Dear Editor, Injection around the C5 nerve root, brachial plexus block (BPB), is linked with a high risk of hemidiaphragmatic paresis (HDP).1 To reduce this, site-specific procedures have been devised, including interscalene, superior trunk, and anterior suprascapular nerve blocks.2,3 Although ultrasound has reduced HDP incidence, clinically significant decreases in lung ventilation persist.4 Ultrasound can measure diaphragmatic excursion, but it cannot quantify regional lung ventilation alterations. Electrical impedance tomography (EIT) is a non-invasive technology that allows continuous, real-time measurement of regional lung ventilation.5 We have correlated regional lung ventilation changes using continuous EIT after BPBs with diaphragmatic function measured using ultrasound. Following institutional ethics approval and informed consent, seven American Society of Anesthesiology (ASA) I–II adult patients undergoing upper limb surgery received ultrasound-guided site-specific BPBs using a standardized low-volume local anesthetic (LA) mixture Table 1.Table 1: Demography, EIT data, and HDP in various casesContinuous EIT monitoring (PulmoVista® 500, Dräger) was performed to analyze ventilation distribution. M-mode ultrasound assessed diaphragmatic excursion at baseline, immediately following, intraoperatively, and postoperatively. Upper lung ventilation did not change significantly. Ipsilateral lower lung ventilation decreased post-block (−23.14, P = 0.011), intraoperative phase (−53.6, P = 0.008), and at 6 h(−18.33, P = 0.002). It normalized by 24 h, with contralateral compensation (+12.02, P = 0.002). No clinical respiratory compromise was observed, but EIT detected hypoventilation preceding ultrasound-detected HDP in two patients Figure 1.Figure 1: (a) Lung ventilation on EIT in various cases; (b) Heatmap of ipsilateral and contralateral ventilation displaying the mean ipsilateral and contralateral lung ventilation values at each procedural phase. EIT = electrical impedance tomographyContinuous EIT was more sensitive than ultrasound in detecting regional ventilation alterations, indicating a physiological separation of diaphragmatic motion and lung aeration.3-5 This hypothesis-generating case series investigated the physiological link between supraclavicular BPBs (SCBPBs), regional lung ventilation, and diaphragm function. The strength of this work is the simultaneous, real-time measurement of lung ventilation and diaphragmatic function in non-intubated patients, which provides insights not possible with ultrasound alone.3,5 Limitations include a small sample size, variety of block procedures, qualitative ultrasonography assessment, and the lack of spirometry or gas-exchange correlation. Regional lung hypoventilation after SCBPBs may occur independently of diaphragmatic paresis and can be detected earlier by EIT than by diaphragm ultrasound. Author contributions SD, NG, and SP: Conceptualization (lead); Methodology (lead); Writing – original draft (lead); Writing – review and editing (equal). NG: Writing – original draf (support), Software and investigation (lead), and writing – review and editing (support). PS supervised the entire study, and all the authors contributed substantially. All authors have read and agreed to the content of the final manuscript. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.
Diwan et al. (Mon,) studied this question.