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Biomedical subjects

W Buhre

Publications and source records attributed to W Buhre.

43 records · Page 3Linked to original sources
PubMed1996

[The effect of nitroglycerin on cerebrovascular circulation, cerebrovascular CO2-reactivity and blood flow rate in basal cerebral arteries].

UNLABELLED: The cerebral haemodynamic effects of vasodilators are of clinical interest because a decrease in mean arterial pressure (MAP) might alter global cerebral blood flow (CBF). Luxury perfusion of the brain, contrast, might be unfavourable in patients with reduced intracranial compliance. Despite the widespread use of nitroglycerine (NTG), little is known about the cerebral haemodynamic consequence of NTG infusions in humans. This prospective, controlled study was designed: (1) to investigate the effects of NTG on CBF and cerebrovascular CO2 reactivity and (2) to compare reference measurements of global CBF with transcranial Doppler monitoring (TCD) of middle cerebral artery flow velocity (VMCA). METHODS: With ethical committee approval and informed patient consent, we investigated ten patients undergoing coronary artery bypass surgery. Measurements were performed under fentanyl/midazolam anaesthesia prior to the start of the operation. First, during a baseline period, ventilation was changed in a random sequence to achieve two different levels of arterial PCO2 (30 and 50 mmHg, respectively). Consequently, measurements were repeated during i.v. infusion of 1.5.micrograms.kg-1.min-1 NTG at identifical PCO2 levels. Measurements of CBF were performed by the Kety-Schmidt technique with argon as an indicator. Simultaneously, VMCA was recorded by use of a 2-Mhz transcranial Doppler system. Cerebral perfusion pressure (CPP) was calculated from the difference between MAP and jugular bulb pressure. Statistical analysis was performed by two-way analysis of variance using a repeated-measures design to assess the effects of NTG application and respiratory changes, respectively. RESULTS: During NTG infusion, CPP decreased slightly by 15-17%. Because of a reduction in cerebrovascular resistance, CBF increased at both levels of PaCO2 by 96 and 69%, respectively. However, VMCA decreased concomitantly. Cerebrovascular CO2 reactivity did not change. CONCLUSIONS: This study demonstrates that during fentanyl/midazolam anaesthesia NTG may cause a major increase in CBF as long as CPP does not decrease considerably. Our results further suggest that NTG causes vasodilation of basal cerebral arteries, inducing a discrepancy between relative changes in CBF and VMCA. Consequently, TCD measurements during infusion of NTG should not be directly compared with preceding measurements of MCA flow velocity.

Blood Pressure↗
PubMed1996

[Prevention of postoperative nausea and vomiting with single and repeat administration of ondansetron--review of the literature on different administration forms].

Postoperative nausea and vomiting (PONV) is still a common perioperative complication and ondansetron has proved to be an effective antiemetic substance in its prevention. The antiemetic effect of single and repetitive application was evaluated in this study. Fifty-one female patients who underwent gynaecological surgical procedures took part in a random double-blind study. Before the start of anaesthesia, 21 patients (group 1) received either a placebo (six patients), 8 mg ondansetron orally (seven patients) or 16 mg orally (eight patients). The remaining 30 patients (group 2), split into subgroups of ten, were given the same preoperative medication as group 1 plus further doses of the same strength 8 and 16 hours after the first intake of the study medication. Metoclopramide was given intravenously if patients had more than one emetic episode or if they asked for it. Nausea and vomiting were documented up to 24 hours after finishing anaesthesia. Metoclopramide had only to be given to patients who had received a placebo. Nausea was felt by 57% (4/7) of the patients after a single dose of 8 mg ondansetron and by 40% (4/10) of the patients after three doses of 8 mg. One patient (14%, 1/7) with a single dose and two patients (20%, 2/10) with a repetitive dose of 8 mg ondansetron vomited. Following a single dose of 16 mg ondansetron, no patient (0/8) had to vomit and 25% (2/8) of the patients had nausea. There were no complications reported by the patients. Ondansetron was shown to be a well-tolerated antiemetic and seems to have a higher reductive effect on PONV when given in a single dose and not repetitively. The prophylaxis of vomiting seems to be more effective than the reduction of nausea. Follow-up studies will have to clarify our findings.

