UNIT 6 Monitors & Equipment Flashcards
What components are present in the high pressure system of the anesthesia machine? What is the gas pressure in this region? How do you do a high pressure leak test?
begins at the cylinder & ends at the cylinder regulators.
components include:
- hanger yoke
- yoke block w/ check valves
- cylinder pressure gauge
- cylinder pressure regulators
The gas pressure is from the cylinder pressure
To do a high pressure leak test: close APL valve and pressurize the circuit to 30 cm H2O and observe the airway pressure gauge. The pressure should remain constant
What components are present in the intermediate pressure system of the anesthesia machine? What is the gas pressure in this region?
begins at the pipeline & ends at the flowmeter valve.
components include:
- pipeline inlets
- pressure gauges
- ventilator power inlet
- oxygen pressure failure system
- oxygen second stage regulator
- oxygen flush valve
- flowmeter valve
gas pressure = 50psi (if pipeline) or 45psi (if tank)
What components are present in the low pressure system of the anesthesia machine? What is the gas pressure in this region?
How do you do a low pressure leak test?
begins at the flowmeter tubes & ends at the common gas inlet.
components:
- flowmeter tubes (Thorpe tubes)
- vaporizers
- check valves
- common gas outlet
gas pressure = slightly above atmospheric pressure
Low pressure leak test is also called the negative pressure leak test. It assesses integrity of low pressure circuit from the flow meter valves to the common gas outlet. The test is done by attaching bulb to common gas outlet and creating -65 cm H2O pressure
What are the 5 tasks of oxygen in the anesthesia machine?
- O2 pressure failure alarm
- O2 pressure failure device (failsafe)
- O2 flowmeter
- O2 flush valve
- ventilator drive gas (if pneumatic bellows)
Describe the pin index safety system.
PISS prevents inadvertent misconnections of gas cylinders
pin configuration on each hanger yoke assembly is different for each gas, making unintended connections of the wrong gas unlikely, but not impossible (>1 washer b/n the hanger yoke & stem of the tank may allow PISS to be bypassed)
air = 1,5 oxygen = 2,5 N2O = 3,5
Describe the diameter index safety system
DISS prevents inadvertant misconnections of gas hoses
What are the maximum pressures and volumes for the cylinders that contain air, oxygen, and N2O?
air (yellow): 1900psi, 625L
oxygen (green): 1900psi, 660L
N2O (blue): 745psi, 1590L
weight full = 20.7lb
weight empty = 14.1lb
The bourdon pressure gauge on an O2 cylinder reads 500psi. If the flow rate is 4L/min, how long will this cylinder provide oxygen?
full = 660L/1900psi
660L/1900psi = X/500psi = 174L 174L/4lpm = 43.5mins
some books use 2000psi
Is it ever safe to use an oxygen cylinder in the MRI suite?
not unless it’s made of nonmagnetic material such as aluminum, copper, titanium, steel
An MRI safe cylinder will have two colors: most of the tank is silver and only the top is the color that signifies the gas it contains
List 3 safety relief devices that prevent a cylinder from exploding when the ambient temperature increases.
gas cylinders should never be exposed to temp >130F or 57 C = fire/explosion
1) fusible plug made of Woods metal (melts at elevated temperature)
2) frangible disk that ruptures under pressure
3) valve that opens at elevated pressures
Give 1 example of how the oxygen pressure failure device (failsafe) might permit the delivery of a hypoxic mixture.
the failsafe device checks pressure (not flow)
if there is a pipeline crossover, then the pressure of the new gas will provide the pressure to defeat the failsafe device & the patient will be exposed to a hypoxic mixture
Give 4 examples of how the hypoxia prevention safety device (proportioning system) might permit the delivery of a hypoxic mixture.
- oxygen pipeline crossover
- leaks distal to the flowmeter valves
- administration of a 3rd gas (helium)
- defective mechanic or pneumatic components
What is the difference b/n the oxygen pressure failure device and the hypoxic prevention safety device?
1) Oxygen pressure failure device (fail safe device)
- shuts off an/or proportionately reduces N2O flow if O2 pressure drops below 20psi
2) Hypoxia prevention safety device (proportioning device)
- prevents you from setting a hypoxic mixture with the flow control valves
- limits N2O flow to 3x the O2 flow (i.e. N2O max = 75%)
- never allows Fio2 to be below 25%!
Describe the structure and function of the flow tube.
internal diameter of flow tube is narrowest at the base & progressively widens along it’s ascent
annular space = area b/n the indicator float & the side wall of the flow tube, also narrowest at the base & widest at the top.
laminar flow is dependent on gas viscosity (Poiseuille)
turbulent flow is dependent on gas density (Graham)
What is the safest flowmeter configuration on the anesthesia machine?
O2 flowmeter should always be furthest to the right
flowmeters are made of glass = the most delicate part of the anesthesia machine. A leak will allow O2 to escape the low pressure system –> delivery of hypoxic mixture
if a leak develops in any of the other flowmeters, it won’t reduce the FiO2 delivered to the patient
How do you calculate the FiO2 set at the flowmeter?
FiO2 = [ (21air flow rate) + (100oxygen flow rate) ] / total flow rate
An anesthesia machine uses fresh gas coupling. How do you determine the total Tv that will be delivered to the patient?
