834 SECTION V • Basic Therapeutics
Proper Conditioning of Inspired Gas
All respiratory therapists (RTs) are trained to measure
patient inspired FiO2 levels regularly and, in ventilatory
care, to monitor selected pressures, volumes, and flows.
However, few clinicians take the steps needed to ensure
proper conditioning of the inspired gas received by
patients.
The most accurate and reliable way to ensure that
patients are receiving gas at the expected temperature and
humidity level is to measure these parameters. Portable
battery-operated digital hygrometer-thermometer systems
are available for less than $300 and are invaluable in ensur-
ing proper conditioning of the inspired gas. When measur-
ing high-humidity environments, hygrometers become
saturated and nonresponsive over time and so should be
used for spot checks only. These devices should be as
common at the bedside as O2 analyzers.
Many heated wire humidification systems have a humid-
ity control. This control does not reflect either absolute or
relative humidity but only the temperature differential
between the humidifier and the airway sensor. If the heated
wires are set warmer than the humidifier, less relative
humidity is delivered to the patient. To ensure that the
inspired gas is being properly conditioned, clinicians
should always adjust the temperature differential to the
point that a few drops of condensation form near the
patient connection, or “wye.” Lacking direct measurement
of humidity, observation of this minimal condensate is the
most reliable indicator that the gas is fully saturated at the
specified temperature. If condensate cannot be seen, there
is no way of knowing the level of relative humidity without
direct measurement—it could be anywhere between 99%
and 0%. HME performance can be evaluated in a similar
manner.48
RULE OF THUMB
You can estimate if an HME is performing well at
the bedside by visually confirming...