Hall Review Flashcards – Anesthesia Equipment and physics
Unlock all answers in this set
Unlock answersquestion
What are orifice,Turbulent, and laminar flows?
answer
Orifice - occurs where gas flows through region of severe constriction. Laminar - when gas flows down parallel sided tubes at rate less than critical. Turbulent, gas flow exceeds critical v
question
What is a major determinants of resistance in orifice and turbulent flow? Laminar flow? What gas is used to reduced resistance in orifice flow?
answer
Resistance is directly proportional to density in orifice and turbulent flow. Helium has low DENSITY, and decreases resistance through areas of airway constriction, esp upper airway. Resistance is directly related to VISCOSITY in laminar flow.
question
What would be a likely cause for admixture of room air in waste gas of disposal system in a vent with an active scavenging system?
answer
The negative pressure relief valve, used in active scavenging systems powered by vacuum system, can trap room system drops low enough. Positive pressure relief valve opens into the OR, soda lime canisters leak to OR if there are leaks.
question
What is LaPlace's Law?
answer
T = PR / 2, relating surface tension, intraalveolar pressure, and radius of alviolae
question
For E size cylinders, what are the colors each for O2, N2O, CO2, and air, in the US?
answer
O2 - green, N20- blue, CO2- gray, Air - Yellow
question
For E size cylinders,in what physical state are the following in cylinder: O2, N2O, CO2, and air?
answer
O2 gas, N2O liquid and gas, CO2 liquid and gas, Air - gas
question
For E size cylinders, what are the full psi and max L volume for O2, N2O, CO2, and air?
answer
O2 - 2000 psi, 625 L ; N2O - 750 psi, 1590 L; Co2 - 838 piso, 1590 L , Air - 1800 psi, 625 L
question
Describe the negative pressure leak test
answer
Established in 1993 by FDA, performed with machine master switch, flow control valve, vaporizers turned off, suction bulb is attached to common gas outlet and compressed until fully collapsed. If a leak is present, the suction bulb will inflate. IT IS UNIVERSAL TO ALL ANESTHESIA machines, regardless whether a check valve is present in the fresh gas outlet
question
What is the purpose of the OUTLET check valve of the anesthesia machine? How about the check valve for each cylinder?
answer
THe outlet check valve positioned downstream from the rotameters and vaporizers but upstream from o2 flush valve, to detect low pressure leaks before the O2 flush valve in the low pressure part of the circuit (vaporizers, rotameters, etc) . The check valve for each cylinder is positioned immediately upon outflow of cylinder as it enters the high pressure circuit, before the pressure regulator. It ONLY permits unidirectional glow of gasses and prevent retrograde flow of gases from the anesthetic machine, thus prevents transfer of gases between compressed gas cylinders.
question
What is the difference between APL and pop off valve?
answer
Nothing
question
What is the fail-safe valve? WIll it prevent delivery of hypoxic gas mixture? Explain?
answer
A pressure sensor shutoff valve that discontinues flow of N2O if O2 pressure falls below 25 psi. It will not prevent delivery of hypoxic gas mixture or pure N2O when the O2 rotamer is off. This is why an O2 analyzer is needed downstream of all gas inputs.
question
What is boyle's law?
answer
For a fixed mass at constant temp, P1V1 = P2V2
question
Can you used a psi reading on an O2 tank to determine volume remaining, and use this to determine remaining volume at a given flow rate?
answer
Yes, using Boyle's law.
question
Describe the function of a working rotameter with a rotating bobbin.
answer
Gas flows between rim of bobbin and wall of thorpe tube, causing the bobbin to rotate. If it's rotating, you know gas is flowing through the rotameter, and the bobbin is not stuck.
question
Describe the route a molecule (or set V) of N2O travels from the cylinder and from the pipeline to the patient.
