Estimation of errors in determining intrathoracic blood volume using thermal dilution in pigs with acute lung injury and haemorrhage †

Relationship of Extravascular Lung Water and Pulmonary Vascular Permeability to Respiratory Mechanics in Patients with COVID-19-Induced ARDS

During acute respiratory distress syndrome (ARDS), the increase in pulmonary vascular permeability and lung water induced by pulmonary inflammation may be related to altered lung compliance. A better understanding of the interactions between respiratory mechanics variables and lung water or capillary permeability would allow a more personalized monitoring and adaptation of therapies for patients with ARDS. Therefore, our main objective was to investigate the relationship between extravascular lung water (EVLW) and/or pulmonary vascular permeability index (PVPI) and respiratory mechanic variables in patients with COVID-19-induced ARDS. This is a retrospective observational study from prospectively collected data in a cohort of 107 critically ill patients with COVID-19-induced ARDS from March 2020 to May 2021. We analyzed relationships between variables using repeated measurements correlations. We found no clinically relevant correlations between EVLW and the respiratory mechanics variables (driving pressure (correlation coefficient [CI 95%]: 0.017 [-0.064; 0.098]), plateau pressure (0.123 [0.043; 0.202]), respiratory system compliance (-0.003 [-0.084; 0.079]) or positive end-expiratory pressure (0.203 [0.126; 0.278])). Similarly, there were no relevant correlations between PVPI and these same respiratory mechanics variables (0.051 [-0.131; 0.035], 0.059 [-0.022; 0.140], 0.072 [-0.090; 0.153] and 0.22 [0.141; 0.293], respectively). In a cohort of patients with COVID-19-induced ARDS, EVLW and PVPI values are independent from respiratory system compliance and driving pressure. Optimal monitoring of these patients should combine both respiratory and TPTD variables.

Gunanti Soeyono DV, Bardosono S, Jusman S, Siagian M, Lubis M. Resuscitation of hemorrhagic shock using normal saline does not damage the glycocalyx in the immediate resuscitation phase

OBJECTIVES:

The objectives were to study the effect of aggressive resuscitation using normal saline on hemodynamics, serum atrial natriuretic peptide (ANP), syndecan-1 (marker of endothelial glycocalyx shedding), and extravascular lung water index (ELWI) following hemorrhagic shock.

METHODS:

Eleven male piglets (Sus scrofa) underwent blood drawing to create 20% drop in mean arterial pressure (MAP). Two-phase resuscitation was performed: Phase 1 using normal saline of an equal volume of blood drawn to create shock and Phase 2 using 40 ml/kg BW of normal saline to simulate hypervolemia and hemodilution. Heart rate, MAP, cardiac index (CI), systemic vascular resistance index, oxygen delivery (DO₂), global end-diastolic volume index, ELWI, hemoglobin (Hb), lactate, ANP, and syndecan-1 at each phase and up to 60 min following Phase 2 resuscitation were recorded.

RESULTS:

Phase 2 resuscitation significantly decreased Hb concentration (P = 0.006), however, DO₂ was maintained (P = 1.000). CI increased from shock to Phase 1 (P = 0.029) and further increase in Phase 2 resuscitation (P = 0.001). Overall, there was a transient increase of ANP following Phase 1 resuscitation, from 85.20 ± 40.86 ng/L at baseline to 106.42 ± 33.71 ng/L (P = 0.260). Serum syndecan-1 and ELWI change at all phases were not significant.

CONCLUSIONS:

We demonstrate compensatory protective mechanism despite overzealous fluid resuscitation. Compensatory increased CI despite decreased Hb maintained DO₂. In the absence of inflammation, serum ANP did not increase significantly, no glycocalyx shedding occurred, subsequently no change in ELWI. We show that factors other than volume overload are more dominant in causing glycocalyx shedding.

Volume Based Resuscitation and Intestinal Microcirculation after Ischaemia/Reperfusion Injury: Results of an Exploratory Aortic Clamping Study in Pigs

OBJECTIVES

In the presence of ischaemia/reperfusion (I/R) induced endothelial injury, volume administration may not correlate with increased microcirculation. The aim of this study was to evaluate intestinal microcirculation after standardised sequential volume loading in an animal model of I/R injury following supracoeliac aortic clamping.

