A Study to Compare Adaptive Support Ventilation vs. Volume Controlled Ventilation for Management of Respiratory Failure in Patients With Neuroparalytic Snake Envenomation

Snake envenoming is a common medical emergency encountered in the tropical countries, and an estimated 35,000 -50,000 people die of snakebite every year in India. The bites of elapid snakes cause predominantly neurotoxicity, which manifests as ocular and bulbar paralysis, and paralysis of the muscles of respiration, with resultant respiratory failure. The management of these patients includes ventilatory support and administration of snake anti-venom. Respiratory failure requiring mechanical ventilatory support is a frequent cause of admission to the intensive care unit (ICU). Mechanical ventilation is a life-saving intervention, and once there is improvement of the underlying indication, it can be withdrawn abruptly in the majority. However, approximately 20-30% of patients still require gradual discontinuation (ie, weaning). This process is not only difficult in patients with chronic respiratory diseases and acute neuromuscular disorders, such as neurotoxic snake bite, but is also associated with important complications, such as nosocomial pneumonia, prolonged ICU stay, and even mortality, especially in those with persistent weaning failure.

Adaptive support ventilation (ASV) is a closed-loop ventilation mode designed to provide a user-set minimum minute ventilation in intubated patients, either actively breathing or passively ventilated. ASV automatically selects a target ventilatory pattern based on user inputs [patient's predicted body weight (PBW), minimum minute volume, and pressure limit] and respiratory mechanics data from the ventilator monitoring system (respiratory system expiratory time constant and dynamic compliance). The algorithm selects ventilatory parameters so as to minimize total work of inspiration, and the ventilator continuously adapts to match changes in respiratory mechanics by using automatic controls for level of inspiratory pressure above positive end-expiratory pressure (PEEP), frequency, and inspiratory time of ventilator-initiated breaths.

In most studies, ASV has been used only in the weaning phase, and patients were ventilated with conventional modes until weaning. However recent studies suggest its role in primary ventilation in the initial phase of respiratory failure. Previous use of ASV in patients with acute respiratory distress syndrome has been described from our center and the use of ASV was equally efficacious to conventional mode of ventilation (volume control). In another study the use of ASV in comparison to pressure control ventilation in patients with acute respiratory failure reduced the weaning duration and total duration of mechanical ventilation. Because ASV can be used from intubation to extubation, it may also offer some advantages before the weaning phase in patients with respiratory failure. Therefore, we hypothesize that ASV may shorten the total mechanical ventilation (MV) duration, weaning duration, and increase the weaning success rates when compared with conventional ventilation in the management of patients with neuroparalytic snake envenomation.