answer
N20 flows from cylinders through a check valve into a pressure regulator (first stage) to 45 psi. N2O from a pipeline joins it (regulated externally to 45-55 psi). The gas then flows past a fail-safe valve that shuts off if fresh O2 flows less than 25 psi. It then goes through a second stage P regulator to ~15 psi, flows through N20 rotameter (controlled flow via needle valve), joins O2 (which enters AFTER N2O), enters through vaporizers. It then passes a pressure relief valve (and enters scavenging if overpressured), passes a outlet check valve, and to the patient breathing circuit.
question
Describe the route a molecule (or set V) of O2 travels from the cylinder and from the pipeline to the patient.
answer
O2 flows from cylinders through a check valve into a pressure regulator (first stage) to 45 psi. O2 from a pipeline joins it (regulated externally to 45-55 psi). There is one pathway that goes via O2 flush valve directly to patient breathing circuit. The other pathway is passes a main on/off switch, an O2 supply low pressure alarm, and flows past sensor for the failsafe valve, which will stop N20 Flow if O2 flow is less than 25 psi at this point (should be 45). It then passes a second stage P regulator to 15 psi, enters rotameter (controlled flow via needle valve), joins flow from all other carrier gases as the LAST GAS to enter the system. It then passes a pressure relief valve (and enters scavenging if overpressured), passes a outlet check valve, and to the patient breathing circuit.
question
What gas is added last to the low pressure circuit? Why?
answer
Oxygen. To present lowest risk of hypoxic mixture - the less circuit AFTER the O2 joins, the less chance of a leak in the post-O2 part of the circuit.
question
How should a high pressure tubing transducer system be calibrated?
answer
System zeroed with transducer at approximate level of aortic root, eliminating effect of fluid column on readings.
question
What is NIOSH?
answer
National Institute for Occupational Safety and Health. It sets guidelines concerning control of waste anesthetic gases.
question
What is the highest allowable trace N2O contamination in ppm for the OR, according to NIOSH?
answer
25 ppm
question
What is Pouiseuille's equation? WHere does it apply?
answer
To laminar flow through a tube, a law of friction. Flow = pi x r^4 x P gradient down tube / (8 x length x viscosity) = pi x r^4 x deltaP / (8 x L x mu)
question
What are the vapor pressures for each major anesthetic agent?
answer
Des - 669, Halothane 243, Iso 240, EN - 172, Sevo - 160.
question
A volatile anesthetic liquid containing what same or similar physical property can be placed in an agent-specific vaporizer to reach the same concentration accurately?
answer
Vapor pressure - Halothane and Iso; Enflurane and Sevo have similar vapor pressure pairs. DES >> H/I > E/ S
question
What compresses the ventilator bellows in the standard anesthesia ventilator?
answer
Compressed O2. Electrical power is used for TIMING CIRCUITS, not to power the bellows.
question
What are five types of rotameter indicators? Which are read at the middle, and which at the upper rim of the indicator?
answer
Ball floats are read in the middle. Skirted and nonskirted Bobbins (bullet shaped), H floats, and nonrotating (I shaped)floats are read at the upper rim.
question
What is the PIN index safety system? PISS..
answer
Used on cylinders to prevent use of wrong cylinder
question
Describe relationship of Pressure and volume in the N2O cylinder in terms of estimating volumes.
answer
There is gas and liquid in the cylinder. The pressure guage reads 750 psi until 3/4 of the *potential* gas has left the cylinder. N2O cylinder contains 1590 L total, so when the psi falls below 750, 400L is left, or less.
question
What pressure is exerted by a 10 cm H20 fluid column in an arterial system? Why is this helpful?
answer
7.5 mmHg. This can be used to estimate pressures based on transducer location relative to zeroed location,
question
What safety precautions should be used in handling compressed gas cylinders?
answer
No extreme temps, unwrapped from packaging, no flames, no oily hands
question
What is the splitting ratio? What kind of vaporizer uses it? What type does a copper kettle use?
