Unit 6 - Equipment and Monitors Flashcards
What are the three pressure systems of the anesthesia machine?
High-pressure, intermediate-pressure, low-pressure.
What does the low-pressure leak test assess?
The integrity of the low-pressure circuit from the flowmeter valves to the common gas outlet.
How is the low-pressure leak test performed?
By attaching a bulb to the common gas outlet and creating negative pressure (-65 cm H2O).
What indicates a failure in the low-pressure system during the leak test?
If the bulb reinflates within 10 seconds.
What does the high-pressure leak test assess?
The integrity of the low-pressure system and the breathing circuit.
How is the high-pressure leak test conducted?
By closing the APL valve, pressurizing the circuit to 30 cm H2O, and observing the airway pressure gauge.
What happens if the pressure does not stay at ~30 cm H2O during the high-pressure test?
There is a leak in the system.
What is the SPDD model in anesthesia machines?
Supply, Processing, Delivery, Disposal.
What is the purpose of the pin index safety system (PISS)?
To prevent connecting the wrong gas cylinder to the anesthesia machine.
What are the PISS configurations for air, oxygen, and nitrous oxide?
- Air = 1,5
- Oxygen = 2,5
- Nitrous oxide = 3,5
What is the diameter index safety system (DISS)?
It prevents connecting the wrong gas hose to the anesthesia machine.
What is the function of the pressure regulator in gas cylinders?
Reduces the 2000 psi to ~45 psi before entering the intermediate pressure system.
How can you determine the content of a gas cylinder?
By its LABEL, not its color.
What is the critical temperature of nitrous oxide?
Approximately 36.5 C.
What is Boyle’s law used for in relation to oxygen E-cylinders?
To calculate how many minutes are left inside an oxygen E-cylinder.
What is the most delicate part of a gas cylinder?
The cylinder valve.
What should be done if you hear a ‘hissing’ sound upon opening a gas cylinder?
Tighten the connection.
What is the risk of placing more than one washer between the cylinder and hanger yoke assembly?
It can defeat the PISS.
What should never be done with a cylinder valve?
Do not oil the cylinder valve.
What does the O2 pressure failure device monitor?
Low oxygen pressure in the anesthesia machine.
What are the three situations that trigger the O2 failsafe device alarm?
- Depleted oxygen tank
- Drop in pipeline pressure
- Disconnected oxygen hose
What is the hypoxia prevention safety device (Proportioning Device) designed to do?
Prevent setting a hypoxic mixture with the flow control valves.
What is the maximum N2O flow allowed by the hypoxia prevention safety device?
3 times the O2 flow (N2O Max ~75%).
What is the function of the traditional flowmeter in an anesthesia machine?
Controls and measures the fresh gas flow towards the vaporizers and common gas outlet.
What does Reynolds’ number indicate about flow?
Flow is laminar (<2000), turbulent (>4000), or transitional (2000-4000).
What does compliance measure in the context of anesthesia circuits?
Change in volume for a given change in pressure.
What is a variable bypass vaporizer?
A vaporizer where fresh gas enters and some bypasses the liquid anesthetic.
What is the purpose of the ‘T’ setting on a vaporizer?
For transport mode to eliminate tipping concerns.
How does the Tec 6 desflurane vaporizer differ from variable bypass vaporizers?
It injects a precise amount of vaporized desflurane directly into the fresh gas flow.
What is the boiling point of desflurane?
22.8 C.
What happens if a vaporizer tips?
It can lead to volatile anesthetic overdose.
What temperature does the desflurane vaporizer heat the liquid anesthetic to?
39 C
What pressure does the desflurane vaporizer pressurize the liquid anesthetic to?
2 atmospheres
What is the vapor pressure of desflurane?
669 mmHg
What is the boiling point of desflurane?
22.8 C
True or False: The Tec 6 vaporizer compensates for changes in elevation.
False
What determines the depth of anesthesia?
Partial pressure of volatile anesthetic in the brain
What is required at higher altitudes regarding the vaporizer dial setting?
A higher setting on the dial
What is the typical location of the oxygen analyzer in the breathing circuit?
Inspiratory limb
What does the oxygen analyzer measure?
Oxygen concentration
What is the primary function of the oxygen analyzer?
Detect hypoxic mixtures
What is the average O2 consumption for an adult?
250 mL/min
What should be done first if the oxygen analyzer alarms?
Turn on the O2 cylinder
What is the second critical step to take when the oxygen analyzer alarms?
Disconnect the pipeline O2 supply
What is the risk of merely turning on the O2 tank without disconnecting the pipeline supply?
O2 tank will not release its contents
What should be done if O2 concentration in the circuit is not increasing after turning on the O2 tank?
Ventilate the patient with an Ambu bag
What does the oxygen flush valve provide?
Path for O2 to travel from intermediate-pressure system to breathing circuit
What O2 flow does the oxygen flush valve provide?
