Assessment of Hypoxia and Physiological Stress Evinced by Usage of N95 Masks among Frontline Dental Healthcare Workers in a Humid Western Coastal Region of India-A Repeated Measure Observational Study.

AIM: To assess the oxygen saturation in DHCWs using N95 and 3 ply surgical masks and determine the presence of any other subjective discomfort in them. SETTINGS AND
DESIGN: A repeated measure observational study conducted at the Tertiary Care Dental Institute situated in Goa, a western coastal region of India recording humid conditions year around. METHODS AND MATERIAL: Participants constituted 60 frontline DHCWs wearing N95 masks and 60 DHCWs working in non-clinical setting wearing surgical masks. After completion of a self-administered questionnaire their oxygen saturation and pulse rate were monitored at baseline, 60mins and 120mins using pulse oximetry. Statistical Analysis: Mann Whitney u test compared oxygen saturation between the two groups. Friedmann and Wilcoxon signed rank test with Bonferroni correction computed differences within group at various time intervals. Binary logistic and linear regression was used to compare the study variables with outcome measure. p value was set at < 0.05. RESULTS AND
CONCLUSION: Oxygen saturation reported a significant drop post one hour of wearing N95 masks which increased in the second hour. Prolonged use of N95 mask in humid environment adds to the body's physiological burden or perceptions of discomfort and exertion. Efforts need to be taken to address this for better compliance to the use of these protective gears. Copyright:

INTRODUCTION

The unprecedented threat to global health in 2020, COVID-19, with its fast-spreading scourge has overwhelmed the health infrastructure of nations and arouse rising concerns about the safety of the dental personnel. It has categorized dentistry into a very high-risk profession as the majority of the routine dental procedures generate aerosols, which can lead to viral contamination of the environment.[1]

With an additional responsibility of keeping the COVID-19 pandemic at bay, the concept of protecting the environment from the wearer has been altered to protect the wearer from the environment.[2] In an attempt to adapt to this “New Normal,” the World Health Organization has robustly drifted from the previous recommendations of three layers of soft nonwoven polypropylene fabric masks (3-ply surgical masks) as a standard of practice, and has mandated wearing impermeable gowns, goggles, face shields, and particulate respirators matching the safety standards of National Institute of Occupational Safety and Health (NIOSH)-certified N95 mask or equivalent for dental professionals. The name “N95” refers to its ≥95% filtering efficiency of particles with a median diameter of >0.3 μm2 and “N” stands for its property of not being resistant to oil. These fit-tested masks provide a secured seal against infectious respiratory droplets.[3]

Prolonged use of N95 masks may, however, invoke several physiological implications.[4] In prior studies, it has been noted that CO2 levels within these masks can increase by 1.8%–3%, possibly due to the accumulation of expired CO2 trapped in the dead space of the N95 mask.[5] Distress could be aggravated in extreme climatic conditions with high temperature and humidity and reduce the compliance among the wearers.[6]

Pulse oximetry provides a convenient, noninvasive, sensitive (92%), and specific (90%) method to measure blood oxygen saturation, display heart rate, and SpO2 derived from photoplethysmography measurements. It senses the changes in the light absorbed by oxygenated and deoxygenated blood by means of spectrophotometry.[7]

Multitude of qualitative and quantitative studies conducted in clinical settings studies till date evaluating the efficacy and effect of wearing the N95 mask among Dental Health Care Workers (DHCWs) are questionnaire-based surveys.[89] There is a dearth of published studies evaluating its effects by measuring oxygen saturation while taking into consideration the work conditions of humid climate and high temperatures experienced by healthcare workers in developing hot tropically situated countries such as India lacking air-conditioned facilities, akin to the setting of the current study which was conducted at a public hospital/government institutionally mediated setup. This study aims at achieving a better assessment of N95 and 3-ply surgical masks on oxygen saturation and determines the presence of any other subjective discomfort such as headache, giddiness, and mental confusion among DHCWs working in the coastal region of India with known humid and hot climatic conditions. This would prove to be invaluable in navigating dental practices with countermeasures in this unchartered arena.

METHODOLOGY

A repeated measures prospective observational study was conducted from July 1–31, 2020 in accordance with the STROBE guidelines.[10] The ethical approval for it was obtained from the Institutional Review Board (Ref. no.: GDCH/IEC/III-2020).

