Basic Intraop Monitoring Flashcards
What does early intervention lead to?
Improved outcomes
What does the data collected by the anesthetic provider reflect?
Physiologic homeostasis
Response to therapeutic interventions
Proper functioning of anesthetic equipment
What year did the AANA produce standards of care that CRNAs should adhere to?
1974 which it has evolved and revised over time
What year did Harvard produce guidelines for anesthesiologists?
1986, ASA closely mirrors those produced by the AANA
What year did the AANA revise the standards to include the scope of practice as well?
1983
What standard determines how a patient should be monitored by an anesthesia provider?
Standard V, monitor the patient’s physiologic condition as appropriate for the type of anesthesia and specific patient needs
What are the five monitors required by Standard V?
Monitor ventilation continuously
Monitor cardiovascular status continuously
Monitor body temperature continuously
Monitor neuromuscular function continuously
Monitor and assess patient positioning
What two factors are the basis of safe anesthetic care?
Continous clinical observation and vigilance
A state of clinical awareness whereby dangerous conditions are anticipated or recognized and promptly corrected
Vigilance in Anesthesia
What is the anesthetic provider continually monitoring?
Patient’s medical status
Effects of anesthesia
Effects of surgical intervention
What is the most important monitor?
The vigilant anesthetist
What are the AANA standard for monitoring?
Oxygenation/ventilation Circulation Body temperature Neuromuscular function Qualified Anesthetist Present
How should oxygenation be measured?
Clinical observation, pulse oximetry and if indicated arterial blood gas analysis
How should we verify intubation of the trachea?
Auscultation, chest excursion and confirmation of carbon dioxide in the expired gas
What should be used to measure ventilation?
Continuous monitoring of end tidal CO2 during controlled or assisted ventilation. Spirometry and ventilatory pressure monitors as indicated
What is the fundamental goal of the anesthetic provider?
Avoidance of hypoxia (airway, airway airway)
What should the anesthetic provider be assessing for adequate oxygenation?
Oxygen analyzer Pulse oximetry Skin color Color of blood ABG (when indicated)
What measures the pipeline gas to ensure O2 is truly being administered?
Oxygen analyzer
Where is the O2 analyzer located?
Inspiratory limb
When will the O2 analyzer notify the provider of low O2 concentrations?
less than 30% low concentration alarm
What two values should the O2 analyzer be calibrated to every day with the AGM check?
Room air and 100%
What is the Alveolar gas equations?
PAO2 = FiO2 x (Pb-47) - PaCO2
In the alveolar gas equation, if you do not have PaCO2 what value can be substituted?
End tidal CO2 can be substituted
What type of sensor is the O2 analyzer?
Electrochemical sensor
What is the structure of the electrochemical sensor of the O2 analyzer?
Cathode and anode embedded in electrolyte gel separated from gas by an oxygen permeable membrane
How does the electrochemical sensor in the O2 analyzer function?
O2 reacts with electrodes, generates electrical signal proportional to O2 pressure (mmHg) in sample gas
What is the standard of care for continuous non-invasive monitoring of oxygenation?
Pulse oximetry
What is a late sign of hypoxemia?
Cyanosis
When was the pulse oximeter introduced to anesthetic practice?
1987
What two principles are combined to explain the use of a pulse oximeter?
Oximetry & plethysmography
What is required in order to use a pulse oximeter?
Pulsatile arterial bed, a blood pressure must be present
What does plethysmography measure?
pulsatile measurement
What are some common sites to place a pulse oximeter?
Finger, toe, ear lobe, bridge of nose, palm and foot (especially in children)
What is the pulse oximeter continuously measuring?
Measurement of pulse rate and oxygen saturation of peripheral hemoglobin (SpO2)
What law dictate how a pulse oximeter works?
Lambert-Beer law of spectrophotometry
At what wavelength does HbO2 absorb light?
960nm (more infrared)
What does the Lambert-Beer Law of spectrophotometry measure?
Oxygenated and reduced Hgb differ in their absorption of red and infrared light
What is being compared in order to calculate an accurate SpO2 reading?
