HE Ming-xin, ZHOU Xiang-dong, ZHOU Ming,2, LUO Ding, CHENG Peng-fei,ZHANG Hua,2,3?

1. International Nursing College of Hainan Medical University, Haikou 571199, China

2. Island Emergency Medicine Innovation Unit, Chinese Academy of Medical Sciences(2019RU013), Haikou 571199, China

3. Key Laboratory of Emergency and Trauma Research of the Ministry of Education, Hainan Medical University, Haikou 571199, China

4. Department of Respiratory Medicine, the First Affiliated Hospital of Hainan Medical University, Haikou 570102, China

Keywords:Critically Ill patient Airway maintenance New cognition Review

ABSTRACT With the advancement of medical technology, artificial airway has been widely used in modern medicine in our country, especially in the treatment and rescue of critically ill patients.However, the establishment of an artificial airway will also affect the original anatomical structure and normal function of the airway, which will cause a series of complications and pose a serious threat to the prognosis of patients. Therefore, effective airway maintenance can not only prevent the occurrence of complications, reduce the physical and mental trauma to the patient, but also optimize the treatment effect. At this stage, domestic and foreign airway maintenance strategies have shown varying degrees of new cognition. This article reviews the latest research status of airway maintenance strateges at home and abroad, hoping to provide clinicians with a reference for the latest cognition in airway maintenance strategies.?Corresponding author: ZHANG Hua, Professor.E-mail: zhanghuashelley@hotmail.com.

1. Introduction

Artificial airway is a gas channel established by inserting a catheter directly into the trachea or through the upper respiratory tract to effectively drain and maintain the airway, as well as provide conditions for mechanical ventilation and treatment of lung diseases.Artificial airway is an important means of rescue and treatment for critically ill patients, while airway maintenance is a key step to help patients get offline as soon as possible and avoid double infection. Poor airway maintenance methods can cause airway obstruction and high mucus secretion, which provides a good environment for the reproduction of airway colonizing bacteria,resulting in the production of a large number of bacterial toxins,and further induces airway mucus high secretion, forming a vicious circle[1,2]. If effective airway maintenance cannot be carried out at this time, the patient's condition will be aggravated, the treatment difficulty will be increased, and the patient's hospital stay will be extended[3]. At present, looking at the airway maintenance strategies at home and abroad, although there are still some controversies and uncertainties, more updated and qualitative new strategies have not been popularized in clinical work in time. Based on this, this article reviews domestic and international airway maintenance and airway secretion cleanup technologies, aiming to clarify the new understanding of current airway maintenance strategies for frontline workers.

2. Airway maintenance

2.1 Fixation of endotracheal tube

The early stage after tracheal intubation is the stage with a higher incidence of unplanned extubation. In foreign countries,the incidence of unplanned extubation ranges from 8% to 35%[4,5], while the domestic incidence rate is 4% to 26%[6, 7]. Tracheal intubation displacement or fall off is the main factor of airway damage. After the artificial airway is established, in addition to proper fixation of the tracheal tube and regular inspections, timely reassessment is required when the patient is irritable or changes in position. To ensure the patient's optimal ventilation, avoid catheter displacement or unplanned extubation. Some scholars[8] conducted a randomized controlled trial of endotracheal tube securement (ETTS)fixation and tape fixation. The results of the study showed that the use of ETTS for fixation can reduce lip ulcers, facial skin tears,and tracheal intubation displacement. But the fixer needs additional cost, and those who have the conditions can be recommended. The commonly used methods of endotracheal tube fixation recommended in clinical practice include: intubation fixation, dental pad and modified fixation, tape-type fixation, band-type fixation, etc. The advantages and disadvantages of various methods are different, and the best fixation method for endotracheal intubation is currently inconclusive. In clinical practice, the choice can be made according to the existing conditions, but it is recommended to use two or more fixation methods to strengthen the tracheal tube at the same time.

