A 37 year old female presented for diag laparoscopy for suspected ectopic pregnancy and mass in the left adnexa.
The procedure was uneventful, however, the surgeon was unable to visualize the ureters after performing a left salpingectomy. She was concerned about the ureters enough to perform a post operative cystoscopy to verify that both ureters remained functional. We verified that the only dye available to us was indocyanine green and methylene blue. I was given methylene blue and injected 3 1/2 mLs. After 20 minutes, no visible dye appeared in the bladder and the procedure was terminated with the plan to follow carefully her course.
There are three common dyes that anesthesiologist are asked to inject patients in order for diagnostic purposes. The anesthesiologist should have familiarity with the properties of any medication they inject. A review of information on these dyes revealed a deficit in my own knowledge in this regard.
Methylene Blue can be used to test ureteral patency after laparoscopic surgery. However, it is not commonly used for this indication. The recommended dose is 50 mg (it comes as a 10mg/mL concentration) for this purpose. Methylene blue does not have FDA approval for this use, and the package insert only asserts its use as a treatment for methemoglobinemia.
Methylene blue is the only medication known to be effective for the treatment of methemoglobinemia, which is the oxidation of the iron in hemoglobin to the ferric form. Normally, the blood has a 1% concentration of methemoglobin (hemoglobin in the ferric form). When the concentration of methemoglobin rises to about 15%, symptoms become apparent and require treatment. The negative effects of this disorder result from hypoxia, as oxygen cannot be efficiently carried by methemoglobin. Symptoms include ashen color skin or cyanosis (methemoglobin from 3 to 20%), headache, dyspnea, lightheadedness (up to 50%), arrhythmias, unconsciousness etc (greater than 50% methemoglobin level). Treatment dose of methylene blue is 1 mg to 2 mg/kg. Ironically, at doses greater than 7 mg/kg can lead to the inducement of methemoglobinemia.
Methylene blue inhibits monoamine oxidase enzyme, and therefore, can result in serotonin syndrome and should be used if with caution in patients taking serotonin reuptake inhibitors or MAO inhibitors.
As methylene blue can be used for verification of ureteral patency via cystoscopy as the urine should turn blue after 10 to 20 min of IV injection, I thought it curious that we had no evidence of blue urine after 30 min. However, joel et al. did publish a look at two cases where injection of methylene blue did not result in any change in urine color . The authors suspected that rapid metabolism of methylene blue to leulomethylene (a colorless metabolite was the cause of this anomaly). Since indigo carmine does not undergo any metabolism prior to excretion into the urine, it would be a superior alternative to methylene blue for detection of ureteral patency using cystoscopy. Indigo carmine's package insert asserts its primary use is for detecting change in urine color after IV injection. There are no drug interactions with indigo carmine, making it a safer alternative as well. The dose recommended is the full 5 mL ampule.
Indocyanine Green is another dye that may be encountered. It's used for determination of cardiac output, hepatic function and ophthalmic angiography (5mg, 0.5 mg/kg, and 40 mg respectively). It is bound to plasma proteins and taken up by hepatocytes without metabolism, and secreted in the bile unchanged. There are reports of the use of indocyanine green to detect ureteral patency via cystoscopy, however, it has been reported to be used in robotic surgery to detect ureters with near infrared light with success. However, the dye was injected directly into the ureters. Recently, I was involved in a case where a patient had an internal hernia with small bowel strangulation leading to questionable viability of the small bowel. Indocyanine green was injection IV and a laser was used to evaluate blood flow and vascular patency to the bowel. This technique is known as laser florescence angiography and uses the florescence properties of indocyanine green to visualize vessels that need to be verified as patent. With the laser set in place, the room lights off, an injection of indocyanine green is given IV, and within a few moments, the area of interest should light up white on the proper viewing screen where vessels are patent. Using this technique, we the surgeons were quickly able to verify that all vessels to the bowel section of interest were patent.
Anesthesiologists are often asked to inject substances that lie outside our typical armamentarium. We have an obligation to understand the possible ramifications of what we inject, and not always assume that it is proper and safe.
Joel AB, Mueller MD, Pahira JJ, Mordkin RM. Nonvisualization of intravenous methylene blue in patients with clinically normal renal function. Urology 2001; 58: 607vii. - See more at: http://www.ashp.org/menu/DrugShortages/CurrentShortages/Bulletin.aspx?id=27#sthash.ado1taUN.dpuf
Blog with interesting cases and/or problems related to anesthesia with discussion based on best evidence in the literature.