Comparison of absorbances of the wavelengths enables oximeter to calculate O2 saturation (ratio of infrared and red transmitted to a photodetector)
At what wavelength does reduced Hgb absorb more light?
660nm (more red)
What is the primary mechanism of action of the pulse oximeter?
Therefore, the basis of oximetry is change in light absorption during arterial pulsations
What does a patient’s Hgb have to be in order for a pulse oximeter to be functional?
> 5
What IV medication causes a large decrease in SpO2 while using a pulse oximeter?
Methylene blue
What are two other types of hemoglobins that could affect the pulse oximeter?
COHb (falsely increased)
MetHb (could be increased or decreased)
What is the correlation between SpO2 and PaO2?
40 50 60 PaO2
70 80 90 SpO2
Where should the precordial stethoscope be placed?
Suprasternal notch or apex left lung
What is the purpose of the precordial stethoscope?
Easily detects changes in breathe sounds or heart sounds
Circuit disconnect
Endobronchial intubation
What can be heard on the precordial stethoscope as anesthesia lightens?
Louder heart sounds from increased rate and contractility
What population can only use an esophageal stethoscope?
Limited to intubated patients
Where should the esophageal stethoscope be placed?
Distal 1/3 of esophagus
What are the advantage of an esophageal stethoscope compared to a precordial stethoscope?
Better quality heart and breath sounds and incorporates a temperature probe
How much CO2 does the average adult produce?
250mL CO2/min
What changes can affect a patient’s CO2 production?
Patient’s condition
Anesthetic depth (deeper decreases metabolism)
Temperature (colder decreases CO2 production)
What is the purpose of Capnography?
Confirms ETT placement Confirms adequate ventilation
What is the most common type of capnography and how does it work?
Sidestream sampling, airway gas aspirated and pumped to measuring device
What are the sampling flow rate?
50-250mL/min pulled from circuit (be aware in peds patients)
What are some limitations to sidestream capnography?
H2O condensation can contaminate the system and falsely elevate readings
Lag time between sample aspiration and reading
How might an attached capnography affects a machine check?
May fail a machine check if sidestream sampling line attached, specifically the pressure check
What could a problem be if CO2 is detected on inspiration?
Incompetent inspiratory valve
What is the normal PACO2-PaCO2 gradient?
2-10mmHg
What does phase I on a capnograph represent?
Corresponds to inspiration, anatomic/apparatus dead space devoid of CO2
What should the phase I level be at?
Should be zero unless rebreathing
What would cause baseline elevation on a capnograph?
CO2 absorbant exhaustedExpiratory valve missing/incompetentBain circuit
What does phase II of a capnograph represent?
Early exhalation/steep upstroke, mixing of dead space with alveolar gas
What would cause a prolonged upstroke of phase I on a capnograph?
Mechanical obstruction (kinked ETT) Slow emptying of lungs (COPD and bronchospasm)
What does phase III on the capnograph represent?
CO2 rich alveolar air, horizontal with mild upslope
Why would phase III on a capnograph be steep?
Steepness is a function of expiratory resistanceCOPDBronchospasm
What does phase IV on a capnograph represent?
Inspiration of fresh gas, return to baseline (near 0)
What might a low plateau on a capnogram represent?
Excessive ventilation
Low CO2 production
Diminished CO2
Significant dead space
What might a high plateau on a capnogram represent?
Hypoventilation
High CO2 production (MH)
What might a flat plateau with wide dips represent on a capnogram?
Less TV are superimposed on normal or mechanically timed exhalations, common when NMBA begin to wear off
What might small dips at the end of a flat plateau that is synchronous with the heart represent on a capnogram?
Cardiac oscillations from hypovolemia
What type of technology does an anesthetic gas analyzer utilize?
Mass spectrometry
How does mass spectrometry work?
Gas sample is ionized by electron beam and passed through a magnetic field, ions then identified by own unique trajectory across magnetic field
What airway pressures are measure by the ventilator?