answer
In variable bypass vaporizers, where total gas flow is split between variable bypass and vaporizer chamber with agent, it is the ratio of flows, which depends on anesthetic agent, temperature, and vapor pressure, and concentration dial setting. This is different from a copper kettle, which is a measured flow vaporizer, where flow of O2 is controlled on a separate flowmeter, mixing with gas emerging from the vaporizer at saturate vapor pressure, to produce desired concentration.
question
How do you determine Vt delivered to a patient in MV?
answer
Both fresh gas flow and TV delivered by bellows contributes to delivered TV to patient because the ventilator Pressure relief valve is CLOSED during inspiration. Add TV from bellows to the portion of FGF that occurs during inspiration, calculated b FGF rate, I:E ratio, and resp rate. For example, with FGF 6, RR 10, and I:E 1:2, duration of each breath is 6 sec (60 sec / 10 breaths), of which 2 seconds ( 2 in, 4 out for total ration 1:2 i:e) is inspiratory. At 6 L /min or 100ml/sec, there is a 200ml augmentation by FGF.
question
What psi is delivered to the anesthetic circuit by the O2 flush valve?
answer
50 psi. THere is no second stage pressure regulator.
question
What volatile gas makes Compound A? Which Co2 absorbing substance is worse at making it?
answer
Sevo. Baralyme > Soda Lime.
question
What gas can be produced with a machine rurnning overnight with high flows? What factors predict its production and what should be done to prevent problems?
answer
CO, with dessicated soda lime (or baralyme). Worse in dry absorbent, more CO produced by baralyme, use of high concentration of volatile anesthetic, high temperature, and specific volatile used (des > En > iso >> Halo/Sevo). You should change the CO2 absorbent.
question
What is the highest allowable trace volatile contamination in ppm for the OR, according to NIOSH, WHEN USED IN CONJUNCTION with N20?
answer
0.5 ppm
question
What safety device is the last mechanism of defense to prevent hypoxic mixture? Where is it located?
answer
The O2 analyzer must be located in the INSPIRATORY limb of the patient circuit, and NOT in the fresh gas supply line.
question
What is the pressure-relief valve, what does it do, and where is it located? What happens if it gets stuck?
answer
AKA the spill valve, it functions as part of the VENTILATOR (mechanical, aka bellows) to allow the release of excess gas from the patient breathing circuit into the waste gas scavenging circuit after full expansion of the bellows. It is a measure to prevent patient barotrauma, which can occur if it is stuck, where pressure would build up in the circle system and would be delivered to the patient.
question
Describe the mechanics of the pressure-relief valve within the bellows circuit, starting with the driving gas, and ending in the scavenger circuit.
answer
During INSPIRATION: Pressurized O2 (driving gas) enters past a TV control dial (set by user), into the bellows chamber and drives the bellows down
question
T or F: The use (initiation or discontinuation) of nitrous oxide can affect the vaporizer output. Why or why not?
answer
True, explained by the solubility of N2O or other carrier gases in the volatile liquid. Nitrous oxide enters the vaporizer chamber and dissolves into the volatile liquid when N2O is initiated, decreasing vaporizer output. When N2O is stopped, N2O agent comes out of volatile solution, transiently increasing vaporizer output.
question
What are the four phases of the capnogram.
answer
Inspiratory baseline, expiratory upstroke, expiratory plauteau, inspiratory downstroke
question
What is the significance of capnogram with inspiratory baseline above 0?
answer
There is rebreathing of CO2. DDx: Exhausted CO2 absorbent, incompetent expiratory valve, or gas channeling through the CO2 absorbent. An incompetent inspiratory valve is possible as well, but would be associated with a slanted inspiratory downstroke.
question
What does the expiratory upstroke of the capnogram represent, and what does it mean when it is slanted?
answer
Fresh gas from anatomic dead space is replaced by Co2 rich alveolar gas, normally steep. DDx for slanted shape includes partial airway obstruction of patient or breathing system (COPD, bronchospasm, kinked ETT), sidestream analyzer sampling too slowly, response of sampler is too slow for patient RR.
