Thomas G. V. Cherpanath

Basic concepts of fluid responsiveness

Predicting fluid responsiveness, the response of stroke volume to fluid loading, is a relatively novel concept that aims to optimise circulation, and as such organ perfusion, while avoiding futile and potentially deleterious fluid administrations in critically ill patients. Dynamic parameters have shown to be superior in predicting the response to fluid loading compared with static cardiac filling pressures. However, in routine clinical practice the conditions necessary for dynamic parameters to predict fluid responsiveness are frequently not met. Passive leg raising as a means to alter biventricular preload in combination with subsequent measurement of the change in stroke volume can provide a fast and accurate way to guide fluid management in a broad population of critically ill patients.

The microcirculatory response to compensated hypovolemia in a lower body negative pressure model

The objective of the present study was to test the hypothesis that controlled, adequately compensated, central hypovolemia in subjects with intact autoregulation would be associated with decreased peripheral microcirculatory diffusion and convection properties and, consequently, decreased tissue oxygen carrying capacity and tissue oxygenation. Furthermore, we evaluated the impact of hypovolemia-induced microcirculatory alterations on resting tissue oxygen consumption. To this end, 24 subjects were subjected to a progressive lower body negative pressure (LBNP) protocol of which 14 reached the end of the protocol. At baseline and at LBNP=-60 mm Hg, sidestream dark field (SDF) images of the sublingual microcirculation were acquired to measure microvascular density and perfusion; thenar and forearm tissue hemoglobin content (THI) and tissue oxygenation (StO2) were recorded using near-infrared spectroscopy (NIRS); and a vascular occlusion test (VOT) was performed to assess resting tissue oxygen consumption rate. SDF images were analyzed for total vessel density (TVD), perfused vessel density (PVD), the microvascular flow index (MFI), and flow heterogeneity (MFIhetero). We found that application of LBNP resulted in: 1) a significantly decreased microvascular density (PVD) and perfusion (MFI and MFIhetero); 2) a significantly decreased THI and StO2; and 3) an unaltered resting tissue oxygen consumption rate. In conclusion, using SDF imaging in combination with NIRS we showed that controlled, adequately compensated, central hypovolemia in subjects with intact autoregulation is associated with decreased microcirculatory diffusion (PVD) and convection (MFI and MFIhetero) properties and, consequently, decreased tissue oxygen carrying capacity (THI) and tissue oxygenation (StO2). Furthermore, using a VOT we found that resting tissue oxygen consumption was maintained under conditions of adequately compensated central hypovolemia.

Cardiopulmonary interactions during mechanical ventilation in critically ill patients

Cardiopulmonary interactions induced by mechanical ventilation are complex and only partly understood. Applied tidal volumes and/or airway pressures largely mediate changes in right ventricular preload and afterload. Effects on left ventricular function are mostly secondary to changes in right ventricular loading conditions. It is imperative to dissect the several causes of haemodynamic compromise during mechanical ventilation as undiagnosed ventricular dysfunction may contribute to morbidity and mortality.

Defining Fluid Responsiveness: A Guide to Patient-Tailored Volume Titration

FLUID RESPONSIVENESS is a strategy used to select patients who will respond with a positive reaction in a physiologic parameter upon fluid administration. Curiously, there is no generally accepted definition of fluid responsiveness. A provisional definition of fluid responsiveness would be “the positive reaction of a physiologic parameter of a certain size to a standardized volume of a certain type of fluid administered within a certain amount of time and measured within a certain interval.” It is clear that these issues need to be resolved before a more detailed and precise definition can be proposed. The aim of predicting fluid responsiveness is to achieve this positive reaction while using the least amount of fluids. Accurate prediction of fluid responsiveness to facilitate patient-tailored fluid titration is crucial, as it has been shown that only half of critically ill patients will respond to fluid loading with an increase in cardiac output. Moreover, unnecessary fluid administration has shown to increase morbidity, mortality, and hospital and intensive care stays. Over the last decade, the rise in the number of publications about fluid responsiveness in the intensive care and operating room has shown the increased interest in this topic. In this review, the authors describe the physiology, requirements, and limitations of fluid responsiveness. Subsequently, using available literature, a practical definition on fluid responsiveness is proposed. The reliability of clinical, static, and hemodynamic parameters is evaluated to predict the response to fluid loading in critically ill patients. Finally, the potential, shortcomings, and use of passive leg raising are discussed in this review.

Effect of extracorporeal CO2 removal on right ventricular and hemodynamic parameters in a patient with acute respiratory distress syndrome.

We present a female patient with severe acute respiratory distress syndrome (ARDS) necessitating intubation and mechanical ventilation on the intensive care unit (ICU). High ventilatory pressures were needed because of hypoxia and severe hypercapnia with respiratory acidosis, resulting in right ventricular dysfunction with impaired haemodynamic stability. A veno-venous extracorporeal CO2 removal (ECCO2R) circuit was initiated, effectively eliminating carbon dioxide while improving oxygenation and enabling a reduction in applied ventilatory pressures. We noted a marked improvement of right ventricular function with restoration of haemodynamic stability. Within one week, the patient was weaned from both ECCO2R and mechanical ventilation. Besides providing adequate gas exchange, extracorporeal assist devices may be helpful in ameliorating right ventricular dysfunction during ARDS.

Pulse pressure variation does not reflect stroke volume variation in mechanically ventilated rats with lipopolysaccharide-induced pneumonia.