In-circuit pressure gaugePeak inspiratory pressureSustained elevated pressure
What alarm on the ventilator would notify the provider that there has been a disconnect somewhere in the circuit?
Low airway pressure
What is the circulation guideline regarding standard V in the AANA monitoring guidelines?
Monitor cardiovascular status continuously via EKG and hear sounds. Record BP and heart rate at least every 5 minutes
What could continuous EKG monitoring detect during anesthesia?
Cardiac dysrhythmias Conduction abnormalities Myocardial ischemia/ ST depression Electrolyte changes Pacemaker function/malfunction
What lead is typically monitored in a three electrode approach?
Lead II
What leads are typically monitored in a five electrode approach?
Six standard limb leads (I,II, III, aVR, aVL and aVF) and one precordial lead (usually V5)
Why would we use five electrodes versus three electrodes?
Better at detecting myocardial ischemia
Allows better differential diagnosis of atrial and ventricular dysrhythmias
What are the two most commonly used leads monitored?
Lead II and V5
What does lead II specifically monitor?
Yields max P wave voltages
Superior detection of atrial dysrhythmias
Detects inferior wall ischemia/ST depression
What does V5 specifically monitor?
5th ICS/anterior axillary line
Detection of anterior and lateral wall ischemia
What is the appropriate size of a blood pressure cuff?
The width must be 20% greater than the mean diameter of extremity
How can blood pressure cuff size affect the reading?
Too narrow increases pressure
Too wide decreases pressure
What is the standard way to measure arterial blood pressure?
Korotkoff sounds
What is the most commonly used method to measure blood pressure during anesthesia?
Automated indirect NIBPM
What are the advantages to using a NIBPM?
Easy and accurate
Versatile in children and obese
May be used on thigh or calf oscillometry
How does a oscillometric device work?
Air pumping inflates cuff –> microprocessorOpens deflation valve –> oscillations sampled
At what measurement does oscillometric devices become less reliable?
When BP falls below 70
What is a major benefit to using oscillometric devices intraoperatively?
Their use has reduced the incidence of undetected HoTN intraoperatively
What type of errors can occur with the use of oscillometric BP devices?
Surgeon leaning on cuff
Inappropriate cuff size
Shivering/excessive movement
Atherosclerosis and HTN
What are some indications for invasive arterial BP monitoring?
Patient requiring BP more often than minute to minute
Critically ill
Anticipated rapid blood loss
Major procedures (cardiac, intracranial, carotid sinus)
Frequent ABGs
Where is the most common site for arterial line placement?
Radial artery
Why isn’t the ulnar artery typically used?
More difficult and more tortuous
Why isn’t the brachial artery a good choice for an arterial line?
Complications may risk limb and its predisposed to kinking
What arterial line location will more than likely cause a distorted wave form?
Dorsalis pedis
Why isn’t the axillary artery a desirable location for an arterial line?
Potential for plexus/nerve damage from hematoma or traumatic cannulation
What are some indication for central line placement?
Fluid management of hypovolemia and shock
Infusion of caustic drugs
Aspiration of air emboliInsertion of pacing leads
TPN
Venous access in patient with poor peripheral veins
What side is preferred for internal jugular line placement?
Right side
Why isn’t an external jugular line ideal?
More difficult to place leading to complications
What are some comorbidities that may require a pulmonary artery catheter?
Valvular heart disease Recent MI ARDS Massive trauma Major vascular surgery
Why has the pulmonary artery catheter lost favor?
TEE less invasive
What does standard V of AANA monitoring guidelines require of body temperature monitoring?
Monitor body temperature continuously on ALL pediatric patients receiving general anesthesia and when indicated on all other patients
What factors affect body temperature?
Ambient room temperature
Scope and length of surgery (abdominal surgeries)
Hypothalamic depression
Intraoperative fluid replacement
What are the four mechanisms of heat loss in the OR?
Evaporation
Convection
Conduction
Radiation
How much does body temperature decrease when one liter of crystalloid is given at room temperature?
