Regional anesthesia was the topic at the Wilhelmsbader Symposium '99 under the direction of Prof. Dr.
P. M. Osswald.
Pharmacology - Neurophysiology - Clinical Aspects
The history of regional anesthesia goes back more than 100 years when August Bier
performed the first spinal anesthesia experiments with cocaine.
The different regional anesthesia techniques became standard methods in today's anesthesia
practice through the evolution of this technique and through the introduction of more
tolerable local anesthetics.
Progresses made in pharmacology and neurophysiology plus the good clinical experiences
with high risk patients led to a renewed interest in regional anesthesia.
New insights in neurophysiology at cellular and molecular levels increased our knowledge
of the pathophysiology of pain. A better understanding of the pharmacological interactions
stimulates the development of new substances with higher selectivity, improved steering
characteristics and greater patient safety.
It is also because of the pharmacological possibilities, e.g. the combination of local
anesthetics and opioids that regional anesthesia techniques contributed remarkably
to the improvement of anesthesia quality and patient comfort.
Regional techniques are effective through the blockade of nociceptive afferences of
the peripheral neuron. This inhibits the propagation to central pain centers and leads
to the modulation of the neuroendocrine stress response. Technical fine tuning of
the standard procedures, the pharmacological option of combined use of local anesthetics
and opioids allow a very effective and save anesthesia and/or analgesia for the patient.
Individual application and weighing risks and benefits in light of a planned procedure
and the postoperative phase increase the acceptance by the patient and render the
best technique possible for the benefit of the patient.
The following contributions of experts in the fields of neurophysiology, pharmacology
demonstrate the “status quo” and the clinical applicability and efficacy of regional
anesthesia procedures.
B. N. Graf speaks of important and new aspects of the pharmacology and toxicology
of local anesthetics. He presents after a brief historical review the pharmacological
profile and the toxic characteristics of Ropivacaine the newest representative of
the pipicoloxylidid derivatives. The stereoselective characteristics of local anesthetics
and the clinical implication of the use of pure optical isomers with the example of
Ropivacaine are explained. Different experimental models have shown that there is
less cardiotoxicity with the S(-)-isomers of Ropivacaine and Bupivacaine. The clinical
use of this knowledge will contribute to the safety of the patient. Following case
reports there seems to be a faster stabilization and a higher rate of “restitutio
ad integrum” in critical situations after intoxication with life threatening cardiac
arrhythmias when Ropivacaine (pure S-isomers) is used compared to the use of clinically
available racemics of Bupivacaine.
Of importance for the clinical practice is the analgesic potency. Ropivacaine administered
epidurally has an almost equipotent analgesic effect compared to Bupivacaine. But
Ropivacaine in low concentrations appears to have a less distinct motor blockade than
Bupivacaine, which can be of advantage in post op pain management and obstetric analgesia.
This characteristic of Ropivacaine is most likely secondary to the different pharmacokinetic,
not because of the stereoselectivity.
Future studies will have to show whether Ropivacaine with its experimentally demonstrated
higher therapeutic range is clinically superior to Bupivacaine.
Mrs. R. L. Moser reports about postoperative cognitive dysfunction in geriatric patients;
in current literature reported as a common problem with an incidence of 60 %.
This complex of symptoms can present from small decrements of cognitive functions
up to the full picture of a delirium and can endanger the patient significantly. This
might result in further complications delaying recovery and prolonging stays on cost
intensive floors. A diffuse reversible impairment of the cerebral oxidative metabolism
probably secondary tissue hypoperfusion appears to be responsible pathophysiologically
for this clinical picture. Etiologic factors include the type of surgery, pharmacological
reasons, preexisting cerebral and cardiovascular diseases, metabolic disorders, infections,
psychological factors as well as the anesthesia technique performed. The crucial question,
whether the incidence of cognitive dysfunction with regional anesthesia techniques
is lower is discussed. This question cannot be answered yet clearly because of the
limited data available at this time.
Appropriate premedication, sufficient pain management, maintenance of an adequate
cerebral perfusion pressure, correction of metabolic derangement and avoidance of
potentially delirium causing substances is important for the prophylaxis of cognitive
dysfunction.
R. Likar presents up-to-date recognition of peripheral opioid receptor as shown in
studies with oral surgery patients. An inflammatory process seems to be necessary
for locally applied opioids to act as analgesic as shown in animal experiments, which
has been confirmed in clinical studies. Locally administered opioids show little adverse
effect - an interesting starting point for the treatment of painful inflammatory processes.
It is becoming more important to look at the efficiency and cost-benefit-ratio in
a health environment where economic pressures are rising.
Regional procedures under an economic viewpoint are analyzed in Mrs. T. Koch's contribution.
It is decisive to look at the total perioperative phase since the overall costs are
mainly determined by the postoperative morbidity and the duration of the stay in cost
intensive units. The perioperative morbidity is influenced by the pathophysiologic
and neurophysiologic effects of the surgical procedure on one side and by the anesthetic
procedure on the other side. There is no study yet that could demonstrate a general
superiority of one anesthesia technique over another; but newer studies suggest some
advantages of epidural anesthesia techniques over general anesthesia in respect of
the quality of anesthesia as well as the modulation of perioperative stress response,
particularly in patients with preexisting cardiovascular diseases.
Including current study results advantages and disadvantages of regional methods are
analyzed and discussed. Economic advantages of regional techniques are evident in
some studies showing lower morbidity and earlier discharges from ICUs and other care
units (post anesthesia care unit, special care units).
Regional techniques with catheter placement are an economic plus because of their
use for postoperative analgesia. The efficacy and acceptance by the patient is very
much determined by the preoperative explanation and introduction of the technique.
It is also determined by the interdisciplinary cooperation between anesthesia and
the operative services. Patient controlled analgesia (PCA) as well as continuous or
intermittent bolus administration of local anesthetics/opioids through a physician
have been established in many hospitals.
Mr. A. Kopf reports of intravenous and epidural PCA. He discusses critically the postulated
advantages of PCA, which appear to consist of an improved quality of analgesia, higher
patient contentment, a decrease of the amount of administered analgesics along with
a reduction of adverse effects of local anesthetics and opioids. Exact analysis of
published data and own experiences lead to the commonly accepted understanding that
careful patient selection and patient education including a 24 h pain service are
a prerequisite for the success of PCA. The author values alternative methods like
physician or nursing controlled analgesia equivalent. Continuous infusion administration
is recommended during the first 24 h for epidural analgesia because of the higher
efficacy. Overall it is important to realize that the efficiency and patient contentment
of acute pain care is determined more by organizational and personnel factors than
by the method itself.
Mr. Gerber presents convincingly the options and advantages of central neuraxial blocks
for vascular surgery. Patients scheduled for peripheral vascular procedures benefit
especially from epidural techniques; a decrease of sympathetically mediated stress
response leads to less activation of the coagulation cascade and simultaneously to
an improvement of the perfusion and rheologic conditions and also to a reduction of
thrombotic occlusive complications. He talks about particular issues regarding the
clinical application and performance of central neuraxial blocks in vascular patients.
The awareness of preoperative, intra- and postoperative anticoagulation and appropriate
laboratory testing is of great implication for the management of regional techniques.
The organizers of the symposium succeeded in pointing out new directions in regional
anesthesia underlined by the contributions from pain physiology, pharmacology and
clinical application through careful selection of topics and experts eliciting new
impulses for the daily practice. The lively discussions of the participants on regional
anesthesia reflects the large interest in this issue. T. Koch, Dresden
