Knowledge Translation Tools to Guide Care of Non-Intubated Patients With Acute Respiratory Illness During the COVID-19 Pandemic

David Leasa; Paul Cameron; Kimia Honarmand; Tina Mele; Karen J. Bosma


Crit Care. 2021;25(22) 

In This Article

Technical Aspects: Mitigation Techniques to Reduce Exhaled Droplet Dispersion

Respiratory care exposes HCPs to respiratory droplets. Mitigation techniques can substantially reduce droplet deposition during NRS. Figure 2 is a picture guide demonstrating device modifications for NIV,[54–56] and Figure 3 is an infographic summarizing risk mitigation techniques for use during AGMPs.

Figure 2.

a Modified ICU NIV. Pictured is the Hamilton C5® ventilator with dual limb circuit but without heated humidifier. Non-vented mask; combined anti-bacterial/viral filter/HME; and flow sensor lines. Filters at inspiratory and expiratory ports. b Modified Hospital NIV. Pictured is the Philips Respironics V60® ventilator with single limb circuit but without heated humidifier. Non-vented mask with anti-asphyxia valve; combined anti-bacterial/viral filter and HME; distal exhalation port; and proximal pressure line. Second filter at inspiratory port. c Modified Home NIV. Pictured is the ResMed Stellar 150® bi-level ventilator with single limb circuit but without heated humidifier. Non-vented mask with anti-asphyxia valve; combined anti-bacterial/viral filter/HME; and distal exhalation port. Second filter at inspiratory port. Oxygen port at rear of device. Insert details the anti-asphyxia valve. NIV non-invasive ventilation, HH heated humidifier, FEP filtered exhalation port, HME heat and moisture exchanger, AAV anti-asphyxia valve; *determined by local practice

Figure 3.

a Infographic. Techniques to reduce droplet dispersion during HFNO and CPAP. Pictorial representation of techniques to reduce droplet dispersion during aerosol-generating medical procedures. b Infographic. COVID-19 Circuit Modifications for Non-Invasive Ventilation. Pictorial representation of circuit modifications for NIV use during the COVID-19 pandemic

High Flow Nasal Oxygen

HFNO is an open-interface high flow oxygen delivery system which may be better tolerated than oxygen by nasal prongs or mask to treat hypoxemia due to COVID-19 pneumonia. Mitigation of droplet transmission associated with HFNO may be achieved using a properly fitting surgical facemask over the HFNO cannula to reduce lateral droplet dispersion[57] (Figure 3a). When using HFNO, deliver 40 to 60 L/min of gas flow and lowest FiO2 possible to maintain SpO2 in the range of 92–96%.[6]

Boussignac CPAP System

The Boussignac CPAP system is a simple method that works using the venturi principle with wall oxygen flow. A ventilator/CPAP device is not required.[58,59] With the Boussignac system, air or oxygen is injected through the micro-channels in the wall of the plastic tube. As gas molecules accelerate through the channels and enter the cylinder, a virtual valve is created, resulting in continuous positive airway pressure (Figure 3A). Oxygen flow of 8 L/min creates a CPAP pressure of 3 cmH2O; 15 L/min results in 5 cmH2O; and 23 L/min (or flush) provides 10 cmH2O of pressure. A bacterial/viral filter should be inserted between the mask and the Boussignac valve.

Helmet CPAP System

CPAP may be delivered via the helmet interface with the inspiratory limb connected to a free flow oxygen system and the expiratory limb connected to a positive end-expiratory pressure (PEEP) valve (Figure 3a).[60] Set oxygen flow at 50–60 L/minute to ensure carbon dioxide (CO2) washout from the helmet; FiO2 may be adjusted but do not set flow lower than 50 L/minute to avoid CO2 rebreathing.[60] Alternatively, the helmet may be connected to a ventilator to deliver CPAP or bi-level pressures.

Non-invasive Ventilation

Where experience exists, delivery of NIV using a helmet interface may offer reduced droplet spread,[61] improved patient tolerance[61] and efficacy[62] over an oronasal mask. The helmet is connected to an ICU ventilator using conventional respiratory circuitry joining two port sites to allow inspiratory and expiratory flow. High flow and short inspiratory time are necessary to pressurize the helmet rapidly. As shown in Table 1, second generation helmets have negligible exhaled air dispersion due to a better seal at the neck.[20]

Where helmets and/or expertise utilizing them are not available, an oronasal non-vented mask (rather than nasal interface) should be used. Proper mask fitting and seal is important for oronasal non-vented masks, to minimise droplet dispersion and maximize effectiveness. Where possible, use a ventilator with a dual limb circuit plus heat and moisture exchanger (HME) filter with a non-vented mask (no anti-asphyxia valve is needed) (see Figure 2a). Sequence of actions: put NIV interface on patient; then turn ventilator on; and turn ventilator off before removing NIV interface. If possible, do not use the device humidifier. Patients will require enhanced mouth care for dryness given increased airflow without humidification. If the patient has secretions with strong cough or is expected to require NIV for a prolonged period, device humidification may be needed and may be used with a dual limb circuit. Increased risk of aerosolization of virus-containing water droplets must be weighed against the risk of mucous plugging.[63]

A single-circuit bi-level ventilator may need to be used if a dual circuit ventilator is not available or not tolerated. In this case, use a fitted oronasal non-vented mask plus anti-asphyxia valve with combined HME-viral/bacterial filter plus exhalation port. An anti-asphyxia valve is mandatory for use with a non-vented mask. The anti-bacterial/viral filter should be placed in the circuit between the mask and the exhalation port (see Figure 2b). Anti-bacterial/viral filters should be changed every 24 h or sooner if soiled as this may increase resistance to flow. Blocked filters can be mistaken for clinical deterioration, and this issue is remedied by changing filters. An external humidifier should not be used.

Initial prescription for single-circuit bi-level ventilation for de novo ARI: quick rise time (~200 ms); high trigger; low cycle; expiratory positive airway pressure (EPAP) 8–12 cm H20; and minimal pressure support (inspiratory positive airway pressure, IPAP ≤ 5 cm H20 above EPAP). Target and monitor for Vt ~4–7 mL/kg ideal body weight and a SpO2 ≥ 92–96%[64] using the lowest FiO2 possible.

Home Mechanical Ventilation Patients

Patients receiving mechanical ventilation at home (e.g., neuromuscular disease) may present to the emergency room with/without respiratory symptoms using a single-circuit bi-level ventilator and vented mask and/or cough assist device in the community. Continuation of this support is essential to their survival. Home NIV circuit modifications are required using an oronasal non-vented mask with anti-asphyxia valve and expiratory port with anti-bacterial/viral filter (see Figure 2c). A variety of circuit modifications can be used.[56] Otherwise, use their home ventilator and prescription, care for them in a single room, and staff should wear AGMP PPE (including N95 mask) while in the patient room.