Comment On: Impact of Ultrasound-Guided Continuous Retrolaminar Block Versus Continuous Erector Spinae Plane Block on Incentive Spirometry Volumes and Pain Scores in Multiple Rib Fractures

Dear Editor, We read the study “The Comparison of Continuous Retrolaminar Block (RLB) and Erector Spinae Plane Block (ESPB) in Patients with Multiple Rib Fractures” with great interest.[1] The authors deserve recognition for conducting a prospective, randomized, double-blinded trial in a high-acuity trauma setting, where regional anesthesia is both essential and challenging to study. By using a catheter-based intensive care unit trauma cohort and a standardized infusion protocol, the study delivers valuable insights into the transition from acute to subacute analgesic management in thoracic trauma. Both ESPB and RLB are safe, technically feasible, and practical regional analgesic techniques for rib fractures. Previous randomized as well as observational studies have demonstrated effective analgesia with both techniques in thoracic pain conditions.[2,3] The authors concluded that “ESPB demonstrated superior inspiratory capacity, pain relief, and reduced morphine consumption compared to RLB.”[1] However, closer examination of the anatomical assumptions, infusion methodology, and statistical interpretation raises questions about whether this conclusion reflects a durable finding or a transient and context-dependent signal. A major issue is the absence of objective dermatomal sensory mapping, such as pinprick or cold testing, to confirm the extent of blockade. The higher incentive spirometry (IS) volumes observed in the ESPB group during the first 24 h were attributed to presumed anterior spread of local anesthetic toward the ventral rami and paravertebral space. Without dermatomal confirmation, this explanation is still speculative. Cadaveric and magnetic resonance imaging studies show that anterior spread from the erector spinae plane to the paravertebral compartment is variable and frequently limited to dorsal rami distribution.[4] Injectate spread in fascial plane blocks is also influenced by tissue compliance, trauma-related edema, and variability in catheter position.[2] Thus, one alternative interpretation is that the early respiratory improvement may reflect heterogeneous neural blockade or systemic absorption from the paraspinal musculature, rather than necessarily indicating consistent coverage of the intercostal nerves by the ESPB. Inclusion of standardized sensory mapping or contrast-enhanced imaging would have strengthened mechanistic attribution and enabled correlation between dermatomal extent and respiratory performance. Furthermore, both groups received a continuous infusion of 0.25% bupivacaine at 0.1 mL/kg/h after a 20-mL bolus. Given a mean patient weight of approximately 81 kg, the infusion rate is 8.1 mL/h. Fascial plane blocks depend on volume and hydrostatic pressure to expand interfascial compartments and maintain spread. Low-flow continuous delivery may not sustain anterior migration across fascial barriers or prevent compartment recoil over time. Programmed intermittent bolus delivery has been shown to enhance fascial spread compared with continuous infusion.[5] Consequently, early differences between ESPB and RLB may, at least in part, reflect infusion-pattern–dependent distribution; whether intrinsic anatomical differences also contribute cannot be determined from the present data. The retrolaminar plane, located closer to deeper fascial layers, may require higher injection pressure to achieve similar anterior dispersion, as observed in comparative studies.[3] Future trials using bolus-augmented infusion strategies would help distinguish anatomical efficacy from delivery-dependent spread. Additionally, morphine consumption was significantly lower in the ESPB group on day 1 (21.47 mg vs. 17.63 mg; mean difference 3.84 mg; 95% confidence interval: 2.45–5.23). Although statistically significant, this represents an approximately 18% reduction confined to a single 24-h period. Cumulative morphine consumption over 4 days did not differ significantly (P = 0.071), and inspiratory capacity converged after the first day. When longitudinal outcomes normalize, superiority should be interpreted as transient rather than sustained. Repeated-measures data were analyzed using serial between-group comparisons rather than mixed-effects modeling, which raises three specific concerns: Inflated type I error from multiple comparisons across time points, inefficient use of repeated observations, and inability to formally assess a group-by-time interaction—the key question of whether the two techniques truly diverge and then converge over time. The convergence of analgesic and respiratory outcomes indicates that both fascial plane techniques attain comparable clinical stabilization over time.[3] IS, the primary endpoint, is effort-dependent and susceptible to motivational and coaching influences. Although patients received standardized physiotherapy encouragement, blinding of physiotherapists was not described. Expectation bias and perceived analgesic adequacy can affect inspiratory effort independent of lung mechanics. Objective respiratory parameters, including PaO2/FiO2 ratios, arterial blood gases, respiratory rate, and oxygen saturation, remained comparable between groups, and no pneumonias or intubations occurred. This agreement on clinically meaningful respiratory outcomes raises the possibility that IS differences may partly reflect behavioral or perceptual factors rather than physiological improvements in pulmonary function, though this remains speculative without direct measurement. Effort-independent endpoints, such as diaphragmatic excursion ultrasound or spirometric flow-volume analysis, may provide a more robust assessment. Finally, the exclusion of patients with flail chest, major lung contusion, and multisystem trauma limits external validity; fascial plane blocks demonstrated here in a relatively stable cohort may behave differently when anatomy is distorted by severe injury. This constraint should be acknowledged when translating these findings to broader trauma practice. To conclude, both ESPB and RLB provide safe and effective analgesia for rib fractures. The apparent superiority of ESPB appears to be confined to an early temporal window and may reflect infusion dynamics and endpoint characteristics as much as anatomical spread. The convergence of outcomes over time warrants cautious interpretation; the absence of a statistically significant difference beyond 24 h does not establish equivalence but does suggest that the clinical gap between techniques may narrow substantially. Future studies incorporating objective sensory mapping, optimized bolus-based infusion strategies, and effort-independent pulmonary outcomes across more extensive trauma populations may better define the relative roles of these fascial plane blocks in thoracic trauma analgesia. Data availability statement No new data were generated. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.