Force-Controlled Retraction during Cardiac Surgery

Cardio-thoracic surgery requires opening the thoracic skeletal cavity to
provide adequate access and exposure. The most common approach is to gain
access through the sternum along the anterior midline (the median sternotomy)
and to harvest the internal mammary artery (lifting the sternum). Access to the
cavity is achieved using mechanical retractors that exert significant forces on
the skeletal cage. Currently, there is no data in the literature regarding the
actual force and pressure generated during cardio-thoracic procedures. However,
retraction is known to cause tissue damage that can result in acute and chronic
pain post-operatively, as well as other co-morbidities.

Our research objective is to test the hypothesis that patient outcomes can be
improved through the development of instrumented retractors for cardiothoracic
surgery. By monitoring and controlling retraction forces, damage to the chest
wall and surrounding tissues can be minimized and post-operative pain can be
reduced. When succesful this retractor can be made commercially available so it
can be used widespread in order to minimize the burden on patients undergoing
median sternotomy.

Randomized double-blinded single center clinical trial.
80 patients will be enrolled in this study, 40 control patients and 40 study
patients. All patients will undergo a standard CABG-operation with the only
difference that a modified retractor will be used that is equipped with a
force-meter with which the forces used to open the thorax can be measured. in
control patients these forces are recorded but not visible to the surgeon,
while in study patients these forces are visible and the surgeon can reduce the
forces used.
After operation patients fill in pain analog scales to keep track of the
experienced pain. Another pain analog scale will be performed at the 2 week
post-operative clinic and more pain analog scale and quality of life
questionnaires will be performed by phone once every three month up one year.
The usage of pain relief medication in hospitals and pain medication at home
will be documented while performing the pain analog scale.

Control group: 40 patients will undergo a median sternotomy according to the
usual median sternotomy procedure. The LIMA will then be harvested using a
modified LIMA-retractor. This retractor records the forces used to open the
thorax.

Intervention group: 40 patienten will undergo a median setrnotomy. The LIMA
will then be harvested using a modified LIMA-retractor. In this case the
surgeon is able to observe the forces and influence these by open the thorax
more gradually.

The potential risks are minimal. All cardiac and chest procedures will be
conducted as they are with all other patients. We will use a commercially
available retractor instrumented with strain gauges that perform precisely the
same functions as conventional retractors, with the added information of the
retraction force profile measurements. The main difference will be slower,
force-controlled retraction, which may add 5 minutes to these procedures.
However, since the total length of this cardiac procedure is usually 2-4 hours
these extra minutes will account for a relatively small additional operation
time.
The burden on the patients is mainly filling in a pain analog scale every day
during their stay at the ward, which costs one minute a day. 2 weeks after
surgery another pain analog scale will be taken and from then on once every
three months. This will take 5 minutes a time.