Predictors of pulmonary edema formation during fluid loading in the critically ill with presumed hypovolemia*

Coexistence of a fluid responsive state and venous congestion signals in critically ill patients: a multicenter observational proof-of-concept study

BACKGROUND

Current recommendations support guiding fluid resuscitation through the assessment of fluid responsiveness. Recently, the concept of fluid tolerance and the prevention of venous congestion (VC) have emerged as relevant aspects to be considered to avoid potentially deleterious side effects of fluid resuscitation. However, there is paucity of data on the relationship of fluid responsiveness and VC. This study aims to compare the prevalence of venous congestion in fluid responsive and fluid unresponsive critically ill patients after intensive care (ICU) admission.

METHODS

Multicenter, prospective cross-sectional observational study conducted in three medical-surgical ICUs in Chile. Consecutive mechanically ventilated patients that required vasopressors and admitted < 24 h to ICU were included between November 2022 and June 2023. Patients were assessed simultaneously for fluid responsiveness and VC at a single timepoint. Fluid responsiveness status, VC signals such as central venous pressure, estimation of left ventricular filling pressures, lung, and abdominal ultrasound congestion indexes and relevant clinical data were collected.

RESULTS

Ninety patients were included. Median age was 63 [45-71] years old, and median SOFA score was 9 [7-11]. Thirty-eight percent of the patients were fluid responsive (FR+), while 62% were fluid unresponsive (FR-). The most prevalent diagnosis was sepsis (41%) followed by respiratory failure (22%). The prevalence of at least one VC signal was not significantly different between FR+ and FR- groups (53% vs. 57%, p = 0.69), as well as the proportion of patients with 2 or 3 VC signals (15% vs. 21%, p = 0.4). We found no association between fluid balance, CRT status, or diagnostic group and the presence of VC signals.

CONCLUSIONS

Venous congestion signals were prevalent in both fluid responsive and unresponsive critically ill patients. The presence of venous congestion was not associated with fluid balance or diagnostic group. Further studies should assess the clinical relevance of these results and their potential impact on resuscitation and monitoring practices.

The emerging concept of fluid tolerance: A position paper

Fluid resuscitation is a core component of emergency and critical care medicine. While the focus of clinicians has largely been on detecting patients who would respond to fluid therapy, relatively little work has been done on assessing patients' tolerance to this therapy. In this article we seek to review the concept of fluid tolerance, propose a working definition, and introduce relevant clinical signals by which physicians can assess fluid tolerance, hopefully becoming a starting point for further research.

Fluid Therapy in Pulmonary Disease: How Careful Do We Need to Be?

Intravenous fluid therapy is a vital and life-saving therapeutic in veterinary medicine. In the absence of heart or lung disease, trauma or sepsis there is limited evidence that fluid therapy will have a detrimental effect on lung function. In healthy dogs there is a reasonable level of experimental evidence that supraphysiologic rates of fluid are required before signs of fluid overload are made evident. In cats, however, this may not be the case. There are higher rates of asymptomatic myocardial disease, but even in the absence of that it seems that some cats may be susceptible to fluid overload. Where systemic inflammation already exists the careful homeostatic and protective mechanisms within the lung are deranged and increases in hydrostatic pressure are more likely to result in fluid movement into the lung tissues. Strategies including restricting the use of intravenous crystalloid fluid administration and using blood products for management of severe hemorrhage are of increasing importance in human trauma and seem to be associated with fewer pulmonary complications, and lower mortality. Managing dogs and cats with sepsis and acute respiratory distress syndrome is already challenging, but ensuring adequate vascular expansion needs to be balanced with avoiding excessive volume administration which may negatively impact pulmonary function. While fluids remain crucial to management of these conditions, there will be an ongoing requirement to balance need without providing excess. The use of point of care ultrasound may provide clinicians with a non-invasive and accessible way to do this.

Effect of liberal versus restrictive fluid therapy on intraoperative lactate levels in robot- assisted colorectal surgery

Background and Aims

Minimally invasive and robotic surgeries need lesser fluid replacement but the role of restricted fluids in robotic surgeries other than prostatic surgeries has not been clearly defined. Our primary aim was to evaluate the effects of a restrictive fluid regimen versus a liberal policy on intra-operative lactate in robotic colorectal surgery. Secondary outcomes were need for vasopressors, extubation on table, post-operative renal functions and length of ICU (LOICU) stay.

