Systemic, but not pulmonary, hemodynamics are depressed during combined high thoraco-cervical epidural and general anesthesia in dogs

Effects of Thoracic Epidural Anesthesia on Neuronal Cardiac Regulation and Cardiac Function

Cardiac sympathetic blockade with high-thoracic epidural anesthesia is considered beneficial in patients undergoing major surgery because it offers protection in ischemic heart disease. Major outcome studies have failed to confirm such a benefit, however. In fact, there is growing concern about potential harm associated with the use of thoracic epidural anesthesia in high-risk patients, although underlying mechanisms have not been identified. Since the latest review on this subject, a number of clinical and experimental studies have provided new information on the complex interaction between thoracic epidural anesthesia–induced sympatholysis and cardiovascular control mechanisms. Perhaps these new insights may help identify conditions in which benefits of thoracic epidural anesthesia may not outweigh potential risks. For example, cardiac sympathectomy with high-thoracic epidural anesthesia decreases right ventricular function and attenuates its capacity to cope with increased right ventricular afterload. Although the clinical significance of this pathophysiologic interaction is unknown at present, it identifies a subgroup of patients with established or pending pulmonary hypertension for whom outcome studies are needed. Other new areas of interest include the impact of thoracic epidural anesthesia–induced sympatholysis on cardiovascular control in conditions associated with increased sympathetic tone, surgical stress, and hemodynamic disruption. It was considered appropriate to collect and analyze all recent scientific information on this subject to provide a comprehensive update on the cardiovascular effects of high-thoracic epidural anesthesia and cardiac sympathectomy in healthy and diseased patients.

The bifunctional effect of propofol on thromboxane agonist (U46619)-induced vasoconstriction in isolated human pulmonary artery

Propofol is known to cause vasorelaxation of several systemic vascular beds. However, its effect on the pulmonary vasculature remains controversial. In the present study, we investigated the effects of propofol on human pulmonary arteries obtained from patients who had undergone surgery. Arterial rings were mounted in a Multi-Myograph system for measurement of isometric forces. U46619 was used to induce sustained contraction of the intrapulmonary arteries, and propofol was then applied (in increments from 10–300 µM). Arteries denuded of endothelium, preincubated or not with indomethacin, were used to investigate the effects of propofol on isolated arteries. Propofol exhibited a bifunctional effect on isolated human pulmonary arteries contracted by U46619, evoking constriction at low concentrations (10–100 µM) followed by secondary relaxation (at 100–300 µM). The extent of constriction induced by propofol was higher in an endothelium-denuded group than in an endothelium-intact group. Preincubation with indomethacin abolished constriction and potentiated relaxation. The maximal relaxation was greater in the endothelium-intact than the endothelium-denuded group. Propofol also suppressed CaCl₂-induced constriction in the 60 mM K⁺-containing Ca²⁺-free solution in a dose-dependent manner. Fluorescent imaging of Ca²⁺ using fluo-4 showed that a 10 min incubation with propofol (10–300 µM) inhibited the Ca²⁺ influx into human pulmonary arterial smooth muscle cells induced by a 60 mM K⁺-containing Ca²⁺-free solution. In conclusion, propofol-induced arterial constriction appears to involve prostaglandin production by cyclooxygenase in pulmonary artery smooth muscle cells and the relaxation depends in part on endothelial function, principally on the inhibition of calcium influx through L-type voltage-operated calcium channels.

[Effects of propofol combined with indomethacin on contraction of isolated human pulmonary arteries]

OBJECTIVE

To investigate the effects of propofol combined with indomethacin on the contractile function of isolated human pulmonary arteries.

METHODS

Human pulmonary artery preparations were obtained from patients undergoing surgery for lung carcinoma. The intrapulmonary arteries were dissected and cut into rings under microscope for treatment with propofol or propofol combined with indomethacin. In each group, the rings were divided into endothelium-intact and endothelium-denuded groups and mounted in a Multi Myograph system. In propofol group, the rings were preconstricted by U46619 to induce a sustained contraction, and propofol (10-300 mmol/L) was then applied cumulatively. In the combined treatment group, the rings were pretreated with indomethacin (100 µmol/L) for 30 min before application of U46619 to induce sustained contraction, and propofol (10-300 µmol/L) was added cumulatively after the tension became stable.

RESULTS

Propofol (10-100 µmol/L) induced constrictions at low concentrations and caused relaxations at higher concentrations (100-300 µmol/L) in the pulmonary artery rings with prior U46619-induced contraction. Propofol caused stronger constrictions in endothelium-intact rings [EC₅₀=4.525∓0.37, Emax=(30.44∓2.92)%] than in endothelium-denuded rings [EC₅₀=4.699∓0.12, Emax=(31.19∓5.10)%, P<0.05]. Pretreatment of the rings with indomethacin abolished constrictions, and the relaxation was more obvious in endothelium-intact group [pD₂=3.713∓0.11, Emax=(98.72∓0.34)%] than in endothelium- denuded group [pD₂=3.54∓0.03, Emax=(94.56∓0.53)%, P<0.05].

