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.
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
- fusible plug made of Woods metal (melts at elevated temperature)
- frangible disk that ruptures under pressure
- 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?
oxygen pressure failure device (fail safe device)
- shuts off an/or proportionately reduces N2O flow if O2 pressure drops below 20psi
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%)
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?
barotrauma (if pressed during inspiration)
awareness (gas doesn’t contain IA)
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?
water is required to facilitate the reaction of CO2 w/ the CO2 absorbent. The granules are hydrated to 13-20% by weight. When it is devoid of H2O, it is said to be 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?
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.
open
- no rebreathing
- no reservoir
- insufflation, simple mask, NC, open drop
semi-open
- no rebreathing
- reservoir
- mapleson, circle system if FGF > MV
semi-closed
- partial rebreathing
- reservoir
- circle system w/ FGF
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
Describe the mapleson breathing circuits
A: FGF, reservoir, APL, pt
B: reservoir, FGF, APL, pt
C: B w/ shorter circuit
D: reservoir, APL, FGF, pt
E: no reservoir, just FGF, pt (aka Ayre’s T piece) 0 valves
F: APL, reservoir, FGF, pt (aka Jackson-Rees) 1 valve
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.
increased alpha angle = expiratory airflow obstruction: COPD, bronchospasm, or kinked ETT
beta angle is increased = in rebreathing
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 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.
optimally damped: baseline is re-established after 1 oscillation
underdamped: baseline is re-established after several oscillations (SBP is overestimated, DBP is underestimated)
overdamped: baseline is re-established after no oscillations (SBP is underestimated, DBP is overestimated)
Causes can include an air bubble or clot in the pressure tubing or 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)
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)
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
Review the circle system and know where the valves are
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
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
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
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
Shivering and venous pulsation seen in tricuspid regurgitation can falsely reduce the SpO2
Check the gas analyzer
This waveform represents sample line leak
Hemorrhage/hypovolemia = acute reduction in EtCO2
Review how these correlate
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!
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
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
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
Atrial- ventricular reentry
Most commonly seen in WPW is orthodromic AV nodal reentry and this is the one you can give lidocaine and adenosine