Methods

American society of anaesthesiologists (ASA) physical status I-II patients scheduled for robot-assisted colorectal surgery were randomised into one of two groups, receiving either 2 mL/kg/h (Group R) or 4mL/kg/h, (group L). Fluid boluses of 250 ml were administered if mean arterial pressure (MAP) <65 mmHg or urine output <0.5 ml/kg/h. Norepinephrine was added for the blood pressure after 2 fluid boluses. Surgical field was assessed by modified Boezaart's scale and surgeon satisfaction by Likert scale.

Results

Demographics and baseline renal functions were comparable. Adjusted intra-operative lactate at 2 h, 4 h, and 6 h and need for noradrenaline and post-operative creatinine were similar. One patient in the group L was ventilated due to hypothermia. The field was better at the 4 h in group R and comparable at other time points. The LOICU stay was longer in Group L.

Conclusion

The use of restrictive fluid strategy of 2 mL/kg/h (group R) does not increase lactate levels or creatinine, improves surgical field at 4 h and shortens ICU stay in comparison to a liberal 4 mL/kg/h (group L) in robotic colorectal surgery.

Effects of 6% Tetrastarch and Lactated Ringer's Solution on Extravascular Lung Water and Markers of Acute Renal Injury in Hemorrhaged, Isoflurane-Anesthetized Healthy Dogs

Background

Tetrastarch can cause acute kidney injury (AKI) in humans with sepsis, but less likely to result in tissue edema than lactated Ringer's solution (LRS).

Objectives

Compare effects of volume replacement (VR) with LRS and 6% tetrastarch solution (TS) on extravascular lung water (EVLW) and markers of AKI in hemorrhaged dogs.

Animals

Six healthy English Pointer dogs (19.7–35.3 kg).

Methods

Prospective crossover study. Animals underwent anesthesia without hemorrhage (Control). Two weeks later, dogs hemorrhaged under anesthesia on 2 occasions (8‐week washout intervals) and randomly received VR with LRS or TS at 3 : 1 or 1 : 1 of shed blood, respectively. Anesthesia was maintained until 4 hour after VR for EVLW measurements derived from transpulmonary thermodilution cardiac output. Neutrophil gelatinase‐associated lipocalin (NGAL) and creatinine concentrations in plasma and urine were measured until 72 hour after VR.

Results

The EVLW index (mL/kg) was lower at 1 hour after TS (10.0 ± 1.9) in comparison with controls (11.9 ± 3.4, P = 0.04), and at 4 hour after TS (9.7 ± 1.9) in comparison with LRS (11.8 ± 2.7, P = 0.03). Arterial oxygen partial pressure‐to‐inspired oxygen fraction ratio did not differ among treatments from 0.5 to 4 hour after VR. Urine NGAL/creatinine ratio did not differ among treatments and remained below threshold for AKI (120,000 pg/mg).

Conclusions and Clinical Importance

Although TS causes less EVLW accumulation than LRS, neither fluid produced evidence of lung edema (impaired oxygenation). Both fluids appear not to cause AKI when used for VR after hemorrhage in healthy nonseptic dogs.

Electrical impedance tomography (EIT) for quantification of pulmonary edema in acute lung injury

Background

Assessment of pulmonary edema is a key factor in monitoring and guidance of therapy in critically ill patients. To date, methods available at the bedside for estimating the physiologic correlate of pulmonary edema, extravascular lung water, often are unreliable or require invasive measurements. The aim of the present study was to develop a novel approach to reliably assess extravascular lung water by making use of the functional imaging capabilities of electrical impedance tomography.

Methods

Thirty domestic pigs were anesthetized and randomized to three different groups. Group 1 was a sham group with no lung injury. Group 2 had acute lung injury induced by saline lavage. Group 3 had vascular lung injury induced by intravenous injection of oleic acid. A novel, noninvasive technique using changes in thoracic electrical impedance with lateral body rotation was used to measure a new metric, the lung water ratio_EIT, which reflects total extravascular lung water. The lung water ratio_EIT was compared with postmortem gravimetric lung water analysis and transcardiopulmonary thermodilution measurements.

