Methemoglobin Levels in Generally Anesthetized Pediatric Dental Patients Receiving Local Anesthetics

Methemoglobin is an abnormal hemoglobin that is formed by the oxidation of one or more of the four heme groups of hemoglobin by oxygen and other exogenous oxidizing agents. The injectable local anesthetic prilocaine that is routinely used in the medical and dental professions is a well known inducer of methemoglobin. The injectable local anesthetic lidocaine has also been suggested to be associated with the development of methemoglobin; however, there is no direct evidence supporting these claims.

The concern with methemoglobin is that it is a dose-dependent toxin. The oxidation of one of the iron groups from a ferrous state to a ferric state alters the molecular structure of the hemoglobin molecule and impairs its ability to bind oxygen. This ultimately results in less oxygen being delivered to peripheral tissues and less carbon dioxide being removed which can cause tissue hypoxia. A small amount (0-2%) of methemoglobin is normally present in the blood as a result of the oxidation of hemoglobin by the prototypical oxidant oxygen. However, when an individual is exposed to an exogenous oxidizing agent of sufficient dosage and potency, methemoglobin levels can rise above 2% and a person can develop what is known as acquired methemoglobinemia. Signs of cyanosis as a result of acquired methemoglobinemia usually become present when methemoglobin blood levels rise above 15%.

Despite the injectable local anesthetic prilocaine being a well known inducer of methemoglobin and lidocaine being a speculated inducer, there are no documented studies or trials in the dental literature as to the extent of the amount of methemoglobin that is formed following the routine use of these injectable local anesthetics.

This investigation will examine the peak blood levels of methemoglobin and the time to the peak levels of methemoglobin following the use of injectable prilocaine and lidocaine when used for dental treatment in pediatric patients under general anesthesia.

This study population will consist of 90 patients, 3 to 6 years of age, scheduled to undergo comprehensive dental rehabilitation under general anesthesia at the Koppel Special Care Dentistry Center at Loma Linda University School of Dentistry. Following enrollment, subjects will be randomized into three equal study groups: 1) 4% prilocaine plain, 2) 2% lidocaine with 1:100,000 epinephrine, and 3) No local anesthetic. All subjects will have a Masimo Radical-7 pediatric, non-disposable, pulse co-oximeter sensor placed on the ring finger of the right hand following the induction of general anesthesia. The sensor will then be connected to a Radical-7 Pulse Co-Oximeter. The pulse co-oximeter will non-invasively monitor and record methemoglobin blood levels at 10 second intervals throughout dental treatment. Following a routine oral examination, radiographs, and prophylaxis, subjects assigned to Groups 1 and 2 will be administered local anesthetic for restorative dental treatment. Group 1 subjects will receive 5mg/kg of 4% prilocaine plain and Group 2 subjects will receive 2.5mg/kg of 2% lidocaine with 1:100,000 epinephrine. Group 3 subjects will not receive local anesthetic. The time of local anesthetic administration and baseline methemoglobin blood levels will be recorded. Methemoglobin blood levels will be monitored and recorded throughout the completion of the dental treatment and during recovery from general anesthesia until subject movement precludes any further monitoring.

Inclusion criteria

• Patient scheduled to undergo comprehensive dental treatment under general anesthesia at the Koppel Special Care Dentistry Center at Loma Linda University School of Dentistry
• ASA I or II health status
• Age greater than 3 years but less than 6 years
• Weigh between 10kg and 25kg

Exclusion criteria

• Patient not requiring restorative dental treatment
• Have a BMI less than the 5th percentile or greater than the 95th percentile for their age and gender