Effect of continuous dialysis on blood ph in acidemic hypercapnic animals with severe acute kidney injury: a randomized experimental study comparing high vs. low bicarbonate affluent

Impact of AKI on metabolic compensation for respiratory acidosis in ICU patients with AECOPD

PURPOSE

Acute exacerbation of chronic obstructive pulmonary disease (AECOPD) can result in severe respiratory acidosis. Metabolic compensation is primarily achieved by renal retention of bicarbonate. The extent to which acute kidney injury (AKI) impairs the kidney's capacity to compensate for respiratory acidosis remains unclear.

MATERIALS AND METHODS

This retrospective analysis covers clinical data between January 2009 and December 2021 for 498 ICU patients with AECOPD and need for respiratory support.

RESULTS

278 patients (55.8%) presented with or developed AKI. Patients with AKI exhibited higher 30-day-mortality rates (14.5% vs. 4.5% p = 0.001), longer duration of mechanical ventilation (median 90 h vs. 14 h; p = 0.001) and more severe hypercapnic acidosis (pH 7.23 vs. 7.28; pCO2 68.5 mmHg vs. 61.8 mmHg). Patients with higher AKI stages exhibited lower HCO3-/pCO2 ratios and did not reach expected HCO3- levels. In a mixed model analysis with random intercept per patient we analyzed the association of pCO2 (independent) and HCO3- (dependent variable). Lower estimates for averaged change in HCO3- were observed in patients with more severe AKI.

CONCLUSION

AKI leads to poor outcomes and compromises metabolic compensation of respiratory acidosis in ICU patients with AECOPD. While buffering agents may aid compensation for severe AKI, their use should be approached with caution.

Factors associated with carbon dioxide transfer in an experimental model of severe acute kidney injury and hypoventilation during high bicarbonate continuous renal replacement therapy and oxygenation membrane support

OBJECTIVE

To investigate the factors influencing carbon dioxide transfer in a system that integrates an oxygenation membrane in series with high-bicarbonate continuous veno-venous hemodialysis in hypercapnic animals.

METHODS

In an experimental setting, we induced severe acute kidney injury and hypercapnia in five female Landrace pigs. Subsequently, we initiated high (40mEq/L) bicarbonate continuous veno-venous hemodialysis with an oxygenation membrane in series to maintain a pH above 7.25. At intervals of 1 hour, 6 hours, and 12 hours following the initiation of continuous veno-venous hemodialysis, we performed standardized sweep gas flow titration to quantify carbon dioxide transfer. We evaluated factors associated with carbon dioxide transfer through the membrane lung with a mixed linear model.

RESULTS

A total of 20 sweep gas flow titration procedures were conducted, yielding 84 measurements of carbon dioxide transfer. Multivariate analysis revealed associations among the following (coefficients ± standard errors): core temperature (+7.8 ± 1.6 °C, p < 0.001), premembrane partial pressure of carbon dioxide (+0.2 ± 0.1/mmHg, p < 0.001), hemoglobin level (+3.5 ± 0.6/g/dL, p < 0.001), sweep gas flow (+6.2 ± 0.2/L/minute, p < 0.001), and arterial oxygen saturation (-0.5 ± 0.2%, p = 0.019). Among these variables, and within the physiological ranges evaluated, sweep gas flow was the primary modifiable factor influencing the efficacy of low-blood-flow carbon dioxide removal.

CONCLUSION

Sweep gas flow is the main carbon dioxide removal-related variable during continuous veno-venous hemodialysis with a high bicarbonate level coupled with an oxygenator. Other carbon dioxide transfer modulating variables included the hemoglobin level, arterial oxygen saturation, partial pressure of carbon dioxide and core temperature. These results should be interpreted as exploratory to inform other well-designed experimental or clinical studies.

Standard vs. carbone dioxide adapted kidney replacement therapy in hypercapnic ARDS patients: a randomized controlled pilot trial (BigBIC)

BACKGROUND

Current continuous kidney replacement therapy (CKRT) protocols ignore physiological renal compensation for hypercapnia. This study aimed to explore feasibility, safety, and clinical benefits of pCO2-adapted CKRT for hypercapnic acute respiratory distress syndrome (ARDS) patients with indication for CKRT.

METHODS

We enrolled mechanically ventilated hypercapnic ARDS patients (pCO2 > 7.33 kPa) receiving regional citrate anticoagulation (RCA) based CKRT in a prospective, randomized-controlled pilot-study across five intensive care units at the Charité-Universitätsmedizin Berlin, Germany. Patients were randomly assigned 1:1 to the control group with bicarbonate targeted to 24 mmol/l or pCO2-adapted-CKRT with target bicarbonate corresponding to physiological renal compensation. Study duration was six days. Primary outcome was bicarbonate after 72 h. Secondary endpoints included safety and clinical endpoints. Endpoints were assessed in all patients receiving treatment.

