Small hemodynamic effect of typical rapid volume infusions in critically ill patients

Sepsis and Septic Shock: Lingering Questions

Sepsis and septic shock are major health conditions in the United States, with a high incidence and mortality. The Surviving Sepsis Campaign, which was formed in 2002, formulates guidelines for the management of severe sepsis and septic shock and has actually demonstrated a reduction in mortality with institution of "sepsis bundles." Despite this, some elements of the guidelines have been questioned, and recent data suggest that strict compliance with bundles and protocols may not be necessary. Still, prompt recognition and treatment of sepsis and septic shock remain of utmost importance.

Fluid bolus therapy in emergency department patients: Indications and physiological changes

OBJECTIVE

The aim of the present paper is to study the indications for fluid bolus therapy (FBT) and its associated physiological changes in ED patients.

METHODS

Prospective observational study of FBT in a tertiary ED, we recorded indications, number, types and volumes, resuscitation goals and perceived success rates of FBT. Moreover, we studied key physiological variables before, 10 min, 1 h and 2 h after FBT.

RESULTS

We studied 500 FBT episodes (750 [500-1250] mL). Median age was 59 (36-76) years and 57% were male. Shock was deemed present in 135 (27%) patients, septic shock in 80 (16%), and cardiogenic shock in 30 (6%). Overall, 0.9% saline (84%) was the most common fluid and hypotension the most common indication (70%). 'Avoidance of hospital/ICU admission' was the goal perceived to have the greatest success rate (85%). However, although mean arterial pressure (MAP) increased (P < 0.01) and heart rate (HR) decreased (P = 0.04) at 10 min (P = 0.01), both returned to baseline at 1 and 2 h. In contrast, respiratory rate (RR) increased at 1 (P < 0.01) and 2 h (P = 0.03) and temperature decreased at 1 and 2 h (both P < 0.001). In patients with shock, 1 h after FBT, there was a median 3 mmHg increase in MAP (P = 0.01) but no change in HR (P = 0.44), while RR increased (P < 0.01) and temperature decreased (P = 0.01).

CONCLUSIONS

In ED, FBT is used mostly in patients without shock. However, after an immediate haemodynamic effect, FBT is associated with absent or limited physiological changes at 1 or 2 h. Even in shocked patients, the changes in MAP at 1 or 2 h after FBT are small.

Physiological changes after fluid bolus therapy in sepsis: a systematic review of contemporary data

Fluid bolus therapy (FBT) is a standard of care in the management of the septic, hypotensive, tachycardic and/or oliguric patient. However, contemporary evidence for FBT improving patient-centred outcomes is scant. Moreover, its physiological effects in contemporary ICU environments and populations are poorly understood. Using three electronic databases, we identified all studies describing FBT between January 2010 and December 2013. We found 33 studies describing 41 boluses. No randomised controlled trials compared FBT with alternative interventions, such as vasopressors. The median fluid bolus was 500 ml (range 100 to 1,000 ml) administered over 30 minutes (range 10 to 60 minutes) and the most commonly administered fluid was 0.9% sodium chloride solution. In 19 studies, a predetermined physiological trigger initiated FBT. Although 17 studies describe the temporal course of physiological changes after FBT in 31 patient groups, only three studies describe the physiological changes at 60 minutes, and only one study beyond this point. No studies related the physiological changes after FBT with clinically relevant outcomes. There is a clear need for at least obtaining randomised controlled evidence for the physiological effects of FBT in patients with severe sepsis and septic shock beyond the period immediately after its administration.

‘Just as water retains no shape, so in warfare there are no constant conditions’

Sun Tzu (‘The Art of War’)

Duration of hemodynamic effects of crystalloids in patients with circulatory shock after initial resuscitation

Background

In the later stages of circulatory shock, monitoring should help to avoid fluid overload. In this setting, volume expansion is ideally indicated only for patients in whom the cardiac index (CI) is expected to increase. Crystalloids are usually the choice for fluid replacement. As previous studies evaluating the hemodynamic effect of crystalloids have not distinguished responders from non-responders, the present study was designed to evaluate the duration of the hemodynamic effects of crystalloids according to the fluid responsiveness status.

Methods

This is a prospective observational study conducted after the initial resuscitation phase of circulatory shock (>6 h vasopressor use). Critically ill, sedated adult patients monitored with a pulmonary artery catheter who received a fluid challenge with crystalloids (500 mL infused over 30 min) were included. Hemodynamic variables were measured at baseline (T0) and at 30 min (T1), 60 min (T2), and 90 min (T3) after a fluid bolus, totaling 90 min of observation. The patients were analyzed according to their fluid responsiveness status (responders with CI increase >15% and non-responders ≤15% at T1). The data were analyzed by repeated measures of analysis of variance.