CONCLUSION

Propofol induces constriction at low concentrations and relaxation at high concentrations in human intrapulmonary arteries with U46619-induced contraction. Indomethacin abolishes the constriction induced by propofol in isolated intrapulmonary arteries, suggesting that propofol potentiates U46619-mediated pulmonary vasoconstriction by promoting the concomitant production of prostaglandin by cyclooxygenase in pulmonary artery smooth muscle cells, and the mechanism for its relaxation effect may partly depend on the endothelium.

Orthogonal Polarization Spectral Imaging of the Microcirculation During Acute Hypervolemic Hemodilution and Epidural Lidocaine Injection

We used Orthogonal Polarization Spectral Imaging to examine the microcirculation of the vaginal mucosa in nine anesthetized patients during two consecutive anesthetic interventions: hypervolemic hemodilution using hydroxyethyl starch followed by thoracic epidural lidocaine. Images taken before and after each intervention were compared. During hypervolemic hemodilution, systolic blood pressures increased significantly, but functional capillary density remained unchanged. Epidural anesthesia decreased systolic and diastolic blood pressures, but there was no change in capillary density, venular diameter, or flow velocity. We concluded that when using Orthogonal Polarization Spectral imaging, no consistent effects on the microcirculation of the vaginal wall can be detected.

Patient-controlled cervical epidural fentanyl compared with patient-controlled i.v. fentanyl for pain after pharyngolaryngeal surgery

BACKGROUND

Analgesia after pharyngolaryngeal surgery is commonly provided through the i.v. route. The aim of the study was to compare cervical epidural administration of fentanyl with the i.v. route for postoperative analgesia after pharyngolaryngeal surgery.

METHODS

In a randomized double-blind study 42 patients received fentanyl via patient-controlled analgesia (PCA) either through the i.v. route (PCA-IV group, n=22) or through the cervical epidural route (PCA-Epid group, n=20). Identical PCA settings were used in the two groups (bolus dose: 1.5 microg kg(-1), bolus: 25 microg, lockout interval: 10 min, maximum cumulative dose: 400 microg per 4 h). Analgesia at rest and during swallowing was evaluated using a visual analogue scale.

RESULTS

Analgesia at rest was better in the PCA-Epid group than in the PCA-IV group but only 2 and 6 h after surgery (P<0.02). There was no difference in analgesia during swallowing. Cumulative doses of fentanyl were similar {PCA-Epid group: 1412 microg (912), PCA-IV group: 1287 microg (1200) [median (IQR)]}. The Pa(o(2)) showed a significant decrease between the preoperative and postoperative period, but this decrease was identical in the two groups [PCA-IV-group: 11.47 (2.4) kPa vs 8.27 (0.9) kPa; PCA-Epid group: 11.33 (1.9) kPa vs 9.20 (2.4) kPa for preoperative and postoperative period respectively].

CONCLUSIONS

The study results show that cervical epidural analgesia provides marginally better pain relief at rest with no decrease in the fentanyl consumption. The use of the cervical epidural administration of fentanyl is questionable because of the possible complications of the technique.

Non-analgetic effects of thoracic epidural anaesthesia

PURPOSE OF REVIEW

This review presents a brief overview of the non-analgetic effects of thoracic epidural anaesthesia. It covers the cardiac, pulmonary and gastrointestinal effects of thoracic epidural anaesthesia. The results of newer studies are of particular importance regarding mortality and major morbidity after thoracic epidural anaesthesia.

RECENT FINDINGS

The clinical effects of thoracic epidural anaesthesia are mainly attributed to a transient thoracic sympathetic block affecting different organs. Furthermore, local anaesthetic itself reabsorbed from the epidural space may contribute to the non-analgetic effects of thoracic epidural anaesthesia. Experimental studies have suggested that thoracic epidural anaesthesia may attenuate the perioperative stress response after major surgery. The possible beneficial mechanisms of action include an improvement of left ventricular function by direct anti-ischaemic effects, a reduction in cardiovascular complications, an advance on gastrointestinal function, and a reduction in pulmonary complications, as well as a positive impact on the coagulation system and the postoperative inflammatory response. However, it is questionable whether these effects of thoracic epidural anaesthesia may lead to an improved perioperative outcome after major surgery. Recent studies have suggested that, despite the superior quality of pain relief and better quality of life, thoracic epidural anaesthesia does not reduce mortality and major morbidity, especially after major abdominal and cardiac surgery.

SUMMARY

Despite this controversy, the numerous positive effects and advantages of thoracic epidural anaesthesia are the reasons for its increasing popularity. However, the advantages of thoracic epidural anaesthesia must be incorporated into a multimodal treatment management aimed at improving outcomes after surgery.