This is the first study focusing on short-term physiological changes (especially lung function) in health workers who worked in COVID–19 isolation wards for over four hours with PPE including N95 FFR, trying to provide reference on formulating scientific working shift system to protect health workers. SARS-CoV–2 is a new pathogen which is extremely contagious. There were more than 3,000 health workers in China and at least 9,000 in US reported infected.[12, 13] More than 40,000 health workers were infected in Europe according to local media. The importance of protecting health worker from high infection risk has been emphasized by many authors.[14, 15] Since droplet mode is one of the main spreading ways, respiratory protection such as medical mask and respirator plays a role in protecting health workers. However, respiratory protection may also bring discomfort.
Spirometry test is widely applied in evaluating patients’ respiratory function. FVC, FEV1, and FEV1/FVC are indicators of obstructive ventilation disorder, usually seen decreased among patients with COPD and bronchial asthma. PEF reflects the function of respiratory muscle and airway resistance while FEF25–75 acts as an indicator of small airway function.[18, 19] All these parameters can reflect lung function objectively. The result of this study showed significant short-term increase of heart rate and decline of FVC % predicted, which indicated that continuously working for hours in isolation wards was not an easy task. Slight obstructive respiratory was observed. Exhalation and inhalation resistance from respiratory protection and fatigue of respiratory muscles after long-duration working might be the contributing factors. Roberge et al conducted a trial on physiological impact of N95 FFR on health workers working for an hour (average wearing time when there was no pandemic), finding no significant difference. However, N95 FFR was not the only equipment influencing lung function in our study while the second layer of surgical mask as well as protective coveralls may also exert impact on lung function. Moreover, health workers in our study had a much longer working duration (averaging 6.5 hours) and higher working intensity, which was just the actual condition under COVID–19 pandemic. These could lead to more significant short-term lung function decline and increase of heart rate. Mental stress from COVID–19 outbreak and facing heavily illness quarantined patients might also facilitate the changes.
Currently available evidence showed negative correlations between lung volume (especially functional residual capacity and expiratory reserve volume) and BMI among both normal and overweight people. Therefore, this study assessed the association between changing levels of respiratory functions and BMI. Decline of FEV1/FVC enlarged as BMI increased among subjects were observed in the result. Similar condition was also recorded between changing levels of FEF25–75 % predicted and BMI. These finding indicated that health workers with higher BMI tended to suffer larger decline of lung function. A possible explanation by Littleton et al was that some airways start to closed as the BMI increase. But this explanation was mainly based on lung function decline among obese people while the mechanism in normal or mild-overweight people remains further research. Considering all subjects in this study generally have a lower BMI, the decline of lung function among health workers with higher BMI might be more significant.
Other lung function parameters measured in this study such as FEV1 % predicted, FEV1/FVC, PEF % predicted, FEF25–75 % predicted all showed lower means but the differences were not significant. It could be influenced by sample size while a larger sample might bring differences. There was no significant difference in SpO2 between before-working and after-working results, which indicated that changes of oxygen diffusion function induced by working in isolation wards with PPE less than nine hours could be compensated or the oxygen diffusion function could not be influenced. However, for those who work in isolation wards repeatedly, whether the acute decline of lung function would exert long-term impact is still unknown. The possibility of conversion from acute to chronic decline should not be ignored. Long-term decline of lung function could be associated with many diseases such as cardiovascular events, restrictive respiratory disorder, COPD, and lead to chronic hypoxemia.
The weight loss of health workers after working in COVID–19 isolation wards was the consequence of dehydration because they could not drink water or urinate during working. The PPE including double layers of protective clothing (protective coveralls covered by surgical gown), double layers of respiratory protection (N95 FFR covered by surgical mask) and double layers of shoe covers would quickly made health workers sweaty and tired. Severe dehydration could lead to various health events such as falls, delirium, renal failure and even deaths. Respiratory infection is also strongly associated with dehydrations. In this study, no health workers showed any symptom of dehydration except for fatigue. No infection of COVID–19 was reported afterwards. Hence, the short-term dehydration induced by working in isolation wards could be compensated but long-term impact on those who worked in isolation wards repeatedly is still unknown.
There was no significant difference between age and changing levels of each parameter. It was deduced that young health workers (ranging from 22 to 39) involved in this study show same impact on physiological function. It was hypothesized that longer working duration would induce more significant changes both in lung function and heart rate. Huang et al recommended a working shift system of continuously working for six hours because working for longer duration made workers feel exhausted and even dizzy. Thus, health workers involved in this study were divided into two groups according to different working duration (less than or over six hours) in isolation wards. No significant difference was observed between these two groups. Therefore, continuous working in isolation wards for six to nine hours would not exacerbate the short-term lung function decline or exert more severe physiological impact comparing to working for four to six hours.
Considering the lung function decline and other physiological impact on health workers and the valid using duration of PPE, the balance between protecting health workers and helping more patients should be kept. First, the application scope of respiratory protection should be carefully evaluated. N95 FFR is recommended consistently in aerosol generating procedure such as endotracheal intubation and collecting respiratory specimens while it is still conflicting whether N95 FFR is necessary in non-aerosol generating procedure.[25–27] Surgical mask is recommended to be worn all times in healthcare facilities. Second, the constant working duration of PPE required limitation. There is no consistent recommendation for constant working duration with PPE in isolation wards. The valid using duration of N95 FFR used to be recommended for eight hours by Centers for Disease Control and Prevention of United States while WHO suggested that using a respirator for more than four hours should be avoided.[27, 28] Working with medical mask or N95 FFR constantly could increase infection risk and induce discomfort such as fascial heat and pain. In this study, no health worker was confirmed infection afterwards, which was a testament of the efficacy of protection when working in isolation wards within nine hours. But six-hours duration might be recommended considering working fatigue.
There are limitations in this study. The imbalance of sex proportion could contribute bias, although it was literally independent when recruiting health workers. There might be more persuasive result if more male health workers could be recruited, because sex distribution was reported in association between lung function and obesity. Age distribution is another disadvantage. Although age in this study was normally distributed, there was no health workers older than 40 years old recruited. The impact of working with PPE in isolation wards within nine hours on elder health workers were still unknown. Moreover, because of the maximum working stress of COVID–19 and the shortage of rest, only 36 health workers in one isolation ward could spent their precious resting time to complete the lung function test in authors’ institution. Large sample study is literally better for more convincing result, but prospective and empty controlled group was not feasible considering the infection risk. After working in COVID–19 isolation wards for certain period such as two or more months, significant decline of lung function might be observed. Mid-term and long-term follow up were absence and some potential impact might be consequently ignored.