Automatically applied ventilator tidal volume and frequency based on body weight provides appropriate arterial blood gas exchange:
A validation study |
| M.J. Banner PhD, B. Craig Weldon MD, A. Gabrielli MD |
| University of Florida, College of Medicine Departments of Anesthesiology, Pediatrics, and Physiology |
| Gainesville, Florida, USA |
Introduction
Traditionally, ventilator tidal volume (VT) based on lean body weight and frequency ( f ) based on clinical
judgment are set manually to apply an appropriate minute ventilation (MV =
VT x f ).
Alternatively, VT and f may be applied
automatically based on a patient’s estimated lean body weight.
We hypothesize that by entering a patient’s lean body weight into a ventilator’s computer with the requisite software, an appropriate
VT and f, and thus MV, can be automatically applied to sustain acceptable arterial blood gas exchange. If correct, then this represents a safe and simple method of applying ventilatory support.
To test this hypothesis, we designed an IRB-approved in vivo study in adult and pediatric patients requiring ventilatory support.
methods
Methods
The i vent201 (VersaMed), a microprocessor controlled, commercially available ventilator driven by a self-contained rotary compressor, was used for applying the automatically delivered
VT and f
(see Figure 1).
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Figure 1.
i vent201 (VersaMed) is a commercially available ventilator used to automatically apply tidal volume and frequency based on a patient’s lean body weight. In addition, the ventilator can function as a standard ICU type ventilator providing most forms of ventilatory support. |
At the outset of ventilatory support, a screen is displayed that queries the clinician to enter the patient’s lean body weight
(see Figure 2 A), then
VT and f, and thus MV, are set automatically, i. e.,
VT varies directly and f varies inversely with body weight
(see Figure 2 B).
Figure A
Figure B |
Figure 2. A&B
In A. a screen displayed on the i vent201 queries the clinician to enter lean body weight, as a result tidal volume and frequency, and thus minute ventilation, are then set automatically.
In B. the relationship between applied tidal volume and frequency at discrete body weights is shown. The ventilator’s software is modeled after this relationship.
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Patient data:
- N = 22
- Weight range: 11 – 94 kg
- Gender: 13 males, 9 females
- Age range: 4 – 84 years
- 8 pediatric and 14 adults
- Of this group, 9 were elective surgical patients with no diagnosed pulmonary abnormalities, while 13 had mild to moderate forms of acute respiratory failure.
All patients had minimal to no spontaneous
breathing, were intubated, and attached to an ICU or OR anesthesia ventilator.
VT and f were set in the traditional manner as described above.
A combined flow / pressure / CO2 sensor was connected to the endotracheal tube (CO2SMO +, Novametrix / Respironics) to measure
VT, f, MV, peak inflation pressure (PIP), partial pressure of end-tidal carbon dioxide (PetCO2), and the physiologic deadspace volume to tidal volume ratio (VD /
VT).
An arterial blood gas was obtained after 30 minutes.
Patients were then switched to the i vent201 ventilator, where
VT, f , and MV were applied automatically as described above. The
same FIO2 and levels of positive end expiratory pressure (PEEP) applied with the standard ICU and OR ventilators were applied with the
i vent201.
All measurements were repeated after 30 minutes.
Data were analyzed using a repeated measures ANOVA; alpha was set at 0.05 for statistical significance.
(continue
to Results)
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