It was conducted at the outpatient services, operation theaters, and oropharyngeal swab collection centers for COVID-19 screening and testing; attached to the Tertiary Care Dental institute in Goa, India. The temperature during the study period ranged from 24°C to 26°C, while the humidity was recorded to be within the range of 70%–85%. The study participants recruited were categorized into Group A (frontline DHCWs utilizing Personal Protective Equipment (PPE) gear with NIOSH-certified N95 face masks and who identified themselves as being routinely positioned within 6 feet of patients) and Group B (DHCWs working at nonclinical settings donning surgical face masks). Protective eyewear and face shields were worn by all the participants.

In the pilot study among 20 participants, it was observed that the mean difference between drops in oxygen saturation levels between N95 and 3-ply mask groups was 1.03. The G* Power Statistical Software (version 3.1.9.2) was utilized to estimate the sample size of 120 participants. Those included in the study were ≥21 years and were willing to give informed consent. Those with cardiac and/or respiratory conditions (emphysema, congenital heart disease, asthma, bronchitis, etc.), influenza-like illness in the past 2 weeks, presence of nail polish/artificial finger nail, tobacco habit, or pregnancy were excluded from the study.

A self-administered questionnaire was completed by all the participants. Data were collected in the morning to eliminate the time-of-day effects on human performance. Monitoring for oxygen saturation and pulse rate at baseline, 60- and 120-min using pulse oximeter (Accu Sure YK Series, India) applied to the second finger of the right hand was done. To eliminate the effect of dehydration, DHCWs were allowed to drink water once after 60 min [Figure 1].

Figure 1

Study flowchart

Data were analyzed using SPSS version 24.0 (SPSS Inc., 2003, Chicago, IL, USA). The data were found to be normally distributed in the Kolmogorov–Smirnov test. In A-Priori analysis setting α at 5% and β at 20%, the power of the study (1-β) was 80%. The demographic characteristics were studied using descriptive analysis. Mann–Whitney u test was used to compare oxygen saturation drop between the two groups. Friedmann test followed by Wilcoxon signed-rank test with Bonferroni correction was computed to study differences within the groups. Binary logistic and linear regression was used to compare the study variables with outcome measure headache and drop in mean oxygen saturation, respectively.

RESULTS

In total, 128 frontline DHCWs participated in the study whose baseline demographic characteristics showed no significant differences [Table 1].

Table 1

Demographic characteristics

	Group A (n, %)	Group B (n, %)	P*
Age
<=35 years	66 (95.65)	55 (93.22)	0.981
>35 years	3 (4.34)	4 (6.78)	0.953
Gender
Male	11 (15.94)	8 (13.56)	0.9723
Female	58 (84.06)	51 (86.94)	0.988
Pre-existing headache	11 (15.94)	9 (15.25)	0.964

*P<0.05: Statistically significant

The mean oxygen saturation at baseline was 98.3 ± 0.97 and 98.29 ± 1.36 in Group A and Group B, respectively. The oxygen saturation dropped to 96.13 ± 2.84 after 60 min and to 97.61 ± 1.99 after 120 min in Group A, which was statistically significant. Group B did not exhibit a similar pattern, with oxygen levels of 98.14 ± 1.16 and 98.17 ± 1.04 at the two-time intervals. The drop was statistically significant between the two groups [Table 2].

Table 2

Mean oxygen saturation and pulse rates

Parameters	Group A			Group B			P
	Mean (SD)		Median (IQR)	Mean (SD)		Median (IQR)
Oxygen Saturation
Baseline	98.3 (0.97)		99 (98-99)	98.29 (1.36)		99 (98-99)	0.582
60 min	96.13 (2.84)		97 (94-99)	98.14 (1.16)		99 (96-99)	0.001ǂ
120 min	97.61 (1.99)		99 (97-99)	98.17 (1.04)		99 (97-99)	0.012ǂ
P		0.000ǂ			0.592
Pulse rate Median (IQR)
Baseline	85 (12.8)		84 (76-94)	83.54 (11.83)		84 (76-89)	0.537
60 min	83.25 (14.13)		82 (73-91.5)	84.97 (14.25)		83 (76-90)	0.522
120 min	84.01 (14.57)		83 (74-94.5)	82.78 (11.42)		82 (74-90)	0.663
P		0.547			0.840

ǂP<0.05: Statistically significant

The most common mask-associated symptom of physiological stress was headache (64.84%); however, few subjects also experienced fatigue (20.31%), giddiness (5.4%), and confusion (4%), and its incidence was more among Group A [Figure 2]. Group A was 6.852 times more likely to experience headaches than Group B. Females had 3.052 higher odds of developing headache than males. Subjects with pre-existing headache disorders were 1.97 more likely to develop headache after wearing a mask. The odds of experiencing headache were 7.94 times more after 120 min of donning the mask as compared to 60 min [Table 3].

