Page 37 - JSOM Summer 2024

FIGURE 1 Experiment setup.

• peak inspired oxygen concentration (FiO ) within 30 minutes; Ventilators were attached to a test lung (TTL, Michigan Instru-
2
• duration of CO -absorbent life (determined by a rise in in- ments, Kentwood, MI) which allows for setting a range of lung
2
spired CO >1%); compliance. Peak FiO was measured (Oxigraf, Sunnyvale, CA)
2
2
• peak delivered gas temperature and humidity; in the ventilator circuit inspiratory limb near the patient con-
• volume of condensate produced in the ventilator circuit; nector with both ventilators and all combinations of ventilator
• effect of 5- and 10-second airway suctioning with in-line settings. Remaining measurements were only made with the
suction catheter on FiO ; and 731 using the RR20/V 450/positive end expiratory pressure
2
T
• effect of 15- and 30-second ventilator circuit disconnect on (PEEP) 5 settings (plus RR30/V 250/PEEP5 and RR20/V 700/
T
T
FiO . PEEP5 for the duration of CO -absorbent life tests). Testing
2 2
was done in duplicate at ground level, 8,000-ft, and 16,000-ft
FIGURE 2 Rebreather system connected to a patient. simulated altitude in a non–human-rated altitude chamber
(Abyss Instruments, Holliston MA) with the exception the ab-
sorbent life test, which was completed 5 times at ground level.
The same altitude chamber was used for all altitude testing.
Nitrogen gas was introduced into the test lung during the FiO
2
testing as needed to maintain a 2%–3% lower expired than in-
spired FiO to simulate normal oxygen consumption. CO was
2
2
introduced into the test lung from a cylinder at 200mL/min
to simulate CO production.
2
Airway suctioning was simulated by placing a closed suction
system (Ballard, Avanos Medical, Inc., Alpharetta, GA) at the
patient connector and activating continuous suction for 5 and
10 seconds. The lowest FiO was measured after the designated
2
TABLE 1 Ventilator Settings For the Evaluation suction time. The FiO recovery time was measured from end
2
of suctioning maneuver until initial FiO was reached. No suc-
RR combinations, PEEP, cm 2
Ventilator (breaths/min)/V , mL H O I:E Breath type tioning material was used for this maneuver.
T 2
SAVe II 30/250
18/450 5 1:2 Volume Statistical Analysis
11/700 Stratified by device, one-way ANOVA was used to model FiO 2
731 30/250 as a function of ventilator settings and altitude, while unpaired
20/450 5 & 20 1:3 Volume t tests were used to model the effect of oxygen flow (1 vs.
20/700 3L/min); the p-value for significance was set at .05.
RR = respiratory rate; I:E = inspiratory:expiratory; PEEP = positive
end expiratory pressure. Five trials were performed for each of three sets of ventila-
tor settings (RR 30/V 250mL, RR 20/V 450mL, RR 20/V
T
T
T
TABLE 2 Test Lung Settings For the Evaluation 700mL, all with PEEP of 5cm H O and lung compliance of
2
80mL/cm H O and 1L/min oxygen flow rate) for the CO -
Compliance, Resistance, CO production, 2 2
2
mL/cm H O cm H O/L/s mL/min absorbent life testing. Between-settings differences in tem-
2
2
Normal 80 5 200 perature, humidity, and minutes to inspired CO >1% were
2
assessed using one-way ANOVA. Pairwise comparisons
ARDS 20 10 200 were done using a t test. Statistical significance was set at
ARDS = acute respiratory distress syndrome. p<.05.
Evaluation of a Rebreathing System | 35