The present study examined the relationship between centrally measured stroke volume variation (SVV) and peripherally derived pulse pressure variation (PPV) in the setting of increased total arterial compliance (CArt). Ten male Wistar rats were anaesthetized, paralysed and mechanically ventilated before being randomized to receive intrapulmonary lipopolysaccharide (LPS) or no LPS. Pulse pressure (PP) was derived from the left carotid artery, whereas stroke volume (SV) was measured directly in the left ventricle. Values of SVV and PPV were calculated over three breaths. Balloon inflation of a catheter positioned in the inferior vena cava was used, for a maximum of 30 s, to decrease preload while the SVV and PPV measurements were repeated. Values of CArt were calculated as SV/PP. Intrapulmonary LPS increased CArt and SV. Values of SVV and PPV increased in both LPS‐treated and untreated rats during balloon inflation. There was a correlation between SVV and PPV in untreated rats before (r = 0.55; P = 0.005) and during (r = 0.69; P < 0.001) occlusion of the vena cava. There was no such correlation in LPS‐treated rats either before (r = −0.08; P = 0.70) or during (r = 0.36; P = 0.08) vena cava occlusion. In conclusion, under normovolaemic and hypovolaemic conditions, PPV does not reflect SVV during an increase in CArt following LPS‐induced pneumonia in mechanically ventilated rats. Our data caution against their interchangeability in human sepsis.

Impact of Positive End-Expiratory Pressure on Thermodilution-Derived Right Ventricular Parameters in Mechanically Ventilated Critically Ill Patients

OBJECTIVES To examine the effect of positive end-expiratory pressure (PEEP) on right ventricular stroke volume variation (SVV), with possible implications for the number and timing of pulmonary artery catheter thermodilution measurements. DESIGN Prospective, clinical pilot study. SETTING Academic medical center. PARTICIPANTS Patients who underwent volume-controlled mechanical ventilation and had a pulmonary artery catheter. INTERVENTION PEEP was increased from 5-to-10 cmH2O and from 10-to-15 cmH2O with 10-minute intervals, with similar decreases in PEEP, from 15-to-10 cmH2O and 10-to-5 cmH2O. MEASUREMENTS AND MAIN RESULTS In 15 patients, right ventricular parameters were measured using thermodilution at 10% intervals of the ventilatory cycle at each PEEP level with a rapid-response thermistor. Mean right ventricular stroke volume and end-diastolic volume declined during incremental PEEP and normalized on return to 5 cmH2O PEEP (p = 0.01 and p = 0.001, respectively). Right ventricular SVV remained unaltered by changes in PEEP (p = 0.26), regardless of incremental PEEP (p = 0.15) or decreased PEEP (p = 0.12). The coefficients of variation in the ventilatory cycle of all other thermodilution-derived right ventricular parameters also were unaffected by changes in PEEP. CONCLUSIONS This study showed that increases in PEEP did not affect right ventricular SVV in critically ill patients undergoing mechanical ventilation despite reductions in mean right ventricular stroke volume and end-diastolic volume. This could be explained by cyclic counteracting changes in right ventricular preloading and afterloading during the ventilatory cycle, independent of PEEP. Changes in PEEP did not affect the number and timing of pulmonary artery catheter thermodilution measurements.

Ventilator-induced central venous pressure variation can predict fluid responsiveness in post-operative cardiac surgery patients

Ventilator‐induced dynamic hemodynamic parameters such as stroke volume variation (SVV) and pulse pressure variation (PPV) have been shown to predict fluid responsiveness in contrast to static hemodynamic parameters such as central venous pressure (CVP). We hypothesized that the ventilator‐induced central venous pressure variation (CVPV) could predict fluid responsiveness.

A mini-fluid challenge of 150 mL predicts fluid responsiveness using Modelflow R pulse contour cardiac output directly after cardiac surgery

STUDY OBJECTIVE The mini-fluid challenge may predict fluid responsiveness with minimum risk of fluid overloading. However, the amount of fluid as well as the best manner to evaluate the effect is unclear. In this prospective observational pilot study, the value of changes in pulse contour cardiac output (CO) measurements during mini-fluid challenges is investigated. DESIGN Prospective observational study. SETTING Intensive Care Unit of a university hospital. PATIENTS Twenty-one patients directly after elective cardiac surgery on mechanical ventilation. INTERVENTIONS The patients were subsequently given 10 intravenous boluses of 50mL of hydroxyethyl starch with a total of 500mL per patient while measuring pulse contour CO. MEASUREMENTS We measured CO by minimal invasive ModelflowR (COm) and PulseCOR (COli), before and one minute after each fluid bolus. We analyzed the smallest volume that was predictive of fluid responsiveness. A positive fluid response was defined as an increase in CO of >10% after 500mL fluid infusion. MAIN RESULTS Fifteen patients (71%) were COm responders and 13 patients (62%) COli responders. An increase in COm after 150mL of fluid >5.0% yielded a positive and negative predictive value (+PV and -PV) of 100% with an area under the curve (AUC) of 1.00 (P<0.001). An increase in COli >6.3% after 200mL was able to predict a fluid response in COli after 500mL with a +PV of 100% and -PV of 73%, with an AUC of 0.88 (P<0.001). CONCLUSION The use of minimal invasive ModelflowR pulse contour CO measurements following a mini-fluid challenge of 150mL can predict fluid responsiveness and may help to improve fluid management.

TCT-128 A systematic review and meta-analysis of extracorporeal life support during cardiac arrest and cardiogenic shock

Veno-arterial extracorporeal life support (ECLS) is increasingly used in patients during cardiac arrest and cardiogenic shock, to support both cardiac and pulmonary function. We performed a systematic review and meta-analysis of cohort studies comparing mortality in patients treated with and without