In comparison with lidocaine and mepivacaine, prilocaine has the advantage of far less cardiac or central nervous system toxicity.14,15 Nevertheless, prilocaine is not available in much of the world. The presence of acquired methemoglobinemia is often assumed.3,16,17 It is triggered not only by prilocaine but also by many other drugs,3,18 – 21 in particular by benzocaine.17 The symptoms are nonspecific and often unrecognized.3,9 Methemoglobinemia is associated with the reduction in the fractional oxygen saturation. Concentrations <15% are usually well tolerated by healthy individuals, but in patients with anemia or cardiopulmonary diseases, clinical symptoms can occur when the concentration exceeds 8%.3 Despite administration of the recommended threshold dose of prilocaine, it was only possible to assess MetHb values up to 6.6%. Further investigations are necessary to analyze the accuracy of the pulse oximeter at higher levels.
Dyshemoglobinemias cannot be identified by conventional pulse oximeters, because their measurements, based on 2 wavelengths of light absorption, only allow the recording of oxyhemoglobin and desoxyhemoglobin.7,22 The pulse CO oximeter Radical 7® measures the light absorption of 8 different wavelengths. In a preclinical study in healthy volunteers, Barker et al. evaluated a predecessor of the pulse oximeter that we used.10 The results (bias 0%, SD ± 0.45%) differ only slightly from the data presented in our clinical study.
In conclusion, we found a high degree of agreement in measurement of MetHb with a CO oximeter and a noninvasive and readily available pulse-oximetric procedure. This may facilitate early diagnosis and treatment, when necessary, of dyshemoglobinemia.
Financial support for the work: Peter Soeding and Hartmut Gehring are employees of the University Clinic of Schleswig— Holstein, Campus Luebeck, Luebeck, Germany. Device was provided by Masimo, Inc., Germany.
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