Raphaël Giraud

Mechanical Ventilation-Induced Reverse-Triggered Breaths: A Frequently Unrecognized Form of Neuromechanical Coupling

BACKGROUND Diaphragmatic muscle contractions triggered by ventilator insuffl ations constitute a form of patient-ventilator interaction referred to as “entrainment,” which is usually unrecognized in critically ill patients. Our objective was to review tracings, which also included muscular activity, obtained in sedated patients who were mechanically ventilated to describe the entrainment events and their characteristics. The term “reverse triggering” was adopted to describe the ventilator-triggered muscular efforts. METHODS Over a 3-month period, recordings containing fl ow, airway pressure, and esophageal pressure or electrical activity of the diaphragm were reviewed. Recordings were obtained from a series of consecutive heavily sedated patients ventilated with an assist-control mode of ventilation for ARDS. The duration of entrainment, the entrainment ratio, and the phase difference elapsing between the commencement of the ventilator and neural breaths were evaluated. RESULTS The tracings of eight consecutive patients with ARDS were reviewed; they all showed different forms of entrainment. Reverse triggering occurred over a portion varying from 12% to 100% of the total recording period. Seven patients had a 1:1 mechanical insuffl ation to diaphragmatic contractions ratio; this coexisted with a 1:2 ratio in one patient and 1:2 and 1:3 ratios in another. One patient exhibited only a 1:2 ratio. The frequency of reverse-triggered breaths had a mean coeffi cient of variability of , 5%, very close to the variability of mechanical breaths. CONCLUSIONS To our knowledge, this is the fi rst time that the presence of respiratory entrainment in sedated, critically ill adult patients who are mechanically ventilated has been documented. The “reverse-triggered” breaths illustrate a new form of neuromechanical coupling with potentially important clinical consequences.

Validation of a new transpulmonary thermodilution system to assess global end-diastolic volume and extravascular lung water

IntroductionA new system has been developed to assess global end-diastolic volume (GEDV), a volumetric marker of cardiac preload, and extravascular lung water (EVLW) from a transpulmonary thermodilution curve. Our goal was to compare this new system with the system currently in clinical use.MethodsEleven anesthetized and mechanically ventilated pigs were instrumented with a central venous catheter and a right (PulsioCath; Pulsion, Munich, Germany) and a left (VolumeView™; Edwards Lifesciences, Irvine, CA, USA) thermistor-tipped femoral arterial catheter. The right femoral catheter was used to measure GEDV and EVLW using the PiCCO2™ (Pulsion) method (GEDV1 and EVLW1, respectively). The left femoral catheter was used to measure the same parameters using the new VolumeView™ (Edwards Lifesciences) method (GEDV2 and EVLW2, respectively). Measurements were made during inotropic stimulation (dobutamine), during hypovolemia (bleeding), during hypervolemia (fluid overload), and after inducing acute lung injury (intravenous oleic acid).ResultsOne hundred and thirty-seven paired measurements were analyzed. GEDV1 and GEDV2 ranged from 701 to 1,629 ml and from 774 to 1,645 ml, respectively. GEDV1 and GEDV2 were closely correlated (r2 = 0.79), with mean bias of -11 ± 80 ml and percentage error of 14%. EVLW1 and EVLW2 ranged from 507 to 2,379 ml and from 495 to 2,222 ml, respectively. EVLW1 and EVLW2 were closely correlated (r2 = 0.97), with mean bias of -5 ± 72 ml and percentage error of 15%.ConclusionsIn animals, and over a very wide range of values, a good agreement was found between the new VolumeView™ system and the PiCCO™ system to assess GEDV and EVLW.

Clinical validation of a new thermodilution system for the assessment of cardiac output and volumetric parameters

