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390 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

BiPAP® is registered to Respironics (Murrayville, PA), a
company that produces a number of non-invasive venti- TABLE 15.3 Indications and contraindications for
lators including the BIPAP Vision, a NIV ventilator com- non-invasive ventilation 77
monly used in the ICU. The acronym NIPSV is primarily
used in European descriptions of NIPPV. Indications
Bedside observations Increased dyspnoea: moderate to severe
Tachypnoea:
>24 breaths per min [obstructive]
>30 breaths per min [restrictive]
Practice tip Signs of increased work of breathing,
accessory muscle use and abdominal
When other members of the ICU team use the term BiPAP/ paradox
BIPAP, clarify if they are referring to non-invasive or invasive Gas exchange Acute or acute-on-chronic ventilatory
ventilation. failure (best indication), PaCO 2
>45 mm Hg, pH <7.35
Hypoxaemia (use with caution), PaO 2 /
FIO 2 ratio <200
PHYSIOLOGICAL BENEFITS Contraindications
The efficacy of NIV in patients with acute respiratory Absolute Respiratory arrest
failure is, at least in part, related to avoidance of inspira- Unable to fit mask
tory muscle fatigue through the addition of inspiratory Relative Medically unstable: hypotensive shock,
positive pressure thus reducing inspiratory muscle work. uncontrolled cardiac ischaemia or
79
Application of positive pressure during inspiration arrhythmia, uncontrolled upper
gastrointestinal bleeding
increases transpulmonary pressure, inflates the lungs, Agitated, uncooperative
augments alveolar ventilation and unloads the inspira- Unable to protect airway
80
tory muscles. Augmentation of alveolar ventilation, Swallowing impairment
demonstrated by an increase in tidal volume, increases Excessive secretions not managed by
secretion clearance techniques
CO 2 elimination and reverses acidaemia. High levels of Multiple (i.e. two or more) organ failure
inspiratory pressure may also relieve dyspnoea. 81 Recent upper airway or upper
gastrointestinal surgery
The main physiological benefit in patients with conges-
tive heart failure (CHF) is attributed to the increase in PaCO 2 : partial pressure of carbon dioxide in arterial blood; PaO 2 : partial
functional residual capacity associated with the use of pressure of oxygen in arterial blood; PaO 2 /FIO 2 : ratio of partial pressure of
oxygen in arterial blood to fraction of inspired oxygen.
PEEP that reopens collapsed alveoli and improves oxy-
82
genation. Increased intrathoracic pressure associated
with the application of positive pressure also may improve
cardiac performance by reducing myocardial work and
oxygen consumption through reductions to ventricular (CHF). Three meta-analyses have shown a reduction in
preload and left ventricular afterload. 82-84 NIV also pre- intubation rates, hospital length of stay and mortality for
serves the ability to speak, swallow, cough and clear secre- COPD patients managed with NIPPV compared to stan-
89-91
tions, and decreases risks associated with endotracheal dard medical treatment. COPD patients most likely to
intubation. 85 respond favourably to NIPPV include those with an
unimpaired level of consciousness, moderate acidaemia,
INDICATIONS FOR NIV a respiratory rate of <30 breaths/minute and who dem-
onstrate an improvement in respiratory parameters within
The success of NIV treatment is dependent on appropri- two hours of commencing NIV. 79,92
86
ate patient selection. Table 15.3 outlines indications
and contraindications to NIV. Early use of NIV in combination with standard therapy
for patients with CHF has also been shown to reduce
Acute Respiratory Failure intubation rates and mortality when compared to stan-
93-95
Evidence supporting the role of NIV in patients with dard therapy alone. A recent meta-analysis found
CPAP reduced hospital mortality whereas NIPPV did not
hypoxaemic respiratory failure is limited and conflict- have an effect on mortality. Both NIV modes were
94
82
ing. For patients with community-acquired pneumonia, shown in this meta-analysis to reduce the need for intu-
NIV has been shown to reduce intubation rates, ICU bation. An early study comparing NIPPV to CPAP in
length of stay and 2-month mortality but only in the patients with CHF reported a higher incidence of myo-
87
subgroup of patients with COPD. Pneumonia also has cardial infarction. Based on this finding, practice guide-
96
been identified as a risk factor for NIV failure. 88 lines from the British Thoracic Society recommend NIPPV
should only be used for patients with CHF when CPAP
Acute Exacerbation of COPD and CHF has been unsuccessful. More recently several studies
97
Strong evidence exists to support the use of NIV for have found no difference in myocardial infarction rates
patients with acute exacerbation of chronic obstructive when comparing the two modes. 98-101 A recent large mul-
pulmonary disease (COPD) and congestive heart failure ticentre randomised controlled trial found NIV delivered