Results

Twenty patients were included, 14 of whom had septic shock. Overall, volume expansion significantly increased the CI: 3.03 ± 0.64 L/min/m² to 3.58 ± 0.66 L/min/m² (p < 0.05). From this period, there was a progressive decrease: 3.23 ± 0.65 L/min/m² (p < 0.05, T2 versus T1) and 3.12 ± 0.64 L/min/m² (p < 0.05, period T3 versus T1). Similar behavior was observed in responders (13 patients), 2.84 ± 0.61 L/min/m² to 3.57 ± 0.65 L/min/m² (p < 0.05) with volume expansion, followed by a decrease, 3.19 ± 0.69 L/min/m² (p < 0.05, T2 versus T1) and 3.06 ± 0.70 L/min/m² (p < 0.05, T3 versus T1). Blood pressure and cardiac filling pressures also decreased significantly after T1 with similar findings in both responders and non-responders.

Conclusions

The results suggest that volume expansion with crystalloids in patients with circulatory shock after the initial resuscitation has limited success, even in responders.

Predicting fluid responsiveness with transthoracic echocardiography is not yet evidence based

An essential part of intensive care is to accurately identify fluid responders among patients with circulatory failure. Over the past few years, new techniques have been assessed for rapid and non-invasive prediction of fluid responsiveness. As transthoracic echocardiography (TTE) is becoming an integrated tool in the intensive care unit, this systematic review examined studies evaluating the predictive value of TTE for fluid responsiveness. In October 2012, we searched Pubmed, EMBASE and Web of Science for studies evaluating the predictive value of TTE-derived variables for fluid responsiveness defined as change in thermodilution cardiac output or stroke volume after a fluid challenge or a passive leg raising test. The use of thermodilution was used as inclusion criterion because it is the only method validated to show the change in cardiac output or stroke volume, which defines fluid responsiveness. Of the 4294 evaluated citations, only one study fully met our inclusion criteria. In this study, the predictive value of variations in inferior vena cava diameter (> 16%) for fluid responsiveness was moderate with sensitivity of 71% [95% confidence interval (CI) 44-90], specificity of 100% (95% CI 73-100) and an area under the receiver operating curve of 0.90 (95% CI 0.73-0.98). Only one study of TTE-based methods fulfilled the criteria for valid assessment of fluid responsiveness. Before recommending the use of TTE in predicting fluid responsiveness, proper evaluation including thermodilution technique as the gold standard is needed.

Inferior vena cava variation compared to pulse contour analysis as predictors of fluid responsiveness: a prospective cohort study

BACKGROUND

Both occult hypoperfusion and volume overload are associated with increased morbidity and mortality in critically ill patients. Accurately predicting fluid responsiveness (FRes) allows for optimization of cardiac performance while avoiding fluid overload and prolonged mechanical ventilation.

OBJECTIVE

To simultaneously assess the ability to predict FRes using the stroke volume variation (SVV) obtained with the Vigileo/Flotrac monitor and inferior vena cava respiratory variation (ΔIVC) measured by standard echocardiography ([ECHO) during mechanical ventilation.

METHODS

We included medical intensive care unit (ICU) patients undergoing mechanical ventilation that required vasopressors, had worsening organ function, and that were well adapted to the ventilator. We excluded patients requiring escalating doses of vasopressors, hemodialysis, with ascites and patients with atrial fibrillation or a heart rate >120/min. Stroke volume index (SVI) and SVV were obtained from the Vigileo monitor whereas ΔIVC was obtained with ECHO (M-mode). Doppler ECHO was used to measure SVI and used to determine FRes (defined by SVI increase ≥ 10%). A data set was obtained before and 30 minutes after a 10-minute fluid challenge (FC) with 500 mL of saline.

RESULTS

In all, 25 patients were prospectively enrolled over an 8-month period. A total of 12 patients had acute respiratory distress syndrome (ARDS), 3 had a cardiac arrest, and 10 had sepsis. The patients' mean age was 61.36 years (±13.7), study enrollment since ICU admission was 3.4 days (±3.39), the Sequential Organ Failure Assessment (SOFA) score was 12.44 (±2.59), and the tidal volume 8.6 mL/kg (±1.68). Of the 25 patients, 8 (32%) were FRes. The correlation coefficient between the baseline ΔIVC and percentage increase in SVI (by ECHO) after an FC was R(2) = .51 with a receiver operating characteristic (ROC) curve of 0.81 while that for the baseline SVV by Vigileo was R(2) = .12 with an ROC curve of 0.57. The mean SVI bias between ECHO and Vigileo was -2 mL/m(2), the precision was -18 to 14 and the mean error was 46%.