Adult↗
PubMed1996

[Clinical use of antiemetic drugs for prevention and therapy of postoperative nausea and vomiting].

The incidence of postoperative nausea and vomiting (PONV) has not decreased significantly for decades. This study was done to evaluate whether there is a standard method or a preferred substance in German hospitals in the prophylaxis and treatment of PONV. Twenty-one randomly selected hospitals were asked to give details about substances, doses and application times and forms in PONV prophylaxis and treatment. Most of the patients with a high risk of emesis were treated prophylactically with droperidol. Dosage and time of application were different in each hospital. Metoclopramide was the second most frequently used substance for both prophylaxis and treatment. Dimenhydrinate, triflupromaxzine, promethazine and acupuncture were used less commonly in prophylaxis. Alizapride and ondansetron were used to treat PONV in only two hospitals. Summarising, this study found no routine standard in the prophylaxis and therapy of PONV. Droperidol and metoclopramide were the most frequently used antiemetics. An overview of the antiemetics involved is given.

Antiemetics↗
PubMed1995

[The effect of an intracardiac left-right shunt on thermodilution measurements of cardiac output. An extracorporeal circulation model].

Thermodilution measurements of cardiac output (CO) by means of Swan-Ganz catheters, in a strict sense, represent pulmonary arterial blood flow (PBF). In principle, this is also true in the presence of intracardiac left-to-right shunts due to atrial or ventricular septal defects. However, early recirculation of indicator may give rise to serious methodological problems in these cases. We sought to determine the influence of intracardiac left-to-right shunts on different devices for thermodilution measurements of CO using an extra-corporeal flow model. METHODS. Blood flow was regulated by means of a centrifugal pump that at the same time enabled complete mixing of the indicator after injection (Fig. 1). Pulmonary and systemic parts of the circulation were simulated using two membrane oxygenators and a systemic-venous reservoir to delay systemic recirculation of indicator. Control measurements of PBF (Qp) and systemic (Qs) blood flow were performed by calibrated electromagnetic flow-meters (EMF). Blood temperature was kept constant using a heat exchanger without altering the indicator mass balance in the pulmonary circulation. Left-to-right shunt was varied at different systemic flow levels applying a Qp:Qs ratio ranging from 1:1 to 2.5:1. Thermodilution measurements of PBF were performed using two different thermodilution catheters that were connected to commercially available CO computers. Additionally, thermodilution curves were recorded on a microcomputer and analysed with custom-made software that enabled iterative regression analyses of the initial decay to determine that part of the downslope that best fits a mono-exponentially declining function. Extrapolation of the thermodilution curve was then based on the respective curve segment in order to eliminate indicator recirculation due to shunt flow. RESULTS. At moderate left-to-right shunts (Qp:Qs < 2:1) all thermodilution measurements showed close agreement with control measurements. At higher shunt flows (Qp:Qs > or = 2:1), however, conventional extrapolation procedures of CO computers considerably underestimated PBF (Fig. 2). This was particularly true when a slow-response thermistor catheter was used (Fig. 3). The reason for this underestimation of Qp was an overestimation of the area under curve because of inadequate mathematical elimination of indicator recirculation by standard truncation methods (Fig. 4). However, curve-alert messages of the commercially implemented software did not occur. A high level of agreement could be consistently obtained using a fast-response thermistor together with individual definition of extrapolation limits according to logarithmic regression analyses. DISCUSSION AND CONCLUSION. Under varying levels of left-to-right shunt, both the response time of thermodilution catheters and the algorithms for calculation of flow considerably influenced the validity of thermodilution measurements of PBF in an extracorporeal flow model. The use of computer-based regression analyses to define the optimal segment for monoexponential extrapolation could effectively eliminate indicator recirculation from the initial portion of the declining thermodilution curve and showed the closest agreement with EMF measurements of Qp. The quality of thermodilution curves with respect to recirculation peaks in the flow model was slightly better than in clinical routine. Nevertheless, the clinical applicability of the modified extrapolation algorithm could be illustrated during pulmonary thermodilution measurements in an exemplary patient with a ventricular septal defect (Fig. 5). PBF at extremely high shunt ratios, however, cannot be assessed by monoexponential extrapolation in principle (Fig. 6). Insufficient elimination of indicator recirculation resulted in flow values that closely resembled systemic rather than PBF. This finding is in accordance with a mathematical analysis of the underlying Steward-Hamilton equation if an infinite number of recirculations would be