IntroductionTranspulmonary thermodilution is used to measure cardiac output (CO), global end-diastolic volume (GEDV) and extravascular lung water (EVLW). A system has been introduced (VolumeView/EV1000™ system, Edwards Lifesciences, Irvine CA, USA) that employs a novel algorithm for the mathematical analysis of the thermodilution curve. Our aim was to evaluate the agreement of this method with the established PiCCO™ method (Pulsion Medical Systems SE, Munich, Germany, clinicaltrials.gov identifier: NCT01405040)MethodsSeventy-two critically ill patients with clinical indication for advanced hemodynamic monitoring were included in this prospective, multicenter, observational study. During a 72-hour observation period, 443 sets of thermodilution measurements were performed with the new system. These measurements were electronically recorded, converted into an analog resistance signal and then re-analyzed by a PiCCO2™ device (Pulsion Medical Systems SE).ResultsFor CO, GEDV, and EVLW, the systems showed a high correlation (r2 = 0.981, 0.926 and 0.971, respectively), minimal bias (0.2 L/minute, 29.4 ml and 36.8 ml), and a low percentage error (9.7%, 11.5% and 12.2%). Changes in CO, GEDV and EVLW were tracked with a high concordance between the two systems, with a traditional concordance for CO, GEDV, and EVLW of 98.5%, 95.1%, and 97.7% and a polar plot concordance of 100%, 99.8% and 99.8% for CO, GEDV, and EVLW, respectively. Radial limits of agreement for CO, GEDV and EVLW were 0.31 ml/minute, 81 ml and 40 ml, respectively. The precision of GEDV measurements was significantly better using the VolumeView™ algorithm compared to the PiCCO™ algorithm (0.033 (0.03) versus 0.040 (0.03; median (interquartile range), P = 0.000049).ConclusionsFor CO, GEDV, and EVLW, the agreement of both the individual measurements as well as measurements of change showed the interchangeability of the two methods. For the VolumeView method, the higher precision may indicate a more robust GEDV algorithm.Trial registrationclinicaltrials.gov NCT01405040.

Transpulmonary thermodilution curves for detection of shunt

PurposeMonitoring using transpulmonary thermodilution (TPTD) via a single thermal indicator technique allows measurement of cardiac output, extravascular lung water (EVLW) and volumetric variables.Methods and resultsThis report describes two cases of systemic-venous circulation shunt generating early recirculation of thermal indicator with overestimation of EVLW.ConclusionIn the case of recirculation of thermal indicator, the observed overestimated EVLW in absence of gas exchanges abnormality could be an indicator suggesting the search for a circulatory shunt.

ScvO(2) as a marker to define fluid responsiveness

BACKGROUND Definition of the hemodynamic response to volume expansion (VE) could be useful in shocked critically ill patients in absence of cardiac index (CI) measurements. The aim of this study is to evaluate whether central venous oxygen saturation variations (ΔScvO(2)) after VE could be an alternative to classify responders (R) and nonresponders (NR) to volume therapy. METHODS A total of 30 patients requiring VE were included in this prospective cohort study, all equipped with radial arterial line and pulmonary artery catheters. CI, mixed venous oxygen saturation (SvO(2)) and ScvO(2) were measured before and after VE. CI, SvO(2), and ScvO(2) changes after volume were analyzed using linear regression. Receiver operating characteristics curve analysis was used to test their ability to distinguish R and NR. RESULTS ΔScvO(2) and SvO(2) variations after VE (ΔSvO(2)) were significantly correlated with CI changes (ΔCI) after VE (r = 0.67 and r = 0.49, p < 0.001, respectively). A ΔScvO(2) threshold value of 4% allowed the definition of R and NR patients with 86% sensitivity (95%CI; 57-98%) and 81% specificity (95%CI; 54-96%). CONCLUSIONS ScvO2 variations after VE was able to categorize VE efficiently and could be suggested as an alternative marker to define fluid responsiveness in absence of invasive CI measurement.

Pulmonary fluid status monitoring with intrathoracic impedance

Various pacemakers can now track diverse hemodynamic parameters that are useful in the management of patients with heart failure. Among these indicators, pulmonary fluid status can be monitored. To the best of our knowledge, this is the first case describing an agreement between a simultaneous detection of an increase in lung water by transthoracic impedance monitoring (OptiVolTM (Medtronic, Inc., Minneapolis, MN), and the transpulmonary thermodilution method (PiCCOTM, Pulsion Medical Systems, Munich, Germany) in a patient with acute pulmonary oedema. The present case suggests that transthoracic impedance monitoring could be a useful tool to guide therapy in critically ill patients with implanted devices and lung fluid congestion.

Cardiac index during therapeutic hypothermia: which target value is optimal?

Mild therapeutic hypothermia is now recognized as standard therapy in patients resuscitated from out-of-hospital cardiac arrest (OHCA), and is recommended in comatose patients suffering from cardiac arrest related to ventricular fibrillation (VF) [1]. In these patients, maintaining an adequate tissue oxygen delivery (DO2) is crucial. However, during hypothermia, clinical signs of hypoperfusion such as cold, clammy skin and delayed capillary refill are not reliable and monitoring devices must, therefore, be used to measure or estimate the cardiac index (CI). However, there are no recommendations regarding the target value of CI in the hypothermic patient. In this article, the authors attempt to provide clinicians with some rationale to guide their therapy for the management of CI in patients treated with mild therapeutic hypothermia.