Vt on vent + FGF - volume lost to compliance
When using a ventilator that couples FGF to Tv, what types of ventilator changes will impact Tv delivered to the patient?
making nearly any change will ultimately impact the Vt delivered to the patient:
Vt increases with:
- decreased rr
- increased I:E ratio (1:2–> 1:1)
- increased FGF
- increased bellows height
Vt decreases with:
- increased rr
- decreased I:E ratio
- decreased FGF
- decreased bellows height
What is the vaporizer splitting ratio?
modern variable bypass vaporizers split fresh gas into two parts:
- gas that enters the vaporzing chamber & becomes 100% saturated w/ IA
- gas the bypasses the vaporizing chamber & doesn’t pick up any IA
before leaving the vaporizer, these two fractions mix & this determines the final anesthetic concentration exiting the vaporizer
by setting the concentration on the dial, you determine the splitting ratio
What is the pumping effect?
can increase vaporizer output
anything that causes gas that has already left the vaporizer to re-enter the vaporizing chamber can cause the pumping effect.
This is generally d/t PPV or use of the O2 flush valve
compare and contrast the variable bypass vaporizer w/ the injector type vaporizer.
variable bypass
- flow over vaporization
- automatic temp compensation
- elevation compensation
injector (des)
- tec6, drager D
- dual circuit (fresh gas isn’t split)
- vaporized by heat, then injected into the fresh gas
- electronically heated to 39C
- no compensation for elevation
What does the O2 analyzer measure?
monitors O2 concentration (not pressure) and is the only device downstream of the flowmeters that can detect a hypoxic mixture.
What are 2 things you must do in the event of an oxygen supply line crossover?
- turn on the O2 cylinder
- disconnect the pipeline
Pressing the O2 flush valve exposes the breathing circuit to ___ O2 flow & ___ O2 pressure.
flow 35-75L/min
pressure 50psi (pipeline pressure
What are 2 risks of pressing the O2 flush valve?
1) barotrauma (if pressed during inspiration) this is why you only want to pressure it during EXHALATION
2) awareness
Describe the function of the ventilator spill valve in relation to using the O2 flush valve
if O2 flush valve is pressed during inspiration, the patient will be exposed to flows of 35-75L/min and a pressure of 50psi.
If it is pressed during expiration, the excess flow will first fill the bellows then the rest is vented out the scavenger
compare and contrast VC & PC ventilation
VCV: delivers a preset Tv over a predetermined time. Since Tv is fixed, the inspiratory pressure will vary as the pt’s compliance changes. Inspiratory flow is constant during inspiration
PCV: present inspiratory pressure over a predetermined time. Since pressure & time are fixed, Tv & inspiratory flow will vary depending on pt’s lung mechanics. Tv goal may not be achieved.
A patient is receiving pressure controlled ventilation. What conditions can alter the Tv delivered to the patient?
decreased w/:
- decreased compliance (pneumoperitoneum, trendelenburg)
- increased resistance (bronchospasm, kinked ETT)
increased w/
- increased compliance (release of pneumoperitoneum, T-burg to supine)
- decreased resistance (bronchodilators, removing a/w secretions)
You notice that soda lime has become exhausted in the middle of a surgical procedure. What is the best action to take at this time?
You may be tempted to increased the MV. Although this removes a greater amount of CO2 from the body, it doesn’t prevent the pt from rebreathing CO2 & may lead to hypercarbia
Instead, if you can’t replace the CO2 absorbent, then you should increase FGF (convert circle system to semi-open system)
What is desiccation & how does it apply to soda lime?
- The granules are hydrated with water by 20%. If it’s dry = desiccated
- ethyl violet informs you about exhaustion but doesn’t provide info about H2O content of the absorbent
in the presence of halogenated anesthetics, desiccated soda lime = increase CO production (des > iso»_space;> sevo) & compound A production (sevo)
List 7 ways to monitor for disconnection of the breathing circuit
4 ways to monitor for circuit disconnect: pressure, volume, EtCO2, vigilance
- precordial stethoscope
- visual inspection of chest rise
- capnography
- respiratory volume monitors
- low expired volume alarm
- low peak pressure alarm
- failure of bellows to rise w/ an ascending bellows (not w/ descending or piston)
What are the OSHA recommendations regarding IA exposure for health care workers in the OR?
Need to know this!
halogenated agents alone <2ppm
N2O alone <25ppm
together: <0.5ppm halogenated, <25ppm N2O
compare and contrast the 4 types of breathing circuits, and list examples of each.
1) open
- no rebreathing
- no reservoir
- insufflation, simple mask, NC, open drop
2) semi-open
- no rebreathing
- reservoir
- mapleson, circle system if FGF > MV
3) semi-closed
- partial rebreathing
- reservoir
- circle system w/ FGF
4) closed
- rebreathing
- has APL that is closed
- just enough to support O2 consumption
What is the purpose of the unidirectional valves in the breathing circuit?
to ensure that gas moves in one direction
- if a valve becomes incompetent, the pt will rebreathe exhaled gas
- the definitive fix is to correct the valve
- if this cannot be done, then a closed or semi-closed system should be converted to a semi-open system
Which Mapleson circuit is most efficient for SV? Which is best for controlled ventilation?
spontaneous: “All Dogs Bite”
- best = mapleson A (A > DFE > CB)
- worst = mapleson B
controlled: “Don’t Be Arrogant”
- best = mapleson D (DFE > BC > A)
- worst = mapleson A
Mapleson A requires FGF 20L/min for controlled ventilation
Bain is modified Mapleson D, to prevent rebreathing FGF 2.5x min ventilation
Mapleson breathing circuit photos
A: FGF at the end by the reservoir, APL is by the patient
B: reservoir, FGF, APL, patient
C: B w/ shorter circuit
D: APL valve is at the end by the reservoir
E: EMPTY! (aka Ayre’s T piece) 0 valves
F: called Jackson-Rees, 1 valve, bag is at the end
What conditions decrease pulmonary compliance? How does this affect the peak pressure and plateau pressure?