Cardiac Output↗
PubMed1994

Application of a transpulmonary double indicator dilution method for postoperative assessment of cardiac index, pulmonary vascular resistance index, and extravascular lung water in children undergoing total cavo-pulmonary anastomosis: preliminary results in six patients.

Total cavo-pulmonary anastomosis (TCPA) is used for the functional correction of an increasing spectrum of congenital heart diseases. The passive pulmonary perfusion after surgical exclusion of the right ventricle has significant implications for the postoperative hemodynamic management of these patients. Because conventional pulmonary artery thermodilution catheters present methodologic problems in patients after TCPA, important cardiovascular variables such as cardiac index (CI) and pulmonary and systemic vascular resistance indices (PVRI, SVRI) usually cannot be assessed directly. In a preliminary series of six patients undergoing TCPA (age 6-22 years), the applicability of a transpulmonary double indicator dilution technique for postoperative determinations of CI, PVRI, SVRI, and extravascular lung water (EVLW) was investigated. After central venous injection of ice-cold indocyanine green (5 mg), thermal and dye dilution curves were recorded in the abdominal aorta using a combined 4F fiberoptic thermistor catheter. Qualitative assessment of the tracer curves did not show major differences in measurements in patients with pulsatile perfusion of the lungs. CI, SVRI, and EVLW could be determined by use of standard algorithms. Pulmonary perfusion pressure for the calculation of PVRI was based on the gradient between central venous and left atrial pressure. The quality of indicator dilution curves allowed determination of flow-related variables in 33 of a total of 34 sets of measurements. No catheter-related problems occurred during or after the period of investigation. Postoperative EVLW was within the range that is commonly accepted as normal for adults. Mean PVRI initially decreased during the postoperative course but showed a significant increase after extubation.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Bedside assessment of intravascular volume status in patients undergoing coronary bypass surgery.

BACKGROUND: Management of intravascular volume is crucial in patients after cardiopulmonary bypass as myocardial dysfunction is common. The purpose of this study was to validate a novel bedside technique for real-time assessment of intravascular volumes. METHODS: Eleven patients undergoing cardiopulmonary bypass were studied. In addition to standard monitors, a fiberoptic thermistor catheter was placed in the descending aorta and central venous injections of 10 ml ice-cold indocyanine green dye were performed. Total blood volume was measured by a standard in vitro technique. Circulating and central blood volume were calculated by using cardiac output, mean transit times, and a newly developed recursive convolution algorithm that models recirculation. Measurements were performed after induction of anesthesia and at 1, 6, and 24 h after surgery. RESULTS: A two-compartment model of the circulation was required for adequate fit of the data. We found a significant correlation between total and circulating blood volumes (r = 0.87). One hour after surgery, central blood volume was decreased by 10% (P < 0.05). At 6 and 24 h after surgery, circulating blood volumes were significantly increased by 29% and 20%, respectively (P < 0.01), although central blood volume was similar to control values. Before surgery stroke volume index correlated with circulating blood volume (r = 0.87) but not with pulmonary capillary wedge and central venous pressures. CONCLUSIONS: This study shows that bedside determinations of intravascular blood volumes are feasible and that these measurements are more indicative of intravascular volume status than are either pulmonary capillary wedge or central venous pressures in the post-cardiopulmonary bypass period. Our data also demonstrate that despite a normal central blood volume both circulating and total blood volume are significantly increased in the immediate post-cardiopulmonary bypass period.

Aged↗