Biomedical Engineering Reference
In-Depth Information
Figure 4.3-5 Surgical drill.
instruments. For example, bone saws, files, drills
(
Figure 4.3-5
), and mallets are commonly utilized in
orthopedic surgery. Surgical instruments are generally
made of carbon steel, stainless steel, aluminum, or tita-
nium, and are available in a range of sizes.
Electrosurgical units
The electrosurgical unit, or Bovie, is a surgical device
used to incise tissue, destroy tissue through desiccation,
and to control bleeding (hemostasis) by causing the
coagulation of blood. This is accomplished with a high-
powered and high-frequency generator that produces
a radio frequency (RF) spark between a probe and the
surgical site that causes localized heating and damage to
the tissue (Gerhard GC, 1988). An electrosurgical gen-
erator (
Figure 4.3-6
) operates in two modes. In the
monopolar mode, an active electrode concentrates the
current to the surgical site and a dispersive (return)
electrode channels the current away from the patient. In
the bipolar mode, both the active and return electrodes
are located at the surgical site.
Figure 4.3-6 Aspen Labs MF 380 electrosurgical unit.
impedance, energy waveform shape, and electrode type
and placement.
Most defibrillators are designed with technology to
monitor the patient's ECG signal and allow for synchro-
nized cardioversion. Synchronized cardioversion is the
delivery of energy to the heart during ventricular de-
polarization, or upon the detection of the QRS complex.
This feature serves to protect the patient by preventing
the inadvertent delivery of energy during the ventricular
refractory period.
Defibrillators
A defibrillator is a medical device that is used to deliver an
electrical shock to the heart. The shock is intended to
correct irregular electrical activity of the heart and to es-
tablish an organized rhythm. A shock of adequate power
and duration will cause the cells of the heart to simulta-
neously repolarize and allow a normal rhythm to return.
The defibrillator uses a capacitor to store the required
energy, measured in joules (i.e., watts per second), to
deliver the shock. A DC power supply charges the ca-
pacitor to the selected energy level.
Electrodes are used to deliver the electrical shock to
the patient. Electrode types include reusable paddles and
adhesive electrodes. External defibrillation is applied to
the chest of the patient with external electrodes or
paddles. An internal paddle set is used when defibrillation
is delivered directly to the heart. Factors governing the
set-up and performance of a defibrillator include patient
Temperature regulation devices
Temperature monitoring and regulation are crucial to
ensure the safety of a surgical patient (Vaughan, 1988).
Although heating and air conditioning controls in the OR
help to maintain a safe surgical environment, a patient is
at risk of suffering from the effects of hyperthermia and,
more commonly, hypothermia. Heat loss can be attrib-
uted to contact with conductive surfaces, exposed body
cavities, cold irrigation solutions, and convective heat loss
due to the considerable flow of air in operating suites. In
addition, the effects of anesthesia can impair the body's
natural mechanisms for maintaining proper temperature.
Several methods are employed to equalize a patient's
body temperature. Blankets, sheets, and clothing are
common methods of preventing heat loss. A blanket