Decreased pulmonary compliance is usually d/t a reduction in the static compliance (PIP & PP increase)
- endobronchial intubation
- pulmonary edema
- pleural effusion
- tension pneumo
- atelectasis
- chest wall trauma
- abdominal insufflation
- ascites
- Tburg position
- inadequate NMB
What conditions increase pulmonary resistance? How does this affect the peak pressure and plateau pressure?
Usually d/t a reduction in dynamic compliance (PIP increases, PP remains unchanged)
- kinked ETT
- endotracheal cuff herniation
- bronchospasm
- bronchial secretions
- compression of the airway
- foreign body aspiration
Describe the 4 phases of the normal capnograph
phase I (A-B) = exhalation of anatomic dead space phase II (B-C) = exhalation of anatomic dead space + alveolar gas phase III (C-D) = exhalation of alveolar gas phase IV (D-E) = inspiration of fresh gas that doesn't contain CO2
Discuss the significance of the alpha and beta angles on the capnograph.
Review all the capnography waveforms
increased alpha angle = expiratory airflow obstruction: COPD, bronchospasm, or kinked ETT
beta angle is increased = in rebreathing but only shows if there’s a unidirectional valve that is incompetent
in the case of CO2 absorbent exhaustion, the beta angle remains normal, but the baseline increases
recall all of the abnormal CO2 waveforms you can (there are 9)
Think of all the causes of increased & decreased EtCO2 that occur as a result of changes in CO2 production
increased EtCO2 d/t increased production:
- increased BMR (increased VO2)
- MH
- thyrotoxicosis
- fever
- sepsis
- seizures
- laparoscopy
- tourniquet or clamp removal
- NaHCO3 removal
- anxiety, pain
- shivering
- increased muscle tone (post NMB reversal)
- medication side effect
decreased EtCO2 d/t decreased production:
- decreased BMR (decreased VO2)
- increased anesthetic depth
- hypothermia
- decreased pulmonary blood flow
- decreased CO, hypotension
- pulmonary embolus
- V/Q mismatch
- medication side effect
Think of all the causes of increased & decreased EtCO2 that occur as a result of changes in alveolar ventilation or equipment malfunction.
INCREASED EtCO2 decreased alveolar ventilation - hypoventilation - CNS depression - residual NMB - COPD - high spinal anesthesia - NM disease - metabolic alkalosis - medication side effect
equipment malfunction
- rebreathing
- CO2 absorbent exhaustion
- unidirectional valve malfunction
- leak in circuit
- increased apparatus dead space
DECREASED EtCO2 increased alveolar ventilation - hyperventilation - inadequate anesthesia - metabolic acidosis - medication side effect
equipment malfunction
- ventilator disconnect
- esophageal intubation
- poor seal w/ ETT or LMA
- sample line leak
- airway obstruction
- apnea
What 2 wavelengths of light are emitted by the pulse oximeter?
What law is used to make the SpO2 calculation?
2 wavelengths of light:
- red light (660nm); preferentially absorbed by deoxyHgb
- near infrared light (940nm); preferentially absorbed by oxyHgb
Beer-Lambert law is used; relates the intensity of light transmitted through a solution and the concentration of a solute within the solution
Which conditions impair the reliability of the pulse oximeter?
decreased perfusion (vasoconstriction, hypothermia, Raynaud’s)
dysfunctional Hgb (carboxyHgb, MetHgb, but NOT HgbS or HgbF)
altered optical characteristics (methylene blue, indocyanine green, indigo carmine, NOT fluorescein)
nonpulsatile flow (CBP, LVAD)
motion artifact (shivering, movement)
other (electrocautery, venous pulsation, NOT jaundice or polycythemia)
What factors affect the accuracy of the NIBP measurement?
ideal bladder length = encircle 80% of the extremity
ideal bladder width = 40% of the circumference of the patient’s arm
falsely increased BP:
- BP cuff too small
- BP cuff too loose
- BP measured on extremity below the level of the heart
falsely decreased BP
- BP cuff too large
- BP cuff deflated too quickly
- BP measured on extremity above the level of the heart
How does the site of measurement affect the BP reading?
as pulse moves from the aortic root toward the periphery, the SBP increased, DBP decreases, and pulse pressure widens. MAP remains constant
at the aortic root: SBP is the lowest, DBP is the highest, PP is the narrowest
at the dorsalis pedis: SBP is the highest, DBP is the lowest, PP is the widest
How does arm position affect the NIBP reading? How about when an arterial line is used?
If BP cuff > heart, BP will be falsely decreased
If BP cuff < heart, BP will be falsely increased
For every 10cm change, the BP changes by 7.4mmHg
For every 1inch (2.5cm) change, the BP changes by 2mmHg
What information can you learn from the arterial BP waveform?
systolic BP = peak diastolic BP = trough pulse pressure = peak-trough contractility = upstroke SV = area under the curve closure of aortic valve = dicrotic notch
Discuss damping and the interpretation of the high pressure flush test.
1) optimally damped: baseline is re-established after 1 oscillation
2) underdamped: baseline is re-established after several oscillations (SBP is overestimated, DBP is underestimated)
3) overdamped: baseline is re-established after no oscillations (SBP is underestimated, DBP is overestimated)
Overdamped causes:
- air bubble or clot in the pressure tubing
- low flush bag pressure
- loss of diacritic notch will tell you if it’s overdamped
How do you determine the appropriate distance to thread a CVC or PA cath?
