For many years, traditional teaching has advised that regional anesthesia (RA) should only be performed in conscious patients, although pediatric practice is an exception to this general rule. But why should children and adults be treated differently when performing a peripheral nerve block (PNB) or neuraxial anesthesia? And why is there a fear of performing RA techniques in anesthetized adults?

In fact, there are very few reports in the literature describing serious complications following RA procedures in anesthetized patients. the most striking example is a paper from 1998 by Bromage and Benumof: ‘Paraplegia Following Intracord Injection During Attempted Epidural Anesthesia Under General Anesthesia’. However, a number of questions remain unanswered in this case report: what was the real cause of this clinical catastrophe? Was it substandard practice to attempt placing an epidural catheter in an anesthetized patient, or was the problem related to a previous laminectomy? Did the combination of nitrous oxide with the use of air for loss of resistance aggravate the situation? Did hypotension contribute to the outcome? Or were there any other factors that played a role?

RA offers improved pain control in some types of surgery or trauma and can be associated with reduced morbidity and mortality in the peri- and post-operative period. Moreover, RA is opioid sparing and reduces post-operative cognitive dysfunction. Consequently, it may be considered poor clinical practice to withhold RA in certain cases, even if the patient has already been sedated or anesthetized.

Why are RA techniques common practice in pediatric anesthesia and widely accepted in a non-compliant adult patient? the answer lies in minimizing distress, avoiding spontaneous and/or hazardous movements and improving patient comfort by abolishing procedural pain. So what are the reasons for preferring full consciousness in the adult population? the answer to this question is that patients are able to provide useful feed-back: they may indicate the presence of paresthesia or pain (in the presence of needle-to-nerve contact), or pain during injection and they may communicate the early warning symptoms of local anesthetic systemic toxicity (LAST). However, it may be questionable whether this feedback is always reliable in a stressed and nervous adult. Nevertheless, the same principle underlies both approaches to RA – namely increased safety and reduced likelihood of complications. But for adult patients, shouldRA in the fully conscious state be the standard of care? Alternatively, could general anesthesia or deep sedation contribute to greater acceptance of RA techniques whilst simultaneously improving safety? Moreover, can we really talk about a ‘standard of care’ in this controversy?

The second ‘ASRA advisory on neurologic complications associated with RA’, does not provide any ‘standard of care’, but offers recommendations, which should be applied on a case by case basis. One reason for this is the difficulty in evaluating how changes in methodology and/or RA practice may reduce the number of nerve injuries. Statistically, when injuries occur only infrequently, large numbers of patients should be compared if changes in RA practice are to demonstrate superior safety. Currently, there is insufficient evidence to suggest a ‘standard of care’, due to the relatively low frequency of long-term injuries with both PNB and neuraxial blocks. Furthermore, it seems that the use of ultrasound for performing PNB during the last decade has not influenced this incidence. Accurate reporting of complications is difficult and varies considerably. This may be due to many factors e.g. the definition of a complication (this seems less heterogenous for neuraxial bocks), the duration of follow-up, the accuracy of data recording and the difficulty sometimes in attributing causality - surgical, anesthetic or both.

What are the recommendations for performing a RA procedure in a conscious versus an anesthetized patient?

Firstly, the risks and benefits of the RA technique in a particular case should be considered.

For neuraxial blocks

1. There is no evidence that ultrasound guidance for neuraxial procedures reduces complications in either conscious or anesthetized patients.

2. Even if warning symptoms, such as paresthesia or pain, or pain on injection are reported inconsistently by adult patients, neuraxial blocks should only rarely be performed during deep sedation or general anesthesia (exceptions are developmental delay and multiple fractures).

3. In children and infants, the benefits of sedation or general anesthesia in providing an immobile patient likely outweigh the risk of performing a neuraxial block.

For peripheral nerve blocks

1. Intra–neural needle insertion does not always lead to functional nerve injury, but intra–fascicular insertion of the needle, and especially injection, should be avoided. Paresthesia is not entirely predictive of peripheral nerve injury (PNI).

2. There is no nerve localization technique for avoiding PNI, but the following practices reduce the risks.

   1. Use a peripheral nerve stimulator: motor responses at currents <0.5 mA indicate close needle to nerve position or possible intra–neural needle placement.

   2. Monitor injection pressure: in animal studies, high injection pressures are associated with fascicular injury. There are no data for humans. During interscalene blockade, high pressure may indicate needle–nerve contact.

   3. Ultrasound guidance: ultrasound can detect intra–neural injections but the resolution is insufficient for detecting intra–fascicular injection. Even experts have difficulty in discerning intra– or extra–neural needle tip position.