METHODS

This was a prospective exploratory pilot animal study. Intestinal I/R injury was induced in eight pigs during experimental thoraco-abdominal aortic repair. After 6 h of I/R, microcirculatory blood flow (mFlux, measured in the ileum using direct laser speckle contrast imaging) and macrohaemodynamic parameters (using trans-cardiopulmonary thermodilution) were measured and measurements were repeated after each of four sequential volume loading steps (VLS1 - 4). Each load was administered over 5 min followed by another 5 min for equilibration.

RESULTS

All animals survived until after VLS4. After 6 h of I/R cardiac output (CO) (p < .001) and mFlux (p < .001) had both decreased. CO increased again after VLS1 (p < .001) and VLS2 (p = .036), whereas mFlux did not change. In contrast, mFlux further decreased after VLS3 (p < .01) and VLS4 (p < .001), whereas CO did not change anymore. Extravascular lung water continued to increase after VLS2 (p = .046) and VLS4 (p = .049).

CONCLUSIONS

I/R leads to impaired intestinal microcirculation, which was not restored by volume administration in spite of improved CO. In contrast, further volume administration exceeding preload reserves was associated with additional decreases in the intestinal microcirculation. The potentially negative effect of excessive volume resuscitation after I/R injury should encourage further translational research.

The effects of differential injection sites of cold saline on transpulmonary thermodilution parameter values

AIM

To investigate the effects of differential sites for cold saline injection on transpulmonary thermodilution parameter values.

METHODS

This was a prospective study. Twelve patients were recruited for the following examinations: control condition (injection site at proximal injection end of the Swan-Ganz catheter), proximal end condition (injection site at sheath of the Swan-Ganz catheter), and distal end condition (injection site at PA end of the Swan-Ganz catheter). Sixty measurements were performed for each condition. The cardiac index, global end diastolic volume index (GEDI), and extravascular lung water index for the three different injection sites were recorded from each patient. In addition, the mean transmission time (MTt), downslope time, and area under the curve obtained from PiCCO-VoLEF-Win software were compared among different groups.

RESULTS

There were no differences in cardiac index and extravascular lung water index values among the three conditions (P>0.05). There were no differences in GEDI between the proximal end condition and control condition (P>0.05), while the GEDI was significantly lower for the distal end condition (493.33±254.65 mL/m(2)) than for the control condition (645.53±234.46 mL/m(2)) (P<0.05) and proximal end condition (717.96±321.63 mL/m(2)) (P<0.01). There were no differences in downslope time and area under the curve among the three conditions (P>0.05). There were no differences in MTt between the proximal end condition and control condition (P>0.05), while the MTt was significantly lower for distal end condition (40.22±16.37 seconds) than for the control condition (42.91±17.93 seconds) (P<0.05) and proximal end condition (47.16±16.64 seconds) (P<0.01).

CONCLUSION

The differential sites for cold saline injection impacted transpulmonary thermodilution parameter values.

Validation of extravascular lung water measurement by transpulmonary thermodilution in a pediatric animal model

OBJECTIVE

The measurement of extravascular lung water using the transpulmonary thermodilution technique enables the bedside quantification of the amount of pulmonary edema. Children have higher indexed to body weight values of extravascular lung water compared with adults. Transpulmonary thermodilution measurements of extravascular lung water in children have not yet been validated. The purpose of this study was to validate the extravascular lung water measurements with the transpulmonary thermodilution method over a wide range of lung water values in a pediatric animal model.

DESIGN

Experimental animal intervention study.

SETTING

Animal laboratory at the Radboud University Nijmegen, The Netherlands.

SUBJECTS

Eleven lambs.

INTERVENTION

Pulmonary edema was induced using a surfactant washout model.