question
What does the expiratory platuea of the capnogram represent, and what does it mean when it is extended/lengthened?
answer
A slow but shallow increase in CO2 due to imperfect V:Q matching in alveolar air units, seen in normal capnogram. When it is extended, this can be due to partial airway obstruction of patient or breathing system (COPD, bronchospasm, kinked ETT).
question
What does the inspiratory downstroke of the capnogram represent, and what does it mean when it is slanted/blunted?
answer
Represents rapid influx of gas washes out Co2 from sampling site, normally very steep. When it's slanted/blunted can be due to incompetnent inspiratory valve, slow mechanical inspiration, slow gas sampling, or CO2 partial rebreathing.
question
What movement of the neck moves the carina upwards in an intubated patient, increasing risk of endobronchial intubation? Which movement increases risk of extubation and pharyngeal intubation
answer
Flexion of the neck: endobronchial intubation; extension: extubation. Lateral rotation - 0.7mm displacement away from carina.
question
What are 2 serious immediate complications of ET extubation and their appropriate interventions?
answer
1) Laryngospasm - 100% O2, jaw thrust; if ineffective, Sux. 2) Aspiration of gastric contents - suction, assess oxygenation and need for reintubation, CXR
question
T or F: Pharyngitis (post-extubation) is more common in males due to thinner lining of posterior VCs compared to females.
answer
False. More common in females for the same reason.
question
What are the delayed complications of tracheal intubation?
answer
Lanrygeal ulceration, tracheitis, tracheal stenosis, VC paralysis, arytenoid cartilage dissociation.
question
What factors in the anesthesia machine help to kill bacteria.
answer
Shifts in humidity and temperture in anesthesia machines may be the most important, but also: high O2 concentration and metallic ions
question
What safety system prevents incorrect connections of gas lines to anesthesia machines?
answer
The diameter index safety sytem. The TANKS use the pin safety system.
question
What is the formula for the vapor effluent gas volume (mL) from a vaporizing chamber of a BUBBLE THROUGH vaporizer?
answer
VO = (CGF x SVP) / (Pb - SVP) VO (vaporizer output in mL) = CGF (carrier gas flow in ml/min) x SVP (saturated vapor pressure, mmHg, of volatile anesthetic) / [Pb (barometric pressure) - SVP].
question
How does flow of carrier gas influence vaporizer output at low / high rates?
answer
At flow rates less than 250 ml/min there is insufficient pressure to advance volatile agent upwards out of the vaporizer reservoir, so output will be less. At high flow rates > 15 L / min there is insufficient mixing in the vaporizer chamber, so output will be less.
question
How does pulse oximetry work?
answer
Estimates SpO2 by measuring light transmitted through pulsatile vascular beds, measuring AC and DC components of light absorbance at 660 and 950 nm, using a ration of absorbance: ratio (R) = (AC660 / DC 660) / (AC940 / DC940)
question
What Hb species are accurately measures by pulse ox, and what species affects the pulse ox?
answer
Oxyhemoglobin and reduced hemoglobin are accurately measures. Fetal Hb has minimal effect due to extinction coefficient similar to adult forms. Carboxy and Methemoglobin cause inaccurate measurements.
question
What dyes affect pulse ox and how?
answer
Dyes that absorb light at 660 or 940 nm affect value of R. Methylene blue has the greatest effect of SaO2 because extinction coefficient is most similar to oxyhemoglobin. Indigo carmine, indocyanine green, elevated bilirubin can also affect the measurements. HbF has little effect.
question
How does Helium affect mass spectrometer readings and why?
answer
Helium is not detected by standard mass spectrometers because it has a mass charge ratio of 4, and is not detected by collector plate system, leading to erroneous reading. Thus the standard (carrier and volatile gases) will be summed to 100% as if helium were not present. In 50% He, all readings would be approx 2x real values . Thus real concentration would be half the read value in 50% He.
