FREE ESSAY ON VENTILATION

VENTILATION

Ventilation is the mechanical process whereby air is taken into and out of the lungs.
Situations in which a patient might require venitlatory support range from apnea to
patients experiencing depressed respiratory function. If the patient's rate of breathing
decreases significantly it can lead to hypercarbia, hypoxia, a lowered pH level and a
decrease in respiratory minute volume. This can result in cardiac or respiratory arrest
if it isn't corrected. 
Expired air ventilation has been accepted as the technique of choice since the late
1950s. It has been shown to be an effective practice for both professionals and lay
persons including young children over 5 years of age. Ventilation using the expired air
of the rescuer can be applied to the mouth or nose of the adult victim and to the mouth
and nose of the infant. Mouth-to-Mouth ventilation and Mouth-to-Nose ventilation can
provide effective ventilatory support to a patient. A major advantage of these methods of
ventilation is that no equipment is required to effectively offer ventilatory support to
the patient. However, the disadvantage of these methods of ventilatory support are that
both methods only offer a limited oxygen supply due to the fact that oxygen expired from
the rescuer will only contain 17 percent oxygen. 
Mouth-to-Mask Ventilation or Pocket Mask Ventilation
A clear, plastic, molded facemask similar to that used in anesthesia may be used to
provide mouth to mask ventilation. A unidirectional valve diverts the patient's expired
air away from the rescuer and traps any macroscopic particles emerging from the patient.
This valve improves the aesthetics and reduces risk of cross infection. The mouth to mask
method is a two handed technique which produces a better seal than that obtained during
single-person bag-valve-mask ventilation. As with mouth-to-mouth ventilation it is
possible to generate high tidal volumes, high airway pressures and increase the risk of
gastric inflation. The addition of a port for the administration of supplemental oxygen
increases the inspired oxygen concentration. A variety of pocket masks are available.
Some of these masks are disposed of after the first use while others may be used many
times. Most are small and compact enough to fit in a pocket and may be carried with the
paramedic. The pocket mask allows an oxygen flow rate of 10 liters per minute. This rate
combined with mouth-to-mouth breathing of the rescuer yields an inspired oxygen rate of
about 50 percent. This is a significantly higher oxygen concentration level than
delivered through the mouth-to-mouth or mouth-to-nose method. 
Inexpensive protection devices made from a piece of plastic film with a valvular orifice
to cover the mouth and nose will provide protection and reduce aesthetic worries of
direct contact with patient's vomitus, saliva, sputum or blood. The main disadvantage is
that the film device requires repositioning for each sequence of breaths. In the
community the bystander is likely to be a relative, friend or colleague of the victim and
resuscitative efforts should not be deterred by the unavailability of a protective
device, as the risk is very small.
Bag-Valve Ventilation
The self-inflating bag can be connected to either a facemask, a tracheal tube, a
laryngeal mask, or a Combitube. The bag consists of an oblong, self-inflating silicone or
rubber bag; two one-way valves, and a transparent facemask. They are available in sizes
for babies, children and adults. The bag-valve device allows room air or oxygen to be
delivered to the patient. When used on its own the bag-valve-mask will allow ventilation
of the patient with ambient air (21% oxygen). This can be increased to around 50% by
attaching an oxygen supply at 5-6 Lmin-1 directly to the bag next to the air inlet valve.
Normally, however, a reservoir bag should be attached, which with oxygen flows of 8-10
Lmin-1, will provide inspired oxygen concentrations of 90%.
Certain ideal criteria have been laid down for bag-valve-mask devices used in
resuscitation 
The requirements recommended include:
The bag material should be transparent and convey a satisfactory feel. 
It should not absorb anesthetic or noxious gases and should possess sufficient recoil to
draw in gases from a reservoir or a draw over anesthesia circuit. 
Both inlet and outlet valves should be of robust construction, competent to prevent
rebreathing or leaks, incapable of malfunction or jamming with a fresh gas flow (of
oxygen) up to 15L/min. 
The valves should be easy to take apart, clean and reassemble (except in disposable
models); incorrect reassembly should be impossible. 
The inlet valve should be capable of being fitted with a filter (to exclude noxious
gases) and an oxygen reservoir bag. 
The patient valve should have standard ISO 15/22 mm fittings. 
The patient valve should incorporate, or be capable of being fitted with, a PEEP valve. 
The bag should be capable of delivering a tidal volume of up to 1500 ml in the adult
version and ventilation rates of up to 45/min in the pediatric version. 
Infant, pediatric and adult versions of the device should be available. 
The device should function adequately during all common environmental conditions and
temperature extremes. 
When used by one person, a considerable degree of skill is required to maintain a patent
airway and gas-tight seal with one hand, while squeezing the bag with the other. This is
only likely to be achieved by someone who regularly uses a bag-valve-mask device. Too
much air leak will result in hypoventilation, while excessive tidal volumes may result in
gastric insufflation and increased risk of regurgitation. If ventilation has to continue
with a bag-valve-mask, the two-person technique is preferable; one person holds the
facemask in place using both hands and an assistant squeezes the bag. In this way a
better seal is achieved, the jaw thrust maneuver is more easily maintained and the
patient's lungs can be ventilated more effectively.
Demand Valve Device
The demand valve device is also commonly referred to as the manually triggered oxygen
powered breathing device. This device will transport 100 percent oxygen to a patient at
its maximum flow rate (40L per minute). This system consists of a high-pressure tube,
which connects to an oxygen supply. A push lever or button easily activates the valve
causing it to open and thus, supplying oxygen to the patient.
Automatic Ventilators
Due to technological advances, compact mechanical ventilators are now available for
pre-hospital use. Mechanical ventilators provide a number of advantages over other types
of ventilatory support discussed previously. Mechanical ventilation is lightweight and
compact which makes it convenient and very easy to use while transporting the patient to
the hospital. Secondly, they are an improvement over the bag-valve device in maintaining
minute volume. The mechanical ventilation system is also able to endure extreme
temperatures. Temperatures ranging from 30 degrees Fahrenheit to 125 degrees Fahrenheit.

Another advantage of mechanical ventilation is that most systems are typically equipped
with both an adjustable ventilatory rate and tidal volume. This will allow the machine to
function intermittently, reverting to controlled mechanical ventilation in patients who
are not breathing. Some are contain a pop-off valve that prevents pressure-related
injuries. A pop-off valve can prove to be detrimental in situations where the patient is
suffering from a pulmonary contusion, bronchospasm, cardiogenic pulmonary edema, adult
respiratory distress syndrome or disorders in which high levels of pressure in the airway
must be surmounted. 
In closing, there are several effective methods of supplying respiratory support to
patients. Although, the mechanical ventilator has many advantages as mentioned earlier,
the bag-valve method proves to have the largest amount of advantages. However, it should
be noted that the bag-valve technique has also proven to be problematic when attempting
to offer respiratory support to nonintubated patients.