Monitoring of hemoglobin oxygen saturation using pulse oximetry has become a standard of care during anesthesia, as well as in the postanesthesia care unit and critical care setting.1–3 Pulse oximeter sensors (probes) are most commonly of the transmittance type and are applied peripherally, such as to a fingertip or an earlobe where they measure the transmission of light through the tissues. The extremities are, however, particularly sensitive to vasoconstriction, hypothermia, and poor perfusion, which may result in pulse oximeter failure (i.e., no value for hemoglobin-oxygen saturation [SpO2], or one that is spurious).4 When this occurs, an SpO2 reading may be obtainable using a reflectance pulse oximeter sensor placed on the forehead.5 Transmittance pulse oximeter probes placed on an extremity (e.g., fingertip) have been associated with patient injury, such as burns, gangrene, or necrosis.6–9 While there are 2 reports of burn injuries associated with the use of a forehead reflectance sensor, to our knowledge there is no report of a pressure injury associated with the use of a forehead sensor and headband.10,11 We report a patient who developed tissue necrosis associated with prolonged application of an OxiMax™ MAX-FAST™ (Nellcor, Tyco Healthcare, Pleasanton, CA) forehead reflectance pulse oximeter sensor.
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The patient was an 80-year-old man scheduled to undergo a reexploration of a wound in the lower lumbar region. His medical history was significant for hypertension, coronary artery disease, hyperlipidemia, peripheral vascular disease, chronic obstructive pulmonary disease, diabetes mellitus, and hypothyroidism. Some months earlier, he had sustained a pathologic compression fracture of the fifth lumbar vertebra, requiring spinal decompression and instrumentation. He subsequently underwent a number of surgical procedures on his lumbar spine. He had been in the intensive care unit (ICU) for approximately 2 months because his postoperative course was complicated by a wound infection in the lumbar region, sepsis, hypotension managed with vasopressors, and respiratory failure requiring eventual tracheostomy. Intermittently, he required IV norepinephrine and vasopressin infusions to treat hypotension. Other medications included cefepime, metronidazole, fluconazole, esomeprazole, metoprolol, levothyroxine, furosemide, fentanyl, midazolam, and subcutaneous heparin. One month after his most recent surgery, the patient was transported fully monitored from the ICU to the operating room for wound reexploration. Monitoring included pulse oximetry from a sensor applied to a finger. During placement of standard American Society of Anesthesiologists monitors, an OxiMax™ MAX-FAST™ forehead pulse oximeter sensor and headband that had been used in the ICU were removed, revealing skin breakdown and tissue necrosis at the site of sensor application (Fig. 1). The sensor cable was also noted to have become folded under the end of the sensor and was emerging at an angle rather than in line with the long axis (Fig. 2). We learned that the forehead sensor had been left on the patient and used intermittently in the ICU as an alternative to a sensor on a digit, when readings were unreliable. The tissue injury was treated conservatively with bacitracin, and the patient recovered after several weeks with no apparent long-term sequelae (Fig. 3).
Pulse oximeter data failure occurs when there is too little signal (i.e., poor perfusion/pulsatile flow) or too much noise (i.e., low signal/noise ratio).4,5 In this regard, a pulse oximeter sensor placed on an extremity is vulnerable to the effects of vasoconstriction, hypothermia, and poor perfusion. The forehead has been proposed as an alternative site by offering a high signal/noise ratio. The area of the skin above the eyebrow receives its blood supply from the supraorbital artery, a branch of the internal carotid artery. Perfusion of this area is therefore more likely to be maintained when that in the extremities is decreased. Furthermore, this area responds to cold or other stimuli with less vasoconstriction than the peripheral sites.4,5 A potential disadvantage is that the forehead site may be associated with spuriously low SpO2 readings in some patients.12 The low readings are likely caused by venous pulsation artifact. To reduce this artifact, a headband that applies up to 20 mm Hg pressure over the forehead sensor is used, which decreases venous pulsation.13 In our patient, an OxiMax™ MAX-FAST™ sensor had been applied to the forehead under a MAX-FAST™ headband that had been adjusted to the recommended tension (i.e., green arrows on the elastic band were within the green tension indicator zone). The manufacturer recommends inspecting the sensor site routinely and changing it after 2 days.14 In Nellcor’s Sensor Application Guide, one of the “Sensor Application Tips” is to “Check the forehead sensor site every 12 hours for skin integrity and sensor adhesion,” and to, “Move the sensor to a new area as necessary.”15 It is likely that the probe had not been checked every 12 hours as per the manufacturer’s recommendations and had been left in place on the patient’s forehead for an unknown period (but likely longer period of time than recommended). Furthermore, the patient’s comorbidities as well as the history of hypoperfusion requiring administration of vasopressors placed him at an increased risk of developing a pressure ischemic injury from the probe. The additional pressure applied from the headband, even with the recommended amount of tension, and the folding of the cable underneath the end of the sensor may also have contributed to the injury in this patient. When using a forehead pulse oximetry sensor and headband, one must be aware of the potential associated risks and educate those using this device, as well as other personnel caring for the patient who is being monitored, so as to prevent use error and potential for adverse outcome. Regular inspection of the sensor site per manufacturer’s instructions should be mandated and assured by inclusion in nursing protocols. To prevent pressure necrosis, the site must be checked frequently and the sensor removed when not in use. One must also be cognizant of the amount of pressure being applied to the forehead and adjust the headband tension accordingly. Care must be taken to ensure that the sensor cable does not become accidentally misplaced under the sensor when the patient moves or is moved. It is also important to identify patients at risk for this type of injury. Our patient’s comorbidities as well as his history of hypoperfusion requiring vasopressors may have increased his risk of developing a pressure ischemic injury from prolonged application of the probe. Fortunately, the situation was discovered and treated in time so that permanent injury was averted.
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