Stephan A. Loer

Perioperative Hemodynamic Monitoring with Transesophageal Doppler Technology

Invasive cardiac output (CO) monitoring, traditionally performed with transpulmonary thermodilution techniques, is usually reserved for high-risk patients because of the inherent risks of these methods. In contrast, transesophageal Doppler (TED) technology offers a safe, quick, and less invasive method for routine measurements of CO. After esophageal insertion and focusing of the probe, the Doppler beam interrogates the descending aortic blood flow. On the basis of the measured frequency shift between the emitted and received ultrasound frequency, blood flow velocity is determined. From this velocity, combined with the simultaneously measured systolic ejection time, CO and other advanced hemodynamic variables can be calculated, including estimations of preload, afterload, and contractility. Numerous studies have validated TED-derived CO against reference methods. Although the agreement of CO values between TED and the reference methods is limited (95% limits of agreement: median 4.2 L/min, interquartile range 3.3–5.0 L/min), TED has been shown to accurately follow changes of CO over time, making it a useful device for trend monitoring. TED can be used to guide perioperative intravascular volume substitution and therapy, with vasoactive or inotropic drugs. Various studies have demonstrated a reduced postoperative morbidity and shorter length of hospital stay in patients managed with TED compared with conventional clinical management, suggesting that it may be a valuable supplement to standard perioperative monitoring. We review not only the technical basis of this method and its clinical application but also its limitations, risks, and contraindications.

Re-evaluating currently available data and suggestions for planning randomised controlled studies regarding the use of hydroxyethyl starch in critically ill patients - a multidisciplinary statement

IntroductionHydroxyethyl starch (HES) is a commonly used colloid in critically ill patients. However, its safety has been questioned in recent studies and meta-analyses.MethodsWe re-evaluated prospective randomised controlled trials (RCT) from four meta-analyses published in 2013 that compared the effect of HES with crystalloids in critically ill patients, focusing on the adherence to presumably correct indication. Regarding the definition of presumably correct indication, studies were checked for the following six criteria (maximum six points): short time interval from shock to randomisation (<6 h), restricted use for initial volume resuscitation, use of any consistent algorithm for haemodynamic stabilisation, reproducible indicators of hypovolaemia, maximum dose of HES, and exclusion of patients with pre-existing renal failure or renal replacement therapy.ResultsDuration of fluid administration ranged from 90 min up to a maximum of 90 days. Four studies considered follow-up until 90-day mortality, three studies 28-/30-day mortality, whereas four studies reported only early mortality. Included studies showed a large heterogeneity of the indication score ranging between 1 and 4 points with a median (25%; 75% quartile) of 4 (2; 4).ConclusionsThe most important question, whether or not HES may be harmful when it is limited to immediate haemodynamic stabilisation, cannot be answered yet in the absence of any study sufficiently addressing this question. In order to overcome the limitations of most of the previous studies, we now suggest an algorithm emphasising the strict indication of HES. Additionally, we give a list of suggestions that should be adequately considered in any prospective RCT in the field of acute volume resuscitation in critically ill patients.

Desflurane inhibits hypoxic pulmonary vasoconstriction in isolated rabbit lungs.

Background Inhalational anesthetics inhibit hypoxic pulmonary vasoconstriction (HPV) in vivo and in vitro with a half-maximum inhibiting effect (ED50) within concentrations applied for general anesthesia. Because it is unknown whether desflurane acts likewise, we studied its effect on HPV in isolated blood-perfused rabbit lungs and compared its ED sub 50 with that of halothane.

