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