70kg patient’s temp is decreased by 0.4C for every liter of fluid given at room temperature
What mechanism looses the most heat in the OR?
Radiation about 40%
What type of heat loss occurs because of air velocity, OR air exchanges?
Convection about 30% heat loss
What type of heat loss occurs because of contact with OR table and can be prevented with the use of blankets?
Conduction
What type of heat loss occurs because of dry inspired gases?
Evaporation
What structure maintains body temperature within a tight range?
Hypothalamus
How does phase I affect thermoregulation?
Convective loss
Vasodilation causes redistribution of blood and temperature
How does phase II affect thermoregulation?
Altered perception of dermatomes in areas anesthetized
What can be done to prevent the convective losses that occurs in stage I of anesthesia?
Pre warm the patient for 30 minutes with warming blanket
When does hypothermia occur?
When environmental heat loss outpaces metabolic heat production
How much can anesthesia decrease body temperature?
1-4°C
How does hypothermia affect wake up and oxygen demand?
May delay awakening Can cause shivering which can increase O2 needs by 400%
What patient population is at the greatest risk for hypothermia?
Elderly
Burn patients
Neonates
Patients with spinal cord injuries
What is considered hypothermia?
Temperature < 36°C
What is considered mild hypothermia and what type of effects does it have on the body?
Mild 33-36°C
Reduced enzyme function
Coagulopathy
What is considered moderate hypothermia and what type of effects does it have on the body?
Moderate
When does hyperthermia occur during anesthesia?
Rarely develops LATE sign of MH Endogenous pyrogens Thyrotoxicosis Anticholinergic blockade Excessive environmental warming
Where is the proper location for esophageal temperature monitoring?
Lower 1/3 of esophagus
What mode of temperature monitoring is rarely used due to effect of perforation?
Tympanic membrane
What are some superficial methods of warming patients?
Forced air warmer –> Most effectiveWarming blanketRadiant heat unit –> no role in OR doesn’t effect mean body temperatureHeated liquids –> burns
What methods of warming are used for warming the core of the patient?
IVF warmers (Hotline)
Gastric lavage
Peritoneal irrigation
What are some passive warming modalities?
Ambient temperatureInsulationHeat and moisture exchanger (artificial nose)Coaxial breathing circuit –> modified baine circuit
At what ambient temperature of the OR will most adults remain normothermic?
> 24°C
What does Standard V of the AANA monitoring guidelines state regarding neuromuscular function?
Monitor neuromuscular function and status when neuromuscular blocking agents are administered
What do we use to monitor neuromuscular function?
Peripheral nerve stimulator, monitors the status of neuromuscular junction when using NMBAs
How does a peripheral nerve stimulator work and what are its functions?
Delivers electrical stimulation to a peripheral motor nerve mechanically evoking a response
Permits titration of drug to optimal effectQuantifies recovery from NMBA
What occurs if a peripheral nerve stimulator is placed on a sensory nerve?
It will not evoke a response
In what order does the onset sequence of NMBA affect the body?
Eyes Extremities Chest Abdominal muscles Diaphragm
What is the first muscle to recover from NMBA and why?
The diaphragm is extremely rich with nicotinic receptors, it is the first muscle to recover function (will see a small cleft in the end tidal pleth)
What sites can be used to monitor neuromuscular blockade?
Ulnar nerve
Facial nerve
Posterior tibial nerve
Peroneal nerve
What does the ulnar nerve innervate and where should the electrodes be placed?
Adductor pollicis muscle, electrodes can be placed at the wrist or the elbow
How should the electrodes be placed on the nerve?
Negative (depolarizing) placed distally
Why isn’t the ulnar nerve an accurate reflection of degree of block of the diaphragm or airway muscles?
These muscles are less sensitive to ND block
Adductor policies still paralyzed but can have coughing, breathing and vocal cord movement
Where should the electrodes be placed when monitoring the facial nerve?
In front of the tragus of the ear and below while avoiding direct muscle stimulation
What muscle is contracting when we stimulate the facial nerve?