How Much Oxygen Does the Human Lung Consume

Background The amount of oxygen consumed by the lung itself is difficult to measure because it is included in whole‐body gas exchange. It may be increased markedly under pathological conditions such as lung infection or adult respiratory distress syndrome. To estimate normal oxygen consumption of the human lung as a basis for further studies, respiratory gas analysis during total cardiopulmonary bypass may be a simple approach because the pulmonary circulation is separated from systemic blood flow during this period. Methods Lung oxygen consumption was determined in 16 patients undergoing cardiac surgery. During total cardiopulmonary bypass their lungs were ventilated with low minute volumes (tidal volume, 150 ml; rate, 6 min sup ‐1; inspiratory oxygen fraction, 0.5; positive end‐expiratory pressure, 3 mmHg). All expiratory gas was collected and analyzed by indirect calorimetry. As a reference value also, whole‐body oxygen consumption of these patients was determined before total cardiopulmonary bypass. In a pilot study of eight additional patients (same ventilatory pattern), the contribution of systemic (bronchial) blood flow to pulmonary gas exchange during cardiopulmonary bypass was assessed. For this purpose, the amount of enflurane diffusing from the systemic blood into the bronchial system was measured. Results The human lung consumes about 5–6 ml oxygen per minute at an esophageal temperature of 28 degrees Celsius. Prebypass whole‐body oxygen consumption measured at nearly normothermic conditions was 198 +/‐ 28 ml/min. Mean lung and whole‐body respiratory quotients were similar (0.84 and 0.77, respectively). Extrapolating lung oxygen consumption to 36 degrees Celsius suggests that the lung consumes about 11 ml/min or about 5% of total body oxygen consumption. Because the amount of enflurane diffused from the systemic circulation into the bronchial system during cardiopulmonary bypass was less than 0.1%, the contribution of bronchial blood flow to lung gas exchange can be assumed to be negligible. Conclusion The lung consumes about 5% of whole‐body oxygen uptake.

Prehospital management of severe traumatic brain injury: concepts and ongoing controversies

Purpose of review Prehospital management affects long-term outcome of patients with severe traumatic brain injury (TBI). This article reviews the current concepts and ongoing controversies of prehospital treatment of severe TBI. Recent findings Prehospital management focuses on the prevention of secondary brain injury and rapid transport to a neurotrauma center for definitive diagnosis and life– as well as brain-saving emergency treatment such as decompressive craniotomy. There is a broad consensus that adequate airway management, prevention of hypoxia, hypocapnia or hypercapnia, prevention of hypotension and control of hemorrhage represent preclinical therapeutic modalities that may contribute to improved survival in severe TBI. The precise role of prehospital endotracheal intubation, osmotic agents and early therapeutic hypothermia needs to be clarified in the context of time required for transportation, local infrastructure, geographical factors and availability of experienced emergency teams. Summary Prehospital management of TBI remains challenging. There are no universal objectives suitable to all patients. Randomized, controlled clinical trials are necessary for developing optimal protocols for paramedic and physician emergency medical teams.

Dopexamine but not dopamine increases gastric mucosal oxygenation during mechanical ventilation in dogs

Objective To compare the effects of dopamine and dopexamine on gastric mucosal oxygenation during mechanical ventilation without and with positive end-expiratory airway pressure (PEEP) and after compensation of the PEEP-induced hemodynamic suppression. Design Randomized controlled animal study. Setting University research department of experimental anesthesiology. Subjects Ten anesthetized dogs with chronically implanted ultrasound flow probes around the pulmonary artery for continuous measurement of cardiac output. Interventions On different days, the dogs randomly received dopamine (2.5 and 5.0 &mgr;g·kg−1·min−1, n = 10), dopexamine (0.5 and 1.0 &mgr;g·kg−1·min−1) without (n = 8) or with pretreatment with a selective &bgr;2-adrenoceptor antagonist (ICI 118,551, n = 7), or saline (control, n = 7). To simulate common clinical situations, these interventions were performed during different ventilation modes: during mechanical ventilation without and with high levels of PEEP, and after compensation of the PEEP-induced systemic hemodynamic suppression by titrated volume resuscitation with hydroxyethyl starch. Measurements and Main Results We continuously measured microvascular hemoglobin saturation (&mgr;Hbo2) by light-guide spectrophotometry in the gastric mucosa. Dopexamine, but not dopamine, significantly increased gastric mucosal &mgr;Hbo2 by about 20%, regardless of the dose and the ventilation mode. Both catecholamines dose-dependently increased cardiac output and oxygen delivery by up to 75% without effects on systemic oxygen saturation. The effects of dopexamine on &mgr;Hbo2 as well as on cardiac output and oxygen delivery were prevented by selective &bgr;2-adrenoceptor-blockade. Conclusions Dopexamine but not dopamine improved gastric mucosal oxygenation in dogs. This effect was independent of the dosage and the ventilation mode. Thus, dopexamine may reverse a decrease in splanchnic oxygenation induced by ventilation with PEEP. The dopexamine-induced increase in gastric mucosal oxygenation was mediated by &bgr;2-adrenoceptors, which explains the superior effects of dopexamine to dopamine on &mgr;Hbo2. The regional effects of both catecholamines were not mirrored by systemic hemodynamics.

