Elke Gaser

Validation of the multiple colored microsphere technique for regional blood flow measurements in newborn piglets

The use of multiple colored microspheres (CMS) for the measurement of regional blood flow (RBF) in almost all organs and tissues of newborn piglets was validated. For this purpose mixtures of different CMS and/or radio-labeled micro-spheres (RMS) were injected into the left ventricle of eight newborn piglets. Regional blood flows (RBF) were quantified using the reference sample method. Flow rates estimated by RMS and CMS were compared for each tissue sample. An excellent correlation (r=0.995–0.999) between CMS and RMS flow rates was found even for organs with low perfusion and tissue samples containing 400–750 CMS. We conclude that the CMS technique is a valid alternative for RBF measurement in newborn piglets, and that all disadvantages arising form radioactive labeling are thereby avoided.

The effects of increasing concentrations of isoflurane and desflurane on pulmonary perfusion and systemic oxygenation during one-lung ventilation in pigs.

During one-lung ventilation (OLV), hypoxic pulmonary vasoconstriction (HPV) reduces venous admixture and attenuates the decrease in arterial oxygen tension by diverting blood from the nonventilated lung to the ventilated lung. In vitro, desflurane and isoflurane depress HPV in a dose-dependent manner. Accordingly, we studied the effects of increasing concentrations of desflurane and isoflurane on pulmonary perfusion, shunt fraction, and Pao2 during OLV in vivo. Fourteen pigs (30–42 kg) were anesthetized, tracheally intubated, and mechanically ventilated. After placement of femoral arterial and thermodilution pulmonary artery catheters, a left-sided double-lumen tube (DLT) was placed via tracheotomy. After DLT placement, Fio2 was adjusted at 0.8 and anesthesia was continued in random order with 3 concentrations (0.5, 1.0, and 1.5 minimal alveolar concentrations) of either desflurane or isoflurane. Differential lung perfusion was measured with colored microspheres. All measurements were made after stabilization at each concentration. Whereas mixed venous Po2, mean arterial pressure, cardiac output, nonventilated lung perfusion, and shunt fraction decreased in a dose-dependent manner, Pao2 remained unchanged with increasing concentrations of desflurane and isoflurane during OLV. In conclusion, increasing concentration of desflurane and isoflurane did not impair oxygenation during OLV in pigs.

Effects of a catecholamine-induced increase in cardiac output on lung injury after experimental unilateral pulmonary acid instillation.

Objectives:Increasing pulmonary blood flow aggravated ventilation-associated lung injury in ex vivo animal experiments, but data were less consistent in an in vivo animal model and do not reflect redistributed lung perfusion seen in clinical acute lung injury. We sought to determine the effects of increased cardiac output on markers of lung injury in an in vivo model of inhomogeneous lung perfusion and injury. Design:Prospective, controlled animal study. Setting:Experimental research laboratory of a university hospital. Subjects:A total of 50 anesthetized, mechanically ventilated, male Wistar rats. Interventions:Unilateral lung injury was induced in rats by left lung acid instillation. After 24 hrs, animals were anesthetized and subjected to mechanical ventilation (tidal volume, 8 mL/kg; positive end-expiratory pressure, 7 cm H2O; Fio2, 0.4) and continuous infusion of either 10 &mgr;g·kg−1·min−1 dobutamine or isotonic saline (control) for 4 hrs. Measurements and Main Results:Cardiac output and differential lung perfusion were recorded throughout the ventilation period. Right and left lung wet-to-dry weight ratio, cytokines and inflammatory cells in lung lavage, and histologic lung injury were measured postmortem. After acid injury, lung perfusion was preferentially distributed to the noninjured lung. Dobutamine increased baseline cardiac output (>70%) and perfusion of both lungs (left, acid-instilled lung: from 16 ± 2 to 29 ± 6 mL/min; right, non–acid-instilled lung: from 54 ± 3 to 98 ± 7 mL/min). There was no difference in left lung injury between dobutamine- and saline-infused animals, but right lung injury was aggravated in dobutamine-infused animals, as indicated by increased lung edema, histologic lung injury, and cell counts in lavage. Conclusions:In the setting of unilateral lung injury and uneven lung perfusion, a dobutamine-induced increase in cardiac output has potentially detrimental effects on the opposite lung.

