[The effect of nitroglycerin on ornipressin (POR 8)-induced systemic and cardiovascular circulatory changes. An...

Local infiltration of ornipressin (OR) is widely used to reduce intraoperative bleeding. However, OR can cause severe side effects including hypertension, deterioration of cardiac performance and coronary vasoconstriction. Suggestions for therapy of haemodynamic side effects of OR include the use of nitroglycerin (TNG). This experimental study was designed to investigate the influence of TNG on changes of systemic haemodynamics and coronary perfusion produced by i.v. administration of OR.

16 anesthetized closed-chest mongrel dogs were studied. Anaesthesia was administered using N2O/O2 (FiO2: 0.33) and enflurane (1Vol%ET). Saline-filled catheters were used to measure intravascular pressures. Left ventricular pressure change (dP/dt) was monitored with a cathetertip manometer. Cardiac output (CO) was determined using thermodilution, myocardial blood flow (MBF) using a Pitot catheter. Baseline values were taken (control) followed by a bolus injection of 0.03 U/kg OR i.v. The dogs were randomly assigned to two groups. Group I (Gr.I) (n = 9) received OR only and group II (Gr.II) (n = 7) was treated by infusion of 4 mg/kg.min TNG 7 to 30 min after injection of OR. Haemodynamic and cardiovascular changes were measured for 60 min at fixed time intervals.

In both groups (Gr.I; Gr.II) OR produced significant changes in systolic (APS) (+29%; +32%) and diastolic (APD) (+47%; +37%) aortic pressure, cardiac index (CI) (-33%; -33%), peripheral vascular resistance (TPR) (+116%); +104%), stroke volume index (SVI) (-23%; -34%), ejection fraction (EF) (-29%; -29% endsystolic volume (ESV) (+39%; +45%) and left ventricular enddiastolic pressure (LVEDP) (+50%; +66%). Myocardial blood flow (MBF) was reduced by 30% and 29% respectively and coronary vascular resistance (CVR) was increased (+97%; +84%). Coronary venous O2 saturation (SO2cor) decreased to 19% and 20% resulting in high AVDO2cor. As compared to Gr.I the administration of TNG resulted in significant decreases of APS, APD, TPR, ESV and LVEDP close to control values. However, administration of TNG did not effect MBF, CVR, SO2cor and AVDO2cor.

Systemic haemodynamic effects of OR include hypertension due to peripheral vasoconstriction and impaired cardiac performance resulting in reduced cardiac output with low EF, high ESV and LVEDP. Concomitantly, OR produces coronary constriction with a distinct fall in MBF. Thus, myocardial oxygen balance is impaired. With TNG peripheral vascular effects of OR can be abolished but there is no effect of TNG on OR-induced reduction of coronary blood flow. Therefore, use of TNG for treatment of cardiovascular complications following the administration of OR must be considered with extreme caution.