\chapter{Diathermy}
Electric current produces heating, unfortunately, it can also cause the detrimental effects associated with
electrocution. These risks decline as the frequency of the current increases and become negligible above 1Mhz.
Nonetheless, the heating effect remains.\\
Diathermy exploits this to produce cutting or coagulation.\\
The electric current can flow between two poles of an instrument (e.g. biploar forceps), in which case there is very
little current flow beyond the immediate vicinity. However, the effects are limited and for more extensive
electrosurgery, a remote 'neutral' plate is used. The name is largely historical as this plate is isolated from the
mains. In order to prevent burning at the neutral plate, it must have a very much larger surface area than that of the
active electrode. As a result, the high current density at the active electrode produces significant heating, while the
low current density at the neutral does not.\\
If the diathermy current were able to return to the machine via other paths, then burns might result. In order to
prevent this, the diathermy power supply is isolated from the mains. Capacitors at each output of the diathermy also
prevent direct currents from other sources from passing through the machine.
\href{http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2492183/pdf/annrcse01495-0038.pdf}{Advantages of isolated diathermy}
\vspace{1in}Surgical diathermy \footnote{T[T]TFF}
\begin{enumerate}
\item Requires a large plate area
\item Uses a sinusoidal waveform
\item Requires the plate to be sited over an area with good blood supply
\item Operates at frequencies below 400kHz
\item Always requires an earth
\end{enumerate}
\vspace{0.5in}Surgical diathermy \footnote{FFTTF}
\begin{enumerate}
\item Commonly delivers 1kW of power
\item Operates at frequencies around 10kHz
\item Requires good contact of the indifferent electrode
\item May be uniploar or biploar
\item May be safely used on patients having cardiac pacemakers
\end{enumerate}
\vspace{0.5in}Regarding surgical diathermy \footnote{TTTFF}
\begin{enumerate}
\item High frequency current is necessary for its action
\item The same frequency current flows through the return plate as through the forceps
\item If the return plate is detached from the patient no current will flow
\item There is a risk of burning the patient at the plate since the same current passes through the plate as through
the patient
\item Earthing is still required even if biploar forceps are used
\end{enumerate}
\vspace{0.5in}Concerning Diathermy\footnote{}
\begin{enumerate}
\item Coagulation mode uses a sine wave pattern
\item Monopolar causes less dissipation than bipolar
\item To avoid ventricular fibrillation, a high frequency at 0.1 MHz is used
\item An isolating capacitor is used to give low impedance to high frequency diathermy current
\item Heating effect is calculated from current divided by area
\end{enumerate}
