“Body Temperature & Pressure, Saturated” & Ambient Pressure Correction in air medical transport
Mechanical ventilation can be especially challenging during air medical transport, particularly due to the impact of varying atmospheric pressure with changing altitudes. The Oxylog® 3000 plus and Oxylog® 2000 plus help to effectively deal with these challenges. D-33481-2011
Artificial ventilation uses compressed the ventilation volumes delivered by the gas to deliver the required volume to the ventilator. Mechanical ventilation in fixed patient. This breathing gas has normally wing aircraft without a pressurized cabin an ambient temperature level and is very is subject to the same dynamics. In case dry. Inside the human lungs the gas of a pressurized cabin it is still relevant expands due to a higher temperature and to correct the inspiratory volumes, as humidity level. These physical conditions the cabin is usually maintained at MT-5809-2008 are described as “Body Temperature & a pressure of approximately 800 mbar Figure 1: Oxylog® 3000 plus Pressure, Saturated” (BTPS), which (600 mmHg), comparable to an altitude The Oxylog® 3000 plus automatically com- presumes the combined environmental of 8,200 ft/2,500 m. pensates volume delivery and measurement circumstances of ––Without BTPS correction, the deli- ––a body temperature of 37 °C / 99 °F vered inspiratory volume can deviate up ––ambient barometrical pressure to 14 % conditions and (at 14,800 ft/4,500 m altitude) from ––breathing gas saturated with water the targeted set volume (i.e. 570 ml vapour (= 100 % relative humidity). instead of 500 ml). ––Without ambient pressure correction, Aside from the challenge of changing the inspiratory volume can deviate up temperatures and humidity inside the to 44 % (at 14,800 ft/4,500 m altitude) patient lungs, the ambient pressure is from the targeted set volume also important to consider. Flight altitudes (i.e. 720 ml instead of 500 ml). MT-5869-2008 in air medical transports can reach up to Figure 2: Oxylog® 2000 plus 14,800 ft/4,500 m. Although helicopter The Oxylog 3000 plus and Oxylog 2000 rescue missions rarely go to altitudes plus automatically correct the delivered that require the body to adapt, alterations volume for BTPS and ambient pressure, associated with the changing ambient while also taking atmospheric pressure pressure can have a significant impact on differences into account. 02 | BTPS & AMBIENT PRESSURE CORRECTION IN AIR MEDICAL TRANSPORT D-33403-2011
Figure 3: Example of a medical interior system With BTPS and ambient pressure correction the operator is able to spend more time on patient care.
BTPS CORRECTION IN OXYLOG altitudes in volume controlled ventilation The Oxylog 3000 plus and Oxylog 2000 plus modes. As a result, the volume delivered correct the delivered and measured to the patient is kept at a constant level, volume of the breathing gas in order to regardless of the altitude. achieve optimal BTPS conditions within the patient’s lungs, where temperature, The Oxylog 3000 plus and Oxylog 2000 plus humidity and pressure differ from those of measure the ambient air pressure via two the outside environment. The correction is internal pressure sensors and measure based on the assumption that the tempera- the flow rate via an internal flow sen - D-33317-2011 ture of the breathing gas delivered by the sor, which is assumed to be delivered at Figure 4: The Oxylog® 3000 plus in action Oxylog (the inspiratory gas) is 21.1 °C/70 °F 1023 mbar (767 mm Hg) which is the pres- as well as dry and that the temperature of sure at sea level + 10 mbar (10 cm H2O) Air- the breathing gas inside the human lungs way Pressure (PAW). Based on the mea- will be 37 °C/99 °F fully saturated. sured ambient pressure, this measured flow rate is then converted into the correct AMBIENT PRESSURE flow at actual ambient pressure conditions, CORRECTION IN OXYLOG which is required for delivering the set In addition to the BTPS correction, the volume in BTPS. The flow rate correction is Oxylog 3000 plus and Oxylog 2000 plus dynamic and is adjusted breath by breath to automatically compensate ambient pres- compensate for aircraft changing altitudes sure changes. Oxylogs automatically cor- and can vary between 1 % and 44 % (44 % rect the volumetric flow rate for changes at 14,800 ft/4,500 m). in ambient pressure due to changing BTPS & AMBIENT PRESSURE CORRECTION IN AIR MEDICAL TRANSPORT | 03
EXAMPLE BTPS AND Note 2: AMBIENT PRESSURE CORRECTION 1023 mbar (767 mmHg) = 1013 mbar If you set a Vt of 500 ml at sea level, the (760 mmHg) ambient pressure at sea
Oxylog 3000 plus and Oxylog 2000 plus level + 10 mbar (10 cmH 2O) PAW. will deliver 447 ml as this volume will 1086 (815 mmHg) mbar = 1023 mbar expand to 500 ml in the patients lungs. (767 mmHg) (see above) + 63 mbar
(47 mmHg) of the PH2O at 37 °C/99 °F. Formula: Vt of 500 ml × (294 Kelvin/ 310 Kelvin1) × (1023 mbar (767 mmHg)/ Note 3:
1086 mbar (815 mmHg)2) = 447 ml. 580 mbar (435 mmHg) = 570 mbar MT-5833-2008 (Assumption of PAW mean = 10 mbar (428 mmHg) ambient pressure at Figure 5: Oxylog® 3000 plus BTPS and ambient pressure correction (10 cmH2O) 14,880 ft/4,500 m + 10 mbar (10 cm H2O) is automatically done PAW. 643 mbar (482 mmHg) = 580 mbar If you set a Vt of 500 ml at an altitude of (435 mmHg) (see above) + 63 mbar
14,800 ft/4,500 m, the ventilator will deliv- (47 mmHg) of the P H2O at 37 °C/99 °F. er 428 ml. Oxylog 3000 plus and Oxylog 2000 plus Formula: Vt of 500 ml × (294 Kelvin/ compensate volume delivery and measure- 310 Kelvin1) × (580 mbar (435 mmHg)/ ment for typical environmental influences 643 mbar (482 mmHg) 3) = 428 ml. during air medical transport by applying (Assumption of PAW mean = 10 mbar (10 BTPS and ambient air pressure correction. cmH2O) The corrections are automatic, dynamic and are adjusted breath by breath to Formula’s explained: compensate for aircraft changing altitudes Note 1: and therefore can help preventing baro- 294 Kelvin ≈ 21 °C and 310 Kelvin trauma. As a result the operator is able to ≈ 37 °C/99 °F. spend more time on patient care. 90 51 611 | 15.06-3 | Communications & Sales Marketing | PP | LE | Printed in Germany | Chlorine-free – environmentally compatible | Subject to modifications | © 2015 Drägerwerk AG & Co. KGaA
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