CONCLUSIONS

ECHO assessment of the IVC variation during mechanical ventilation may prove to be a useful technique to predict FRes and guide fluid resuscitation in the ICU. The SVV obtained with the Vigileo monitor failed to predict FRes likely due to lack of calibration and the use of a complex algorithm that may be unreliable in patients with sepsis.

Approach to the patient with sepsis

This article reviews the current understanding of sepsis, severe sepsis, and septic shock. The article details definitions and epidemiology pertinent to the sepsis syndrome. A brief discussion of mechanisms of disease is followed a description of organ-specific failures related to sepsis. A concise review of the latest treatment options for each organ dysfunction is provided.

Fluid therapy in resuscitated sepsis: less is more

Fluid infusion may be lifesaving in patients with severe sepsis, especially in the earliest phases of treatment. Following initial resuscitation, however, fluid boluses often fail to augment perfusion and may be harmful. In this review, we seek to compare and contrast the impact of fluids in early and later sepsis; show that much fluid therapy is clinically ineffective in patients with severe sepsis; explore the detrimental aspects of excessive volume infusion; examine how clinicians assess the intravascular volume state; appraise the potential for dynamic indexes to predict fluid responsiveness; and recommend a clinical approach.

Volume management in critically ill patients: New insights

In order to turn a fluid challenge into a significant increase in stroke volume and cardiac output, 2 conditions must be met: 1) fluid infusion has to significantly increase cardiac preload and 2) the increase in cardiac preload has to induce a significant increase in stroke volume. In other words, a patient can be nonresponder to a fluid challenge because preload does not increase during fluid infusion or/and because the heart (more precisely, at least 1 of the ventricles) is operating on the flat portion of the Frank-Starling curve. Volumetric markers of cardiac preload are therefore useful for checking whether cardiac preload effectively increases during fluid infusion. If this is not the case, giving more fluid, using a venoconstricting agent (to avoid venous pooling), or reducing the intrathoracic pressure (to facilitate the increase in intrathoracic blood volume) may be useful for achieving increased cardiac preload. Arterial pulse pressure variation is useful for determining whether stroke volume can/will increase when preload does increase. If this is not the case, only an inotropic drug can improve cardiac output. Therefore, the best option for determining the usefulness of, and monitoring fluid therapy in critically ill patients is the combination of information provided by the static indicators of cardiac preload and arterial pulse pressure variation.

Fluid challenge revisited

OBJECTIVE

To discuss the rationale, technique, and clinical application of the fluid challenge.

DATA SOURCE

Relevant literature from MEDLINE and authors' personal databases.

STUDY SELECTION

Studies on fluid challenge in the acutely ill.

DATA EXTRACTION

Based largely on clinical experience and assessment of the relevant published literature, we propose that the protocol should include four variables, namely 1) the type of fluid administered, 2) the rate of fluid administration, 3) the critical end points, and 4) the safety limits.

CONCLUSIONS

A protocol for routine fluid challenge is proposed with defined rules and based on the patient's response to the volumes infused. The technique allows for prompt correction of fluid deficits yet minimizes the risks of fluid overload.

LEARNING OBJECTIVES

On completion of this article, the reader should be able to: 1. Explain the signs of hypovolemia. 2. Describe how to administer a fluid challenge. 3. Use this information in a clinical setting.

The influence of tidal volume on the dynamic variables of fluid responsiveness in critically ill patients

