Analysis of Transpulmonary Thermodilution Data Confirms the Influence of Renal Replacement Therapy on Thermodilution Hemodynamic Measurements

Changes of cardiac output and velocity time integral in blood return at the end of renal replacement therapy predict fluid responsiveness in critically Ill patients with acute circulatory failure

OBJECTIVES

To observe if blood return, also defined as the blood infusion test (BIT) could predict fluid responsiveness in critically ill patients with acute circulatory failure and renal replacement therapy (RRT).

METHODS

This was a single-center, prospective, diagnostic accuracy study. Before BIT, the passive leg raise test (PLRT) was performed to record the change of cardiac output (ΔCO) by pulse contour analysis, and ΔCO >  = 10% was defined as the fluid responder. Meanwhile, the change in velocity time integral (ΔVTI) was recorded by ultrasound. Later, the ΔCO and ΔVTI during BIT were recorded 5-10 min after PLRT. The receiver-operating characteristic curves of ΔCO and ΔVTI of BIT were performed in predicting the fluid responder defined by PLRT.

RESULTS

A total of 43 patients with acute circulatory failure undergoing RRT were enrolled in the present study, and 25 patients (58.1%) were recognized as responders during PLRT. According to the receiver-operating characteristic curves, the cutoff value of ΔCO was 10% and ΔVTI was 9% during BIT with the area under curve of 0.96 and 0.94, respectively.

CONCLUSIONS

BIT in RRT could identify fluid responsiveness in critically ill patients with shock.

TRIAL REGISTRATION

ChiCTR-DDD-17010534. Registered on 30/01/2017 (retrospective registration).

Transpulmonary thermodilution in patients treated with veno-venous extracorporeal membrane oxygenation

BACKGROUND

We tested the effect of different blood flow levels in the extracorporeal circuit on the measurements of cardiac stroke volume (SV), global end-diastolic volume index (GEDVI) and extravascular lung water index derived from transpulmonary thermodilution (TPTD) in 20 patients with severe acute respiratory distress syndrome (ARDS) treated with veno-venous extracorporeal membrane oxygenation (ECMO).

METHODS

Comparative SV measurements with transesophageal echocardiography and TPTD were performed at least 5 times during the treatment of the patients. The data were interpreted with a Bland-Altman analysis corrected for repeated measurements. The interchangeability between both measurement modalities was calculated and the effects of extracorporeal blood flow on SV measurements with TPTD was analysed with a linear mixed effect model. GEDVI and EVLWI measurements were performed immediately before the termination of the ECMO therapy at a blood flow of 6 l/min, 4 l/min and 2 l/min and after the disconnection of the circuit in 7 patients.

RESULTS

170 pairs of comparative SV measurements were analysed. Average difference between the two modalities (bias) was 0.28 ml with an upper level of agreement of 40 ml and a lower level of agreement of -39 ml within a 95% confidence interval and an overall interchangeability rate between TPTD and Echo of 64%. ECMO blood flow did not influence the mean bias between Echo and TPTD (0.03 ml per l/min of ECMO blood flow; p = 0.992; CI - 6.74 to 6.81). GEDVI measurement was not significantly influenced by the blood flow in the ECMO circuit, whereas EVLWI differed at a blood flow of 6 l/min compared to no ECMO flow (25.9 ± 10.1 vs. 11.0 ± 4.2 ml/kg, p = 0.0035).

CONCLUSIONS

Irrespectively of an established ECMO therapy, comparative SV measurements with Echo and TPTD are not interchangeable. Such caveats also apply to the interpretation of EVLWI, especially with a high blood flow in the extracorporeal circulation. In such situations, the clinician should rely on other methods of evaluation of the amount of lung oedema with the haemodynamic situation, vasopressor support and cumulative fluid balance in mind.

TRIAL REGISTRATION

German Clinical Trials Register (DRKS00021050). Registered 03/30/2020 https://www.drks.de/drks_web/navigate.do?navigationId=trial.HTML&TRIAL_ID=DRKS00017237.

