“Respiratory arrest”的意思、由来-开放百科全书

Respiratory arrest is caused by apnea (cessation of breathing) or respiratory dysfunction severe enough it will not sustain the body (such as agonal breathing). Prolonged apnea refers to a patient who has stopped breathing for a long period of time. If the heart muscle contraction is intact, the condition is known as respiratory arrest. An abrupt stop of pulmonary gas exchange lasting for more than five minutes may damage vital organs especially the brain, possibly permanently. Lack of oxygen to the brain causes loss of consciousness. Brain injury is likely if respiratory arrest goes untreated for more than three minutes, and death is almost certain if more than five minutes.

Damage may be reversible if treated early enough. Respiratory arrest is a life-threatening medical emergency that requires immediate medical attention and management. To save a patient suffering from respiratory arrest, the goal is to restore adequate ventilation and prevent further damage. Management interventions include supplying oxygen, opening the airway, and means of artificial ventilation. In some instances, an impending respiratory arrest could be predetermined by signs the patient is showing, such as the increased work of breathing. Respiratory arrest will ensue once the patient depletes their oxygen reserves and loses the effort to breathe.

Respiratory arrest can be used interchangeably with complete respiratory failure. The former refers to the complete cessation of breathing, while respiratory failure is the inability to provide adequate ventilation for the body’s requirements. However, both lead to death without intervention. Respiratory arrest is also different from cardiac arrest, the failure of heart muscle contraction. If untreated, one may lead to the other.

Signs and symptoms

One common symptom of respiratory arrest is cyanosis, a bluish discoloration of the skin resulting from an inadequate amount of oxygen in the blood. If respiratory arrest remains without any treatment, cardiac arrest will occur within minutes of hypoxemia, hypercapnia or both. At this point, patients will be unconscious or about to become unconscious.^[1]

A condition that frequently precedes respiratory arrest is respiratory distress, which is a gradual, subtle imbalance in patient response that can result in eventual respiratory failure and arrest. Symptoms of respiratory compromise can differ with each patient. Complications from respiratory compromise are increasing rapidly across the clinical spectrum, partly due to expanded use of opioids combined with the lack of standardized guidelines among medical specialties. While respiratory compromise creates problems that are often serious and potentially life-threatening, they are almost always preventable with the proper tools and approach. Appropriate patient monitoring and therapeutic strategies are necessary for early recognition, intervention and treatment.^[2]

Impending respiratory arrest

Before respiratory arrest officially occurs, patients may experience some neurologic dysfunctions, such as feeling agitated, confused, and struggling to breathe. Tachycardia, sweating, intercostal retractions, and sternoclavicular retractions may occur as well. Patients who have an impaired central nervous system or respiratory muscle weakness may experience irregular patterns of respiration and feeble, gasping attempts to breathe. Patients who developed respiratory arrest from the cause of a foreign body in the airway may choke, call the attention of people nearby to their neck, and give out a harsh sound. By monitoring a patient’s oxygen and carbon dioxide levels, practitioners can prepare for ensuing respiratory arrests in patients. Infants that are under three months may develop respiratory arrest without any signs of warning and must be carefully taken care of. The development of respiratory arrest could come from infection, metabolism disorders, or respiratory fatigue. Another group of patients that should be on the watch list are asthmatics or patients with other chronic lung diseases. They can be become hypercapnic or tired after bouts of respiratory distress. These symptoms will lead to apnea without any signs of warning.^[3]

Causes

Diagnosis

Diagnosis requires clinical evaluation. If there was a foreign body obstructing the airway, the first option would be to locate the foreign body. The presence of a foreign body can be detected from resistance to ventilation from the mouth-to-mask or bag-valve-mask ventilation. The foreign body can be extracted during laryngoscopy for endotracheal intubation.^[7]

Clearing and opening the upper airway

The first step to diagnosing patient is to clear and open the upper airway with correct head and neck positioning to determine the cause of respiratory arrest. The practitioner must lengthen and elevate the patient’s neck until the external auditory meatus is in the same plane as the sternum. The face should be facing the ceiling. The mandible should be positioned upwards by lifting the lower jaw and pushing the mandible upward. If a foreign body can be detected, the practitioner may remove it with a finger sweep of the oropharynx and suction. It is important that the practitioner does not cause the foreign body to be lodged even deeper into the patient’s body. Foreign bodies that are deeper into the patient’s body can be removed with Magill forceps or by suction. A Heimlick maneuver can also be used to dislodge the foreign body. The Heimlick maneuver consists of manual thrusts to the upper abdomen until the airway is clear. In conscious adults, the practitioner will stand behind the patient with arms around the patient’s midsection. One fist will be in a clenched formation while the other hand grabs the fist. Together, both hands will thrust inward and upward by pulling up with both arms.^[8]

