Purpose: Pulse oximetry is a standard American Society of Anesthesiologists (ASA) monitor. At times, monitoring sites will not be available due to reasons such as burn, crush, amputation, poor perfusion or presence in a surgical field. In the case presented here, all known monitoring sites were eliminated resulting in the need to obtain an oral pulse oximetry measurement from the hard and soft palate. Case History: A 45-year-old male suffered critical burns from a propane tank explosion, sustaining 80% total body surface area (TBSA) full-thickness burns. During surgical debridement, the pulse oximetry sensor had to be moved so that the operation could continue. No traditional site was available; therefore, the only remaining option was to obtain oxygen hemoglobin saturation measurements from the mouth using an oral airway and a disposable pulse oximetry sensor. Comments: In situations where no other pulse oximetry sites are available, oral airway oximetry may be attempted while observing other trends in oxygenation and ventilation throughout the anesthetic.
Pulse oximetry is a standard ASA monitor that is required for all patients undergoing any anestheti. Both traditional transmissive pulse oximetry (placed on the ear, finger or toe), and reflectance forehead oximetry are widely available to most anesthesia providers. Also, available, in some hospital settings, is esophageal oximetry—not an option at the institution of this case report. The two common types of pulse oximetry are transmissive and reflectance. A transmissive pulse oximeter uses spectrophotometry to measure light absorption at two wavelengths: red light @ 660nm and infrared light @ 940nm. Since oxygenated and deoxygenated blood absorb light differently, the communication of these diodes through tissue can be used to create a ratio that appears as a waveform and an oxygen saturation percentage (SpO2 ). Reflectance forehead oximetry measures the scattered transmission of light through tissues at multiple wavelengths to determine the differences in the oxygenated and deoxygenated hemoglobin; also appearing as a waveform and an oxygen saturation percentage.
Esophageal oximetry, like the forehead oximeter, uses reflectance technology . When compared to transmissive pulse oximetry measured on the finger, and arterial blood gas oxygen saturation, the correlation and reliability of the forehead sensor in the presence of low oxygen saturations has not been established in ICU, ventilator-dependent patients, but has performed reliably in healthy, awake patients . Esophageal oximetry has been seen to detect changes in oxygen saturation up to 94 seconds earlier and has demonstrated more accurate readings in shock patients when compared with other oximeters [6,7]. Traditional transmissive pulse oximetry also has limitations including delays in reporting physiological changes versus the display on the monitor, inability to accurately reflect shifts in the oxyhemoglobin dissociation curve, falsely elevated readings in the presence on carboxyhemoglobin (from carbon monoxide poisoning or cigarette smoking) or potentially incorrect readings of 85% after injections of methylene blue, indocyanine green, indigo carmine, isosulfan blue, or clinical presence of methemoglobinemia; and potential inaccurate readings if the patient saturations fall below 80% . More commonly seen barriers to achieving accurate readings include nail polish, hypotension/hypovolemia, motion, a cold extremity, ambient light, darker skin pigmentation, severe anemia, and electromagnetic interference . Despite these barriers in achieving accurate readings, pulse oximetry remains a standard in all anesthetics and is a key factor in patient care and safety . The importance of pulse oximetry has been repeatedly discussed and the safety impact continues to be reported from low-income countries having to make the choice between pulse oximetry and other costly equipment in operating theaters . We present a case report of a male with significant burn burden presenting to the operative theater for urgent debridement. Given the importance of using pulse oximetry, we were forced to come up with a novel approach to oxygen saturation monitoring with transmissive pulse oximetry. We use this case report to describe this approach using an oral airway and a standard disposable transmissive pulse oximetry sensor.
45-year-old male experienced critical burns from a propane tank explosion, sustaining 80% total body surface area (TBSA) full-thickness burns. This included his head, face, neck, right forearm, right hand, left forearm, left hand, right lower leg, right foot, left lower leg, and left foot. Partial thickness burns involved the face, right lower leg, right foot, left lower leg, and left foot and accounted for an additional 5% TBSA. Along with these injuries, his physical examination demonstrated an inhalational injury and was intubated prior to transport to Vanderbilt University Medical Center.
