In busy clinical practice it is not uncommon that an intrathecal injection of local anesthetic in attempt to accomplish spinal anesthesia, perfectly performed, fails. Indeed, despite the reliability of the technique, the possibility of failure can never be completely eliminated. Managing a patient with an ineffective or inadequate spinal anesthetic can be challenging, and prevention is better than cure.
In this chapter, we discuss systematically the potential mechanisms by which spinal anesthesia may fail: detail strategies to decrease the failure rate and protocols for managing an incomplete spinal anesthetic.
Inability to reach the subarachnoid space, errors in drug preparation or injection, unsatisfactory spread of the injectate within the cerebrospinal fluid (CSF), ineffective drug action on neural tissue, and difficulties relating to patient expectations and psychology rather than genuine block failure.
The dense neuraxial blockade obtained by the administration of a spinal (intrathecal) injection of local anesthetic is widely held to be among the most reliable regional techniques. The anatomy is usually straightforward to palpate and identify, the technique for needle insertion simple and easy to teach, and the presence of CSF acts as both a definite endpoint for needling and a medium for carriage of local anesthetic within the subarachnoid space. The simplicity of the procedure was succinctly described by Labat, one of the pioneers of regional anesthesia, almost 100 years ago.1
Two conditions are, therefore, absolutely necessary to produce spinalanaesthesia: Puncture of the dura mater and subarachnoid injection of an anesthetic agent.
Gaston Labat, 1922
Yet, despite this simplicity, failure is not uncommon. What constitutes failure? At the most basic level, a spinal anesthetic has been attempted but the satisfactory conditions for proceeding with surgery are not obtained. Failure encompasses a spectrum that includes the total absence of any neuraxial block or the development of a partial block that is of insufficient height, duration, or quality.
In experienced hands, most anesthesiologists would expect the failure rate of spinal anesthesia to be low, probably less than 1%. A retrospective analysis of almost 5000 spinal anesthetics by Horlocker and colleagues2 reported inadequate anesthesia in less than 2% of cases, and failure rates of under 1% have been described.3 Yet, the “failed spinal” demonstrates remarkable interinstitutional variation, and in some published reports, it may be much higher. One American teaching hospital quoted a surprising failure rate of 17%, with the majority of failures deemed “avoidable.”4 A second institution reported a 4% failure rate—more in keeping with expectations, but nonetheless significant.5 Analyzing their failures, “errors of judgement” were felt to be the main causative factor. The suggestion from these reports is that with meticulous attention to detail and appropriate management, most failures of spinal anesthesia could be prevented.
Patients undergoing an operation under spinal block expect reliable surgical anesthesia, and an inadequate block will generate anxiety for both ...