Bag-valve-mask (BVM) ventilation devices

Resistance to bag valve mask may suggest presence of a foreign body that is obstructing airways and commonly used as a diagnostic tool and treatment for respiratory arrest. The bag-valve-mask device has a self-inflating bag with a soft mask that rests on the face. When the bag is connected to an oxygen supply, the patient will receive 60 to 100% of inspired oxygen. The purpose of bag-valve-mask is to provide adequate temporary ventilation and allow the body to achieve airway control by itself. However, if the bag-valve-mask is left on for more than five minutes, air may be introduced into the stomach. At that point, a nasogastric tube should be inserted to take the accumulated air out. During this process, practitioners must carefully position and maneuver the bag-valve-mask in order to keep airways open. An oropharyngeal airway is used during bag-valve-mask ventilation to prevent oropharynx soft tissues from blocking the airway. An oropharyngeal airway may cause gagging and vomiting. Therefore, an oropharyngeal airway must be sized appropriately. It should be as long as distance between corner of patient’s mouth and angle of the jaw is calculated correctly. For children, pediatric bags can be used. Pediatric bags have a valve that limits peak airway pressures to around 35–40 cm of water. Practitioners must tweak valve settings to accurately determine each of their patients to avoid hypoventilation or hyperventilation.^[9]

Treatment

Treatment involves clearing the airway, establishing an alternate airway, and providing artificial ventilation that can include modes of mechanical ventilation. There are many ways to provide an airway and to deliver breathing support. The list below includes several options.

Laryngeal mask airways

The laryngeal mask airway (LMA) is a tube with an inflatable cuff. A laryngeal mask airway can be positioned in the lower oropharynx to prevent airway obstruction by soft tissues and to create a safe channel for ventilation. The laryngeal mask airway is the standard rescue ventilation when endotracheal intubation cannot be accomplished. To insert the laryngeal mask airway into the patient, the deflated mask should be pressed against the hard palate, rotated past the base of the tongue, and reaching the pharynx. Once the mask has been placed in the correct position, the mask can be inflated. Some benefits of the laryngeal mask airway include minimization of gastric inflation and protection against regurgitation. A potential problem the laryngeal mask airway poses is that over inflation will make the mask more rigid and less able to adapt to the patient’s anatomy, compressing the tongue and causing tongue edema. In that case, the mask pressure should be lowered or a larger mask size should be used. If non-comatose patients are given muscle relaxants before the insertion of the laryngeal mask airway, they may gag and aspirate when the drugs are worn off. At that point, the laryngeal mask airway should be removed immediately to eliminate the gag response and buy time to start at new alternative intubation technique.

Endotracheal intubation

A tracheal tube is inserted into the trachea through the mouth or nose. Endotracheal tubes contain high-volume, low-pressure balloon cuffs to minimize air leakage and the risk of aspiration. Cuffed tubes were made originally for adults and children over 8 years old, but cuffed tubes have been used in infants and younger children to prevent air leakage. Cuffed tubes can be inflated to the extent needed to prevent air leakage. The endotracheal tube is a guaranteed mechanism to secure a compromised airway, limit aspiration, and bring about mechanical ventilation in comatose patients. The endotracheal tube is a great method for patients who are comatose, have an obstructed airway, or need mechanical ventilation. The endotracheal tube also allows suctioning of the lower respiratory tract. Drugs that can be inserted through the endotracheal tube during cardiac arrest are discouraged. Before intubation, patients need correct patient positioning and ventilation with 100% oxygen. The purpose of ventilation with 100% oxygen is to denitrogenate healthy patients and prolong the safe apneic time. Tubes with an internal diameter of over 8mm are acceptable for most adults. Insertion technique includes visualizing the epiglottis, the posterior laryngeal structure, and not passing the tube unless tracheal insertion is ensured.^[10]

Surgical airway

Surgical entry is required when the upper airway is obstructed by a foreign body, massive trauma has occurred, or if ventilation cannot be accomplished by any of the aforementioned methods. The requirement of the surgical airway is commonly known as the response to failed intubation. In comparison, surgical airways require 100 seconds to complete from incision to ventilation compared to laryngeal mask airways and other devices. During emergency cricothyrotomy, the patient lies on his back with neck extended and shoulders backward. The larynx is held in one hand by the practitioner while the other hand is holding a blade to incise the skin through the subcutaneous tissue and into the midline of the cricothyroid membrane to access the trachea. A hollow tube is used inserted into the trachea to keep the airway open. A tracheal hook is used to keep the space open and prevent retraction. Complications may include hemorrhage, subcutaneous emphysema, pneumomediastinum, and pneumothorax. Cricothyrotomy is used as emergency surgical access due to being fast and simple. Another surgical airway method is called tracheostomy. Tracheostomy is done in the operating room by a surgeon. This is the preferred method for patients requiring long-term ventilation. Tracheostomy uses skin puncture and dilators to insert the tracheostomy tube.^[11]

