Comment on “From the Operating Room to the Cave: Ultrasound-Guided Locoregional Anesthesia in the Setting of Cave Rescue—A Description of 2 Cases”

To the Editor:

We read the recently published article authored by Moser et al. ¹ in Wilderness & Environmental Medicine with great interest. The authors have done a commendable job of successfully managing the cases in highly challenging conditions. We want to highlight some concerns and suggestions through this correspondence.

The authors have highlighted the role of regional anesthesia (RA) in the cases of 2 patients in the setting of cave rescue. Local anesthesia (LA) ropivacaine was administered to both patients. Expressing LA as volume and concentration is standard practice, but instead, it is mentioned in milligrams. ¹ The authors highlighted their concern about the most important complication of RA, the local anesthesia systemic toxicity (LAST). However, the body weight of the patients are not mentioned for both patients. So, it is unclear if the drug doses were calculated randomly or based on weight. Optimal LA dosing should be based on the body weight to avoid adverse reactions, including LAST.^2-4 A total of 190 and 210  mg of drugs were used in the first and second patients, respectively, which is the maximum limit for a 70-kg patient. ¹ In the interscalene brachial plexus block (ISBPB), 10 to 15 mL of 0.25 to 0.5% ropivacaine is enough to block the desired nerve under ultrasonography (USG) guidance, so a minimum of 25  mg to a maximum of 75  mg of drugs is enough.^5,6 Phrenic nerve block is the most common and undesirable complication with ISBPB.^3,6,7 Phrenic nerve block results in diaphragmatic palsy, which is detrimental in patients with limited respiratory reserve.^3,7,8 The first patient had a clavicle fracture, and chest trauma can be suspected in such patients. So, while administering ISPBP, the detailed risk versus benefit must be evaluated, or alternative nerve block techniques can be used in such patients.^7-9 In addition, by limiting the dose (concentration and volume of drugs), the phrenic nerve block can be minimized.^5-7 We are delighted that the authors have kept the intralipid to manage LAST. Management of LAST starts with Airway, Breathing and Circulation, so it is not mentioned whether the resuscitative equipment and drugs were kept ready. ¹ The article lacks mention of monitoring the patient’s vital signs during and after the procedure, which is important for early detection of LAST when such high doses of the drug are used. ²

In the first patient, repeated doses of IV fentanyl and ketamine were administered. ¹ Here, we want to highlight that the American Society of Regional Anesthesia recommends against performing blocks in anesthetized or heavily sedated patients unless the benefits outweigh the risks. ⁹ The rationale is that sedation removes the ability to report pain as the presenting feature of neuronal injection, resulting in nerve injury. ⁹ So, precaution must be taken in such patients while performing RA. Additionally, in the nerve block technique, the length of the needle used and the technique of USG (either in-plane or out-of-plane) were not mentioned. ³ There is also insufficient information about the patient’s pain score and how much pain was reduced after the performance of the nerve block, which has a direct implication on the success or failure of the nerve block technique. ³

Further, the readers would be interested to know why the authors selected clonidine as an adjuvant in the first patient, especially in a highly challenging setup like a cave and a polytrauma patient. ¹ Clonidine can cause severe hypotension and bradycardia when used for nerve block.^10,11 This can mask important physiological warning signs in trauma patients. ⁹ Clonidine prolongs the duration of analgesia and sensory block by about 2  h, but in addition, it prolongs motor block, which is undesirable.^10,11 In patients in whom ISBPB is administered, prolonged phrenic nerve block and resulting diaphragmatic palsy due to clonidine are also undesirable.^3,7,9,10

To summarize, appropriate drug titration is essential in an outside intraoperative or emergency department setting. The LA dose (volume and concentration) to be used should be based on body weight. Resuscitative equipment should be available for monitoring when the area of the block is richly vascular. If drugs like adrenaline are used to prolong the duration of analgesia, then a more dilute solution of LA can be used. Clonidine should be avoided in polytrauma patients due to the possible masking of important warning physiological signs. Risk versus benefit must be evaluated while selecting any technique of block. We hope the above points will add more information to the published manuscript.