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206 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

ventricular ejection time difficult), or pulmonary oedema, with a small amount of air, injected into the peripheral
pleural effusions or chest wall oedema (which alter vein to produce images of the heart functions. 66
bioimpedance readings irrespective of any changes in In the critical care setting, the preparation of critically ill
cardiac output). The use of transthoracic bioimpedance patients for this examination is important. The nurse
in critically ill patients is variable, due in part to limita- needs to help the sonographer to position the patient to
tions of its usefulness in patients who have pulmonary achieve best results. For TOE preparation, fasting time
oedema. 87,88
must be followed to avoid complications such as respira-
tory aspiration. The nurse will also need to assist the
anaesthetist and the TOE operator, and continue to
monitor the patient’s clinical conditions during the
Practice tip procedure.
Current evidence-based literature suggests that haemody- BLOOD TESTS
namic measurements such as CVP, PAWP and PAP can be accu-
rately measured with the patient’s position of supine to head A number of blood tests are often conducted to assist the
– up to 60 degrees. 28 clinical assessment of the critically ill patients in the criti-
cal care setting.

Full Blood Count
DIAGNOSTICS The full blood count (FBC) assesses the status of three
major cells that are formed in the bone marrow: red
Apart from the haemodynamic monitoring methods to blood cells (RBC), white blood cells (WBC) and platelets.
facilitate cardiac assessment of patients’ clinical condi- Although normal values have been given (see Appendix
tion, a variety of diagnostic tests are often used. Echocar- C), for critically ill patients changes will occur in certain
diography and blood tests are the most commonly used conditions. For example, Hb is reduced in the presence
in critical care. Other tests such as Computerised Tomo- of haemorrhage and also in acute fluid overload causing
graphy (CT) and Nuclear medicine cardiac examination haemodilution.
are also used when indicated. Exercise stress tests and
cardiac angiography are also used and are reviewed in Haemoconcentration can occur during acute dehydra-
Chapter 10. tion, which would show as a high Hb. Similar conditions
will also affect the haematocrit. WBC levels will be ele-
ECHOCARDIOGRAPHY vated during episodes of infection, tissue damage and
inflammation. When infections are severe, the full blood
Echocardiography (shortened to ECHO) is often used in count will show a dramatic rise in the number of imma-
critical care to assess patients’ cardiovascular conditions ture neutrophils. Platelets are easily lost during haemor-
such as heart failure, hypertensive heart disease, valve rhage, and spontaneous bleeding is a danger when the
disease, and pericardial disease in critically ill patients. It count falls to below 20 × 10 /L. 91,92
9
adopts a technique of detecting the echoes produced by
a heart from a beam of very high frequency sound – the Electrolytes
ultrasound. Two dimensional, three dimensional and
contrast ECHO images can be obtained using non- The assessment of electrolyte levels in critically ill patients
invasive transthoracic technique or the invasive trans- is important in diagnosing the patient’s condition. Elec-
oesophageal technique (TOE). The transthoracic ECHO trolyte imbalances, such as potassium and calcium level
uses a transducer probe externally to the heart to obtain changes, can cause cardiovascular abnormalities such as
images (same as a normal ultrasound technique). This arrhythmias. Electrolyte levels are often checked regularly
method is painless and does not require sedation. The in critically ill patients.
TOE technique involves placing a transducer probe into The functions of electrolytes and their cardiac implica-
the oesophageal cavity to assess the function and struc- tions are listed in Table 9.5.
ture of the heart. This method produces better images of
66
the heart than the normal ECHO. However this method Cardiac Enzymes
requires sedation during the procedure and the patient
needs to fast for a few hours prior to the examination. Recent studies have revealed that cardiac troponin levels
are elevated in critically ill septic patients who do not
Two-dimensional ECHO images are valuable resources have evidence of MI. Further, mortality rates are higher
for assessment of the function and structure of the heart. in troponin-positive patients than in those who are
Three dimensional images offer more realistic visualisa- troponin-negative, suggesting that this may become an
tion of the heart’s structure and function. The contrast important enzyme to measure; however, more research is
ECHO provides enhanced images of left and right ven- still required to refine the testing. 93,94 For patients with
tricular definition to facilitate the diagnosis of complex suspected acute myocardial infarction, testing of the
cardiac conditions such as congenital heart defects, valve enzyme troponin T or I is now standard. But not all criti-
stenosis and regurgitation. 83,89,90 The contrast ECHO tech- cally ill patients with elevated cardiac troponin levels
nique uses gas air microbubbles, produced by hand- should be treated as having myocardial infarction unless
95
agitating a syringe containing 10 mL of normal saline there is support from other data. All injured cells release