question
T or F: If a volatile vaporizer is filled with a volatile of a higher saturated vapor pressure than the intended designated volatile, there will be a higher than expected output concentration.
answer
T. In order of vapor pressures from lowest to highest: Sevo (160)<= Enflur (172) <<< Iso(240) <= Halothane(243) <<< Des (669)
question
How does atmospheric pressure affect rotameter function? Does gas flow matter, and how?
answer
Gas density (directly proportional to atmospheric pressure) decreases with increasing altitude, whereas viscosity does not. The magnitude of the influence of alittude on rotameter depends on rate of gas flow. At low flows, laminar flow predominates, which is influence by gas viscosity, so there is minimal effect from low barometric pressure, and rotameter would be accurate. At high flows, turbulent flows predominate (influenced by density), so gas flow through the rotameter will be GREATER than expected at high flows.
question
Describe the 3 - 5 letter pacemaker code.
answer
1- Chamber paced (A, V, D); 2 - chamber sensed (A, V, D, O); 3 - response to sensing (I, T, D), 4 - programmability or rate modulation ( O, R), 5- multisite pacing (A, V, D).
question
What kind of pacemaker is used for patients with AV node dysfunction but intact sinus node activity?
answer
VDD - Ventricles paced, atria and ventricle sensed, inhibition and triggered response.
question
What are common mechanisms of trace gas pollution and what are ways to prevent them? What is the most common?
answer
Poor mask seal is the most common (use tight seal), any leakage site in the high or low pressure system or scavenging system - vaporizer, rotameter, Co2 absorber (regular machine checks), leakage at the ETT. Use of high gas flows in a circle system has no effect on gas contamination (no reduction) but could contribute to contamination if there is a leak.
question
What is the mathematical relation allowing prediction of volatile anesthetic uptake based on uptake in the first minute?
answer
The amount taken up in the first minute = amount taken up between squares of any two consecutive minutes. - eg - if 50cc taken up in first minute, 50cc is taken up between 4th (2x2) and 9th (3x3) minute, 9th(3x3) and 16th minute, 16th and 25th minute and so on.
question
What do the following do to the SSEPS: Volatile anesthetics, barbituates, etomidate, midazolam, opioids, muscle relaxants?
answer
Volatiles and barbituates decrease amplitude and increase latency, with a clinically insignificant degree in opioids. Midazolam decreases amplitude without change in latency. Etomidate increases latency and amplitude. Muscle relaxants have no effect on SSEP.
question
T or F - Sterile disposable anesthetic breathing system use (compared with reusable systems hygenically cleaned) and use of bacterial filter in anesthesia machines decreases risk of postoperative pulmonary infection.
answer
False. No significant difference.
question
Why does frost appear outside N2O cylinder during GA?
answer
Vaporization of liquid requires transfer of heat from objects in contact of liquid ( metal cylinder, surrounding air), and at high gas flows, vaporization is increased.
question
For noncardiac surgery, what temperature sites correlate with central temperature, and can warn adequately of MH?
answer
PA, esophageal, axillary, Nasopharngeal, tympanic membrane. Skin is insufficient for early MH detection.
question
What is a Thorpe tube? How does it work?
answer
A vertically positioned tapered tube containing a rotameter, smallest in diameter in the bottom. Gas enters below the float, elevating it until at rests when gravity balances the fall of pressure across the float. Rate of flow depends on pressure drop along the tube, resistance of the gas flow, Temperature, atmospheric pressure, and density and viscosity of the gases. Different gases have different desities and viscosities and are not interchangeable.
question
What is critical velocity in terms of gas flow, and what is the relevance to the use of Helium in patients with tracheal stenosis?
answer
Critical velocity is the flow at which a gas goes from laminar to turbulent. Helium has a GREATER critical velocity than N2, thus allowing more laminar flow. Helium also has a lower density than N2 (in Air), thus decreasing resistance to flow in turbulent flow. For these two reasons, there is decreased WOB.
