Definition

·  Very high frequency AC, 0.5-2MHz

·  Note >100kHz no electrocution, only heating

Heating determinants

Proportional to

·  Current magnitude

·  Current density (high at the stick, low at the plate. Amp/cm2)

·  Current duration

Heating power

·  = current (A) x potential difference (V) per unit time

·  = I² x R (where R is inversely proportional to area)

Cut

·  100% duty cycle

·  0.5MHz

·  250-3000V

Coag

·  6% duty cycle

·  1-1.5MHz

·  Up to 9000V

·  Spray coagulation: arcing from the tip

·  Contact coagulation: contact with tip, desiccation occurs

Blend

·  Combination of both waveforms

Monopolar

·  Two connections: active electrode (high density) and neutral plate (low density)

·  More effective burning

Bipolar

·  Two sticks, high current density at each

·  More precise burning

Problem

Solution

Stray capacitance:

-Interfere with pulse oximetry or EEG

·  Plate and patient at earth potential

·  Machine incorporated into LIS

·  Use of low pass filters in other devices

Interference with cardiac devices:

-PPM: may falsely detect output

-AICD: may falsely detect ventricular arrhythmia

·  Place plate so that path avoids device

·  Use bipolar

·  Place magnet -> VOO or DOO mode

Plate burn

·  Put on intact skin, ensure good contact

Smoke -> cancer

·  Suction

·  Wear a mask

Fire, explosion

·  Avoid use near high concentration O₂

·  Use lower PiO₂, avoid N₂O in airway surgery

·  Allow prep to dry

Definition

·  Light amplification by stimulated emission of radiation

Features

·  Monochromatic

·  Collimated (parallel)

·  In phase (some point in wavelength)

Components

·  Energy source

·  Medium (gives name – e.g. CO₂)

·  Mirrors (optical resonator)

·  Aperture

How it works

·  Source excites molecules, electrons move to higher energy level

·  Electron moves down level -> photon

Classification

·  According to max possible exposure (MPE)

·  Class 1 (harmless) to Class 4 (incl medical)

·  Based on ability to burn skin and retina

Hazards

·  Skin

·  Eyes – painless retinal burn, focused by cornea and lens

·  Fire

Medium

Spectrum

Use

CO₂

Gas

Far infrared

Cut, coag

Larnyx, sinus

NdYAG

Solid

Near infrared

Prostate, thyroid

Argon

Gas

Blue-green

Retina, AVM

Bladder

General

·  Education and training

·  Dedicated person

·  Signs

·  Goggles outside

·  Non-reflective equipment

Surgical

·  Minimise exposure and use

·  Non-reflective matte surfaced instruments

Anaesthetic

·  Gas: FiO₂ <0.3, avoid N₂O

·  Tube: laser-resistant or covered or use jet vent instead

·  Cuff: saline or dye filled

·  Eyes: covered