The influence of haemodialysis on haemodynamic measurements using transpulmonary thermodilution in patients with septic shock: an observational study

CRRT influences PICCO measurements in febrile critically ill patients

The aim of this study was to investigate whether continuous renal replacement therapy (CRRT) influences the global end-diastolic volume index (GEDVI), cardiac index (CI), and extravascular lung water index (EVLWI) measured by Pulse Index Continuous Cardiac Output (PICCO) in febrile patients. Fifteen fever patients were included in this study. CI, GEDVI, EVLWI, heart rate (HR), and mean arterial pressure (MAP) were measured at five time-points: before CRRT (T0), immediately after CRRT started (T1), 15 min after CRRT started (T2), immediately after CRRT stopped (T3), and 15 min after CRRT stopped (T4). Results have shown that CI and GEDVI were decreased significantly in T1 (CI: 4.09 ± 0.72 vs 2.81 ± 0.58 L/min m², P = 0.000 and GEDVI: 727.86 ± 63.47 vs 531.07 ± 66.63 mL/m², P = 0.000). However, CI and GEDVI were significantly increased in T3 (CI: 4.09 ± 0.72 vs 7.23 ± 1.32 L/min m², P = 0.000 and GEDVI 727.86 ± 63.47 vs 1339.17 ± 121.52 mL/m², P = 0.000). There were no significant differences in T2 and T4. Among the five-time points, no measurement errors were observed with regards to HR, MAP, and EVLWI. Therefore, the data herein contained suggests that PICCO measurements should begin 15 min after the start or stop of CRRT.

Central Venous Line and Dialysis Catheter Position Affects Drug Clearance during Continuous Renal Replacement Therapy in an Animal Model

In intensive care, drugs are commonly administered through central venous catheters (CVC). These catheters and central venous dialysis catheters (CVDC) are often placed in the same vessel for practical reasons. The aim of this experimental study was to investigate if the position of CVC and CVDC influences the elimination of infused drugs, during continuous renal replacement therapy (CRRT). In a randomized, cross-over model, anesthetized piglets received both a CVC and a CVDC in a jugular vein. Another CVDC was placed in a femoral vein for comparison. After baseline measurements, CRRT was performed in either of the CVDC, each CRRT-period separated by another baseline period. Hypotension was induced by peripherally given sodium nitroprusside. In the CVC, both gentamicin and noradrenaline were administered. Noradrenaline was titrated to reach a target blood pressure. When CRRT was performed using the CVDC in the same vessel as the drugs were infused, the plasma concentration of gentamicin was reduced compared with when the infusion and CVDC were in different vessels (5.66 [standard deviation (SD) ± 1.23] vs. 7.76 [SD ± 2.30] mg/l [p = 0.02]). The noradrenaline infusion rate needed to reach the target blood pressure was more than doubled (0.32 [SD ± 0.16] vs. 0.15 [SD ± 0.08] µg/kg/min [p = 0.006]). This experimental study indicates that the removal of drugs is increased if infusion is in close vicinity of the CVDC, during CRRT.

Effect of hemodialysis on impedance cardiography (electrical velocimetry) parameters in children

BACKGROUND

Pediatric hemodialysis (HD) patients have a high incidence of cardiovascular morbidity and mortality. The study aim was to investigate whether impedance cardiography (electrical velocimetry, EV) is suitable as a hemodynamic trend monitoring tool in pediatric patients during HD.

METHODS

Measurements by EV were obtained before, during, and after HD in a prospective single-center pediatric observational study. In total, 54 dialysis cycles in four different pediatric patients with end-stage kidney disease on chronic HD were included. EV parameters analyzed were heart rate (HR), stroke volume (SV), stroke volume index (SI), cardiac output (CO), cardiac index (CI), thoracic fluid content (TFC), index of contractility (ICON), stroke volume variation (SVV), variation of ICON (VIC), R-R interval (TRR), pre-ejection period (PEP), left ventricular ejection time (LVET), and systolic time ration (STR). Systemic vascular resistance index (SVRI) was calculated.