Volatile Anesthetics Modulate Gene Expression in Breast and Brain Tumor Cells

Gene expression is increasingly used for diagnostic, prognostic, and therapeutic purposes in clinical practice. We tested the hypothesis that volatile anesthetics (VA) affect gene expression of tumor cells. Cells from the neuronal cell line SH-SY5Y and from the breast cell line MCF-7 were exposed ex vivo to enflurane, isoflurane, desflurane, halothane, sevoflurane, or nitrous oxide. Microarray gene expression profiles were studied. We observed significant differences in gene expression levels of cell cultures and response in time when exposed to different VA. Some genes used for predictive genetic fingerprints for breast cancer were affected by VA. Our findings suggest that VA modulate gene expression in breast and brain tumor cell cultures in a unique and time-dependent manner.

Effects of ventilation and nonventilation on pulmonary venous blood gases and markers of lung hypoxia in humans undergoing total cardiopulmonary bypass.

Objective: To assess the effects of lung oxygenation and ventilation vs. lung collapse on pulmonary markers of lung hypoxia. Design: A prospective, nonrandomized, nonblinded comparative study. Setting: University department of anesthesiology and cardiothoracic surgery. Subjects: Twelve adult patients undergoing coronary bypass grafting requiring total cardiopulmonary bypass. Interventions: Single lung ventilation during total cardiopulmonary bypass (tidal volume, 150 mL; respiratory rate, 6 breaths/min; inspiratory oxygen fraction, 0.5) while the contralateral lung was allowed to collapse completely without oxygenation. Measurements and Main Results: At the beginning and at the end of total cardiopulmonary bypass (duration, 59‐65 mins), blood was aspirated from the right and left pulmonary veins and the radial artery for measurement of blood gases and concentrations of endothelin‐1, big‐endothelin, thromboxane B2, lactate, and lactate dehydrogenase. Nonventilation during total cardiopulmonary bypass compared with ventilation resulted in lower pulmonary venous PO2 values (57 ± 15 torr [7.6 ± 2.0 kPa] vs. 103 ± 23 torr [13.7 ± 3.1 kPa]) and higher thromboxane B2 concentrations (488 ± 95 pg/mL vs. 434 ± 92 pg/mL). The concentrations of endothelin‐1, big‐endothelin, lactate, and lactate dehydrogenase in the pulmonary veins did not differ significantly between nonventilated and ventilated lungs. Conclusions: Development of pulmonary tissue hypoxia during 1 hr of nonventilation and cardiopulmonary bypass with completely inhibited pulmonary arterial blood flow is unlikely, suggesting that enough oxygen is stored in or is provided to the collapsed lung. Thus, nonventilation during total cardiopulmonary bypass does not appear to contribute to postoperative respiratory dysfunction by causing pulmonary tissue hypoxia. These results, however, do not exclude that mechanical factors of ventilation might benefit the lung during cardiopulmonary bypass.

