Search PubMed⌕ Search

Biomedical subjects

A Weyland

Publications and source records attributed to A Weyland.

At least 37 records · Page 2Linked to original sources
PubMed1999

Heart transplantation after successful donor postpartum pulmonary embolectomy.

A fulminant pulmonary embolism can be treated surgically if thrombolytic therapy is contraindicated. A 31-year-old woman developed a fulminant pulmonary embolism after right-sided deep venous thrombosis 1 day after undergoing a cesarean section. A pulmonary embolectomy with cardiopulmonary bypass was performed, but the patient was brain-dead. After 2 days of echocardiographic observation, her heart was explanted for a 61-year-old man with ischemic cardiomyopathy. His right heart data were unremarkable, and he remains well 16 months after transplantation. Despite the sudden strain on the right ventricle that occurs with a pulmonary embolism, such a heart may be transplanted successfully after a pulmonary embolectomy.

Adult↗
PubMed1999

[Does method of anesthesia modify postoperative ischemia incidence? A study of patients after aortocoronary bypass operations].

In the postoperative period after coronary artery bypass graft surgery, the physician's enhanced attention should be focused on the incidence of myocardial ischaemia. The increased stress in the awakening patient as well as the return of autonomous reflexes can be the cause of imbalances in myocardial oxygen supply and uptake. Therefore, a probable influence of the pharmacologic profile of the intraoperatively applied anaesthetics on the incidence of postoperative myocardial ischaemia is of importance for adapting therapy on ICU to minimize any ischaemic risk. After approval by the ethics committee, a prospective randomized study was performed in 40 male patients who underwent coronary artery bypass graft surgery. The aim of the study was to compare balanced anaesthetic techniques performed with fentanyl and halothane, isoflurane and enflurane, respectively, with total intravenous anaesthesia performed with fentanyl and midazolam. An index to classify detection of ischaemia into three categories (ischaemia, probable ischaemia, no ischaemia) was established, based on measurements of myocardial lactate extraction and ST-segment analysis. Simultaneously, measurements of haemodynamic parameters and serum concentrations of catecholamines and intraoperatively applied anaesthetics were taken. In 8% of all measurements (30% of all patients) ischaemia was detected in the observation period and in 37% of all measurements (72.5% of all patients) probable ischaemia was detected. No significant difference was found concerning the incidence of myocardial ischaemia between all groups. The results of this investigation indicate that the application of inhalational anaesthetics for maintaining anaesthesia in coronary artery bypass graft surgery does not increase the risk of postoperative myocardial ischaemia.

Adult↗
PubMed1998

Effects of 1 MAC desflurane on cerebral metabolism, blood flow and carbon dioxide reactivity in humans.

We investigated the cerebral haemodynamic effects of 1 MAC desflurane anaesthesia in nine male patients scheduled for elective coronary bypass grafting. For the measurement of cerebral blood flow (CBF) a modified Kety-Schmidt saturation technique with argon as inert tracer gas was used. Measurements of CBF were made before induction of anaesthesia and 30 min after induction under normocapnic, hypocapnic and hypercapnic conditions in sequence. Changes in mean arterial pressure after induction of anaesthesia and during the course of the study were minimized using norepinephrine infusion. In comparison with the awake state under normocapnic conditions, desflurane reduced mean cerebral metabolic rate of oxygen (CMRO2) by 51% and mean cerebral metabolic rate of glucose (CMRglc) by 35%. Concomitantly, CBF was significantly reduced by 22%; jugular venous oxygen saturation (SjvO2) increased from 58 to 74%. Hypo- and hypercapnia caused a 22% decrease and a 178% increase in CBF, respectively. These findings may be interpreted as the result of two opposing mechanisms: cerebral vasoconstriction induced by a reduction of cerebral metabolism and a direct vasodilator effect of desflurane. CBF alterations under variation of PaCO2 indicate that cerebrovascular carbon dioxide reactivity is not impaired by application of 1 MAC desflurane.

Aged↗
PubMed1998

Effects of respiratory alkalosis and acidosis on myocardial blood flow and metabolism in patients with coronary artery disease.

