Dialysis

Hemodialysis (HD) (NE/M 1998 338:1428 * 339 1054)

• Physiology: blood flows along one side of semipermeable membrane, dialysate along other.

Fluid removal (ie. Na HjO) via transmembrane pressure (TMP) gradient Solute removal via transmembrane concentration gradient and inversely proportional to size (.. effective removal of K. urea, and Cr. but not PO«).

• Typical orders: duration, volume removal goals. K and Ca in dialysate bath, anticoagulation

• Complications: hypotension, arrhythmia, access complications, disequilibrium syndrome

Vascular Access

Advantages

Disadvantages

AV Fistula

Highest patency Lowest risk of bacteremia

Long maturation time (2-6 mo) Primary nonfunction (20%)

AV Graft

Easier to create than AVF Maturation time (2-3 wks)

Poor 1 patency, often requiring thrombectomy or angioplasty

Use as bridge to AVF AVG

Highest risk of bacteremia 1 blood flow I HD efficiency

Continuous Veno-Venous Hemofiltration (CWH) <nejm 1997:3361303)

• Physiology: based on ultrafiltration rather than dialysis. Blood under pressure passes down one side of a highly permeable membrane allowing water and solutes to pass across the membrane via TMP gradient. Filtrate is discarded. Replacement fluid is infused (solute concentrations similar to plasma, except no K. urea. Cr. PO«). Fluid balance precisely controlled by adjusting amounts of filtrate and replacement fluid.

• Access: double-lumen central venous catheter

• Typical orders: volume removal goals, replacement fluid buffer: HCOj (requires heparin to prevent machine from dotting) vs. citrate (hepatically metabolized to HCOj; provides anticoagulation w in machine via Ca chelation; need Ca infusion to maintain serum Ca)

• Complications: hypotension. 1 PO«. access complications; 1 ICa (citrate toxicity in Pts with hepatic dysfunction look for i ICa but normal I serum Ca and AG metabolic acidosis)

• Potential advantages over HD: less hypotension, better volume control, removal of inflammatory mediators: however, no survival advantage (Lancet 2006:368 379)

Peritoneal Dialysis (PD) (Pent tool I* 2001:21 2S)

• Physiology: peritoneum acts as membrane. Fluid balance controlled by choosing dialysate glucose concentration (higher concentrations pull more fluid into peritoneum); longer dwell times pull less fluid as glucose equilibrates across peritoneum

• Access: temporary catheter inserted midline, permanent catheter inserted in OR

• Typical orders for CAPD (continuous ambulatory peritoneal dialysis):

PD fluid 1.5%. 2.5%. or 4.25% dextrose buffer (lactate). Na . K1. Ca21. Mg2

infuse 10 min. dwell 30 min-5.5 h. drain 20 min

• Can use overnight cycler device that infuses & drains more rapidly, with shorter dwells.

while Pt sleeps. Called automated or continuous cycling peritoneal dialysis (APD.CCPD).

• Complications

Peritonitis (abdominal pain, tenderness, cloudy drainage) diagnosis: WBC 100 and .-50% PMNs spectrum: 60-70% GPC. 15-20% GNR. remainder no bacteria or fungal Rx: abx IV or in PD. catheter removal for certain pathogens (eg. yeast, pseudomonas) Hyperglycemia: exacerbated by inflammation, long dwell times, and higher [glc]

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