SS Electricity - Fall23.pptx

Electricity Clay Freeman, DNP, CRNA Science in Anesthesia 1 Objectives Readings: Nagelhout: Chap. 15 Davis: Chap. 14, 15, 16 • Detail Ohm’s Law • Detail mechanisms of electrical currents & grounding • Describe the Line item Monitor & its function • Discuss OR electrical risks 2 Principles of...

Electricity Clay Freeman, DNP, CRNA Science in Anesthesia 1 Objectives Readings: Nagelhout: Chap. 15 Davis: Chap. 14, 15, 16 • Detail Ohm’s Law • Detail mechanisms of electrical currents & grounding • Describe the Line item Monitor & its function • Discuss OR electrical risks 2 Principles of Electricity Electricity is the flow of a charge. • Actual electrons do not move but rather their “charge” does Law of Conservation of Electric Charge: Amount of electric charge in the universe is constant • Charges are transferred • Electron Flow is negative to positive Coulomb’s Law: Describes the electrostatic attraction or repulsion between charges. • Electrostatic force follows a concentration gradient 3 Electromagnetic Radiation An electrical flow also has a magnetic field which occurs in tandem Oscillating magnetic and electric disturbances travel at 90° to each other while the waves move perpendicular An electric current produces a magnetic field. • Vice versa: A magnetic field produces an electric current in a 4 Ohm’s Law BP(V) = CO(I) · SVR(R) V=I·R Current  I (Amperes) Voltage  V (Volt) Resistance  R (Ohm) Current: I=V/R Amount of flow of electric charge Voltage: Electrostatic potential that pushes the charge. Describes the energy potential (electrical) gradient. Resistance: R=V/I Measure of opposition. Energy required to push electrons through a material 5 Electrical Flow 120 Volts Amper es Volta ge Resistan ce 0 Volts Electrical potential also influenced by material properties:  Insulators: oppose the flow of electric charge. Substances with stable/bound electrons  Conductors: any substance that permits the flow 6 Electrical Flow Electrical flow is delivered as either direct or alternating Direct Current - maintains the same polarity at all times so that flow is maintained in one direction. • Batteries Alternating Current - polarity direction is reversed periodically. • Everything else 7 Electrical Flow - Sine Waves voltage and current waveforms form a sinusoidal pattern Electricity is delivered at set frequencies (Repetitions) Frequency is the number of complete cycles per second Frequency is measured in hertz (kilohertz, 8 Clinical Examples 9 Power Energy expenditure is measured by electrical power P=VxI P (watts) = V (volts) x I (amps) Ex) 120 V x 15 A = 1800 Watts Power indicates the rate at which work is performed • Joule = watt-second Components convert the electrical power into other forms of energy (heat, light, motion) 10 Electrical Circuit Typical Electrical Circuit: Hot and neutral lead connect to a device to create a circuit for a flow of energy o Hot lead (+) o Neutral (-) o ~ Ground lead (three prongs) • Ground lead connects to the chassis of the device to return leaked energy to the Earth for dissipation Groun d 11 Types of Circuits Grounded System 12 Types of Circuits Ungrounded System No physical contact from power company into OR Grounded Non-grounded Isolation Transformer utilizes electromagnetic induction to provide galvanic isolation 13 Line Isolation Monitor LIM measures resistance which is created by leakage and unintentional grounding of lines 14 Line Isolation Monitor LIM measures ohms but machine is calibrated display ampere (mA)  Alarms at > 5 mA 15 A series of unfortunate events 1) Faulty equipment causes leakage which activates LIM alarm and “Grounds” the circuit 2) A “grounded” provider handles faulty equipment while it is active Hot Neutr al 16 Mechanisms of Shock Electrical shock occurs when a person completes or becomes part of an electrical circuit. Risks in the OR  “Wet procedure location”; surrounded by electricity, and equipment/wires 17 Types of Shock MACROSHO CK MICROSHO CK 18 Macroshock “Macroshock refers to large amounts of current conducted through the patient’s skin and other tissues” - Nagelhout Current Effect 1 mA 5 mA 10-20 mA >20 mA >50 mA 50-100 mA >2 A Threshold of perception max harmless current intensity Max "let go“ before sustained contraction Tetany of skeletal muscles Pain, Mechanical injury Threshold for ventricular fibrillation Asystole 15-30 A: Common household circuit breakers 19 Electrical Injury Factors that determine the degree of injury are:  Amount of current (Amperes)  Resistance encountered  The voltage  Current pathway  Duration of contact  Type of current AC more dangerous than DC due to muscle tetany • Also, it takes approximately 3x as much DC as AC to cause ventricular fibrillation 20 Electrical Injury The 3 major mechanisms of electrical induced injury are: 1. Electroporation alters cell membrane resting potential & electrolyte distribution 2. Conversion of electrical energy into thermal energy, resulting in burns and coagulative necrosis. 