# Calculation of V’alv, VDaw and VDaw/VTe

02.03.2018
Author: Clinical Experts Group, Hamilton Medical, Reviewer: N/A

How do Hamilton Medical ventilators calculate V`alv and VDaw/VTE, and what are these parameters used for?

Calculation of alveolar minute ventilation (V`alv) and dead space fraction VDaw/VTE:

Alveolar minute ventilation in l/min:  V'alv = RR * Vtalv = RR * (Vte - VDaw)

V'alv:     Alveolar minute ventilation
RR:        Respiratory rate
Vtalv:    Alveolar tidal volume
VDaw:  Anatomical dead space volume, calculated using the Vds-PIE slope method (1)
VTE:     Expiratory tidal volume

In short, the alveolar minute ventilation (V`alv) reflects Area X in Figure 1 multiplied by the respiratory rate.

Dead Space Fraction in %: VDaw/VTE = 100 x VDaw/VTE

VDaw:  Anatomical dead space volume, calculated using the Vds-PIE slope method (1)
VTE:     Expiratory tidal volume

The dead space fraction puts the expiratory tidal volume VTE in relation to the anatomical dead space volume VDaw.

Alveolar minute ventilation:

An increase in V‘alv can be seen after an effective recruitment maneuver and induces a transient increase in V‘CO2.
A decrease in V‘alv can indicate that fewer alveoli are participating in the gas exchange, for example, due to pulmonary edema.

The dead space fraction gives you an indication of how effective the ventilation is. A rising VDaw/Vte ratio may be an early sign of ARDS. In a normal lung, the VDaw/Vte ratio is between 25% and 30%. In patients with ARDS, a dead space fraction ≥ 60% was associated with higher mortality (2).

Relevant devices*: HAMILTON-G5/S1 (SW v2.6x); HAMILTON-C1/T1 (SW v2.2.x); HAMILTON-C2/C3 (SW v2.0.x); HAMILTON-C6 (SW v1.0.x)

* Some features are options. Not all devices and features are available in all markets.

References:

1. G.Wolff, J. X. B., W. Weibel, C.L. Bowes, R.Muchenberger & W.Bertschmann. (1989). Anatomical and series dead space volume: concept and measurement in clinical practice. Applied cardiopulmonary pathophysiology, 2, 299-307.
2. Kallet, R. H., Zhuo, H., Liu, K. D., Calfee, C. S., & Matthay, M. A. (2014). The Association Between Physiologic Dead-Space Fraction and Mortality in Subjects With ARDS Enrolled in a Prospective Multi-Center Clinical Trial. Respiratory Care, 59(11), 1611-1618. doi:10.4187/respcare.02593.

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volumetric capnography, dead space fraction, alveolar ventilation, capnography, capnogram
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Date of Printing: 20.05.2019
Disclaimer:
The content of this Knowledge Base is intended for informational purposes only. Hamilton Medical AG provides no warranty with respect to the information contained in this Knowledge Base and reliance on any part of this information is solely at your own risk. For detailed instructions on operating your Hamilton Medical device, please refer to the official Hamilton Medical Operator’s Manual for the respective device.