~ 35-75 L/min
What pressure does the oxygen flush valve expose the breathing circuit to?
~ 50 psi
What is the minimal expiratory pressure needed to open the ventilator spill valve?
3 cm H2O
What happens if the oxygen flush valve is excessively used?
Dilutes the partial pressure of the volatile agent
What type of ventilator does not add intrinsic PEEP?
Piston ventilator
What is the main benefit of a piston ventilator?
Does not consume tank oxygen during pipeline failure
What does the positive pressure valve in a piston ventilator guard against?
Excessive pressure in the breathing circuit
What is the function of the negative pressure valve in a piston ventilator?
Guards against negative end-expiratory pressure
What is the classification of a bellows ventilator based on its movement?
Ascending or descending
What is the primary risk associated with descending bellows?
Can fill with entrained room air if circuit disconnect occurs
What is the tidal volume in volume-controlled ventilation determined by?
Patient’s compliance
What does pressure-controlled ventilation deliver?
Preset inspiratory pressure
True or False: A negative deflection just before a breath indicates a patient triggered breath.
True
What is the main feature of Controlled Mandatory Ventilation (CMV)?
Delivers a preset tidal volume & RR on a fixed schedule
What does Assist Control (AC) ventilation provide for spontaneous breaths?
Full preset tidal volume
What mode allows the patient to breathe spontaneously between machine-initiated breaths?
Synchronized Intermittent Mandatory Ventilation (SIMV)
What does Pressure-Control Ventilation with Volume Guarantee (PCV-VG) ensure?
Guaranteed predetermined tidal volume
What is the purpose of the scavenger system?
Removes excess gas from the breathing circuit
How many components does the scavenger system have?
5 components
What happens during spontaneous ventilation regarding the APL valve?
Controls gas released to the scavenger
What are the two major problems that can occur with CO2 absorbents?
- Exhaustion
- Desiccation
What color does the indicator dye turn when soda lime is exhausted?
Purple
What should be done if soda lime is exhausted and cannot be replaced?
Increase the fresh gas flow
What is the main benefit of Calcium Hydroxide Lime (Amsorb Plus) compared to soda lime?
No CO production
What is a major drawback of Calcium Hydroxide Lime (Amsorb Plus)?
Absorbs less CO2
What does the scavenger interface communicate with in a closed system?
Atmosphere with pressure valves
What is the most common source of preventable equipment-related complications in anesthesia?
Circuit disconnection
What is the function of the scavenger in anesthesia?
To remove waste gas
The scavenger can be active or passive.
How does the APL valve function during spontaneous ventilation?
Controls the amount of gas that remains in the circuit and the amount that is released to the scavenger.
What determines the amount of gas released to the scavenger during mechanical ventilation?
The ventilator spill valve.
What is the most common source of preventable equipment-related complications in the breathing circuit?
Circuit disconnection.
Where does circuit disconnection most commonly occur?
At the y-piece between the ETT and the breathing circuit.
What is the second most common cause of a leak in the breathing circuit?
CO2 absorbent canister.
What can cause a poor seal (leak) in the CO2 absorbent canister?
Common after the granules have been changed or a defective CO2 absorber canister.
List other sources of low pressure in the breathing circuit.
- Malfunction of the bag/ventilator selector switch
- Incompetent ventilator spill valve
- Leaks in the breathing circuit
- Leaks in the anesthesia machine
- Moisture buildup in flow sensor.
What are the four ways to detect a circuit disconnect?
- Volume
- Pressure
- ETCO2
- Vigilance.
Which monitor is NOT a disconnect monitor?
The oxygen analyzer.
What should be done if unable to ventilate due to low pressure?
Ventilate the patient with an Ambu bag and oxygen tank while providing TIVA.
What complications can excessive pressure inside the breathing circuit lead to?
- Barotrauma
- Pneumothorax
- High PEEP
- Subcutaneous emphysema
- Decreased venous return
- Decreased cardiac output
- Hypotension
- Cardiovascular collapse
- Death.
What is a potential etiological factor for high pressure in the breathing circuit?
Ventilator spill valve malfunction.
What should be done if a ventilator spill valve malfunctions during a procedure?
Remove the patient from the ventilator and use a backup source of ventilation.
What should be removed to avoid high pressure from the CO2 absorbent?
Plastic wrap.
What does OSHA recommend for maximum exposure to halogenated agents?
Halogenated agents should be < 2 ppm.
What should the maximum exposure to nitrous oxide be according to OSHA?
Nitrous oxide should be < 25 ppm.
What are the determinants of exposure to waste gases?
- Amount of OR ventilation & turnover
- Functional status of anesthesia equipment
- Practice as a CRNA
- Ensuring a good mask fit
- Using cuffed ETT
- Turning off the FGF when not in use.
What are the four types of breathing circuits?
