Hemodynamic consequences of continuous arteriovenous hemofiltration

Inferior Vena Cava Collapsibility Index: Clinical Validation and Application for Assessment of Relative Intravascular Volume

Accurate assessment of relative intravascular volume is critical to guide volume management of patients with acute or chronic kidney disorders, particularly those with complex comorbidities requiring hospitalization or intensive care. Inferior vena cava (IVC) diameter variability with respiration measured by ultrasound provides a dynamic noninvasive point-of-care estimate of relative intravascular volume. We present details of image acquisition, interpretation, and clinical scenarios to which IVC ultrasound can be applied. The variation in IVC diameter over the respiratory or ventilatory cycle is greater in patients who are volume responsive than those who are not volume responsive. When 2 recent prospective studies of spontaneously breathing patients (n = 214) are added to a prior meta-analysis of 181 patients, for a total of 7 studies of 395 spontaneously breathing patients, IVC collapsibility index (CI) had a pooled sensitivity of 71% and specificity of 81% for predicting volume responsiveness, which is similar to a pooled sensitivity of 75% and specificity of 82% for 9 studies of 284 mechanically ventilated patients. IVC maximum diameter <2.1 cm, that collapses >50% with or without a sniff is inconsistent with intravascular volume overload and suggests normal right atrial pressure (0-5 mmHg). Inferior vena cava collapsibility (IVC CI) < 20% with no sniff suggests increased right atrial pressure and is inconsistent with overt hypovolemia in spontaneously breathing or ventilated patients. These IVC CI cutoffs do not appear to vary greatly depending on whether patients are breathing spontaneously or are mechanically ventilated. Patients with lower IVC CI are more likely to tolerate ultrafiltration with hemodialysis or improve cardiac output with ultrafiltration. Our goal for IVC CI generally ranges from 20% to 50%, respecting potential biases to interpretation and overriding clinical considerations. IVC ultrasound may be limited by factors that affect IVC diameter or collapsibility, clinical interpretation, or optimal visualization, and must be interpreted in the context of the entire clinical situation.

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.

Continuous Renal Replacement Therapy (CRRT) in the Intensive Care Unit

This review is specifically designed to address the topic of CRRT based on the needs and interests of intensivists. Some of the materials, concepts, and formulas presented in this review have been drawn from a previous chapter authored by myself and intended for individuals whose primary interest is specifically dialysis[1]. Since this previous chapter was authored in 1994, similar material presented in this review has been updated in order to present the most current information.

Renal replacement therapies: physiological review

INTRODUCTION

A physiological review on renal replacement therapies (RRT) is a challenging task: there is nothing "physiologic" about RRT, since the most accurate, safe and perfectly delivered extracorporeal therapy would still be far from "physiologically" replacing the function of the native kidney.

METHODS

This review will address the issues of physiology of fluid and solute removal, acid base control and impact on mortality during intermittent and continuous therapies: different RRT modalities and relative prescriptions will provide different "physiological clinical effects" to critically ill patients with acute kidney injury (AKI), with the aim of restoring lost "renal homeostasis". On the other side, however, the "pathophysiology" of RRT, consists with unwanted clinical effects caused by the same treatments, generally under-recognized by current literature but often encountered in clinical practice. Physiology and pathophysiology of different RRT modalities have been reviewed.

CONCLUSION

Physiology and pathophysiology of RRT often coexist during dialysis sessions. Improvement in renal recovery and survival from AKI will be achieved from optimization of therapy and increased awareness of potential benefits and dangers deriving from different RRT modalities.

Influence of continuous hemofiltration on the hemodynamics of trauma patients

BACKGROUND

The aim of this prospective randomized controlled study was to investigate the effects of continuous venovenous hemofiltration on the hemodynamics and respiratory function of critically ill trauma patients with multiple organ dysfunction syndrome.

METHODS

Thirty consecutive critically ill, mechanically ventilated, trauma patients with multiple organ dysfunction syndrome (without kidney failure) who had invasive hemodynamic monitoring for management of hypotension or hypoxemia were randomized to treatment with or without continuous venovenous hemofiltration. Hemodynamics profile was recorded immediately before and at 6, 12, 24, and 48 hours after the hemofiltration was started (mean of three set data each time). No changes in ventilatory parameters were performed during the study.

RESULTS

Thirty patients were analyzed (15 with and 15 without hemofiltration). Both groups were similar in age (36 +/- 18 versus 36 +/- 14 years) and severity scores (Injury Severity Score, 32 +/- 16 versus 30 +/- 11; Acute Physiology and Chronic Health Evaluation II score, 22 +/- 7 versus 21 +/- 6; Goris score, 5.2 +/- 1.7 versus 5.2 +/- 1.8) and received similar inotropic support. We found a significant improvement in mean arterial pressure (80 +/- 9 to 94 +/- 8 (mm Hg), p = 0.01) and partial pressure of oxygen in arterial blood/inspiratory oxygen supply index (124 +/- 40 to 204 +/- 44, p = 0.03) in the intervention group during the study period. We did not find any other significant change in variables studied.