Figure 2

Subjective discomfort in participants

Table 3

Regression analysis with independent variables predicting the outcome- “Headache”

Variable	With headache n=83	Without headache n=45	P	Odds ratio (95% Confidence interval)
Age (years) (Mean±S.D.)	27.12±3.85	24.23±4.72 years	0.465	0.965 (0.878-1.061)
Gender
Male	10 (52.63)	9 (47.3)	0.048†	3.052 (1.132-9.621)
Female	73 (66.97)	36 (33.03)
Type of mask
N95 mask	52 (75.36)	17 (24.64)	0.00†	6.852 (2.449-19.175)
Surgical 3-ply	31 (52.54)	28 (47.46)
Pre-existing headache
Present	15 (78.95)	4 (21.05)	0.042†	1.97 (1.04-3.66)
Absent	68 (81.92)	41 (91.11)
Time interval between wearing N95 face mask to onset of headache
60 min	16	112	0.00†	7.935 (2.490-25.280)
120 min	85	43

†P<0.05: Statistically significant

The type of mask significantly predicted the drop in mean oxygen saturation levels at 60 min [Table 4].

Table 4

Linear regression analysis to predict the ‘difference in oxygen saturation level (dependent variable), from baseline to 60 and 120 min’ with age, gender (male vs female) and group (type of mask- N95 vs 3-ply) as the independent variable

Variable	B	P	Lower CI	Upper CI
Baseline to 60 min
Constant	2.138	0.40	−2.89	7.16
Type of mask	0.32	0.047*	0.0824	0.558
Age	−0.012	0.85	−0.143	0.119
Gender	0.094	0.90	−1.448	1.637
Baseline to 120 min
Constant	−0.30	0.87	−3.97	3.37
Type of mask	−0.173	0.66	−0.967	0.621
Age	−0.018	0.71	−0.113	0.078
Gender	0.880	0.12	−0.248	2.007

P>0.05: Non-Significant, NS; *P<0.05: Statistically Significant; CI – Confidence interval; B – Regression coefficient

DISCUSSION

Universal social distancing and mandates for masking-up are emanations of the combat against the COVID-19 pandemic. Several studies have unequivocally shown that masks are essential for protection against the virus-laden aerosols and droplets. This airborne virus can infect up to a distance of 6 feet. Therefore, the health care professionals, especially dentists, who work in close proximity of the patients, need to follow stringent personal protection protocols including usage of N95 masks.[11]

The NIOSH recommended fit test for N95 mask considers only the fit aspect and not the comfort and physiological tolerance, which play a crucial role in determining its prolonged usage. N95 masks are reportedly known to reduce oxygen intake by up to 20% even in an individual with no existing comorbidity.[4]

In the current study, a significant drop in oxygen saturation was reported post one hour of wearing N95 masks, which increased in the second hour but was still lower than the baseline value. A negative pressure dead space is invariably developed between properly fitted internal surface of N95 masks and the wearer's face. The initial drop can be attributed to decreased O2 inhalation and increased inhalation of exhaled CO2 trapped within the breathing zone of N95 masks, which is directly related to the dead space.

Respiration being a complex process[12] regulated by neuronal and chemical processes in a healthy individual, alteration in O2 saturation is corrected by the body itself. Several other factors such as prior experience of prolonged usage of masks and/or intense physical activity could help the N95 mask wearer to acclimatize to the low oxygen level.[13] This can explain the increase in O2 in the second hour. This study's findings are in accordance with a study conducted among frontline healthcare workers during the COVID-19 pandemic, which concluded that long-term usage of N95 masks (>2 h) leads to retention of CO2 and eventually to hypoxemia.[14] The possible rationale for no significant reduction being noted in oxygen saturation among surgical mask wearers in this study is the inadequate facial seal allowing leakage of air around the mask.[3]