RESULTS

EV did measure significant changes in cardiovascular parameters associated with HD. The following parameters increased after HD: HR (9%), SVV (19%), VIC (33%), PEP (8%), and STR (18%). A decrease after HD was measured in SV (18%), SI (18%), CO (10%), CI (10%), TFC (10%), ICON (7%), TRR (7%), LVET (8%), and LVET (8%). SVRI was not affected by HD. The changes were correlated to ultrafiltration. HD cycles without fluid withdrawal also altered cardiovascular parameters.

CONCLUSIONS

Pediatric HD with and without fluid withdrawal changes hemodynamic EV monitoring parameters. Possibly EV may be useful to optimize HD management in pediatric patients.

Sustained low efficiency dialysis should not be interrupted for performing transpulmonary thermodilution measurements

Background

Treatment of multiple organ failure frequently requires enhanced hemodynamic monitoring. When renal replacement is indicated, it remains unclear whether transpulmonary thermodilution (TPTD) measurements are influenced by renal replacement therapy (RRT) and whether RRT should be paused for TPTD measurements. Our aim was therefore to investigate the effect of pausing RRT on TPTD results in two dialysis catheter locations.

Materials and methods

In total, 62 TPTD measurements in 24 patients (APACHE: 32 ± 7 [mean ± standard deviation (SD)]) were performed using the PiCCO™ system (Pulsion, Germany). Patients were treated with sustained low efficiency dialysis (SLED; Genius™ system, Fresenius, Germany) as RRT. Measurements were taken during ongoing hemodialysis (HD, HDO), during paused HD (HDP) and immediately after termination of HD and blood restitution (HDT). Dialysis catheters were placed either in the superior vena cava (SVC, 19 times) or in the inferior vena cava (IVC, 5 times). Statistical analysis was performed to assess the effects of the measurement setting, SLED (blood flow rate) and the catheter location, on cardiac index (CI), global end-diastolic volume index (GEDVI) and extravascular lung water index (EVLWI) as measured by TPTD. Multilevel models were used for the analysis due to the triplicate measurements and due to 12 out of 19 SVC and 2 out of 5 IVC patients having more than one TPTD measured.

Results

CI and GEDVI were significantly higher at time point HDP compared to both HDO and HDT. In contrast, values for EVLWI were lower at HDP when compared to HDO and HDT. These findings were independent of the site of dialysis catheter insertion and blood flow rate.

Conclusions

PiCCO™ measurements assessed at paused SLED significantly deviate from ongoing and terminated SLED. Therefore, the dialysis system should not be paused for measurements. TPTD measurements in patients with PiCCO monitoring seem sufficiently reliable during ongoing SLED as well as after its termination. An effect of dialysis catheter location (SVC vs IVC) and blood flow rate on PiCCO™ measurements could not be shown.

Development of a Physiologically Based Pharmacokinetic Modelling Approach to Predict the Pharmacokinetics of Vancomycin in Critically Ill Septic Patients

BACKGROUND AND OBJECTIVES

Sepsis is characterised by an excessive release of inflammatory mediators substantially affecting body composition and physiology, which can be further affected by intensive care management. Consequently, drug pharmacokinetics can be substantially altered. This study aimed to extend a whole-body physiologically based pharmacokinetic (PBPK) model for healthy adults based on disease-related physiological changes of critically ill septic patients and to evaluate the accuracy of this PBPK model using vancomycin as a clinically relevant drug.

METHODS

The literature was searched for relevant information on physiological changes in critically ill patients with sepsis, severe sepsis and septic shock. Consolidated information was incorporated into a validated PBPK vancomycin model for healthy adults. In addition, the model was further individualised based on patient data from a study including ten septic patients treated with intravenous vancomycin. Models were evaluated comparing predicted concentrations with observed patient concentration-time data.

RESULTS

The literature-based PBPK model correctly predicted pharmacokinetic changes and observed plasma concentrations especially for the distribution phase as a result of a consideration of interstitial water accumulation. Incorporation of disease-related changes improved the model prediction from 55 to 88% within a threshold of 30% variability of predicted vs. observed concentrations. In particular, the consideration of individualised creatinine clearance data, which were highly variable in this patient population, had an influence on model performance.

