Intrathecal administration of high-dose morphine solutions decreases the pH of cerebrospinal fluid

Abstract

Terminally ill patients suffering from intractable cancer pain are treated in our hospital on an outpatient basis with a percutaneous intrathecal (i.t.) catheter and a portable pump delivering morphine continuously. In a patient showing an increased demand of morphine the dose was raised from 1.5 to 2 mg/h, but pain intensity did not decrease. Subsequently a 1.5 ml dose of 5% lidocaine was administered; however, no motor or sensory block was observed. After controlling the catheter position and passage through the catheter, a sample of cerebrospinal fluid (CSF) was taken and the pH was measured. It was found to be outside the physiological range of 7.19 (normal range: 7.27-7.37), possibly explaining the decreased activity of the local anesthetic. The purpose of this study was to determine the influence of morphine, with or without sodium metabisulfite, on pH in vitro, using artificial CSF (ACSF) and on pH in vivo during i.t. administration of morphine. An in vitro model was used to measure pH changes by adding a morphine solution (concentrations of 0.5, 2, 5 and 10 mg/ml) with and without sodium metabisulfite to ACSF solutions (Elliott B). Fourteen patients were consecutively selected for continuous administration of morphine. An i.t. catheter was inserted, tunnelled and connected with an external pump (Provider 5500, Abbott, Chicago, IL). CSF was aspirated and pH was measured with a blood-gas system (Ciba-Corning 288, Medfield, USA). In vitro, morphine solutions with or without sodium metabisulfite added to an Elliott B solution (pH = 7.47, 37 degrees C) caused a concentration-related decrease in pH.(ABSTRACT TRUNCATED AT 250 WORDS)

Successful use of ketamine for intractable cancer pain

“…Furthermore, the presence of undesirable side effects can restrict adequate pain control. The use of intrathecal or intraventricular catheters may be an option to avoid systemic toxicity [14], but this is only indicated in well-selected patients [10], and local toxicity remains a concern [19]. New treatment modalities are thus needed for the treatment of intractable cancer pain.…”

Dissociative Mental State in a Patient with an Intrathecal Drug Administration System

“…It is possible that a larger concentration of morphine was actually present, which, when unstable in a solution, led to a cloudy yellow appearance. Morphine-induced CSF pH value changes have previously been noted (12), with implications for stability of analgesic compounding mixtures. We believe that our patients' symptoms may have been caused by an abnormally large concentration of morphine in the pump.…”

Inadvertent intrathecal injection of tramadol

“…Another potential mechanism is via an alteration in the CSF pH. It is known that intrathecal injections of morphine do lower the pH of the CSF, 17 and it is possible that the addition of tramadol compounded this, although there is no evidence for this.…”