- Open breathing systems
- Semi-open systems
- Semi-closed systems
- Closed systems
Open systems do not allow controlled ventilation; semi-open systems prevent rebreating exhaled gases; semi-closed systems allow rebreating exhaled gases; closed systems have complete rebreathing.
What characterizes an open breathing system?
Does not allow for controlled ventilation or precise inspired gas concentrations.
What is a semi-open breathing system?
Contains a gas reservoir but does not allow the patient to rebreathe exhaled gases. FGF is greater than the patient’s minute ventilation.
What defines a semi-closed breathing system?
Contains a gas reservoir and a CO2 absorbent, allowing the patient to rebreathe exhaled gas. FGF is less than the patient’s minute ventilation.
What is the function of the unidirectional valve in breathing circuits?
Increases airway resistance in semi-closed systems.
What is a closed breathing system?
Contains a reservoir and a CO2 absorbent, where the gas added to the circuit matches the amount consumed by the patient.
What configurations can the circle system take based on FGF and APL settings?
- Semi-open
- Semi-closed
- Closed
What is the purpose of the adjusting pressure limiting valve (APL)?
Determines how much gas remains in the circuit and how much is directed to the scavenger.
What happens if either unidirectional valve malfunctions?
Converts the region between the Y-piece and the affected valve to apparatus dead space, risking hypercarbia.
What is the most common site for a disconnect in a breathing circuit?
The Y-piece.
What are the two types of pulmonary compliance?
- Static compliance
- Dynamic compliance
What does static compliance measure?
Lung compliance when there is no airflow.
What does dynamic compliance measure?
Compliance of the lung/chest wall during air movement.
What is peak inspiratory pressure (PIP)?
Maximum pressure in the patient’s airway during inspiration.
What is plateau pressure (PP)?
Pressure in the small airways and alveoli after the target tidal volume is achieved.
What does capnography measure?
ETCO2 concentration over time, assessing metabolism, circulation, and ventilation.
What are the four phases of the capnographic waveform?
- Phase I - Baseline
- Phase II - Expiratory upstroke
- Phase III - Expiratory plateau
- Phase IV - Inspiration
What does an increased α angle in capnography suggest?
Expiratory airway obstruction.
What does an increased β angle in capnography indicate?
Rebreathing due to a faulty inspiratory valve.
What is the relationship of SpO2 to the oxyhemoglobin dissociation curve?
SpO2 monitoring is most useful when the patient’s PaO2 aligns with the steep portion of the curve.
What is the pulse oximeter based on?
The Beer-Lambert law.
What wavelengths of light does a pulse oximeter use?
Red light (660 nm) and near-infrared light (940 nm).
What are the common factors that can affect the reliability of a pulse oximeter?
- Dysfunctional hemoglobin
- Decreased perfusion
- Altered optical characteristics
- Ambient light
- Non-pulsatile flow
- Motion artifact
What are the limitations of pulse oximetry?
Does not quantify hemoglobin amount or dissolved O2, not a good monitor of ventilation or bronchial intubation.
What method is most commonly used for measurement of exhaled gas?
Infrared absorption spectrophotometry.
What does the auscultation method for indirect BP measurement rely on?
Korotkoff sounds.
What are the ideal dimensions for a BP cuff bladder?
Length: 80% of extremity circumference; Width: 40% of extremity circumference.
What complications can arise from the oscillatory method of BP measurement?
Pain, neuropathy, bruising, limb ischemia, compartment syndrome, measurement errors.
What happens to BP readings if the cuff location is above the heart?
The BP reading will be falsely decreased due to less hydrostatic pressure.
What happens to BP readings if the cuff location is below the heart?
The BP reading will be falsely increased due to more hydrostatic pressure.
What are some complications of the oscillatory method?
- Pain
- Neuropathy (Radial, ulnar, or median)
- Bruising
- Limb ischemia
- Compartment syndrome
- Measurement errors
- Interference with IV medications if IV is distal to the cuff
What is the relationship between systolic BP and the arterial waveform?
Systolic BP = Peak of the waveform.
What is the relationship between diastolic BP and the arterial waveform?
Diastolic BP = Trough of the waveform.
How is pulse pressure calculated?
Pulse pressure = Peak value minus trough value.
What does the upstroke of the arterial waveform indicate?
Contractility.
What does the area under the curve of the arterial waveform represent?
Stroke volume.
What is indicated by the dicrotic notch in the arterial waveform?
Closure of the aortic valve.
Where should the transducer be positioned for accurate invasive blood pressure measurement?
At the level of the right atrium.
What is the consequence of damping on arterial BP measurement?
It can lead to under-damping or over-damping affecting the accuracy of SBP, DBP, and MAP.
What characterizes an under-damped system in BP measurement?
SBP is overestimated, DBP is underestimated, and MAP is accurate.
What causes an under-damped system?
- Stiff (Non-compliant) tubing
- Catheter whip (artifact)
What characterizes an over-damped system in BP measurement?
