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Moisture
Output
Moisture output is the most important characteristic of the device used
in the intensive care unit. I believe an artificial nose used in the ICU
should deliver 28-32mg H2O/L at the tidal volume typically seen in your
practice. This agrees with the AARC consensus conference recommendation.
Clinicians should also realize that the ISO 9360 testing used to determine
moisture output serves as a method to rank devices. The actual humidity
delivered to the the patient will vary based on tidal volume, flow, and
patient temperature.
Dead Space
Dead space is important during care of spontaneously breathing patients
and small infants. In the operating room, when patients are paralyzed,
dead space does not represent an important issue in adults. In the ICU,
however, dead space of artificial noses has been shown to adversely effect
ventilation, CO2 elimination, and the work of breathing.
I believe the smallest dead space device possible should be used. Ideally,
dead space should be less than 50ml in adults. This value should be adjusted
for patient tidal volume (eg., the smaller the tidal volume, the lower
the dead space should be used).
Resistance
Resistance should be as low as possible with a value less than 3.0cm H2O/L
being acceptable. Remember, the endotracheal tube will always be the largest
resistor in the system.
Resistance should not increase significantly following use (total should
remain less than 3.0cm H2O/L). Resistance is not important in the operating
room where patients are paralyzed. In spontaneously breathing patients,
resistance becomes a greater concern, particularly in combination with
dead space
Cost
Cost is important in any equipment decision. In the operating room, where
short term ventilatory support of patients with previously healthy lungs
is the rule, cost may be the most important factor in the decision-making
process. In the ICU, I believe cost is less important than moisture output,
dead space and resistance.
Filtration
Filtering gases as they travel to and from the patient may help reduce
colonization in the ventilator circuit and ventilation equipment.
In the ICU, filtration does not effect the incidence of nosocomial pneumonia.
The role of filtration may be more important in the operating room, where
rebreathing via the circle system occurs.
Design
Design features of the device may also play a role in the purchase decision.
The shape, weight and additional features may be important in some instances.
For instance, a port for monitoring expired CO2 is important in the operating
room, but not typically required in the ICU.
The device should be lightweight, transparent (to allow secretions to
be seen), and facilitate connection between ventilator circuit and artificial
airway.
Recommendation
I always prefer a device with a minimum moisture of 28mg H2O/L, a dead
space of approximately 40 ml, a resistance of less than 2.5cm H2O/L, no
filter, and right angle connections to eliminate the need for a flex tube
(which increases dead space). The device which meets these specifications
and provides the best cost value would be my choice. We use artificial
noses on all patients in the recovery room and cardiac surgery intensive
care unit. In the surgical ICU, artificial noses are used in approximately
65% of patients, and in the medical ICU, approximately 30% of patients.
This is based on the algorithm, previously published.
Artificial noses are safe and cost effective when used appropriately.
Our laboratory results are compiled from ISO 9360 testing over the past
several years, using a broad array of devices.
Richard T. Branson,
RRT
Assistant Professor of Surgery
Robert S. Campbell,
RRT
Senior Research Associate
Kenneth Davis,
Jr., MD
Associate Professor of Surgery and Anesthesia
University of Cincinnati Medical Center.
Cincinnati, Ohio
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