Effect of Inhalational Anesthetics and Positive-pressure Ventilation on Ultrasound Assessment of the Great Vessels

Abstract

Background Bedside ultrasound has emerged as a rapid, noninvasive tool for assessment and monitoring of fluid status in children. The inferior vena cava (IVC) varies in size with changes in blood volume and intrathoracic pressure, but the magnitude of change to the IVC with inhalational anesthetic and positive-pressure ventilation (PPV) is unknown. Methods Prospective observational study of 24 healthy children aged 1 to 12 yr scheduled for elective surgery. Ultrasound images of the IVC and aorta were recorded at five time points: awake; spontaneous ventilation with sevoflurane by mask; intubated with peak inspiratory pressure/positive end-expiratory pressure of 15/0, 20/5, and 25/10 cm H2O. A blinded investigator measured IVC/aorta ratios (IVC/Ao) and changes in IVC diameter due to respiratory variation (IVC-RV) from the recorded videos. Results Inhalational anesthetic decreased IVC/Ao (1.1 ± 0.3 vs. 0.6 ± 0.2; P < 0.001) but did not change IVC-RV (median, 43%; interquartile range [IQR], 36 to 58% vs. 46%; IQR, 36 to 66%; P > 0.99). The initiation of PPV increased IVC/Ao (0.64 ± 0.21 vs. 1.16 ± 0.27; P < 0.001) and decreased IVC-RV (median, 46%; IQR, 36 to 66% vs. 9%; IQR, 4 to 14%; P < 0.001). There was no change in either IVC/Ao or IVC-RV with subsequent incremental increases in peak inspiratory pressure/positive end-expiratory pressure (P > 0.99 for both). Conclusions Addition of inhalational anesthetic affects IVC/Ao but not IVC-RV, and significant changes in IVC/Ao and IVC-RV occur with initiation of PPV in healthy children. Clinicians should be aware of these expected vascular changes when managing patients. Establishing these IVC parameters will enable future studies to better evaluate these measurements as tools for diagnosing hypovolemia or predicting fluid responsiveness.

International evidence-based guidelines on Point of Care Ultrasound (POCUS) for critically ill neonates and children issued by the POCUS Working Group of the European Society of Paediatric and Neonatal Intensive Care (ESPNIC)

“…Conversely, a collapsed IVC may be suggestive of hypovolemia. Clinicians performing POCUS should be aware of its limitations especially in children on mechanical ventilation and neonates (especially when an umbilical central venous catheter is placed) in whom no validated normative data yet exist [18,19]. Moreover, mechanical ventilation (especially with high mean airway pressure), spontaneous breathing effort and some concomitant conditions may reduce the reliability of IVC evaluation to predict fluid responsiveness [20].…”

Pediatric emergency medicine point-of-care ultrasound: summary of the evidence

“…Positive pressure ventilation and vasopressors may have variable impact on the size and respiratory variation of the IVC [153, 154]. …”

Getting to know a familiar face: Current and emerging focused ultrasound applications for the perioperative setting

“…Caval indices change with the initiation of positive pressure ventilation. A greater variation in IVC diameter is observed during spontaneous breathing as compared to mechanical ventilation . In healthy children undergoing elective surgery, the median IVC respiratory variation while spontaneously breathing was 43% (interquartile range [IQR] 36%‐58%) and after initiation of mechanical ventilation was 9% (IQR 4%‐14%) .…”

“…A greater variation in IVC diameter is observed during spontaneous breathing as compared to mechanical ventilation . In healthy children undergoing elective surgery, the median IVC respiratory variation while spontaneously breathing was 43% (interquartile range [IQR] 36%‐58%) and after initiation of mechanical ventilation was 9% (IQR 4%‐14%) . In adults, IVC respiratory variation of >40%‐50% during spontaneous breathing and >12%‐18% during mechanical ventilation are considered predictive of fluid responsiveness .…”