Neonatal respiratory problems account for most admissions to intensive care units in the immediate newborn period. The goal of respiratory treatment is to provide oxygen to the tissues and carbon dioxide removal in a safe and effective manner. Mechanical ventilation is a method to mechanically assist or replace spontaneous breathing. This technique involves a machine called a ventilator.
Positive pressure ventilation can be delivered by two kinds of machines using two different principles: Conventional Mechanical Ventilation & Advanced High frequency ventilation.
Conventional ventilation is the more familiar mode used in most NICU set ups but in certain diseases and in worsening respiratory disease, higher mode like high frequency ventilation is now becoming an increasingly popular mode due to its lesser side effects and clinical advantage over the conventional ventilators in select situations, when applied with efficient ventilators and with expertise and rigorous monitoring.
High frequency ventilation is a gentle form of ventilation using supraphysiological breathing rates (180 - 900 breaths per minute) with small tidal volumes. The settings used vary widely depending upon patient size, age, and disease process.
HFV is commonly referred to as lung protective ventilation. The benefits of HFV over conventional mechanical ventilator are:
- Reduces Ventilation induced Lung Injury (VILI)
- Minimising atelectrauma
- Improving alveolar recruitment and ventilation ( CO2 removal)
- Improved gas exchange
- Decreased time on ventilator, Shorter hospital stay
- Improved survival
There is a continuous sweep flow of the gas in the machine & a piston moves to and fro to produce oscillation. Oscillations are superimposed on the gas in the patient circuit using an electrically-driven diaphragm, similar to an audio loudspeaker cone. These oscillations in the gas, through the patient circuit reach the lungs and delivers gas volume at the alveoli. Different complex mechanisms of gas transfer come into play in HFOV compared to normal mechanical ventilation.
Since the use of HFV more than 25 years ago, it has been used successfully worldwide in large number of sick newborn babies. Hundreds of medical publications demonstrate its safety and efficacy. In fact, current clinical evidences suggest that HFV is safer than conventional mechanical ventilation when it comes to ventilator induced lung injury & overall patient survival. The use of HFOV has reduced the need for ECMO (like cardiopulmonary bypass) in meconium aspiration syndrome, a life-threatening respiratory illness in the neonate where the baby aspirates its stool at delivery.
If used with inadequate expertise and monitoring, can have complications like pneumothorax, drop in blood pressure and worsening respiratory condition.
Timely institution of High frequency ventilation is the key to successful outcomes with HFV. Certain oxygenation indices help in guiding early use or escalation to high frequency ventilation. Careful selection of the patient helps in situations where, difficult ventilation is anticipated and ventilation induced lung injury is the key concern like congenital diaphragmatic hernia (where a defect in the diaphragm leads to presence of intestines in the thorax).
Certain situations where pressures on the right side of the heart are high as in Persistent Pulmonary Hypertension with respiratory illness, a combination of HFV and inhaled Nitric Oxide gas are used to decrease the pressures.
The cost of the HFV is slightly higher than the conventional mechanical ventilator, due to the complexity of the machine & need for special skills to operate it. However, this cost is compensated by decreased time on ventilator, shorter hospital stay, minimal complications & improved survival and therefore is a cost-effective option in select cases.