Surgery – Respiratory method or device – Means for supplying respiratory gas under positive pressure
Reexamination Certificate
2000-08-25
2004-09-21
Bennett, Henry (Department: 3743)
Surgery
Respiratory method or device
Means for supplying respiratory gas under positive pressure
C128S203110, C128S205140, C128S205130, C128S203280, C128S207140, C128S207160, C137S908000
Reexamination Certificate
active
06792947
ABSTRACT:
TECHNICAL FIELD
The invention relates to a flow control valve for preventing gastric distention and aspiration of stomach contents due to excessive gas flow rates delivered to patients by controlling the flow rate of pressurized air from a manually operated resuscitation device, such as a Bag-Valve-Mask device, pocket mask, face shield, or endotracheal tube.
BACKGROUND OF THE ART
In the relevant art of pulmonary resuscitation using manually operated resuscitation devices, the Bag-Valve-Mask resuscitator (commonly referred to as a “BMV”) has been the primary method of ventilating the patient in respiratory arrest for some 40 years. The BVM device is well known to those in the relevant art and examples of BVM designs are shown in U.S. Pat. Nos. 4,532,923 and 4,622,964 to Flynn. Cardio-pulmonary resuscitation (CPR) can be administered mouth-to-mouth without protection but recently to protect the patient and emergency medical personnel, use of various protective manually operated devices is common. For example, one way valves, patient exhalation valves and fabric shields are fitted to pocket masks and face shields in order to inhibit cross-contamination.
The clinical application of manually operated resuscitation devices including BVM devices, pocket masks, and face shields however is not based on scientific fact but rather on historical usage and the lack of an inexpensive alternative. Potentially dangerous excessive gas flow rates and pressure delivered to the patient have been documented using mechanical BVM's as well as the exhaled breath from the operator using pocket masks and face shields. The skill and training of the operator alone determines the efficacy of resuscitation when manually operated devices are used.
Clinical evidence that supports the use of BVMs is rare, whereas there is an abundance of evidence that clearly identifies BVMs as generally ineffective in providing adequate ventilations to the patient [for example,
A. H. A. Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiac Care
—J. A. M. A. Oct. 28, 1992:2171-2295].
The BVM consists of a self inflating balloon at one end having a one way intake valve that allows gas to be drawn into the balloon as the balloon recoils after it has been manually squeezed by the user. The intake valve self seals when the inflated bag is squeezed, and opens when the bag is permitted to recoil naturally. On the other end of the balloon, a one way output valve permits the gas to leave the bag when squeezed directing the flow of gas to the patient through a facemask, or other airway adjunct. The output valve opens when the inflated bag is squeezed, and self seals when the bag is permitted to recoil naturally. The output valve when sealed diverts the exhausted gas from the patient out through an expiratory port on the valve housing. As a result of cyclical manual squeezing and recoil of the balloon, gas is pumped through the balloon to the patient mask.
The original BVM was a development from the “Black Anaesthesia Bag” whereby the black bag was supported internally by a foam, self inflating balloon causing the bag to recoil to its original shape when the squeezed bag was permitted to recoil when released.
Many versions of the BVM have been developed all with the same negative feature, namely that the delivered flow, tidal volume, airway pressure and frequency are totally dependent upon the operator's skill and hand size. The inability to control the output from the BVM has been subject of many studies and has been well documented. Prior to creation of the present invention, this problem has not been overcome. [For example: Cummins R. O. et al,
Ventilation Skills of Emergency Medical Technicians: A Teaching Challenge for Emergency Medicine
, Ann. Emerg. Med, October 1986; 15:1187-1192; Stone B. J. et al,
The Incidence of Regurgitation During Cardiopulmonary Resuscitation: A Comparison Between the Bag Valve Mask and Laryngeal Mask Airway
, Resuscitation 38 (1998) 3-6; Elling, B. A. et al,
An Evaluation of Emergency Medical Technician's Ability to Use Manual Ventilation Devices
, Ann. Emerg. Med. 12:765-768, December 1983; Rhee, K. J. et al,
Field Airway Management of the Trauma Patient, The Efficacy of Bag Mask Ventilation
, Am. J. Emerg. Med. 1988;6:333-336; Manoranian, C. S. et al,
Bag
-
Valve
-
Mask Ventilation; Two Rescuers Are Better Than One: Preliminary Report
, Critical Care Medicine, 1985;13:122-123; Lande, S. et al,
Comparing Ventilatory Techniques During CPR
, J. E. M. S. May 1982; Harrison, R. R. et al,
Mouth
-
to
-
Mouth Ventilaion: A Superior Method of Rescue Breathing
, Ann. Emerg. Med., 11:74-76, February 1982].
Additionally, the requirements of ventilation have changed in recent years causing more concern over the use of the BVM and the volume, frequency of ventilation, airway pressures and flows that the average skilled operator can deliver. A number of the above clinical papers have documented this inability by even highly skilled operators to consistently deliver correct volumes and ventilation rates without causing problems for the patient including gastric distention and aspiration of stomach contents leading to patient morbidity and even death. Not only BVM's result in unsatisfactory ventilation but any manually operated resuscitation device including pocket masks and face shield yields similar results due to the reliance on the skill and training of the operator.
The quality of ventilation delivery when operator powered devices are used is particularly unpredictable and varies greatly according to experience, training and general coordination ability. To provide adequate ventilation, the emergency medical technician should pay attention to consistently timed tidal volumes of approximately equal volume and pressure dependant on the body size and age of the patient. However emergency care personnel are often under extreme stress and have many other duties to perform in urgent care situations that tend to reduce the attention and level of care directed to ventilation techniques.
While normal breathing requires muscle action (diaphragm, intercostals and others) to produce a negative pressure (subatmospheric or vacuum) within the chest to draw air into the lungs, artificial ventilation is accomplished by forcing air or oxygen into the lungs under an external positive pressure.
The positive pressure required to deliver a set volume (tidal volume) of gas to a patient is dependent on two factors: (1) the compliance, stiffness or elasticity of the lung, and (2) the resistance to gas flow within the conducting airways. For example, a “stiff” lung that is damaged by pulmonary fibrosis, disease or trauma requires a higher pressure to deliver a set tidal volume than a normal elastic lung. Similarly, gas will encounter less resistance through a normal airway that is not narrowed by bronchospasm or asthma, kinked by a poor airway opening technique, or plugged with blood, mucous, vomit or other debris.
As a result, manual and automatic ventilation techniques must accommodate a range of pressures. With a cormnon tidal volume of gas that is delivered, the patient's lung and airway condition will determine the pressure needed to ventilate the patient. However, there is a safe upper limit to the pressures that can be used to prevent lung damage. The danger of pneumothorax or lung rupture due to excessive pressures is considered to occur between 75 and 85 cmH
2
O.
Regarding the peak flow rates required to adequately ventilate an adult in respiratory arrest a generally accepted rate is a tidal volume of one liter at 12 breath cycles per minute. The breathing rate of 12 breath cycles/minute equals 5 seconds/breath cycle (60/12). Assuming that it takes about one half the length of time to inhale as to exhale (1:2 IE Ratio), the inhale portion of the breathing cycle takes approximately 1.5 seconds/inhaled breath (5 seconds/3=1.67 or approx. 1.5). The ideal flow rate therefore is approximately 40 liters/minute derived by (1 liter per inhaled breath/1.5 seconds pe
Bennett Henry
Kusner & Jaffe
O-Two Systems International Inc.
Patel Mital
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