Respiratory-related variabilities in stroke volume and arterial pulse pressure (Delta%Pp) are proposed to predict fluid responsiveness. We investigated the influence of tidal volume (Vt) and adrenergic tone on these variables in mechanically ventilated patients. Cyclic changes in aortic velocity-time integrals (Delta%VTI(Ao), echocardiography) and Delta%Pp (catheter) were measured simultaneously before and after intravascular volume expansion, and Vt was randomly varied below and above its basal value. Intravascular volume expansion was performed by hydroxyethyl starch (100 mL, 60 s). Receiver operating characteristic curves were generated for Delta%VTI(Ao), Delta%Pp and left ventricle cross-sectional end-diastolic area (echocardiography), considering the change in stroke volume after intravascular volume expansion (> or =15%) as the response criterion. Covariance analysis was used to test the influence of Vt on Delta%VTI(Ao) and Delta%Pp. Twenty-one patients were prospectively included; 9 patients (43%) were responders to intravascular volume expansion. Delta%VTI(Ao) and Delta%Pp were higher in responders compared with nonresponders. Predictive values of Delta%VTI(Ao) and Delta%Pp were similar (threshold: 20.4% and 10.0%, respectively) and higher than that of left ventricle cross-sectional end-diastolic area at the appropriate level of Vt. Delta%Pp was slightly correlated with norepinephrine dosage. Delta%Pp increased with the increase in the level of Vt both before and after intravascular volume expansion, contrasting with an unexpected stability of Delta%VTI(Ao). In conclusion, Delta%VTI(Ao) and Delta%Pp are good predictors of intravascular fluid responsiveness but the divergent evolution of these two variables when Vt was increased needs further explanation.

Tissue Doppler imaging estimation of pulmonary artery occlusion pressure in ICU patients

OBJECTIVE

Earlier reports suggested that transthoracic (TTE) determination of the ratio of mitral inflow E wave velocity to early diastolic mitral annulus velocity (E/E') measured by tissue Doppler imaging (TDI) closely approximates PAOP in cardiac patients. However, the value of E/E' for PAOP assessment in ICU patients has not been evaluated. This study assessed whether the E/E' ratio provides an accurate estimation of pulmonary artery occlusion pressure (PAOP) in mechanically ventilated ICU patients.

DESIGN AND SETTING

Prospective, open, clinical study in the ICU of a university hospital.

PATIENTS

Twenty-three consecutive mechanically ventilated patients.

INTERVENTIONS

Volume expansion in 14 patients.

MEASUREMENTS AND RESULTS

Doppler TTE or TEE mitral inflow and TDI mitral annulus velocities were determined and compared with PAOP measured using a Swan-Ganz catheter. Of all the Doppler variables studied the best correlations were observed between PAOP and the lateral (r=0.84) and medial (r=0.76) annulus E/E' ratio and remained highly significant when the analysis was restricted to TEE (r=0.91 and 0.86) or TTE (r=0.73 and 0.61). The sensitivities and specificities of estimating PAOP at 15 mmHg or higher were, respectively, 86% and 81% for lateral E/E' above 7.5 and 76% and 80% for medial E/E' above 9. PAOP changes after volume expansion (700+/-230 ml) were limited and accurately assessed by repeated E/E' determinations.

CONCLUSIONS

In mechanically ventilated ICU patients TTE or TEE E/E' determinations using TDI closely approximate PAOP.

Respiratory variations of aortic VTI: a new index of hypovolemia and fluid responsiveness

In 12 mechanically ventilated and anesthetized rabbits, we investigated whether the magnitude of respiratory changes in the aortic velocity time integral (VTI(Ao)), recorded by transthoracic echocardiography (TTE) during a stepwise blood withdrawal and restitution, could be used as a reliable indicator of volume depletion and responsiveness. At each step, left and right ventricular dimensions and the aortic diameter and VTI(Ao) were recorded to calculate stroke volume (SV) and cardiac output (CO). Respiratory changes of VTI(Ao) (maximal - minimal values divided by their respective means) were calculated. The amount of blood withdrawal correlated negatively with left and right ventricular diastolic diameters, VTI(Ao), SV, and CO and correlated directly with respiratory changes of VTI(Ao). Respiratory VTI(Ao) variations (but not other parameters) at the last blood withdrawal step was also correlated with changes in SV after blood restitution (r = 0.83, P < 0.001). In conclusion, respiratory variations in VTI(Ao) using TTE appear to be a sensitive index of blood volume depletion and restitution. This dynamic parameter predicted fluid responsiveness more reliably than static markers of cardiac preload.

Volume expansion using pentastarch does not change gastric-arterial CO2 gradient or gastric intramucosal pH in patients who have sepsis syndrome

OBJECTIVE

In hypovolemic patients with sepsis syndrome, to determine the effects of colloid volume infusion using 10% pentastarch on abnormal gastric tonometer measurements (gastric intramucosal CO2 tension, gastric intramucosal-arterial PCO2 gradient, and gastric intramucosal pH [pHi]) and on cardiac index, global oxygen delivery, and hemoglobin.

DESIGN

Prospective prepost intervention study.