*Changed systemic and cerebral hemodynamics and oxygen supply due to gradual hemorrhagic hypotension induced by an external PID-controller in newborn swine

An experimental design including an external closed-loop PID-(proportional-integral-differential-)controller is presented which enables the induction of gradual hemorrhagic hypotension at different stages of blood flow reduction up to stages of critically disturbed systemic and regional hemodynamics and oxygen supply. For this purpose nine newborn piglets (12-26 hours old, body weight 1626+/-160 g) were anesthetized and artificially ventilated. Gradual hemorrhagic hypotension was induced at four different steady state stages (stage 1 = 60 mmHg; stage 2 = 50 mmHg; stage 3 = 40 mmHg; stage 4 = 35 mmHg) every 30 minutes by gradual blood withdrawal using external PID controller equipment. Cardiac output and brain regional blood flows were measured by the colored microsphere technique. Systemic and brain regional hemodynamics and O2 supply, metabolic parameters and blood catecholamine concentrations were obtained under baseline conditions and at every 25th minute of the four different steady state stages. About 35 percent of the calculated total blood volume (cTBV) was withdrawn in order to reach the first stage of hemorrhagic hypotension. Further blood withdrawal of about 10 percent of the cTBV, about 5 percent of the cTBV, and about 3 percent of the cTBV were necessary to reach the other respective hypotensive stages. Gradual hemorrhagic hypotension led to an increasing reduction of the cardiac output at every hypotensive stage up to about 20 percent of the baseline value (p<0.05). This was accompanied by a concomitant increase of the total peripheral resistance to about 2.5 fold (p<0.05) and a huge increase in the blood catecholamine concentrations (epinephrine: about 64 fold; norepinephrine: about 35 fold). The induced redistribution of the circulating blood volume was shunted to the vital organs. Therefore, brain cortical blood flow was slightly increased at stage 1 and stage 2. A significant reduction of rCBF did not occur until stage 4 (p<0.05). Regional cerebrovascular resistance was concomitantly reduced at stage 1 and stage 2 (p<0.05) and thereafter again slightly elevated. Brain cortical oxygen consumption was maintained up to stage 2, reduced by about 20% at the next stage of hemorrhagic hypotension (p<0.05) and reached the lowest level of about 50% from baseline at stage 4 (p<0.05). Excellent accuracy and stability was shown at each stage for the external PID controller equipment, so that each given setpoint of the instantaneous mean arterial blood pressure was reached and stabilized even at the lowest hypotensive stage (stage 1: 59.53+/-0.23; stage 2: 50.03+/-0.56; stage 3: 39.18+/-1.75; stage 4: 35.28+/-0.45 mmHg (mean+/-SD)). We conclude that the experimental design presented, with an external PID controller to induce gradual hemorrhagic hypotension in newborn piglets is sufficient for producing functional states with changed systemic and cerebral features with high stability and accuracy, enabling a systematic study of disturbed regional hemodynamics and energy metabolism under steady state conditions even under critically changed states of the systemic cardiovascular regulation.

The effects of xenon or nitrous oxide supplementation on systemic oxygenation and pulmonary perfusion during one-lung ventilation in pigs

During experimental one-lung ventilation (OLV), the type of anesthesia may alter systemic hemodynamics, lung perfusion, and oxygenation. We studied whether xenon (Xe) or nitrous oxide (N2O) added to propofol anesthesia would affect oxygenation, lung perfusion, and systemic and pulmonary hemodynamics during OLV in a pig model. Nine pigs were anesthetized, tracheally intubated, and mechanically ventilated. After placement of arterial and pulmonary artery catheters, a left-sided double-lumen tube was placed via tracheotomy. IV anesthesia with propofol was supplemented in random order with N2O/O2 60:40 or Xe/O2 60:40 or N2/O2 60:40. All measurements were made after stabilization at each concentration. Differential lung perfusion was measured with colored microspheres. Oxygenation (Pao2: 90 ± 17, 95 ± 20, and 94 ± 20 mm Hg for N2/O2, N2O/O2, and Xe/O2) and left lung perfusion (16% ± 5%, 14% ± 6%, and 18.8% for N2/O2, N2O/O2, and Xe/O2) during OLV did not differ among the 3 groups. However, mean arterial blood pressure (78 ± 25, 62 ± 23, and 66 ± 23 mm Hg for N2/O2, N2O/O2, and Xe/O2) and mixed venous saturation (55% ± 12%, 48% ± 12%, and 50% ± 12% for N2/O2, N2O/O2, and Xe/O2) were reduced during N2O/O2 as compared with the control group (N2/O2). Supplementation of IV anesthesia with Xe or N2O does not impair oxygenation nor alter lung perfusion during experimental OLV.

