Page 513 - ACCCN's Critical Care Nursing

490 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

but develop ARF as a complication, or coexisting organ addition to their established role in ICU of caring
failure secondary to a primary problem with their heart for critically ill patients using mechanical ventilation
or other major organ system. The pathogenesis and epi- and haemo dynamic interventions. Physician-prescribing
demiology of ARF have thus changed. rights also favoured this role for nursing in Australia and
New Zealand, as the ICU physician can prescribe renal
Historically, ARF was treated in the ICU with the use of
peritoneal dialysis (PD), which did not require specialist dialysis without the referral of the patient to a nephrolo-
8,49,50
nurses or physicians. This simple technique removes gist that is required in other countries. In the Austra-
45
wastes by infusing a dialysis fluid into the abdomen, lian context, this resulted in the provision of renal support
allowing diffusion and osmosis to occur between the for critically ill patients by ICU nurses alone, or in a
50
peritoneum and fluid before draining out again in shared role with renal dialysis nurses.
46
repeated cycles. This was performed by the ICU nurse Different approaches or models of care are created by
and prescribed by ICU physicians, but was inadequate in many factors, including the presence of a dialysis service
its clearance of waste and fluid volume, and was associ- in a hospital, the number of patients requiring treatment
ated with infection, limiting respiratory function and in an ICU per annum, physician rights of prescribing as
exacerbated glucose intolerance. 14,47 specified by health insurance scheme structures, and the
number, professional competence and flexibility of the
In 1977 Peter Kramer, a German ICU physician, frustrated nursing workforce available for an ICU or dialysis service
with the limitations of PD and the delays in gaining a in a given hospital. 44,50,51
dialysis nurse and machine to attend the ICU, developed
a new dialytic technique by inserting a catheter into the
femoral artery and allowing blood to flow to a membrane Refinement of Renal Replacement Therapy
and back to the femoral vein. As the blood passed through Although CAVH as developed by Kramer was useful in
48
the membrane, plasma water was filtered out. The tech- removing excessive body water and some wastes, a dialy-
nique was called continuous arteriovenous haemofiltra- sis blood pump enabled a much more efficient technique
tion (CAVH). It was later renamed slow continuous for therapeutic benefit in the ICU patient with ARF. The
ultrafiltration (SCUF), as it enabled the removal of plasma use of roller blood pumps to generate pressure and a reli-
water in addition to dissolved wastes (convective clear- able flow of blood, thus eliminating the need for arterial
ance of solutes) at a flow rate of 200–600 mL/h by passive puncture and access, was introduced by two German
drainage from the membrane as blood flowed through it. groups. This approach, termed continuous veno-venous
49
Kramer reported ‘considerable therapeutic potential’ after haemofiltration (CVVH), could reliably pump blood at
treating 12 patients in the ICU, although suggesting that a constant rate and achieve ultrafiltration volumes of
this level of ultrafiltration and waste clearance was inad- 1000 mL/h. This therapy was able to remove large volumes
equate for optimal support of ARF in many critically ill of plasma water and, if run continuously with similar
6
patients. This marked the beginning of continuous RRT amounts replaced by a balanced plasma water substitute,
in the ICU as an intervention prescribed and managed by an effective clearance of wastes similar to a high-intensity
ICU nurses and doctors for patients with ARF. A sche- dialysis treatment could be achieved without cardiovas-
matic diagram of Kramer’s original technique is illus- cular instability.
trated in Figure 18.9.
With further modifications to the circuit and filter set-up,
The increase in demand for chronic renal failure dialysis a diffusive component was added to the therapy by
made it problematic to provide any service to patients in running a dialysate volume through the haemofilter,
the ICU with ARF by dialysis nurses. Dialysis for patients flowing between the membrane fibres and countercurrent
in the ICU was often delayed or unavailable while using to blood flow. This was termed continuous veno-venous
the same human and material resources from a dialysis haemodiafiltration (CVVHDf). To deliver continuous
unit. It was thus inevitable that in the ARF context ICU forms of veno-venous RRT required the introduction of
49
nurses would adopt the role of the dialysis nurse, in blood pumps from modified dialysis machines into the
ICU, and created a major education and training need for
52
critical care nursing. This was first met in the Australian
setting by dialysis nurses until independent practice was
CAVH achieved. This training often used old dialysis machines
and equipment that had been superseded in the chronic
dialysis setting by new, more efficient dialysis machines.
The old machines were suitable for the ICU to use because
of their technical simplicity, with low or no purchase
42
cost. As CRRT became more widespread in the ICU, this
encouraged manufacturers to design and market purpose-
built CRRT machines with automation, intelligence soft-
Filtrate ware for alarm detection and practical solutions. 53
Convection
As already noted, in the Australian and New Zealand
setting CRRT is provided by ICU nursing staff with
FIGURE 18.9 CAVH used in the ICU in the late 1970s. Patient arterial blood
pressure provides flow to the membrane, and blood returns via a large vein. medical prescription by ICU physicians, with nephrolo-
Plasma water removal occurs via filtration and is pressure-dependent. gists focused on chronic disease and care of patients
48