelength of oxygenated hgb
960nm
Wavelength of deoxygenated hgb
660nm
How does pulse ox calculate spo2
Ratio of infrared (oxyhgb) to red (deoxyhgb)
Basis of oximetry is change in light absorption during arterial pulsations
What affects accuracy of pulse ox
High intensity light Patient movement Electrocautery Peripheral vasoconstriction Hypothermia Cardiopulmonary bypass Presence of other hemoglobins - COHb - false pos -MetHb - false neg or pos IV injected dyes (methylene blue decreases spo2) Hgb <5 will not register
Pleth variability index (PVI)
Indication of pulse strength at indicator site
Useful in measuring goal-directed fluid therapy and fluid responsiveness
Oxyhgb dissociation curve
PaO2 30 is SpO2 60
PaO2 60 is SpO2 90
PaO2 40 is SpO2 75
Hypoxia definition
O2 sat < 90
Precordial stethescope
Easily detects change in heart lung sounds
- Used to detect circuit disconnection
- Rapid changes in anesthetic depth
Held in place with double sided tape
Placed in suprasternal notch or apex of left lung
Esophageal stethescope
Soft plastic catheter placed into these distal 1/3 of the esophagus through mouth or nose to monitor heart and breath sounds and temp
Only use on intubated patients
Contraindicated in patients with esophageal varices
Respiratory gas analysis
Allows measurement of VA
Most commonly a non-dispersive infrared method (side stream sampling, gas absorbs infrared energy at specific wavelengths, complex algorithm and microprocessor)
50-250ml/min is the rate of processing
Capnography
Confirms ETT placement and adequate ventilation
Most often side-stream sampling
-airway gas aspirated and pumped into device at sampling flow rates of 50-250 ml/min
What is the normal adult CO2 production and what makes it change
250 ml CO2/min
Patients condition
Anesthetic depth
Temperature
What are the limitations of capnography
H2O condensation can contaminate system and falsely elevate readings
There is a lag time between sample aspiration and reading
Et CO2 is less than alveolar CO2 and that’s less than Pa CO2
This is a fact i just wanted to remember
PACO2 -PaCO2 gradient
Normal = 2-10
Abnormal can be due to
- gas sampling error
- prolonged expiratory phase
- V/q mismatch
- airway obstruction
- embolic states
- COPD
- Hypoperfusion
Capnograph
1 - inspiration (baseline) - should be NO CO2
2 - early exhalation - rapid rise with steep upstroke - dead space mixed with alveolar gas
3 - CO2 rich alveolar air (horizontal portion/mild upslope)
4 - return to baseline (inspiration of fresh gas)
Why would phase 1 (baseline) of your capnograph be elevated
CO2 absorbant exhausted
Expiratory valve missing/incompetent
Bain circuit
Why would there be a prolonged upstroke during phase 2 of your capnograph
Mechanical obstruction (kinked ETT) Slow emptying of lungs (COPD, bronchospasm)
What is the steepness of phase 3 of your capnograph a function of?
Expiratory resistance
COPD, bronchospasm
Capnograph with a notch in phase 3
Caused by inadequate NMB as diaphragm responds with patients attempt to breathe
“Curare cleft”
Or caused by surgeon pressing on abdomen
If your capnograph fails to return to baseline, what does that mean
You are rebreathing CO2
Slow rise of phase 2 of capnograph
Some sort of expiratory obstruction
what Monitors are on an mechanical vent
Tidal volume
Airway pressure
Disconnect alarm
What leads do you typically monitor in your EKG to best show myocardial ischemia
2 and V5
Why would you choose a 5 lead over a 3 lead ekg system
The 5 lead system is better at detecting myocardial ischemia and allows a better differential diagnosis of atrial and ventricular dysrhythmias
Lead 2
Yields max p wave voltages
Superior detection of atrial dysrhythmias
Detects inferior wall ischemia/ST depression
V5
5th ICS/anterior axillary line
Detection of anterior and lateral wall ischemia
BP Cuff width
20% greater than mean diameter of the extremity
- too narrow = artificially high pressure
Oscillometric device
Air pump inflates cuff - linked to microprocessor - opens deflation valve - oscillations sampled
Non invasive
Errors for oscillometric BP
Surgeon leans on cuff Inappropriate size - too big = low reading - too small = high reading Shivering or excessive motion Atherosclerosis and HTN - systolic low - Diastolic high
A-line when to use
Used when you need continuous BP monitoring, critically ill patients, if you are anticipating blood loss, for major procedures, or if you need frequent ABGs
What are the most common IABP sites
Radial (most common), ulnar (more tortuous), brachial (predisposed to kinking), femoral (prone to pseudoaneurysm and atheroma formation), DP (distorted waveform), axillary (potential for plexus nerve damage from hematoma or traumatic cannulation)
CVP indications
Fluid management of hypovolemia and shock
Infusion of caustic drugs
Aspiration of air emboli
Insertion of pacing leads
TPN
Venous access in patients with bad peripheral veins
Where do you place CVP
Right IJ (preferred - straight to heart)
Subclavian
EJ
AC (special kit with long catheter)
PA catheterization indications
Poor LV function, evaluate response to fluids, pressors/dilators, inotropes, valvular heart disease, recent MI, ARDS, trauma, vascular surgery
In a 70 kg patient, a liter of crystalloid at room temp will lower body temp by
0.4 degrees celcius
In a 70 kg patient a unit of RBC will lower body temp
0.2 degrees C
What method of heat lost is most prevalent in the OR
Radiation
Convection
Heat loss due to air velocity (fan)
Conduction
Heat loss due to contact of two objects
Evaporation
Heat loss due to sweat evaporating off skin
Unintentional hypothermia
Phase 1 - steep drop in core temp during first hour
Phase 2 - slower decline during the next 3-4 hours
Phase 3 - steady state equilibrium
What part of brain normally maintains core body temp and what is that range called
Hypothalamus
“Interthreshold range”
Do anesthetics inhibit thermoregulation?
