Fundamentals of Arterial Blood Gas Interpretation.

Acid-base disturbances in patients with cardiopulmonary or other disorders are common and are often misinterpreted or interpreted incompletely. Treating acid-base disorders in greater detail facilitates pathophysiologic understanding and improved therapeutic planning. Understanding the ratiometric relationship between the lungs, which excrete volatile acid as carbon dioxide, and the kidneys, which contribute to maintenance of plasma bicarbonate, allows precise identification of the dominant acid-base disturbance when more than a simple disorder is present and aids in executing a measured treatment response. Concordantly, mapping paired values of the partial pressure of carbon dioxide (PCO2) and the bicarbonate concentration ([HCO3 -]) on a Cartesian coordinate system visually defines an acid-base disorder and validates the ratiometric methodology. We review and demonstrate the algebraic and logarithmic methods of arterial blood gas analysis through the example of a complex acid-base disorder, emphasizing examination of the PCO2-to-[HCO3 -] ratio.

Development and validation of a risk score to prioritize patients for evaluation of access stenosis.

BACKGROUND: Access flow dysfunction, often associated with stenosis, is a common problem in hemodialysis access and may result in progression to thrombosis. Timely identification of accesses in need of evaluation is critical to preserving a functioning access. We hypothesized that a risk score using measurements obtained from the Vasc-Alert surveillance device could be used to predict subsequent interventions. METHODS: Measurement of five factors over the preceding 28 days from 1.46 million hemodialysis treatments (6163 patients) were used to develop a score associated with interventions over the subsequent 60 days. The score was validated in a separate dataset of 298,620 treatments (2641 patients). RESULTS: Interventions in arteriovenous fistulae (AVF; n = 4125) were much more common in those with the highest score (36.2%) than in those with the lowest score (11.0). The score also was strongly associated with interventions in patients with an arteriovenous graft (AVG; n = 2,038; 43.2% vs. 21.1%). There was excellent agreement in the Validation datasets for AVF (OR = 2.67 comparing the highest to lowest score) and good agreement for AVG (OR = 1.92). CONCLUSIONS: This simple risk score based on surveillance data may be useful for prioritizing patients for physical examination and potentially early referral for intervention.

Continuous Renal Replacement Therapy for the Management of Acid-Base and Electrolyte Imbalances in Acute Kidney Injury.

Continuous renal replacement therapy (CRRT) is used to manage electrolyte and acid-base imbalances in critically ill patients with acute kidney injury. Although a standard solution and prescription is acceptable in most clinical circumstances, specific disorders may require a tailored approach such as adjusting fluid composition, regulating CRRT dose, and using separate intravenous infusions to mitigate and correct these disturbances. Errors in fluid prescription, compounding, or delivery can be rapidly fatal. This article provides an overview of the principles of acid-base and electrolyte management using CRRT.

Treatment of Severe Metabolic Alkalosis with Continuous Renal Replacement Therapy: Bicarbonate Kinetic Equations of Clinical Value.

Concomitant severe metabolic alkalosis, hypernatremia, and kidney failure pose a therapeutic challenge. Hemodialysis to correct azotemia and abnormal electrolytes results in rapid correction of serum sodium, bicarbonate, and urea but presents a risk for dialysis disequilibrium and brain edema. We describe a patient with Zollinger-Ellison syndrome with persistent encephalopathy, severe metabolic alkalosis (highest bicarbonate 81 mEq/L), hypernatremia (sodium 157 mEq/L), and kidney failure despite 30 hours of intravenous crystalloids and proton pump inhibitor. We used continuous renal replacement therapy (RRT) with delivered hourly urea clearance of ~3 L/hour (24 hour sustained low efficiency dialysis with regional citrate anticoagulation protocol at blood flow rate 60 ml/min and dialysate flow rate 400 ml/min). To mitigate a pronounced decrease in plasma osmolality while removing urea from this hypernatremic patient, dialysate sodium was set to start at 155 mEq/L then at 150 mEq/L after 6 hours. Serum bicarbonate, urea, and sodium were slowly corrected over 26 hours. This case demonstrates how to regulate and predict the systemic bicarbonate level using single pool kinetic modeling during convective or diffusive RRT. Kinetic modeling provides a valuable tool for systemic blood pH control in future combined use of extracorporeal CO2 removal and continuous RRT systems.

