• truncal blocks
• acute pain
• pediatrics

To the Editor,

Having read carefully the report by Moore and colleagues1 on the novel use of continuous erector spinae plane (ESP) blockade for postoperative analgesia after pediatric liver transplant and being very familiar with both pediatric pain management and liver transplantation, I have few comments regarding (1) block placement, (2) pain assessment, and (3) block safety.

I am not sure if the ESP catheter was positioned deep to the fascial plane of the erector spinae muscle. In figure 1,1 there is a visible fluid collection and a needle shadow between two bony structures, and the medication did not appear to spread cranial to caudal, or lifting the erector spinae muscle off the tip of transverse processes. In figure 2,1 a second fluid collection and the catheter over the needle device were visualized in a different plane, above T8 transverse processes,1 and I wonder if the catheter was positioned superficial to the erector spinae muscle.

The authors were impressed with the reduction in perioperative opioid consumption and compared the daily morphine equivalent consumption (mg/kg/day) (ME) of two patients with 10 prior transplant recipients. Because of wide interindividual differences in opioid pharmacokinetics, a daily ME individual consumption could be more appropriate rather than reported mean/SD. In addition, considering the ESP catheters were removed on postoperative day (POD) 4, a daily ME comparation for the first 4 days after surgery would be more accurate, instead of 6 days reported. Of note, ME consumption for POD 1 appears to be 0.28 mg/kg, not 0.179 mg/kg.

The self-reported pain scale Wong-Baker FACES seems not optimal for the patient with intellectual disability. In addition, the professionals can underestimate pain2 and his reduced opioid consumption may not represent a true ESP blockade opioid sparing effect.

Although the intraoperative ME administration for the second patient was minimal, significant hypotension indirectly could influence opioids administration. For the same patient, is unclear why the preoperative morphine consumption was used to illustrate ESP blockade opioids reduction. The mechanism of preoperative pain (venous congestion of the liver, stretching the liver capsule) is different from postoperative pain (incisional pain, visceral pain, muscle spasm) and associated comorbidities (anxiety, pleural effusions, ascites) could influence preoperative morphine administration. To provide further inside into the effectiveness of the ESP blockade, the sensory changes should be reported.

The authors describe this application of ESP catheters as being safe, but I have few concerns to share.

First, during liver transplantation transient hypotension is common and severe hemodynamic instability, including hypotension, bradycardia, dysrhythmias and even cardiac arrest can occur during reperfusion. These patients with impaired metabolic capacity and intraoperative liver blood flow could be at significant risk of perioperative local anesthetic toxicity. The patients with chronic end-stage liver disease have a decreased ropivacaine clearance, on average by 60%,3and it is not clear why recommended ropivacaine hourly infusion (0.5 mg/kg/hour) was exceeded intraoperatively (0.83 mg/kg/hour) and postoperatively (0.66 mg/kg/hour). An anesthetized patient cannot report any signs of local anesthetic toxicity and the hemodynamic disturbances will make this diagnostic very challenging. As the ESP block may involve an intravenous regional anesthetic mechanism,4 it is advisable to use the lowest local anesthetic effective dose and to monitor the blood level (which they did not report).

Second, the erector spinae block mechanism of action is controversial and should be father studied to promote rationale of using ESP catheter for pediatric liver transplantation. The authors speculated that indirect paravertebral blockade contributed to early returned of bowel function. If ropivacaine spread into the paravertebral space during ESP blockade holds true, the intraoperative ESP continuous infusion would imply some risks such hypotension and bradycardia, and this will limit the use of the local anesthetic specially during the anhepatic and reperfusion transplant phases (which they did not stop).

Finally, we recognized that Moore and colleagues1 describe this technique for pediatric liver transplantation for the first time. Placing the nerve block catheters deep to erector spinae muscle (an area not easily compressible) in a coagulopathic patient can result in perioperative bleeding. Long lasting hematoma-induced pain can increase medical costs and decrease patient and family satisfaction.5 6

We need controlled trials to demonstrate the ESP continuous blocks efficacy, safety and application for pediatric liver transplantation.