BACKGROUND: Variation of the arterial carbon dioxide partial pressure (PaCO2) is not uncommon in anesthetic practice. However, little is known about the myocardial consequences of respiratory alkalosis and acidosis, particularly in patients with coronary artery disease. The aim of the current study was to investigate the effects of variation in PaCO2 on myocardial blood flow (MBF), metabolism, and systemic hemodynamics in patients before elective coronary artery bypass graft surgery. METHODS: In 10 male anesthetized patients, measurements of MBF, myocardial contractility, metabolism, and systemic hemodynamics were made in a randomized sequence at PaCO2 levels of 30, 40, and 50 mmHg, respectively. The MBF was measured using the Kety-Schmidt technique with argon as a tracer. End-diastolic left ventricular pressure and the maximal increase of left ventricular pressure were assessed using a manometer-tipped catheter. RESULTS: The cardiac index significantly changed with varying PaCO2 levels (hypocapnia, - 9%; hypercapnia, 13%). This reaction was associated with inverse changes in systemic vascular resistance index levels. The MBF significantly increased by 15% during hypercapnia, whereas no change was found during hypocapnia. Myocardial oxygen and glucose uptake and the maximal increase of left ventricular pressure were not affected by varying PaCO2 levels. CONCLUSIONS: In anesthetized patients with coronary artery disease, short-term variations in PaCO2 have significant effects on MBF but do not influence global myocardial oxygen and glucose uptake. Changes in systemic hemodynamics associated with respiratory alkalosis and acidosis are caused by changes in systemic vascular resistance rather than by alterations in myocardial contractility.

Acidosis, Respiratory↗
PubMed1998

Influence of arterial carbon dioxide tension on systemic vascular resistance in patients undergoing cardiopulmonary bypass.

BACKGROUND: The effects of induced hypothermia in cardiac surgical patients are not yet fully understood. Despite numerous studies on the effects of acid-base management on organ blood flow, only little information is available on the effects of alpha-stat versus pH-stat management on systemic haemodynamics. We therefore compared the effect of alpha-stat and pH-stat acid-base management on systemic haemodynamics in a prospective, controlled, cross-over study. METHODS: Twenty patients undergoing coronary artery bypass surgery were included in the study. Cardiac output was measured by thermodilution. Cardiac index and systemic vascular resistance were calculated according to standard formulae. Measurements were performed under hypo- and hypercapnia after induction of anaesthesia. Measurements were repeated at the end of two 30-min periods of pH-stat and alpha-stat acid-base management, respectively. RESULTS: Systemic vascular resistance at the lower PaCO2-levels (hypocapnia and alpha-stat, respectively) was significantly higher than those at the higher level (hypercania and pH-stat, respectively). The periods of different PaCO2-levels were comparable with respect to haematocrit, blood viscosity and temperature. Systemic vascular resistance was not significantly different from the control period. CONCLUSIONS: This study demonstrates that during hypothermic cardiopulmonary bypass, systemic vascular resistance under alpha-stat acid-base management is higher than under pH-stat management. As obvious from measurements during the control period, this finding can be completely explained by the difference in PaCO2.

Aged↗
PubMed1997

[S-(+)-Ketamine and circulation].

