Fabrice Brunet

Noninvasive cardiac output monitoring by aortic blood flow determination: Evaluation of the Sometec Dynemo-3000 system

OBJECTIVEnThe Sometec Dynemo-3000 system allows the permanent measurement of descending aorta diameter by an echographic (A-scan) device and the blood flow velocity by a pulse Doppler velocimeter. The Dynemo-3000 then furnishes a new hemodynamic parameter, i.e., descending aortic blood flow (ABF), which is a fraction of the cardiac output (CO). We evaluate the ability of this system to measure the aortic diameter and to accurately detect ABF changes.nnnDESIGNnA case study prospective trial.nnnSETTINGnA 24-bed medical intensive care unit of a 1,100-bed university hospital.nnnPATIENTSnTwenty critically ill patients fully sedated, mechanically ventilated, and monitored by a pulmonary artery catheter.nnnINTERVENTIONSnCO values determined by conventional thermodilution method (TD-CO) and ABF were recorded during the study, which included two initial baseline periods, a dobutamine infusion (5 microg/kg/min) interval of 30 mins, and a third baseline period. To assess the accuracy of A-scan, aortic diameter was measured by transesophageal echocardiography. The difference between echocardiography and A-scan was used to determine bias and precision for aortic diameter measurements. TD-CO and ABF variations were analyzed using Kruskal-Wallis and Wilcoxon tests. Association between TD-CO and ABF values was determined by calculating the linear correlation coefficient. The ability of ABF to detect a TD-CO >6.0 L/min and its variations >13% was analyzed by determination of sensitivity, specificity, and positive (PPV) and negative (NPV) predictive values.nnnMEASUREMENTS AND MAIN RESULTSnAortic diameter measurements by A-scan and bidimensional methods were 23.0+/-2.8 mm (SD) and 24.2+/-2.7 mm, respectively. Bias and precision were 1.1 mm and 1.4 mm (95% confidence interval: -1.9 to 3.7), respectively. During the course of dobutamine infusion, we observed a significant increase of TD-CO mean value from 6.65+/-1.53 L/min to 9.30+/-2.5 L/min (p=.0008), and a parallel and significant increase in ABF mean value from 4.34+/-1.18 L/min to 5.70+/-1.63 L/min (p= .0029). Absolute TD-CO and ABF values had a correlation coefficient of 0.80. For detection of an increased TD-CO, PPV and NPV were 87% and 86%, respectively. For detection of TD-CO changes >13%, PPV and NPV were 80% and 94%, respectively.nnnCONCLUSIONSnThe Dynemo-3000 system is able to display the real aortic diameter, which is one of the most important components of this noninvasive ultrasonic technique. When compared with TD-CO, the ABF determination provided by this ultrasonic device constitutes a reliable noninvasive tool for estimating CO and tracking its changes.

Improved synchrony and respiratory unloading by neurally adjusted ventilatory assist (NAVA) in lung-injured rabbits

With increasing pressure support ventilation (PSV), a form of pneumatically triggered ventilation, there can be an increase in wasted inspiratory efforts (neural inspiratory efforts that fail to trigger the ventilator). With neurally adjusted ventilatory assist (NAVA), a mode of ventilation controlled by the electrical activity of the diaphragm (EAdi), synchrony should be maintained at high levels of assist. The aim of this study was to evaluate the response to increasing levels of PSV and NAVA on synchrony and diaphragm unloading in lung-injured rabbits. Animals were ventilated on PSV or NAVA in random order, each at three levels. We measured neural and ventilator respiratory rates, EAdi, transdiaphragmatic pressure (Pdi), and tidal volume (Vt). At low PSV, 95% of neural efforts were triggered, compared with high PSV, where only 66% of the neural efforts were triggered. During NAVA, all neural efforts were triggered, regardless of level. Increasing NAVA levels reduced EAdi and Pdi-time products by 48% (p < 0.05) and 66% (p < 0.05). In contrast, increasing PSV did not reduce the diaphragm electrical activity-time product and increased the transdiaphragmatic pressure-time product (p < 0.05) due to the increased wasted efforts. We conclude that synchrony with the ventilator is an important determinant for diaphragm unloading.

Influence of neurally adjusted ventilatory assist and positive end-expiratory pressure on breathing pattern in rabbits with acute lung injury.

