Ch 15 - Electrosurgery and Lasers 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
What is power?
Power is the work performed expressed in watts
W = VI =RI^2
What is the difference between electrosurgery and electorcautery?
- Electrosurgery = Passing an electrical current from an instrument through tissues in order to achieve a desired result
- Electrocautery - Used electrical current to heat a metal instrument first before applying it to a targeted area
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
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 occurs 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?
- Seried of interrupted waves at a higher voltage
- Generator power setting 30-50W (spikes of V as high as 9000V can be produced at 50W)
At what temperature does collagen denaturation occur? Dessication? Rupture? Char/carbonisation?
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 continue 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 bleed 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.
What are some disadvantages of monopolar electrosurgery?
- Does not function well in liquid
- Potential for burns ar grounding pad
- Increase in histo scores of wound inflammation
- Delays in wound healing
What are some advantages and disadvantages of bipolar electrosurgery?
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
What are the main mechanisms of injury from stray injury when using electrosurgery devicies in minimally invasive surgery?
- Insulation failure
- Direct coupling (touches another metal instrument)
- Capacitive coupling - When 2 conductors or instruments are seperated by an insulator (air) and form stored energy
What size vessels is the LigaSure approved for?
- Blood vessels 7mm or smaller (potential for ineffective haemostasis if vessels are thin walled or low in collagen)
List benefits of Harmonic Ultrasonic device over electrosurgical units
- Simultaneously cuts and coagulates tissue
- Lower temperatures (50-100C vs 150-400C)
- Minimal lateral thermal spread
- Virtually no charring, desiccation or sticking
- Reduces smoke and vapour
However, does not reliable seal vessels >3mm
What does laser stand for?
Light Amplification by Stimulated Emission of Radiation