Orbicularis oculi, can feel twitches by placing hand over the eye brow
What gland does the facial nerve innervate?
Parotid gland
What nerve is the best indicator of ND blockade of the diaphragm and airway muscles?
Facial nerve
Where should you place the electrodes for posterior tibial nerve stimulation?
Place electrodes behind medial malleolus of tibia
What movements should result from posterior tibial nerve stimulation?
Plantar flexion
Where should yo place the electrodes for peroneal nerve stimulation?
Place electrodes on the lateral aspect of the knee
What movements should result from peroneal nerve stimulation?
Dorsiflexion of the foot
What are the five types of peripheral nerve stimulation?
Single twitch Train of four Tetanic stimulation Post-tetanic stimulation Double burst stimulation
Define what occurs during a single twitch stimulation.
Single pulse delivered every 10 seconds, increasing block results in diminished response
What is the most commonly used nerve stimulating setting in anesthesia?
Train of four
Define what occurs during train of four stimulation.
Four repetitive stimuli, ratio of responses to 1st and 4th twitches are sensitive indicator of ND relaxation
How many receptors are block with each loss of twitch?
Loss of 4th twitch = 75% receptors blockedLoss of 3rd twitch = 80% receptor blockedLoss of 2nd twitch = 90% receptors blocked
What is considered clinical relaxation?
75-95% block
What will you see on a TOF with a non-depolarizing NMBA?
Fade with each twitch
What other scenario might you see the same results in theTOF as non-depolarizing NMBA?
Phase II block from Succs
What will you see on a TOF with a depolarizing NMBA?
Same height just diminishes over time
Define what occurs during tetanic stimulation?
Tetany at 50-100Hz, five seconds at 50 Hz evoked tension approximates tension developed during maximal voluntary effort
What occurs with tetanic stimulation in the presence of ND relaxants?
Fade occurs
When will a sustained response occur in tetanic stimulation?
When TOF > 70%
What type of peripheral nerve stimulation is useful when all twitches are suppressed?
Post-tetanic count
Define what occurs in Post-tetanic count?
Apply tetanus at 50 Hz for 5 seconds, wait 3 seconds, apply single twitches every second up to 20
What does the number of twitches tell you when using post-tetanic count?
The number of twitches is inversely related to the depth of block
Define what occurs in double burst stimulation.
There are three short 50 Hz impulses followed by 750 sec by another 3 bursts
Why might you use double burst stimulation over train of four for monitoring twitches?
More sensitive that TOF for visual evaluation of fade
What two methods of peripheral nerve stimulation are appropriate to use during induction of anesthesia?
Single twitch
Train of four
What two methods of peripheral nerve stimulation are appropriate to use during maintenance of anesthesia?
Train of four
Post tetanic count
What two methods of peripheral nerve stimulation are appropriate to use during emergence of anesthesia?
Train of four
Double burst stimulation
What do the NM monitoring guidelines state for which nerve to monitor during induction and emergence?
Monitor facial nerve for onset and ulnar nerve for recovery
How long might recovery take if you only have 1/4 twitches?
As long as 30 minutes
How long might recovery take if you only have 2-3 twitches?
Reversal may take 10-12 minutes following long acting relaxants and 4-5 minutes after intermediate
How long might recovery take if you only have 4/4 twitches?
Adequate recovery within 5 minutes of neostigmine and 2-3 minutes with edrophonium
What is the Bispectral index score tool utilized for during anesthesia?
Used to assess depth of anesthesia, however, not currently standard of care
What are some reported advantage of BIS monitoring?
Reduced risk of awareness
Better management of responses to surgical stimulation
Faster wake up (controversial)
Most cost effective use of anesthetics
What does the BIS measure?
EEG signal with index ranging from 0-1000 = isoelectric
100 = awake CNS
What things in the OR can effect the reading of the BIS monitor?
Electro-cautery EMG Pacer spikes EKG signal Patient movement
What BIS number is associated with increased risk of recall?
> 70
What BIS number is the level suggested for anesthesia?
40-60