2.2 Airbag management

The retentate above the air sac is an important source of the pathogen of ventilator associated pneumonia (VAP)[9]. After the artificial airway is established, the patient's swallowing function is restricted, and oral secretions and gastroesophageal reflux will be blocked by the airbag and stay above the airbag, forming a retentate on the airbag. The airbag can reduce the displacement of secretions down the respiratory tract but cannot completely block it. Therefore,the application of a catheter with a suction function on the airbag can more effectively avoid aspiration[10]. Airbag inflation is only for patients who have established an artificial airway and require mechanical ventilation. Patients who do not require mechanical ventilation should not inflate into the airbag. According to this, the size of the airbag pressure will affect the blood circulation of the tracheal wall. Excessive airbag pressure can cause pressure on the tracheal wall. In severe cases, it can cause ischemia, necrosis and perforation. It can also induce airway spasm and cause breathing difficulties. Low airbag pressure will also cause air leakage ,aspiration and increase the incidence of VAP. Generally, the airbag pressure should be controlled at 25-30 cm H2O[10]. Appropriate airbag pressure can effectively protect the airway wall. Although it is not necessary to deflate the airbag daily, it is still necessary to check the airbag pressure regularly. There are many methods for evaluating the pressure inside the airbag, including cuff pressure monitoring(CPM), minimal leak technique (MLT) and minimal occlusive volume (MOV). The use of these techniques and appropriate treatment can effectively ensure ventilation and prevent the compression injury of the airbag to the mucosa[11]. Talekar et al.[12]compared the two methods of estimating the pressure inside the airbag and directly measuring the pressure inside the airbag (using a pressure gauge), and the results showed that direct measurement of the airbag can more effectively avoid over-inflation or underinflation of the airbag. Related domestic guidelines also suggest that it is not appropriate to use the finger touch method of inflating based on experience[13]. Based on the above research, it is recommended to use an airbag pressure gauge to check the airbag pressure regularly,which can monitor the airbag pressure more accurately and effectively.

2.3 Airway humidification

After the artificial airway is established, the upper respiratory tract loses the function of heating and humidifying the inhaled gas. In addition, the higher air flow through the airway during mechanical ventilation can easily cause the lower respiratory tract to lose water, dry mucous membranes, dry secretions and impaired expectoration, occurrence or aggravation of lung infection. So it is necessary to give airway humidification at the same time. At present, airway humidification methods mainly include intermittent bolus injection humidification, infusion tube continuous drip infusion, continuous injection pump humidification, artificial nose,atomized humidification and other methods[14]. The effect of airway humidification can be judged by humidity. Humidity is the amount of water vapor contained in a gas, usually expressed in terms of absolute humidity (AH) and relative humidity (RH) [15]. AH is the total amount of water vapor in the gas, expressed in milligrams of water per liter of gas (mg/L). RH is the percentage of water vapor in the gas relative to its maximum carrying capacity (%) [15].Temperature affects relative humidity. The American Association for Respiratory Care (AARC)[16] believes that the recommended temperature of the inhaled gas at the Y-tube is 37℃, and the relative humidity is 100% and the absolute humidity is 44mg/L.Plotnikow[15] et al. have also been confirmed in subsequent related studies. Regarding whether it is necessary to inject 5-10 mL normal saline to dilute the sputum and stimulate the cough reflex in patients before suctioning, so as to facilitate the discharge of sputum in the lungs, the results of a number of randomized controlled trials abroad indicate that it is not recommended to push before suctioning.Because normal saline perfusion can increase the migration of microorganisms from the tracheal intubation to the lower respiratory tract, increasing the risk of lung infection[17]. At the same time, bolus injection of normal saline will cause oxygen saturation recovery slows down and aggravates hypoxia[18, 19]. The latest point of view is that the choice of airway humidification temperature of 37 ℃has been unified, and the point of view that it is not recommended to inject normal saline before sputum suction has also become consistent. In clinical practice, it can be operated according to reference standards.

3. Airway secretion cleaning technology

Endotracheal suctioning (ETS) refers to an operation technique that uses mechanical methods to remove secretions accumulated in the lungs to keep the airway unobstructed and control lung infections,especially important for patients with artificial airways[16].Although it is a necessary treatment, sputum suction itself may also increase the risk of certain complications, such as airway mucosal damage, airway spasm, hypoxemia, atelectasis, infection, increased intracranial pressure, Changes in hemodynamic parameters, etc., in severe cases, cardiac arrest or even death may occur. So its necessity needs to be evaluated [20-22].