The S-(+) isomer of ketamine has about twice the analgesic potency of the clinically used racemic mixture. Therefore, the known side effects may be reduced when one-half of the usual dose is administered. Several prospective, randomised, and double-blinded studies have been performed to assess whether the S-(+) isomer of ketamine is superior to the racemic mixture with respect to circulatory side effects. Studies in young, healthy volunteers showed that heart rate (HR) and arterial blood pressure (ABP) rise significantly after injection of 2 mg/kg ketamine racemate and 1 mg/kg S-(+) isomer without any significant difference between groups. In the study of Doenicke et al. plasma levels of adrenaline (A) were higher in the racemate group, whereas no difference was found in elevated plasma levels of noradrenaline (NA). Premedication with midazolam blunted major haemodynamic changes. The investigation of Adams et al. confirmed that HR and ABP rise significantly after injection of 2 mg/kg ketamine racemate and 1 mg/kg S-(+) isomer without any significant difference between groups. In this study, no differences were found between groups concerning elevated plasma levels of A and NA. A further study in healthy volunteers also showed comparable haemodynamic changes following i.m.injection of 1.0 mg/kg ketamine racemate or 0.5 mg/kg S-(+) isomer without any significant difference between groups. In a previous clinical study including 40 elderly patients undergoing elective orthopaedic surgery, total intravenous anaesthesia (TIVA) was performed with S-(+)-ketamine or ketamine racemate as an analgesic compound. For induction of TIVA, patients received 0.1 mg/kg midazolam and 1 mg/kg S-(+)-ketamine or 2 mg/kg racemic ketamine, respectively. Throughout surgery, a continuous infusion of 2 mg/kg per hour S-(+)-ketamine or 4 mg/kg racemic ketamine was administered. Three patients in the racemate group showed severe arterial hypertension after induction of anaesthesia and were withdrawn from the study. In both groups plasma A and NA levels as well as HR and ABP increased significantly. In our own randomised, double-blinded study, haemodynamic effects of 2 mg/kg S-(+)-ketamine and 4 mg/kg ketamine racemate, respectively, were investigated in 14 patients undergoing elective aorto-coronary bypass surgery. In both groups HR and ABP significantly increased in 3 patients, each although all patients were deeply sedated with midazolam. One patient in the S-(+)-ketamine group showed severe arterial hypertension and tachycardia after induction of anaesthesia and was withdrawn from the study. With respect to haemodynamic changes, the pharmacodynamic effects of ketamine racemate and S-(+)-ketamine are comparable. Therefore, it can be concluded that neither ketamine nor S-(+)-ketamine should be used in patients who suffer, e.g., from arterial hypertension and coronary artery disease.

Anesthetics, General↗
PubMed1997

[Pathogenesis of venous congestion symptoms after Fontan operation].

To evaluate a possible common pathogenetic denominator, we compared hemodynamic data of 18 patients who had an uneventful long-term course after a Fontan procedure, with the respective data of patients who developed symptoms of central venous congestion either in the immediate postoperative period (n = 10) or during late follow-up (n = 6). We found a coincidence of increased early postoperative venous pressures (CVP; 17.1 +/- 2.9 mm Hg) with relatively high cardiac indices (3.6 +/- 0.6 l/min.m-2) as compared to 2.4 l/min.m-2 in the group of patients with a symptom-free long-term course but no significant difference in total pulmonary resistance between the two groups. The increased CVP (17.2 +/- 2.9 mm Hg) in patients with late chronic central venous congestion is primarily due to increased total pulmonary resistance (552 +/- 131 dyn s/cm5.m-2). Both groups of patients with central venous congestion display a ratio of systemic to total pulmonary resistance lower than 4.5 whereas symptom-free patients have a significantly higher resistance ratio (6.8 +/- 2.3) and a highly significant increase in peripheral resistance to values of 2687 +/- 527 dyn s/cm5.m-2 as compared to 1486 +/- 340 dyn s/cm5.m-2 in the early postoperative group. Correspondingly, mean arterial pressure of the symptom-free patients is significantly elevated (93 +/- 11 mm Hg) as compared to a control group (81 +/- 11 mm Hg). Based on our theory an increase in systemic arterial resistance may lead to a fall in mean capillary filtration pressure and therefore counteract central venous congestion. To support this, we briefly present cases where pharmacologic enhancement of systemic arterial resistance was effective in the treatment of venous congestion whereas pharmacologic lowering of systemic resistance induced venous congestion.

Adolescent↗
PubMed1997

Acute affect of mitral calve replacement on extravascular lung water in patients receiving colloid or crystalloid priming of cardiopulmonary bypass.

