Abstract
To the Editor:
We thank Dr Mohanty and colleagues for their valuable comments 1 and important additions regarding our recently published article. 2
We agree that expressing local anesthetic (LA) dosing as the amount of substance per patient's weight is standard practice, usually in milligrams per kilogram (mg/kg). However, physicians should not rely solely on the weight in kg and should be aware that other factors may play a role in LA's calculations, such as body composition, age, critical illnesses, or site of block. 3 The choice of LA, concentration, and volume is the responsibility of the physician in charge of the patient. Both concentration and volume may vary according to personal preferences, aim of the block, and patient characteristics. Obviously, the calculation of a safe and effective LA dose is a prerequisite before injection and, in such circumstances, should be done by physicians with extensive experience in locoregional anesthesia.
For adult patients without pre-existing comorbidities and with normal body mass index, we used a maximum amount of Ropivacaine of 3 mg/kg of actual body weight.
Regarding the technical details of the procedures, both patients were lying flat under a warm shelter (special tent), inside a sleeping bag, and monitored during the whole periprocedural period with pulse oximetry and noninvasive blood pressure. Both parameters were in the normal range for both patients, who were breathing room air. We did not bring an oxygen reservoir because it would have been too heavy and too dangerous to transport and comes with explosion hazards in confined spaces where portable stoves are used. Although there are continuous electrocardiogram monitoring devices compatible with the extreme conditions prevailing in caves, 4 the Swiss cave rescue organization doesn’t own such a device. An intravenous access was in place for both patients with a running crystalloid infusion, as well as emergency drugs (epinephrine, atropine, midazolam, intralipids) and all necessary resuscitative equipment, such as airway cannulas, ventilation bag, mask, and manual suction device. After assessment of intact neurovascular status, all blocks were performed under standard sterile conditions using sterile gloves and masks. Needles were 22G 50mm and 80mm B-Braun Stimuplex© isolated with neurostimulation in sentinel mode (1Hz, 0,8mA) for the interscalene brachial plexus block (ISBPB) and the popliteal block (lateral entry, patient lying flat, probe on the posterior aspect of the knee) respectively, both under in-plane needling technique. The fascia-iliaca block of the second patient was performed with an 80mm needle (same brand and type), using in-plane technique (lateral entry toward midline, probe parallel to the inguinal crease), without neurostimulator, directed under the iliac fascia. All three injections were preceded by a cautious test dose, followed by slow, fractionated injections under ultrasound (US) vision. For Case 1, ISBPB and popliteal block were provided sequentially, approximately with a 30 minutes interval, in order to allow clinical monitoring between injections and plasmatic peak level of LA following local reabsorption.
During and immediately before the injections, neither patients received any additional analgesics nor sedatives. They were both fully awake, cooperative, and able to report paresthesia or pain during the procedures. Fentanyl and ketamine were administered only during the initial on-site management and mobilization for the primary and secondary survey to treat severe pain visual analog scale (VAS) score of 10/10. Following installation in the warm shelter and immobilization of injured limbs, both patients’ VAS scores decreased (≤3/10), with World Health Organization level I analgesics and intermittent low-dose ketamine. As there was, therefore, a significant time interval between IV sedatives and opioids, we did not expect any significant side effects of these agents during nerve block procedures.
As far as clonidine is concerned, the dosing regimens have been well-described and extensively studied. This additive is safe, up to 2 mcg/kg, without hemodynamic consequences or bradycardia. 5 We agree that its use would be contraindicated in a polytrauma patient in the initial phase of management. In both cases, however, patients were assessed for contraindications for clonidine use (hemodynamic instability, initial bradycardia, residual sedation) before using it. Block procedures were performed 12 h (Case 1) and 40 h (Case 2), respectively, after the trauma on stabilized patients. The aim of this adjuvant was to prolong analgesia as long as possible and avoid the need to reinject in difficult conditions during transport. Perineural catheter insertion could have been an alternative, but this has never been described in such an environment and would probably pose various concerns like asepsis and catheter migration.
Finally, the choice of interscalene block was made with the aim of anesthetizing, with a single injection, the multiple lesions of the right arm: the fracture of the outer third of the clavicle 6 and that of the distal end of the radius. Phrenic nerve palsy is a concern, indeed; however, adequate precautions related to the injection technique may minimize its risk. 7 An alternative would have been to target the suprascapular nerve for analgesia of the lateral third of the clavicula, combined with a standard brachial plexus block for the distal radius fracture. This would have required undressing the patient, exposing her further to the cold environment. We used an extrafascial injection, as low as possible down the brachial plexus, which has shown to diminish the incidence and severity of hemidiaphragmatic paresis compared to intrafascial injection (90–21%) while providing similar analgesia. 8 A thorough lung US, shown to be more sensitive than a chest radiography, 9 excluded a pneumothorax before the procedure.
To summarize, clinical standards and guidelines should be followed as closely as possible to ensure patients’ safety while bearing in mind that the extreme conditions of cave rescue force physicians to adapt outside their comfort zone and may not allow for full compliance with them. 10