- you must know the distance from the site of entry to the vena cava junction
- you must know the distance from the VC junction to where the tip of the catheter should be placed
insertion site –> RA junction:
- SC = 10cm
- R IJ = 15cm
- L IJ = 20cm
- femoral = 40cm
- R median basilic = 40cm
- L median basilic = 50cm
RA junction –> catheter tip
- RA = 0-10cm
- RV = 10-15cm
- PA = 15-30cm
- PAOP position = 25-35cm
What are the 3 waves and 2 descents on the CVP waveform? What does each one signify?
a wave = RA contraction
c wave = tricuspid valve elevation into RA (RV contraction)
x descent = downward movement of contracting RV
v wave = RA passive filling
y descent = RA empties through open tricuspid valve
How do the waves and descents on the CVP waveform correlate w/ the electrical events in the heart?
A wave = RA contraction, just after P wave
C wave = RV contraction, just after QRS
X descent = RA relaxation, ST segment
V wave = passive filling of RA, just after T wave begins
Y descent = RA empties through tricuspid valve, after T wave ends
What factors increase or decrease the CVP?
increase:
- transducer below the phlebostatic axis
- hypervolemia
- RV failure
- tricuspid stenosis or regurg
- pulmonic stenosis
- pHTN
- PEEP
- VSD
- constrictive pericarditis
- cardiac tamponade
decrease
- transducer above phlebostatic axis
- hypovolemia
What conditions cause loss of the a wave on the CVP waveform?
occurs when synchronized contraction of the RA is lost
- afib
- V pacing
What conditions cause an increased “a wave” on the CVP waveform?
large a wave is produced when the atria contracts and empties against high resistance
- tricuspid stenosis
- diastolic dysfunction
- MI, ischemia
- chronic lung dz –> RV hypertrophy
- AV dissociation
- junctional rhythm
- V pacing (async)
- PVCs
What conditions cause a large v wave on the CVP waveform?
- tricuspid regurg
- acute increase in intravascular volume
- RV papillary m ischemia
How does the waveform change as the PA cath is guided into position? What are the normal pressures at each step?
- RAP 1-10mmHg (CVP waveform)
- RVP 15-30/0-8mmHg (larger, steeper waveform)
- PAP 15-30/5-15mmHg (“step up” in the waveform + dicrotic notch)
- PAOP 5-15mmHg (mirrors CVP waveform)
Don’t place in PAOP in a patient with LBB, bc placement can cause a RBB. If you do it with a LBB they can get complete heart block. If it’s in the Left IJ = there is also a risk of chylothorax rupture. PAOP cath should be placed in West zone 3
PAOP rupture risks:
1. Anti coagulation
2. Hypothermia
3. Advanced age
The tip of the PA cath should be positioned in West lung zone ___?
zone III
in this region, there is a continuous column of blood b/n the tip of the PAC & the LV. Since LVEDP reflects back through the pulmonary circulation, a tip positioned in zone III provides the most accurate LVEDP estimate.
What is the equation for mixed venous oxygen saturation?
SVO2 = SaO2- [VO2/(Q1.34Hgb*10)]
Q = CO VO2 = O2 consumption
normal = 65-75%
What conditions are associated with a decreased SvO2? How about an increased SvO2?
decreased d/t:
- increased consumption (stress, pain, thyroid storm, shivering, fever)
- decreased delivery (decreased PaO2, decreased Hgb, decreased CO)
increased d/t:
- increased delivery (increased PaO2, increased Hgb, increased CO)
- decreased consumption (hypothermia)
relate the phases of the cardiac action potential to the EKG
phase 0, depolarization (Na+ inward) = QRS
phase 1, initial repolarization (Cl- in, K+ out) = QRS
phase 2, plateau (Ca++ in, K+ out) = ST segment
phase 3, final repolarization (K+ out) = T wave
phase 4, resting phase (Na+ out) = end of T wave –> QRS
What region of the myocardium does each EKG lead monitor? What coronary arteries are monitored by each lead?
We commonly use 12 leads to look at the heart’s electrical activity from a variety of different angles. We can divide these leads into 3 groups:
- bipolar leads (3), I, II, III
- limb leads (3), aVR, aVL, aVF
- precordial leads (6), V1-V6
CxA = I, aVL, V5, V6 (lateral) RCA = II, III, aVF (inferior) LAD = V1-V4 (septum, anterior)
List the conditions that can cause L & R axis deviation
R axis deviation:
- COPD
- acute bronchospasm
- cor pulmonale
- pHTN
- PE
L axis deviation
- chronic HTN
- LBBB
- aortic stenosis or regurg
- mitral regurg
recite the heart block poem
if “R is far from “P” then you have a first degree
longer, longer, longer, drop then you have a Wenckebach
if some “P”s don’t get through then you have a Mobitz II
if “P”s and “Q”s don’t agree then you have a third degree
What is the mechanism of action for each antiarrhythmic class (I-IV)? List examples of each.
I Na+ channel blockers:
IA; mod phase 0 depression, prolongs phase 3 repol
- quinidine, procainamide, disopyramide
IB; weak phase 0 depression, shortened phase 3 repol
- lidocaine, phenytoin
IC; strong phase 0 depression
- flecainide, propafenone
II BB; slows phase 4 repol in SA node
- esmolol, metoprolol, atenolol, propanolol
III K+ channel blockers; prolong phase 3 repol (increased QT), increased effective refractory period
- amiodarone, bretylium
IV CCB; decreased conduction velocity via AV node
- verapamil, diltiazem
Adenosine hyperpolarizes and is useful for WPW but avoid in asthmatics
What EKG findings are consistent with Wolff Parkinson White syndrome?
