QinHao1*, Li Jie2*, Wang Qixing3*, Wang Jun1,Jing Guoqiang4, DaiBing5, NiZhong6, Wang Shengwen7, Ge Huiqing8, Luo Fengming6, Xia Jingen9, Chen
Rongchang10, ZhangWei1#, Liang Zongan6#； Respiratory Therapy Group, Respiratory Disease Branch, Chinese Medical Association
1. The First Affiliated Hospital of Naval Military Medical University（Shanghai 200433）
2. Rush University（Chicago, Illinois, USA 60612）
3. Tenth People's Hospital Affiliated to Tongji University（Shanghai 200072）
4. Affiliated Hospital of Binzhou Medical College（Binzhou, Shandong 256603）
5. The First Affiliated Hospital of China Medical University（Shenyang, Liaoning 110001）
6. West China Hospital of Sichuan University（Chengdu, Sichuan 610041）
7. The First Affiliated Hospital of Xi'an Medical College（Xi’an，Shanxi 710077）
8. Shao Yifu Hospital Affiliated to Zhejiang University School of Medicine（Hangzhou, Zhejiang 310020）
9. China-Japan Friendship Hospital（Beijing 100029）
10. Shenzhen Respiratory Disease Research Institute（Shenzhen,Guangdong 518020）
The New Coronavirus Pneumonia (NCP) is a pneumonia caused by 2019-nCoV infection. Its severe and critically ill patients often have hypoxemia and dyspnea and need to receive correct respiratory support treatment. For acute hypoxic respiratory failure, High-flow nasal canula (HFNC) has a greater advantage than traditional oxygen therapy, which can reduce the intubation rate and 90-day mortality. HFNC has played an important role in the treatment of MERS-CoV pneumonia and H1N1 pneumonia. HFNC also plays an important role in the current treatment of NCP severe and critically ill patients. Figure 1 shows an HFNC unit attached to a patient..
Figure 1: A HFNC unit attached to a patient
The epidemic situation is still developing. Not all medical personnel using HFNC are specialized in respiratory or critical illnesses. They are not familiar with the operation of HFNC. The use of HFNC and subsequent disinfection treatment methods require training. Experts from the respiratory therapy group of the Respiratory Disease Branch of the Chinese Medical Association discussed some common problems in the application of HFNC during the NCP treatment process, and formed an expert consensus on the subject. This expert consensus uses the current commonly used HFNC device as an example for explanation, so that first-line medical staff can quickly master the use and disinfection of HFNC, benefit patients, and avoid increasing the risk of virus transmission. This expert consensus starts with the principles and parameter settings of HFNC and the use and sterilization methods of different high-flow oxygen inhalation devices. It aims to standardize the use of HFNC in NCP patients and provide guidance for front-line clinical care.
• 2019-nCoV is sensitive to ultraviolet light and heat, of 56 ° C temperature and 30 minutes exposure. Ether, 75% ethanol, chlorine disinfectant, peracetic acid, chloroform and other lipid solvents can effectively de- activate viruses, but chlorhexidine can't de-activate 2019-nCoV.
• The connection and use of different HFNC devices are slightly different, but the principles and basic processes are the same. The user needs to pay attention to whether the machine and the tubing are correctly connected and whether the parameters (temperature, flow rate, and oxygen concentration) are set reasonably, and make dynamic adjustments based on the patient's subjective feelings, vital signs, and test results.
• It is recommended to use disposable tubing and nasal congestion. It is for dedicated use. It is not recommended for routine replacement. Replace it when there is obvious contamination. The size of the nasal congestion model is less than or equal to 50% of the patient's nostrils. Whether the joint is worn correctly directly affects the diffusion distance of exhaled air. The device is wet and the humidification water in the tank needs to be connected externally. The humidification water is sterilized and distilled water is used. It is recommended to use an automatic water injection humidification tank. If a non-automatic water injection humidification tank is used, it should be replenished regularly in time to prevent excessive temperature.
• In order to reduce the spread of aerosols and the generation of droplets, it is recommended that when using HFNC, follow the sequence of starting-up, setting initial parameters, wearing nasal congestion, and delivering air, then remove the nasal plug. When using or discontinuing HFNC, patients should not be interrupted by oxygen supply. According to the requirements to cure the disease, the necessary devices such as nasal catheter oxygen inhalation, non-invasive ventilator or tracheal intubation can be prepared in advance.
• The device failure alarm should be promptly checked and dealt with. If the failure cannot be eliminated, the machine should be replaced in time or changed to other breathing support methods.
• After the high-flow device is used, it is necessary to turn off the oxygen source before shutting down. The removed disposable pipes, humidification tanks and nasal plugs are destroyed as medical waste. The surface of the machine is wiped and disinfected with 75% ethanol, and specific disinfection pipes are used to disinfect the internal loop of the machine and replace the air filter cotton sheet.
1. The definition, principle and physiological mechanism of HFNC
1.1 High-flow nasal cannula（HFNC) refers to a kind of oxygen therapy method of high-flow inhaled gas through high-flow nose plug which can provide patients with adjustable and relatively constant oxygen concentration（0.21～1.0）, temperature（31～37°C）and humidity high flow (80L / min, different according to brand and model).
