No risk of metal toxicity in combined spinal-epidural anesthesia

Using the single level needle-through-needle technique for combined spinal- epidural anesthesia (CSE) may introduce very fine metal particles abraded b y the spinal needle from the inner ground edge of the Tuohy needle into the patient. Either the local anesthetic administered epidurally or the peridu ral catheter may also pass intrathecally through the hole in the dura made by the spinal needle. To examine these concerns, the needle-through-needle technique was simulated in an in vitro model (18-gauge Tuohy needle; 27- or 29-gauge Quincke needle). The presence of abraded metal particles was iden tified by atomic absorption spectrography (AAS). The needles were then exam ined under an electron microscope. Metal particles could not be identified by using AAS in the needle-through-needle technique after normal clinical u se, nor could traces of use be revealed by using an electron microscope to examine the Tuohy needle. With intentionally rough handling and caudal orie ntation of the spinal needle tip, minimal scratches could be seen by using an electron microscope, but there were no metal particles detected by AAS. In an anatomical preparation, the possible passage of the epidural catheter anesthetic through the dural puncture hole into the cerebrospinal fluid co mpartment was investigated endoscopically. Neither passage of dyed epidural local anesthetic nor penetration of the epidural catheter into the cerebro spinal fluid compartment could be demonstrated by endoscopy. We conclude th at the needle-through-needle technique is an acceptable way of performing C SE anesthesia. Endangering the patient by an unintentionally intrathecal mi splacement of the epidural catheter seems to be very unlikely based on our in vitro model if small spinal needles (27- or 29-gauge) are used. Implicat ions: Atomic absorption spectrography shows no contamination of the intrath ecal compartment by abraded metal particles from the Tuohy needle by combin ed spinal-epidural anesthesia with the needle-through-needle technique. In vitro, neither passage of dyed epidural local anesthetic nor penetration of the epidural catheter into the cerebrospinal fluid compartment could be de monstrated by endoscopy.