MEASUREMENTS AND MAIN RESULTS

Between the lavages, extravascular lung water index was estimated using transpulmonary single and double indicator dilution. Two additional lambs were used to estimate extravascular lung water index in lungs without pulmonary edema. The final extravascular lung water index results were compared with the extravascular lung water index estimations by postmortem gravimetry (EVLWIG). The results were analyzed using both correlation and Bland-Altman statistics. Extravascular lung water index by transpulmonary thermodilution (EVLWITPTD) correlated significantly with either EVLWIG (r = 0.88) or with extravascular lung water index by transpulmonary double indicator dilution (EVLWITPDD) (r = 0.98). The mean bias with EVLWIG was 12.2 mL/kg (limits of agreement ± 10.9 mL/kg) and with EVLWITPDD 2.4 mL/kg (limits of agreement ± 3.8 mL/kg). The percentage errors were 41% and 14%, respectively. The bias became more positive when the mean of EVLWITPTD and EVLWIG increased (r = 0.72; p = 0.003).

CONCLUSIONS

EVLWITPTD was significantly correlated to the postmortem gravimetric gold standard, although a significant overestimation was demonstrated with increasing pulmonary edema.

Sildenafil prevents the increase of extravascular lung water and pulmonary hypertension after meconium aspiration in newborn piglets

Meconium aspiration syndrome causes respiratory failure after birth and in vivo monitoring of pulmonary edema is difficult. The objective of the present study was to assess hemodynamic changes and edema measured by transcardiopulmonary thermodilution in low weight newborn piglets. Additionally, the effect of early administration of sildenafil (2 mg/kg vo, 30 min after meconium aspiration) on this critical parameter was determined in the meconium aspiration syndrome model. Thirty-eight mechanically ventilated anesthetized male piglets (Sus scrofa domestica) aged 12 to 72 h (1660 ± 192 g) received diluted fresh human meconium in the airway in order to evoke pulmonary hypertension (PHT). Extravascular lung water was measured in vivo with a PiCCO monitor and ex vivo by the gravimetric method, resulting in an overestimate of 3.5 ± 2.3 mL compared to the first measurement. A significant PHT of 15 Torr above basal pressure was observed, similar to that of severely affected humans, leading to an increase in ventilatory support. The vascular permeability index increased 57%, suggesting altered alveolocapillary membrane permeability. Histology revealed tissue vessel congestion and nonspecific chemical pneumonitis. A group of animals received sildenafil, which prevented the development of PHT and lung edema, as evaluated by in vivo monitoring. In summary, the transcardiopulmonary thermodilution method is a reliable tool for monitoring critical newborn changes, offering the opportunity to experimentally explore putative therapeutics in vivo. Sildenafil could be employed to prevent PHT and edema if used in the first stages of development of the disease.

Emerging trends in minimally invasive haemodynamic monitoring and optimization of fluid therapy

BACKGROUND

For decades the pulmonary artery catheter has been the mainstay of cardiac output monitoring in critically ill patients, and pressure-based indices of ventricular filling have been used to gauge fluid requirements with acknowledged limitations. In recent years, alternative technologies have become available which are minimally invasive, allow beat-to-beat cardiac output monitoring and permit assessment of fluid requirements by volumetric means and by allowing assessment of heart-lung interaction in mechanically ventilated patients.

METHODS

A qualitative review of the basic science behind the transpulmonary dilution technique used in the measurement of cardiac output, global end-diastolic volume and extravascular lung water; the basic science and validation of pulse contour analysis methods of real-time cardiac output monitoring; the application and limitations of these technologies to guide rational fluid therapy in surgical and critically ill patients.

RESULTS

Transpulmonary dilution techniques correlate well with pulmonary artery catheter-derived measurement of cardiac output. Volumetric measures of preload appear to be superior to central venous and pulmonary artery occlusion pressures. Dynamic indices of preload responsiveness such as stroke volume variation are more useful than static measures in mechanically ventilated patients.

CONCLUSION

In fully mechanically ventilated patients, dynamic measurements of heart-lung interaction such as stroke volume variation are superior to static measures of preload in assessing whether a patient is volume-responsive (i.e. will increase stroke volume in response to a fluid challenge). For patients who are not fully mechanically ventilated, pulse contour analysis allows real-time assessment of increases in cardiac output in response to passive leg-raising.