Changes in cardiac output with hemodialysis relate to net volume balance and to inferior vena cava ultrasound collapsibility in critically ill patients

Cardiac output may increase after volume administration with relative intravascular volume depletion, or after ultrafiltration (UF) with relative intravascular volume overload. Assessing relative intravascular volume using respiratory/ventilatory changes in inferior vena cava (IVC) diameters may guide volume management to optimize cardiac output in critically ill patients requiring hemodialysis (HD) and/or UF.We retrospectively studied 22 critically ill patients having relative intravascular volume assessed by IVC Collapsibility Index (IVC CI) = (IVCmax-IVCmin)/IVCmax*100%, within 24 h of cardiac output measurement, during 37 intermittent and 21 continuous HD encounters. Cardiac output increase >10% was considered significant. Net volume changes between cardiac outputs were estimated from "isonatremic volume equivalent" (0.9% saline) gains and losses.Cardiac output increased >10% in 15 of 42 encounters with IVC CI <20% after net volume removal, and in 1 of 16 encounters with IVC CI ≥20% after net volume administration (p = 0.0136). All intermittent and continuous HD encounters resulted in intradialytic hypotension. Net volume changes between cardiac output measurements were significantly less (median +1.0 mL/kg) with intractable hypotension or vasopressor initiation, and net volume removal was larger (median -22.9 mL/kg) with less severe intradialytic hypotension (p < 0.001). Cardiac output increased >10% more frequently with least severe intradialytic hypotension and decreased with most severe intradialytic hypotension (p = 0.047).In summary, cardiac output may increase with net volume removal by ultrafiltration in some critically ill patients with relative intravascular volume overload assessed by IVC collapsibility. Severe intradialytic hypotension may limit volume removal with ultrafiltration, rather than larger volume removal causing severe intradialytic hypotension.

Lower blood return temperature than core temperature as a causal factor of decreased cardiac output assessed by transpulmonary thermodilution during blood purification

We aimed to evaluate whether cardiac output assessed by transpulmonary thermodilution during blood purification is affected by the difference between the blood return temperature and core temperature. We applied different blood return temperatures using a thermostat bath during blood purification in four pigs. After the blood return temperature stabilized and blood purification process stopped, the cardiac output assessed by transpulmonary thermodilution was measured. The thermostat bath was set at 35°C, 40°C, 45°C, and 50°C, with the order changed at random; four measurements were made at each temperature. Cardiac function was evaluated by echocardiography when ice-cold saline was administered in a pig. A decrease in the blood return temperature resulted in decreased cardiac output assessed by transpulmonary thermodilution, whereas an increase resulted in increased cardiac output assessed by transpulmonary thermodilution. Echocardiography revealed that the change in the blood return temperature did not affect the left ventricular ejection fraction.

Physician factors in utilizing haemodynamic data in patient care

PURPOSE OF REVIEW

To focus on the missing link between accuracy and precision of monitoring devices and effective implementation of therapeutic strategies.

RECENT FINDINGS

Haemodynamic monitoring is generally considered to be an essential part of intensive care medicine. However, randomized controlled trials fail to demonstrate improved outcome unequivocally as a result of hemodynamic monitoring. This absence of solid proof renders doctors to hesitance to apply haemodynamic monitoring in clinical practise. Profound understanding of the underlying mechanisms, adequate patient selection and timing, meaningful representation and software-supported interpretation of data all play an important role. Furthermore, protocol adherence and human behaviour seem to form the often missing link between a solid physiologic principle and clinically relevant outcome. Introduction of haemodynamic monitoring should therefore not be limited to theoretical and practical issues, but also involve integration strategies. By learning from others, we might be able to implement haemodynamic monitoring in such a way that it has potential to modify the course of a disease.

SUMMARY

The clinical success of haemodynamic monitoring goes far beyond accuracy and precision of monitoring devices. Understanding of the factors influencing the effective implementation of therapeutic strategies plays an important role in the meaningful introduction of haemodynamic monitoring.

Influence of Blood Purification and Differential Injection Sites of Cold Saline on Transpulmonary Thermodilution Values

We aimed to investigate the effects of blood purification and cold saline injection sites on the transpulmonary thermodilution values. We measured the cardiac output of eight pigs in every combination of cold saline injection (left jugular and femoral veins) and blood purification sites (right jugular and femoral veins), with or without blood purification. We examined the influence of the difference between the presence and absence of blood purification, vascular sites for blood purification, and sites for cold saline injection on the transpulmonary thermodilution values. Cardiac output measured during blood purification using transpulmonary thermodilution was underestimated; however, there was no difference between vascular sites. Cardiac output measured via injection of cold saline into the femoral vein was higher than that obtained through injection of cold saline into the jugular vein, with or without blood purification.