Transmitted Lung Pressures With Biphasic Chest Cuirass

Conventional mechanical ventilation is known as positive pressure ventilation (PPV) because
the machine delivers positive pressure directly into the airways to ventilate and expand the
lungs. In a healthy lung, inflation occurs when the pressure inside the lung is greater than
the pressure outside the lung. This transpulmonary pressure is the difference between the
pressure inside the lung (in the alveolus) and the pressure just outside the lung (the
pleural cavity). Since positive pressure ventilation delivers pressure directly into the
airways, the transpulmonary pressure is increased by making the lung pressure more positive.
This is markedly different than physiologic breathing and carries an increased risk of
ventilator-associated lung injury1. In the setting of sick lungs, where the pressure required
to open collapsed areas of lung may be more than areas of healthy lung, this higher pressure
can in turn cause damage to the areas of healthy lung. The known effects of this
ventilator-associated lung injury from positive pressure ventilation can be avoided with the
use of negative pressure ventilation. In negative pressure ventilation (NPV), the
transpulmonary pressure is increased by making the pleural pressure more negative. This is
achieved by using a plastic shell that covers the chest and generates negative pressure
between the plastic shell and the chest. This pressure is distributed more evenly across a
large surface of the chest wall and results in more uniform lung expansion. As a result, NPV
results in better oxygen delivery and less lung injury than positive pressure ventilation2.

However, despite the extensive use of NPV in other countries, there is little data available
regarding the transpulmonary pressure that these machines can generate; i.e. how well does
negative pressure in the plastic shell transmit to the pleural cavity to expand the lung.
There is a large amount of data supporting the use of biphasic cuirass ventilation to
minimize lung damage3 and improve hemodynamics4-9, but no studies have been done to date that
look at the transpulmonary pressure and how it differs depending on age and size. It is still
unclear what optimal pressure is required via the chest cuirass to expand and ventilate the
lungs via. It is also unknown what maximum pressures can be used before the lung becomes
overinflated and complications arise.

This study will examine the correlation between the transpulmonary pressure and the actual
setting on the biphasic chest cuirass device is the primary study end point.

Inclusion Criteria:

1. Are between the age of 6 months and 5 years

2. Undergo circumcision, hypospadias repair, or orchidopexy in the operating room of the
John R. Oishei Children's Hospital

Exclusion Criteria:

1. Previous history of chronic lung disease or cyanotic heart disease or

2. Patients with significant chest wall abnormalities or other abnormalities that
preclude proper placement of the biphasic chest cuirass.