Intermittent Hemodialysis & Critical Illness

What’s wrong with hemodialysis in acutely ill patients in ICU?

Hemodialysis clears fluid out of the intravascular space at a rapid rate, usually faster than it can be replaced from the extravascular space. In generally healthy patients this often causes hypotension. In ICU patients, who often have intravascular hypovolemia (decreased oncotic pressure due to capillary leak), this hypotension may be disasterous. Such a drop in blood pressure may precipitate ischemic injury to various organs, particularly the recovering kidneys, which have temporarily lost pressure-flow autoregulation (new ischemic injuries have been demonstrated after HD sessions). This delays renal recovery. Further, many patients, particularly those with head injuries, cannot tolerate the osmotic changes associated with hemodialysis.

The other problem with IHD is the nature of intermittent therapy. Patients who are otherwise healthy (except for chronic renal failure) have tremendous venous capacitance, and can tolerate fluid accumulation between dialysis sessions. Critically ill patients with leaky capillaries may develop significant pulmonary edema between sessions, and daily IHD is often required. Indeed  CRRT, by it's nature is clears more urea, creatinine and fluid than IHD.

Feeding and nutrient delivery is a significant problem in critical illness. The patients are severely catabolic; there is significantly more metabolic byproducts to be cleared. To prevent further loss of protein, feeding is essential, and fluid restriction is not an option. If an intermittent dialysis strategy is used, then, in early critical illness, daily therapy is probably required.

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