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 patients 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 isnt 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 patients 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.
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.
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.
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.