I. Background
In 1981, Sullivan et al. in Australia first reported satisfactory results of continuous positive airway pressure (CPAP) in the treatment of sleep apnea hypoventilation (SAHS), and in 1985, due to the improvement of nasal mask technology, transnasal CPAP treatment was widely used and has become the main means of treatment for adult SAHS patients. In 1991, the Bi-level Positive Airway Pressure (BiPAP) ventilator, which can adjust inspiratory positive pressure (IPAP) and expiratory positive pressure (EPAP) respectively, was used in clinical practice, and in 1993, the intelligent CPAP (Auto-CPAP), which can increase or decrease pressure according to the change of upper airway resistance, was introduced with good comfort, and its technology is now more mature. Because CPAP is inexpensive, it is still the treatment of choice for most patients. In China, CPAP was applied to treat SAHS in the early 1990s, and a domestic CPAP ventilator was developed, which achieved good results.
CPAP, also known as positive end-expiratory pressure under voluntary breathing (PEEP), refers to the application of a certain positive pressure to the airway throughout the respiratory cycle under the condition of sufficient voluntary breathing. The BiPAP ventilator provides high pressure support during inspiration and lower pressure levels during the expiratory phase, increasing comfort and effectively reducing CO2 levels, and is the primary mode of noninvasive ventilation for the treatment of respiratory failure. CPAP provides feedback to increase or decrease the pressure level depending on the patient’s upper airway resistance and the presence or absence of respiratory events including airflow limitation, snoring, hypoventilation and apnea, keeping the upper airway open while effectively reducing the mean therapeutic pressure. It can be used in the sleep laboratory to assist in pressure titration, or in the home.
II. Rationale of transnasal mask continuous positive airway pressure ventilation for SAHS
The possible mechanisms of action of CPAP for sleep apnea include, first, using the “airflow support mechanism” of positive airflow to increase the positive pressure in the pharyngeal cavity to counteract the negative inspiratory pressure, prevent airway collapse, and keep the upper airway open; computed tomography and MRI both clearly show the most significant effect of lateral airway expansion. Second, positive pressure ventilation increases lung volume and indirectly dilates the upper airway. When lung volume increases, the stretching effect on the upper airway can increase the stiffness of the upper airway wall structures, thus producing the effect of opening the airway. It has been shown that when negative pressure is applied to the chest and abdomen of patients with OSA, their AHI can subsequently decrease. Third, airflow stimulates pressure and mechanoreceptors in the upper airway, which increases the tone of the upper airway dilator muscles. However, some studies found that the “temporal” electromyographic activity of the upper airway muscles was not enhanced during CPAP treatment, and the increase in tone may be related to the enhanced “tonic” activity of the muscles. Fourth, it can eliminate local tissue edema and reduce the thickness of the lateral pharyngeal wall; Fifth, long-term application can improve the sensitivity of the respiratory center to low oxygen and high CO2, and improve the respiratory regulation function.
III. What kind of SAHS patients need long-term non-invasive ventilation therapy
The severity of SAHS patients is the main basis for deciding whether they need long-term home CPAP treatment. Although there are no accepted criteria for evaluating the condition of SAHS, the completion of multicenter clinical trials such as the Sleep heart health study (SHHS), in particular, has provided evidence-based medical evidence for the development of treatment criteria for SAHS. According to the U.S. Medicare policy, the criteria for reimbursement of CPAP ventilators are: AHI > 15 breaths/h; 5< AHI > 14 breaths/h but with daytime symptoms such as cognitive impairment, daytime sleepiness, combined hypertension and other cardiovascular disorders. CPAP includes various brands of CPAP and intelligent CPAP (auto-CPAP) ventilators. The main basis is that SHHS has demonstrated that an AHI above 15 breaths/h can lead to an increase in cardiovascular and cerebrovascular complications. We believe that this criterion is of greater reference value, taking into account both laboratory indicators and clinical aspects.
IV. Titration of the optimal CPAP therapeutic pressure
The appropriate CPAP pressure is the key to ensure the success of treatment, which should be able to remove apnea and snoring during all sleep periods and various positions of sleep, and to eliminate upper airway airflow limitation (flow limitation) as much as possible. This optimal pressure can vary within a small range and is not an absolute value. CPAP pressure should be increased during supine sleep, REM sleep, weight gain, after heavy alcohol consumption, during cold or rhinitis attacks. After a phase of treatment, especially after significant weight loss, the required pressure level decreases in some patients.