RESULTS

From September 2021 to May 2023 40 patients (80% male) were enrolled. 19 patients were randomized to the control group, 21 patients were randomized to pCO2-adapted-CKRT. Five patients were excluded before receiving treatment: three in the control group (consent withdrawal, lack of inclusion criteria fulfillment (n = 2)) and two in the intervention group (lack of inclusion criteria fulfillment, sudden unexpected death) and were therefore not included in the analysis. Median plasma bicarbonate 72 h after randomization was significantly higher in the intervention group (30.70 mmol/l (IQR 29.48; 31.93)) than in the control group (26.40 mmol/l (IQR 25.63; 26.88); p < 0.0001). More patients in the intervention group received lung protective ventilation defined as tidal volume < 8 ml/kg predicted body weight. Thirty-day mortality was 10/16 (63%) in the control group vs. 8/19 (42%) in the intervention group (p = 0.26).

CONCLUSION

Tailoring CKRT to physiological renal compensation of respiratory acidosis appears feasible and safe with the potential to improve patient care in hypercapnic ARDS.

TRIAL REGISTRATION

The trial was registered in the German Clinical Trials Register (DRKS00026177) on September 9, 2021 and is now closed.

Validation of a low-cost continuous renal replacement therapy dialysate fluid controller for experimental purposes

BACKGROUND

Continuous renal replacement therapy (CRRT) support is crucial for critically ill patients and it is underexplored in specific situations. Experimental CRRT offers a means to gain insights into these scenarios, but the prohibitive cost of CRRT machines limits their accessibility. This study aimed to develop and validate a low-cost and precise dialysate controller for experimental CRRT.

RESULTS

Our results demonstrate a commendable level of precision in affluent flow control, with a robust correlation (R2 = 0.99) for continuous flow and a strong correlation (R2 = 0.95) for intermittent flow. Additionally, we observed acceptable agreement with a bias = 3.4 mL (upper limit 95% = 43.9 mL and lower limit 95% = - 37 mL) for continuous flow and bias = - 20.9 mL (upper limit 95% = 54 mL and lower limit 95% = - 95.7 mL) for intermittent flow, in this way, offering a precise CRRT dose for the subjects. Furthermore, we achieved excellent precision in the cumulative ultrafiltration net (UFnet), with a bias = - 2.8 mL (upper limit 95% = 6.5 mL and lower limit 95% = - 12 mL). These results remained consistent even at low affluent flow rates of 8, 12, and 20 mL/min, which are compatible with CRRT doses of 25-30 mL/kg for medium-sized animals. Moreover, the acceptable precision of our findings persisted when the dialysate controller was subjected to high filter dialysate chamber pressure for an extended duration, up to 797 min.

CONCLUSIONS

The low-cost dialysate controller developed and tested in this study offers a precise means of regulating CRRT in experimental settings. Its affordability and accuracy render it a valuable instrument for studying CRRT support in unconventional clinical scenarios, particularly in middle-income countries' experimental ICU laboratories.

Clinicopathological factors associated with the presence of hypercapnia at admission in hospitalised cats with decompensated chronic kidney disease

AIMS

To evaluate associations between clinicopathological variables and hypercapnia measured in cats with decompensated chronic kidney disease (CKD) on admission to a veterinary hospital.

METHODS

This is a retrospective, cross-sectional study of cats (n = 39) that presented to a tertiary veterinary hospital in Argentina between June 2015 and December 2017 with blood creatinine concentrations >140 μmol/L, and abdominal ultrasound results consistent with CKD. Data recorded included venous partial pressure of CO₂ (PvCO₂), blood pH, haematocrit and concentrations of glucose, potassium, sodium, corrected sodium (Na⁺_c), and ionised calcium in blood. A logistic regression model was used to assess associations between the presence of hypercapnia (PvCO₂ ≥ 44.7 mmHg) and the other clinicopathologic variables. The duration of hospitalisation was compared in cats with and without hypercapnia using the Wilcoxon Rank Sum test.

RESULTS

The final study population comprised 39 cats. Eleven cats (28.2%) had hypercapnia. In the logistic regression model, two independent variables were associated with the presence of hypercapnia at admission in cats with CKD: the concentration of creatinine in blood (OR = 1.06 (95% CI = 1.016-1.108); p = 0.007) and Na⁺_c (OR = 1.33 (95% CI = 1.08-1.63); p = 0.005). There were no statistically significant differences in the length of hospital stay between the two groups.

CONCLUSIONS AND CLINICAL RELEVANCE

There appears to be an association between elevated concentrations of creatinine and Na⁺_c in blood, and hypercapnia in cats with CKD, suggesting careful assessment of blood gas and electrolyte parameters during hospitalisation is required. Further prospective studies are needed to evaluate the mechanisms behind this association and the association of hypercapnia with disease outcome including mortality.

Extracorporeal CO2 Removal Integrated within a Continuous Renal Replacement Circuit Offers Multiple Advantages

Extracorporeal CO2 removal within a continuous renal replacement therapy circuit offers multiple advantages for the regulation of the CO2 extraction. The authors review the impact of the dialysate solution, the buffer, and the anticoagulation on CO2 removal. They propose a theoretical model of the ideal circuit for the optimization of CO2 extraction.