NO-Inhalation bei herzchirurgischen Eingriffen: Relevanz für die Rechtsherzfunktion?

Zusammenfassung

Der rechte Ventrikel ist durch extrakorporale Zirkulation (EKZ) mehr gefährdet als der linke. Eine beeinträchtigte rechtsventrikuläre Funktion kann von einer Senkung der Nachlast profitieren. Durch Inhalation von Stickstoffmonoxid (NO) kann ein pulmonaler Hypertonus ohne Auswirkungen auf den Systemkreislauf gesenkt werden. In der vorliegenden Arbeit wurde deshalb der Einfluß einer NO-Inhalation auf pulmonalarteriellen Druck (PAP), pulmonalvaskulären Widerstand (PVR) und Rechtsherzparameter unmittelbar nach EKZ untersucht. An der Studie nahmen 20 Patienten mit mäßiggradigem pulmonalen Hochdruck teil. 10 Patienten inhalierten 30 ppm NO, die anderen dienten als Kontrollgruppe. Meßzeitpunkte lagen 10 min nach EKZ (Ausgangswerte), 3, 10 und 20 min nach Start sowie 10 min nach Beendigung der NO-Inhalation. Es fand sich ein signifikanter Abfall von PAP und PVR ohne begleitende Verbesserung der Rechtsherzfunktion. In der Kontrollgruppe wurden Veränderungen von PAP und PVR in vergleichbarer Größenordnung beobachtet. Es ist somit fraglich, ob die beobachteten Effekte spezifisch für die NO-Inhalation sind. Hohe endogene NO-Konzentrationen in dieser Phase, wie im Tierexperiment gefunden, könnten dieses Verhalten erklären. Eine klinische Verbesserung der Rechtsherzfunktion nach EKZ konnte bei unseren Patienten durch NO-Inhalation nicht erreicht werden.

Abstract

The right ventricle is more jeopardized by a cardiopulmonary bypass than the left one. Impaired right ventricular performance may profit from an afterload reduction. A selective reduction in pulmonary artery pressure (PAP) or pulmonary vascular resistance (PVR) without impairment of the systemic circulation seems to be possible by inhalation of nitric oxide (NO). Therefore in the present study we looked for influences of NO inhalation on PAP, PVR and right heart parameters immediately after weaning from the bypass. The dependence of endothelial function on age, preoperative heart function and extracorporeal circulation is well established. The relevance of such parameters on NO inhalation was also investigated.

Methods. After ethical approval and informed consent were obtained, 20 patients with moderately increased PAP were included in the study. Ten patients inhaled NO at a concentration of 30 ppm; the other group served as a control group. Measurement points were 10 min after the end of extracorporeal circulation (baseline), 3, 10, and 20 min after the start, as well as 10 min after the end of NO inhalation. NO was injected near the tube into the tubing system during inspiration; dosage and monitoring of the concentration were achieved by means of a chemiluminometer. Measured parameters consisted of PAP, PVR, right ventricular ejection fraction and volumes, systemic blood pressure and resistance, central venous pressure, pulmonary capillary wedge pressure, and oxygenation parameters (p_aO₂, p_vO₂, p_aCO₂).

Results. The decrease in PAP (from 29.7±3.9 to a minimal 25.4±4.3 mm Hg, P<0.05) and in PVR (from 169.4±51.9 to a minimal 116.3± 60.9 dyn·s·cm⁻⁵, P·0.05) did not improve right heart function. A similar significant increase in SVR was observed in the NO group and in the control group. Age, haemodynamic parameters or duration of the ischaemic phase of the cardiopulmonary bypass did not influence the course of PAP or PVR. Changes in PAP (from 30.0±4.0 to a minimal 26.7±3.6 mm Hg, P<0.05) and PVR (from 149.0±41.5 to a minimal 125.2±51.5 dyn·s·cm⁻⁵, in the control group were not statistically different from those in the NO group. Indicators of intoxication like an increase in NO₂ or methaemoglobin concentrations or changes in compliance or resistance were not observed.

Conclusions. Patients with moderate pulmonary hypertension did not profit from NO inhalation immediately after weaning from the cardiopulmonary bypass. The decreases in PAP and PVR found in the NO or control group did not improve right-heart function. When the NO and control group were compared, specific effects of NO inhalation on PAP and PVR must be questioned This could perhaps be explained by data from animal experiments, which found high endogenous NO levels in situations with elevated cytokine levels. Cytokines are increased after extracorporeal circulation. Oxygenation was not impaired by inhalation of relatively high concentrations of NO. For all investigations with NO inhalation not preceded by steady-state conditions, a control group is recommended.