CONCLUSION

PBPK modelling incorporating literature data and individual patient data is able to correctly predict vancomycin pharmacokinetics in septic patients. This study therefore provides essential key parameters for further development of PBPK models and dose optimisation strategies in critically ill patients with sepsis.

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

BACKGROUND

Transpulmonary thermodilution (TPTD) is used frequently in the intensive care unit to determine cardiac index (CI), intrathoracic blood volume index (ITBVI), and extravascular lung volume index (EVLWI). Renal replacement therapy (RRT) influences TPTD results, but the underlying mechanisms are not completely understood. We hypothesized that RRT blood flow induces errors in TPTD measurements.

METHODS

We analyzed TPTD data available from the PiCCO® plus hemodynamic measurement device on a personal computer using a proprietary Pulsion Medical Systems software. By using the dialysis catheter to inject the thermal indicator, 20 measurement series were performed in 12 intensive care unit patients determining CI, ITBVI, and EVLWI during RRT with the blood pump stopped, and at flows of 100 and 200 mL/min, respectively.

RESULTS

Data export was successful in 17 measurement series and showed a significant decrease in measured CI (6.5 ± 2.5 vs 5.4 ± 1.9 L/min/m, P < 0.001) and ITBVI (1358.8 ± 274.5 vs 1132.8 ± 218.3 mL/m, P < 0.001) with RRT and a significant increase in EVLWI (8.6 ± 4.4, 10.2 ± 4.5 mL/kg, P < 0.001). Blood temperature before and the temperature decrease after injection of the thermal indicator were unchanged by RRT. Mean transit time and downslope time of the thermodilution curve, however, were both increased with the RRT blood pump running (P ≤ 0.001).

CONCLUSIONS

Analysis of TPTD data shows that thermodilution curve forms are modified with RRT, resulting in an erroneous calculation of thermodilution-derived hemodynamic parameters.

Transpulmonary thermodilution (TPTD) before, during and after Sustained Low Efficiency Dialysis (SLED). A Prospective Study on Feasibility of TPTD and Prediction of Successful Fluid Removal

BACKGROUND

Acute kidney injury (AKI) is common in critically ill patients. AKI requires renal replacement therapy (RRT) in up to 10% of patients. Particularly during connection and fluid removal, RRT frequently impairs haemodyamics which impedes recovery from AKI. Therefore, "acute" connection with prefilled tubing and prolonged periods of RRT including sustained low efficiency dialysis (SLED) has been suggested. Furthermore, advanced haemodynamic monitoring using trans-pulmonary thermodilution (TPTD) and pulse contour analysis (PCA) might help to define appropriate fluid removal goals.

OBJECTIVES, METHODS

Since data on TPTD to guide RRT are scarce, we investigated the capabilities of TPTD- and PCA-derived parameters to predict feasibility of fluid removal in 51 SLED-sessions (Genius; Fresenius, Germany; blood-flow 150 mL/min) in 32 patients with PiCCO-monitoring (Pulsion Medical Systems, Germany). Furthermore, we sought to validate the reliability of TPTD during RRT and investigated the impact of "acute" connection and of disconnection with re-transfusion on haemodynamics. TPTDs were performed immediately before and after connection as well as disconnection.

RESULTS

Comparison of cardiac index derived from TPTD (CItd) and PCA (CIpc) before, during and after RRT did not give hints for confounding of TPTD by ongoing RRT. Connection to RRT did not result in relevant changes in haemodynamic parameters including CItd. However, disconnection with re-transfusion of the tubing volume resulted in significant increases in CItd, CIpc, CVP, global end-diastolic volume index GEDVI and cardiac power index CPI. Feasibility of the pre-defined ultrafiltration goal without increasing catecholamines by >10% (primary endpoint) was significantly predicted by baseline CPI (ROC-AUC 0.712; p = 0.010) and CItd (ROC-AUC 0.662; p = 0.049).

CONCLUSIONS

TPTD is feasible during SLED. "Acute" connection does not substantially impair haemodynamics. Disconnection with re-transfusion increases preload, CI and CPI. The extent of these changes might be used as a "post-RRT volume change" to guide fluid removal during subsequent RRTs. CPI is the most useful marker to guide fluid removal by SLED.