Safe Use of Pulse Oximetry During Verteporphin Therapy

Abstract

Photodynamic therapy (PDT) is a relatively uncommon treatment modality, which is occasionally used intraoperatively at extraocular sites. Verteporphin is a photosensitizing chemotherapeutic drug used in PDT that is activated by exposure to red light in the presence of oxygen (1). The resulting free-radical damage can selectively destroy tissues that preferentially take up verteporphin and are exposed to appropriate wavelengths and intensities of light. PDT is most commonly used to treat neovascularization associated with macular degeneration. Laser diodes at 690 nm are often used as a light source for PDT, which is near the absorption peak of verteporphin (689 mn). Verteporphin is also finding new uses in the treatment of intracranial malignancies. PDT may present significant difficulties for patient care because patients remain photosensitive for 5 days after the administration of verteporphin. Photofrin (porfimer sodium), a similar, but longer lasting drug, results in 30 to 90 days of photosensitivity after administration (2). Standard 2-wavelength pulse oximeters emit light at 660 nm, which is within the range that can activate photofrin, and is close to the absorption maximum of verteporphin. Farber et al. (3) reported that prolonged exposure to pulse oximetry caused second-degree nonthermal skin “burns” after photofrin administration, although healing occurred without skin grafting. In a similar report, a second-degree “burn” resulted in loss of a fingernail (4). During a clinical trial, cutaneous injury developed in several volunteers (5), prompting several letters as well as a newspaper article, which produced serious financial repercussions for the manufacturer of a similar photosensitizing drug (6–11). Some of these reports highlighted the need to give close attention to the injection technique and drug preparation, because some compounds are highly insoluble in water and may precipitate upon injection with local injury (12). During the photosensitive period, patients are normally kept in dark environments, and extravasation of the drugs on injection may require shielding from sunlight for much longer than the usual photosensitive period. Of major concern for anesthesiologists is that perioperative lighting requirements for avoidance of cutaneous damage result in conditions in which lighting is insufficient to observe for cyanosis. The avoidance of pulse oximetry because of the risk of skin damage may pose additional hazards because of the inability to adequately monitor oxygenation. We adopted the following use of pulse oximetry for a patient with satisfactory results. Case Report A 53-year-old man with a recurrent left parietal malignant meningioma was scheduled for intracranial resection and intraoperative photochemotherapy with verteporphin. After the induction of general anesthesia, positioning of the patient, and exposure of the tumor, 32 mg of verteporphin was administered IV over 10 min. The room lighting was kept on for the first 30 min after the administration because of surgical requirements. Because room lighting enabled our assessment of the patient’s skin color visually during this time, we attempted to minimize patient exposure to pulse oximetry by performing intermittent checks for periods of a few seconds at intervals of 5–10 min. Although we recognize that pulse oximetry is superior to visual inspection of skin color, intermittent pulse oximetry still allowed us to identify small, long-term changes in oxygen saturation that would not be otherwise apparent. After this time, the operating room lights were turned off to avoid cutaneous damage. Continuous pulse oximetry was then used at rotating sites for the remainder of the 6-h surgical procedure, allowing only 7–15 min intervals at each site. We chose to use each phalanx as one site, allowing a potential for 14 different sites on each hand and foot. Each site was marked to avoid reuse on a subsequent occasion. Daily patient observation for 5 inpatient days, and telephone contact 2 weeks postoperatively, confirmed no cutaneous injury. Although no specific protocols have been promoted by the manufacturers of the photosensitizing drugs or pulse oximeters for use in the above situation, we found that limited use of pulse oximetry during the most critical aspects of anesthesia care can be performed without pulse oximeter-induced cutaneous damage. One should always be aware that published experience on the safe use is limited, and unstudied factors may increase the potential for skin damage in this situation. Although photofrin may require administration long in advance of PDT, verteporphin can be administered immediately before intraoperative PDT, and therefore is likely to be administered by anesthesiologists. Because anesthesiologists may not have experience or training in the administration of chemotherapy, attention to existing protocols and specific knowledge of each drug is essential to avoid injury to either patient or physician.