Pseudocholinesterase deficiency
Overview
A rare disorder where deficiency of the enzyme pseudocholinesterase results in prolonged apnea when succinylcholine (muscle relaxant used during surgery) is administered.
Symptoms
* Prolonged apnea following surgery * Respiratory difficulty during surgery
Causes
o Much apnea is physiologic and normal –Post-sigh apnea is normal –Newborns, especially premature babies, may have irregular breathing as their respiratory control center matures –Periodic breathing at high altitude * Prolonged apnea is respiratory arrest, and inadequate ventilation is respiratory failure, and both require immediate intervention * Apnea may be divided into central, obstructive, and mixed apnea; etiologies vary by age * Central apnea in infants –Apnea of prematurity –Congenital central hypoventilation syndrome (CCHS, or Ondine curse) –CNS depression (sepsis, shock, drug effect, RSV, seizure or postictal state) –Respiratory muscle failure (e.g., myotonia, infantile botulism) o Obstructive apnea in infants –Upper airway obstruction (severe laryngomalacia, choanal atresia, macroglossia, micrognathia, subglottic stenosis or web, laryngospasm) –Lower airway: Rarely causes obstructive apnea (tracheal stenosis, rings, slings) o Central apnea in children –CNS (drug-induced CNS depression, CCHS, abnormal CNS brainstem anatomy and function, sepsis/septic shock) –Respiratory muscle failure (muscular dystrophy, myotonia, myasthenia gravis) o Obstructive apnea in children –Upper airway obstruction, obstructive sleep apnea syndrome (OSAS), tonsillar and adenoidal hypertrophy, macroglossia, micrognathia, subglottic stenosis, laryngospasm o Mixed apnea –CNS depression and decreased upper airway tone –Gastroesophageal reflux leading to increased parasympathetic activity and/or laryngospasm –Respiratory muscle failure and adenoidal hypertrophy o Apparent life-threatening events (ALTE) o Trauma may cause apnea at any age
Diagnosis
The most important diagnostic test is an all-night polygraphic recording (polysomnography). This will differentiate between obstructive and nonobstructive sleep apnea. If obstructive sleep apnea is suspected, a referral should be made to an ear, nose, and throat specialist. If there are abnormalities on the neurologic examination, a neurologic consultation should be sought. If idiopathic nonobstructive sleep apnea is suspected, the patient should be referred to a pulmonologist. A therapeutic trial of continuous positive airway pressure may be done. Some cases should have evaluation for a pituitary tumor, a thyroid profile, and a trial of tricyclic drugs and progesterone.
Treatment
* Central apnea therapy depends on cause; an infant may need no more than monitoring or supplemental O2. * Severe central apnea, especially with respiratory muscle failure, may need to be treated with artificial respiration (via nasal/face mask or tracheotomy tube) * CCHS may be treated long term with diaphragmatic pacing * Other causes of central apnea require targeted therapy (i.e., antibiotics for sepsis, O2 for severe hypoxia) * Severe obstruction is bypassed with tracheostomy, or overcome with positive pressure ventilation * Weight loss is an important adjunct in treating severe OSAS * Respiratory stimulants (e.g., caffeine) may help some babies with apnea of prematurity * Vigorously treat causative factors (e.g., GERD) * Apnea monitors are of little proven value in the management or treatment of apnea, yet frequently used