SETTING

Tertiary care, university-affiliated 15-bed general systems intensive care unit.

PATIENTS

Patients were studied who had sepsis syndrome, who had pulmonary arterial catheters in place, who were hypovolemic (pulmonary arterial occlusion pressure [PAOP] <15 mm Hg), and who had a gastric arterial PCO2 gradient >10 mm Hg.

INTERVENTIONS

Baseline measurements of gastric intramucosal CO2 tension, gastric intramucosal-arterial PCO2 gradient, and pHi, as well as arterial lactate, pulmonary arterial occlusion, central venous and systemic arterial pressures, thermodilution cardiac output, and temperature. Boluses of 500 mL pentastarch were administered to a total of 1,000 mL or until PAOP was >18 mm Hg. Measurements were repeated at 30 mins and 120 mins postinfusion of pentastarch.

MAIN RESULTS

Volume infusion using pentastarch did not change gastric PCO2, gastric-arterial PCO2 gradient, or pHi. Volume expansion with pentastarch significantly increased cardiac index, global oxygen delivery, and PAOP. Administration of pentastarch decreased hemoglobin and arterial lactate at 30 mins but not at 120 mins.

CONCLUSIONS

Volume expansion using a colloidal solution of 10% pentastarch does not change abnormal intramucosal CO2 tension, gastric-arterial PCO2 gradient, or pHi in critically ill hypovolemic patients who have sepsis syndrome despite increasing cardiac index, oxygen delivery, and pulmonary artery occlusion pressure.

Rational manipulation of oxygen delivery

BACKGROUND

Optimization of oxygen delivery remains the best method to prevent and the only way to treat common intensive care unit syndromes such as sepsis, multiple organ dysfunction, and acute lung injury. This paper reviews the elements of oxygen delivery, describes how clinical interventions work through those elements to alter oxygen delivery, reviews theoretical and empirical data relating to manipulation of each element, and distinguishes between therapeutic means and clinical endpoints in the care of the critically ill.

MATERIALS AND METHODS

Recent literature is reviewed. Relevant equations are detailed. Computer models and patient data illustrate key points.

RESULTS

Clinical interventions intended to improve oxygen delivery all work through at least one of seven variables (oxygen saturation, hemoglobin concentration, heart rate, mean arterial blood pressure, systemic vascular resistance, end-diastolic volume, and ejection fraction). Because interventions that increase oxygen delivery are always accompanied by physiologic costs, cavalier application of any therapy in the intensive care unit may actually decrease oxygen delivery, harming the critically ill patient. Various clinical indicators may be used as endpoints to guide therapy.

CONCLUSIONS

While a systematic consideration of the elements of oxygen delivery reveals weaknesses in experimental evidence guiding optimal treatment of shock, reasonable strategies as well as avoidable pitfalls emerge from the data. Furthermore, facility with each of the elements of oxygen delivery makes ICU management easier to teach and to apply.

The use of transesophageal echocardiography for preload assessment in critically ill patients

IV volume is often administered to patients in an intensive care unit (ICU) to improve cardiovascular function. We investigated the relationship between stroke volume (SV) and left ventricular (LV) size by using transesophageal echocardiography (TEE) in a population of 20 ICU patients and 21 postoperative cardiac surgical patients. We also examined whether LV end diastolic area (EDA), by TEE, could identify patients who increased SV by 20% or more (responders) after 500 mL of pentastarch administration. There was only a modest relationship (r = 0.60) between the EDA and the SV in all patients. No relationship could be found between the pulmonary capillary wedge pressure (PCWP) and the EDA in all patients. Both responder and nonresponder PCWP increased significantly after volume administration. Only responder EDA increased significantly after volume administration. Responders had significantly lower EDA (15.3 +/- 5.4 cm(2)) and PCWP (12.2 +/- 2.2 mm Hg) when compared with nonresponders (20.2 +/- 4.8 cm(2)) and 15.9 +/- 3.1 mm Hg, respectively). Few ICU patients and only those with a small EDA responded to volume administration. It was not possible to identify an overall optimal LV EDA below which most patients demonstrate volume-recruitable increases in SV.

IMPLICATIONS

In a ventilated intensive care unit and cardiac surgical population, transesophageal echocardiography and pulmonary artery catheter are sensitive in detecting changes in preload after volume administration. Few patients demonstrate volume-recruitable increases in stroke volume when compared to cardiac surgical patients. It is not possible to establish an overall end diastolic threshold below which a large proportion of ventilated patients respond to volume administration.