Results

A significant correlation was found between extravascular lung water as measured by postmortem gravimetric analysis and electrical impedance tomography (r = 0.80; p < 0.05). Significant changes after lung injury were found in groups 2 and 3 in extravascular lung water derived from transcardiopulmonary thermodilution as well as in measurements derived by lung water ratio_EIT.

Conclusions

Extravascular lung water could be determined noninvasively by assessing characteristic changes observed on electrical impedance tomograms during lateral body rotation. The novel lung water ratio_EIT holds promise to become a noninvasive bedside measure of pulmonary edema.

Effect of dobutamine on extravascular lung water index, ventilator function, and perfusion parameters in acute respiratory distress syndrome associated with septic shock

BACKGROUND

The role of dobutamine in the relief of pulmonary edema during septic shock-induced acute respiratory distress syndrome (ARDS) remains undetermined, due to a lack of controllable and quantitative clinical studies. Our objective was to assess the potential effects of dobutamine on extravascular lung water index (ELWI) in septic shock-induced ARDS, reflecting its importance in pulmonary edema. At the same time, ventilator function and perfusion parameters were evaluated.

METHODS

We designed a prospective, non-randomized, non-blinded, controlled study to compare the differences in PiCCO parameters after 6 h of constant dobutamine infusion (15 μg/kg/min), in the baseline parameters in 26 septic shock-related ARDS patients with cardiac index ≥ 2.5I/min/m(2) and hyperlactatemia. These patients (12 survivors/14 non-survivors) were monitored using the PiCCO catheter system within 48 h of onset of septic shock. The dynamic changes in ELWI, which is typically used for quantifying the extent of pulmonary edema, were evaluated, and the corresponding ventilator function and tissue perfusion parameters were also measured.

RESULTS

Decreasing ELWI (p = 0.0376) was accompanied by significantly decreased SVRI (p < 0.0001). Despite a significant increase in cardiac output (p < 0.0001), no differences were found in ITBI or GEDI. Moreover, the required dose of norepinephrine was decreased (p = 0.0389), and urine output was increased (p = 0.0358), accompanied by stabilized lactacidemia and MAP. Additionally, airway pressure was moderately improved.

CONCLUSION

During the early stage of septic shock-induced ARDS, dobutamine treatment demonstrated a beneficial effect by relieving pulmonary edema in patients, without a negative elevation in preload or hemodynamics, which might account for the improvements in ventilator function and tissue hypoperfusion.

Cardiac preload responsiveness in children with cardiovascular dysfunction or dilated cardiomyopathy: a multicenter observational study

OBJECTIVES

To characterize cardiac preload responsiveness in pediatric patients with cardiovascular dysfunction and dilated cardiomyopathy using global end-diastolic volume index, stroke volume index, cardiac index, and extravascular lung water index.

DESIGN

Prospective multicenter observational study.

SETTING

Medical/surgical PICUs of seven Spanish University Medical Centers.

PATIENTS

Seventy-five pediatric patients (42 male, 33 female), median age 36 months (range, 1-207 mo), were divided into three groups: normal cardiovascular status, cardiovascular dysfunction, and dilated cardiomyopathy.

INTERVENTIONS

All patients received hemodynamic monitoring with PiCCO2 (Pulsion Medical System SE, Munich, Germany). We evaluated 598 transpulmonary thermodilution sets of measurements. In 40 patients, stroke volume index, cardiac index, and global end-diastolic volume index were measured before and after 66 fluid challenges and loadings to test fluid responsiveness at different preload levels.