The goal of CPAP pressure titration is to discover the most appropriate therapeutic pressure for long-term CPAP application. Conventional pressure titration can be done manually in the sleep chamber under the guidance of polysomnography monitoring. To ensure that the patient can sleep well and to build patient confidence in the treatment, the CPAP pressure can be set by switching to a more comfortable BiPAP ventilator. However, because this method is cumbersome and laborious and time-consuming, some easier alternatives are available.
One is to divide the patient’s sleep breathing monitoring time into two parts, with the diagnosis confirmed in the first half of the night and the therapeutic pressure of CPAP set in the second half of the night. In the United States, this may make some medical economic sense because of the expense of pressure titration. Our experience is that this method is feasible for critically ill patients and is not very successful for mildly ill patients who are prone to missed diagnoses and treatment failure.
The second is to set the therapeutic pressure of CPAP at the patient’s home after diagnosis, without relying on the help of polysomnography. Our practice is to use a portable oximeter to monitor dynamic SaO2 in the patient’s home during the first night, and the results are used as the base value before treatment. The patient is then taught to use the CPAP machine by a technician in the hospital during the day, and an empirical therapeutic pressure, usually 8-12 cm of water column, is selected, taking into account the patient’s body size and severity of the disease. Most of the patients were able to master the use of the machine and the adjustment of the nasal mask after 2-3 nights of study and trial, and their family members were instructed to pay attention to the occurrence of snoring or apnea during their sleep, and if so, to increase the pressure by 2 cm water column, and to contact the doctor by telephone at any time to report the use and solve any problems in time. After about 1 week of trial, after the patient could master the use of the ventilator and snoring disappeared, the dynamic SaO2 during sleep was measured again and compared with the result before treatment, if the lowest SaO2 was above 90% and there was no obvious fluctuation of blood oxygen, the pressure was proved to be appropriate, otherwise, the CPAP pressure was continued to be adjusted upward. This model of combining daytime titration with home follow-up reduces both the cost to the patient and the workload of the sleep center staff, and is worth promoting in sleep labs with some experience.
Third, machines are now available that can automatically adjust the appropriate CPAP pressure, which can be applied while the patient is sleeping, depending on their upper airway resistance. The optimal range of the required CPAP pressure can be automatically reported the next day. However, the results must be interpreted by an experienced physician to identify possible air leaks and to avoid overestimation of the titrated pressure level. In addition, most Auto-CPAP machines with automatic titration give a pressure level that is 95% of the confidence limit level of the maximum pressure throughout the night, but sometimes this pressure is still low and patients may unconsciously remove the nasal mask or wake up during sleep at night during home treatment.
For the few patients who failed to be debugged by the above methods, they were admitted to the ward and used the CPAP machine under the close supervision of doctors and technicians. After 3-4 days of learning and debugging, most of them were able to achieve good results and could be discharged after a week.
Special attention should be paid to the fact that the optimal pressure level titrated in the sleep laboratory is often not the pressure level required by the patient in home therapy and should be increased by 1-2 cm of water column when prescribed.
Increase CPAP pressure by 1 cmH2O every 5-10 minutes, and within minutes or even cycles of breathing if needed, typically up to 18 cmH2O
Apply respiratory airflow pressure sensors to record apnea and severe hypoventilation
1. Leaky nasal mask or open mouth breathing
2.Apply jaw brace
3.Apply warming and humidification
4. Switch to BiPAP ventilator
Remove inspiratory airflow restriction
Increase CPAP pressure by 1 cmH2O every 10-15 minutes, up to 18 cmH2O
Apply respiratory airflow pressure sensor to record airflow restriction leading to awakening
1. Leakage of nasal mask or open mouth breathing
2.Apply jaw brace
3.Apply heated wet
4. Switch to BiPAP ventilator
Removal of arousal and leg movement
Increase CPAP pressure by 1 cmH2O every 5-10 minutes, but not more than 4 cmH2O required to remove airflow limitation, or until CSA and hypoventilation occur
EEG monitoring of arousal and limb movements
If the frequency of CSA and hypoventilation events increases, lower the CPAP level to the pressure required to remove airflow limitation
Remove oxygen desaturation
Increase CPAP pressure by 1 cmH2O every 5-10 minutes, but not more than 4 cmH2O required to remove airflow limitation, or until CSA and hypoventilation occur
Monitor oxygen saturation
1.Oxygenation
2. Switch to BiPAP ventilator
V. Side effects of CPAP therapy and treatment
CPAP ventilator is non-invasive, easy to use and has no serious side effects. Comprehensive literature reports that caution should be exercised when using CPAP ventilator in the presence of the following diseases in patients with SAHS CT or X-ray examination of the chest reveals the presence of pulmonary blisters with the possibility of spontaneous rupture; the presence of pneumothorax or mediastinal emphysema; significantly lower blood pressure and uncorrected shock; intracranial pneumothorax or cerebrospinal fluid leakage; CPAP should be avoided during the period of acute otitis media, and can be continued after the infection has improved. Other general side effects are seen and do not affect the long-term application of the patient after timely treatment.