SBP is underestimated, DBP is overestimated, and MAP is accurate.
What causes an over-damped system?
- Air bubble in the pressure tubing
- A clot in the catheter
- Low flush bag pressure
- Kinks
- Loose connection
What is the optimal damping condition for arterial BP measurement?
The baseline is re-established after 1 oscillation from the square wave test.
Where should the tip of the CVP catheter be placed?
Just above the junction of the vena cava and the right atrium.
What are the risks associated with placing the tip of the CVP catheter inside the right atrium?
- Increased risk of dysrhythmias
- Thrombus formation
- Cardiac perforation
Where should the tip of the PA catheter reside?
In the pulmonary artery, distal to the pulmonic valve (25-35 cm from the VC junction).
What is the highest risk associated with accessing the left IJ for central line placement?
Injuring the thoracic duct (risk of chylothorax).
What is the most common complication while obtaining central line access?
Dysrhythmias.
What should be done if dysrhythmias occur during central line access?
Withdraw the catheter and start over.
What is a contraindication for floating a PAC in a patient?
Left bundle branch block.
What is the classic presentation of pulmonary artery rupture?
Hemoptysis.
When does the incidence of catheter-related infection increase?
After three days.
What does the CVP waveform reflect?
The pressure inside the right atrium
The CVP waveform includes three peaks (a, c, v) and two troughs (x, y).
At what anatomical location should the CVP be zeroed?
Fourth intercostal space at the mid anteroposterior level (Phlebostatic axis)
Measurement is best taken at end-expiration.
What is the normal range for CVP in adults?
1-10 mmHg
What are the components that affect CVP?
- Intravascular volume
- Venous tone
- Right ventricular compliance
What could cause a missing ‘a’ wave in a CVP waveform?
- Atrial fibrillation
- V-pacing if the underlying rhythm is asystole
What could cause a large ‘a’ wave in a CVP waveform?
- Tricuspid stenosis
- Diastolic dysfunction
- Myocardial infarction
- Chronic lung disease leading to RV hypertrophy
- AV dissociation
- Junctional rhythm
- V-pacing-asynchronous
- PVCs
What could cause a large ‘v’ wave in a CVP waveform?
- Tricuspid regurgitation
- RV papillary muscle ischemia
- Large increase in intraventricular volume
What is the relationship between RA pressure and CVP?
RA pressure is the same as CVP (0-10 mmHg)
What happens to PA pressure during diastole?
The diastolic pressure rises and a dicrotic notch is formed during pulmonic valve closure
What is the normal range for PAOP (Wedge pressure)?
5-15 mmHg
What suggests the PA catheter tip is NOT in West Zone 3?
- PAOP > pulmonary artery end-diastolic pressure
- Non-phasic PAOP tracing
- Inability to aspirate blood from the distal port when balloon is wedged
What conditions can cause PAOP to overestimate LVEDP?
- Mitral valve disease (stenosis or regurgitation)
- COPD
- Pulmonary hypertension
- PEEP
- Non-West Zone 3 placement PAC
- Impaired LV compliance (ischemia)
- Left to right cardiac shunt
- PPV
- Tachycardia
What is the most common method of measuring cardiac output?
Thermodilution method
What is the significance of averaging three separate injections in cardiac output measurement?
Improves accuracy of the final value
What is a key factor that influences mixed venous oxygen saturation (SvO2)?
- Cardiac output (L/min)
- Oxygen consumption (mL O2/min)
- Hemoglobin (g/dL)
- Hemoglobin saturation (%)
What is the normal range for mixed venous oxygen saturation (SvO2)?
65-75%
What factor can create a high CO state affecting SvO2?
Sepsis
What does pulse contour analysis measure?
Preload responsiveness as a function of how stroke volume changes during the respiratory cycle
What is required for accurate pulse contour analysis?
The patient must be receiving positive pressure ventilation
What is the threshold for assuming preload responsiveness in a hypovolemic patient?
A 200-250 mL fluid bolus improves SV more than 10%
What are factors that reduce the accuracy of pulse contour analysis?
- Spontaneous ventilation
- Open chest
- RV dysfunction
- Dysrhythmias
- Small tidal volume
- PEEP
What is the positioning of the esophageal Doppler probe?
Approximately 35 cm from the incisors (T5-6 or at the third sternocostal junction)
What are conditions that reduce the reliability of esophageal Doppler data?
- Aortic valve disease (stenosis or regurgitation)
- Aortic cross-clamping
- Disease of the thoracic aorta
- After cardiopulmonary bypass
- Pregnancy
What is the sequence of the cardiac conduction system?
- SA node
- Internodal tracts
- AV node
- Bundle of His
- Bundle branches
- Purkinje fibers
Which internodal tract gives rise to the Bachmann bundle?
Anterior internodal tract
What is the conduction velocity of the SA and AV nodes?
