There are a number of commonly-encountered situations in which the pulmonary and cardiac functions of a patient are impaired or absent, thereby necessitating corrective action if the patient's life is to be maintained.
In one such life-threatening situation, the patient's cardiac function is substantially normal but the patient either is not breathing or is having difficulty in breathing, i.e., the patient's pulmonary function is either absent or substantially impaired. The appropriate corrective action normally taken is to reproduce the patient's pulmonary function by manual or automated ventilation of the patient's lungs.
In manual ventilation, a person first clears the patient's airway (e.g., the mouth, larynx, and the trachea) by removing any obstructions therein and by tilting the patient's head back and by elevating the patient's chin. After the airway has been cleared, the person reproduces the pulmonary function by either breathing into or discharging a bag respirator into the patient's mouth at a predetermined rate, e.g., twelve times per minute, to periodically inflate (and deflate) the patient's lungs through the airway. The primary disadvantage of manual ventilation is that the technique is relatively inefficient in reproducing the pulmonary function, inasmuch as only a small percentage of the normal oxygenation of the patient's blood through lung inflation is obtained. Yet another disadvantage results from the fact that a person trained in the technique must be readily available to provide manual ventilation.
To overcome the noted disadvantages of manual ventilation, ventilators have been developed that provide automated ventilation. Typically, such ventilators include a source of pressurized gas containing or consisting of oxygen, an airway apparatus that is adapted to be inserted into the patient's airway, and a control apparatus including appropriate valves for coupling the airway apparatus alternately to the source of pressurized gas and to the atmosphere so as to alternately inflate and deflate the patient's lungs. The control apparatus may be designed so as to selectively vary not only the rate at which the patient's lungs are inflated but also the characteristics of lung inflation and deflation, e.g., the maximum gas pressure that is applied to the lungs during inflation, the maximum volume of gas that is introduced into the lungs during inflation, the rate of pressure increase and decrease, and the relative durations of each alternate inflation and deflation.
In another life-threatening situation, the patient's pulmonary and cardiac functions are both absent. The appropriate corrective action normally taken is the use of cardiopulmonary resuscitation (CPR) which involves ventilation of the patient's lungs to reproduce the pulmonary function and concurrent compression of the patient's chest to reproduce the cardiac function. CPR may be effected either by a manual technique or by use of an automated CPR apparatus.
A typical manual CPR technique that is designed for use by a single person comprises the following steps. The person first clears the patient's airway, in the manner previously described, and then reproduces the pulmonary function by either breathing into or discharging a bag respirator into the patient's mouth to inflate the patient's lungs through the airway. The person then reproduces the cardiac function by compressing the patient's chest immediately above the sternum at a predetermined rate, e.g., sixty compressions per minute, in order to compress the patient's heart so as to force blood through the patient's circulatory system. Since a single person cannot both compress the patient's chest and ventilate the patient at the same time, the technique involves repetitive cycles of a predetermined number of chest compressions, e.g., fifteen, followed by a predetermined number of ventilations, e.g., two.
Although manual CPR techniques have saved countless lives, they are subject to the disadvantage that they must be used by a person who has been trained in these techniques. In order to have any chance of restoring the patient to normal health, CPR must be started within a certain period of time after the patient has been stricken. Accordingly, if a trained person is not readily available, the patient will most likely die. Another disadvantage of manual CPR techniques is that they are relatively inefficient in reproducing the cardiac and pulmonary functions. For example, manual CPR techniques can at best result in only a small percentage of the normal blood flow to the patient's brain and only a small percentage of the normal oxygenation of the patient's blood through lung inflation.
The efficiency of CPR may be increased by the use of automated CPR apparatus, sometimes referred to as resuscitators. Although the structure and operation of resuscitators differ, they typically include a ventilator similar to that previously described and a reciprocable chest plunger that is positioned by an appropriate mounting frame above the patient's chest or that is secured to the patient's chest by a plurality of straps. A control apparatus is provided which causes the reciprocable chest plunger to be extended to and from the patient's chest so as to alternately compress and decompress the patient's chest and which causes the airway apparatus of the ventilator to be alternately coupled to a source of pressurized gas and to the atmosphere. Typically, a resuscitator is operated in a cyclical mode, each cycle including a plurality of successive chest compressions and decompressions (e.g., five) followed by a single lung inflation and deflation.
The resuscitators known to the prior art are bulky and heavy, and therefore not easily transportable. The manner in which CPR is effected by such resuscitators, e.g., the rates of chest compression and decompression and of lung inflation and deflation relative to each other, the relative numbers of chest compressions and decompressions and of lung inflations and deflations during each cycle, and the duration and amount of chest compressions and of lung inflations relative to each other, is rather inflexible so that it is difficult to tailor CPR to the specific needs of the patient. Further, the reciprocable chest plunger is capable of causing significant injury to the patient.
In yet another, life-threatening situation, the patient's pulmonary function is substantially normal but the cardiac function of the patient is impaired. The appropriate corrective action normally taken is to apply drugs to the patient or to provide circulatory assistance to the patient by the use of a apparatus such as an intra-aortic balloon which is surgically inserted into the aorta through the patient's arterial system and which is inflated and deflated at a rate that is synchronized to the electrical heart activity of the patient. As can be appreciated, a trained person is required to properly apply drugs to the patient and a trained physician is required to use an apparatus such as an intra-aortic baloon.
Apparatus of the types previously described are also disadvantageous in that they are designed for use in a specific life-theatening situation, e.g., for ventilation, or for CPR, or for circulatory assistance. Since a specific life-threatening situation cannot be known in advance, it is therefore necessary to maintain on hand each type of apparatus.
Recently, it has been discovered that the mechanism for causing blood to flow through the circulatory system during CPR may not be the force that is transmitted to the heart through the chest during each chest compression, but rather the amount of intrathoracic pressure that is generated as a result of chest compression (and lung inflation) in that portion of the thorax in which the heart and lungs are located. It therefore has been postulated that an increase in intrathoracic pressure during CPR should increase the efficiency of CPR. Reference, for example, Rudikoff et al., Mechanisms of Blood Flow During Cardiopulmonary Resuscitation, CIRCULATION, v. 61, No. 2, pp. 345-352 (1980). However, there are no commercially-available automated apparatus which utilize this discovery to accordingly increase the intrathoracic pressure of the patient during CPR (and during circulatory assistance).
It is therefore an object of this invention to provide an apparatus which can be selectively controlled to automatically ventilate the lungs of a patient, or to automatically effect cardiopulmonary resuscitation, or to automatically provide circulatory assistance to the patient.
It is another object of this invention to provide such an apparatus which provides CPR and circulatory assistance by increasing the intrathoracic pressure of the patient.
It is yet another object of this invention to provide such an apparatus which is small in size and light in weight, and therefore easily transportable.
It is a further object of this invention to provide such an apparatus which is capable of flexibly controlling the manner in which ventilation, CPR and circulatory assistance are effected.
It is yet a further object of this invention to provide such an apparatus which provides more efficient CPR and more efficient circulatory assistance than currently-available apparatus and techniques.