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498 P R I N C I P L E S A N D P R A C T I C E O F C R I T I C A L C A R E

TABLE 18.6 Comparison of CRRT and IHD

Factors CRRT IHD
Blood pressure Less instability because of lower blood and Removal of large volumes of fluid in a short
stability dialysate flow rates and the continuous nature time frame, causing hypotension and
of the treatment with slower fluid removal rate blood pressure instability during treatment
Waste clearance Control of urea and creatinine (key wastes) Peaks and troughs of urea and creatinine
achieved slowly and steadily; critical in associated with daily or second daily
managing patients with intracranial pathologies treatments
Nutritional support Larger volumes of nutritional fluid can be Continuous feeding difficult because of fluid
administered with concurrent clearance of volume requirement and accumulation
products of protein digestion and fluid load while off treatment
Electrolyte, acid–base Ability to adjust dose of treatment and Potential acute changes in pH during
and body water replacement of electrolytes, acid–base balance treatment; acid and electrolyte
homeostasis and body water balance to meet patient needs accumulation while off treatment
as necessary
Neurotrauma and Fare much better when managed by CRRT Fluid shifts can aggravate cerebral oedema
surgery patients without acute changes in solute levels such as and be life-threatening; IHD
urea and sodium contraindicated for patients with raised ICP
Sepsis or severe Blood-borne mediators in sepsis and Diffusive and intermittent process in IHD not
infections inflammatory illness (cytokines) better removed as effective at removing the mediators of
by the convective process in CRRT (CVVH) inflammation due to molecular size

loss of body fluid and dehydrate the patient. Regular to initiate treatment may result in patients developing a
weighing of patients may assist in assessing this situation. worsening acidosis, higher potassium and urea levels,
Electrolyte disturbances may also occur despite use of reduced or no nutritional intake and oedema with heart
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balanced replacement solutions. Particular attention failure. This suggests that prescribing IHD and using the
should focus on regular assessment of fluid and electro- limited resources of dialysis nurses for a service to the
lytes, especially potassium, sodium, phosphate and mag- ICU is inefficient, resulting in patients deteriorating
nesium levels (see Chapter 19). further before treatment. As the IHD treatment may also
be poorly tolerated when started and then seen as less
PROPOSED BENEFITS OF CRRT AND ‘well tolerated’ when delay has created less stable patients,
COMPARISONS WITH IHD this can be avoided by the prompt initiation of CRRT.
As a continuous therapy, CRRT is considered a better Depending on nursing organisational structures, CRRT
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therapy than IHD for critically ill patients for a number can be cheaper in the ICU, where one nurse cares for the
of reasons (see Table 18.6). Critically ill patients are often critically ill patient and the CRRT. This is a primary argu-
haemodynamically unstable and tolerate large fluid shifts ment supporting CRRT in the Australian and New Zealand
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poorly (see Chapter 20). The CRRT approach may be context, where an IHD treatment means two nursing
better at improving blood pressure stability than IHD. It salaries are apportioned to one patient for the period of
has also been proposed that CRRT may be beneficial to treatment in the ICU. There are mixed models, where a
patients with severe sepsis through the continuous clear- dialysis nurse initiates and terminates a treatment, leaving
ance of inflammatory mediators, which are linked to the the ICU nurse to manage the machine and treatment for
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systemic inflammatory response syndrome. Despite this, the time in between. Comparison of approaches is,
CRRT alone may not be of any benefit to this condition, however, difficult because of variable staffing and system
as many mediators in sepsis are not cleared via convec- structures in different countries. What little evidence is
tion and antiinflammatory mediators may also be available suggests that cost differences between CRRT and
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removed, which may have a counter effect to the pro- IHD are minimal, however this depends on how this is
inflammatory mediator removal. 91 calculated and what the costing includes, and reports
highlight a great deal of variation between centres and
The continuous nature of fluid removal and replacement 99
in CRRT facilitates fluid management and the administra- countries for items included.
tion of nutrition, either enterally or parenterally. This is
in contrast to the intermittent profile of fluid removal to CONTINUOUS RENAL REPLACEMENT
a point of relative hypovolaemia at treatment end, to MACHINES
relative hypervolaemia at treatment commencement seen
with the use of IHD, even on a daily schedule. There are many machines available for CRRT in the ICU.
Identifying the machine that a particular ICU should use
The efficiency in initiation and application, the nursing or purchase is a common question from nurses, and there
workload and costs of the two approaches are also impor- is limited literature available to guide this decision,
tant considerations. Delays in waiting for dialysis nurses however recent literature provides some comparisons of