- delta wave caused by ventricular preexcitation
- short PR interval
- wide QRS complex
- possible T wave inversion
What conditions increase the risk of torsades de pointes?
POINTES:
1) Phenothiazines
2) Other drugs: methadone, droperidol, amio w/ hypokalemia
3) ICH
4) No known
5) Type I antiarrhythmics
6) Electrolytes (low K+, Ca++, Mg++) NEED TO KNOW!
7) Syndromes Romano Ward and Timothy syndrome
Tx: Mg or cardiac pacing
What is the treatment for torsades de pointes?
reversing the underlying cause and/or shortening the QT interval
- magsulfate
- cardiac pacing to increase HR will reduce the AP duration & QT interval
List 5 indications for cardiac pacemaker insertion
- symptomatic SA node disease
- symptomatic AV node disease
- long QT syndrome
- dilated cardiomyopathy
- IHSS
What is the significance of the NBG pacemaker identification code?
position I = chamber paced position II = chamber sensed position III = response to sensed event position IV = programmability position V = pacemaker can pace multiple sites
How does atrial pacing affect the QRS complex? How about ventricular pacing?
a-paced = no QRS change v-paced = widened QRS
What conditions increase the risk of failure to capture?
when the myocardium becomes more resistant to depolarization
- hyper/hypokalemia
- hypocapnia (affects K+ shift)
- hypothermia
- MI
- fibrotic tissue buildup around pacing leads
- antiarrhythmic medications
How does the cerebral oximeter work? What value is considered a significant change from baseline?
utilizes near infrared spectroscopy to measure cerebral oxygenation (similar to SpO2)
- doesn’t have the ability to detect pulsatile flow, thus it’s primarily a measure of venous oxyHgb saturation & oxygen extraction
- decreased delivery –> increased extraction –> decreased venous Hgb sat
- >25% change from baseline suggests a reduction in cerebral oxygenation
Describe the different types of EEG waveforms.
beta
- high frequency, low voltage
- awake mental stimulation & “light” anesthesia
delta
- <4 cycles/sec
- GA, deep sleep, brain ischemia or injury
burst suppression
- GA, hypothermia, CPB, cerebral ischemia (esp if unilateral)
isoelectricity
- very deep anesthesia, death
- 1.5- 2 MAC isolectricty or complete suppression
How do brain waves change during GA?
- induction = increased beta wave activity
- light anesthesia = increased beta wave activity
- theta & delta waves predominate during GA
- deep anesthesia produces burst suppression
- 1.5-2MAC, GA = isoelectricity
name 2 drugs that are likely to reduce the reliability of the BIS value
N2O (increases amplitude of high frequency activity & reduces amplitude of low frequency activity). This doesn’t affect the BIS value
ketamine increases high frequency activity –> can produce a BIS that is higher than the level of sedation/anesthesia would otherwise suggest.
What is the difference b/n micro and macro shock?
macroshock: comparatively larger amount of current that is applied to the external surface of the body. Impedance of the skin offers a high resistance, so it takes a larger current to induce vfib
microshock: smaller amount of current applied directly to the myocardium. High skin resistance is bypassed, so takes smaller current to induce vfib
What are the key threshold values for macroshock and microshock?
microshock:
10mcA max allowable current leak in the OR
100mcA vfib inside
macro:
- 1mA touch perception
- 50mA loss of consciousness
- 100mA v.fib SKIN TO SKIN
What is the role of the line isolation monitor? What should you do if it alarms?
assesses the integrity of the ungrounded power system in the OR. It tells ou how much current could potentially flow through you or a patient if a second fault occurs
- primary purpose is to alert the OR staff of the first fault
- does NOT protect you from macro/micro shock
- will alarm when 2-5mA of leak current is detected
- if alarm sounds, the last piece of equipment that was plugged in should be unplugged.
- the maximum allowable leak in the OR is 10 Ua
A nondepolarizing block is characterized by several factors when assessed by a peripheral nerve stimulator. What are three of the factors?
1) Decrease in twitch tension
2) Fade during repetitive stimulation
3) Post-tetanic potentiation
(Got this from prodigy)
What type of EEG activity would most likely be seen during the awake state?
Things that affect EEG?
Beta: High frequency, low voltage activity
Things that affect BIS and EEG: nitrous and ketamine
In an oxygen-driven ventilator, the amount of oxygen required to operate the ventilator is
Based off the minute ventilation of the patient
Also if your pipeline supply runs out: switch to hand bagging them
According to U.S. Department of Transportation, the gas cylinder label must include:
- Serial number
- Date of last inspection
- Type of metal used to construct cylinder
- Max filling psi
- Manufacturer/Owner
Which monitor will be the first to detect an oxygen pipeline crossover?
Oxygen analyzer
A negative deflection is observed on the airway pressure wave from when the mechanical ventilator is activated. Which mode of ventilation is the pt most likely receiving? (Select 2)
A. Controlled mandatory ventilation
B. Inverse ration ventilation
C. Biphasic positive airway pressure
D. Pressure support
Biphasic positive airway pressure and pressure support
A negative deflection before a breath indications a patient triggered breath. A machine initiated breath will only show a positive deflection
Which situations would produce negative pressure inside the breathing circuit? (Select 2)
A. Tear in the bellows
B. OGT placed in trachea
C. Circuit disconnect
D. Malfunction of closed system scavenger
B. And D.
What is the most likely cause of a lower than expected concentration of sevo inside the breathing circuit?
