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
What are the characteristics of a laser beam?
- Monochromic (photons of the smale waveform)
- Spatial coherence (parallel photons)
- Temporal coherence (photons in phase with each other)
- Collimated (travel in a linear direction)
These photons will have consistent energy released at the same wavelength, amplitude, frequency and time allowing it to be focused 100x better than ordinary light
What is power density in regard to lasers?
Power density is directly proportional to the power (W) that a laser can deliver and inversely proportional to the surface area that the beam strikes
PD = W/cm^2
What is the focal length of most lasers
1-3mm
What are the 4 basic laser-tissue interactions?
- Absorption
- Transmission
- Scatter
- Reflection
What are the three forms of tissue injury formed by lasers?
- Photothermal - Energy of light converted to heat causing ablation and coagulation
- Photochemical - Energy of light breaks chemical bonds
- Photomechanical - Direct destruction of the cell lipid bilayer membrane and DNA (lithotripsy and cancer ablation)
List some potential uses of a CO2 laser. What size vessels will it seal?
- Oral surgery
- Skin recon
- Upper airway surgery
- Staphylectomy
- Perianal/rectal surgery
Seals vessels <0.6mm
What form of laser is good for cutting bone? Why?
Er:YAG
It is absorbed by hydroxyapatite
What are the safety considerations when using a laser?
- Toxic smoke production - must have a suction evacuation device
- Fire Hazard
- Ocular hazard - wave-length specific safety goggles
- Potential mutagenesis
