Basic Priniciples of Anesthesia Midterm
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Used CO2 to perform surgery and asphyxiate small animals, closest to surgical anesthesia
1st surgical anesthetic use of ether on humans
unsuccessful demonstration with N20 at MGH
chloroform and morphine
1st rapid acting IV anesthetic
- thiopental developed after- more potent and rapid acting
Sr. Mary Bernard
1st CRNA is the US
mother of anesthesia, developed 1 drop method, trained nurses and doctors, most famous CRNA of 19th c.
established Lakeside Hospital School of Anesthesia, founder of AANA (then NANA)
Omnibus Budget Reconciliation Act of 1986
- -Allowed CRNAs to bill DIRECTLY for services, so no disincentive to use a CRNA
- -Payments developed for CRNA alone, MD alone, and CRNA/ MD
- -Tax Equity and Fiscal Responsibility Act of 1982
- -Sought direct reimbursement for CRNA care
- -Developed 4:1 ratio for supervision
- -Anesthesiologists are reimbursed based on supervision
- -7 conditions must be met before payment by Medicare given
High pressure part of the anesthesia machine
cylinders and hangar yokes, cylinder primary pressure regulators, cylinder pressure gauge, check valve assembly
Medium pressure part of the anesthesia machine
cylinder supply source (45 psig), pipeline source (50-55 psig), oxygen pressure failure devices (O2 failure safety device, O2 supply failure alarms), O2 flush valve, flow control valve
Low pressure part of the anesthesia machine
Flow meter indicators and tubes, check valve, low flow pressure reducing regulator (if present), vaporizers, common gas outlet
scavenging system purpose
- -collection and removal of waste anesthetic gases from the OR
- -standards set by OSHA
Cylinder pressure of O2
Cylinder pressure of N2O?
What cylinder pressure enters the anesthesia machine?
40-45 psig (reduced by pressure reducing device)
What's the pipeline pressure?
- AKA pop-off valve
- -limits max pressure during manual vent.
- -open when pt spontaneously breathing
- -downstream of PEEP
- -adjustable pressure limiting valve
- -releases excess gas to scavenger system in manual vent
- -prevents barotrauma
misfilling, contamination, tipping, overfilling, underfilling, simultaneous admin of 2 volatiles, leaks (awareness)
Oxygen cylinder color
Air cylinder color
Oxygen E and H cylinder volume in L
N20 E and H cylinder volume in L
Air E and H cylinder volume in L
DOT and cylinders
DOT publishes requirements for manufacture, labeling, filling, qualification, transport, storage, maintenance, and disposition of medical gas cylinders
Per DOT, what information must be permanently stamped on the outside of cylinders?
- 1) type, material, and service pressure of cylinder
- 2) cylinder serial number
- 3) identifying symbol of user, purchaser, or manufacturer
- 4) manuf. date, original test date, inspectors official mark, 110% filling
- 5) manufacturers identifying symbol
- 6) retest markings
- 7) owner (around the neck)
Why is a diaphragm valve better than other valves (packing type)?
- -Stem is separated by a seat
- -Valve can be opened with just 1/2 or 3/4 turn
- -Seat does not turn so it's less likely to leak
- -Diaphragm prevents leakage
- -Better with flammable gases since leaking is less likely
Pressure relief valves on the cylinders
- -Vents tank's contents to atm P if pressure increases to a dangerous level
- -3 types (rupture disc, fusible plug, and pressure relief valve)
Type of pressure relief device on a cylinder, non reclosing
- -Type of pressure relief device on a cylinder, non reclosing
- -Melts at 212 F
- -Made of Wood's Metal
Pressure relief valve
- -spring loaded device
- -is recloseable
parts of the hanger yoke system
- -conical depression (holds tank into back of the machine)
- -washer (forms a seal)
- -check valve assembly
- -its a HIGH pressure system that connects the cylinder to the machine
3 purposes of the hanger yoke
- 1) orients cylinder
- 2) gas tight seal
- 3) unit direction of flow (check valve assembly), one way flow of gas out of cylinder into machine
Pin position of O2 on the hangar yoke
2 and 5
Pin position of N2O on the hangar yoke
3 and 5
Critical temp of N20?
Formula for how long an existing O2 tank will last
safety and health of employees in all industries
enforces medical gas purity
- -all who produce, transport, or use medical gases must comply with safety regs.
- -published number of standards
Advantages of circle system over Mapleson
- -CC adds components to avoid problems of Mapleson, such as:
- -like high FGF needed to prevent CO2 rebreathing, this cause waste of anesthetic gases, OR pollution, and loss of pt heat and humidity
How does the circle system differ from the Mapleson?
- -Low FGF can be used to allow rebreathing (economical, environmental, and physiologic advantages)
- -Normocarbia can be achieved with MH
- -length of tubing can vary
Components of the circle system
- -inspiratory and expiratory limb (length of tube does not affect amount of dead space or rebreathing)
- -inh and exh check valves (unidirectional flows)
- -APL valve
- -FGF inlet (gas enters CC from common gas outlet)
- -Y connector
- -Reservoir bag (allows accumulation of gas during exh so it's available for the next inh)
- -Canister with CO2 absorbent
fail safe valve
- -permits flow of other gases (N20, air, volatiles) only if there is sufficient O2 pressure to prevent hypoxic mixtures
- -all gas except O2 passes thru FSV
- -maintains O2 conc of at least 25% (+ or - 3%)
- -controlled by O2 pressure
O2 / N20 ratio controller
permits flow of N20 only if there is sufficient O2 pressure to prevent hypoxic mixture
soda lime components
80% calcium hydroxide, 15% water, 4% sodium hydroxide, 1% K hydroxide
80% calcium hydroxide, 20% barium hydroxide
how should the flowmeters on the anesthesia machine be arranged to prevent hypoxia if there's a crack?
