During outbreak of COVID-19, people use mask in public for infection prevention and patients with AECOPD are no exception. Even if there was no previous respiratory failure or hypercapnia, the results of this study indicated that the patients with AECOPD should be careful to use mask, due to the increased risk for inducing hypercapnia from 40 mmHg to 49 mmHg, and increased SBP with 11.39 mmHg.This was the first self-paired study on the safety of using mask in patients with AECOPD, which could lead to respiratory failure, aggravate exacerbation of COPD and elevate systolic pressure. Hypercapnia was defined by PaCO2 > 45 mmHg in arterial blood gas (ABG) analysis, and the development of hypercapnia may drive COPD progression. Patients in group C who have used masks before arriving in hospital with meanPaCO2 of 49 mmHg could be diagnosed with hypercapnia. High concentrations of carbon dioxide pressure in bloodstream stimulates breathing, increases heart rate and leads to expansion of blood vesselwhich lead to discomfort,, anxiety and headache, shortness of breath. Much more as a predicting maker of COPD severity, hypercapnia increased airway contraction and resistance in severe COPD patients were taken a turn for better after correction of hypercapnia. Previous study provides evidence that CO2 acts as a signaling molecule in mouse and human airway smooth muscle cells, high CO2 activated calcium-calpain signaling and consequently leas to smooth muscle cell contraction in mouse airway smooth muscle cells. Hypercapnia could change autonomic nerve function which increase heart rate and blood pressure, especially at higher workloads[17, 18]. The sympathetic nervous system will be activated and affect the body although hypercapnia and hypoxemia are corrected immediately, especially cardiovascular autonomic nervous reflex.
COPD patients suffer weakness and muscle fatigue including respiratory muscle fatigue aggravates respiratory dysfunction [19, 20]. Therefore, using mask as airtight as possible increase work of breathing due to high respiratory resistance, heat pressure, In particular, N95 masks filter particles with a diameter of less than 0.1um,increaseexpiratory resistance impacted ventilation and can be associated with decreased peak flows and minute ventilation[21, 22].In addition, the increased flow resistance of mask with a concomitant decrease in alveolar ventilation can bring out an increase in tidal volume, a decrease in minute ventilation.Therefore ,dyspnea may gradually worsen with the progression of respiratory muscle fatigue in patient with AECOPD. The respirator affected with moisture is particular clear. It can be seen that body fluids are on the surface of the respirator, which increase breathing resistance because of water vapor carried on the exhaled breath and the droplets expelled when speaking. A study reported average peak inspiratory pressures of decreasing in 12.4 mm H2O and average peak expiratory pressures of increasing in 11.9 mm H2O at 50% maximal oxygen consumption. Patients are unable to exhale more carbon dioxide and increased more oxygen consumption when exercise and resistance load. On the other hand, masks may cause carbon dioxide re-respiration. Previous investigation has shown that tidal volume decrease and CO2 retention increased along with the increasing in inspiratory resistance. An increase in inspiratory resistance from 3 mm H2O to 18 mmH2O pressure results in a relative 3 percent increase in end-tidal CO2 level, and increasing the inspiratory resistance to 28 mmH2O pressure results in a 10 percent relative increase in end-tidal CO2 level.In particular, study reported that N95 use produces an average increment of 126% and 122% in inspiratory and expiratory flow resistance, which indicated that using mask may causes or exacerbates hypercapnia in COPD patients even if tolerated. Cases have been reported that mask can cause carbon dioxide re-breathing due to its sealing [26, 27]. It is particularly important for COPD patients that mask with visible body fluids on the surface and excessive mask dampness result in high respiratory resistance which increases with ongoing use and frequency. Furthermore,retention of bacteria, viruses, particles within the filter of masks and respirators also increase respiratory resistance by plugging up the stomata. Thus, even bacterial or virus infection induces acute exacerbation of COPD; using mask may also exacerbate the severity of disease.
Our data showed that all the patients did not use masks before the COVID-19 outbreak, and no one showed discomfort obviously such as dizziness after using masks mentioned in this study. However, wearing masks on people is affected by disease, environmental factors, breathing, exercise load and surgical mask filter and fit performance [6, 28]. General population feels discomfort because of wearing mask could lead to anxiety, breathing rate and depth accelerated. In patients with AECOPD who cough, expectorate and feel dyspnea, the condition may be further aggravated and may lead to respiratory failure. Most of the patients wearing masks did not feel discomfort or exacerbation of their original symptoms significantly, however, our study showed that PaCO2elevation in the blood gas analysis could be detected in the patients before the onset of symptoms, and the body was in a compensatory state. Observed abnormal physiology may be influenced by the patient’s chronic deviation from normal values resulting in oversight of possible aggravating risk factor. The impact of using masks on AECOPD patients may be covered up by the primary symptoms of the disease, which makes us ignore. Patients usually spent more than 30 minutes from home to hospital. Monitoring vital signs in patients may potentially allow clinicians to intervene medical diagnosis and treatment quickly. Improper use of masks and long transport process of patient with acute exacerbation may lead to hypercapnia. The study suggests that longer ambulance journeys may lead to a greater risk of hypercapnia if unduly high concentration of oxygen are given during AECOPD , so that use inhalants to improve discomfort or the body compensates for hypercapnia when using mask repeatedly, it will bring out repeated episodes of hypercapnia which result in aggravation if clinician cannot identify the cause. Considering COPD patients often comorbid with bronchial asthma, bronchiectasis and tuberculosis, we should pay attention to the safety of using mask because of respiratory resistance related to carbon dioxide emissions. The use of masks causes significant increase in PaCO2, bicarbonate and residual base in patients while some patients develop hypercapnia, which may aggravate disease if they are used for a long time. The balance between the risks and benefits of using mask in AECOPD patients is unclear. People with underlying diseases infected with COVID-19 are more likely to become more severe and complicated[30, 31],nevertheless༌mask as a prevent measure, the safety of which should be concerned. Therefore, when the elderly with respiratory disease, heart disease, or stroke wear mask to prevent infectious diseases, they should consult their physician regardless of the type of mask. At the same time, patients with nasopharyngeal carcinoma, thoracic deformity or myasthenia gravis need attention. Identification of such high-risk patients could provide an opportunity for appropriate and timely treatment.
COPD is performed by malnutrition, low immunity, and susceptibility to infection ,what should patients with COPD do during pandemic when masks have to be worn to prevent infection, especially in hospital? How can we make masks filter out bacteria and viruses while reduce breathing resistance is a potentially important problem.N95 with exhalation valve may be the option to reduce respiratory resistance if respiratory protection is not affected. On the other hand, no matter whether the patient has acid-base imbalance, lung function assessment and blood gas analysis should be carried out .It is necessary to use masks carefully to avoid aggravating respiratory failure in case of acute exacerbation while the PaCO2of patients increased potentially. Furthermore, AECOPD patient would use NIV if necessary. In addition, people could go out less to avoid infection during the stable stage of COPD. It is easy to be hospitalized repeatedly due to acute exacerbation, which is combined with nosocomial infection because of malnutrition and low immunity.
Patient is hypocalcemia in group C, which may related to the usage of gluococorticoid and diuretics and deficiency of intake. Studies show that patients with AECOPD comorbid with hypocalcaemia are susceptible to co-infection. The change in the acid-base is closely related to hydroelectrolyte imbalance which conforms to the effect of chloride ions on the imbalance of acid-base as other previous study . The increased PCO2 caused by using masks and hydro electrolyte imbalance should be reviewed and maintain during the stable period of COPD. In the following research, we will further study the influence of electrolyte abnormality on long-term acid-base imbalance and prognosis of patients.