3.1 Indication of Attraction

Artificial airway is an important channel for mechanical ventilation treatment in critically ill patients. Whether it is tracheal intubation or tracheotomy, the patient’s cough reflex will be weakened, airway mucociliary clearance will be reduced, and secretions will increase and stay in the airway. In the tract, cleaning up airway secretions is an essential nursing measure. Regarding the choice of the timing of suction, whether to suction on time or on-demand according to clinical indications, a large number of foreign studies have shown that frequent and regular suction can damage the airway mucosa and make patients feel pain and discomfort, and the risk of complications occur increases accordingly. It is recommended to perform ondemand sputum suction based on clinical indications [16, 20, 23].On the contrary, if the secretions in the airway are not cleaned up in time, it can cause airway obstruction, hypoxia, and formation of sputum. Therefore, the following indicators are recommended as indications for sputum suction: (1) The volume pressure curve loop on the ventilator screen has jagged changes and/or there are obvious sputum sounds in the airway on auscultation; (2) When the ventilation mode of the ventilator is volume control, the peak airway pressure increases or the tidal volume decreases when pressure is controlled; (3) Blood oxygen saturation and/or arterial blood gas analysis value deteriorates; (4) Obvious secretions can be heard in the airway; (5) The patient lacks autonomy coughing ability;(6) Acute respiratory distress; (7) Suspected aspiration caused by stomach contents or upper respiratory tract secretions[16]. In addition to the above, when "Jifei Needle" appears in the lungs, sputum suction treatment should also be given in time. Studies have shown that the use of this guide can effectively reduce the incidence of sputum suction complications[24]. Clinical indications for on-demand sputum suction can refer to this guideline for operation.

3.2 Suction tube model

The larger the diameter of the suction tube, the smaller the weakening of the suction negative pressure in the airway, and the better the effect of suction,but the more severe the collapse of the lung caused by the suction process[25]. The model of adult suction tube is usually 10-16F (3.33-5.33 mm). It is recommended that the outer diameter of the suction tube should not exceed 50% of the inner diameter of the artificial airway. The suction tube with side holes has better suction effect than none. Side hole[26, 27]. In clinical practice, the suction tube should be selected according to the inner diameter of the artificial airway, and the side hole is preferred.

3.3 Suction negative pressure

The suction pressure can directly affect the sputum suction effect and the occurrence of complications. Excessive pressure can cause mucosal damage in the airway, and too little pressure can make it hard to absorb sputum. Therefore, proper suction pressure is a key measure for effective suction and reducing complications[16].The AARC[16] guidelines recommend that the suction pressure of adults is ＜150 mmHg (1 mmHg=0.133 KPa). The Chinese Society of Nursing [27] recommended in the group standards for airway care for patients with tracheotomy and non-mechanical ventilation in 2019 that the suction pressure for adults is 80-120 mmHg, and the negative pressure can be appropriately increased for those with thick sputum. Some scholars[28] used 3 different suction pressures(80 mmHg, 150 mmHg, 250 mmHg) for intra-airway suction in 47 intensive care patients in a prospective study. Compared with sputum negative pressure, 250 mmHg sputum suction negative pressure is more effective and equally safe, and does not increase the occurrence of other complications. However, the study subjects in the article excluded patients with chronic obstructive pulmonary disease,chronic kidney damage, acute pulmonary hemorrhage, immune system impairment, coagulation dysfunction, bronchospasm, etc.The inclusion of patients is relatively limited, and the result coverage is not wide enough. Further research is needed. At present, there are still some controversies about the suction pressure. Clinicians can refer to the suction pressure standard according to the specific situation of the patient.

3.4 Subglottic attraction

Subglottic secretion drainage (SSD) uses a tracheal tube with an SSD device to connect a negative pressure suction device to continuously or intermittently suck the secretion on the subglottic airbag [27]. A large number of foreign research results show that SSD can effectively prevent the occurrence of VAP and ventilatorassociated events (VAE), thereby shortening the duration of mechanical ventilation [29]. As for the impact of ICU hospitalization time and mortality, scholars hold different views. Some scholars[30] believe that SSD can effectively prevent VAP and ICU hospitalization time, while Mao[31] et al. showed in a 2016 metaanalysis SSD can effectively reduce the incidence of VAP, but there is no statistical difference in the impact on mortality and ICU stay.There is still controversy at home and abroad about whether the use of SSD affects the length of hospitalization and mortality. And whether the SSD uses continuous suction or intermittent suction in the suction time, whether continuous suction will cause hypoxia and tracheal mucosal ischemia, and there is less evidence on the number and time of daily suction during intermittent suction. Whitch one of these two methods is more advantageous remains to be further studied. But it does not hinder its current clinical application.