A. Bellows leak
B. Delivery at altitude
C. Tipped vaporizer
D. Pumping effect
Bellows leak- it allows gas to escape from circuit and there’s a risk of awareness
Good to know: Descending bellows are more dangerous, more risk of barotrauma. Gas outside bellows is high pressure.
Ascending bellows are “safer”
Review the circle system and know where the valves are
This is different than the breathing circuits. Review both!
Circle system has unidirectional valves and CO2 absorbent
Semi- open circuit: FGF exceeds minute ventilation
Semi-closed circuit: FGF is < 1 minute ventilation
Closed circuit: FGF is just enough to support pt’s O2 consumption
Disadvantages of circle system: unidirectional valves can malfunction:
- if it’s stuck open: rebreathing
- if it’s stuck closed: obstruction
Advantages of mapleson circuit:
- Less airway resistance so it’s good for peds
- Convenient
- Bain circuit prevents heat loss
Disadvantages of mapleson circuits:
- more apparatus dead space
- requires high FGF to prevent rebreathing
- loss of heat/humidity (except for Bain, it prevents heat loss)
- unrecognized kinking seen in Bain circuit
Bain circuit
- tested with pethick test before use
- inner tubing has FGF
- outer tubing has exhaled gas (this is how incoming FGF is warmed)
- prevents heat loss
- disadvantage is inner tube is at risk of kinking/disconnection
- modified mapleson D
- can be used for spontaneous and controlled
- to prevent rebreathing FGF should be 2.5x min ventilation
Which component in the circle system protects the patient from excess airway pressure during SV?
The reservoir bag- it does it exceed internal pressure of 60 cm H2O if the bag is inflated 4x its size
Which factors affect the extent of rebreathing exhaled gas in the circle system?
- FGF
- Arrangement of components in the circuit
- Proper functioning of the unidirectional valves
Benefits of mapleson circuit? Select 2
A. Low airway resistance
B. Allows rebreathing of exhaled gas
C. Simplicity of design
D. Minimal fresh gas requirement
A & C
Disadvantages: risk of rebreathing CO2 and there is a higher FGF requirement compared to a circle system
Benefits of using low fresh gas flow in a circle system include: select 2
A. Faster FA/FI equilibriation
B. Increased humidity in the system
C. Reduced risk of barotrauma
D. Slower reduction in body temperature
B & D
Lower FGF preserves humidity in the breathing system and slower reduction in body temperature
What components are excluded from the mapleson circuit? Select 2
A. Unidirectional valves
B. APL valve
C. Carbon dioxide absorber
D. Reservoir bag
A & C.
No unidirectional valves or carbon dioxide absorber
Dynamic compliance formula
Dynamic compliance = TV / PIP - PEEP
What pulmonary compliance is a function of both airway resistance and elasticity of the chest wall?
Dynamic compliance
Static compliance is a function of elasticity only
Compliance:
Change in volume / change in pressure
NEED TO KNOW THIS!!!!!!!!!!!!
Think compliance and volume!
Review this image
What occurs with an increased PIP with no change in PP?
NEED TO KNOW THIS
Increased resistance
- kinked ETT
- bronchospasm
- ETT cuff herniation
- bronchial secretions
- compression of airway
- foreign body aspiration
What is occurring here?
List of examples:
Increased PIP and PP: causing decreased compliance
- Atelectasis
- Endobronchial intubation
- Pulmonary edema
- Pleural effusion
- Pneumo
- Chest wall edema
- Abdominal insufflation
- Ascites
- Trendelenburg
- Inadequate muscle relaxation
Mainstream in-line CO2 monitor:
Attached to ETT, faster, doesn’t require water trap or pumping mechanism, there is increased apparatus dead space
Sidesteam- S for slower
Sidestream CO2 monitor
Slower, requires water trap to prevent contamination, has pumping mechanism
Biphasic expiratory plateau
- occurs after single lung transplant
- second peak is the alveolar gas from diseased lung, air is trapped in it so longer time constant
- biphasic expiratory plateaus seen in severe kyphoscoliosis
- Metabolic acidosis (hyperventilation)
- P.E. (Increased Deadspace)
- Inadequate seal with LMA (equipment failure)
This waveform shows abnormally low EtCO2 which can result from reduced CO2 production, increased Deadspace, hyperventilation, or equipment failure
Best SpO2 reading locations on body
Fast: Ear, nose, tongue, esophagus, forehead
Middle: finger
Slow: toe
Pulse ox reads 80%, estimate the PaO2:
50 mmHg
SpO2 80% = PaO2 mmHg?
SpO2 70% = PaO2 mmHg?
SpO2 90% = PaO2 60 mmHg
SpO2 80% = PaO2 50 mmHg
SpO2 70% = PaO2 40 mmHg
Right or left shift in oxyhemoglobin curve?
Increased 2,3 DPG
Increased CO
Increased H+
Decreased pH
Right shift (occurs in metabolically active tissue)
Right or left shift in oxyhgb curve?
- decreased co
- decrease H+
- increase pH
Left shift (occurs in lungs)
Pulse oximter is a useful monitor of:
A. Ventilation
B. Bronchial dilation
C. Anemia
D. Vascular compression
D. Vascular compression (think about Innominate artery compression during mediastinoscopy)
Pulse oximeter is a noninvasive monitor of what 3 things
1) hemoglobin saturation
2) heart rate
3) fluid responsiveness
4) assess perfusion
IT DOES NOT: assess bronchial intubation, anemia
Methomoglobin
Absorbs what two nm equally?