This patient presented to the operating room for excision and grafting of feet, right arm, right hand as well as dermabrasion of his face. There was no plan to graft his left hand during this operation, and it remained wrapped in burn dressings and under sterile draping. This extremity was not an option to use as a monitoring site due to the presence of a fresh skin graft that would be compromised by removal of the dressing. Upon arrival, his hemoglobin oxygen saturation (SpO2 ) was being monitored with a disposable pulse oximetry sensor (Covidien Ref: MAXFAST lot: 1626000488) on his forehead, secured with a padded elastic strap placed circumferentially around his head, and attached to a cable communicating with a Phillips monitoring system. Intraoperatively, the pulse oximetry sensor remained on the forehead until after grafts of the feet and right hand were completed. This was the point at which finding a site to take a pulse oximetry measurement became extremely challenging. Scrotal measurements were attempted without success. Therefore, to solve this monitoring challenge, our standard disposable pulse oximetry sensor was taped over an oral airway and then placed in the patient’s mouth in the standard insertion manner for an oral airway (Figure 1). Once in place, we were able to achieve pulse oximetry readings with an observed consistent waveform, averaging pulse oximetry readings of 94% (SD 0.05). We used this monitoring technique for the remainder of the procedure and were able to successfully obtain SpO2 measurements throughout.
Figure 1. A picture demonstration of the components and steps taken to construct the SpO2 sensor used for oral monitoring of the patient’s hemoglobin oxygen saturation.
Additional factors used to assess oxygenation, in addition to pulse oximetry, included: inspired / expired FiO2 ratio (I/E), arterial blood gasses, mucus membrane color, and persistent end-tidal CO2 . I/E mismatches can occur due to inhalation injury, fluid replacement and/or shifts commonly seen in burn patients, fluctuations in temperature from intraoperative exposure of burned skin to ambient OR temperature, blood loss, and blood administration. We were able to obtain arterial blood gasses that demonstrated appropriate PaO2 levels (PaO2 >300) (Table 1). To minimize the risks of overoxygenation, we titrated our inspired O2 to arterial PaO2 measurements (Table 1). The mucus membranes were all within the burn and surgical field.
Table 1. Table summary of the vital signs compared to arterial blood gas measurements during procedure in the operating room.
Figure 2. A picture demonstration of the barriers experienced to monitoring sites during procedure in the operating room.
The forehead: This was where the pulse oximetry sensor was placed to obtain measurements in the Intensive Care Unit and now unable to remain on head due to need for burn debridement.
The ears, nose and lips: There was no intact skin remaining near the ears, nose or lips. Burns were covered in Sulfamylon cream on the bilateral ears and this prevented our ability to take SpO2 measurements at these locations. The nose and lips were part of the sterile field that was being debrided and were not an option for measurement sites.
The back of the neck: The back of the neck was considered as a possible site but was also covered in burn. Other challenges included moisture from chlorhexidine wash of the sterile face, blood from the surgical site and debrided skin slid to the back of the neck, disrupting the integrity of the adherent pulse oximetry sensor.
The fingers: These commons sights were not available in for this case. The left hand was wrapped in burn pack dressings and unavailable. The right hand was freshly grafted and prepped into the sterile field.
The toes: The toes were also grafted during the surgery and presented the same challenges as described with the fingers. The penis and scrotum: The penis and scrotum had intact, healthy skin. Pulse oximetry was attempted on these sites and a reliable tracing was unable to be obtained.
An adherent pulse oximetry was placed over an oral airway and this was how we were able to obtain real-time oxygen hemoglobin saturation during the patient’s urgent procedure (Figure 1). Pulse oximetry readings were observed with perfusion numbers less than 0.5, a somewhat consistent waveform, and a number reading between 88-100%. The average pulse oximetry reading was about 94% (SD 0.05). At the cessation of the case, an examination of the airway displayed no mucosal abrasions or negative outcomes from contact made between the pulse oximetry measurement device and the soft tissue within the mouth and throat. The patient had an uneventful intensive care unit stay and there were no issues with monitoring as soon as the surgery was completed because the forehead once again became available for monitoring. This patient was discharged home approximately one month later. This method of monitoring did obtain a consistent waveform and oxygen hemoglobin saturations that correlated with multiple arterial blood gases. Measurements of capillary density on the tongue have demonstrated the ability to provide very reliable SpO2 measurements. This novel approach to monitoring can be considered and used when the standard, more traditional sights are not an option. However, continued evaluation of this anatomical site to provide accurate SpO2 measurements is necessary.
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