Online Hemoglobin and Oxygen Saturation Sensing During Continuous Renal Replacement Therapy with Regional Citrate Anticoagulation.

Optical hemoglobin and oxygen saturation sensor (OHOS) monitor when used in combination with other hemodynamic tools may be useful for continuous hemodynamic monitoring during ultrafiltration. The stand-alone OHOS monitor can easily be deployed predialyzer into the extracorporeal circuit of continuous renal replacement therapy (CRRT) systems. To maximize the accuracy of the OHOS in 24 hr CRRT systems, clotting in the optical blood chamber and the presensor dilution incurred by replacement fluid should be minimized. Sustained low-efficiency dialysis (SLED) with regional citrate anticoagulation is a therapy that incorporates an OHOS and maintains the overall reliability of hemoglobin (Hb) and saturation sensing. The system operates at a blood flow rate of 60 ml/min and a fixed acid citrate infusion rate of 150 ml/hr. The presensor dilution incurred by concentrated citrate infusion would result in a minimal Hb dilution (<0.7 g/dl) while minimizing optical blood chamber clotting during 24 hr SLED.

Iron repletion is associated with reduction in platelet counts in non-dialysis chronic kidney disease patients independent of erythropoiesis-stimulating agent use: a retrospective cohort study.

BACKGROUND: Iron deficiency is common in non-dialysis chronic kidney disease (ND-CKD) patients and, on occasion, requires parenteral iron therapy. We investigated the effect of intravenous iron repletion on platelet counts in ND-CKD patients with and without concomitant darbepoetin administration. METHODS: We conducted a retrospective analysis of ND-CKD patients with iron deficiency anemia treated with low molecular weight iron dextran (LMWID) between 2005 and 2009 at our CKD clinic. The primary end-point was change in platelet count 60 days post infusion of LMWID in those with and without concomitant darbepoetin administration. Secondary end-points were the correlations between changes in platelet count and iron indices. RESULTS: A total of 108 patients met inclusion and exclusion criteria. The decrease in platelet counts in response to iron repletion was statistically significant (305.72 ± 108.86 vs 255.58 ± 78.97, P = < .0001). The decrease in platelet count was independent of concomitant darbepoetin use. Bivariate regression analysis between baseline platelet count and transferrin saturation by iron (TSAT) showed a negative association (ßTSAT = -5.82, P = .0007) and moderate correlation (R = 0.32). Following iron treatment, the within individual changes in platelet count in 60 days were not related to changes in TSAT (ßΔTSAT = -0.41, P = .399) and demonstrated a poor correlation (R = 0.10). CONCLUSIONS: Parenteral iron treatment by LMWID is associated with reduction in platelet counts in iron deficient anemic ND-CKD patients. However, ESA use in the majority of patients prior to intravenous iron administration could have altered platelet production through bone marrow competition.

Treatment of severe hyponatremia in patients with kidney failure: role of continuous venovenous hemofiltration with low-sodium replacement fluid.

Patients with hypervolemic hyponatremia and kidney failure pose a special therapeutic challenge. Hemodialysis to correct volume overload, azotemia, and abnormal electrolyte levels will result in rapid correction of serum sodium concentration and place the patient at risk for osmotic demyelination syndrome. We present a patient with acute kidney injury and severe hypervolemic hypotonic hyponatremia (serum sodium<100 mEq/L) who was treated successfully with continuous venovenous hemofiltration. This teaching case illustrates the limitations of hemodialysis and demonstrates how to regulate the sodium correction rate by single-pool sodium kinetic modeling during continuous venovenous hemofiltration. Two methods to adjust the replacement fluid to achieve the desired sodium concentration are outlined.

Intravenous iron dextran as a component of anemia management in chronic kidney disease: a report of safety and efficacy.

