1. Field of Invention
Aspects of the present invention relate to a medical device for and method of monitoring the vital signs of a patient. In particular, there is a device for intubation verification and respiratory gas monitoring, and a method thereof.
2. Background
Endotracheal intubation into the trachea of a patient is well-known and widely used in practice. Such intubation is performed when normal ventilation of the patient's lungs may be impaired. Failure to artificially ventilate an apneic patient rapidly could result in serious brain damage or death.
During patient intubation, a flexible tube, also known as an endotracheal tube is used; wherein a distal end of the tube is placed within the patient's trachea. The proximal end of the tube can be attached to a resuscitator bag or any other device, supporting the respiratory process. During patient intubation, there is a risk of an accidental misplacement of the endotracheal tube into the esophagus. This condition can in itself cause death and disability if not quickly detected.
A patient consumes oxygen and exhales carbon dioxide during the respiratory process. Thus, sensing of carbon dioxide in a patient's exhaled gas is commonly used to detect proper placement of endotracheal tube.
In addition, as the endotracheal tube is properly installed into the trachea, it is clinically important to monitor the production of carbon dioxide to maintain adequacy of patient resuscitation. Normally there is 5% of carbon dioxide present in a patient's exhaled esophageal gas, indicating proper placement of an endotracheal tube as well as adequate resuscitation or ventilation.
In the prior art, two major categories of carbon dioxide detectors have been described. One of these categories includes devices which utilize chemical calorimetric carbon dioxide detectors. In many cases, devices are single patient use and disposable. The detector of such devices includes a chemical substance, which changes its color in presence of carbon dioxide. By looking at the change in color, a caregiver can verify presence of carbon dioxide in a patient's exhaled gas. Although calorimetric detectors are portable, light weight disposable devices, and widely utilized in practice, they suffer from significant disadvantages.
One of the many disadvantages is that the color change is not visible in a reduced lighting environment, such as in ambulances, in fire or car accident scenes at night, etc. These devices have a relatively short shelf life, since the chemical substance deteriorates with time; thus, the device must be disposed. To assure a large area of color indication, such devices utilize a relatively large gas to surface contact area, thereby increasing “dead space”—extra volume inside the airway adapter, where the inhaled and exhaled gases mix up. This problem reduces not only productivity of resuscitation, but also slows down the color change process in the detector, making it more difficult for a caregiver to reliably observe changes in color.
Another disadvantage is that chemical substances which are sensitive to carbon dioxide are very often sensitive to moisture; condensed moisture and secretions might negatively affect a calorimetric device performance. Furthermore, when being used in “flight for life” patient transportation or high in the mountains, a calorimetric device is not capable of reflecting an accurate percent of carbon dioxide in exhaled gas, since it can not compensate for reduced ambient pressure.
In another category of existing devices electro-optical sensing is utilized. It is well known that carbon dioxide absorbs infrared light. By determining the amount of absorbed infrared light, the presence and concentration of carbon dioxide can be determined.
In one particular existing device, there is described an elector-optical sensing device consisting of: a disposable single patient airway adaptor for passing respiratory gas through, which is detachable from the reusable monitoring portion; a detector used as a part of the monitoring portion, having a light source for irradiating infrared radiation and an infrared radiation detector for detecting the infrared radiation that has passed through the respiratory gas; a monitor body, having a display surface for indicating the concentration of a respiratory carbon dioxide gas, for measuring the concentration of respiratory carbon dioxide gas by receiving a signal from the detecting portion; where the detecting portion is mounted onto the monitor body forming one unit. The monitoring body contains a power source (batteries) to operate the device.
Although this device overcomes some of the disadvantages of calorimetric devices; it however has its disadvantage—a large weight and size; as a result of integrating the detecting portion, power source, and electronic circuitry inside the monitoring body of the device. Such a device having a large weight and size and attached to the endotracheal tube introduces a number of significant problems, including the ease in which it can accidentally pull out the endotracheal tube from the trachea. Another considerable problem occurs in cases of vibration presented in ambulances during patient transportation. A heavy device in close proximity with a patient's face, is likely to injure the patient's skin or eyes.
In the same electro-optical sensing device there is described a detection portion separated from the monitoring body by an electrical cable. Separating the detection portion from the monitor body, which includes the power source, electronic circuitry and display, reduces the weight applied directly to the endotracheal tube. However, splitting the device into two parts connected with electrical cable causes a major inconvenience to the caregiver, requiring the caregiver to hold the monitor body while resuscitating and transporting the patient.