CONCLUSIONS

Continuous venovenous hemofiltration is associated with a significant improvement in hemodynamic and respiratory variables in critically ill trauma patients with multiple organ dysfunction syndrome. This improvement can help in the management of these patients. Further work is necessary to define whether this technique can reduce the high mortality of this disease.

Should continuous renal replacement therapy be used for 'non-renal' indications in critically ill patients with shock?

Accumulating experience with the use of continuous renal replacement therapy (CRRT) in critically ill patients with acute renal failure suggests that these treatment modalities have distinct advantages relative to conventional dialysis in terms of solute clearances, fluid removal and hemodynamics, which may translate in improved renal and patient outcome. Recent data point to a possible beneficial effect of CRRT on the clinical course, independent from an impact on fluid balance, in critically ill patients with shock which is attributed to the continuous elimination of inflammatory mediators from the circulation. This has raised the question as to whether CRRT might be used for 'non-renal' indications such as the systemic inflammatory response syndrome (SIRS) and multiple organ dysfunction syndrome (MODS). In some animal models of experimental septic and non-septic shock, (short-term) hemodialysis and hemofiltration were found to improve hemodynamics and/or gas exchange. However, data were inconsistent and the clinical relevance questionable. Observations from both uncontrolled and controlled clinical studies (comprising only a small number of patients) support the hypothesis that CRRT may exert beneficial effects on the clinical course in critically ill patients with SIRS and MODS, independent from volume removal. Although several mediators known to play a role in the development of SIRS/MODS may pass hemofiltration membranes, quantitative data on the extent of its extracorporeal clearance relative to the production rate and endogenous clearance is often lacking. In addition, this aspecific elimination with CRRT may also effect levels of anti-mediators, which may be harmful. Ultrafiltrate properties include depression of cardiac performance, induction of proteolysis and immunosuppressive activity suggesting that water-soluble factors responsible for these deleterious effects are removed from the circulation by convection. However, no significant survival advantage has yet been shown for critically ill patients with SIRS/MODS when treated with CRRT as an adjunct to conventional therapy. Only prospective controlled studies of appropriate sample size, which requires a multicenter approach, might answer the question whether use of CRRT may alter the clinical course and outcome in critically ill patients with SIRS and MODS. Until such studies are performed, the rationale for the use of CRRT in the absence of conventional indications for dialytic support remains unproven.

Refractory congestive heart failure: overview and application of extracorporeal ultrafiltration

Congestive heart failure (CHF) from ischemic cardiomyopathy has emerged as an epidemic health problem. The pathogenesis of CHF is characterized by heightened activity of many neuroendocrine factors, including norepinephrine, angiotensin II, and arginine vasopressin, which lead to heightened systemic vascular resistance and further impedance of left ventricular ejection. Once CHF reaches New York Heart Association (NYHA) class III or IV with heightened activity of the many neurohumoral factors, it tends to be refractory to conventional therapy of vasodilators, inotropic agents, and diuretics. Treatment of refractory CHF appears to require a break in the neurohumoral hemodynamic vicious cycle, and ultrafiltration appears able to produce this interruption. Ultrafiltration has been shown to be successful in patients with NYHA class III to VI CHF and urine output less than 1,000 mL/d. It relieves pulmonary edema, reduces ascites and peripheral edema, and enhances the response to subsequent diuretic therapy. In patients with refractory CHF, the ability to provide adequate volume removal, thus improving overall volume status, normalizing filling pressures, and reducing clinical symptoms, offers an improvement in overall quality of life. Early results have shown that ongoing therapy actually may be associated with decreased hospital readmissions or, at the very least, shortened intensive care unit length of stay.

Haemodynamic effects of arteriovenous and venovenous haemofiltration in piglets

The aim of this study was to compare the early haemodynamic effects of continuous arteriovenous haemofiltration (CAVH) with those of continuous venovenous haemofiltration (CVVH) in normal and endotoxic piglets, within the framework of a two-period cross-over trial. Sixteen domestic piglets (weight 6-18 kg) underwent 1 h of CAVH followed by 1 h of CVVH or 1 h of CVVH followed by 1 h of CAVH. Six were pre-treated with a graded endotoxin infusion to simulate clinical sepsis. The main measurements included: heart rate; mean arterial (MAP), pulmonary artery, central venous and pulmonary artery occlusion pressures; thermodilution cardiac output; and calculated systemic (SVRI) and pulmonary vascular resistance indexes. Each measurement was performed immediately before and 30 min after commencement of each technique of filtration. Commencement of haemofiltration in normal piglets caused minimal haemodynamic effects. In endotoxic piglets, commencement of filtration, whether CAVH or CVVH, caused a haemodynamic change which was significantly more pronounced in the first filter (SVRI -39%, MAP -32%) than the second filter (SVRI +22%, MAP +0.9%) (SVRI, P=0.01, first filter vs. second) (MAP, P=0.009 first filter vs. second). In conclusion, there were no significant differences between the early haemodynamic effects of CAVH and CVVH in normal or endotoxic piglets. The haemodynamic effects of either technique may become more significant in the presence of sepsis.

