Neonatal Ventilators : Frequently Asked Questions

Q1.What is sychronised intermittent manadatory ventilatioin (SIMV)?
SIMV is a mode where ventilator breaths are delivered at fixed rate but are synchronised with the patient’s own breath. However, unless the inspiratory times are indentical the patient may start with exhalation while ventilator is still in the inspiratory phase, resulting in partial asynchrony.

Q2. What is patient triggered ventilation mode (assist /control ventilation)?
PTV is a combination mode in which the ventilator delivers a positive pressure breath in response to the patient’s effort (assist), provided it exceeds the preset threshold criteria. This mode also provides the safety of guaranteed mechanical breath rates as set by the operator (backup rate) if no patient effort is detected (control). The backup control rate ensures a minium mandatory minute ventilation in case the patient stops making an inspiratory effort.

Q3.What are the advantages of PTV ?
PTV requires the least amount of patient effort and produces improved oxygenation at the same mean airway pressure . There is less exposure to oxygen and lower pressures are requires for ventilation.

Q4. What is pressure support ventilation (PSV) and how does it work ?
PSV is defined as patient controlled ventilation which is gererally flow –cycled . This is meant to assist the patient’s spontaneous breathing with an inspiratory pressure “Boost’. In PSV, once the breath is triggered by patient’s inspiratoty effort , a preset system pressure is rapidly achieved and maintained throughout inspiration by adjustment of machine inspiratory flow. The inspiration ends when the inspiratory flow falls below a preset level.

Q5. Are there any advantages of using PSV mode ?
PSV reduces the work of breathing created by the resistive forces of endotracheal tubes and the ventilatory circuit . It is mostly used as weaning mode, but can be used as primary modality in patients with respiratory failure in presence of respiratory drive . PSV is better customized to support and synchronise with the patient’s effort because the patient has control of both the inspiratory flow rate and inspiratory time.

Q6. Do we need high frequency ventilators in India ?
Conventional ventilators are useful in nearly 90-95% neonates with respiratory failure. Rarely , in a situation of conventional ventilator failure , as in PPHN or when the baby develops pulmonary air leaks (Pulmonary interstitial emphysema, Pneumothorax), high frequency ventilator is indicated. HFV would be justified in units which have more than 80 percent intact survival rates for ventilated babies between 1 and 1.5 kgs.

Q7. Can I run a ventilator with out a compressor , only on oxygen cylinders ?
One needs to have compressed air at 45-55 PSI pressure from central source or a compressor to run a ventilator . Big oxygen cylinders, kept in series as “mini manifold” outside NICU may provide oxygen sources if centralized oxygen facilities are lacking in the unit. Remember, these cylinders will need frequent replacement depending on the consumption of oxygen.

Q8.What are the common brands of neonatal ventilators available in the Indian market?
The common brands of neonatal ventilators available in India are summarized below along with their costs and upgradability :-
(Abstracted from “Neonatal Equipment, 2nd Ed, 2001 by Deorari and Paul)