O2 should be most downstream (closest to vaporizer and pt)
- -sevo degradation
- -increased risk with low flow (want at least 2 LPM) or closed circuit
- -increased risk with baralyme (vs. soda lime)
- -dried CO2 absorbent
- -can occur with any volatile but most often with des
- -baralyme > soda lime
- -low FGF rates
- -increased anesthetic conc.
- -higher temp leads to increased CO production
Second stage regulator
- O2 pressure dropped to 14 psig
- N2O pressure dropped to 26 psig
- -eliminates fluctuations in pressure supplied to flow indicator
- -bourdon gauge will still read 40-45 psig, so we won't even know it's there
Properties of soda lime.
- -Sodium hydroxide is the catalyst for CO2 absorption.
- -Turns violet when exhausted (but fluorescent lights can do this also)
- -CO2 absorption is a chemical process
- -Won't work if it's dried out!!!!!!
If the CO2 absorbent is exhausted how do you replace it?
Remove top canister and put new canister on the bottom
Clinical signs CO2 absorbant is exhausted
- -Increase ETCO2
- -Increased inspired CO2
- -Resp. acidosis
- -SNS stim (flushing, cardiac abnormalities)
- -Increased bleeding at surgical site
Vaporizer safety features
- -temp and altitude compensation
- -outside of breathing circuit
- -variable bypass (regulated output)
- -can't use more than one volatile agent at a time
- -keyed filling systems
What happens if you put the wrong agent in the vaporizer?
- -Pt gets the wrong conc. of the drug!
- -Ex: halothane (VP 240) in sevo (VP 170) vaporizer you'll get higher output
NIOSH acceptable waste gas levels for N20 (alone or with a volatile)
NIOSH acceptable waste gas levels for volatiles (alone or with N20)
latent heat of vaporization
- -energy for vaporization (either from liquid itself or outside source)
- -amt of energy consumed by a given liquid as it's converted to a vapor
- -speed with which heat flows thru a substance
- -increase thermal conduction means better heat conduction, we want high TC to maintain a uniform internal temp
- -number of calories required to increase the temp of 1g of a substance by 1 C
- -want high specific heat to minimize temp changes associated with vaporization
VP of des, sevo, and iso
- des 669 mmHg
- sevo 157 mmHg
- iso 238 mmHg
Passive humidity in the breathing circuit
HME, low flow, closed circuit
Active humidity in the breathing circuit
heated humidifier, flow over heated water bath, heated wire circuits
Vaporizor output is accurate between what flows?
- >250 ml and < 15L
- outside of this range will decrease volatile conc.
What happens if FGF is too low?
not enough flow to deliver the anesthetic gases and hypoxia
What happens if FGF is too high?
barotrauma, awareness, valve sticks
Major injuries associated with prone position.
eye, neck, breast, facial edema, VAE, brachial plexus, SC, thoracic outlet syndrome
Most HD and respiratory issues associated with prone position can be prevented with proper positioning, but what can happen with improper positioning?
Decreased CO, increased venous pooling, abd compression can decrease preload and TLC
Major injuries associated with lateral position.
damage to dependent eye and ear, brachial plexus, ulnar, peroneal nerve
HD issues associated with lateral position
hypotension with flexion or use of kidney rest, abd compresses the great vessel causing decreased venous return
Major injuries associated with lithotomy position.
peroneal, femoral, obturator, sciatic, and saphenous nerve, back pain, compartment syndrome
Perfusion issues r/t sitting position
- -hypotension, decreased CO and SV, increased HR and SVR to maintain MAP
- -decreased cerebral perfusion (good for cranis)
- -decreased renal blood flow
HD and respiratory issues assoc with supine
- -FRC and TLC reduced
- -Increased venous return, increased HR and myocardial contractility
- -Increased ICP, increased myocardial work, facial and pharyngeal swelling, increased PIPs, ETT movement, aspiration, decreased FRC
- -All worsened with increased degree of tilt
Most common nerve injury lithotomy position?
peroneal, femoral, obturator, sciatic, saphenous
Most common nerve injury lateral position?
brachial plexus, ulnar, peroneal
Most common nerve injury supine position?
Most common nerve injury prone position?
When would a VAE occur?
- -most common in sitting position
- -air is entrained due to negative pressure gradient between RA and veins of operative site
- -Sudden decrease ETCO2
- -Increase ETN2
- -Mill wheel murmur
Best means of monitoring for VAE intraop
Dopler on right side of heart, continuously monitor for mill wheel murmur
causes of compartment syndrome
- -lithotomy (#1), lateral, or prone
- -decreased muscle perfusion
- -trauma, embolism, tumor, vascular insufficiency
- -swelling of tissues in muscle compartment
- -due to radial nerve injury
- -1st, middle, and ring fingers affected
- -can't abduct thumb
- -can't extend metacarpal
pulmonary perfusion in lateral position
-V/Q mismatch as dependent lung has increased perfusion and non dependent lung has increased ventilation
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