Continuous renal replacement therapy for critically ill patients: an update

Despite continuous progress in intensive care during the last decades, the outcome of critically ill patients in whom acute renal failure (ARF) develops is still poor. This outcome may be explained partially by the frequent occurrence of ARF as part of multiple organ systems failure (MOSF). In this complex and unstable patient population, the provision of adequate renal support with either intermittent hemodialysis or peritoneal dialysis may pose major problems. Continuous renal replacement therapy (CRRT) is now increasingly accepted as the preferred treatment modality in the management of ARF in these patients. The technique offers adequate control of biochemistry and fluid balance in hemodynamically unstable patients, thereby enabling aggressive nutritional and inotropic support without the risk of exacerbating azotemia or fluid overload. In addition, experimental and clinical data suggest that CRRT may have a beneficial influence on hemodynamics and gas exchange in patients with septic shock and (nonrenal) MOSF, independent of an impact on fluid balance. We review both technical and clinical aspects of various continuous therapies, including their impact on serum drug levels and nutrient balance. In addition, an attempt is made to clarify the possible beneficial role of CRRT in reducing patient morbidity and mortality in the ICU.

Acute continuous hemodiafiltration: a prospective study of 110 patients and a review of the literature

One hundred ten critically ill patients with acute renal failure receiving acute continuous hemodiafiltration (ACHD) in our intensive care unit were studied prospectively. Acute continuous hemodiafiltration consisted either of continuous arteriovenous hemodiafiltration or of continuous veno-venous hemodiafiltration, and was used for 17,817 hours (mean duration of patient treatment, 161.9 hours), resulting in a fall from a mean pre-ACHD urea of 35.7 mmol/L to a plateau value of 16.8 mmol/L at 72 hours of treatment. The mean urea clearance achieved was 24.9 mL/min. Eighty of these patients (72.7%) were receiving artificial ventilation at the time of ACHD and 45 (40.9%) had more than four failing organs. The mean APACHE II score was 27.7. Despite the degree of illness severity, 42 patients (32.2%) survived to discharge from hospital. The use of ACHD was associated with hemodynamic stability, rapid normalization of electrolytes, and the ability to freely administer drugs, blood, and/or blood products. It also allowed for maintenance of an aggressive, nitrogen-rich, nutritional regimen. Support of these critically ill patients with acute renal failure using ACHD was achieved safely and without the employment of additional dialysis-trained nursing staff. Our own experience and a review of the available literature strongly suggest that the advantages associated with the use of ACHD therapies are clinically significant and support the view that ACHD is a modality of renal replacement most suited to critically ill patients with acute renal failure.

Solute clearances with high dialysate flow rates and glucose absorption from the dialysate in continuous arteriovenous hemodialysis

The purpose of this study was to determine the effects of high inlet dialysate flow rates (IDFR) on the clearances of urea and creatinine and to measure the absorption of glucose through the dialyzer in continuous arteriovenous hemodialysis (CAVHD). Ten anuric acute renal failure patients in the intensive care unit were studied. Increasing the IDFR from 0 to 33.3 mL/min (0 to 2 L/h) produced linear increments in the clearances of urea and creatinine, whereas further increases in the IDFR from 33.3 to 66.7 mL/min (2 to 4 L/h) produced less important, but still significant, increases in the clearances. At 66.7 mL/min, the clearances for urea and creatinine were 48.5 +/- 3.4 and 42.2 +/- 2.5 mL/min, respectively. Using a dialysate with a glucose concentration of 25.3 mmol/L (0.5 g/dL), the net transfer of glucose through the dialyzer did not change significantly, from 16.7 to 66.7 mL/min of IDFR. Increasing the inlet dialysate glucose concentration from 25.3 to 75.8, 126.3, and 214.6 mmol/L (0.5 to 1.5, 2.5, and 4.25 g/dL) at a fixed IDFR of 16.7 mL/min produced linear increments in the net glucose transferred to the patient, from 0.12 +/- 0.02 to 0.67 +/- 0.05, 1.25 +/- 0.06 and 2.30 +/- 0.14 mmol/min, respectively (21.4, 121.0, 225.7, and 414.5 mg/min). No significant changes in the ultrafiltration and plasma flow rates through the dialyzer were recorded at these different IDFR or inlet dialysate glucose concentrations. Ten patients were treated for 4 days or more with 16.7 mL/min (1 L/h) IDFR CAVHD with excellent control over kidney function parameters.(ABSTRACT TRUNCATED AT 250 WORDS)