question
What is the formula for FiO2 through a NC, and what is the max flow? What factors influence this formula?
answer
Assuming a NORMAL breathing pattern, each L/min of NC flow increases FiO2 by 0.04 above 0.21, to a maximum of 0.45. However with larger Vt or faster RR, FiO2 will be lower than expected.
question
In a closed scavenging system, what happens to the reservoir bag during expiration and inspiration? Why? What does it mean with the opposite happens?
answer
The reservoir bag expands during expiration and deflates during inspiration. During inspiration in MV, the ventilator pressure relief valve closes, directing ventilator bellows into patient breathing circuit. If the PRV is incompetent, there will be a direct communication between breathing circuit and scavenging circuitm and the reservoir bag would inflate during inspiration.
question
What color nail polish affects pulse oximetry the most and what can you do to prevent this?
answer
Blue - has peak absorbance similar to that of adult deoxyhemoglobin (660). You can remove the fingernail polish. Turning the probe 90 degrees can help.
question
What is the minimum MACROshock current required to elicit VFIB? Microshock?
answer
Macroshock: 50 - 100 mA (miliAmps), Microshock: 10 uA (microAmps).
question
What is the line isolation monitor?
answer
An alarm that goes off when grounding occurs in the OR or when the max curent that a short circuit could cause exceeds 2-5 mA. It does not interrupt electrical current or in itself prevent micro or macroshock.
question
What is the Pressure relief valve in the closed scavenging system?
answer
PRV is a positive pressure relief valve that prevents transmission of excessive pressure buildup to the patient.
question
T or F: Older variable bypass vaporizers do not compensate for changes in barometric pressure output. Explain how to calculate for the compensation.
answer
True. Lower pressures lead to higher vaporizer output. A % vaporizer dial setting will set a specific splitting ratio of flows between the bypass and vaporizer reservoirs, to create a specific volume of vapor at sea level pressures. When the same ratio of flow is used in a lower atmospheric pressure, barometric pressure is decreased, leading to greater Vapor volume, in principle using Boyle's law (P1V1=P2V2). The following equation applies: Vapor volume (mL) = Carrier gas (mL) x vapor pressure / (barometric - vapor pressure) = carrier gas volume x (ratio of vapor pressure to non vapor pressure)
question
What is the equation relating vaporizer volume output (mL) through a carrier gas (mL) relating vapor and barometric pressures?
answer
Vapor volume (mL) = Carrier gas (mL) x vapor pressure / (barometric - vapor pressure) = carrier gas volume x(ratio of vapor pressure to non vapor pressure)
question
What is the proper size of a BP cuff (oscillometric)?
answer
Width 40% of arm circumference.
question
What BP cuff malpositionings cause elevated BP?
answer
Width too small (<40% arm circuference), BP cuff too loose.
question
What is the most frequent cause of mechanical ventilator failure related to insuffucient O2 delivery to patient?
answer
Disconnection from patient.
question
What is the esopheal detector device?
answer
A bulb compressed (negative pressure), attached to ETT, and will remain compressed/collapsed if put into the esophagus, as the esophagus will collapse. Results in up to 30% rate of removal of correctly placed ETT tubes, however.
question
What is the typical difference between PaCO2 and ETCo2
answer
5-10mmHg, due to dead space ventilation. Shunt doesn't affect this.
question
If a vaporizer is tipped, what should be done before patient use?
answer
When the vaporizer is tipped, gas is spilled into the bypass chamber. High gas flow, low concentration (dial on) for 30 minutes.
question
What does the "T" dial setting on the vaporizer mean / do?
answer
Transport - if it spills during transport, the vaporizer chamber is separated from the bypass chamber, eliminating danger from spill over during tipping.
question
Which agents have similar splitting ratios?
answer
Splitting ration is ration of gas flows in the variable bypass vaporizer. Halothane/Iso (1:47), and Sevo/En (1:27/1:29).