Prior studies have identified resistance to breathing and inhalation of insufficient oxygen as the prime cause of respiratory fatigue on wearing N95 masks.[415] Shortage of oxygen further stimulates the sympathetic nervous system and increases the heart rate possibly leading to respiratory fatigue and overall discomfort among the N95 masks wearers of this study.[16] Moreover, discrepancy in respiratory fatigue between the two groups could be ascribed to the temperature variations between the masks. This study was conducted in the tropical state of Goa in the monsoon season at a time when humidity is at its peak. Humid air saturated with moisture prevents evaporation of body sweat and may block the pores of the N95 mask filter.[6] Consequently, the temperature rises inside the N95 mask owing to the retained moisture from exhaled CO2 and the accumulated facial sweat and is relatively higher as compared to surgical masks indicating greater heat stress, discomfort, and breathing resistance among N95 wearers.[15]

The present study also elucidates the fact that respondents wearing N95 masks complained of subjective discomforts, which could negatively affect their compliance and work efficiency. Several etiological factors could have contributed to this kind of physiological stress in this cohort. First, N95 mask-induced hypoxia can alter cerebral hemodynamics by vasodilatation of intracranial blood vessels, possibly leading to headache.[14] Second, compression or irritation of superficial sensory nerves innervating the head, face, and neck region by tight fitting elastic head straps securing N95 masks and eye goggles could have triggered a cervicogenic headache among the participants. The sensitization of peripheral nerves by traction forces can elicit a pain reflex traveling via the trigeminal nerve through the trigeminal ganglia and brainstem to the cortex, which could have been perceived as a headache by the subjects.[8] Furthermore, high humidity at the workplace can result in collection of warm moist air inside the mask and protective eyewear giving rise to thermal discomfort and headache.[17]

The results of this study are in congruence with the literature stating that females have a higher predisposition for headaches.[18] Additionally, it reports a positive correlation between pre-existing headache disorders and N95 mask-induced headache. Several other factors such as work pressure, irregular sleep pattern, emotional stress, erratic meal timings, and inadequate hydration could have triggered or aggravated physiological stress and headache among the participants who are otherwise prone to develop migraine or any other headache disorders. The results are in keeping with a recent study conducted among frontline COVID healthcare workers which reported that females with pre-existing headache disorders had a greater likelihood to develop N95 mask-induced headache when they worked for more than 3 h.[8]

Certain limitations have been identified during the conduction of this study. First, the study was conducted in the tertiary dental Health Care institution of Goa, (with no air-conditioning facility) when the humidity and temperature were at their peak. The ethical review board of the institution recommended sipping water after an hour if the participants wished to. However, practically none of the subjects could stop their procedure midway and removed the mask for sipping water. Second, the study sample predominantly comprised of relatively young and healthy participants. Third, the investigator was unable to observe the participants for the entire 120-min duration due to diverse study settings such as the operation theater. Thus, further research recruiting susceptible elderly DHCWs with more specific data (e.g., skin tone and body mass index) in varied climatic conditions would prove to be valuable in expanding the evidence of this topic. A randomized crossover study design conducted in a more controlled environment for a longer duration can be carried out to increase the generalizability of findings in future studies.

CONCLUSION

Wearing N95 masks in humid environments while performing dental procedures adds to the body's physiological burden or perceptions of discomfort and exertion. Therefore, issues of comfort and tolerance need to be addressed further to increase DHCW's adherence to its use. Scheduled work breaks while performing lengthy procedures (up to 120 min or more) wearing N95 masks could reduce the frequency and severity of headaches. The importance of adequate hydration and balanced nutritious meals should be highlighted. Group sessions for meditation and breathing exercises can be organized to decrease stress/anxiety and increase their energy levels. A well-ventilated, relaxed workplace will increase their comfort and work efficiency. However, the aforementioned suggestions are only impediment measures. Research and development into redesigning and improving the in-vogue design of N95 masks are warranted to negate discomfort associated with wearing the same, such as pressure headache and mask acne for the DHCWs. The triad of ensuring preventive public health safety, astute personal protection, and physiological comfort shall go a long way in the path of the “New Normal” to combat re-emerging infectious diseases.

Ethics

The approval for conducting this study was obtained from the Institutional Ethics Committee (Approval no. GDCH/IEC/III-2020).

Financial support and sponsorship

Nil.

Conflicts of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.