2006 OPEN FORUM Abstracts
HUMIDIFICATION DURING NONINVASIVE POSITIVE PRESSURE VENTILATION
Matthew P.
Branconnier, RRT, EMT; Kelly J. Gornnert, BS, RRT; Dean R. Hess, PhD,
RRT, FAARC. Respiratory
Care Department
,
Massachusetts
General
Hospital
,
Boston
,
MA
.
Background. Noninvasive positive pressure ventilation (NPPV) is
used increasingly in patients with acute respiratory failure. Humidification of
the inspired gas is not provided universally during NPPV and little has been
reported on this subject. We conducted this study to evaluate the amount of
humidity delivered with several approaches to humidification using a model incorporating
a ventilator designed for NPPV. Methods. All evaluations were conducted using a Respironics Vision BiPAP
ventilator. The ventilator was set for an inspiratory
pressure (IPAP) of 15 cm H2O, an expiratory positive airway pressure
(EPAP) of 5 cm H2O, and a respiratory rate of 20/min. A standard BiPAP single limb circuit with an integrated leak port was
used. The patient end of the circuit was connected to the hygrometer, which was
attached to a Michigan Instruments TTL test lung. Psychometric measurements of relative
humidity (RH) and absolute humidity (AH)
were made using methodology previously described (Chest 1999; 115:1646). In brief, a device to separate inspiratory and expiratory gas flow using 2 unidirectional
valves was inserted between the BiPAP circuit and the
test lung. Two thermal probes, 1 dry and 1 wet
(cotton wetted with water), were placed in the inspiratory
part of the device. The temperatures were measured by the 2 probes (Fisher
Scientific Dual Thermometer) and recorded after 30 min equilibrium. RH and AH were
calculated using standard formulae. Five approaches to humidification were
studied: 1) no humidification, 2) unheated passover
humidification using a Hudson Concha Therm III, 3) heated passover
humidification using a Concha Therm
III with the temperature probe placed at the position of a water trap 60 cm
from the outlet of the humidifier and adjusted to 30 C (trap), 4) heated passover humidification using a Concha
Therm III with the temperature probe placed at the
distal end of the BiPAP circuit and adjusted to 30 C
(mask), 5) heated passover humidification using a Concha Therm IV and heated wire
circuit with temperature adjusted to 31 C at the distal end of the BiPAP circuit and the humidity setting at the default
position. Each approach to humidification was studied with 21% and 100% oxygen
set on the BiPAP ventilator. Psychometric data were
collected in triplicate. The amount of water that accumulated in the circuit
was measured volumetrically. Results. There were significant differences in the delivered
humidity between the 5 approaches that we tested (P < 0.001; see figure). With
the temperature probe at the distal end of the circuit, the average rain-out in
the circuit was 31 ± 4 mL/h. There was no appreciable rain-out
for the heated wire circuit.
Conclusions. Without humidification, the absolute humidity
of the gas delivered to the patient is very low with the BiPAP
Vision ventilator. Use of a heated humidifier significantly increases the
absolute humidity. Use of a heated wire circuit reduces the amount of water
accumulating in the circuit. Further work is needed to determine the optimum
humidity during NPPV.