660 nm and 940 nm
The 1:1 absorption reads 85%.
It falsely underestimates SpO2 if O2 sat >85%
It falsely overestimates if SpO2 if O2 sat <85%
Carboxyhemoglobin absorbs what nm?
660 nm same degree as oxyhgb, they will look the same on the pulse oximeter
How do these affect pulse ox reliability
- Hgb S and F
- Jaundice
- Fluorescein
- Polycythemia
- Acrylic nails
THESE DO NOT AFFECT IT
THINGS THAT DO: LVAD, CABG, Shivering, icg, methylene blue, vasoconstriction, Raynaud’s
Most common method of measuring exhaled gases inside the breathing circuit?
A. Mass spectrometry
B. Raman scattering
C. Piezoelectric crystals
D. Infrared absorption
D. Infrared absorption
PIP increase with unchanged plateau pressure: increased resistance
- kinked ETT
- bronchospasm
Dysfunctional inspiratory unidirectional valve. Stuck in the open position leads to rebreathing exhaled CO2, this increases PaCO2 and etCO2 but the gradient becomes SMALLER
Where as venous embolism increases dead space and the gradient increases
Carboxyhemoglobin bc it absorbs the same 660 nm light as oxyghemoglobin (pulse ox can’t distinguish between them)
Creating falsely increased SpO2 and overestimation of PaO2
Carboxyhemoglobin concentration shifts curve to the left (hemoglobin binds to another atom prevent it from carrying oxygen)
Shivering and venous pulsation seen in tricuspid regurgitation can falsely reduce the SpO2
Check the gas analyzer
This waveform represents sample line leak
What is the most reliable monitor for detection of bronchial intubation?
A. Pulse ox
B. O2 analyzer
C. Chest auscultation
D. Capnograph
C. Chest auscultation
Key takeaway pulse ox and capnography are NOT reliable monitors to detect bronchial intubation
Which monitors can be used to measure O2 concentration in the breathing circuit?
1) Clark electrode
2) Paramagnetic analysis- self calibrating and doesn’t need to be replaced
3) Galvanic cell- calibrated daily, consumable and needs to be replaced often
INFRARED ABSORPTION SPECTROPHOTOMETRY CANT MEASURE O2
Hemorrhage/hypovolemia = acute reduction in EtCO2
Review how these correlate
Central venous pressure is:
A. Falsely increased by placing the transducer above the zero point
B. Increased by PEEP
C. Decreased by pericardial tamponade
D. Unchanged by a VSD
B. Increased by PEEP
PEEP increases PVR
CVP is a function of
Intravascular volume
Venous tone
RV compliance
Things that decrease CVP: transducer is above phlebostatic axis and hypovolemia
Normal CVP in adult:
When do you measure it during respiratory cycle?
1-10mmHg
Measure CVP at end expiration
Things that increase it: PEEP, RV failure, tricuspid stenosis and regurgitation
Tricuspid stenosis
Diastolic dysfunction
A wave correlates with atrial contraction, if a wave increases it is due to tricuspid stenosis or decrease compliance of the right ventricle (diastolic dysfunction), AV dissociation
Large V wave on CVP:
Tricuspid regurgitation and RV papillary muscle ischemia
When the tip enters the pulmonary artery:
The diastolic blood pressure increases and Diacrotic notch appears during pulmonary valve closure
Review PA catheter
RAP is the same as CVP
RVP: 15-30/ 0-8 diastolic is equal to CVP
PAP: 15-30/ 5-15 diastolic rises and dicrotic notch forms
PAOP (wedge pressure): 5-15
Look at each range
PA catheter
Review the waveform and values
PAOP reads pressures in the left atrium!
When does pulmonary artery occlusion pressure overestimate left ventricular end-diastolic volume?
A. PA cath tip in west zone 3
B. PEEP
C. Diastolic dysfunction
D. Aortic insufficiency
PAOP overestimates LVEDV: PEEP and Diastolic dysfunction
PAOP underestimates LVEDV: Aortic insufficiency
When would standard CO thermodilution method be used over continuous cardiac output?
When measuring CO with the thermodilution method what factors can overestimate CO?
What factors make it unable to predict CO?
CO standard thermodilution technique is used for a hemodynamic ally unstable patient
things that cause overestimation of CO:
- Low volume and too warm of injectate = overestimation of CO
- Partially wedged PAC
- Thrombus tip on catheter
Intracardiac shunt and tricuspid regurgitation = unable to predict effect on CO
Factors that increased mixed venous oxygen saturation:
A. SNP
B. Thyroid storm
C. Sepsis
D. Anemia
name other things that increase mixed venous oxygen saturation:
SNP and sepsis
things that increase SvO2:
Increase O2 delivery:
- O2 therapy, increased hgb, increased CO
Decrease O2 consumption:
- hypothermia, cyanide toxicity
Name things that decrease SvO2 mixed venous oxygen saturation:
Increased O2 consumption: stress, pain, thyroid storm, shivering, fever
Decrease O2 delivery: decreased SaO2, anemia
2 conditions that limit reliability of the esophageal Doppler monitor:
A. Hypovolemia
B. Aortic valve disease
C. Aortic cross clamp placement
D. Esophageal disease
Alveolar valve disease and Aortic cross clamp
Other limitations: after CPB, pregnancy, and disease of thoracic aorta
Reverse T burg
Light anesthesia and anemia
SvO2 is reduced by things that increase O2 consumption or decrease O2 delivery
Dorsalis pedis artery
Because systolic BP increases along the arterial tree
22/9
Tip of PA cath is in the main Pulmonary artery
PAP Systolic range 15-30
PAP Diatolic range 5-15
What is the most accurate measurement provided by oscillometric method of blood pressure measurement?