0.02-0.10 m/sec (Slow)
What is the function of the AV node in the cardiac conduction system?
Acts as the gatekeeper of electrical impulses into the ventricle
What does the P wave represent in an EKG?
Atrial depolarization begins
What does the PR-interval indicate in an EKG?
Atrial depolarization complete
What does the QRS complex represent in an EKG?
Atrial repolarization + ventricular depolarization
What does the ST-segment indicate in an EKG?
Ventricular depolarization complete
What does the T wave represent in an EKG?
Ventricular repolarization begins
What can cause PR-interval depression?
Pericarditis
What do Q waves suggest if the amplitude is greater than 1/3 of the R wave?
Myocardial Infarction (MI)
What are the normal values for a P wave duration?
0.08-0.12 sec
What are the normal values for a PR interval?
0.12-0.20 sec
What is the normal duration for a Q wave?
<0.04 sec
What is the normal duration for a QRS complex?
<0.10 sec
What is the normal QTc duration for men?
Men < 0.45
What is the normal QTc duration for women?
Women < 0.47
What is the mean electrical vector?
The average current flow of all action potentials at a given point in time
What indicates a positive deflection in the EKG?
The vector of depolarization travels towards a positive electrode
What indicates a negative deflection in the EKG?
The vector of depolarization travels away from a positive electrode
What is a biphasic deflection in the EKG?
The vector of depolarization travels perpendicular to a positive electrode
How does the heart depolarize?
From the Base to the apex & from the endocardium to the epicardium
In what direction does the heart repolarize?
Apex to base & from the epicardium to the endocardium
What does the T wave indicate about repolarization?
The vector of repolarization travels in the opposite direction as the vector of depolarization
What are the three groups of EKG leads?
- Bipolar leads (I, II, III) * Limb leads (aVR, aVL, aVF) * Precordial leads (V1 - V6)
What does the axis represent in an EKG?
The direction of the mean electrical vector in the frontal plane
What is the normal range for the electrical axis?
Between -30 & +90 degrees
What indicates left axis deviation?
More negative than -30 degrees
What indicates right axis deviation?
More positive than 90 degrees
What can cause axis deviation?
- Areas of hypertrophy * Areas of myocardial infarction (MI)
What is sinus arrhythmia?
The SA node’s pacing rate varies with respiration
What is sinus bradycardia?
HR < 60 BPM, usually due to increased vagal tone
What is the first-line treatment for sinus bradycardia?
Atropine
What is sinus tachycardia?
HR > 100 BPM
What can precipitate myocardial infarction (MI) in patients with CAD?
Sinus tachycardia
What characterizes atrial fibrillation?
Chaotic electrical activity in the atrium with an irregular rhythm and absence of a P wave
What is the treatment for acute onset atrial fibrillation?
Cardioversion starting at 100 joules
What is atrial flutter?
An organized supraventricular rhythm with a characteristic ‘saw tooth’ pattern
What is a characteristic feature of junctional rhythm?
HR 40-60 bpm
What are premature ventricular contractions (PVC)?
PVCs originate from foci below the AV node, resulting in a wide QRS complex
What is the most common cause of sudden cardiac death?
Ventricular fibrillation (V-fib)
What is the treatment for asystole?
CPR; it is not a shockable rhythm
What is Brugada syndrome characterized by?
Pseudo-RBBB & persistent ST elevation in V1-V2
What is the defining feature of 1st-degree heart block?
PR interval > 0.20 sec
What is the mnemonic for Mobitz type 1 heart block?
‘Longer, longer, longer, drop then you have a Wenckebach’
What is Mobitz type 2 heart block characterized by?
Some P’s conduct to the ventricles, while others don’t
What is the treatment for 3rd-degree heart block?
A pacemaker or isoproterenol
What is adenosine used for in antiarrhythmic treatment?
Slows conduction through the AV node
What are reentry pathways?
The most common cause of tachyarrhythmias
What is Wolff-Parkinson White syndrome?
A pre-excitation syndrome with an accessory conduction pathway
What does Torsades de Pointes literally translate to?
Twisting of the spikes
What is the acute treatment for Torsades de Pointes?
Magnesium sulfate and cardiac pacing
What does failure to capture in a pacemaker mean?
The pacemaker delivers an electrical stimulus but fails to trigger myocardial depolarization
How does a magnet affect a pacemaker?
Usually converts to asynchronous mode
What is the common pacing mode for pacemakers?
- VVI * AAI * DDD
What is the effect of a magnet on a pacemaker?
Consult with the manufacturer to determine how a magnet affects the pacemaker
This is crucial for understanding the implications of using a magnet with a pacemaker.
What happens to an ICD when a magnet is applied?
Suspends the ICD & prevents shock delivery
This is important for ensuring patient safety during procedures.
What is the effect of a magnet on a pacemaker when used with an ICD?
