Neuraxial blockade and patient risk

Abstract

EDITOR: The report by Bogdanov and colleagues [1] of complication-free interscalene brachial plexus blockade performed in 548 patients under general anaesthesia should not support the common use of this practice. Although the authors highlight the absence of cervical spinal cord damage during block administration, we feel that the more relevant complications of interscalene block regarding its practice in awake vs. asleep patients are intravascular and intraneural injection. Moreover, estimating the incidence of rare events from small sample sizes is a well-known problem in clinical research, and is all the more salient when those rare events may be catastrophic. Furthermore, what may be safe and reasonable practice in the hands of the expert may not apply to the practice of someone still progressing on the learning curve or the student. In a study by Borgeat and colleagues, the overall rate of complications following interscalene block was found to be 0.4% [2]; however, the exact frequency of intravascular and intraneural injection during interscalene block is unknown. Benumof has reported on cases of permanent loss of neurological function following brachial plexus blocks performed under general anaesthesia or heavy sedation [3]. Intravascular injection can lead to local anaesthetic toxicity, including seizures and cardiac arrest. Intraneural injection may lead to permanent sensory and motor deficits [4]. These complications should be easier to avoid in an awake patient. It is widely believed that the most sensitive indicator of intraneural injection of local anaesthetic is severe pain and a withdrawal reaction immediately upon injection. This response cannot be assessed in the deeply sedated patient or the patient under general anaesthesia. Although both an increased resistance to injection and the persistence of a motor response at a stimulating current of less than 0.2 mA are suggested indicators of potential intraneural injection [5,6], they are not reliable. Similarly, intravascular injection can be caught early and terminated by acting on information only available through an awake, communicating patient. Soliciting feedback on the presence or absence of early warning signs of systemic toxicity such as tinnitus, perioral numbness or subtle changes in mental status allows one to stop the injection short of seizure and/or cardiovascular collapse. Furthermore, aspiration alone may not adequately protect against intravascular needle placement; despite immobile needle techniques, small movements in needle position may lead to transient intravascular placement and over-vigorous aspiration may result in collapse of the vein wall against the needle aperture resulting in a ball-valve effect and inability to aspirate blood. Hadzic and Vloka have also postulated intravascular ‘channelling’ of local anaesthetic under high injection pressures into blood vessels and lymphatics traumatized during needle placement [6]. In our opinion, the importance of patient feedback to the safe application of the interscalene brachial plexus block has been underestimated, particularly in the case of the nonexpert. Although the experience of Bogdanov and colleagues was complication-free, a series of 548 patients is inadequate to define the incidence of rare complications compared to that incidence in an awake patient population. As the outcome of these rare complications has the potential to be catastrophic, we feel the standard of practice for the performance of an interscalene block should incorporate all measures which can minimize risk, including maintaining communication with the patient. B. J. Egan A. R. Brown Department of Anesthesiology, New York Presbyterian Hospital, Columbia University Medical Center, New York, USA