Despite numerous studies on extravascular lung water (EVLW) in patients undergoing coronary artery bypass surgery, few data are available on the perioperative time course of EVLW in patients undergoing mitral valve replacement for mitral valve insufficiency (MVI). We have investigated 26 patients undergoing elective mitral valve replacement in order to determine the influence of the preoperative degree of mitral valve insufficiency (degree III or IV) and the effect of different priming solutions for cardiopulmonary bypass. Crystalloid priming with Ringer's lactate was compared with human albumin priming solution. Measurement of EVLW was performed using the thermo-dye dilution technique, before and 1, 6 and 24 h after surgery. Before operation, EVLW is increased significantly in patients with MVI degree IV (MVI-degree IV) compared with patients with degree III (MVI-degree III) and patients undergoing coronary artery bypass surgery. During the postoperative time course a significant decrease in EVLW was observed in patients with MVI-degree IV whereas in patients with MVI-degree III the amount of EVLW did not change. However, compared with patients undergoing coronary artery bypass surgery, EVLW remained above normal in both groups. There was no interaction between the type of priming solution and the postoperative time course of EVLW, and no differences in respiratory variables or duration of mechanical ventilation were observed between groups.

Adult↗
PubMed1996

[Anesthesiologic aspects of pregnancy and delivery in a patient following a modified Fontan procedure ].

The number of patients with congenital cyanotic heart disease who reach child-bearing age is increasing. This is partly a consequence of the high long-term survival and the haemodynamic benefits resulting from the Fontan procedure, which is used for the definitive palliation of such cyanotic heart disease as tricuspid atresia and single ventricle. However, so far little experience has been recorded with pregnant patients who have undergone right ventricular exclusion procedures. The particular physiology of a univentricular heart and a passive, non-pulsatile blood flow through the lungs has significant implications for the anaesthetic obstetric management of these patients. We report a case of successful pregnancy and caesarean delivery after a modified Fontan procedure. CASE REPORT. The patient was a 30-year-old pregnant woman with a singleton pregnancy. At the age of 20, after four palliative shunt operations, she had undergone a modified Fontan operation due to tricuspid atresia with a single ventricle, d-transposition of the great arteries, pulmonary atresia and a single atrium. Following the Fontan repair, she initially suffered from intermittent Wolff-Parkinson-White syndrome and isorhythmic AV dissociation. The pregnancy was uneventful, and caesarean section was scheduled for 32 weeks' gestation. Because of the increased risk of thrombosis, the patient was treated with s.c. heparin preoperatively; for this reason, epidural anaesthesia was excluded, though it may otherwise be preferred for such patients. Amoxicilline was used to prevent endocarditis. At the date of caesarean delivery her body weight was 54 kg and boy height, 155 cm. Before induction of anaesthesia, a central venous and a radial artery catheter were placed for invasive pressure monitoring. An exaggerated left lateral tilt position was used to avoid aortocaval compression. After careful preoxygenation, anaesthesia was induced with 24 mg etomidate, 1.5 mg norcuronium, and 75 mg succinylcholine. Halothane 0.5-0.7% in oxygen was used during the first few minutes of surgery. Central venous pressure under mechanical ventilation was 20 mmHg, while the heart rate varied between 70 and 90 bpm. Delivery was accomplished 8 min after the induction of anaesthesia. The Apgar scores after 1 and 5 min were 9 and 10, respectively. Anaesthesia was continued with fentanyl, midazolam and nitrous oxide 50%. The remainder of surgery was unevenful. The child is now 5 years old and healthy. The mother has a near-normal activity level and does not need any help to care for her child. DISCUSSION. After a modified Fontan repair, i.e. atriopulmonary or total cavopulmonary anastomosis, the pulsatile pulmonary blood flow is converted to a passive, non-pulsatile blood flow that depends critically both on the pressure gradient between right (RAP) and left atrial pressure (LAP) and on pulmonary vascular resistance (PVR). Thus, the maintenance of an adequate transpulmonary pressure gradient and avoidance of an increase in PVR are of major importance for the obstetric anaesthetic management in patients who have undergone right ventricular exclusion procedures. Impairment of venous return caused by slight caval compression or high airway pressure may reduce cardiac output more critically than in patients with a normal circulation. CONCLUSION. This case demonstrates that the haemodynamic consequences of pregnancy and of caesarean delivery under general anaesthesia can be tolerated in post-Fontan patients despite the absence of a contractile pulmonary ventricle.

Adult↗
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

[Intraoperative acute aortic obstructive embolism].

