ICU Management & Practice, Volume 20 - Issue 1, 2020


With the number of COVID-19 cases increasing in the intensive care units, there is a high risk of infection for healthcare professionals. What kind of masks can be used and what are the most effective strategies to protect against airborne particles?

Currently, there is an increasing number of patients in the intensive care units (ICUs) due to COVID-19 all over the world (some more than others). Since there is a high risk of infection for healthcare professionals (HCP), it is necessary to pay attention to their protection, starting with masks. N95 filtering face piece respirators and surgical masks are commonly used to protect the human respiratory system against fine airborne particles (WHO 1999).

What is the Evidence Behind Masks?

Viral particles are one of the smallest known bioaerosol agents, with a diameter of 20 to 300nm, that can easily penetrate through the human respiratory system (Reponen et al. 2001). Small particles of < 5 μm and < 10 µm diameter readily penetrate until the alveolar space and below the glottis, respectively (Tellier 2019). Previous studies (Oberg et al. 2008; Lee et al. 2008) showed that particles of up to 3,1um in diameter are not adequately filtered by surgical masks, what may include SARS-CoV-2, assuming that its size is similar to SARS-CoV [0,08-0,14um] (Ksiazek et al. 2003).

Surgical masks started to be used to prevent wound infection in the surgery room from staff-generated respiratory bacteria since the early 1900s (Lipp and Edwards 2002; Belkin 1996). Its application has evolved into the prevention of employee exposures, including respiratory viral transmissions (Johnson et al. 2009). Nevertheless, there is an ongoing debate about the use of surgical masks as respiratory protection devices. They are not National Institute for Occupational Safety and Health (NIOSH) certified (Balazi et al. 2006), and it remains uncertain whether they can prevent the transmission of SARS-CoV-2 (Feng 2020; Oberg and Brosseau 2008).

On the other hand, the NIOSH lists nine categories of respirators (N95, N99, N100, P95, P99, P100, R95, R99, and R100). Among these, N95 respirators, with a filtration efficiency of at least 95% a particle size of 0.3 μm (NIOSH 1996), have been recommended by the Centers for Disease Control and Prevention (CDC) for HCP to protect them from infectious diseases potentially spread through the air.

In the ICU setting, we found only one study about COVID-19 related to masks, published the 16th of March: a case report of 41 health workers in contact with the same COVID-19 patient during at least 10 minutes, closer than 2 metres, performing an aerosol-generating procedure (AGP) (endotracheal intubation, extubation, noninvasive ventilation, and open circuit exposure) that used either a surgical mask or an N95 mask (respirator). After two weeks of isolation, they presented neither symptoms nor positive swabs (Ng et al. 2020).

Indeed, the panel of the Surviving Sepsis Campaign for COVID-19 (Alhazzani et al. 2020) makes recommendations and suggestions of whether to use surgical masks or respirators for AGP, non-AGP and for usual care for non-ventilated COVID-19 patients, purely based on evidence extrapolated from other viruses to SARS-CoV-2. Besides, if we search for studies after the time point when the virus appeared (December 2019) we find not more than two studies, and unrelated to COVID-19 (Radonovich et al. 2019; Long et al. 2020).

Regarding cardiopulmonary resuscitation, as an AGP, all staff should wear airborne personal protective equipment (PPE) including an N95 mask or similar (according to local indications) before commencing chest compressions, and if available, an automated compressor device should be used to minimise required staff and exposure (Alhazzani et al. 2020; Edelson 2020).

What are Public Health Institutions’ Position?

WHO (WHO 2020) states that HCP should:

  • Wear a medical mask when entering a suspected or confirmed COVID-19 patient´s room.
  • Use a particulate respirator at least as protective as a US NIOSH N95, EU standard FFP2, or equivalent in settings where AGPs are performed.

CDC (Center for Diseases Control and Prevention 2020) states that HCP should:

  • Wear a facemask at all times while they are in the healthcare facility.
  • Put on an N95 respirator (or higher-level respirator) or facemask (if a respirator is not available) before entry into the patient room or care area.

Moreover, other institutions and organisations recommend the respirators over surgical masks for protection, together with the rest of the PPE [cloth masks are not PPE (Center for Diseases Control and Prevention 2020)] and precaution in the performance of procedures to guarantee the staff safety (Matos et al. 2020; Nicola et al. 2020; Abi Saleh et al. 2020).

What About the Resources?

Low-middle income countries are also dealing with the pandemic, and there is a high concern in their ICUs about the staff protection and the limited resources they might face in this situation.

Supported by the Oxford University Press for the Infectious Diseases Society of America (IDSA), Bahl et al. write: “the ability of countries to respond effectively depends on the safety and confidence of the health workforce, especially in low-income countries with low ratios of HCWs [Health Care Workers] per head of population, and protective measures are crucial to ensure a functional health workforce” (Bahl et al. 2020).

This reasoning led to proposals of alternatives to overcome the scarcity of PPEs (Table 1) (Bong 2020).

Hitherto, the CDC states that standard respirators and facemasks should be removed and discarded after using them, and reusable respirators must be cleaned and disinfected according to manufacturer’s reprocessing instructions prior to re-use. Meanwhile, other institutions are testing other decontamination procedures to allow the reuse of respirators (FDA 2020).

In brief, it is inevitable to pay attention to our world as a whole helping the less privileged to have fatal outcomes, and indeed prevention and protection might be the answer (Bong 2020).

Do we Need RCTs to Prove the use of Masks?

There is only a randomised controlled trial registered in (NCT04296643) in which nurses will be randomised to use either medical masks or N95 respirators when providing care to patients with COVID-19. This Canadian multi-centre randomised controlled trial will assess whether medical masks are non-inferior to N95 respirators when nurses provide care involving non-aerosol generating procedures.

Since this an important issue for healthcare workers and patients, it is crucial to clearly understand the role of masks in the ICU. 

Key Points

  • It is necessary to pay attention to protection of healthcare workers, including use of appropriate masks.
  • N95 filtering face piece respirators and surgical masks are commonly used to protect the human respiratory system against fine airborne particles.
  • Viral particles are one of the smallest known bioaerosol agents, with a diameter of 20 to 300nm, that can easily penetrate through the human respiratory system.
  • Particles of up to 3,1um in diameter are not adequately filtered by surgical masks, what may include SARS-CoV-2, assuming that its size is similar to SARS-CoV.
  • The WHO recommends medical masks when entering a COVID-19 patient's room and a particulate respirator when performing aerosol generating procedures.
  • The CDC recommends wearing a facemask at all times while in a healthcare facility and an N95 respirator or higher before entry into a patient room or care area.


AGP: Aerosol-generating procedure

CDC: Centers for Disease Control and Prevention

DIY:   Do it Yourself

EU:    European Union

FDA: Food and Drug Administration

HCP: Healthcare professionals

HCWs: Healthcare workers

ICU:   Intensive Care Unit

IDSA: Infectious Diseases Society of America

NIOSH: National Institute of Occupational Safety and Health

PPE:  Personal protective equipment

RCT:  Randomised Controlled Trial

WHO: World Health Organization


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