K. Lebedinskiy, S. Parvanian, I. Puzanova
Background and Goals: It is generally accepted, that nitroglycerin (NG) acts in dose-dependent manner, and arteriolar dilation requires higher i.v. infusion rates than venous dilation (1). Our aim was to determine the exact NG infusion rate to achieve selective venous dilation.
Material and Methods: On institutional approval and informed consent, 10 healthy volunteers (group A), 23 ICU patients, receiving NG for common indications (group B), and 7 ICU patients recovering after elective CABG (group C) were included in prospective study. All the patients had stable circulation and received neither inotropic nor vasoactive medication. Groups A and B received i.v. NG infusion in ascending rates (0.01 to 0.1 mkg kg–1 min–1). Hemodynamic variables were measured using impedance cardiography (Diamant, Russia). In group C patients NG i.v. infusion (0.05 and 0.1 mkg kg–1 min–1) was readministered for the short time just before Swan-Ganz pulmonary artery catheter removal (S/5 monitor, GE) and ICU discharge.
Results: In A and B groups the earliest hemodynamic change was significant systemic vascular resistance decline leading to stroke volume rise without shift of heart rate. This result prompted us to compare preload and afterload dynamics during NG infusion using invasive monitoring in group C. The latter data are shown in the table (Mean±SD, *– p<0.01 vs base variable level):
Parameters |
Base level |
NG, mkg kg–1 min–1 |
|
|
0.05 | 0.1 | |
SVI, ml?m-2 |
31.8±2.2 |
34.6±3.3* |
39.8±5.7* |
HR, min-1 |
82±14 |
79±14 |
81±15 |
SVRI, dyn?s?cm-5?m-2 |
2799±457 |
2608±492* |
2181±444* |
PVRI, dyn?s?cm –5?m-2 |
269±83 |
227±80 |
174±76* |
CVP, mm Hg |
7.8±2.1 |
7.8±2.7 |
5.5±1.4* |
PAOP, mm Hg |
13.8±1.2 |
14.4±2.9 |
11.0±0.6* |
Conclusion: In all the groups, afterload decrease followed by stroke volume rise surprisingly left behind preload decline. Since even low-rate NG i.v. infusion causes circulatory changes typical for arterial dilation, despite undoubted venodilator properties, the selectivity of NG as a venous dilator in clinical settings may be revised.
Reference:
1). Abrams J. Am J Cardiol 1992; 70: 30–42.
© K. Lebedinskiy et al., 2007