Yes they inhibit central thermal regulation by interfering wiht hypothalmic function
Dose-dependent
isoflurane produces a dose dependent decrease in vasoconstrictor threshold
At a rate of 3 degrees celcius for each percent of isoflurane
Spinal/regional epidural causes phase 1 hypothermia d/t
Vasodilation and internal redistribution of heat
Spinal regional anesthesia causes unintentional hypothermia in phase ii d/t
Regulatory impairment that allows continued loss d/t altered perception of temp d/t blocked dermatomes
How long should you prewarm patients and why
30 minutes
Because it decreases the central peripheral temperature gradient
Hypothermia ranges
<36
Mild = 33-36
Moderate = 32
At what temp do you start to see reduced enzyme function
36 degrees
At what temp do you start to see coagulopathy issues
36
At what temp is the fibrillatory threshold
32
why is surgery a problem that causes hypothermia
Environmental heat loss outpaces metabolic heat production
Anesthesia impairs normal response
What are anesthesia considerations of hypothermia
May delay awakening or cause shivering (this increases myocardial o2 consumption)
Which patients are at greatest risk for hypothermia
Elderly
Burn
Neonates
Patients with spinal cord injuries
Causes of intraop hyperthemia
Malignant hyperthermia Endogenous pyrogens Thyrotoxicosis or pheo d/t increased met rate Anticholinergic blockade of sweating Excessive environmental warming
Monitoring site for temps
Esophagus (lower 1/3) - best indicator of trend of heat gained/loss
Nasopharynx
Rectum
Bladder (pretty accurate)
Tympanic
Blood (PA catch) - great choice
Skin - not that accurate but good for monitoring trends
Bair hugger
Forced air warmer - most effective
Decreased radiant and convective losses
Decreased post op shivering and PACU stay
Concern for post op infection rates?
Warming blanket
Circulates water - minimally effective
Radiant heat unit
Not ok for OR, not impact on mean body temp
Heated liquids
Very dangerous because it can cause burns
IV fluid warmers
Core modality
Warmed liquid transfer of heat
Delivers fluids at the highest temp of any tech
Not as effective in shorter cases
Gastric lavage
Warms body core
Impractical intraop
Peritoneal irrigation
Encourage use of warm irrigation during intra-abdominal procedures
Ambient temp
Hugely important
Ambient temp >24C, most adults remain normothermic without needing other measures
Insulation
Passive warming where you cover extremities and head
Heat and moisture exchanger
Passive warming in circuit “artificial nose” - retains moisture and heat from patient
Coaxial breathing circuit
Warms and humidifies Inspiratory gases
“King circuit”
Why do we monitor neuromuscular blockade
Assess depth of blockade and degree of recovery
Peripheral nerve stimulator
Monitors effect of NM blocking agents on NM junction
- know and compare to baseline
- quantify by feel
Delivers electrical stimulation to a peripheral motor nerve which evokes a mechanical response
Titration of drug to optimal
Quantifies recovery from NMB
Monitoring sites for a peripheral nerve stimulator
Ulnar nerve - adductor pollicis stimulation
Facial - orbicularis occuli
Posterior tibial nerve
Peroneal nerve
Place electrodes over nerves to avoid direct muscle stimulation
Ulnar nerve
Innervates adductor pollicis muscle - abducts thumb
Black (neg) at crease of wrist and red lead 1-2 cm proximal to black electrode
Most common monitoring site
Is the ulnar nerve an accurate reflection of degree of block
The adductor pollicis muscle is more sensitive to ND block than diaphragm or airway muscles, so you may be paralyzed there but still have coughing/breathing/vocal cord movement
Which nerve has the least chance of muscle stimulation via electrode placement for TOF
Ulnar nerve
Facial nerve
Lies within the parotid gland
Place electrodes in front of Tragus of ear and below (negative over nerve)
Orbicularis oculi - closes eyelid
Corrugated supercili - furrows brow
Which nerve site for PNS is the better indicators of ND blockade of diaphragm and airway than peripheral muscles
Facial nerve
Posterior tibial nerve
Place electrode behind medial malleolus of tibia and results in plantar flexion
Black - 2 cm poster to MM of foot
Red - 2 cm above MM of foot
What does the flexor hallucinations brevis muscle do
This is the sole of the foot and it flexes the big toe
Peroneal nerve
Electrodes on lateral aspect of knee that elicits Dorsiflexion of foot
Single twitch
Single pulse delivered every 10 seconds
0.1Hz (stimulus every 10 seconds)
Increasing block results in diminished response
