Systemic vasodilation with p.o. nitroglycerin
as a prognostic test for hypotension after spinal block
K.M. Lebedinski, D.A. Shevkulenko
Department of Anaesthesiology and Reanimatology,
Medical Academy of Postgraduate Studies, St. Petersburg , Russia
Background and goals of the study: while taking into consideration all the known risk factors, one can not predict severe hypotension – most frequent circulatory side effect of spinal anaesthesia (SA) – in a certain patient . Our aim was to investigate the possibility of its individual prognosis based on the analogy between local and systemic vasodilation.
Material and methods: 58 ASA I–III patients, aged 22–89, scheduled for elective general, orthopedic and gynecological surgery under SA, were enrolled in this prospective open study. Nitroglycerin (NG, 500 mkg p.o., mean 7.0 ± 1.6 mkg kg–1) was given before the anaesthesia under continuous monitoring of cardiac (CI) and systemic vascular resistance (SVRI) indexes derived from impedance cardiography and NIBP. Left ventricle power was described with the specific index (LVPI, W·m –2), calculated as 0.0022·CI·mean BP. After crystalloid fluid loading (6.2 ± 3.8 ml kg–1) and on leveling circulatory effect of NG, SA was performed from the puncture in L 3–4 interspace in lateral position with 0.5% isobaric bupivacaine (0.2 ± 0.05 mg kg–1). Mean level of sensory blockade (pin prick test) was Т8. Hypotension was defined as a decrease in mean BP below 75% of preceding values, resistant to fluid loading at maximal rate and thus requiring vasopressor support.
Results: In regard to BP shift due to SA all the patients were distributed between normo- (N-, 44) and hypotensive (H-, 14) groups. N- and H-groups were comparable in regard to age, gender, body weight and length , and did not significantly differ by the doses of NG and bupivacaine, fluid pre-load and time interval between NG test and puncture. In all the patients circulatory response to NG was quite similar to SA one, beginning with SVRI decrease which was followed by cardiac output rise. While increase in CI immediately after NG was significantly higher in N-group (mean +42.9% of preceding values versus +22.2% in H-group, P=5.5·10–5), the most demonstrative difference between the two was LVPI changes. In N-group NG provoked LVPI rise by 29.7%, but in H-group the same index typically decreased or, at least, remained stable (mean shift –0.77%, P=1·10 –6).
Conclusion: preoperative systemic vasodilation with p.o. nitroglycerin may be used as simple, fast, safe and relevant prognostic test for hypotension after spinal block.
1. Carpenter RL, Caplan RA, Brown DL et al. Anesthesiology 1992; 76 : 906–16.
© K.M. Lebedinski, D.A. Shevkulenko, 2006