MEASUREMENTS AND MAIN RESULTS

Global end-diastolic volume versus predicted body surface area exhibits a power-law relationship: Global end-diastolic volume = 488.8·predicted body surface area (r = 0.93). Four levels of cardiac preload were established from the resulting "normal" global end-diastolic volume index (= 488.8·predicted body surface area). Stroke volume index and cardiac index versus global end-diastolic volume index/normal global end-diastolic volume index built using a linear mixed model analysis emulated Frank-Starling curves: in cardiovascular dysfunction group, stroke volume index (geometric mean [95% CI]) was 27 mL/m (24-31 mL/m) at "≤ 0.67 times normal global end-diastolic volume index," 37 mL/m (35-40 mL/m) at "> 0.67 ≤ 1.33 times normal global end-diastolic volume index" (Δ stroke volume index = 35%; p < 0.0001; area under the receiver-operating characteristic curve = 75%), 45 mL/ m (41-49 mL/m) at "> 1.33 ≤ 1.51 times normal global end-diastolic volume index" (Δ stroke volume index = 21%; p < 0.0001; area under the receiver-operating characteristic curve = 73%), and 47 mL/m (43-51 mL/m) at "> 1.51 times normal global end-diastolic volume index" (Δ stroke volume index = 4%; p = 1; area under the receiver-operating characteristic curve = 54%). In dilated cardiomyopathy group, stroke volume index was 21 mL/m (17-26 mL/m) at "> 0.67 ≤ 1.33 times normal global end-diastolic volume index," 27 mL/m (21-34 mL/ m) at "> 1.33 ≤ 1.51 times normal global end-diastolic volume index" (Δ stroke volume index = 29%; p = 0.005; area under the receiver-operating characteristic curve = 64%), and 25 mL/m (20-32 mL/m) at "> 1.51 times normal global end-diastolic volume index" (Δ stroke volume index = -8%; p = 1; area under the receiver-operating characteristic curve = 54%).

CONCLUSIONS

This study provides "normal" values for global end-diastolic volume index and limits of cardiac preload responsiveness in pediatric patients with cardiovascular dysfunction and dilated cardiomyopathy: 1.33 times normal global end-diastolic volume index represents the upper limit of patent cardiac preload responsiveness, with the highest expected responsiveness being below 0.67 times normal global end-diastolic volume index. The maximum response of the Frank-Starling relationship and therefore the level of no additional preload reserve is 1.33 to 1.51 times normal global end-diastolic volume index. Above 1.51 times normal global end-diastolic volume index preload responsiveness is unlikely, and the risk of pulmonary edema is maximal.

Optimal range of global end-diastolic volume for fluid management after aneurysmal subarachnoid hemorrhage: a multicenter prospective cohort study

OBJECTIVES

Limited evidence supports the use of hemodynamic variables that correlate with delayed cerebral ischemia or pulmonary edema after aneurysmal subarachnoid hemorrhage. The aim of this study was to identify those hemodynamic variables that are associated with delayed cerebral ischemia and pulmonary edema after subarachnoid hemorrhage.

DESIGN

A multicenter prospective cohort study.

SETTING

Nine university hospitals in Japan.

PATIENTS

A total of 180 patients with aneurysmal subarachnoid hemorrhage.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Patients were prospectively monitored using a transpulmonary thermodilution system in the 14 days following subarachnoid hemorrhage. Delayed cerebral ischemia was developed in 35 patients (19.4%) and severe pulmonary edema was developed in 47 patients (26.1%). Using the Cox proportional hazards model, the mean global end-diastolic volume index (normal range, 680-800 mL/m) was the independent factor associated with the occurrence of delayed cerebral ischemia (hazard ratio, 0.74; 95% CI, 0.60-0.93; p = 0.008). Significant differences in global end-diastolic volume index were detected between the delayed cerebral ischemia and non-delayed cerebral ischemia groups (783 ± 25 mL/m vs 870 ± 14 mL/m; p = 0.007). The global end-diastolic volume index threshold that best correlated with delayed cerebral ischemia was less than 822 mL/m, as determined by receiver operating characteristic curves. Analysis of the Cox proportional hazards model indicated that the mean global end-diastolic volume index was the independent factor that associated with the occurrence of pulmonary edema (hazard ratio, 1.31; 95% CI, 1.02-1.71; p = 0.03). Furthermore, a significant positive correlation was identified between global end-diastolic volume index and extravascular lung water (r = 0.46; p < 0.001). The global end-diastolic volume index threshold that best correlated with severe pulmonary edema was greater than 921 mL/m.

