Damage to the conus medullaris following spinal anaesthesia: 1

Professor Reynolds' seven closed-case reports of iatrogenic injury to the spinal cord remind us of the tragic history of subarachnoid anaesthesia, and how fragile a hold this powerful technique has in contemporary anaesthetic practice (Reynolds. Anaesthesia 2001; 56: 238–47). Needle injury to the spinal cord during induction of subarachnoid block may occur in the best of hands, using standard textbook technique [1]. Therefore, the question arises: how can the safety of standard technique be improved upon? The answer to this is quite simple: adopt the loss-of-resistance-to-negative-pressure test (LORT), preferably with a Whitacre type pencil-point needle [2]. The LORT has a long and respectable history from the days of diagnostic cisternal puncture via the atlanto-occipital membrane, when it was used as an appropriate manoeuvre to avoid accidental needle trauma to the underlying hindbrain. Strangely, our specialty seems to have forgotten this simple technique that performs two essential functions when adapted to the more demanding anatomic constraints of spinal subarachnoid anaesthesia. First, it provides safety to an underlying spinal cord by signalling the precise moment to halt advance of the spinal needle. Second, the transmitted negative pressure collapses the subdural space, ensuring that the entire dose of any injected medication will enter the subarachnoid space, and none will become accidentally sequestered in the subdural space as a result of the needle point pushing the pia-arachnoid membrane inwards, away from the overlying dura mater. Technical success requires that two essential details be observed. A very firm, clenched-fist grip is required on the needle hub, while the dorsum of the hand is braced against the patient's back so that advance of the spinal needle can be halted in a fraction of a millimetre at the instant when cerebrospinal fluid (CSF) squirts back into the vacuum of the ‘seeking’ negative-pressure syringe. After the needle has been advanced 2–3 cm into the tissues, the stilette is removed, the ‘seeking’ glass syringe is attached and its plunger withdrawn between thumb and middle finger while the index finger exerts counter pressure against the rim of the syringe barrel to create a negative pressure of approximately 600 mmHg. This transmitted vacuum effectively clamps the pia-arachnoid membrane onto the overlying dura at the moment of dural puncture and obliterates the potential subdural space, while the process of confirming free reflux of CSF through 27- or 29-gauge needles is speeded up dramatically as CSF gushes back into the monitoring vacuum syringe on the instant of entering the subarachnoid space [2]. Mastery of this simple hydraulic manoeuvre provides optimal security against accidental injury to an underlying spinal cord, while at the same time increasing the probability that the entire dose of spinal medication will be delivered into the subarachnoid space, and that none will become accidentally sequestered in the subdural space. Given these advantages of precision and safety, the question arises: Why is this simple and clinically effective technique not being taught and practised as the preferred, standard routine for safe performance of subarachnoid puncture and spinal anaesthesia in contemporary practice?

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