Measurement of extravascular lung water using the single indicator method in patients: research and potential clinical value

Extravascular lung water includes all of the fluid within the lung but outside of the vasculature. Lung water increases as a result of increased hydrostatic vascular pressure or from an increase in lung endothelial and epithelial permeability or both. Experimentally, extravascular lung water has been measured gravimetrically. Clinically, the chest radiograph is used to determine whether extravascular lung water is present but is an insensitive instrument for determining the quantity of lung water. Bedside measurement of extravascular lung water in patients is now possible using a single indicator thermodilution method. This review critically evaluates the experimental and clinical evidence supporting the potential value of measuring extravascular lung water in patients using the single indicator method.

Comparison of three methods of extravascular lung water volume measurement in patients after cardiac surgery

INTRODUCTION

Measurement of extravascular lung water (EVLW) by using the lithium-thermal (Li-thermal) and single-thermal indicator dilution methods was compared with the indocyanine green-thermal (ICG-thermal) method in humans.

METHODS

Single-center observational study involving patients undergoing cardiac surgery with cardiopulmonary bypass. Paired measurements were taken 1, 2, 4, and 6 hours after surgery. Bland-Altman analysis was used to calculate bias and limits of agreement. Data are presented as mean (SD) or median (IQR).

RESULTS

Seventeen patients were recruited (age, 69 years (54 to 87 years); Parsonnet score 10 (0 to 29)). Sixteen ICG-thermal measurements were excluded after blinded assessment because of poor-quality indicator dilution curves. EVLW volume as measured by the ICG-thermal technique was 4.6 (1.9) ml/kg, compared with 5.3 (1.4) ml/kg for the single-thermal method. Measurements taken with the Li-thermal method were clearly erroneous (-7.6 (7.4) ml/kg). In comparison with simultaneous measurements with the ICG-thermal method, single-thermal measurements had an acceptable degree of bias, but limits of agreement were poor (bias, -0.3 ml/kg (2.3)). Li-thermal measurements compared poorly with the ICG-thermal reference method (bias, 13.2 ml/kg (14.4)).

CONCLUSIONS

The principal finding of this study was that the prototype Li-thermal method did not provide reliable measurements of EVLW volume when compared with the ICG-thermal reference technique. Although minimal bias was associated with the single-thermal method, limits of agreement were approximately 45% of the normal value of EVLW volume. The Li-thermal method performed very poorly because of the overestimation of mean indicator transit time by using an external lithium ion electrode. These findings suggest that the assessment of lung water content by lithium-indicator dilution is not sufficiently reliable for clinical use in individual patients.

Model-based identification of PEEP titrations during different volemic levels

A cardiovascular system (CVS) model has previously been validated in simulated cardiac and circulatory disease states. It has also been shown to accurately capture all main hemodynamic trends in a porcine model of pulmonary embolism. In this research, a slightly extended CVS model and parameter identification process are presented and validated in a porcine experiment of positive end-expiratory pressure (PEEP) titrations at different volemic levels. The model is extended to more physiologically represent the separation of venous and arterial circulation. Errors for the identified model are within 5% when re-simulated and compared to clinical data. All identified parameter trends match clinically expected changes. This work represents another clinical validation of the underlying fundamental CVS model, and the methods and approach of using them for cardiovascular diagnosis in critical care.

How to measure and interpret volumetric measures of preload

PURPOSE OF REVIEW

To update the situation over the past few years on the clinical application of volumetric measures of preload in critically ill patients.

RECENT FINDINGS

Cardiac filling pressures monitoring is unreliable for assessing cardiac preload in mechanically ventilated critically ill patients. The transpulmonary dilution indicator technique was shown to better identify preload than pulmonary arterial catheterization. Measuring static preload index as intrathoracic blood volume or global end diastolic volume provides a good preload index, either in experimental or in different clinical settings.

SUMMARY

Volumetric measures of preload are good preload indexes. These data are to be interpreted together with the clinical patient's condition, conventional hemodynamic data and the course of illness in critically ill patients. In order to evaluate whether the application of a predefined therapy algorithm based on volumetric monitoring can improve patients' outcome, more studies are needed.