CONCLUSIONS

Our findings suggest that global end-diastolic volume index impacts both delayed cerebral ischemia and pulmonary edema after subarachnoid hemorrhage. Maintaining global end-diastolic volume index slightly above normal levels has promise as a fluid management goal during the treatment of subarachnoid hemorrhage.

The role of invasive techniques in cardiopulmonary evaluation

PURPOSE OF REVIEW

To discuss the role of the invasive monitoring techniques pulmonary artery catheter (PAC) and transpulmonary thermodilution (TPD) for cardiopulmonary monitoring in the critically ill patient.

RECENT FINDINGS

Characterization of the nature of hemodynamic alterations and hemodynamic optimization can be achieved both with PAC and TPD. Some recent trials suggest that volumetric measurements may be preferred in conditions with preserved left ventricular systolic function, whereas pressure measurements should be preferred in patients with altered left ventricular systolic function. Extravascular lung water is strongly associated with outcome and may be used to reflect the impact of fluid management strategies. The time response of this measurement needs still to be better defined.

SUMMARY

This review highlights that PAC and TPD have an important role in cardiopulmonary monitoring of critically ill patients. Both techniques can be used efficiently to diagnose the nature of circulatory or respiratory failure and to monitor the effects of therapies. The choice of the technique should be guided by the patient's condition and the need for additional measurements rather than based on physician's preferences.

Dose and type of crystalloid fluid therapy in adult hospitalized patients

OBJECTIVE

In this narrative review, an overview is given of the pros and cons of various crystalloid fluids used for infusion during initial resuscitation or maintenance phases in adult hospitalized patients. Special emphasis is given on dose, composition of fluids, presence of buffers (in balanced solutions) and electrolytes, according to recent literature. We also review the use of hypertonic solutions.

METHODS

We extracted relevant clinical literature in English specifically examining patient-oriented outcomes related to fluid volume and type.

RESULTS

A restrictive fluid therapy prevents complications seen with liberal, large-volume therapy, even though restrictive fluid loading with crystalloids may not demonstrate large hemodynamic effects in surgical or septic patients. Hypertonic solutions may serve the purpose of small volume resuscitation but carry the disadvantage of hypernatremia. Hypotonic solutions are contraindicated in (impending) cerebral edema, whereas hypertonic solutions are probably more helpful in ameliorating than in preventing this condition and improving outcome. Balanced solutions offer a better approach for plasma composition than unbalanced ones, and the evidence for benefits in patient morbidity and mortality is increasing, particularly by helping to prevent acute kidney injury.

CONCLUSIONS

Isotonic and hypertonic crystalloid fluids are the fluids of choice for resuscitation from hypovolemia and shock. The evidence that balanced solutions are superior to unbalanced ones is increasing. Hypertonic saline is effective in mannitol-refractory intracranial hypertension, whereas hypotonic solutions are contraindicated in this condition.

Tonic regulation of vascular permeability

Our major theme is that the layered structure of the endothelial barrier requires continuous activation of signalling pathways regulated by sphingosine-1-phosphate (S1P) and intracellular cAMP. These pathways modulate the adherens junction, continuity of tight junction strands, and the balance of synthesis and degradation of glycocalyx components. We evaluate recent evidence that baseline permeability is maintained by constant activity of mechanisms involving the small GTPases Rap1 and Rac1. In the basal state, the barrier is compromised when activities of the small GTPases are reduced by low S1P supply or delivery. With inflammatory stimulus, increased permeability can be understood in part as the action of signalling to reduce Rap1 and Rac1 activation. With the hypothesis that microvessel permeability and selectivity under both normal and inflammatory conditions are regulated by mechanisms that are continuously active, it follows that when S1P or intracellular cAMP are elevated at the time of inflammatory stimulus, they can buffer changes induced by inflammatory agents and maintain normal barrier stability. When endothelium is exposed to inflammatory conditions and subsequently exposed to elevated S1P or intracellular cAMP, the same processes restore the functional barrier by first re-establishing the adherens junction, then modulating tight junctions and glycocalyx. In more extreme inflammatory conditions, loss of the inhibitory actions of Rac1-dependent mechanisms may promote expression of more inflammatory endothelial phenotypes by contributing to the up-regulation of RhoA-dependent contractile mechanisms and the sustained loss of surface glycocalyx allowing access of inflammatory cells to the endothelium.