Objective. We aimed to demonstrate safety and efficacy of intravenous (IV) low molecular weight iron dextran (LMWID) during treatment of anemic stage 3 and 4 chronic kidney disease (CKD) patients. Methods. Efficacy data was obtained by retrospective chart review of 150 consecutively enrolled patients. Patients were assigned per protocol to oral or IV iron, with IV iron given to those with lower iron stores and/or hemoglobin. Iron and darbepoetin were administered to achieve and maintain hemoglobin at 10-12 g/dL. Efficacy endpoints were mean hemoglobin and change in iron indices approximately 30 and 60 days after enrollment. Safety data was obtained by retrospective review of reported adverse drug events (ADEs) following 1699 infusions of LMWID (0.5-1.0 g). Results. Mean hemoglobin, iron saturation, and ferritin increased significantly from baseline to 60 days in patients assigned to LMWID (hemoglobin: 11.3 versus 9.4 g/dL; iron saturation: 24% versus 12.9%; ferritin: 294.7 versus 134.7 ng/mL; all P values < 0.0001). Iron stores and hemoglobin were maintained in the group assigned to oral iron. Of 1699 iron dextran infusions, three ADEs occurred. Conclusions. Treatment of anemia in CKD stages 3 and 4 with LMWID and darbepoetin is efficacious. The serious ADE rate was 0.06% per infusion.

Effect of intravenous ascorbic acid in hemodialysis patients with EPO-hyporesponsive anemia and hyperferritinemia.

BACKGROUND: Although erythropoietin (EPO)-hyporesponsive anemia in hemodialysis patients most commonly results from iron deficiency, the contributory role of chronic inflammation and oxidative stress in its pathogenesis is poorly understood. We conducted an open-label prospective study to assess the effect of vitamin C, an antioxidant, on EPO-hyporesponsive anemia in hemodialysis patients with unexplained hyperferritinemia. METHODS: Forty-six of 262 patients in an inner-city hemodialysis center met the inclusion criteria (administration of intravenous iron and EPO for > or = 6 months at a dose > or = 450 U/kg/wk, average 3-month hemoglobin [Hb] level < or = 11.0 g/dL [< or = 110 g/L], ferritin level > or = 500 ng/mL (microg/L), and transferrin saturation [TSAT] < or = 50%). Patients were excluded if they had a clear explanation for the EPO hyporesponsiveness. Four patients refused to participate. The remaining patients were randomly assigned; 20 patients to receive standard care and 300 mg of intravenous vitamin C with each dialysis session (group 1) and 22 patients to receive standard care only (group 2). Study duration was 6 months. During the study, 1 patient from group 1 was removed (upper gastrointestinal bleeding) from final analysis. Monthly assessment included Hb level, mean corpuscular volume, iron level, iron-binding capacity, ferritin level, TSAT, and Hb content in reticulocytes. In addition, biointact parathyroid hormone, aluminum, C-reactive protein (CRP), and liver enzymes were measured every 3 months. RESULTS: Age, sex, race, and time on dialysis therapy were similar in both groups. At 6 months, Hb levels significantly increased from 9.3 to 10.5 g/dL (93.0 to 105.0 g/L) in group 1, but not group 2 (9.3 to 9.6 g/dL [93.0 to 96.0 g/L]; P = 0.0001). Similarly, TSAT increased from 28.9% to 37.3% in group 1, but not group 2 (28.7% to 29.3%; P = 0.0001). EPO dose (477 to 429 versus 474 to 447 U/kg/wk), iron-binding capacity (216 to 194 versus 218 to 257 microg/dL [38.7 to 34.7 versus 39 to 46 micromol/L]), and CRP level (2.8 to 0.9 versus 2.8 to 2.2 mg/dL) decreased significantly in group 1, but not in controls. Changes in Hb content in reticulocytes and ferritin level also were statistically significant in group 1. There was no change in biointact parathyroid hormone levels. Although serum iron levels and intravenous iron doses changed within each group, changes were equal between the 2 groups. CONCLUSION: In hemodialysis patients with refractory anemia and hyperferritinemia, vitamin C improved responsiveness to EPO, either by augmenting iron mobilization from its tissue stores or through antioxidant effects.