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

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