UNLABELLED: We report a case of acute embolic obstruction of the aorta in a 36-year-old patient undergoing coronary artery bypass surgery. After declamping of the aorta at the end of extracorporeal circulation, blood pressure measured in the femoral artery dropped to 10-20 mmHg. Neither clinical signs of arterial hypotension nor a dysfunction of the arterial line could be observed. Cannulation of the left radial artery revealed a normal systemic blood pressure. After the end of surgery, pale and pulseless lower extremities were observed, suggesting arterial obstruction. A 6 X 3 cm embolus occluding the aortic bifurcation could be extracted with a Fogarty catheter; its origin was presumably an aneurysmatic area of the left ventricle. Surgical manipulation had mobilised the mural thrombus, which caused Leriche's syndrome after aortic declamping and defibrillation of the heart. CONCLUSION: In case of sudden alterations of lower extremity perfusion, anaesthetists and surgeons should consider the rare complication of acute embolic obstruction of the aorta originating from intracardiac thrombotic material. Routine monitoring with transoesophageal echocardiography should thus be considered in patients at risk for intracardiac thrombus formation.

Acute Disease↗
PubMed1995

One-stage surgery of coronary arteries and abdominal aorta in patients with impaired left ventricular function.

BACKGROUND: Coronary artery disease (CAD) is common in patients with abdominal aortic aneurysms (AAA). Some patients will present with the combination of unstable angina, impaired left ventricular function, and a large symptomatic (ie, leaking, expanding) AAA. In this subgroup of high-risk patients, aortic cross-clamping may have a deleterious effect on cardiac function, whereas coronary artery bypass graft surgery before aneurysmectomy (staged operation) carries the risk of perioperative aneurysm rupture. One-stage surgery, ie, myocardial revascularization and simultaneous aortic aneurysm repair, has been proposed in this situation. This article summarizes our results with the combined one-stage approach in patients with symptomatic CAD, impaired left ventricular function, and large symptomatic aortic aneurysms or severe aortic occlusive disease. As yet, this cohort is the largest reported in the English literature. METHODS AND RESULTS: In 25 patients (24 men) with a mean age of 69.4 years (range, 55 to 80 years), we performed combined open heart and intra-abdominal aortic surgery. Eighteen patients had severe three-vessel disease and impaired left ventricular function (ejection fraction, < 35%). In addition, 3 of these patients had severe aortic valvular stenosis and/or insufficiency. Seven patients had one- or two-vessel disease with a low left ventricular ejection fraction in the range of 15% to 30%. All patients were in New York Heart Association functional class III or IV. Twenty-one of 25 patients had symptomatic infrarenal AAA (perianeurysm hematoma was present in 9 patients, and 12 patients had signs of beginning perforation). Four patients with aortoiliac occlusive disease and limb ischemia were simultaneously operated on. The surgical procedure started with the performance of coronary artery bypass graft surgery. After completion of myocardial revascularization, aortic aneurysm repair was performed while extracorporeal circulation was continued for mechanical cardiac assist until aortic surgery was fully accomplished. An average of 3.3 (3 to 5) coronary bypass grafts were placed, including 17 internal thoracic artery grafts. In addition, three aortic valves were replaced. In the abdominal aortic position, 12 straight tube grafts and 13 bifurcation grafts were implanted, and three renal and two carotid arteries were simultaneously repaired. The total time of surgery varied from 2.3 to 8.5 hours, with a mean time of 3.9 +/- 1.4 hours. One intraoperative myocardial infarction occurred despite open grafts. Intensive care unit treatment lasted 1 to 13 days, with a mean of 3.6 +/- 2.5 days. Three patients (12%) died after surgery--1 because of acute renal failure induced by an adverse reaction to heparin, 1 because of myocardial infarction, and 1 because of multiorgan failure. One-year actuarial survival rate was 88%, which compares favorably with survival after isolated AAA surgery in this high-risk patient subgroup and equals survival in patients with severe CAD and severely depressed myocardial function. CONCLUSIONS: One-stage surgery is a possible approach to highly symptomatic patients with severe multivascular disease and has acceptable early morbidity and mortality. Patients with severely impaired left ventricular function and unstable CAD carry a high risk of left heart failure and/or myocardial infarction during abdominal aortic surgery. Extracorporeal circulation protects the heart from the hemodynamic changes after aortic clamping or declamping during abdominal aortic surgery. The present study demonstrates that one-stage procedure is a reasonable option for this patient subgroup.

