1. Can Surgery be Made Safer ?
Charles E Meisch
Managing Partner
NBS Medical Products Inc.
Surgery is the branch of medicine dealing with manual operative procedures
for the correction of deformities, defects, injuries, and the diagnosis of
certain diseases. Traditionally, these procedures required open surgery
known as a laparotomy. Within the last few years minimally invasive
surgery, specifically laparoscopy which deals with the abdomen, has become
a replacement for many open procedures.
Many of the general procedures are performed using a rigid scope placed
into the abdominal cavity by small trocars. A mini scope is inserted
allowing direct visual observation. Additional trocars create space for
micro instruments to repair, remove, or diagnose problems without large
surgical cuts in the abdomen.
What is laparoscopy?
Laparoscopy is abdominal exploration using a type of endoscope called a
laparoscope. To improve visualization of the peritoneal cavity and ease
instrument manipulation during laparoscopy, the abdominal cavity must first
be filled with an insufflating gas producing a pneumoperitoneum.
Laparoscopic insufflators are specialized pressure-limiting gas flow
regulators that make it easy to establish and maintain a pneumoperitoneum.
To establish the pneumoperitoneum, one end of a piece of low-pressure tube
ranging in length from approximately 8 to 10 ft is connected to the
insufflator outlet port. The other end of the tube is connected to an
insufflation needle called a Veress needle.
Advances in Filters and Membranes
Early insufflators used reusable silicone tubing (generally one-quarter inch I.D.)
that allowed CO2 gas to flow from the insufflator through the tube and into the patient.
Within the last 10 years it became obvious that foreign gases going into the body
should be filtered and bodily fluids that might accidentally flow back through
the tube should be stopped prior to going into the insufflator. Once into
the insufflator, it becomes difficult to clean and recondition these
expensive units. Most Endoscopic companies who sell insufflators now offer
them with disposable tubing containing filters. The filters are usually
rated at .1 micron but can be anywhere from .1 to .3 microns and should be
hydrophobic.
When using low flow insufflators (9.9 to 15 l/min), standard off the shelf
gas filters are sufficient. But at the 20, 30, or 40 l/min range, special
filters are required. Some companies developed unique filters.
As the insufflator cycles gas into the filter it should not directly hit a flat filter membrane (flat
meaning the filter housing itself is flat in nature encompassing the
membrane). A baffle system is necessary to give gas, as the insufflator cycles, enough
time to get through the filter and not excessively cause back pressure, which could
momentarily and prematurely shut off the insufflator. Some flat filters, or using the wrong
membranes cause problems with the operation of the equipment, false shut downs, and
allowing overpressure alarms to go off. Other problems are false readings due to lack of
flow from the filter. The blocking of the filter, or other obstacles in the pathway may not
allow achievement of accurate pneumoperitoneum.
Membranes themselves have also evolved. Filter companies can design gas
filters that are hydrophobic both in the respiratory and in the
Insufflation area. Filters are available that produce the optimum amount of

2. flow at the least amount of cost. Using a flat filter on a high flow
insufflator at 1.8 to 2 cycles per second can damage the filter and not let
gas pass through or reach filter micron size.
Insufflators have also improved from 9.9 to 30 liters per minute, or even
higher flow rates. They all function in a similar nature and contain
sophisticated electronic feedback devices. Once set, high-flow units fill
the peritoneum to the appropriate pressure and maintain it as the body
absorbs some of the gas. Trocars may also leak some gas. Aside from the
geometry of the filter itself testing will clearly show that trying to push
a high flow of gas through a 1/4 inch hole with no reservoir becomes
virtually impossible.
Along with the geometry of the filter housing, filter membranes also
evolved. Aerosol droplets can bypass filters malfunctioning insufflators.
This also increases maintenance, physically restricts airflow, and more
seriously may lead to bacterial growth in the insufflator.
During the late 1950's, membrane technology expanded. Osmotic transfer of
salts across the membrane began in the area of desalinization and has lead
into kidney dialysis. Membranes could be designed to pass air but not pass
water and also filter out aerosols and bacteria from the air stream. This
membrane would be an analogous to a toy that makes soap bubbles where a
water film forms in a hoop. As air blows into the hoop a pressure
differential causes the film to bulge out and form a bubble. Reducing hoop
diameter increases the differential pressure (not force) needed to distort
the film, creating a fine net the size of the original hoop. With the
differential pressure increase the total force across the net is higher.
Another characteristic to consider is hydrophobicity. Air would be free to
move through the net until the net was touched by a liquid which would form
a film blocking the movement of air until the differential pressure across
the net was too great or the liquid was evaporated. Obviously, the net
would have to be some material which would cause liquid to form a film
across the intercies. The specific composition of membranes with these
properties is generally a trade secret of the membrane manufacturer,
however, the most common material is Teflon. The Teflon sheet is either
mechanically perforated or stretched to form tears or holes in the
material. Another method is to coat a netlike substrate with a chemical,
generally a silicone compound. This creates a hydrophobic membrane that
lets air flow freely until the membrane is wetted. At this point air-flow
is stopped as long as pressure differential is below the maximum level.
Air-flow through the filter must be maintained by the membrane. The
membrane must have sufficient small intercies to stop or entrap aerosol
fluids and microbes. Microbes are carried by the aerosol fluids. The
membrane must be secured either mechanically or by heat sealing in the exit
area of the filter.
Test results of new membranes are encouraging. Air flows at a normal rate
until liquid covers one side, when the filter shuts down. This saves the
insufflator from damage. Bacteriological testing showed these membranes
stopped pathogens and aerosols as well as any commercial microbial filters
and met HEPA and ULPA criteria.
Surgery Developments
Surgery was not at a stand still during the development of new filters and
membranes. New surgical tools were introduced that were micro in size along
with both laser and electrical knives. Both tools minimize bleeding by

3. cauterizing while cutting, however they produce dense smoke in the abdomen.
No one really knew what the smoke consisted of, but most agreed that it was
best kept out of the air. The solution was to develop a new type of filter
that could be connected to an exit port of a trocar and capture the smoke.
Lab tests showed that in the presence of this dense smoke, filters not
designed for smoke elimination could shut down in 30 seconds. Analysis of
the smoke showed it contained proteins, peptides, amino acids, and other
breakdown particles. In other tests, electron microscopic studies showed a
layer of these breakdown products had formed over the surface of the
membrane blocking airflow. Filter companies have spent a tremendous amount
of time and money to develop an inexpensive yet disposable smoke evacuator.
A filter that combines fluid stoppage along with smoke and bacterial
filtration to cleanse the expelled gas is now available. It is obvious that
this is needed to control cross contamination and infection and to protect
operating personnel from smoke caused by laser and electro surgery. The
designs have been rigorously tested and proven reliable. In the future,
technology will continue to improve. This is just another stepping stone in
the final attempt of surgeons to alleviate discomfort, shorten hospital
stays, curtail cross contamination, and protect operating room personnel.