Suspend the ICD & prevents shock delivery with NO effect on the pacemaker function
Understanding this interaction is key for managing patients with both devices.
What can cause asynchronous pacing in a pacemaker?
Failure to sense (Under sensing)
This can lead to serious complications if not addressed.
What is the ‘R on T’ phenomenon?
Occurs if the pacemaker fires during ventricular repolarization
This is a critical point to monitor in pacemaker patients.
What is meant by ‘failure to output’ in a pacemaker?
A pacing stimulus is not produced when it should be produced
Recognizing this failure is essential for effective management.
What does ‘failure to capture’ refer to?
When the pacemaker delivers an electrical stimulus but fails to trigger myocardial depolarization
This is a key concept in understanding pacemaker functionality.
What factors can impair pacemaker performance?
Electromagnetic interference, electrode displacement, wire fracture, conditions like:
* Hyperkalemia
* Hypokalemia
* Hypocapnia
* Hypothermia
* Myocardial infarction
* Fibrotic tissue buildup around pacing leads
* Antiarrhythmic medications
Awareness of these factors is crucial for patient management.
What is the best option for surgical electrocautery in patients with pacemakers?
Use a bipolar device
This minimizes the risk of interference with the pacemaker.
Is MRI typically contraindicated for patients with pacemakers or ICDs?
Yes, although some newer devices may be compatible with MRI
This is an important consideration for imaging in patients with these devices.
What procedure is NOT contraindicated for patients with pacemakers?
Lithotripsy (beam directed away from pulse generator) & electroconvulsive therapy
Understanding these exceptions is vital for patient care.
What is the most critical preoperative information to have for patients with pacemakers?
The patient’s underlying rhythm
This knowledge is essential for preparing for potential device failure.
How can pacemaker failure be treated?
With isoproterenol, epinephrine, or atropine depending on the underlying rhythm
Treatment should be tailored to the individual patient’s needs.
Should succinylcholine be avoided in patients with a pacemaker?
No, it should not be avoided
While theoretically it could affect depolarization, it is not typically an issue in practice.
What is the purpose of using a peripheral nerve stimulator?
To evaluate onset, depth, and recovery of neuromuscular blockade
Clinical evaluation alone is not enough to guarantee adequate recovery.
What does TOF stand for in the context of peripheral nerve stimulation?
Train of Four
TOF delivers a series of 4 twitches at 2 Hz.
What TOF ratio indicates clinical recovery from neuromuscular blockade?
> 0.9
A reversal agent is indicated when the TOF ratio is < 0.9.
What is the common frequency and duration of a tetanus stimulus?
50 Hz for 5 seconds
Tetanus is a more sensitive method of assessing recovery from neuromuscular blockade.
What is double burst stimulation (DBS)?
Delivers 2 short bursts of 50 Hz tetanus 0.75 seconds apart
Easier to detect fade with DBS than it is with TOF.
What occurs during post-tetanic potentiation?
The twitch response is stronger after a tetanic stimulus than at baseline
This is assessed using a post-tetanic count (PTC).
How is cerebral oximetry used?
Utilizes near-infrared spectroscopy (NIRS) to measure cerebral oxygenation
Measures venous oxygen saturation & oxygen extraction in the brain.
What can contaminate the signal in cerebral oximetry?
Scalp hypoxia
NIRS may falsely interpret scalp hypoxia as brain ischemia.
What does an EEG measure?
Electrical activity in the cerebral cortex
Offers little information about subcortical structures, spinal cord, or peripheral nerves.
What EEG waveforms are associated with general anesthesia?
Slower frequency and taller amplitude
Waveforms change during anesthesia.
What is the target BIS value for general anesthesia?
40-60
The bispectral index monitor (BIS) translates raw EEG data into this number.
What is the difference between macroshock and microshock?
Macroshock is a larger amount of current applied externally, while microshock is a smaller amount applied directly to the myocardium
100 milliamperes can cause ventricular fibrillation for macroshock, and as little as 100 microamperes can cause it for microshock.
What is the role of the line isolation monitor (LIM) in the OR?
Assesses the integrity of the ungrounded power system
It informs staff when the OR becomes grounded.
What type of current does a surgical electrocautery device deliver?
High-frequency current (500,000-1 million Hz)
Used to cut, coagulate, dissect, or destroy tissue.
What is the maximum yearly radiation exposure for adults?
5 rem
For pregnant workers, the maximum exposure is 0.5 rem/year.
What does the mnemonic ABCDEFGHI help evaluate in chest X-rays?
Assess film quality, bones, cardiac, diaphragm, effusion, fields, great vessels, hila, and impression
It provides a systematic approach to reviewing CXR.
What is the normal position for an endotracheal tube (ETT)?
Mid-trachea, 4-5 cm above the carina
The carina is typically at the T4-T5 interspace.
What is the deep sulcus sign indicative of?
Air accumulation in the anterior inferior thorax adjacent to the diaphragm
Appears as an abnormal lucency over the costophrenic angle.