Aged↗
PubMed1995

Oxygen cost of breathing for assisted spontaneous breathing modes: investigation into three states of pulmonary function.

OBJECTIVE: We investigated the effects of continuous positive airway pressure (CPAP) and pressure support ventilation (PSV) on the oxygen cost of breathing (VO2resp) for different states of pulmonary function. Additionally VO2resp was measured during spontaneous breathing. DESIGN: This was done in a controlled and prospective study. Ventilatory modes were applied randomly. SETTING: Measurements were performed in a quiet room on volunteers (VOL) and inpatients treated for chronic obstructive pulmonary disease (COPD). Post-operative patients after aortocoronary bypass surgery (ACB) were studied on the cardio-thoracic intensive care unit just before and after extubation. PATIENTS: Healthy volunteers (n = 14), postoperative patients after aorto-coronary bypass surgery (n = 15) and patients with COPD (n = 9, xFEV1 47.7%) were the objects of study. INTERVENTIONS: Demand flow CPAP (5 mbar) and PSV (7 mbar, PEEP 5 mbar), using the Hamilton Veolar ventilator, were investigated in comparison to spontaneous breathing. MEASUREMENTS AND RESULTS: VO2 was measured by a Datex Deltatrac metabolic monitor. VO2resp was calculated by subtraction of total oxygen uptake (VO2tot) in controlled mode ventilation (CMV) from that in the respective spontaneous breathing mode. For VOL and COPD patients who were not intubated, a CPAP facemask connected to a short 7.5 mm tube was used as connection to the ventilator. Breathing spontaneously under a canopy system VOL showed a VO2resp of 4.5 +/- 4.0% compared to 9.2 +/- 3.5% for ACB and 15.4 +/- 7.7% for COPD. CPAP changed the VO2resp to 7.8 +/- 3.9%, 12.0 +/- 4.0% and 9.1 +/- 3.6% respectively. PSV reduced the VO2resp to 7.9 +/- 3.8% in ACB and 7.7 +/- 5.5% in COPD. CONCLUSIONS: This investigation confirms findings that postoperative patients have a mild increase in VO2resp. COPD exhibit the highest increase in VO2resp. Tracheal tubes, masks and CPAP on a demand flow apparatus increases VO2resp in volunteers and postoperative patients after cardiac surgery. The same amount of CPAP in contrary reduces VO2resp in patients with COPD. Pressure support ventilation can offset the additional VO2resp induced by CPAP but at the same level does not further reduce VO2resp in COPD patients.

Adult↗
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↗
PubMed1995

[Is cerebral venous oxygen saturation an indicator of cerebral circulation?].

The arteriovenous oxygen content difference (avDO2) of the brain is dependent on O2 consumption (CM-RO2) and cerebral blood flow (CBF). With unchanging arterial O2 content, avDO2 is inversely related to cerebral venous O2 saturation (SO2). Measurement of SO2 in the jugular bulb not only provides information about the O2 balance of the brain, but may give an important estimation of CBF if a clinically useful correlation is proven. The aim of the present study was to verify this aspect. METHODS. Sixty-two male patients undergoing coronary revascularisation were investigated. The study was approved by the local Ethical Committee and each patient gave written informed consent on the preoperative day. At four points during the perioperative course arterial and cerebral venous SO2 and CBF were measured. Cerebral venous blood was sampled from a catheter in the superior bulb of the right internal jugular vein. CBF was measured using the argon wash-in technique. All sampled data were pooled and evaluated. RESULTS. As expected from theory, cerebral venous SO2 and avDO2 showed a close linear relationship (r = -0.892). However, only a weak hyperbolic relationship was found between cerebral venous SO2 and CBF. In addition, no direct correlation between CMRO2 and SO2 in the jugular bulb could be demonstrated. CONCLUSIONS. In this clinical study, a close relationship between cerebral venous SO2 and CBF was not found. This was primarily due to the high variability of cerebral O2 uptake. Changes in cerebral venous SO2 may therefore not be used as an estimate of perioperative changes in CBF.

Cerebrovascular Circulation↗