Effect of radiographic contrast media on renal perfusion - First results

BACKGROUND

Intra-arterial administration of radiographic contrast media (CM) is discussed to impair renal perfusion. The pathogenesis of contrast-induced Nephropathy (CIN) is still not clarified.

OBJECTIVE

This trial was performed to prove the effects of two CM with different molecular structure on renal perfusion.

METHODS

A prospective, randomized study on 16 pigs was designed to compare the outcome after application of a low-osmolar iodinated CM (770 mOsm/kg H2O - Group1) and an iso-osmolar iodinated CM (290 mOsm/kg H2o - Group2).Color Coded Doppler Sonography (LOGIQ E9, GE, Milwaukee, USA) was applied for measuring the Renal Resistive Index (RRI) before and after the first, fifth, and tenth bolus of CM. Statistics was performed using analysis of variance for repeated measurements with the Factor "CM".

RESULTS

All flow spectra were documented free of artifacts and Peak Systolic Velocity (PSV), Enddiastolic Velocity (EDV) and RRI respectively could be calculated. Mean PSV in Group 1 led to a decrease while in Group 2 PSV showed a significant increase after CM (p = 0,042). The course of the mean EDV in both groups deferred accordingly (p = 0,033). Mean RRI over time significantly deferred in both groups (p = 0,001). It showed a biphasic course in Group 2 and a decrease over time in Group 2.

CONCLUSION

While iso-osmolar CM induced an increase of PSV and EDV together with a decrease of RRI, low-osmolar CM could not show this effect or rather led to the opposite.

Effects of different gain settings during assisted mechanical ventilation using respiratory unloading in rabbits

Compared with conventional modes of patient-initiated mechanical ventilation, respiratory mechanical unloading aims at improving the match between ventilator pressure profiles and the specific derangements in lung mechanics. This may reduce lung barotrauma. The ventilator pressure increases either in proportion to the volume or to the flow of spontaneous breathing (elastic or resistive unloading), thereby selectively decreasing elastic or resistive work of breathing. The clinician sets a gain of increase in pressure per unit of volume or flow. In an attempt to develop criteria for selecting an appropriate gain, we investigated the effects of unloading using increasing gains that either partially compensated or overcompensated lung elastance or resistance. We studied spontaneously breathing, anesthetized, and tracheotomized rabbits. Compared with continuous positive airway pressure, respiratory unloading decreased the electromyographic activity of the diaphragm and increased minute ventilation in normal (n = 5) and surfactant-depleted (n = 6) animals when the gain was partially compensating. Fluctuations in systemic blood pressure associated with breathing decreased. The end-expiratory lung volume remained unchanged. Overcompensation of lung elastic recoil during elastic unloading with an excessive gain caused large tidal volumes associated with a cyclic decrease in blood pressure. Overcompensation of resistance induced oscillations. Complete inhibition of spontaneous breathing occurred with a further increase in gain. We conclude that respiratory unloading with an appropriate gain enhances the effect of diaphragmatic muscle activity on ventilation. A stable breathing pattern ensues whenever a regular spontaneous effort is present. However, excessive gain causes large tidal volumes during elastic unloading or oscillations during resistive unloading.