Drugs to aid intubation

Patients with respiratory arrest can be intubated without drugs. However, patients can be given sedating and paralytic drugs to minimize discomfort and help out with intubation. Pretreatment includes 100% oxygen, lidocaine, and atropine. 100% oxygen should be administered for 3 to 5 minutes. The time depends on pulse rate, pulmonary function, RBC count, and other metabolic factors. Lidocaine can be given in 1.5 mg/kg IV a few minutes before sedation and paralysis. The purpose of administering lidocaine is to blunt the sympathetic response of an increased heart rate, blood pressure, and intracranial pressure caused by laryngoscopy. Atropine can be given when children produce a vagal response, evidenced by bradycardia, in response to intubation. Some physicians even give out vecuronium, which is a neuromuscular blocker to prevent muscle fasciculations in patients over 4 years old. Fasciculations may result in muscle pain on awakening. Laryngoscopy and intubation are uncomfortable procedures, so etomidate may be delivered. Etomidate is a short-acting IV drug with sedative analgesic properties. The drug works well and does not cause cardiovascular depression. Ketamine is an anesthetic that may be used as well, but it may cause hallucinations or bizarre behavior upon awakening. Thiopental and methohexital may be used as well to provide sedation, but they tend to cause hypotension.^[12]

Volume-cycled ventilation

The purpose of mechanical ventilators is to deliver a constant volume, constant pressure, or a combination of both with each breath. Any given volume will correspond to a specific pressure on the pressure-volume curve and vice versa in any case. Settings on each mechanical ventilator may include respiratory rate, tidal volume, trigger sensitivity, flow rate, waveform, and inspiratory/expiratory ratio. The volume-cycled ventilation includes the volume-control function and delivers a set tidal volume. The pressure is not a fixed number but it varies with resistance and capacitance of the respiratory system. The volume-cycled ventilation is the simplest and most efficient of providing ventilation to a patient’s airway compared to other methods of mechanical ventilation. Each inspiratory effort that is beyond the set sensitivity threshold will be accounted for and fixed to the delivery of the corresponding tidal volume. If the patient does not breathe enough, then the volume-cycled ventilation will initiate a breath for the patient to bring up the breathing rate to the minimum respiratory rate. The synchronized intermittent mandatory ventilation (SIMV) is a similar method of mechanical ventilation that also delivers breaths at a fixed rate and volume that corresponds to the patient’s breathing. Unlike the Volume-Cycled Ventilation, patient efforts above the fixed rate are unassisted in the synchronized intermittent mandatory ventilation (SIMV).^[13]

Pressure-cycled ventilation

The pressure-cycled ventilation includes pressure control ventilation and pressure support ventilation. Both methods offer a set inspiratory pressure. The tidal volume varies depending on the resistance and elastance of the respiratory system. Pressure-cycled ventilation can help alleviate symptoms in patients with acute respiratory distress syndrome by limiting the distending pressure of the lungs. The pressure control ventilation is specifically a pressure-cycled form of assist-control ventilators. Assist-control ventilators describe a mode of ventilation that maintains a minimum respiratory rate regardless of whether or not the patient initiates a spontaneous breath. Each inspiratory effort that is beyond the sensitivity threshold delivers full pressures support for a fixed inspiratory time. There is maintenance of a minimum respiratory rate. In the pressure support ventilation, the minimum rate is not set. Instead, all breaths are triggered by the patient. The way that the pressure support ventilation works is by assisting the patient with a constant pressure until the patient’s inspiratory flow fallows below a threshold. The longer, deeper inspiratory flows by the patient will result in a larger tidal volume. This method of mechanical ventilation will help patients assume more work of breathing.^[14]

Noninvasive positive pressure ventilation (NIPPV)

Noninvasive positive pressure ventilation is the delivery of positive pressure ventilation through a tight-fitting mask that covers the nose and mouth. It assists patients who can spontaneously breathe. Noninvasive positive pressure ventilation delivers end-expiratory pressure with a volume control setting. There are two ways that noninvasive positive pressure ventilation can be delivered: continuous positive airway pressure or bilevel positive airway pressure. In continuous positive airway pressure, constant pressure is maintained throughout cycles of respiration with no additional inspiratory support. In bilevel positive airway pressure, both expiratory positive airway pressure and inspiratory positive airway pressure are set by the physician. Noninvasive positive pressure ventilation should not be administered to people who are hemodynamically unstable, gastric emptying impaired, bowel obstructed or pregnant. In these circumstances, swallowing large amounts of air will result in vomiting and possibly death. If frequent arrhythmias, myocardial ischemia and shock arrhythmias occur, practitioners should change delivery to endotracheal intubation or conventional mechanical ventilation. People who should not use noninvasive positive pressure ventilation include obtunded patients or ones with secretions. Noninvasive Positive Pressure Ventilation can be used in an outpatient setting for patients with obstructive sleep apnea.^[15]