Anesthetic Considerations for Patients With Obstructive Sleep Apnea.

Introduction:

Obstructive sleep apnea positively correlates with obesity and age, which are increasing in prevalence in recent times. Around 80 percent of (OSA) cases go undiagnosed. The increasing OSA cases are of major concern to anesthesiologists in delivering optimum care as these cases are closely linked to perioperative morbidity and mortality. The main challenges that increase the risk include,

• Potent upper airway obstruction.

• Difficult tracheal intubation.

• Postoperative respiratory depression and airway obstruction.

What Is Obstructive Sleep Apnea (OSA)?

The upper airway is obstructed in OSA while asleep, which makes the diaphragm and the chest muscles work hard to open the obstructed airway to get the air into the lungs. This is characterized by shallow breathing, snoring, and sometimes even breathing is stopped briefly and resumes with sudden arousal from sleep or a body jerk or loud gasp. This also causes disturbed sleep, and the patient may or may not be aware of it.

What Are the Causes of OSA?

Anatomical:

1. Central obesity (neck).

2. Micrognathia (unusually small lower jaw) or retrognathia (backward positioning of lower jaw).

3. Underdeveloped maxilla - Treacher-Collins syndrome (a genetic disorder associated with abnormal development of head and face).

4. Pharyngeal encroachment (swollen tonsils, tumors, swelling, large tongue).

Neuromuscular:

1. Bulbar palsies (a neurological disorder caused by damage to lower cranial nerves).

2. Neurological degenerative disorders.

3. Myopathies - muscle weakness. (Duchenne dystrophy - a genetic disorder in boys that causes muscle weakness).

Predisposing Factors:

1. Alcohol.

2. Sedative drugs.

3. Sleep deprivation.

4. Increased nasal resistance.

5. Hypothyroidism.

What Happens in OSA?

• When the negative airway pressure that develops during inspiration (breathing in) is greater than the muscular distending pressure, sleep apnea occurs, causing airway collapse. Obstruction can occur throughout the upper airway, above, below, or at the level of the uvula. Because there is an inverse relationship between obesity and the pharyngeal area, the smaller size of the upper airway and pharyngeal area in the obese patient causes more negative pressure to develop for the same inspiratory flow.

• In neurogenic diseases (diseases of the nervous system), insufficient neural drive to the airway, dilator muscles, or improperly coordinated drive to the diaphragm causes obstruction, leading to apnea.

• Obstruction can occur during any sleep state but is often noted during rapid eye movement (REM) sleep. However, nasal continuous positive airway pressure (CPAP) can improve the situation by keeping the pressure in the upper airways positive, thus acting as a ‘splint’ to maintain airway patency.

• If the pharyngeal collapse and the loss of pharyngeal muscle tone are partial but still great enough to cause the inspired air to flutter around the uvula and/or the tongue and/or the epiglottis, there will be snoring and hypopnea (shallow breathing). The presence of apnea and hypopnea during sleep is called sleep-disordered breathing (SDB).

• To survive each obstructive episode, the patient has to have some sort of arousal (mini-arousal) due to increased inspiratory effort and the response to arterial hypoxemia (low blood oxygen level) and hypercarbia (high blood carbon dioxide level).

• Each arousal causes sympathetic nervous system stimulation, which, in turn, leads to complications like sympathetic and pulmonary hypertension as well as myocardial ischemia (heart attack).

What Are the Signs and Symptoms of OSA?

The symptoms of OSA result from the consequences of obstructed breathing during sleep.

The individual experiences cycles of sleep, obstruction, arousal, restoration of breathing, and falling asleep again. This results in poor-quality sleep.

The signs include:

• Snoring.

• Excessive daytime sleepiness.

• Neck circumference >17.

• BMI (basal metabolic index) > 35.

Symptoms include:

• Morning headaches.

• Daytime sleepiness.

• Fatigue.

• Tiredness/lack of energy.

• Overt choking or gasping episodes.

• Associated hypertension.

How Is Obstructive Sleep Apnea Diagnosed?

Obstructive sleep apnea (OSA) can be diagnosed by:

• CT (computed tomography) scan.

• Pulse oximetry.

• Polysomnography test.

What Are the Risk Factors for OSA?

• Obesity.

• Hypertension.

• Coronary artery disease, myocardial dysfunction, arrhythmias.

• Pulmonary arterial hypertension.

• Gastroesophageal reflux.

What Are the Measures Taken to Manage OSA Patients Undergoing Surgery?

• Preoperative assessment and preparation.

• Intraoperative management.

• Postoperative pain management.

• Postoperative care.

Preoperative Assessment: A preoperative assessment becomes critical, as polysomnography (the yardstick in the diagnosis of OSA is not always affordable). Therefore, presumptive clinical diagnosis can be derived from the following :

• History of Sleep Disordered Breathing: arousal from sleep, daytime somnolence, airway difficulty with previous anesthetics, and morning headaches.

• Physical Examination: Body mass index, neck circumference (>17 inches in males and >16 inches in females), and presence of co-morbidities are checked. Furthermore, it should also include an evaluation of the airway, nasopharyngeal characteristics, as well as tonsil and tongue volume.

Presumptive diagnosis does play a major role as it helps in:

• Pre-procedure identification.

• Confirming and quantitating the diagnosis with a sleep study, thereby delaying surgery if necessary.

• Preparing appropriate perioperative management plan.

Preparation:

• Perioperative optimization with CPAP (continuous positive airway pressure) or BiPAP (bilevel positive airway pressure) therapy should be considered, particularly if OSA is severe. Patients who use CPAP devices at home should be advised to bring their devices to the facility for postoperative use.

• Other treatment modalities, such as corrective surgery, mandibular advancement devices, and oral appliances, should be considered when feasible.

