Ch 15 - Electrosurgery and Lasers Flashcards

1
Q

Define electrical voltage, current and resistance and how the relate in regards to Ohm’s law

A
  • 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

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2
Q

What is power?

A

Power is the work performed expressed in watts

W = VI =RI^2

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3
Q

What is the difference between electrosurgery and electorcautery?

A
  • 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
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4
Q

List differences of radiowave surgery as compared to electrosurgery

A
  • Radiowave used current in the higher frequency range (>4MHz as compared to 500kHz)
  • Less tissue penetration
  • Less lateral tissue damage
  • No ground plate required
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5
Q

How does pure cut mode on monopolar deviced work in terms of waveform etc

A
  • 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

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6
Q

How does coag mode work in terms of waveform etc?

A
  • 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)
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7
Q

At what temperature does collagen denaturation occur? Dessication? Rupture? Char/carbonisation?

A
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8
Q

What percentage of the time is current available due interrupted coagulation waveforms?

A
  • 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
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9
Q

What are fulgaration coagulation and desiccation coagulation?

A
  • 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.
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10
Q

What are some disadvantages of monopolar electrosurgery?

A
  • Does not function well in liquid
  • Potential for burns ar grounding pad
  • Increase in histo scores of wound inflammation
  • Delays in wound healing
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11
Q

What are some advantages and disadvantages of bipolar electrosurgery?

A

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

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12
Q

What are the main mechanisms of injury from stray injury when using electrosurgery devicies in minimally invasive surgery?

A
  • 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
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13
Q

What size vessels is the LigaSure approved for?

A
  • Blood vessels 7mm or smaller (potential for ineffective haemostasis if vessels are thin walled or low in collagen)
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14
Q

List benefits of Harmonic Ultrasonic device over electrosurgical units

A
  • 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

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15
Q

What does laser stand for?

A

Light Amplification by Stimulated Emission of Radiation

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16
Q

What are the characteristics of a laser beam?

A
  • 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

17
Q

What is power density in regard to lasers?

A

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

18
Q

What is the focal length of most lasers

A

1-3mm

19
Q

What are the 4 basic laser-tissue interactions?

A
  • Absorption
  • Transmission
  • Scatter
  • Reflection
20
Q

What are the three forms of tissue injury formed by lasers?

A
  • 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)
21
Q

List some potential uses of a CO2 laser. What size vessels will it seal?

A
  • Oral surgery
  • Skin recon
  • Upper airway surgery
  • Staphylectomy
  • Perianal/rectal surgery

Seals vessels <0.6mm

22
Q

What form of laser is good for cutting bone? Why?

A

Er:YAG
It is absorbed by hydroxyapatite

23
Q

What are the safety considerations when using a laser?

A
  • Toxic smoke production - must have a suction evacuation device
  • Fire Hazard
  • Ocular hazard - wave-length specific safety goggles
  • Potential mutagenesis