Impact of caudal block on functional residual capacity and ventilation distribution in anaesthetized preschool children

Introduction: In children, general anaesthesia is often performed in combination with regional anaesthesia and caudal block (CB) is probably the most commonly used central neuroaxial blockade. The administration of local anaesthetics results in a motor blockade. The impact of this motor blockade induced by CB on the functional residual capacity (FRC) and ventilation distribution is unknown. The aim of this study was to determine the impact of CB versus control on FRC and ventilation distribution in preschool children. We hypothesized that an effective CB would lead to an increase of FRC and ventilation distribution while these parameters would remain unchanged in the control group. Methods: After approval from the local Ethics Committee, 52 preschool children (15–30 kg, 3–8 years) without cardiopulmonary disease who were to undergo elective surgery requiring combined general/regional anesthesia with a CB, were randomly allocated into two groups: CB (n = 26) or control (n = 26). Anesthesia was standardized using a propofol TCI for children. All children were breathing spontaneously via a laryngeal mask airway. FRC and lung clearance index (LCI), a measure of ventilation distribution, were calculated using a sulfur‐hexafluoride gas (SF₆) multibreath washout technique. A blinded reviewer performed off‐line analyses of the data. Following the first measurement in the supine position (baseline), all children were turned into the left‐lateral position. The CB group received a CB (0.2 ml·kg^‐1 bupivacaine 0.25% + epinephrine 1: 200 000 test dose and 0.8 ml·kg^‐1 bupivacaine 0.175%), while in the control group no intervention took place. After 5 min in the lateral position, all children were turned back to the supine position. After 15 min, the effectiveness of the CB was tested by pinching the skin at the L1 level with any movement being taken as a noneffective block (n = 0), and the second FRC assessment was performed in both groups. Results: At baseline, FRC and LCI were similar for the two groups. In the CB group, FRC (mean ± SD) increased from 17.0 ± 4.3 ml·kg^‐1 to 20.5 ± 5.1 ml·kg^‐1 (P < 0.0001) after an effective CB while FRC in the control group remained unchanged (17.2 ± 4.9 ml·kg^‐1 to 17.1 ± 4.8 ml·kg^‐1 (P = 0.0757). At the same time, the LCI decreased from 12.0 ± 2.5 to 9.37 ± 1.7 (P < 0.0001) in the CB group, while it remained constant in the control group (10.8 ± 2.7 vs 10.7 ± 2.6, P = 0.1515). Conclusions: CB resulted in a significantly increased FRC and ventilation distribution, whereas these parameters did not change in the control group. This indicates that a CB could have a major impact on respiratory function in anaesthetized, spontaneously breathing children. Additionally, the constant values for FRC and LCI in the control group showed that there was no ‘over‐time’ effect on these two parameters during the assessed study period. Acknowledgement: The study was funded by the Department of Anaesthesia, University of Basel, Switzerland and by the Swiss Association of Anaesthesia and Reanimation (SGAR).