This invention is directed to an apparatus and a method for measuring blood oxygenation from locations within the oral cavity of a subject, for example, a small child or a small/newborn animal.  More particularly, the invention relates to using pulse oximeter sensors to perform reflective pulse oximetry within the oral cavity of a subject. 
With a few exceptions, tradition and technology have favored transillumination pulse oximetry in the operating theater.  The principle of operation of the pulse oximeter is fairly simple but is arguably the most important development in anesthesia monitoring in the twentieth century.  Two wavelengths of light (usually 660 nm and 940 nm) are used to spectrophotometrically determine the ratio of oxidized to reduced hemoglobin noninvasively as well as to determine the pulsatility of blood plethysmographically. 
However, reflectance oximetry rather than transillumination oximetry was the earliest investigative form of the technique for taking oximeter readings.  Transillumination pulse oximetry, without question, is the most effective form when oximetry is obtained through skin.  However, when skin is not interposed as a barrier to capillary bed access, reflectance pulse oximetry easily can be achieved with very accurate results.  Indeed, it is used commonly and effectively among intrapartum and neonatal patients whose capillary beds are easily accessed through their skin.  The technique has also been applied to adult and pediatric burn patients by placing the reflectance sensor in wounds or over hyperemic sites such as healed partial thickness burns.  The effect is achieved by the backscattering of incident bispectral light that traverses and, on reflection from nonabsorptive collagenous tissues, retraverses formed elements in the blood back to the oximeter elements.  Rather than superseding transillumination pulse oximetry, this technique broadens the scope of possible monitoring sites, adding to the clinician""s armamentarium. 
Presently, the most common application of this in a medical setting is via transillumination through the capillary bed of a peripheral digit.  However, young patients such as babies are apt to remove or reject foreign objects such as finger oximeters or inserted tubes upon realizing their placement when recovering from anesthesia or awaking from sleep.  Sick children, in particular, are more likely to be restless and easily agitated and thus will resist any attempts to have medical readings taken like temperature or oximeter readings.  Additionally, it is not unusual for multitrauma and thermally injured patients to either have severe peripheral vasoconstriction or to have severely damaged (or missing due to amputation) peripheral vascular beds. 
There are other often overlooked capillary beds readily accessible in most adult burn patients and young children that are as amenable to reflectance oximetry similar to the forehead of the premature infant.  The buccal surface, posterior soft palate, hard palate, lingual surfaces, and gums of a burned patient and/or child are seldom compromised no matter how severe the burn, and the capillary beds are very close to the surface in those areas.  Transillumination pulse oximetry of the tongue and cheek has been documented as a viable method of monitoring, but not everyone has the equipment available to place a transilluminating pulse oximeter on the tongue or cheek. 
Recent studies indicate that oral pulse oximetry is a superior modality when compared to peripheral transillumination pulse oximetry.  A variety of studies have shown that oral pulse oximeters are more reliably and rapidly responsive than peripheral pulse oximeters.  However, these studies use oral transillumination pulse oximetry, held in place via complex devices or pieces of improvised malleable metal.  Oral secretions, equipment failure, and placement difficulty often render these techniques ineffective. 
Prior pulse oximeter sensors inserted through the mouth are usable only when the patient is under general anesthesia.  These pulse oximeter sensors are inserted to reach the larynx area, for example, U.S. Pat.  No.  5,282,464 to Brain et al.  Another known method uses transillumination pulse oximetry of the posterior tongue, but this method possibly may not be used with a patient, who is awake, for example, U.S. Pat.  No.  5,205,281 to Buchanan.  Also, the posterior tongue is not the most accessible body part to take oximetry measurements. 
Notwithstanding the usefulness of the above-described devices, and the above-identified recognized viability of transilluminating pulse oximetry, a need exists for a more convenient method for obtaining oximeter readings from a subject. 
The invention while addressing the problems of the prior art obtains advantages that were not achievable with the prior art apparatuses and methods. 
An object of this invention is to provide an effective method for taking pulse oximetry measurements from oral capillary beds. 
Another object of the invention is the use of reflectance pulse oximetry via the oral cavity for a variety of surgical, anesthetic, or critical care procedures or situations to include patients that are awake, undergoing general anesthesia, or recovering from general anesthesia. 
Another object of the invention is to allow for lingual placement of a pulse oximeter sensor for reflectance readings to provide efficient and clinically accurate pulse oximetry measurements. 
Another object of the invention is to allow for buccal placement of a pulse oximeter sensor for reflectance readings to provide efficient and clinically accurate pulse oximetry measurements. 
Yet another object of the invention is to monitor oxygen levels in newborns and young children who are difficult to monitor because of their natural restlessness and young age. 
Still another object of the invention is to monitor oxygen levels in severely burned ICU patients who are difficult to monitor. 
An advantage of the invention is an improvement in the quality of care resulting from using a straightforward method with easily used devices to take internal oximetry measurements and readings. 
Another advantage of the invention is that EMS crews and personnel will be able to use this invention easily in the field during, for example, emergency situations. 
Another advantage of the invention is improved pulse oximetry readings. 
Another advantage of the invention is reflectance pulse oximetry requires less power to function and thus less heat is produced than transilluminance pulse oximetry.  The decrease in produced heat lowers the risk the subject will be burned. 
Yet another advantage of the invention is that ambient light will not degrade the oximeter readings because the invention is within the mouth of a subject. 
The apparatus and the method accomplish the above objectives and achieve the advantages.  The apparatus and the method are easily adapted to a wide variety of situations. 
Furthermore, intraoral buccal, palatal, or lingual placement of a pulse oximeter probe in a configuration relying upon reflected light will provide pulse oximetry measurements comparable to those obtained by peripheral pulse oximetry.  Test protocols suggest that buccal and palatal reflectance pulse oximetry provides a simple, accurate means of monitoring arterial oxygen saturation in the severely burned patient where oximetric monitoring presents a challenge. 
Furthermore, the apparatus to perform this method is extremely useful in cases where it is difficult at best or not even possible to attach prior art pulse oximeter sensors with clips or straps to the patient.  The types of patients that this apparatus would be useful with are critically ill or injured patients including newborns, babies, young children, young animals, and burn or trauma patients without alternative sites and maxillofacial injuries.