Twitch height will be depressed only when 75% of ach receptors are blocked and will disappear with 90% blocked
Train of four
4 repetitive stimuli - twitches progressively fade as relaxation increases
Ratio of 1st to 4th twitches are sensitive indicator of ND relaxation
TOF - lose 4th twitch =
75% receptors blocked
TOF - lose 3rd twitch =
80% receptors blocked
TOF - lose 2nd twitch =
90% receptors blocked
How many receptors are required to be blocked to be considered clinical relaxation
75-90% blocked
0 twitches on TOF =
90-98% receptors blocked
TOF ratio
Amplitude of 4th twitch divided by amplitude of 1st twitch
Partial ND block - ratio decreases (inversely proportional to degree of block)
Partial depolarizing blockade - amplitude of every twitch decreases, but ratio remains 1
Tetanic stimulation
Tetany at 50-100Hz
5 sec @50Hz evoked tension approximates tension developed during max voluntary effort
ND = fade occurs
How many receptors are blocked when you get a sustained response to tetanic stimulation
70%
disadvantage to tetanic stimulation
Painful - don’t use when awake
Post tetanic count
Useful when all twitches suppressed during TOF
Apply tetanus at 50Hz for 5 seconds
Wait 3 seconds
Apply single twitches every second up to 20
**number of twitches is inversely related to depth of block
If your goal is to keep them profoundly blocked, the goal is 0
Double burst stimulation
Less painful than tetany
3 short 50 Hz in pulses followed by 750ms followed by another 3 bursts
More sensitive than TOF for visual evaluation of fade
DBS3,3
What patterns of stimulation do you use during induction
Single twitch
TOF
Which stimulation pattern do you use during maintenance
TOF and post-tetanic count
What stimulation pattern do you use during emergence
TOF and double burst stimulation
When giving a NMB drug, which is most sensitive? Aka what is paralyzed first
Eyes (extraocular)
What muscle recovers quickest from blockade
Diaphragm and vocal cords
What site should you monitor for onset
Facial
What site should you monitor for recovery
Ulnar
TOF 1/4 twitches = how long to recovery?
30 minutes
TOF 2-3 twitches = how long until reversal
10-12 minutes following long acting relaxants and 4-5 minutes after immediate relaxants
4/4 twitches time to recovery?
5 minutes with neostigmine and 2-3 minutes with edrophonium
Why does hypothermia limit interpretation of evoked responses?
It increases skin impedance
Most reliable clinical signs of recovery
Sustained head lift x 5 sec
Sustained leg lift X 5 sec
Sustained hand grip x 5 sec
Max inspiratory pressure 40-50 cm H2O or >
Quantitative nerve monitoring
Device that quantifies degree of NM blockade
More reliable accurate and objective
Acceleromyography
Piezoelectric sensor measures muscle acceleration (voltage generated on contraction)
Change in muscle length without change in tension
It is not essential that sites that are being monitored remain mobile
Used primarily in research
Electromyography
Muscle action potential recorded, electrical activity proportional to force of contraction
Kinemyography
Quantifies muscle movement with motion sensor strip containing piezoelectric sensors
Mechanomyography
Detects contraction force, converts to electrical signal, signal amplitude reflects contraction strength
Phonomyography
Muscle contraction produces low-frequency sounds, calculates muscle response
bispectral index score
Used to assess the depth of anesthesia (optional)
This is good for
- reduced risk of awareness
- better management of responses to surgical stimulation
- faster wake up (controversial)
- more cost effective use of anesthetics
BIS scoring
100= awake >70 = greater recall risk 40-60 = general anesthesia 0 = isoelectric EEG
BIS readings are affected by
Electrocautery EMG Pacer Spikes EKG signal Patient movement
What indicates that BIS score is accurate
SQI high and EMG low
Cerebral oximetry
Assess cerebral O2 sat using near infrared spectrophotometry
Noninvasive
Detects decreases in CBF in relation to CMRO2
Difference in transmitted and received light determines regional oxygen saturation
Light source adheres to patient forehead, light transmits through tissue and cranium
Allow for transmission and absorption of light by hemoglobin to determine saturation
What would decrease cerebral oximetry reading?
Drop in BP
Partial pressure of CO2 in arterial blood
Regional blood volume
Hgb concentration
Goal of cerebral oximetry (number)
Keep within 75% of baseline reading
A greater than 20% reduction from baseline is correlated with regional and global ischemia
