Ch 15 Electrosurgery and Laser Flashcards
Define electrical voltage, current and resistance and how the relate in regards to Ohm’s law
Volatage (V) = the difference in potential between two points. (The force that drives particles across a potential difference). Volts
Current (I) = Represents the flow of electons. Amperes
Resistance (R) = The impedence to the flow of the electrons. Ohms
Ohm’s Law: V = IR or 1 volt = 1 amp x 1 ohm
Tissues with high resistance include calloused tissues and bone, whereas vascular tissues have very low tissue impedance
What is power?
Power is the work performed expressed in watts
W = VI =RI^2
the keyed number on the electrosurgical unit
What is the difference between electrosurgery and electorcautery?
Electrosurgery = Passing an electrical current from an instrument through tissues in order to achieve a sedired result = diathermy
The electrical current always travels the path of least resistance, always seeks ground, and must involve a complete circuit.
Electrocautery - Used electrical current to heat a metal instrument first before applying it to a targeted area
heat is produced when moving electrons encounter tissue resistance
List differences of radiowave surgery as compared to electrosurgery
Radiowave used current in the higher frequency range (>4MHz as compared to 500kHz)
Less tissue penetration
Less lateral tissue damage
No ground plate required
Electrosurgery requires a circuit for current flow: monopolar and bipolar
Tissue cutting occurs when there is sufficient energy to ionize the air gap between the active electrode and target tissue
continuous waveform at a low voltage makes the most effective cutting current; however, little hemostasis is achieved.
How does pure cut mode on monopolar deviced work in terms of waveform etc
Current is deliverely uninterrupted 100% of the time (and therefore V is low as W=VI)
Best cutting achieved with electrode held slightly away from tissue
Generator power settings 50-80W
Cutting occues where there is sufficient energy to ionise the air gap between the active electorde and target tissue, concentrating the spark to a small area and generating tissue temp in excess of 100C
How does coag mode work in terms of waveform etc?
Series of interrupted waves at a higher voltage
Generator power setting 30-50W (spikes of V as high as 9000V can be produced at 50W)
thermal effect of energy on tissues is dependent on
power settings (watts),
electrode dwell time or length of exposure,
the volume of tissue treated,
the contact type of the tissue to the active electrode
current (I) density
tissue impedance (R)
At what temperature does collagen denaturation occur? Dessication? Rupture? Char/carbonisation?
range considered necessary for protein or collagen denaturation and subsequent tissue shrinkage
What percentage of the time is current available due interrupted coagulation waveforms?
Current is available 6% of the time to heat the tissue.
Remaining 94% of the time the tissue cools to produce a coagulation effect
Higher voltage allows the current to contniue through the dynamic impedence of dehydrated or dessicated tissue
What are fulgaration coagulation and desiccation coagulation?
Fulgaration coagulation - holding the electrode slightly away from the tissue with a resulting arc and spark. Good if a discrete bleeded cannot be identified.
Desiccation Coagulation is achieved by direct contact of the electrode and tissue. Heats tissue more efficiently with deeper necrosis and thermal spread.
Coaptive coagulation is a type of desiccation coagulation which occurs when the lumen of a vessel is occluded by a metal instrument.
Monopolar (unipolar) electrosurgical
It provides hemostasis for vessels ≥2 mm diameter
current passes through the patient’s body toward the inactive electrode or grounding plate before returning to the generator.
patient is part of the electrical circuit
late be well secured under the patient and kept as large as possible for dispersing energy and avoiding burns
What are some pros/cons of monopolar electrosurgery?
compared to scapel
decreased operative time, blood loss, and postoperative pain, compared to scalpel incisions.
Does not function well in liquid
Potential for burns ar grounding pad
Increase in histo scores of wound inflammation compared to scapel
Delays in wound healing
bipolar
Bipolar devices consist of active and return electrodes incorporated into a single hand-held instrument so that the electrical current passes between the tips of the two electrodes
pros/cons bipolar
Advantages
- Much more precise
- Can be used in a wet environment
- Lower voltage and power setting
- Cosidered to be safer
Disadvantages
- Increased time for coagulation
- Charring and adherence can lead to tearing
- Limited use for dissection and ineffectual for cutting
