Page 425 - ACCCN's Critical Care Nursing

402 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

off; arterial line filters between the heat exchanger and ● unstable pelvic fractures
arterial cannula, to trap air thrombi and emboli; pressure ● prone positioning
monitors placed before and after the oxygenator, that ● haemodynamic support devices (IABP, LVAD, ECMO)
measure the pressure within the circuit and detect rising ● femoral catheterisation for continuous renal replace-
circuit pressures commonly caused by thrombus or circuit ment therapy
or cannulae occlusion; and continuous venous oxygen ● large abdominal wounds
saturation and temperature monitoring. On commence- ● following femoral sheath removal.
ment of ECMO the circuit is primed with fresh blood. The As some degree of semirecumbent position is preferable
acid–base balance and blood gas of the primer is adjusted to supine positioning, patients with suspected or existing
to ensure that the pH is within the normal range (7.35– spinal injury, pelvic fractures or being managed
7.45) and PaO 2 is adequate. ECMO can be delivered via with prone positioning can have the head elevated by
veno-arterial access which requires cannulation of an tilting the whole bed. Patients with femoral cannulation
artery. This method bypasses the pulmonary circulation and large abdominal wounds can usually achieve
while providing cardiac support to the systemic circula- 25–30 degree positioning.
tion and achieves a higher PaO 2 with lower perfusion
rates. The alternative is veno-venous access, used for Clinical practice audits conducted internationally and in
patients in respiratory failure with adequate cardiac func- Australia and New Zealand indicate that compliance with
tion as there is no support of systemic circulation. Perfu- a 45 degree semirecumbent position rarely occurs, even
sion rates are higher, the mixed venous PO 2 is elevated when taking into consideration contraindications. 208-212
and the PaO 2 is lower. 199 Similarly, interventions to improve compliance failed to
demonstrate adherence to the 45 degree backrest position
Nitric Oxide that can be sustained by the patient over time. 213,214
Nitric oxide (NO) is an endothelial smooth muscle relax- Due to uncertainty over compliance with 45 degree
semirecumbency in the original trial conducted by
ant. Inhaled NO is effective in the dilation of pulmonary Drakulovic, and the lack of difference in VAP rates
204
arteries resulting in reduced pulmonary shunting and despite difficulty achieving compliance with semirecum-
reduced right ventricular afterload due to reduced pulmo- bency in the van Niewenhoven study, new studies are
207
nary artery tone. Pulmonary shunting refers to failure of required to confirm the equivalence or lack of inferiority
uptake of alveolar gas by the pulmonary vascular bed due of lower degrees of backrest elevation to the strict
to vascular constriction or interstitial oedema. Inhaled 45 degree semirecumbent position.
NO has a role in the management of pulmonary hyper-
tension and was previously thought to have a role in
management of refractory hypoxaemia for patients with
ARDS. However, the most recent systematic review and Practice tip
meta-analysis of NO in ARDS comprising 14 RCTs and
1303 participants reported no effect on overall mortality Backrest elevation is difficult to estimate accurately. Use an
despite a statistically significant improvement in oxygen- objective measurement device such as an inclinometer or
ation in the first 24 hours, and some risk of renal impair- protractor.
ment among adults. 200

POSITIONING
Regular repositioning of critically ill patients is essential Lateral Positioning
for lung recruitment, prevention of atelectasis and main- Patients with unilateral lung disease experience a mis-
tenance of skin integrity (see Chapter 6). match of ventilation to perfusion if the consolidated
(pneumonic) or atelectic lung is placed in the dependent
215
Head of Bed Elevation position. Continuous lateral rotational therapy is a
positioning therapy advocated for the prevention and
Supine positioning has been associated with aspiration
of abnormally-colonised oropharyngeal and gastric management of respiratory complications associated
216
contents 201-203 and increased incidence of VAP compared with immobility. The most recently reported multicen-
to a semirecumbent position, defined as backrest eleva- tre randomised controlled trial found a significant reduc-
204
tion at 45 degrees. Guidelines and care bundles for the tion in VAP and shorter durations of ventilation and ICU
217
prevention of VAP recommend semirecumbent position- stay. Continuous lateral rotation therapy requires a
ing for all mechanically-ventilated patients. 71,205,206 A special bed system enabling rotation of the upper part of
more recent trial has however questioned the feasibility the body to a maximum angle of 90 degrees.
of 45 degree semirecumbent positioning as this backrest
elevation was only achieved for 15% of study observa- Prone Positioning
207
tions. There was also no differences in VAP incidence Prone positioning has been shown to improve oxygen-
between the supine and semirecumbent group. Contra- ation and intrapulmonary shunt fraction when compared
indications to backrest elevation include:
218
with rotational turning during the first 72 hours of ALI
219
● suspected or existing spinal injury and in patients with multiorgan failure. Prone posi-
● intracranial hypertension (for 45 degree elevation) tioning may also decrease the risk of VAP due to