External Dead Space in Ventilated COVID-19 Patients

Covid-19 patients under mechanical ventilation are currently managed with a lung protective
strategy derived from ARDSnet recommendations. In order to minimize the risk of spread of
coronavirus, filters and associated respiratory tubing are incorporated to the breathing
circuit, thus increasing apparatus dead space with subsequent increase in dead space
ventilation. Considering the already often compromised ability for these patients to
adequately clear carbon dioxide (VCO2), adding an external dead space can potentially have a
substantial impact on CO2 homeostasis. The study will use volumetric capnography (Vcap) to
investigate the influence of external dead space on VCO2 and calculated alveolar dead space.

Objective: 1) To investigate the efficacy of Vcap to detect changes in dead space, VCO2 and
shape factor parameters before and after disconnection of external dead space.

2) To register the external dead space impact on arterial carbon dioxide tension (PaCO2).

3) To calculate the alveolar dead space based on Vcap data and arterial blood gas analysis
results.

Design and setting: Prospective observational study in an intensive care center for Covid-19
patients in a university hospital.

Patients: Covid-19 positive patients of all age groups under mechanical ventilation.
Exclusion criteria is ongoing ECMO treatment

Measurements and results: Vcap and Tcap parameters will be registered during mechanical
ventilation and correlated to an arterial blood gas sample. Part of the apparatus dead space
will then be reduced via removal of the heat and moister exchange filter (HME) with added
tubing resulting in a reduction in volume of approximately 80 ml (i.e. the known volume of
the HME filter and associated tubing). After the apparatus dead space is removed, the Vcap
will be recorded for approximately 15 minutes and an arterial blood gas will be drawn at the
end of the period. The HME and associated tubing will then be reattached to the breathing
circuit and Vcap and Tcap parameters will be recorded for approximately 30 minutes and an
arterial blood gas will be drawn. Vcap data will be analyzed for dead space, slope of phase
III, VCO2 and associated shape factor parameters and compared with Tcap parameters. Changes
in Vcap parameters will be tested for statistical significance using one and two-way ANOVA
for repeated measures and Bland-Altman analysis will be used for comparison.