A. SBP
B. DBP
C. MAP
D. Pulse pressure
MAP
Atrial systole and ventricular diastole
A wave is produced when the right atrium contracts to prime the right ventricle
Aortic insufficiency
PAOP underestimates the LVED, so left ventricular volume is more than what is predicted by the PAOP
Things that cause PAOP to overestimate the LVEDV include:
Myocardial ischemia
COPD
Left to right shunting
What components of the CVP waveform correlate with ventricular systole?
What correlates with ventricular diastole?
C wave and x descent: ventricular systole
A wave and y descent: ventricular diastole
What rhythm is this?
Wenckebach
2nd degree mobitz 1
Longer, longer, drop you have wenckebach
What rhythm is this?
First degree block
R is far from P you have first degree
What rhythm is this?
If some P’s don’t get through you have Mobitz 2
There is a p but no QRS
What rhythm is this?
P’s and Q’s don’t agree you have 3rd degree
Which heart blocks may need a pacemaker?
Second degree mobitz type 2 block
Third degree block
Atrial- ventricular reentry
Pt with WPW develops a.fib what is the best tx?
Procainamide + cardioversion and (ablation for both)
We dont know if it’s ortho or antidromic so we are going to just give the safest options
WPW orthodromic
Narrow or wide QRS? How can you treat it?
- More common
- Atrial- ventricular reentry
- Narrow QRS
- Can cardiovert, do vagal maneuvers, adenosine, BB, veramapil, amiodarone
- Delta wave on the slope of R wave
- Ablation is definite treatment for both types of WPW
Things that can increase likelihood of torsades
- hyperventilation, lasix, methadone, droperidol, bradycardia, zofran, hypomagnesia = prolong QT
Tx: mg and cardiac pacing
What frequency would you use for superficial structure on U.S.?
> 10 mHz if it’s < 3cm below the skin
WHO national colors for
Air, O2, N2O
Air= white and black
O2= white
N2O= blue
How much PEEP do bellows have?
2-3 cmH2O
15 rule for LMA
<15 degree tilt
<15 pressure for insufflation
< 15 mins for insufflation
Role of the scavenger system
Mapleson circuit review
Ventricular AP:
What electrolyte can raise the threshold potential?
What electrolyte can raise the resting membrane potential?
What is Hyperpolarization?
- Calcium can raise the threshold potential
- Potassium can raises the resting membrane potential
- Hyperpolarization- an example is giving cardiplegia, it causes it to go far away down from the resting potential (MORE NEGATIVE). Absolute refractory period means another depolarization can’t occur here.
Where do you measure ST changes?
J-point
It’s an issue if it’s greater or less than 1
Also, EKG changes with peaked T waves can mean hyperkalemia and intracranial hemorrhaging!
What heart block is this?
Wenckebach or Mobitz 1
What heart block is this?
Mobitz 2
What heart block is this?
Third degree
What rhythm is this
TOF:
Tetanus:
Single twitch:
Double burst:
Post tetanic:
-TOF: 4 twitches at 2 Hz for 2 seconds. Ok to extubate TOF > 0.9
- Tetanus: 50 Hz for 5 seconds
- Single twitch: single twitch 0.1-1 Hz
- Double burst: 2 short bursts of 50 Hz. Easier to detect DBS than TOF. Painful
-Post tetanic: 50 Hz for 5 seconds, followed by single twitches that fade in strength
What concept explains why train-of-four should NOT be performed immediately after assessing tetany with a peripheral nerve stimulator?
A) Fade
B) Phase 1 block
C) Post-tetanic potentiation
D) T4/T1 ratio
C) Post-tetanic potentiation
Sustained tetany can cause post-tetanic facilitation, so it can impact the results of subsequent TOF assessment.
For this reason, the results of TOF won’t be accurate for up to 6 minutes following tetanus assessment
Which method provides the GREATEST margin of safety against the risk of macroshock in the operating room?
A) Isolate the ground from the main power supply
B) Use equipment that has a three-pin plug
C) Plug all equipment into GFI outlets
D) Ensure the line isolation monitor is activated
A) Isolate the ground from the main power supply
An ungrounded power supply provides a margin of safety against the risk of macroshock
This arrangement requires an isolation transformer, and the integrity of the system is assessed by a line isolation monitor (LIM).
**The LIM does not (by itself) protect against the risk of injury, so it wasn’t the best answer in the context of this question. All it does is alarm at 2-5 MA!
CXR for COPD
ETT CXR confirmation
4-5 cm above the carina look for the clavicle
Pneumo on CXR
Deep sulcus- is simple pneumothorax
The deep sulcus sign is an abnormal lucency over the ipsilateral costophrenic angle in a supine patient with pneumothorax. The lucent area often extends over the upper quadrant of the
Ultrasound
Frequency, wavelength, amplitude
Just read over it
Frequency- measure of pitch, higher frequency = shorter wavelength
Amplitude- sound’s loudness
Pizeoelectric
Hyperchoic, hypoechoic, anhechoic
Hyper- high frequency. Bone.
Hypo- low frequency. Organs, skin, fat
Anhechoic- cyst, ascities
POCUS abdominal ultrasound
Gastric antrum
- Empty: bull’s eye anhechoic circle around
- Clear fluids: rounder anhechoic
- Food: hyperechoic and high risk !