   4. Tangential needle approach: a tangential approach to the nerve reduces the risk of epineurium perforation and intra–neural injection.

For peripheral nerve blocksThese recommendations are not substantiated by high level evidence, as there is no data to support the practice of RA in either fully conscious or anesthetized patients. Neural injuries cannot be reliably avoided when judgement is based on clinical symptoms (paresthesias and/or pain), the use of specific techniques or adjunct equipment such as ultrasound.

Recent multi-center studies in pediatric regional anesthesia, including thousands of blocks, have demonstrated a very low complication rate. Most of these blocks were performed during deep sedation or with general anesthesia. Thus, for the pediatric anesthesia community there seems little doubt - performing RA procedures in sedated or anesthetized children should be a ‘standard of care’.

With regard to the adult population, however, the ‘awake or asleep’ controversy continues. a German retrospective analysis of RA-related acute complications and patient satisfaction, conducted in 42 654 patients (25 004 awake, 15 121 sedated and 2 529 anesthetized) showed that LAST and pneumothorax rates where independent of conscious state, but that ultrasound guidance reduced the incidence of pneumothorax in supraclavicular blocks when compared with landmark techniques. There was an increased risk of bloody punctures when PNB was performed in sedated and anesthetized patients, probably secondary to vasodilatation. However, this was not observed in neuraxial bocks. Furthermore, the number of skin puncture attempts during sedation/general anesthesia was not reduced in PNB’s or in neuraxial blocks. the incidence of accidental dural puncture was similar for conscious and sedated/anesthetized patients. the incidence of postoperative paresthesia following PNB in the sedated/anesthetized population was reduced, which might favor patient safety with this technique. Sedation for PNB, as well as neuraxial blocks, was associated with greater patient satisfaction.

Ultrasound allows considerable reduction in the dose/volume of local anesthetic necessary to achieve an adequate PNB and may help avoid intravascular injections. Both of these advantages reduce the risk of LAST.

Considering the infrequent complication rate in the limited numbers of cases currently reported in the literature, sedation should be recommended during PNB procedures, if there are no contraindications and the patient gives consent. Neuraxial blocks, as well as perhaps interscalene blocks, should only be performed in anesthetized patients by experienced anesthesiologists, in very specific situations.

Based on the foregoing commentary, it seems unreasonable to withhold sedation or anesthesia while performing RA, provided adequate vigilance is maintained. the decision to perform RA during general anesthesia has to be made on a case by case basis, with attention for the following:

1. an appropriate indication, after full explanation of the risks and benefits (informed consent)

2. the wishes of the patient

3. the availability of appropriate equipment

4. use of the most appropriate technique e.g. PNB using ultrasound guidance, a low current nerve stimulator, injection pressure monitoring and tangential (blunt) needle approach

5. presence of an experienced anesthesiologist

When these 5 criteria are met, RA can be performed safely in a deeply sedated patient or under general anesthesia, keeping in mind, that RA procedures carry risks whether the patient is asleep or awake.

In conclusion, there is no current evidence to recommend RA procedures be performed in either conscious or sedated/anesthetized patients, with the exception of pediatric practice, where this is the standard of care.

In adults, RA can be performed in the anesthetized patient, provided sufficient care is exercised: the pros and cons should be explained to the patient and informed consent obtained, the wishes of the patient should be respected, the procedure should be performed in accordance with the most recent advances in the field of RA and by an experienced anesthesiologist. Caution is advised for neuraxial and interscalene blocs, as complications can be very serious.

Literature

1. The second ASRA practice advisory on neurologic complications associated with regional anesthesia and pain medicine. Executive summary 2015. J. Neal et al. RAPM 2015;40(5).

2. Awake, sedated or anaesthetised for regional anaesthesia block placements? C. Kubulus et al. Eur J Anaesthesiol 2016; 33:715–724.

3. Asleep Versus Awake and Standard of Care. J. Neal et al. RAPM 2017;42(5).

4. Pediatric Regional Anesthesia Network (PRAN): a Multi–Institutional Study of the Use and Incidence of Complications of Pediatric Regional Anesthesia. D. Polaner et al. Anesth Analg 2012;115(6).

5. A prospective analysis of interscalene brachial plexus blocks performed under general anesthesia. G. Misamore et al. J Shoulder Elbow Surg 2011;20:308–314.

6. Ultrasound–guided approach to nerves (direct vs. tangential) and the incidence of intraneural injection: a cadaveric study. L. Sermeus et al. Anaesthesia 2017 Apr;72(4):461–469.