1, help the patient to establish confidence CPAP treatment requires long-term adherence, the doctor should patiently explain to the patient about sleep apnea, obtain the cooperation of the patient and family members, and establish the confidence of successful treatment.
2. The unsatisfactory treatment effect on the first night does not mean treatment failure Because of the memory and comprehension of many SAHS patients, even under the strict guidance of experienced doctors, it usually takes 3 nights or even longer to try and feel the effect of treatment more deeply. The key to shortening this time is for the patient and family to work closely with the physician to resolve any problems that arise during use in a timely manner. Strengthening communication between patients can also help patients build confidence in overcoming the disease and gain useful experience.
3.Sleep rebound will occur at the beginning of CPAP treatment At the beginning of CPAP treatment, patients with severe SAHS will experience an increase in REM and NREM III and IV sleep abnormalities, i.e. “sleep rebound”, which usually lasts about 1 week. “Sleep rebound” is important because during REM sleep, the patient’s ability to respond to multiple stimuli is reduced and it is difficult to wake up. Therefore, it should be closely observed at the early stage of treatment, and it is important to set the CPAP pressure sufficient to overcome the airway obstruction during REM sleep to ensure the patient’s life safety.
4.The treatment of nasal mask leakage The nasal mask should be of appropriate size, comfortable and soft, and be replaced in time; the headband should be loosened and tightened with balanced force; for those with special facial morphology, some loose material can be padded between the nasal mask and the skin.
5.Skin allergy and nasal ulcers In the initial stage of CPAP application, many SAHS patients have facial indentation or skin redness due to nasal mask pressure and gas stimulation, which can subside on their own after getting up for several hours. In addition to the correct and skillful use of the nasal mask, it can be replaced with a bubble-type nasal mask and a soft pad placed between the skin and the nasal mask. If there is skin breakdown or severe allergy, CPAP ventilator should be discontinued.
6.Eye irritation or conjunctival redness It is related to the irritation of the eyes by air leakage above the nasal mask, and conjunctivitis may occur in severe cases, so the size, position and tightness of the nasal mask should be adjusted.
7.Dry mouth Most of SAHS patients have dry mouth before treatment, and it will disappear naturally after treatment. If it does not disappear, it may be related to the set CPAP pressure is not enough or too high, and must be reset. If necessary, apply jaw rest and strengthen wetting.
8. Nasal blockage and nasal dryness 15-45% of patients will have nasal discomfort, which is related to cold air irritation causing mucosal congestion and edema or acute attacks of allergic rhinitis, in addition to the original nasal disease that has not been treated. Enhance wetting and warming, and ephedrine nasal drops before bedtime. If the patient develops allergic rhinitis, hormone drops can be applied to the nose.
9, fear Some patients just put on the nasal mask, exerting a very small CPAP pressure, they feel uncomfortable holding their breath, very afraid, called “claustrophobia”, not because the pressure is too high, but only a temporary psychological feelings. Patients should be asked to maintain a calm mood and breathe according to their usual rhythm. Add the “pressure delay” function or switch to BiPAP ventilator will be reduced.
10. Automatic interruption of treatment at night Some patients unknowingly remove the nasal mask in their sleep and cannot insist on applying it throughout the night, mostly in the early stage of treatment, which may be related to insufficient pressure setting. It may also be due to the set CPAP pressure being too high or the nasal mask leaking.
11, the impact of noise CPAP ventilator has a certain amount of noise, which sometimes affects the sleep of family members and patients. It can be replaced with a low noise CPAP ventilator, change the expiratory valve, put the ventilator into a well ventilated glass cover, and sleep with earplugs.
12. Long-term tolerance of CPAP ventilator in OSA patients The biggest problem in the use of CPAP is that some patients cannot adhere to its use for a long time, and the literature reports that the long-term usage rate is 60-80%. The performance of the machine, the severity of the patient’s condition, and the degree of awareness of the hazards of SAHS are all related to the ability to adhere to the application. Popularization of relevant scientific knowledge, experienced technical support, close follow-up during treatment and timely handling of various problems are the keys to ensure long-term patient application.
