1. You are evaluating the following patients for the possibility of renal replacement therapy. You only have one dialysis circuit available. Which patient should you treat first?
a) Patient with BUN of 110. No clinical evidence of bleeding and otherwise normal mental status.
b) Pt. mechanically ventilated due to ARDS and on epinephrine 0.05 mcg/kg/min for shock. Most recent ABG: pH 7.18 PCO2 70 paO2 65 lactate 3.4
c) Pt. on mechanical ventilation for ARDS with 13% fluid overload, making 0.3 cc/kg/hr of urine with lasix IV q6h
d) Pt. with K of 7.5 after calcium chloride, insulin/glucose, albuterol, kayexalate, bicarbonate X1. Otherwise asymptomatic with NSR.
2. Your patient has liver failure and requires CRRT for fluid overload due to AKI as well as ammonia clearance. Their most recent iCa was 1.1 with a total calcium of 13.5 and a circuit calcium of 0.35. Which of the following would be an inappropriate treatment?
a) Hold citrate and calcium infusions until the patient's total calcium has normalized
b) Reset the patient's citrate and calcium rates to the initial rates
c) Decrease the blood flow rate and citrate rate
d) Increase the dialysate infusion rate
3. Which of the following is matched incorrectly?
a) Adsoprtion- molecules bind to the membrane, removing them from the patient's blood
b) Diffusion- molecules move across a concentration gradient across a semi-peremeable membrane
c) Convection- Solvent is pushed through pores due to pressure gradients
d) Ultrafiltration- Fluid is forced through pores as a result of pressure gradients
ANSWERS & EXPLANATIONS
1. D. The typical indications for renal replacement therapy are often taught as AEIOU (acidosis, electrolyte abnormality, ingestion, overload, uremia). However, no absolute cutoffs exist for the degree of acidosis, uremia, or fluid overload. It is primarily based upon the clinical situation and symptoms (ie mental status changes, uremic pericarditis or platelet dysfunction leading to oozing/bleeding, limited efficacy of vasoactive agents secondary to degree of acidemia, and evolving literature regarding perhaps ~10% fluid overload being a relative indication for renal replacement therapy). The patient with a K of 7.5 despite initial therapy, although they have a normal EKG and rhythm at this point, is at the highest risk for immediate life threatening complications and thus should receive renal replacement therapy first.
2. A- This patient demonstrates citrate lock, a situation that occurs when the amount of citrate being delivered to the patient (used for regional anti-coagulation of the CRRT circuit) overwhelms the body's ability to clear the citrate (typically due to liver dysfunction as citrate is primarily cleared hepatically). Hence, the patient's ionized calcium remains the same but their total calcium (which also measures the calcium bound to citrate) increases. Treatments for citrate lock include increasing the dialysate infusion rate to clear more citrate and prevent it from reaching the patient, reset the patient's citrate and calcium rates to the initial rates (which decreases the citrate rate), decreasing the blood flow rate and citrate rate (less blood requires less citrate to anticoagulate), or holding the citrate and calcium infusions for a short period of time. This last method requires close monitoring of patient and circuit ionized calcium as the circuit may clot if no citrate is being run and the ionized calcium of the circuit increases too much. Hence, answer A is incorrect in that one may need to restart citrate before the patient's total calcium has normalized.
3. C- Convection describes solute drag as a result of solvents (i.e. fluid) moving across a semipermeable membrane and taking the solute with it