Mechanical ventilation of the neonate could be defined as movement of gas into and out of the lung by an external source connected directly to the patient via an endotracheal tube or tracheostomy.
The origins to the modern day ventilation can be traced to the Old Testament(Goldsmith JP, 2011) with description of the mouth to mouth resuscitation technique. Description of endotracheal intubation by
Hippocrates in 400BC is one of the earliest evidence to support artificial breathing support. This was followed by report from Paracelsus after 2000 years using bellows and oral tube.
In 1879, a simple rubber bulb connected to a tube inserted into the upper airway ‘aerophore pulmonaire’, was the first device specifically designed for suction and short-term ventilation of newborn infants. Alternate compression and suction provided fresh air and ventilation achieved by passive exhalation.
Later foot compression of the bellows to provide longer term positive pressure ventilation was published by O’Dwyer in 1887 (O'Dwyer, 1885).
Bloxsom (Bloxsom, 1950) in 1950, suggested it was the oxygen uptake in the respiratory tract which was the most important mechanism to initiate respiration. However, he felt that change of pressures aided this mechanism. He believed that positive pressure is the only mechanism
to overcome the respiratory resistance. He argued that tracheal
intubation was fraught with danger of lung perforation and suggested use of positive pressure air lock. This machine produced alternate positive and negative pressure in a tightly sealed cylindrical steel chamber.
The earliest use of servo controlled ventilator is reported by Donald & Lord (Donald and Lord, 1953). Their case series reported a device that actively assisted lung expansion and rapid oxygenation. They reported success by means of achieving lung expansion. This was an apt
inference and not merely limiting to success to survival or death. In an era when there was high infant mortality in the first month of life, largely due to prematurity, atelectasis and intracranial haemorrhage and health care largely ‘laisser-faire or let them be’, good nursing, airway clearance and oxygen supplementation was a breakthrough. They used clinical spirometry to assess respiratory efficiency in babies with atelectasis, a photoelectric pick up mechanism to trigger the respirator and synchronise to the infant’s spontaneous breathing to ‘amplify’ spontaneous breathing efforts. The infant thus controlled the machine with feeble respiratory efforts. Solenoid operated valves reduced the inertia of the cranks, bellows and pistons.
The Kennedy tragedy in 1963 boosted research and development in the field of premature care and respiratory support. Atelectasis of the
open, CPAP was delivered via endotracheal tube with remarkable improvement. Until then most of the respiratory support was provided by adult machines, modified for use in babies, and utilised intermittent gas flow delivered by the ventilator.
In 1971, using continuous gas flow Kirby and co-workers developed a new generation neonatal ventilator. This device not only helped in
spontaneous breathing between the mandatory breaths, but also helped prevent dead space breathing noted in the intermittent gas flow types. Spontaneous breathing also overcame the need for paralysis and the problem of babies ‘fighting the ventilator’. This combination of
spontaneous breathing under constant flow and intermittent mechanical breaths was termed Intermittent Mandatory Ventilation (IMV) and
became the standard method of neonatal ventilation(KIRBY et al., 1972)
Over the decades the technology to support newborn breathing has seen an exponential progression. Current generation of neonatal ventilators have undergone series of modifications and refinements. This includes improving response times and delivering accurate tidal volume consistently, a problem with the old generation ventilators. Now the microprocessor technology with complex computer algorithms has replaced the use of solenoid activated switch for delivery of gas and accurate mixing and stopwatch to control inspiratory time. The new generation ventilators utilise computer based safety mechanisms and
have replaced spring-loaded manometer for monitoring peak inspiratory pressure used in the first generation ventilators.
With increasing survival of premature babies and technological advances, the survival of premature babies has increased. This has resulted into a new complication of prematurity, bronchopulmonary dysplasia (BPD). BPD was first described by Northway et.al (Northway WH, 1967), seen in moderate premature babies and related to the iatrogenic reason of ventilation induced lung injury from the ventilation practices. Designs to minimise this led to alternate forms of respiratory support- High Frequency Ventilation and patient triggered ventilation modalities. The current generations of ventilators allow synchronising infant’s breath with ventilator and allow infant to control the ventilation. The use of pulmonary graphics and judicious use of lung distension through breath to breath monitoring allow minimising iatrogenic lung injury through artificial ventilation(Donn and Sinha, 2006).
For respiratory management of premature babies the discovery of exogenous surfactant complemented the advances in ventilation strategies. The pioneering work of Avery and Mead (Avery, 1959) reported surfactant deficiency was critical for development of lung atelectasis. This breakthrough has clearly shown to have a significant impact on newborn survival along with antenatal steroid treatment to prevent surfactant deficiency.
Although improved technology and their availability has led to newer ventilation techniques, this has not led to a significant change in the neonatal outcomes (Costeloe et al., 2012). Mechanical ventilation though is the mainstay in treatment of preterm infants with surfactant deficiency; it still remains a major contributor to adverse neonatal outcomes related to iatrogenic lung injury.
Thus, it is not only important to recognise who to ventilate and how to ventilate, but an important part of jigsaw is to recognise when to commence weaning and the best mode of weaning infants from
mechanical ventilation. Early weaning could facilitate earlier extubation and perhaps reduce the extent of ventilation induced lung injury. At present clinicians continue to have differences in practices and our study attempts to explore if pressure support ventilation can assist in faster weaning of preterm infants from mechanical ventilation.