What characterizes tension pneumothorax on a chest X-ray?
Depressed diaphragm, flattened right cardiac border, contralateral mediastinal shift
Also includes tracheal deviation.
What is echolocation?
A process where bats emit ultrasonic sound waves and listen for echoes
It helps them map their environment.
What is the frequency range of clinical ultrasound?
1,000,000-20,000,000 Hz
This range is much higher than human hearing.
At what speed does sound propagate through air?
343 m/sec
What is the speed range of sound propagation through bone?
3,000 - 5,000 m/sec
In what situation can there be no sound propagation?
In a vacuum
What process do bats use to map their environment?
Echolocation
How do bats produce ultrasonic sound waves?
By chirping
What does a piezoelectric material do?
Transduces electric energy to mechanical energy & vice versa
What happens when electrical current is applied to a piezoelectric material?
It vibrates & emits sound waves
What piezoelectric material is commonly used in modern ultrasound transducers?
Lead zirconate titanate
What does the ultrasound transducer do?
Emits ultrasound waves into the body and listens for echoes
What determines the vertical placement of each dot on the ultrasound screen?
Time delay for the echo to return
What determines the horizontal placement of each dot on the ultrasound screen?
The particular crystal that receives the returning echo
What does the brightness of each dot on the ultrasound screen indicate?
The amplitude of the returning signal
What does echogenicity describe?
A tissue’s ability to transmit or reflect sound waves
What are hyperechoic structures and give an example?
Appear bright and produce strong echoes; e.g., Bone
What are hypoechoic structures and give an example?
Appear darker and produce weak echoes; e.g., Solid organs (Liver)
How do muscles typically appear on an ultrasound?
Hypoechoic
What appearance do muscle surfaces often produce?
Hyperechoic fascial lines
What do anechoic structures appear as and provide examples?
Appear black; e.g., Vascular structures, cysts, ascites
How do vascular structures appear in ultrasound imaging?
As black circles in short-axis and black tubes in long-axis
What is a characteristic of arteries in ultrasound imaging?
Pulsatile & relatively non-compressible
What is a notable feature of veins in ultrasound imaging?
They don’t pulsate & are easy to compress
What should raise suspicion for deep vein thrombosis in ultrasound imaging?
A distended & non-compressible vein
How do peripheral nerves near the neuraxis typically appear?
Anechoic (Black)
What is the appearance of distal peripheral nerves?
Hyperechoic (White) with a honeycomb appearance
What accounts for the greater degree of echogenicity in distal peripheral nerves?
Fascia & connective tissue
What is resolution in ultrasound imaging?
The ability to see two separate things as two separate things.
What are the three types of resolution in ultrasound?
- Axial (Beam depth)
- Lateral (Beam width)
- Elevational (Beam thickness)
What is the near zone in ultrasound?
The region between the transducer and the focal zone.
What is the focal zone in ultrasound?
The region where the beam is the narrowest (x- & y-axis) & thinnest (z-axis).
What is the far zone in ultrasound?
The region beyond the focal zone.
Where is image resolution best in ultrasound?
In the focal zone.
What is attenuation in ultrasound?
The process that reduces image quality as sound waves propagate through the body.
What are the factors that contribute to attenuation?
- Absorption
- Reflection
- Scatter
- Refraction
What is absorption in ultrasound?
US waves are lost to the body as heat.
What is reflection in ultrasound?
The process where a sound bounces off a tissue boundary of differing acoustic impedance.
What is scatter in ultrasound?
Occurs when the US wave encounters an object smaller than the wave, causing echoes to scatter.
What is refraction in ultrasound?
The bending of the US wave that encounters a tissue boundary at an oblique angle.
What is a short-axis view in ultrasound?
Looks at a structure in cross-section.
What is a long-axis view in ultrasound?
Looks at a structure along its length.
What is the tradeoff in transducer selection?
Between image resolution and depth of tissue penetration.
What is the effect of lower frequencies in ultrasound?
Allows seeing deeper inside the body but sacrifices image resolution.
What is the effect of higher frequencies in ultrasound?
Produces the best resolution at the expense of not visualizing deep structures.
Describe a linear array transducer.
Has a flat footprint with piezoelectric crystals arranged in parallel, producing a geometrically accurate image.
Describe a curvilinear array transducer.
Has a convex footprint and produces a fan-like image, typically operates in the lower frequency range.
Describe a phased array transducer.
Very narrow in the nearfield, fans out with increasing depth, best for accessing small acoustic windows.
What does gain adjust in ultrasound imaging?
The strength of the returning echoes displayed on the screen.
What does the depth control do in ultrasound?
Determines how deep you can see into the body.
What does focus adjust in ultrasound imaging?
Ensures the target sonoanatomy resides in the focal zone.
What does the ‘B’ in B-mode stand for?
Brightness of the pixels on the screen.
