Continuous versus intermittent mask use by nurses in COVID times (CIMNIC) – A CUSUM study

INTRODUCTION

Coronavirus disease 2019 (COVID-19), the latest pandemic witnessed by the current generation, started at a small place in Wuhan, China in December 2019 and later became a global health crisis within a short period.^[1,2] By February 23, 2022, the disease had already affected approximately 425 million people across the world with nearly 6 million deaths and numbers still counting.^[3] The high infectivity of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the pathogen responsible for the COVID-19 outbreak, has been attributed to its airborne transmission.^[4] The tiny, 0.06–0.12 µ SARS-CoV-2 virus, spreads through either droplet (>5 µ) during coughing and sneezing or aerosol (<5 µ) production during loud speaking and even in quiet breathing.^[5] Aerosol-generating procedures such as intubation, positive pressure ventilation, bronchoscopy, upper gastrointestinal endoscopy, airway toileting and dental extraction are common in healthcare settings which put healthcare workers at significantly higher risk of contracting the disease than the general population.^[6] N-95 face masks or equivalent filtering face piece 2 (FFP2) respirators, which can filter up till 95% of 0.3-micron and larger particles usually, provide adequate protection against airborne COVID-19 transmission by trapping the coronavirus due to its rapid brownian motion.^[7] Hence, the World Health Organization and Centers for Disease Control and Prevention have universally recommended N-95 face masks or FFP2 respirators for healthcare providers, as a part of personal protective equipment (PPEs), while dealing with high-risk patients for COVID-19 transmission.^[3,7]

Recently, serious concerns have been raised regarding the safety of these protective face masks, especially by healthcare providers. People have complained of suffocation, breathlessness, sweating, and feeling of discomfort after using them for a prolonged period.^[8-10] This led to hindrance on part of users to follow recommended preventive practices adequately and predisposing them to increased risk of cross-infections.^[11] Arora and colleagues have highlighted the unmet need to address various practical issues with the use of PPEs to minimise infection spread.^[12] Few alternatives have been tried to improve the safety while retaining the efficacy of facemasks such as nano-treatment and various other types of surgical masks but with limited benefits.^[8,13] Sickbert-Bennett et al. tried using a surgical face mask to improve user acceptance but found objectionable efficacy.^[14] None of the surrogate strategies have been an ideal replacement for conventional respirators till date. Therefore, we planned to conduct this CIMNIC study to compare the safety profile of respirators in nurses, during their continuous or intermittent use, in real-time using cumulative sum (CUSUM) and conventional statistics.

MATERIAL AND METHODS

RESULTS

Outcomes

The mean baseline SpO₂ in the two study groups was similar, while post-shift saturations were significantly different [Table 1]. There was a marked drop in (mean ± 2SD) SpO₂ values in the continuous group as compared to the intermittent group (4.688 ± 39.351 vs. 1.169 ± 2.626) after using the FFP2 respirator. There were 296 (n-525) recordings of ≥a 3% drop in SpO₂ after continuous mask use as compared to only 291 (n-984) in the intermittent mask use phase. The weightage for each success and failure was + 1.127 and −0.872, respectively. The upper and lower CUSUM control lines were plotted at CUSUM scores of +28.59 and −28.93, respectively, using data from the continuous mask group. The real-time CUSUM plot for intermittent mask use crossed the upper control line within the initial 30 readings [Figure 1] and thereafter always remained above the upper CUSUM control line [Figure 2]. The subjective comfort score parameters were appreciably more affected in the continuous group as compared to others [Table 1 and Figure 3]. Overall (the mean ± 2SD) discomfort level was significantly less in nurses when they were provided a 15-min mask-free period in between their shifts (7.28 ± 3.216 vs. 8.89 ± 1.610 in the intermittent and continuous group, respectively).

Table 1: Comparison of clinical parameters in the study groups.

Parameter	Continuous group	Intermittent group	P value
Number of observations (n)	525	984
Female: Male	520:5	983:1
Mean±SD
Age (in years)	30.34±4.477	33.17±12.506
% Oxygen saturation (SpO2)			0.264
Baseline	99.48±39.302	97.56±2.188	<0.001
Post-shift	94.79±1.972	96.39±1.507	0.007
∆SpO2	4.688±39.351	1.169±2.626	<0.001
Post shift subjective scores (on a scale of 10)
Humid	8.31±2.059	6.49±2.953	<0.001
Hot	8.49±1.910	6.56±3.100	<0.001
Breath resistance	8.28±1.773	6.48±2.869	<0.001
Itchy	7.63±2.474	6.10±3.240	0.001
Tight	8.17±2.364	6.59±3.201	<0.001
Salty	6.93±3.402	5.82±3.718	0.041
Smelly	7.40±2.939	6.22±3.411	0.015
Body fatigue	8.18±2.165	6.83±3.122	0.001
Nose pain	8.56±1.847	7.56±2.896	0.007
Headache	8.55±1.909	6.98±3.217	<0.001
Overall discomfort	8.89±1.610	7.28±3.216	<0.001

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Figure 1:

Cumulative sum graph with the two control lines and initial data from the intermittent mask use group.

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Figure 2:

Cumulative sum graph for the complete data of intermittent mask use group.

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Figure 3:

Comparison of subjective scores on a scale of 10 in the study groups.