Effect of Secondary Prehospital Risk Factors on Outcome in Severe Traumatic Brain Injury in the Context of Fast Access to Trauma Care

BACKGROUNDnPrevention of secondary prehospital risk factors such as hypoxia and hypotension is likely to improve patient prognosis in severe traumatic brain injury (TBI). Because the Dutch trauma care organization is characterized by fast access to specialized trauma care due to the geographical situation, we investigated whether and to what extend secondary risk factors, such as hypoxia and hypotension, and measures, such as endotracheal intubation, affect outcome in severe TBI in the context of a region with fast access to trauma care.nnnMETHODSnThe medical records of 339 subsequent computed tomography-confirmed patients with TBI with a Glasgow coma scale (GCS) score≤8 who were primarily referred to a Level I trauma center in Amsterdam or Nijmegen in the Netherlands were retrospectively analyzed.nnnRESULTSnMultinomial logistic regression revealed that the strongest outcome predictors in our population were a disturbed pupillary reflex (odds ratio [OR], 5.8), a GCS score of 3 (OR, 4.9), and arterial hypotension (OR, 3.5). Interestingly, we observed no differences between intubated and nonintubated patients with respect to metabolic and respiratory parameters or mortality whereby the injury severity score was slightly higher in endotracheally intubated patients (32 [25-41]) versus nonintubated patients (25 [22-29]).nnnCONCLUSIONnIn agreement with others, GCS, a disturbed pupil reflex, and arterial hypotension were predictive for the prognosis of primarily referred patients with severe TBI in the Netherlands. In contrast, in the perspective of slightly higher injury scores in intubated patients, prehospital endotracheal intubation was not predictive for patient outcome.

Effects of partial liquid ventilation with perfluorocarbons on pressure-flow relationships, vascular compliance, and filtration coefficients of isolated blood-perfused rabbit lungs

OBJECTIVESnThe density of perfluorocarbons is almost twice that of blood. Therefore, we hypothesized that partial liquid ventilation with these fluids markedly affects pulmonary hemodynamics and filtration coefficients. To test these hypotheses we studied pressure-flow relationships, vascular compliances, capillary pressures, and filtration coefficients in normal and perfluorocarbon-ventilated rabbit lungs.nnnDESIGNnControlled animal study with an ex-vivo isolated lung preparation.nnnSETTINGnResearch laboratory for experimental anesthesiology at the Heinrich-Heine-University of Düsseldorf.nnnSUBJECTSnFourteen New Zealand White rabbits.nnnINTERVENTIONSnThe lungs were perfused under zone 3 flow conditions with autologous blood at various flow rates (50 to 250 mL/min, closed circuit, roller pump, 37 degrees C) and ventilated with 5% CO2 in air (positive end-expiratory pressure: 2 cm H2O, tidal volume: 10 mL/kg, respiratory rate: 30 breaths/min) without (control group, n=7) and with (n=7) perfluorocarbon administered intratracheally (15 mL/kg).nnnMEASUREMENTS AND MAIN RESULTSnPulmonary arterial, left atrial, and airway pressures, as well as blood reservoir volume (reflecting changes in pulmonary blood volume) and lung weight, were measured continuously. Inconsistent with our hypothesis, we found no significant differences between both groups in the slopes and intercepts of the pressure-flow relationships. There were no significant differences in capillary pressures determined by double occlusion (6.7+/-1.2 vs. 6.3+/-1.3 cm H2O for control group, p=.53), vascular compliances (0.51+/-0.10 vs. 0.47+/-0.09 mL/cm H2O for control group, p=.38), and filtration coefficients (0.33+/-0.06 vs. 0.37+/-0.07 mL/min/mm Hg/100 g wet weight for control group, p=.80, Mann-Whitney).nnnCONCLUSIONSnPartial liquid ventilation with perfluorocarbons has no relevant effects on pulmonary filtration coefficients and global hemodynamic variables of isolated zone 3 lungs. These findings suggest that right ventricular afterload is not changed with partial liquid ventilation. It is likely, however, that intrapulmonary blood flow is redistributed toward less-dependent regions, although relevant global hemodynamic changes are absent during partial liquid ventilation.