Infraklavikulärer Plexuskatheter in der perioperativen und chronischen Schmerztherapie Ergebnisse einer prospektiven Untersuchung unter Nutzung des vertikal infraklavikulären Zugangs

ZusammenfassungZielsetzung. Ziel der Untersuchung war die Evaluation des vertikalen infraklavikulären Zugangs zum Plexus brachialis für die Anlage eines Plexuskatheters zur perioperativen und chronischen Schmerztherapie. Methodik. Nach Identifikation des Plexus brachialis nach der von Kilka et al. beschriebenen Technik wurde durch eine geeignete Punktionskanüle ein flexibler Kunststoffkatheter für die Applikation von Lokalanästhetika in die Gefäß-Nerven-Scheide vorgeschoben. Protokolliert wurden Verlauf der Katheteranlage, Therapiedauer, Wirksamkeit, Komplikationen und der Grund für die Katheterentfernung. Ergebnisse. Bei 210 Patienten wurden insgesamt 226 Plexuskatheter über den vertikalen infraklavikulären Zugang gelegt. Bei 88% der Patienten war eine suffiziente regionale Schmerztherapie bis zur Katheterentfernung oder über mindestens 48 h möglich. Die mediane Therapiedauer (Minimum–Maximum) betrug 7 Tage (1–240) mit einer längeren Katheterliegedauer (Median 11 Tage) bei Patienten mit chronischer Schmerzsymptomatik. Nahezu 30% der Katheter lagen 10 Tage oder länger, und 4,4% lagen länger als einen Monat. In 3 Fällen traten interventionspflichtige Komplikationen auf, während in ca. 10% geringgradige Probleme (Materialprobleme, Rötung der Punktionsstelle) registriert wurden. Schlussfolgerungen. Die Anlage eines infraklavikulären Plexuskatheters stellt ein geeignetes Verfahren für die Schmerztherapie an der oberen Extremität dar. Der Zugang erscheint vorteilhaft bei Patienten, die verletzungsbedingt den Arm nicht abduzieren können. Ermutigend sind mehrwöchige komplikationslose Behandlungsverläufe bei Patienten mit lang dauernder Schmerzsymptomatik.AbstractObjectives. The aim of this prospective study was to evaluate the vertical infraclavicular approach to the brachial plexus for the insertion of a catheter to achieve continuous analgesia in postoperative patients and patients with chronic upper limb pain. Methods. The brachial plexus was identified using the technique described by Kilka et al. and a flexible catheter (diameter 0.85 mm) was introduced 3–5 cm into the perineural sheath via the punction cannula. Regional anlgesia was achieved by intermittent injection of local anaesthetic agent. Placement of the catheter, duration and effectiveness of treatment, complications and reasons for catheter removal were recorded using a standard protocol. Results. A total number of 226 plexus catheters were placed in 210 patients. Consecutive regional analgesia for at least 48 h was possible in 88%. Analgesia was sufficient in 76% of patients up to the time of catheter removal. The median (minimum– maximum) duration of catheterisation in the whole collective was 7 days (1–240) and 11 days in patients with chronic pain. Almost 30% of the patients were treated for 10 days or longer and 4.4% were treated for 1 month or longer. Major complications occurred in only three cases, while technical problems and minor complications (redness at puncture site) occurred in 10% of cases. Conclusions. The placement of an infraclavicular plexus catheter is a suitable method for pain management in the upper limb. This approach may have advantages in patients with severe injuries who cannot abduct the arm. Our results are encouraging in terms of catheterisation time, patient comfort and incidence of complications.