What is M-Mode in ultrasound?
Illustrates the relative movement of structures over time.
What does the Doppler effect describe?
The change in the perceived frequency of a sound wave due to relative motion.
What happens to frequency when the source moves towards an observer?
The frequency appears to increase (positive Doppler shift).
What happens to frequency when the source moves away from an observer?
The frequency appears to decrease (negative Doppler shift).
What factors affect the degree of Doppler shift?
- Frequency of the US beam
- Blood flow velocity
- Angle of insonation
What color represents a positive Doppler shift?
Red.
What color represents a negative Doppler shift?
Blue.
What does the angle of insonation affect in Doppler imaging?
The evaluation of the Doppler shift.
What is the convention for viewing short-axis in ultrasound?
The orientation marker points towards the patient’s anatomic right.
What is the convention for viewing long-axis in ultrasound?
The orientation marker points towards the patient’s head.
How should the transducer be held for optimal imaging?
Near the base, like a pencil, with wrist and forearm anchored.
What is the angle of incidence in ultrasound?
The angle at which ultrasound waves encounter a structure.
What is in-plane needling?
When the needle runs parallel to the transducer.
What is out-of-plane needling?
When the needle is introduced perpendicular to the transducer.
What is the initial orientation of the transducer when placed on the patient?
Perpendicular to the skin
What must be manipulated to obtain high-quality images during ultrasound?
The transducer along its three axes
What is the purpose of tilting the transducer?
Helps orient the US beam perpendicular to an underlying structure
What does rocking the transducer promote?
Better contact between the patient and the transducer
What is the effect of sliding the transducer?
Maintains the same angle of incidence while moving up and down
What does compression of the transducer improve?
Image resolution
What is rotation of the transducer used for?
Transitioning from short- to long-axis imaging or vice versa
What can artifacts in ultrasound imaging cause?
Can make you see structures that don’t exist or prevent you from seeing existing structures
What is the common artifact caused by high acoustic impedance of the skin compared to air?
Air artifact
What is produced by a hyperechoic structure like bone?
Acoustic shadow
What is acoustic enhancement?
Increased brightness when an US wave reaches a fluid-filled structure
What occurs during a mirror image artifact?
US beam gets trapped between two highly reflective tissues
What is reverberation similar to?
Mirror image artifact
What does bayoneting produce the appearance of?
The needle bending
Does ultrasound always propagate through soft tissue at 1,540 m/sec?
No
What affects the propagation velocity of sound waves?
The medium through which sound travels
Do sound waves always propagate in a straight line?
No
Does brightness always directly parallel the degree of reflection?
No
Do all echoes that return to the transducer originate only from structures in the beam’s axis?
No
What is the purpose of point-of-care ultrasound (POCUS) in cardiac assessment?
To help answer binary (Yes/No) questions about the patient’s clinical status
POCUS is not intended to replace comprehensive echocardiographic examinations.
What are the three standard imaging windows for the basic cardiac exam?
- Parasternal long-axis (PLAX)
- Parasternal short-axis (PSAX)
- Apical 4-chamber
- Subcostal 4-chamber
- Subcostal IVC
How should the patient be positioned for the Parasternal long-axis (PLAX) view?
In the left lateral decubitus position
This position brings the heart closer to the anterior chest and reduces lung artifact.
What is the correct orientation for the transducer in the Parasternal short-axis (PSAX) view?
Rotate 90 degrees clockwise with the orientation marker pointing to the patient’s left shoulder.
Where should the transducer be placed for the Apical 4-chamber view?
At the point of maximum impulse with the orientation marker pointing to the patient’s left side and the US beam towards the patient’s right shoulder.
In the Subcostal 4-chamber view, where should the transducer be positioned?
In the middle just inferior to the xiphoid process, with the orientation pointing to the patient’s left side.
How is the Subcostal IVC view obtained?
Rotate the transducer 90 degrees from the Subcostal 4-chamber position and tilt the beam in the posterior direction.
What is the utility of lung ultrasound?
Useful for diagnosing pneumothorax or endobronchial intubation (absence of lung sliding).
What do A lines in lung ultrasound indicate?
Horizontal lines resulting from reverberation artifact due to the pleura acting as a strong reflector.
What do B lines in lung ultrasound suggest?
Vertical lines that can indicate normal findings or suggest pathology such as pulmonary edema.
What is the target area in gastric ultrasound?
Gastric antrum, which can appear flat or like a small oval (often called the ‘Bull’s eye’).
How should the patient be positioned for gastric ultrasound?
In the right lateral decubitus position.
What can be estimated by measuring the cross-sectional area (CSA) of the gastric antrum?
Gastric volume.
Fill in the blank: A lines are __________ that result from reverberation artifact.
Horizontal lines
True or False: B lines are always pathological.
False
What view is obtained by placing the transducer just inferior to the xiphoid process?
Subcostal 4-chamber