1.2 HFNC mainly includes four parts: air-oxygen mixing module, heating and humidification module, connecting pipe and nasal plug joint. The air-oxygen mixing device mixes air and oxygen in front of the turbine / fan according to the preset oxygen concentration, and the turbine accelerates after mixing generate high-speed airflow. The heating and humidification module heats and humidifies the high-speed airflow and then delivers the gas to the patient at a constant temperature, constant humidity and constant flow rate through the connecting pipe and the nasal plug connector, which plays the role of breathing support as shown in figure 2.
1.3 The advantages of HFNC: (1) Provides a stable and higher than normal nasal catheter inhalation oxygen concentration, the oxygen absorption concentration does not change with the change of the patient's breathing state, which can meet the patient's need for spontaneous breathing; (2) The high-flow airflow can reach or exceed the patient's active inhalation, the maximum inspiratory flow rate, reducing inspiratory resistance and breathing work, reducing oxygen consumption; (3) The gas can be heated and humidified to 37 ° C and 44mg / L, reducing the consumption of heat and water in patients with respiratory distress and making airway mucus. The cilia function is kept in the best state, which is conducive to the drainage of secretions and reduces the incidence of lung infections; ⑷ high-flow airflow flushes the upper airway dead space, reduces anatomical dead space, improves patient ventilation; ⑸ high-flow airflow provides a certain level positive airway pressure which has the functions of opening alveoli, increasing lung volume, and improving ventilation; ⑹HFNC does not require a completely closed circuit, no obvious facial pressure, easy to eat and communicate, and patients have high compliance.
Figure 2: HFNC Mode
2. The application time and parameter setting of HFNC
2.1 Indications: For patients with NCP, meeting the following diagnostic criteria for severe NCP: (1) Respiratory distress, respiratory rate ≥30 times / min; (2) In resting state, it means oxygen saturation ≤93%; (3) Arterial blood oxygen partial pressure (PaO2)/ Inhaled oxygen concentration (FIO2) ≤300mmHg.
It is worth noting that at present there is no unified conclusion on the indications for the clinical application of HFNC. Published clinical studies have confirmed that HFNC is mainly suitable for the treatment of patients with mild to moderate hypoxic respiratory failure. For severe hypoxic breathing, the use of HFNC in patients with respiratory failure and respiratory failure with hypercapnia should be closely monitored. If there is no obvious improvement in oxygenation after 1 to 2 hours of use, it should be changed to a higher level of respiratory support as soon as possible
2.2 Contraindications: (1) Sudden cardiac arrest and emergency tracheal intubation for invasive mechanical ventilation; (2) Weak spontaneous breathing and poor upper airway protection; (3) Severe hypoxic respiratory failure (PaO2 /FIO2<100mmHg) and severe ventilation dysfunction (PaCO2> 45mmHg and pH <7.25); ⑷ upper airway obstruction; nasal and facial trauma cannot use nasal congestion; ⑸ people who refuse to use
2.3 Parameter setting observation index and withdrawal standard
(1) Parameter setting: ① Type I respiratory failure: the initial setting of the gas flow (Flow) is 30-40 L / min, and gradually increase the flow to 50-60 L / min after the patient tolerates; adjust FI02 to maintain the pulse oxygen saturation (SpO2) at 92% ～ 96%, combined with the dynamic adjustment of blood gas analysis; if the oxygenation target is not reached, FI02 can be gradually increased and raised to a maximum of 1.0; the temperature setting range is 31 ～ 37 ℃, according to the patient ’s comfort and tolerance, and sputum Liquid viscosity is adjusted appropriately. ② Type Ⅱ respiratory failure: the initial setting of the gas flow (Flow) is 20-30L / min, which is adjusted according to the patient's tolerance and compliance; if the patient's carbon dioxide retention is obvious, the flow can be set at 45-55L / min or even higher to reach the patient The maximum flow that can be tolerated; titrate FIO2 to maintain SpO2 at 88% to 92%, combined with dynamic adjustment of blood gas analysis; temperature setting range is 31 to 37 ℃, according to patient comfort and tolerance, and sputum viscosity adjustment.
(2) Observation indicators during use: After using HFNC, the patient's vital signs should be monitored, especially the respiratory rate and SpO2. If there is a decrease in breathing frequency, a rise in SpO2, and a decrease in FIO2 for a period of time, it means that the patient responds well to HFNC and can continue to be used; otherwise, the patient's condition deteriorates, and it is necessary to consider increasing the gas flow and FIO2 and decide whether to switch to a higher level of breathing support mode according to the clinical situation.
(3) Withdrawal HFNC standard: gradually reduce HFNC parameters after primary disease control or improvement. If the following criteria are met, HFNC evacuation can be considered: inspiratory flow <30 L / min and FIO2<0.4
As a new oxygen therapy method, HFNC provides new options for respiratory support in patients with severe and critical NCP. From the perspective of practicality, this expert consensus chose the current widely used HFNC as an example to adapt to HFNC. The license, contraindications, usage process and post-disinfection treatment are explained. For the HFNC models not included, please refer to the instruction manual and these guidlines for use. Severe and critical NCP are progressing rapidly. When using HFNC, you should closely observe the changes in the condition and adjust the treatment plan in time to achieve better results.
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