3.5 Shallow suction and deep suction

Shallow suction (SS) is estimated by the length of the tracheal tube worn, and is the name of airway suction performed when the distal end of the suction tube reaches the end of the tracheal tube. Its advantage is that SS can reduce the irritation of tracheal mucosa during sputum suction, prevent airway mucosal damage and other undesirable complications[16, 32]. But for secretions in the deep trachea, using SS has the risk that the secretions cannot be effectively cleaned up. Deep suction (DS) is the airway suction performed when the suction tube is inserted into the artificial airway until resistance is encountered, and the suction tube is retracted by 1 cm. Due to the deep insertion of the catheter when using DS, the tip of the suction tube can stimulate the tracheal wall, which may cause edema, congestion, and damage to the airway wall mucosa. In severe cases, bradycardia may even occur[16, 32]. But it is more sensitive to those who have more secretions and are in a deeper position. So it should still be used as needed. In clinical use, SS is recommended for patients with less secretion, shallow location, and better cough ability. For patients with more secretion, deeper location, and weak cough ability, DS is recommended.

3.6 Open suctioning systems and close suctioning systems

Open suctioning systems (OSS) refers to the method of inserting a sterile suction tube into the airway for suction under the premise of disconnecting or stopping mechanical ventilation. When OSS is implemented, the ventilator needs to be disconnected. This operation may reduce lung volume and cause hypoxemia, and may induce alveolar collapse[33]. The airway is open to the outside world during sputum suction, and the secretions are easily exposed to the air during the process of sputum suction to stimulate their coughing, and cross-infection occurs. Close suctioning systems(CSS) refers to the use of closed suction devices for airway suction without disconnecting or stopping mechanical ventilation. Some scholars[34] studied the effect of CSS on intracranial pressure and cerebral perfusion pressure over OSS. However, some scholars have shown in a prospective study that the difference between the effects of OSS and CSS on patients’ heart rate, mean arterial pressure, and blood oxygen saturation is not large. The two attracting methods are equally safe, and in terms of cost, OSS is relatively CSS costs less[35]. Regarding the impact of pain, related scholars have shown that CSS has lower pain levels than OSS[36, 37]. For the comparison of the advantages of OSS and CSS, AARC [16] recommends that it is safer to suck sputum without disconnecting the patient from the ventilator.It is recommended to be used clinically. Because CSS requires special devices, if conditions do not permit, the use of OSS should meet the requirements of sterile protection. In addition, the size of the CSS suction pressure and the replacement time of the closed suction device still need to be studied.

4. summary

As an important means of rescue and treatment of critically ill patients, artificial airway is not only a channel of life for patients and medical staff, but also a new challenge. At present, there are many researches on airway maintenance at home and abroad, but there are still some doubts and controversies in clinical practice.This article reviews and combs the relevant domestic and foreign research literature in recent years, starting with airway maintenance and airway secretion cleaning technology, and explores the airbag pressure, suction indication, suction tube model, airway humidification temperature and humidity, find out that evidence has become the same. Medical staff can refer to relevant standards to implement operations. However, the best way to fix the tracheal tube, the size of suction negative pressure, the duration of SSD suction and the number of suctions, and the selection and use time of CSS negative pressure have not yet reached a complete consensus. It is urgent for clinicians to conduct real-world research.

Author's contribution

He Ming-xin: Complete the collection and analysis of relevant literature and the writing of the first draft of the paper; Zhou Xiangdong: the project creator and guide the writing of the paper; Zhou Ming, Luo Ding, Chen Peng-fei: Participate in the analysis and sorting of the literature data; Zhang Hua: the project creator and the person in charge, guide the writing of thesis.

All authors declare no conflict of interest.