3. Mechanical injury from falls or violent muscle contraction. 21 Electrical Injury ~ Electricity follows the the path of least resistance ~ Body tissues differ in their resistance; tissues with greater moisture and electrolyte content conduct better. High resistance: skin, bone, fat Low resistance: nerves, muscle, vasculature 2 Important concepts: • Skin burns can appear mild, meanwhile, internal tissues and organs are severely damaged • The diffusion of current in the body tends to go in multiple directions 22 Ohm’s Law Applied: Resistance Skin Impedance is not a constant Factors that determine amount of current delivered in a shock are impedance and voltage potential I= V/R Ex) I=120v/10,000 ohms I = 0.0024 A or 2 mA - Now, consider the presence of moisture or cannulation ~500 ohms of resistance if skin is wet I=120 v/500 ohms = 240mA Decreased skin resistance allows for deeper burns that are more likely to involve internal structures23 Electrical Injury Classifications 4 categories of electrical injury: True: Circuit interruption with entry and exit wounds. • Unpredictable internal injury Flash (arc): external/skin only injury Flame: external source of fire injury (ex. Clothing) Lightning: DC exposure ~1/100 second at > 10,000,000 V. Temps up to 30,000 Kelvin. • Mostly superficial burns • Mechanical injury d/t rapid heating of surround air creates a shockwave up to 20 atms 24 Electrical Injury management Early clinical manifestations: • • • • • • • Thermal burns Trauma Respiratory arrest Rhabdomyolysis Compartment syndrome Seizures Sinus Tachycardia  Ventricular fibrillation Chronic manifestations: • Neuropsychological trauma • Chronic pain Electrical injury should be managed as a multisystem injury:  Evaluate subsequent traumatic injury (blunt trauma, unstable c-spine, etc)  High-voltage injuries = ↑ likelihood for rhabdomyolysis o If myoglobinuria, implement kidney protective strategies  Fluid Resuscitation: Extravasation unpredictable with included visceral 25 injury Microshock 1 A = 1,000 mA (milliamperes) = 1,000,000 μA (microamperes) Therapeutic: Currents delivered directly to the myocardium via intracardiac electrodes (ie. pacer wires) Iatrogenic: Current delivered inadvertently due to the presence of irrigation or cannulation Current Density = Current / Tissue surface area Microshock 100 μA (0.1 Ventricular mA): fibrillation Ex) 100mA to cause V-fib in macroshock Vs 0.1mA to create V-fib in microshock 26 Radiofrequency (Electrosurgery) Device focuses energy towards tissue which provide resistance in order to produce heat for cutting & coagulation.  Heat Produced = Current2 / Area Operates at a frequency of 500,000 - 1,000,000 Hz • Too high to fibrillate the heart  However, interferes with other electrical equipment (EKG, pulse oximeters, electrical implants, computers) Associated with lower postoperative day 1 pain 27 The ESU is identified as the ignition source in up to scores Electrosurgery Types of ESU: Monopolar – high current density generates heat at local tissue. Energy passes through patient to a dispersive pad and is returned to ESU. Bipolar – Comparatively lower voltage. Current passes between two forcep electrodes. No dispersive pad necessary Types of Currents: Cutting – continuous, low voltage, high density mode for concentrated high heat Coagulation – interrupted, high voltage, low density mode for dispersed dehydration 28 Regulator (That’s you) Dispersion pad should be positioned to guide energy away from implants and devices Also, Improper dispersion pad placement is a risk for electrical burn to alternate sites (EKG pads, temp probes) Avoid placement on Bony prominences, near implants/prosthesis, hairy areas, scarred/discolored tissue, or poorly perfused areas Last Resort: Electromagnetic interference reduced when surgeon uses bipolar. • If not feasible: short, intermittent, and irregular monopolar bursts at lowest energy setting possible 29 Electrocautery 30 Additional Resources • Anesthesia Equipment: Principles and Applications. 3rd ed. Ehrenwerth, Eisenkraft, Berry. Chap 24. • Clinical Anesthesia. 8th ed. Barash. Chap 5. • LIM: https://www.youtube.com/watch?v=xrI-eOUu8qg 31