Page 711 - Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice
P. 711

698        SPECIAL THERAPY



                                      Adequate anticoagulation   of the degree of clotting (loss of membrane surface area),
                                      Inadequate anticoagulation
               250                                               which could be used to trigger contingencies to modify
                                                                 the anticoagulation protocol or to stop the treatment.
              Fiber bundle volume (ml)  150                      tingency to replacement of the hemodialyzer, increase the
                                                                 For example, a 25% to 30% decline in clearance predicts
               200
                                                                 a similar magnitude of clotting and could prompt a con-
                                                                 blood flow rate, initiate saline flushing of the extracorpo-
                                                                 real circuit, or discontinue the treatment for fear of
               100
                                                                 greater blood loss. It should be recognized that these
                                                                 techniques only detect clotting in the fiber bundle and
               50
                                                                 could fail to detect severe clotting in the arterial or venous
                0                                                header of the dialyzer or clotting in the venous drip cham-
                  0  30  60  90  120 150 180 210 240 270 300 330
                                                                 ber, which could cause a sudden and catastrophic inter-
                                 Dialysis time (min)             ruption of the treatment and loss of the entire
            Figure 29-9 Mean   SD changes in fiber bundle volume of high-  extracorporeal blood volume. In some cases obstruction
            flux dialyzers during hemodialysis treatments in a dog using adequate
            heparin administration (squares) and treatments using inadequate  of the arterial or venous headers with cessation of all flow
            heparin (approximately half) dosing (triangles). Progressive clotting  of blood in the extracorporeal circuit can develop without
            of the dialyzers develops after 180 minutes of treatment, and can be  activation of the arterial or venous pressure alarms and
            detected and monitored by sequential changes in fiber bundle  continued rotation of the blood pump.
            volume.                                                It is possible to accurately and sequentially measure the
                                                                 fiber bundle volume of the dialyzer in vivo in real-time
                                                                 during the course of the dialysis session using indicator
            within the blood pool. Clotting in the fiber bundle also  dilution techniques with ultrasonic detectors. 90  The fiber
            can be recognized by darkened streaks in the bundle,  bundle volume is computed from the ultrasound-
            but this appearance will vary with different membranes.  detected transit time of an injected saline bolus through
            Evidenceof fibrindepositionandclottingcanbeidentified  the dialyzer. The volume of blood in the bundle is deter-
            more readily by flushing the extracorporeal circuit period-  mined from the relationship, FBV ¼ Q b   T, where FBV
            ically with saline to displace the blood in the circuit. Serial  is the volume in the blood compartment of the dialyzer,
            flushing helps clear developing clots to prevent their  Q b is the extracorporeal blood flow rate, and T is the
            extension and to document worsening of the clotting.  mean transit time through the dialyzer. A decrease in
               At a constant blood flow and ultrafiltration rates, pro-  mean transit time reflects the increased velocity of blood
            gressive clotting in the fiber bundle can be identified by a  flowing through a smaller volume. A decrease in bundle
            progressive increase in transmembrane pressure (TMP).  volume reflects the loss of flowing blood channels due to
            As the surface area of the dialyzer declines with clotting  clotting.
            of the fiber bundle volume, a greater TMP is required
            to achieve the ultrafiltration goal set in the ultrafiltration  HEMODIALYSIS PRESCRIPTION FOR
            controller. Some delivery systems permit adjustment of  CHRONIC KIDNEY DISEASE
            the “maximum TMP” setting to a value just above the  Experience with long-term intermittent hemodialysis for
            TPM established for the treatment. If clotting occurs  animals with chronic kidney disease is less than for acute
            and the TPM increases above this preset value, a “maxi-  uremia, yet hemodialysis is clearly indicated, effective, and
            mum TMP alarm” will sound to alert the operator to   affords a good quality of life for animals with CKD. Many
            the increasing TPM and likely clotting. This process  of the considerations used to prescribe acute hemodialysis
            works very well for the early detection of clotting in the  are equally valid for chronic dialytic therapy. Adequacy
            fiber bundle, but the maximum TMP limit must be      standards for animals with CKD await future definition,
            readjusted if the blood flow or the ultrafiltration rates  but intensive hemodialysis provided every 2 to 3 days
            are changed during the treatment.                    can augment its medical management. As animals are
               Evidence of clotting in the fiber bundle can also be  supported beyond their fated life expectancy with dialysis,
            detected by decreasing dialyzer performance throughout  the spectrum and severity of uremic signs increase. Collec-
            the treatment. Dialyzer performance can be monitored  tively, chronic malnutrition, fluid overload, hyperkalemia,
            by sequential bedside measurements of the urea clearance  hyperparathyroidism, metabolic bone disease, refractory
            of the dialyzer (at constant blood flow) or by real-time  hypertension, progressive anemia, infection, and drug
            measurement of ionic dialysance available and displayed  interactions and toxicities replace concerns of hypother-
            on some dialysis delivery systems (See previous Dialysis  mia, hypovolemia, and dialysis disequilibrium syndrome
            Adequacy section). Progressive or sudden decreases in  so prevalent in animals with acute kidney injury.
            clearance suggest active clotting in the dialyzer. These  The dialysis prescription for chronic kidney disease is
            monitoring techniques provide a quantitative prediction  targeted to reduce the azotemia maximally during each
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