CARDIAC EFFECTS OF HIGH THORACIC EPIDURAL ANAESTHESIA DURING BICYCLE EXERCISE: AN ECHOCARDIOGRAPHIC STUDY

Thoracic epidural anaesthesia (TEA) is considered to be the gold standard
anesthetic approach in lung surgery and also widely applied in patients
undergoing cardiac surgery.
The cardiac sympathetic outflow emerges from C5 to T5 levels, with the main
supply to the ventricles from T1 to T4 1. High thoracic epidural
anaesthesia(HTEA) results in blockade of these nerves and changes in heart
rate, left and right ventricular function and myocardial oxygen demand may
occur. Besides excellent postoperative analgesia and prevention of
postoperative pulmonary complications, TEA provides cardiac protection 2, may
avoid vasoconstriction of atherosclerotic coronary arteries 3 and may increase
the diameter of stenoticepicardial coronary arteries in patients with coronary
artery disease 4.
There are several studies on the effect of thoracic epidural anaesthesia on
left ventricular (LV) function, but the results are controversial 5, 6, 7, 8.
These studies were performed in baseline conditions, where cardiac
sympathicotonus is low and sympathicolysis by TEA might not be that
influential. The influence of upper TEA on circulation during physical exercise
has already been tested 9, 10, but these studies used questionable study
designs (repeated exercise tests) and the executed echocardiographic exam was
very limited. Furthermore, the influence of upper TEA on the performance of
the right ventricle (RV) under physical exercise has not been evaluated.
Recently, Rex and colleagues 11 demonstrated that in pigs TEA strongly
inhibited the positive inotropic response of the RV to acute pulmonary
hypertension, suggesting an important role for sympathetic nervous system.
Reason for us to conduct a study that non-invasively evaluates the effects of
TEA on biventricular systolic and diastolic function during exercise by using
pulsed wave tissue Doppler imaging. Tissue Doppler imaging (TDI) allows for
quantitative assessment of LV and RV function by measuring systolic and
diastolic velocities of the mitral and tricuspid annulus 12. We hypothesize
that the circulatory and cardiac effects of TEA will be most pronounced during
circumstances of increased sympathicotonus, which will be induced by an
exercise test on a bicycle. Cardiac function will be evaluated non-invasively
by trans-thoracic echocardiography (TTE), measuring systolic and diastolic
velocities of the mitral and tricuspid annulus by pulsed and colour coded TDI.
The increased sympathicotonus induced by bicycle ergometry in this study might
mimic conditions of increased sympathicotonus encountered during surgery and
acute hemodynamic changes. Therefore, this study might give some insight into
the effects of TEA on heart function and circulation during dynamic
circumstances such as surgery, making the results clinically relevant.

The primary objective of this study consists of:
To evaluate the HTEA effects on systolic and diastolic cardiac function in rest
and after different levels of exercise.

The seconderyobjectives of this study consists of:
To assess the difference in hemodynamic response between bicycling with and
without thoracic epidural anaesthesia

The design is a randomized cross over design with two study arms. We chose this
design to increase the power, allowing a smaller patient sample. This design
also eliminates the effect of timing of the tests on treatment effects. We
assume no carryover effects due to infusion of local anesthetics or due to
performing an exercise test.

Eighteen patients scheduled for thoracic surgery (full lateral thoracotomies or
pleurodesis by video-assisted thoracoscopic surgery/VATS) under thoracic
epidural anaesthesia (TEA) and general anaesthesiawill be assigned randomly to
one of the two study arms. The randomization will be performed using a computer.
After epidural administration of either NaCl 0,9 % or ropivacaine 0.75 %
patients will perform an exercise test on a bicycle. Each patient will perform
this exercise test at two different time periods:

Test period 1: Day before surgery.
Test period 2: Immediately before surgery.


In study arm A, the patient will receive an epidural dose of 6 ml of NaCl 0.9 %
in period 1 and 6 ml of ropivacaine in period 2. In study arm B patients
receive an epidural dose 6 ml of ropivacaine 0.75 % in period 1 and 6 ml of
NaCl 0.9% in period 2.

The study will be performed preoperatively in awake patients in the recovery
room. An arterial line 20 G will be inserted after local infiltration with
lidocaine 1% in the radial or brachial artery to monitor arterial blood
pressure (Edward Lifesciences LLC, Irvine, Ca, USA) and CO (Vigileo/FloTrac
system (software version 1.01; Edwards Lifesciences, Irvine, CA)). Intravenous
access will be established and an infusion of NaCl 0.9 % will be administered
at a rate of 5 mL/kg/h 17 starting with the epidural injection of ropivacaine
0.75 % or NaCl 0.9 %. All patients will receive an epidural catheter on the day
before surgery. All patients will perform an execise test according to a preset
protocol, starting 30 minutes after injection of NaCl 0.9 % (control group) or
ropivacaine 0.75 % (epidural group).
TTE examination and hemodynamic measurements will take place before epidural
injection, 30 minutes after epidural injection, three times during bicycle
ergometry exercise test and 10 minutes after recovery from the exercise test.

After having performed the first test on the day before surgery, patients will
return to the ward with an intravenous line and an epidural catheter. The
arterial line will be removed before returning to the ward and reinserted
before the second test the next day.

All echo data will be stored and analyzed in EchoPAC. Echodata from different
workloads and different study arms will be separated and labeled by one
researcher and stored under these labels in EchoPac systems. This way, another
investigator analyzing the echo data will be blinded to the study arm of the
patient, the patient number, the time period and to the workload.

RISKS AND ALTERATIONS VS ROUTINE

Thoracic epidural anaesthesia, insertion of an intravenous line and arterial
line are all part of normal routine for thoracic surgery. Supine bicycle
ergometry is not part of normal routine, but because of the supine positioning
during cycling and the patient being relatively young, we don*t expect any
additional risk*s or problems related to supine bicycle ergometry. TTE is a
noninvasive tool without known side effects. Participation in this study
implies extra time of the patients. We expect this study requires an extra 2.5
hours compared to normal routine. To our opinion this study doesn*t add any
additional risks compared to normal routine.

The study will be completed when the last TTE exam has been finished. The
investigation will not interfere with clinical care in any way. Monitoring,
dosage of drugs, sedation, treatment of complications and postoperative care
will be treated according to the department*s routine for each specific case.
The anaesthesiologist responsible for the patient during surgery will be
informed about the possible existence of dermatomal analgesia (the epidural
group) after TEA and will also be informed about problems encountered during
the study. After finishing the study, patients with or withoutinsufficient
dermatomal analgesia will receive an additional injection of LA through their
epidurals as part of the normal analgesic regime for surgery