Prediction of pulmonary edema by plasma protein levels in patients with sepsis

PURPOSE

The difficulties of fluid therapy in patients with septic shock are to maintain sufficient vascular volume while preventing pulmonary edema formation. Thus, it is important to find a biomarker that can reliably predict pulmonary edema formation after fluid loading. We evaluated the association of plasma protein levels with the increase in extravascular lung water index (ΔEVLWI) after fluid loading.

METHODS

This was an observational study in which we retrospectively reviewed medical records of septic patients in whom hemodynamic variables were measured by transpulmonary thermodilution technique before and after fluid loading. Plasma protein levels were measured before fluid loading. Patients were divided into 2 groups according to the changes in EVLWI (ΔEVLWI ≥ 10%) after fluid loading. Diagnostic performance of plasma proteins in predicting pulmonary edema formation was assessed.

RESULTS

A total of 62 patients were included, and 27 of them showed a ΔEVLWI 10% or higher after fluid loading. Plasma albumin and transferrin were significantly lower in this group than in the group with ΔEVLWI less than 10% (21.7 ± 5.8 vs 25.3 ± 5.0 g/L for albumin, P < .05; 107.9 ± 50.1 vs 136.8 ± 44.2 mg/dL for transferrin, P < .05). Areas under the curve of albumin and transferrin were 0.68 (cardiac index, 0.54-0.83) and 0.72 (cardiac index, 0.59-0.86), respectively. At a cutoff value of 87.9 mg/dL, transferrin had a sensitivity of 0.91 in predicting ΔEVLWI 10% or higher.

CONCLUSIONS

Plasma transferrin and albumin levels were associated with ΔEVLWI 10% or higher after fluid loading. The high sensitivity of both biomarkers indicated that patients with normal values were less likely to develop pulmonary edema after fluid loading.

Fluid management in acute kidney injury

Fluid management in critical illness has undergone extensive reevaluation in the past decade. Since a significant percentage of critically ill patients develop acute kidney injury (AKI), optimal fluid management is even more paramount to prevent the ill effects of either underhydration or overhydration. The concepts of early goal-directed fluid therapy (EGDT) and conservative late fluid management permeate current clinical research, and the independent association between fluid accumulation and mortality has been repeatedly demonstrated. A number of prospective randomized trials are planned to provide an adequately powered assessment of the effect of EGDT or earlier renal replacement therapy initiation in patients with, or at risk for AKI. The aim of this analytical review is to use existing clinical and physiological studies to support a 3-phase model of fluid management in the critically ill patient with AKI.

Extravascular lung water does not increase in hypovolemic patients after a fluid-loading protocol guided by the stroke volume variation

Introduction. Circulatory failure secondary to hypovolemia is a common situation in critical care patients. Volume replacement is the first option for the treatment of hypovolemia. A possible complication of volume loading is pulmonary edema, quantified at the bedside by the measurement of extravascular lung water index (ELWI). ELWI predicts progression to acute lung injury (ALI) in patients with risk factors for developing it. The aim of this study was to assess whether fluid loading guided by the stroke volume variation (SVV), in patients presumed to be hypovolemic, increased ELWI or not. Methods. Prospective study of 17 consecutive postoperative, fully mechanically ventilated patients diagnosed with circulatory failure secondary to presumed hypovolemia were included. Cardiac index (CI), ELWI, SVV, and global end-diastolic volume index (GEDI) were determined using the transpulmonary thermodilution technique during the first 12 hours after fluid loading. Volume replacement was done with a strict hemodynamic protocol. Results. Fluid loading produced a significant increase in CI and a decrease in SVV. ELWI did not increase. No correlation was found between the amount of fluids administered and the change in ELWI. Conclusion. Fluid loading guided by SVV in hypovolemic and fully mechanically ventilated patients in sinus rhythm does not increase ELWI.