| Abstract | OBJECTIVE: Before a patient can be connected to a mechanical ventilator, the controls of the apparatus
need to be set up appropriately. Today, this is done by the intensive care professional. With the advent of
closed loop controlled mechanical ventilation, methods will be needed to select appropriate start up
settings automatically. The objective of our study was to test such a computerized method which could
eventually be used as a start-up procedure (first 5-10 minutes of ventilation) for closed-loop controlled
ventilation. DESIGN: Prospective Study. SETTINGS: ICU's in two adult and one children's hospital.
PATIENTS: 25 critically ill adult patients (age > or = 15 y) and 17 critically ill children selected at
random were studied. INTERVENTIONS: To stimulate 'initial connection', the patients were
disconnected from their ventilator and transiently connected to a modified Hamilton AMADEUS ventilator
for maximally one minute. During that time they were ventilated with a fixed and standardized breath
pattern (Test Breaths) based on pressure controlled synchronized intermittent mandatory ventilation
(PCSIMV). MEASUREMENTS AND MAIN RESULTS: Measurements of airway flow, airway
pressure and instantaneous CO2 concentration using a mainstream CO2 analyzer were made at the mouth
during application of the Test-Breaths. Test-Breaths were analyzed in terms of tidal volume, expiratory
time constant and series dead space. Using this data an initial ventilation pattern consisting of respiratory
frequency and tidal volume was calculated. This ventilation pattern was compared to the one measured
prior to the onset of the study using a two-tailed paired t-test. Additionally, it was compared to a
conventional method for setting up ventilators. The computer-proposed ventilation pattern did not differ
significantly from the actual pattern (p > 0.05), while the conventional method did. However the scatter
was large and in 6 cases deviations in the minute ventilation of more than 50% were observed.
CONCLUSIONS: The analysis of standardized Test Breaths allows automatic determination of an initial
ventilation pattern for intubated ICU patients. While this pattern does not seem to be superior to the one
chosen by the conventional method, it is derived fully automatically and without need for manual patient
data entry such as weight or height. This makes the method potentially useful as a start up procedure for
closed-loop controlled ventilation. |