Indicator dilution measurements of extravascular lung water: basic assumptions and observations

Since they were introduced more than five decades ago, a variety of single-pass indicator, thermal, and osmotic dilution approaches have been developed for detecting and measuring excess fluid in the lungs. This brief review discusses why studies of the extravascular lung water (EVLW) continue to intrigue physiologists and clinicians and the likelihood that they will become sufficiently reliable for more widespread use. Emphasis is placed on the basic assumptions that underlie these measurements and limitations imposed by the nature of the data that are collected. A distinction is made between approaches that are based on compartmental models of solute and water exchange and those that represent extensions of more conventional washout procedures, which have been utilized extensively for measurements of gas volumes in the lungs. Although the compartmental approach has been used to simplify indicator dilution studies by eliminating the need for a vascular indicator, it is based on assumptions that may not be realistic. Early recirculation inevitably limits the period in which observations can be made and impairs detection of those portions of the lungs with decreased perfusion. These general principles are also used to develop a new method of analyzing osmotic transient studies. A short account is given of EVLW observations that have been made in animals and humans. Both the sensitivity and specificity of EVLW measurements in humans are uncertain, and the normal clinical range of EVLW remains in doubt.

Bedside assessment of extravascular lung water by dilution methods: temptations and pitfalls

OBJECTIVES

To review the advantages and limitations of dilution methods to assess extravascular lung water (EVLW) at the bedside and to discuss the clinical value of EVLW measurements.

DATA SOURCE

Experimental and clinical studies were searched in PUBMED by using "extravascular lung water" and "dilution method" as keywords and further selected as studies investigating either the reliability or the clinical usefulness of dilution methods to assess EVLW. Related articles and the reference lists of selected studies were scanned for additional relevant references.

CONCLUSIONS

Both the double-indicator (thermo-dye) dilution and the single-indicator (cold saline) dilution methods showed close agreement with gravimetric measurement of EVLW (the reference ex vivo method) and have the advantage of being available at the bedside. Most limitations of dilution methods have been described in experimental conditions and lead to an underestimation of EVLW. These limitations include large pulmonary vascular obstruction, focal lung injury, and lung resection. Dilution methods provide an easy and clinically acceptable estimation of EVLW in most critically ill patients, including those with acute respiratory distress syndrome (ARDS). Assessing EVLW may be useful to predict outcome, to diagnose pulmonary edema, to better characterize patients with ARDS, to guide fluid therapy, and to assess the value of new treatments or ventilatory strategies in patients with pulmonary edema.

Extravascular lung water determined with single transpulmonary thermodilution correlates with the severity of sepsis-induced acute lung injury

OBJECTIVE

To find out if the extravascular lung water index (EVLWI) and the derived permeability indexes determined by the single transpulmonary thermodilution technique are associated with markers of acute lung injury in human septic shock.

DESIGN

Prospective, observational study.

SETTING

Mixed intensive care unit of a 900-bed university hospital.

PATIENTS

Thirty-eight consecutive adult patients with septic shock and acute lung injury.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The variables were assessed over a 72-hr period and included hemodynamics, EVLWI, and pulmonary vascular permeability indexes determined with the single indicator transpulmonary thermodilution technique, lung compliance, oxygenation ratio (Pao2/Fio2), lung injury score, cell counts, and the plasma concentration of endothelin-1. At day 1, EVLWI was elevated (>or=7 mL/kg) in 28 (74%) patients and correlated with lung compliance (r=-.48, p=.002), Pao2/Fio2 (r=-.50, p=.001), lung injury score (r=.46, p=.004), roentgenogram quadrants (r=.39, p=.02), and platelet count (r=-.43, p=.007). At day 3, EVLWI correlated with compliance (r=-.51, p=.002), Pao2/Fio2 (r=-.49, p = .006), and lung injury score (r=.53, p=.003). At day 3, EVLWI and pulmonary vascular permeability indexes were higher in nonsurvivors (p<.05). The plasma concentration of endothelin-1 (mean+/-sd) was significantly higher in patients with elevated EVLWI (>or=7 mL/kg) (3.85+/-1.40 vs. 2.07+/-0.38 pg/mL, respectively). Twenty-two (59%) patients died before day 28.

CONCLUSIONS

In human septic shock, EVLWI demonstrated moderate correlation with markers of acute lung injury, such as lung compliance, oxygenation ratio, roentgenogram quadrants, and lung injury score. In nonsurvivors, EVLWI and permeability indexes were significantly increased at day 3. Thus, EVLWI might be of value as an indicator of prognosis and severity of sepsis-induced acute lung injury.