Patient-Ventilator Dyssynchrony Induced by Mechanical Ventilation in a Dog With Tetanus: The Reverse Triggering
C. Stefanello; A. Botto; G. Grossi; M.S. Calabria; Rocchi P.M.; Pelizzola M.
Background
Patient-ventilator dyssynchronies are a serious problem in the intensive care unit. Reverse triggering (RT) is a dyssynchrony occurring in mechanically ventilated patients that might be under-recognized and potentially causing lung injury.
Case Presentation
A 9-year-old, female English setter (BW 14 kg) was presented for lateral recumbency and marked extensor rigidity of four limbs. Complete blood works and x-rays were unremarkable. A diagnosis of tetanus was made based on the clinical signs. The dog progressively showed hypoventilation requiring mechanical ventilation (MV). After 72 hours of controlled ventilation the anesthesia was titrated (only midazolam CRI 0.2–0.5 mg/kg/h) and a pressure regulated volume control ventilation was set (tidal volume 210 ml, bpm 15, inspiratory flow trigger 1 l/min). After one day, the MV was still completely controlled because the patient was unable to start a breath by herself. A drop in the airway pressure (Paw) waveforms occurred in a repetitive pattern that was associated to an increase in flow waveforms and in tidal volume, greater than the passive ventilator breaths. To better analyze the patient spontaneous effort esophageal pressure was evaluated showing a typical pattern of a passive patient during positive pressure ventilation. The esophageal pressure waveforms were positive during inspiration except for a drop corresponding to the drop in Paw waveforms suggesting the activation of the inspiratory muscles. A RT was suspected; therefore, sedation and ventilation supports were reduced causing the resolution of the dyssynchrony. The dog was euthanized at day 7 for financial constraints.
New/Unique Information
RT is a patient inspiratory effort that is delayed in timing relative to the passive expansion of the lungs and chest wall by machine-initiated breaths. Several potential mechanisms may underlie RT: ventilator settings, respiratory drive, level of consciousness, sedatives and opiates. This case shows how prolonged RT can potentially cause excessive tidal volume ventilation predisposing to increased risk of volutrauma. The waveforms analysis is essential to detect this dyssynchrony and optimize the ventilation to avoid potential lung injury. This is the first report of RT in a veterinary patient. Further studies are needed to understand predisposing factors, clinical effects and possible management of RT.
E-mail: angelica.botto.ab@gmail.com