Week 7 - OR Electrical, Fire, Laser, MRI Safety Flashcards
What law is electricity based on?
Ohm’s Law: V = I x R
V= potential difference I = current (represents flow) R = resistance
How is current measured?
Amperes (A) or Milliamperes (mA)
1 A = 1,000 mA
What are the types of current?
Alternating Current (AC): consists of current that reverses direction at regular intervals/Primarily to transmit electricity over long distances ex: outlets in OR
Direct Current (DC): flows in a single direction ex: batteries, laryngoscope handles, and backup battery for anesthesia machines
What is the frequency of a waveform and how is it measured?
Frequency of a waveform is the number of cycles that occur per one second
Measured in Hertz (Hz) or megahertz (MHz)
What type of frequencies is the human body more sensitive to?
More sensitive to lower frequencies (10 to 200 Hz) and less sensitive to higher frequencies (> 500,000 Hz)
What is the typical frequency in the OR?
60 Hz
-this is a low-frequency that is capable of the greatest risk of exciting and damaging human tissues (heart being most vulnerable)
When does an electrical shock occur?
when a person completes an electrical circuit
-one must be in contact with an active electrical circuit at two points
How can an electrical shock cause damage?
- Disruption of normal, physiological function of cells (muscle contractions, respiratory paralysis, cardiac arrhythmias)
- Burn/heat: as electrical current passes through resistance, it raises the temp of a substance (may not always be visible, but there can be a significant thermal injury to internal organs)
- degree of injury is directly related to the amount of current (Amperes) conducted & the time the current is conducted
What are the effects of different levels of current with 60 Hz?
1 mA = tingling/pain
5 mA = pain
15 mA = tonic muscle contraction/pain
50 mA = respiratory tonic muscle contraction/respiratory arrest
70-100 mA = ventricular fibrillation/cardiac arrhythmias/local burns
What is microshock?
- Very small currents applied DIRECTLY to the myocardium (only 20-100 microamperes are needed to induce cardiac arrhythmias)
- Since this amount of current is well below the threshold of perception and electrical circuit protection used in the OR, we must be aware of the risk of microshock in “susceptible” pts
Who are susceptible patients to microshock?
Those who have a direct conduit into the heart, capable of conducting electricity
*Pacemakers, AICDs, pulmonary artery catheters, central venous catheters
Describe a grounded electrical system
Current makes its way back to the ground
- typically, it was grounded through a pad on the patient (however, any grounding object can serve as a method of ground return)
- Alternative routes create the potential for burns
*Only ONE system fault creates potential for a shock
Describe an isolated electrical system
Circuit is completed not by the ground, but rather by the built-in generator circuitry (brings the current back to the circuit)
Consists of: Isolation transformer and Line isolation monitor
*TWO faults are required before a shock is possible with this system (one fault turns it into a grounded system)
What are the benefits of an isolated electrical system?
- Burn risk to patient is reduced (alternate grounding pathways to ground are mitigated, but there still is a risk of return electrode site burn)
- Two faults are required before shock is possible
What is the line isolation monitor?
- Monitors integrity of the isolated electrical system
- Gives a reading of how much “connection” there is between the supposedly isolated wall power wires and the ground – “Leakage” current
- Alarms (typically 2mA) if an unacceptably amount of current to the ground is possible (means the system is no longer isolated, but rather is grounded, thus only one additional fault could result in a shock)
- When monitor is alarming, try unplugging the last piece of equipment, as it is typically the problem
How does the electrosurgery units: Monopolar Cautery work?
- The active electrode is in the wound
- Current flows through the patient to the patient return electrode
- The return electrode is attached somewhere else on the patient
- For patients with pacemaker/metal/stimulators: place grounding pad away from the object and in a way where path between surgical site and grounding pad don’t intersect the device (burn can still occur if pad wasn’t applied correctly)
How does the electrosurgery units: Bipolar Cautery work?
- The active and return electrode are at the site of surgery (the two tines of the forceps)
- Only the tissue grasped is included in the electrical circuit
- No patient return electrode is needed
- Cutting ability is less effective
*safer than monopolar cautery to use in patients with pacemakers
What are the three equipment categories?
B & BF are for body surfaces only, but not to be connected to the heart
CF are safe to connect to the heart (EKG, CVP)
What are the indications for a pacemaker and for implantable cardioverter-defibrillator (ICD)?
Pacemaker: for recurrent, symptomatic bradycardia (sick sinus syndrome, atrio-ventricular block)
ICDs: for patients at risk of or with a history of arrhythmias requiring defibrillation
How do pacemakers work?
Fixed/Asynchronous: just pace the heart regardless of underlying rhythm
Demand: senses the heart and when the HR falls below a preset threshold, it begins to pace the heart – when the HR is above the preset threshold, it will inhibit pacing the heart
How do ICDs work?
ICDs are also pacemakers
-pacemaker function may be set so low that it is never used or the pacemaker can be very active in a patient that is pacemaker dependent
Senses the heart rhythm and if a high heart rate is detected, it will either overdrive pace the heart or give a defibrillating shock
What does each letter in the Pacemaker Designation represent?
1st = Paced Chamber (O, A, V, or D) 2nd = Sensed Chamber (O, A, V, or D) 3rd = Response to sense event (O, I, T, or D) 4th = Rate modulation (O or R) 5th = Multisite pacing (O, A, V, or D)
How do you interpret pacemaker designations?
1) Paced Chamber 2) Sensed Chamber 3) Response to Sensed Event
If 2 sensed, the pacemaker will 3 1.
Ex: VVI - if ventricle (2) sensed, the pacemaker will inhibit (3) the ventricle (1)
VAT - if atria (2) sensed, the pacemaker will trigger (3) the ventricle (1)
What effect does a magnet have on a pacemaker?
it “reprograms” the pacer into a fixed/asynchronous pacing mode (VOO, AOO, or DOO)
the paced rate of the magnet is manufacturer dependent but usually between 85-100 bpm
What effect does a magnet have on an ICD?
it turns off the ICD
the ICD won’t sense tachyarrhythmias nor give any defibrillation shocks or overdrive packing
*Has no effect on the pacemaker function
What is the risk of not placing a magnet on an ICD with monopolar cautery? Risk of placing the magnet?
Risk of Not Placing: the ICD can sense the monopolar cautery as a shockable rhythm and defibrillate the patient unnecessarily
Risk of Placing: while the magnet is on, the ICD will not defibrillate the patient, even if the patient goes into a shockable rhythm (if this occurs, take the magnet off or defibrillate with external R2 pads)
What is the risk of not placing a magnet on a pacemaker with monopolar cautery? Risk of placing the magnet?
Risk of Not Placing: while cautery is in use, the pacemaker can interpret this as electrical activity of the heart and not pace the patient (can be in asystole during time of cautery)
Risk of Placing: if patient’s HR is higher than the asynchronous rate, you can have an R on T phenomenon and cause an arrhythmia (use magnet only if pt’s HR is lower than the asynchronous rate of the magnet)
When is it recommended to place a magnet on an ICD with or without a pacemaker?
Place magnet if using monopolar cautery above the level of the umbilicus
- To prevent unintended defibrillation with misinterpretation of cautery
- if dependent on pacemaker function – need to have it reprogrammed by EP lab to asynchronous setting