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DISCUSSION

The standard of care FFP2 respirators (N-95 mask) are associated with physical and subjective discomfort when used for a protracted duration. Breathing difficulties and tiredness are common findings along with headache and local pain as reported previously. The number of analysable recordings in the two phases was 525 and 984, respectively, in our study. This difference can be explained by a varied number of shifts by nurses as per the hospital policies. The mean age of participants in the two time sets were 30.34 and 33.17 years, which is due to the different quantum of work by the same nurse’s cohort [Table 1].

The mean baseline SpO₂ in the two groups were similar; however, there was a significant drop in SpO₂ by 4.688% in the continuous mask group as compared to less than one-third drop in the intermittent group. Nurses have experienced a significant downward SpO₂ trend during routine clinical duties in both groups. As per the British Thoracic Society guidelines for oxygen use, a drop in SpO₂ of 3% or more from baseline may indicate an alarming situation even if SpO₂ is >94% in a healthy person, which warrants further evaluation.^[17] This translates to an enormous risk of hypoxemia in healthcare workers who are using respirators continuously.

CUSUM is a statistical technique used commonly in industries for quality control assessment. After assigning positive and negative weights for previously defined successes (S) and failures (F) from a standard process, the original sequence of S and F is randomly reordered 10,000 times using the bootstrapping method.^[18] The highest and lowest limits of CUSUM are defined for each iteration, that can occur by chance, and thereafter upper CUSUM control line (mean upper CUSUM + 2SD) and lower CUSUM control line (mean lower CUSUM – 2SD) are drawn using data from all the iterations.^[18] Gupta et al. have derived, validated and patented a CUSUM software for easy weightage calculations, boot strapping and for drawing control lines.^[19] S and F from any new intervention can be plotted in real time to compare it against the standard of care. If the real-time graph remains in between two CUSUM control lines, then the new intervention is not considered statistically distinct from the standard one. On the other hand, if the graph crosses any CUSUM control line then there is significant difference between the two interventions. Puliyel and Puliyel have earlier used this technique for competency monitoring of trainees during cataract extraction.^[18]

CUSUM has been used earlier by Gupta et al. to identify the effect of nebulised hypertonic-saline against epinephrine in children with bronchiolitis.^[19] Kinsey et al. assessed antimicrobial treatment in neutropenic patients using this technique.^[20] Ravn et al. have evaluated clinical competence of medical trainees using CUSUM analysis.^[21] Fortea-Sanchis et al. used CUSUM charts to assess the nodal analysis quality in colon cancer.^[22] This statistical tool has a distinct advantage over others, in terms of real time monitoring of experimental trial. Any potentially harmful process can be immediately stopped if the graph crosses the lower CUSUM control line at any point of time in between the study. We have used CUSUM statistics to highlight the importance of mask-free period in prevention of significant hypoxemia in healthcare workers. The healthcare workers experienced significantly less desaturations during the intermittent mask use phase as compared to standard of care.

Researchers have evaluated subjective discomfort in people using respirators. Dugdale and Walensky found N-95 masks as suffocating, uncomfortable and intolerable when used for prolonged duration.^[23] Li et al. have demonstrated that people using N-95 mask experienced higher heart rates, more temperature and humidity as compared to surgical facemask during their study in 10 healthy subjects who were subjected to treadmill exercise.^[8] Locatelli et al. highlighted discomfort and skin irritation experienced by healthcare workers using FFP mask.^[16] Zhu et al. have found increased mean nasal resistance and discomfort level with increasing duration of N-95 mask use in their work on 87 healthcare workers.^[9] Farronato et al. in their survey including 256 dentists found strong association of headache, discomfort and impaired work ability with prolonged respirator use.^[6] Rosner in their cross-sectional study among 343 health-care professionals found that prolonged use of facemask causes headache, rash, skin breakdown and impaired cognition.^[24] Purushothaman et al. have highlighted significant discomfort in 250 healthcare workers while wearing facemask for prolonged duration, in their questionnaire based study.^[10] We have also found significant adverse subjective feelings in participants for all 10 study parameters with mean discomfort level of 8.89 and 7.28, on a scale of 0–10, in two different time periods [Table 1]. Prolonged intermittent hypoxia and discomfort level will potentially cause personal health hazard and professional dissatisfaction in users.

There have been active search for safe and effective alternatives to N-95 mask/FFP2 respirators. Zhu et al. have found less increase in nasal resistance and associated discomfort in healthcare employees with use of surgical facemask as compared to N-95 mask.^[9] Shenal have studied various types of respiratory protection in health-care settings and concluded highest level of discomfort while using N-95 and medical mask combination followed closely by N-95 masks when used alone.^[13] They observed that the powered air-purifying respirators were associated with minimal discomfort which was still significant with prolonged duration of use. After careful literature search, we were unable to find any widely acceptable cost-effective interventions, which can be utilised in resource poor countries, to improve the safety of existing face masks while retaining their efficacy. In our study, there was a significant improvement in comfort level of nurses with the introduction of 15 min break in between their 6 h duty shift [Table 1]. Intermittent use of respirators might be less harmful than their continuous use in healthcare workers while retaining their protective efficacies.

CONCLUSION

CIMNIC study provides an applicable insight to important health aspects of care takers while using protective face masks. An intervening mask free period at periodic intervals is warranted as one of the preventive health strategy for healthcare workers. CUSUM methodology was quiet useful to monitor the effects of intermittent mask use in real-time.