Long-term prognosis after extracorporeal life support in refractory cardiogenic shock – results from a real-world cohort

AIMS The current study presents data from a real-world cohort of patients with refractory cardiogenic shock (CS) undergoing extracorporeal life support (ECLS) with the aims of reporting clinical experience, objectifying complications as well as survival, and identifying predictors of mortality. METHODS AND RESULTS Eighty-three patients with refractory CS underwent percutaneous ECLS implantation performed by interventional cardiologists. Follow-up was performed at hospital discharge as well as at 18 months (IQR 15-36). Good clinical outcome was defined as survival with a Cerebral Performance Category (CPC) of 1-2. Median age was 61 years (IQR 50-72) and cardiopulmonary resuscitation prior to ECLS implantation was performed in 46 patients (55.4%). Aetiologies of CS were acute myocardial infarction (63.9%), acute deterioration of ischaemic cardiomyopathy (6.0%) or non-ischaemic acute heart failure (16.9%), valvular heart disease (9.6%), and interventional complications (3.6%). Although initial ECLS weaning was successful in 47 patients (56.6%), in-hospital mortality was 68.7%. Of all 83 patients initially undergoing ECLS implantation, only 15 patients (18.1%) were alive at follow-up, 13 (15.7%) with a CPC of 1-2. Age was identified as an independent predictor of mortality (p=0.04). CONCLUSIONS Despite ECLS support, the long-term prognosis of patients with CS refractory to standard treatment remains poor.

Peri-operative massive pulmonary embolism management: is veno-arterial ECMO a therapeutic option?

Pulmonary embolism remains an important clinical problem with a high mortality rate. The potential for sudden and fatal hemodynamic deterioration highlights the need for a prompt diagnosis and appropriate intervention. The purpose of the present case report is to describe a successful peri‐operative veno‐arterial extra corporeal membrane oxygenation (VA‐ECMO) implantation for assumed massive pulmonary embolism associated with high hemodynamic instability and severe hypoxemia. A 52‐year‐old female victim of a motorcycle accident had been operated on for unstable fractures that required optimal repair. Despite subcutaneous administration of 40 mg enoxaparin on day 0 and day 1, the patient developed a massive pulmonary embolism leading to peri‐operative pulseless activity. As intravenous thrombolysis was strictly contraindicated, a VA‐ECMO was successfully implanted and permitted to stabilize the patients hemodynamics. The hemodynamic and respiratory status improved by day 3, and the ECMO was removed. A vena cava filter was implanted before successful and definitive stabilization of the femoral fracture and the L2 fracture on days 4 and 5. The patient was able to be mobilized 2 days after the surgery and was transferred to a rehabilitation ward on day 15. At that time, her cognitive functions had fully recovered. ECMO can provide lifesaving hemodynamic and respiratory support in patients with massive pulmonary embolism who are too unstable to tolerate other interventions, who have failed other therapies or for whom other therapies are contraindicated.

Impact of epinephrine and norepinephrine on two dynamic indices in a porcine hemorrhagic shock model.

BACKGROUND Pulse pressure variations (PPVs) and stroke volume variations (SVVs) are dynamic indices for predicting fluid responsiveness in intensive care unit patients. These hemodynamic markers underscore Frank-Starling law by which volume expansion increases cardiac output (CO). The aim of the present study was to evaluate the impact of the administration of catecholamines on PPV, SVV, and inferior vena cava flow (IVCF). METHODS In this prospective, physiologic, animal study, hemodynamic parameters were measured in deeply sedated and mechanically ventilated pigs. Systemic hemodynamic and pressure-volume loops obtained by inferior vena cava occlusion were recorded. Measurements were collected during two conditions, that is, normovolemia and hypovolemia, generated by blood removal to obtain a mean arterial pressure value lower than 60 mm Hg. At each condition, CO, IVCF, SVV, and PPV were assessed by catheters and flow meters. Data were compared between the conditions normovolemia and hypovolemia before and after intravenous administrations of norepinephrine and epinephrine using a nonparametric Wilcoxon test. RESULTS Eight pigs were anesthetized, mechanically ventilated, and equipped. Both norepinephrine and epinephrine significantly increased IVCF and decreased PPV and SVV, regardless of volemic conditions (p < 0.05). However, epinephrine was also able to significantly increase CO regardless of volemic conditions. CONCLUSION The present study demonstrates that intravenous administrations of norepinephrine and epinephrine increase IVCF, whatever the volemic conditions are. The concomitant decreases in PPV and SVV corroborate the fact that catecholamine administration recruits unstressed blood volume. In this regard, understanding a decrease in PPV and SVV values, after catecholamine administration, as an obvious indication of a restored volemia could be an outright misinterpretation.