Mechanical ventilation has undergone many changes, particularly with the creation of additional modes of ventilation. Automatic tube compensation (ATC) is one of the newer, more unique modes. It is designed to precisely overcome the calculated resistance of the airway by adjusting the delivered pressure in accordance to flow rates generated by the patient. We report a case of respiratory myoclonus with unusual results while utilizing ATC.
A thirty-six year old male presented to the emergency department in cardiopulmonary arrest and was successfully resuscitated after thirty minutes. He developed multiple organ failure. Head CT did not reveal any acute neurological process. Examination revealed minimal brainstem activity. Within twenty-four hours, vasopressors were weaned off and hepatic transaminases normalized, but his renal failure required hemodialysis and his respiratory failure necessitated continued mechanical ventilatory support. Seizure activity was noted on the second hospital day, confirmed by EEG, and resolved with anticonvulsant therapy. Medically, the patient stabilized, but continued to have severe anoxic encephalopathy. A tracheostomy (8.0 mm) was performed for airway protection and maintenance of mechanical ventilatory support. Four weeks after his admission, he developed myoclonus involving his right sternocleidomastoid and intercostal muscles and diaphragm. These were refractory to benzodiazepines, dantrolene, and phenytoin. While receiving pressure support ventilation of 10 cm H2O, tidal volumes of 350 ml were produced by the myoclonic jerks. This continued for several days while efforts were made to wean mechanical ventilation. Unexpectedly, during a spontaneous breathing trial utilizing automatic tube compensation, the myoclonic contractions produced peak inspiratory pressures (PIP) of 70 cm H2O and tidal volumes in excess of one liter. When the % support was reduced from 100% to 20%, the PIP decreased to 25 cm H2O and tidal volumes of 700 ml.
Respiratory myoclonus is a rare phenomenon. It is also known as Leeuwenhoek’s disease, as Antoine van Leeuwenhoek was the first to describe it in 1723. Fewer than one hundred cases have been reported and only four of which were involving patients on mechanical ventilation. In most cases, discomfort due to diaphragmatic “fluttering” is described, but actual impairment of ventilation is not. ATC is designed to deliver positive pressure proportional to the inspired flow. This pressure overcomes the estimated resistance of an artificial airway, which is proportional to the tube length and internal diameter as well as the flow rate. We postulate that in the ATC mode, sudden respiratory mycoclonic contractions can produce an abrupt, marked increase in flow rate that generates very high airway pressure and correspondingly large tidal volume. A literature review and discussion with Nellcor Puritan Bennett representatives suggests ours is the first reported case of this phenomenon.
Respiratory myoclonus can produce high inspiratory flow rates that generate excessive pressure and tidal volumes when utilizing automatic ube compensation.
J.C. Perry, None.