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Modifying the baricity of local anaesthetics for spinal anesthesia by temperature adjustment - model calculations: A-5

Heller, A. R.; Zimmermann, K.; Seele, K.; Rösse, T.; Koch, E.; Litz, R. J.

European Journal of Anaesthesiology: May 2005 - Volume 22 - Issue - p 2
ESA Best Abstract Prize Competition (BAPC)

Department of Anesthesiology, University Hospital Dresden, Dresden, Germany

Background and Goal of Study: The baricity of local anaesthetics (LA) in relation to cerebrospinal fluid (CSF) determines LA distribution in the subarachnoid space (SAS). While LA are hyper- or isobaric at room temperature, baricity drops within minutes after administration in the SAS. LA become hypobaric and therefore lead to uncontrolled cranial extension during spinal anaesthesia (SPA). The aim of the study was to describe temperature-dependent changes in LA baricity using mathematical model analysis.

Materials and Methods: After institutional approval and written informed consent baricity of LA commonly used for SPA A = Bupivacaine 0.5%; B = L-Bupivacaine 0.5%, C = Ropivacaine 0.5%; D = Articaine 2%,as well as baricity of CSF of patients undergoing SPA (n = 7) were measured using a high precision densiometer (DMA 450 Paar, Graz, Austria, precision 0.00001 g/ml, 0.00001°C). Temperature was adjusted to 5, 20, 30, and 37°C. The density of aqueous solutions such as LA behaves in a temperature dependent non-linear manner which can be described by a 3rd degree polynomial equation. For clinical purpose, however, consideration of a simple quadratic equation is as applicable concerning precision (p < 0.0005; r2 = 0.999).

Results: are depicted in the table below.



Density of CSF was 1.000646 ± 0.000086 g/ml. Mathematical conversion of the calculated equation enables determination of the temperature in °C at which LA are isobaric (A) 35.08357; (B) 37.02509; (C) 35.08357; (D) 39.38092.

Conclusion: Baricity of CSF is just one of the factors affecting the cranial extent during SPA. Thus, the clinical impact of our findings e.g. on hemodynamic stability must be confirmed in clinical studies.

© 2005 European Society of Anaesthesiology