- Ohm’s Law and principles of electricity
:
Ohm’s Law is E = I x R where E is electromotive force, I is current,
and R is resistance. This law of electricity can also be used for fluids with
a slight variation. Q = Delta P/R where Q is flow, Delta P is change in
pressure, R is resistance. This law has significance in that if forms the
basis for the physiological equation for BP where
BP = CO x SVR
- Direct and alternating currents
:
Direct current (DC) electrons flowing through a conductor always flow
in one direction. i.e. Batteries. Alternating current (AC) or the wall
outlet – alternates the direction of current between positive and negative
60 x per second. Watt is the amt of electricity work being done per
unit of time. One watt = E X I where E is volts and I is current. A watt is
the product of voltage and amperage. Wattage can be used for a term to measure
work and heat produced in electrical circuit. Wattage = square of amperage x
resistance. You can calculate amps if you know the volts and current. A 60
watt Light bulb on 120 volt circuit = ½ amp of current to operate since 60 is
divided by 120. Another measure to consider is the amt of electrical work
being done in terms of the joules. Ohm’s Law will apply only to DC not AC
since AC has more complex form of resistance known as impedance. Impedance
is the sum of forces that oppose electron movement in AC circuits. Ohm’s Law
for AC is E = I x Z where Z is impedance which is measured by resistance plus
capacitance. An insulator is a substance that opposes the flow of
electrons and therefore has high impedance to flow. It is the opposite of
conductor. A conductor allows the flow of electrons. Current is
the flow of electrons in one direction. Capacitance consists of 2
parallel conductors separated by an insulator and has an ability to store a
charge. It can measure the substance’s ability to store a charge. A battery
or DC is a source of power. 2 plates with an insulator in between. The circuit
is not complete so no discharge of stored energy. When you attach a conductor
it will then complete the circuit and have DC. AC flow will not need anything
to complete the circuit.
- Shock hazards
:
Macro: Large amt of current –
experienced at body surface through intact skin. Severity is r/t density of
current, amt of contact time and resistance of skin (i.e. – wet or dry skin)
and Micro: Small amts of current directed through a conduit – sources
such as an indwelling IV, temp pacer wire, swans. It needs a source to direct
it through the body to the heart. You may not even notice if you received
these shocks.
Types of shocks:
Sensations – 60 hertz AC for 1 second
1 milliamp = macroshock – tingling
10-20 mamp = "let go threshold" when
exceed 20 mamps – muscle contract and can’t let go
50 mamps = pain
100-300 mamps= Vfib (possibly) – resp system
remains intact
6000 mamps = or 6 amps = sustained myocardial
contraction, temp resp paralysis and if current density is high enough will
burn.
Micro:
100 microamps = Vfib
10 microamps – max Number that machine can
leak into environment. If machines leak more than that they need to go get
fixed.
- Concepts of power grounding
:
Grounding to electrically oriented people means grounding electrical power
where in the OR grounding is of electrical equipment. Differences btw power
equipment – power supply at home is grounded, in the OR it is not grounded.
All equipment and not the power supply in the OR are grounded. Normally power
is grounded – place to ground to is earth. Hospital is not earth grounded
but equipment is grounded. If power in the OR were grounded to earth then
anyone in the room could complete the circuit and become grounded. If the
patient were to become grounded would receive shocks.
Grounding pads for the electrocautery machine
– the pad is placed on the pt’s thigh usually to prevent them from being
grounded. It needs to be a large surface area to dissipate the heat and you
must look at the site and monitor it for burns.
- Line isolation monitors
:
In the OR it monitors the integrity of source of power. It will alarm when
power flows to ground at 2-5 microamps. If it leaks more than that it will
throw off the circuit breaker. It means a piece of equipment is not working
well so you must find the piece of equipment. The alarm could also be a result
of the cumulative affect of all the pieces of equipment plugged in and each
one having a small leak. If this happens then unplug the unessential pieces.
Each OR has its own system. The patient is the most vulnerable in the room for
suffering from shocks. The alarm doesn’t necessarily mean that current is
flowing but that there is a potential flow and there are affects if it leaks.
The patient grounding pads are so large to increase the surface area that
current passes through. If the area is small the current would cause a burn.
"Is patient grounded" Means that you are isolating the pt from being
grounded to ground which would complete the loop so it goes through the pad
and to the machine rather than using the pt as the ground.
- Current flow
:
ECG, pacemaker, MRI, CAT scan, fluid and invasive monitors, peripheral nerve
stimulators, defibrillator:
- Patterns of nerve stimulation
:
There are two types of neuromuscular blockers used 1. Depolarizing blocker and
2. Nondepolarizing agent.
The depol agent is succinalcholine which mimics
acetylcholine. It is 2 ach molecules bound together. It comes on fast and goes
off fast.