Objective:To evaluate the influence of neurally adjusted ventilatory assist (NAVA) and positive end-expiratory pressure (PEEP) on the control of breathing in rabbits with acute lung injury. Design:Prospective animal study. Setting:Experimental laboratory in a university hospital. Subjects:Male White New Zealand rabbits (n = 18). Intervention:Spontaneously breathing rabbits with hydrochloric acid-induced lung injury were ventilated with NAVA and underwent changes in NAVA gain and PEEP (six nonvagotomized and five vagotomized). Seven other nonvagotomized rabbits underwent 4 hrs of ventilation with hourly titration of PEEP, Fio2, and NAVA gain. Measurements and Main Results:We studied diaphragm electrical activity, respiratory pressures, and breathing pattern. After lung injury, 0 cm H2O of PEEP resulted in high tonic and no discernible phasic diaphragm electrical activity in the nonvagotomized rabbits; stepwise increases in PEEP (up to 11.7 ± 2.6 cm H2O) reduced tonic but increased phasic diaphragm electrical activity. Increasing the NAVA gain reduced phasic diaphragm electrical activity to almost half and abolished esophageal pressure swings. Tidal volume remained at 4–5 mL/kg, and respiratory rate did not change. In the vagotomized group, lung injury did not induce tonic activity, and phasic activity and tidal volume were several times higher than in the nonvagotomized rabbits. Four hours of breathing with NAVA restored breathing pattern and neural and mechanical breathing efforts to pre-lung injury levels. Conclusions:Acute lung injury can cause a vagally mediated atypical diaphragm activation pattern in spontaneously breathing rabbits. Modulation of PEEP facilitates development of phasic diaphragm electrical activity, whereupon implementation of NAVA can efficiently maintain unloading of the respiratory muscles without delivering excessive tidal volume in rabbits with intact vagal function.

Hemodialysis for acute renal failure in patients with hematologic malignancies

Objective.To assess the prognosis of patients with hematologic malignancies in acute renal failure who require hemodialysis. Design.Retrospective study. Setting.ICU. Patients.Forty-three consecutive patients. Methods.Prognostic analysis using both univariate and multivariate (stepwise regression) methods. Results.Fifteen (35%) patients recovered from acute renal failure and 12 (28%) were discharged from the ICU. The prognosis of patients with acute renal failure linked to sepsis is poorer than the prognosis of the patients with acute renal failure from other etiologies. Only one patient survived in the former group (n = 26) and 11 in the latter group (n = 17); p < .0001 in multivariate analysis. When accompanied by associated respiratory failure, mortality rate was higher (93% vs. 33%; p < .0001). The Simplified Acute Physiology Score (SAPS) calculated within the first 24 hr of admission was significantly (p < .001) related to mortality when the SAPS was >13. The presence of neutropenia and the type of hematologic malignancy were not related to a worse prognosis. Tolerance to hemodialysis appeared good, and complications were rare. (Crit Care Med 1991; 19:346)

Appropriateness of diagnosis and orientation of 996 consecutive patients admitted in an emergency department with flow-based organization.

Background Recent data, focused on the inability to transfer emergency patients to inpatient beds, has shown this to be the single most important factor contributing to overcrowding. Our Emergency Department (ED) was reorganized in the year 2000 based on the optimization of patients flow. In this model, the emergency team had to refer patients to units fitting best to their condition with minimal delays. Objectives To evaluate adequacy of both diagnosis between emergency room and hospitalization wards and patients orientation in the context of an early discharge from the ED. Methods We collected data from 996 consecutive nontrauma patients for whom an admission was decided. Duration of stay in the ED and all related parameters were studied. Patients were categorized according to the adequacy of the diagnosis proposed at ED discharge as compared with the final diagnosis at hospital discharge. The patients orientation appropriateness was also assessed. Results Despite a median duration of time of 6u2009h (21u2009min–54u2009h) diagnostics made by the emergency physicians and the patients orientation were considered as adequate in most of the cases (66 and 96%, respectively). Fast track developed with medical intensive care and cardiology intensive care allowed referral of patients requiring these specific units within 2.2u2009h (27u2009min–17u2009h) and 2u2009h (41u2009min–8u2009h), respectively. The ED length of stay was highly influenced by the admission location and by the patients age. Conclusion A short time of stay in the ED is compatible with both a good diagnosis and a good orientation of ED patients requiring admission for specialized care.

Human polymorphonuclear leukocyte metabolism and lipoperoxidation during adult respiratory distress syndrome treated by extracorporeal carbon dioxide removal

Abstract Circulating polymorphonuclear leukocyte (PMNs) oxidative metabolism and lipoperoxidation were evaluated in patients with the adult respiratory distress syndrome (ARDS) treated with low-frequency positive-pressure ventilation and extracorporeal carbon dioxide removal. Chemiluminescence (CL) of resting PMNs from ARDS patients was significantly enhanced relative to controls ( P P P P 2− production was observed after pre-incubation with normal and ARDS serum. Plasma malondialdehyde (MDA) and α 1 proteinase inhibitor-elastase levels were significantly increased in ARDS patients plasma ( P P r = 0.824; P r = 0.46; P = 0.056). Our results show that oxygen metabolism and plasma elastase levels in circulating PMNs from ARDS patients are significantly enhanced. Furthermore, ARDS PMN functions are not enhanced by exogenous stimuli. No correlation between PMN functions and peroxidation was found in ARDS sera. These findings confirm that PMNs are primed during ARDS, but free radical production seems to be only one of the events responsible for the increased lipoperoxidation.