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200 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

other modalities are now being explored, including right problems and the need for repeated dressing changes.
ventricular end-diastolic volume evaluation via fast- These include beard growth, diaphoresis and poor control
response pulmonary artery catheters, left ventricular of oral secretions.
end-diastolic area measured by echocardiography and The subclavian approach is used often, perhaps because
intrathoracic blood volume measured by transpulmonary of a reported lower risk of catheter-related bloodstream
thermodilution. 40
infection. 46,47 Coagulopathy is a significant contraindica-
Central venous pressure monitoring tion for this approach, as puncture of the subclavian
artery is a known complication. There is also a risk of
Central venous catheters are inserted to facilitate the pneumothorax, which rises if the patient is receiving
monitoring of central venous pressure; facilitating the intermittent positive pressure ventilation (IPPV).
47
administration of large amounts of IV fluid or blood; Complications of any central venous access catheters
providing long-term access for fluids, drugs, specimen include air embolism, pneumothorax, hydrothorax and
collection; and/or parenteral feeding. CVP monitoring haemorrhage. 44
has been used for many years to evaluate circulating
blood volume, despite discussion as to its validity to do Pulmonary artery pressure (PAP) monitoring
so. 41-43 However, it is a common monitoring practice and Pulmonary artery pressure monitoring began in the
continues to be used. Therefore clinicians need to be 1970s, led by Drs Swan, Ganz and colleagues, and was
48
aware of possible limitations to this form of measure- subsequently adopted in ICUs worldwide. Pulmonary
ment and interpret the data accordingly. CVP monitoring artery catherisation facilitates assessment of filling pres-
can produce erroneous results: a low CVP does not always sure of the left ventricle through the pulmonary artery
mean low volume and it may reflect other pathology, wedge (occlusion) pressure (see Figure 9.20). 45,49 By using
including peripheral dilation due to sepsis. Hypovolae- a thermodilution pulmonary artery catheter (PAC),
mic patients may have normal CVP due to sympathetic cardiac output and other haemodynamic measurements
nervous system activity increasing vascular tone. An can also be calculated. PAP monitoring is a diagnostic
increase in CVP can also be seen in patients on mechani- tool that can assist in determination of the nature of a
cal ventilation with application of PEEP. 41-43
haemodynamic problem and improve diagnostic accu-
Central venous catheters used for haemodynamic moni- racy. In addition to measuring PA pressures, PAC may also
toring are classed as short-term percutaneous (non- be used for accessing blood for assessment of mixed-
tunnelled) devices. Short-term percutaneous catheters are venous oxygenation levels (see Chapter 13).
inserted through the skin, directly into a central vein, and
usually remain in situ for only a few days or for a The beneficial claims of PAP monitoring have, however,
50
maximum of 2–3 weeks. They are easily removed and been questioned, with some proposing a moratorium.
37
changed, and are manufactured as single- or multi-lumen In response, two consensus conferences were held in the
types. However, they can be easily dislodged, are throm- USA to make recommendations for future practice. It was
bogenic due to their material, and are associated with a concluded that there was no basis for a moratorium on
high risk of infection. 37,44 the use of PACs; instead, education and knowledge about
the use of this technology must be standardised and
A number of locations can be used for central venous monitored. Further research was indicated, particularly
access. The two commonly used sites in critically ill focusing on the use of PACs. 51,52 More recently, an obser-
patients are the subclavian and the internal jugular veins. vational cohort study of 7310 patients found that PAC use
Other less common sites are the antecubital fossa (gener- was not associated with an overall higher mortality,
ally avoided but may be used when the patient cannot be although the authors concluded that severity of illness
positioned supine), the femoral vein (associated with should be examined when considering the use of this
53
high infection risk), and the external jugular vein measurement tool. The PAC-Man study, a randomised
(although the high incidence of anomalous anatomy and controlled clinical trial, suggested that the use of PAC did
54
the severe angle with the subclavian vein make this an not improve the critically ill patients’ outcome. A sys-
55
unpopular choice). 44 tematic review on PAC use by Harvey et al. by the
Cochrane Collaboration suggested that more empirical
Internal jugular cannulation has a high success rate for
insertion; however, complications related to insertion via studies are needed to identify the appropriate patient
this route include carotid artery puncture and laceration groups that could benefit from the use of PAC and the
of local neck structures arising from needle probing. 44,45 protocols for their use. In the meantime, proponents for
There are a number of key structures adjacent to the vein, continuing clinical use of the PAC argue that it provides
including the vagus nerve (located posteriorly to the a physiological rationale for diagnosis and assists in the
internal jugular vein); the sympathetic trunk (located titration of therapies such as inotropes, which would
29,49,51
behind the vagus nerve); and the phrenic nerve (located otherwise be potentially dangerous.
laterally to the internal jugular). Damage can also occur Since the benefit of use of PAC is still arguable, the indica-
46
to the sympathetic chain, which leads to Horner’s syn- tions of PAP monitoring are largely based on clinical
drome (constricted pupil, ptosis, and absence of sweat experience. PAP monitoring may be indicated for adults
gland activity on that side of the face). Central venous in severe hypovolaemic or cardiogenic shock, where there
catheters inserted in the internal jugular vein pose a may be diagnostic uncertainty, or where the patient is
number of nursing challenges which can cause fixation unresponsive to initial therapy. The PAP is used to guide