• Patients with OSA may be extremely sensitive to all central nervous system depressant drugs, with a potential for upper airway obstruction or apnoea with even minimal doses of these drugs. So when prescribing preoperative medication with sedatives, including benzodiazepines or opioids, care should be taken to limit the usage as far as possible.

• It is recommended that a patient who had corrective airway surgery should be assumed to remain at risk for OSA complications unless the sleep studies and symptoms have normalized.

Intraoperative Management:

Intraoperative concerns to reduce the perioperative risk in OSA patients rely on the following:

• Selection of anesthetic technique.

• Airway management.

• Patient monitoring.

• Selection of Anesthetic Technique

  • Local or regional anesthesia should be preferred whenever possible. Regional anesthesia minimizes the effect of anesthetic agents on respiratory drive, potentially reducing or eliminating the impact of anesthetic agents on subsequent sleep apnoeas and maintaining arousal responses during apnoeic episodes; hence, airway management issues are also avoided.

  • Ventilation should be continuously monitored in patients requiring moderate sedation using capnography, as they are more prone to unseen airway obstruction. In patients using CPAP preoperatively, the use of CPAP during moderate sedation is beneficial.

  • A secure airway in general anesthesia is better than an obscure airway in deep sedation, especially for surgeries that tend to mechanically limit the airway passage.

  • As opioids are associated with pronounced respiratory depression, patients with OSA benefit from prophylactic multimodal analgesia techniques using nonopioid analgesics, including local/regional anesthesia, like Acetaminophen, NSAIDs, Ketamine, and alpha-2- agonists.

  • Residual muscle relaxation should be adequately antagonized; otherwise, minimal muscle relaxants can affect the airway muscles and result in airway obstruction.

• Airway Management

  • Not all patients with OSA are difficult to intubate. However, patients with OSA can be assumed to have redundant or excess oropharyngeal tissue, macroglossia, and so on. Thus, considerable care should be exercised in managing the airway in these patients.

  • If an “awake” tracheal intubation is planned, sedatives and opioids must be utilized judiciously. Thus, proper preparation will depend on thorough topical and nerve-block anesthesia of the upper airway.

  • If intubation is to be done with the patient asleep, it is important to fully oxygenate the patient because the obese patient with a relatively small functional residual volume and high oxygen consumption desaturates much more rapidly during obstructive apnoea compared to a normal patient.

  • Laryngoscopy must be performed in the optimal “sniff” position.

  • Mask ventilation must be performed optimally, which may require two anesthesia providers using two or three-handed bilateral jaw thrust and mask seal. Options to come out of “cannot ventilate, cannot intubate” situations must be immediately available at the anesthetizing location.

• Extubation:

  • The risk of airway obstruction following extubation is increased in OSA patients and is further increased when nasal packing is done following nasal surgery; therefore, packing around a nasopharyngeal airway (creating a passage for gas exchange) should be considered.

  • Patients should be extubated when awake and in a semi-upright position until and unless contra-indicated by a medical condition or a surgical procedure, as they are at increased perioperative risk from OSA.

• Patient Monitoring

  • Patients with sleep apnoea may be at increased risk for coronary artery disease or myocardial dysfunction; monitoring for myocardial ischemia and rhythm disturbances is crucial.

  • Transesophageal echocardiography is increasingly being used for noncardiac surgery and may be useful in selected patients with sleep apnoea because it can provide insight into heart function and pulmonary artery pressures.

  • If the patient with OSA has morbid obesity, an intra-arterial catheter may be helpful as noninvasive blood pressure monitoring is unreliable or not possible.

• Postoperative Pain Management

  • In the postoperative setting, sleep architecture is disturbed. During the first three days after surgery, pain scores are highest, and deep stage 3 and 4 NREM and REM sleep are often suppressed. High levels of pain result in increased analgesic requirements; thus, the danger of life-threatening apnoea during drug-induced sleep is increased.

  • Opioids can cause airway obstruction by pharyngeal collapse, as well as poor ventilation, leading to hypoxemia and hypercapnia.

  • In the next three days, deep REM sleep rebounds. During this phase of recovery, the danger of natural deep sleep-induced apnoea is increased.

  • Thus, the risk of prolonged apnoea during sleep is increased for approximately one week for the postoperative OSA patient.

  • Nonsteroidal anti-inflammatory drugs and other modalities ( for example, ice and transcutaneous electrical nerve stimulation) should be considered to reduce opioid requirements.

• Postoperative Care

  • Recurrent hypoxemia may be better treated with CPAP (continuous positive airway pressure) along with oxygen rather than oxygen alone. Patients who use CPAP preoperatively should use CPAP postoperatively, as it may reduce the risk of airway obstruction and respiratory depression. Continuous positive airway pressure, however, should be used only after patients are awake, alert, and feasible.

  • If possible, patients should be placed in non-supine positions (head end of bed raised 30°) throughout the recovery process. Patients are under constant vigilance as long as they are under the high-risk category.

  • In the case of an obese OSA patient, when parameters of the BMI (body mass index) and AHI (apnea-hypopnea index) are mild, the patient can be shifted to the ward.

  • When one of the factors of associated cardio-pulmonary disease is severe, the patient is shifted to ICU (intensive care unit).

  • The ASA (American Society of Anesthesiologists) has recommended regulations for the perioperative management of Patients with obstructive sleep apnea” suggest OSA patients be monitored for three hours longer than their non-OSA counterparts before discharge from the facility.

Conclusion

Timely diagnosis of OSA conditions (which in 80 to 90 percent of cases goes undiagnosed) in people who are at risk can help the doctor in giving the optimum care. Having adequate knowledge of the clinical implications and diagnosis of OSA is crucial for anesthesiologists to reduce the risks associated with operating OSA patients and improve perioperative care.