13.Treatment of CPAP treatment failure
The vast majority of SHAS patients can tolerate CPAP treatment, and the success rate of trial in the sleep laboratory is over 95%. It is very unlikely that treatment failure is really caused by the patient, and is mostly due to the failure of the physician to follow up and deal with the problems encountered by the patient in a timely manner. Therefore, before determining whether a patient can tolerate CPAP treatment, it is important to actively look for reasons for treatment failure. One, unskilled or incorrect use of CPAP; two, improper pressure setting; three, correct diagnosis; four, poor machine performance, unreasonable size or construction of the nasal mask; five, combination of other sleep disorders; and six, alcohol consumption or untreated nasal disorders.
The following measures are considered for true treatment failures: first, switching to more comfortable BiPAP ventilators and intelligent CPAP ventilators; second, jaw surgery, UPPP surgery or even tracheostomy; third, wearing an oral orthosis.
VI. CPAP treatment for special patients
1, central sleep apnea Less than 10% of central sleep apnea patients, mostly coexist with OSA, and CPAP treatment is also effective. For those who do not have high PaCO2 during the day, CPAP is suitable; for hypoventilated patients with CO2 retention during the day, the application of BiPAP ventilator is beneficial to reduce respiratory work and eliminate CO2z retention.
2.Patients with complete loss of upper teeth The lower part of the nasal mask depends on the support of the upper dental arch in order to prevent air leakage. The CPAP ventilator can only be used after the upper teeth are completely lost and dental implants or dentures are worn.
3. Apnea caused by hypothyroidism Taking thyroxine is the fundamental treatment. CPAP treatment before oral thyroid hormone can reduce hypoxia, improve cardiac function, and prevent hypoxemia caused by apnea from aggravating organ damage when hormone replacement therapy increases oxygen consumption of the body. If apnea disappears, CPAP therapy can be discontinued, but if it is still frequent, CPAP therapy should be applied for a long time.
4, COPD combined with OSA These patients are called overlap syndrome, CPAP treatment can be given at the same time continuous oxygen, COPD acute exacerbation, such as CO2 is significantly elevated, BiPAP ventilator should be used to prevent aggravation of CO2 retention. In addition, these patients often have poor tolerance to CPAP ventilator, and those with more intense cough should be treated with appropriate cough suppression.
5. Perioperative treatment for patients with SAHS Studies have shown that patients with OSA have an increased risk of asphyxia during preoperative anesthesia and postoperative recovery, and require appropriate monitoring and upper airway protection, especially for those undergoing surgery in and around the upper airway. For patients with severe SAHS undergoing elective surgery, CPAP treatment can be given for 1-2 weeks before surgery to correct hypoxia and sleep disorders and improve the combined complications such as hypertension. After the extubation of general anesthesia, sequential CPAP treatment can be performed in a timely manner.
6.Treatment of critically ill patients A few patients with SAHS may be admitted due to sudden exacerbation or serious complications such as acute respiratory failure, cardiovascular and cerebrovascular diseases. In most cases, non-invasive ventilation, especially BiPAP ventilator therapy, can achieve good results, and for a few who cannot cooperate, vomiting, coughing violently or unstable blood pressure, tracheal intubation or even tracheotomy may be required to convert to CPAP or BiPAP after the condition is stabilized. Special attention should be paid to the critically ill, who should be actively treated first, not first given sleep breathing monitoring.
The possible causes of drowsiness even after CPAP treatment are shown in Table 3. These patients can be divided into two categories: first, the drowsiness improves significantly at the beginning of CPAP treatment, but then returns after a period of treatment; second, the drowsiness does not improve during CPAP treatment. For these patients, an objective evaluation of their CPAP compliance should be performed, followed by an understanding of whether other sleep disorders, such as episodic sleeping sickness and periodic leg movement syndrome, are comorbid. The rate of combined SAHS in adults with episodic sleep disorders is as high as 50-80%, and it is common to see patients with episodic sleep disorders who are seen with SAHS. For the few patients who have ruled out these causes but still have subjective or objective sleepiness, drugs that can improve sleepiness such as modafinil can be administered concurrently and their application has been approved by the FDA.
Follow-up in the treatment of sleep apnea syndrome
Studies have shown that if a patient with SAHS only purchases a CPAP ventilator without follow-up, the success rate of long-term treatment is almost zero, while 80% of patients can be effectively treated with good follow-up.