DOES NITROUS-OXIDE AFFECT CORONARY MICROCIRCULATION - AN INTRAVITAL MICROSCOPIC STUDY IN THE CANINE HEART

The safe use of nitrous oxide, in particular in patients with coronary artery disease, has been questioned. This study was designed to deter mine whether nitrous oxide directly affects global coronary hemodynami c variables and coronary arteriolar microvessels in the absence of cha nges of myocardial oxygen consumption. In dogs the effects of nitrous oxide were evaluated during normotension (NT, intravenous [IV] piritra mid, nitrogen/oxygen; and NT/N2O, IV piritramid, nitrous oxide/oxygen) and during hypotension (MAP 60 mm Hg) (HT, IV piritramid, halothane, nitrogen/oxygen; and HT/N2O, IV piritramid, halothane, nitrous oxide/o xygen). The diameter of coronary arteriolar microvessels (range, 20-45 0 mu m) was assessed by intravital fluorescence microscopy. Myocardial blood flow was determined by radioactive microspheres. Systemic and c oronary hemodynamics, as well as arteriolar microvessel diameters, wer e comparable between NT and NT/N2O. During HT, nitrous oxide (HT/N2O) affected neither systemic nor coronary hemodynamics. Moreover, there w as no obvious difference in the diameters of coronary microvessels bet ween HT and HT/N2O. In conclusion, nitrous oxide, whether at normotens ive or hypotensive conditions, neither influences coronary arteriolar tone nor reduces or redistributes myocardial blood flow.