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494 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

A
CRRT vascular access catheter
lumen design profiles

Double ‘D’ design or ‘D’ and ‘O’ : one
lumen extended longer for return blood

Inner and outer lumen : ‘Coaxial’ with
side holes at tip for drawing blood int
outer lumeno

Side by side : Double ‘O’ :one FIGURE 18.15 (A) Vascular access catheters for CRRT. Dual-lumen, Bard® Niagara™
lumen extended longer for return blood and Gambro Dolphin Protect™ catheters; (B) Concept diagram of catheter lumen
B profiles used for dual lumen CRRT catheters.

via an artery and returning it to a vein, the term arterio- min for an adult CRRT circuit. Catheters are made with
venous (AV) is used. 75,76 In this system there is no mechan- different arrangement of the lumens revealing variation in
ical blood pump required, as the patient’s arterial blood their cross section profile (see Figure 18.15b) There is no
pressure provides a flow of blood in the EC. Veno-venous evidence to suggest which profile is better, but the larger
haemofiltration (CVVH) has the advantages of requiring the internal diameter, the less likely flow will be obstructed
only a single venipuncture, a reliable blood flow delivered during patient care with CRRT. After a catheter is threaded
from a blood pump, and alternative venous access sites if into a vein, the blood flow may be adequate, but later
77
site infection or access is difficult. While it is easy to during patient care it may obstruct due to different nursing
establish flow within AV-driven circuits and no complex interventions and patient movement, which may alter
system of blood pumps and pressure sensors is necessary, blood flows within the low pressure venous system. 70
this method is susceptible to flow problems associated
with low patient arterial blood pressure and high venous Insertion sites may be affected by nursing care interven-
pressures, a common occurrence in critically ill patients. tions. Placement of the catheter is usually in the subcla-
vian or femoral vein, and occasionally in the internal
78
The dual-lumen catheter used for veno-venous access has jugular vein. Anecdotally, the subclavian position is
an internal diameter of 1.5–3 mm and the ends of the more easily managed for dressing and securing, continu-
catheter are sufficiently separated from each other in the ous observation and patient comfort, but is more prob-
patient’s vein to prevent filtered blood from mixing with lematic in terms of flow reliability. Intrathoracic pressure
unfiltered blood when used in the recommended changes associated with physiotherapy or spontaneous
77
sequence. This ensures that filtered blood does not patient coughing and breathing, coupled with the upright
simply pass back through the artificial kidney, where there position of patients, may hinder blood flow from the
would be minimal waste clearance compared with ‘fresh’ subclavian-sited access catheter. While these issues are
unfiltered blood; this design is illustrated in Figure 18.15a. not encountered with a femoral-placed catheter, flow
The catheter must be small enough to place into a vein problems can arise due to side lying and flexion at the
but large enough to provide blood flow of at least 200 mL/ groin or hip. 42