consistency of sputum. Whichever system is in use,
assessment of the patient is essential (Kelly et al.,
2004). Excessively thick or thin secretions, crusting
in the artificial airway, water in the circuit or
changes in airway pressures may suggest inappropriate
humidification. A holistic approach involving
adequate systemic hydration is also important.
Breathing
A comprehensive understanding of the adequacy
of ventilation and oxygenation in the mechanically
ventilated patient is essential as some if not all of
the respiratory effort is coordinated by the ventilator.
Necessary information is gathered from performing
a physical assessment and from analysis of
laboratory and patient monitoring data.
Physical assessment provides invaluable information
concerning the patient’s interaction with
the ventilator. The presence of dyspnoea, dyssynchronous
chest and abdominal movement, the use
of accessory muscles and agitation may suggest
the ventilation settings are inappropriate for the
patient’s requirements (Hillman and Bishop, 2004).
Physical assessment of the patient may also alert
the clinician to subtle changes in the patient’s respiratory
status which otherwise may have gone
unnoticed. Altered breath sounds and asymmetrical
chest movement, for example, may indicate the
development of a pneumothorax when other signs
such as dyspnoea and rapid, shallow breathing are
masked by sedation and full mandatory ventilation.
Monitoring data from the ventilator also aids in
understanding the patient’s respiratory status and
the appropriateness of the ventilator settings. Respiratory
rate, tidal volume, minute volume and airway
pressures as absolute values reflect the current
delivery of ventilatory support. When analysed as
trends over time, such data can provide information
about the status of lung function and the patient’s
respiratory effort (Jubran and Tobin, 1996).
Monitoring of gas exchange is a routine aspect of
caring for a mechanically ventilated patient. Arterial
blood gas (ABG) analysis is the gold standard
for determining arterial carbon dioxide and oxygen
levels. The complications and costs associated
with repeated ABG analysis however support the
use of non-invasive monitoring techniques. Pulse
oximetry and capnometry are relatively simple
and effective tools for monitoring gas exchange. A
meta-analysis indicated that pulse oximeters are
accurate to ±2% for oxygen saturations greater
than 70% (Jensen et al., 1998). Capnometers
provide a numerical reading of end-tidal carbon
dioxide levels. Reviews by Capovilla et al. (2000)
and Frakes (2001) suggest that in the context of
stable ventilation/perfusion dynamics and cardiac