The nondepol come in 3 flavors. They are slow
to work and slow to wear off and are variable with each pt. 1. Short, 2.
Intermediate, 3. Long. Terms determine how long they work
1st nondepol was curare,
detubocurare is long acting, rockuronium works faster and is intermediate
acting 80-95 dose should last 45 minutes to one hour, vecuronium is
intermediate, pancuronium is pavulon, is long acting and is cheaper,
mivacurium is short acting, slow onset, rapid metabolism, is broken down by
pseudocholinesterase in the blood and can get a large histamine release;
cisatricurium is interm – special in that it isn’t metab like the rest but
is broken down by Hoffman’s elimination thus is used in pt’s with renal
disease.
The actual nerve stimulators: Use the
ulna most frequently with wrist pads. Can use tetanus or TOF (Train of Four)
The depol agent will give you twitches 30 sec after the agent, you should see
tetany (sustained muscle contraction) Causes general depol of all skeletal
muscles which causes a contraction. Will not have tetany for succs until after
5-6 minutes. With the nondepol 30minutes later will have "fade" 1st
electrical stim will give a good response then the next 3 stims will be less
since there is a partial blocking at the neuromuscular junction. Succs will
never have fade. It is an
"all or none" response. The TOF complete depol of al and have no
twitches until after 5-6 min and then see all 4 twitches back and no fade.
Succs uses the TOF and even if sees 4/4 twitches can still have 70% of neuro
blockade. Judge the extent of block by the depth of breathing and you can
always reverse with anticholinergic agents, which moves the drug off the ach
receptor sites. Can use the facial nerve at temple or ulna nerve, which is a
closer indication of diaphragmatic blockade. The diaphragm will come back
before the ulna and facial nerves. IN order to give a reversal agent you must
have a least one twitch back and no longer need muscle relaxation. If you give
the reversal without any twitches you can further the block.
- Principles of defibrillation
:
Use joules which is power in watts x seconds. The most effective time to defib
is at end expiration since there is less resistance and if using ventilator
will have more control over breathing. With each subsequent defib the
resistance decreases by 10%. With each defib myocardial muscle sustains more
damage. Must be aware of this and know that if the pt received multiple shocks
will probably need inotropic support especially in the heart room and coming
off bypass pump. The proper placement of electrodes are ant/post – higher
success rate but this position can be modified if need be. Usually don’t
need to defib anyone except in Cath lab with AICD insertions, pacers. Can have
pt awake or asleep.
- Lasers:
Must know the type of laser being used and what the appropriate eye protection
is. Different lasers absorb different things. LASER = light amplification by
stimulated emission of radiation.
Argon lasers
– show up as blue-green. The Hgb in pigments absorbs it. It is used for eye
surgery since it is poorly absorbed by water and can then be used for the
vessels in the back of the eye – it can be used to irradiate tissue and hgb
since it isn’t absorbed by vitreous of the eye.
CO2 laser
– mostly used for ENT surgery – emits infrared beam, which you can’t see
so they’ve put Helium/Neon laser with it, which emits a red beam (aiming
beam), tissues poorly absorb He/Ne. CO2 is very precise, almost no blood loss.
The heat generated produces immediate coagulation and it creates minimal
edema, which is important in airways. CO2 is absorbed by water in all tissues.
Yag laser
– works can penetrate tissues deeper than CO2 laser. Used for gyn procedures
– lap and regular abd. It is absorbed by dark tissue not by water. It also
has no color so the He/Ne is added for the infrared siting device.
- Hazards of laser use
:
Must cover the pt’s eyes with wet NS or H2O soaked gauze. Must also wear
goggles for you.
CO2 – wear pink glasses or clear plastic
Yag – wear brown or dark color glasses such
as green
Argon – yellow colored glasses
Must also wear a highly filterable mask esp if
they are doing gyn surgery to laser off venereal warts or cancerous tissue
since there is a plume of laser produced here and you don’t want to breathe
in this plume of viral disease or cancer.
- Anesthetic care of patients during laser
surgery
: If pts are having ENT
laser surgery you should use an ETT specific for laser surgery. The laser tube
contains a cuff that you fill with NS or water and blue dye in it so you can
see it if the cuff leaks. If this happens then reduce the FiO2 to minimum you
can for pt tolerance. If after all this you still have an airway fire then:
- Airway fire management
:
Turn off O2 source. Flood the area with irrigation and suction and remove the
burning plastic thing in the trachea. Reintubate and bronch and lavage. Avoid
using N2O since it can propagate a fire. PVC is very flammable and will have
flame and smoke. This is detectable right away so you flood the field. The pt
will have a very sore throat like an inhalation burn from a fire.
- Operating room fire management
: