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Patient Positioning does not Influence Inferior Vena Cava Diameter: An Observational Study with Ultrasound via Intercostal Window
Abstract Number: O2-05
Abstract Type: Original Research
Introduction: It has been recently suggested that the resuscitation of pregnant women should be performed in the supine position to optimize chest compressions, with alleviation of aorto-caval compression provided by manual left uterine displacement(1,2). It remains to be determined how the efficacy of manual uterine displacement compares to the traditional method of wedging/tilting. Measurements of the Inferior Vena Cava(IVC)diameter by ultrasound have been correlated with patient’s volume status and preload,and may prove useful in answering that question(3). The objective of this study was to compare the IVC diameter in pregnant women using the two different methods of alleviation of the aorto-caval compression.
Methods: This was a prospective observational study. We enrolled term non-labouring pregnant women. We excluded women with cardiac disease, severe preeclampsia, multiple gestation and breech presentation. The IVC was visualized using the intercostal window (3) with women placed in 4 different positions: supine (S), left lateral (LL), 30-degree left lateral tilt (LLT), and supine with manual left uterine displacement (MUD) position. The IVC was measured approximately 2 cm distal to the branching of the hepatic vein in the short-axis. The maximum (max) IVC diameter was measured during expiration and minimum (min) IVC diameter during inspiration. The IVC index was calculated using the formula CI=(max−min)/max(4). Random effects models were used to compare mean diameters across the different positions.
Results: 30 women were studied. No differences were observed in the IVC index across all positions. There was a significant difference in the IVC max and IVC min across the different positions; the diameter in LLT was smaller than in supine position.(Table 1)
Conclusion: Contrary to our hypothesis, the different methods of alleviation of aorto-caval compression did not produce favorable changes in IVC as compared to the supine position. Furthermore, the commonly used LLT produced the worst outcome. These findings are in keeping with those of Fields et al(3)who showed that the response of IVC diameter of pregnant women to positioning is unpredictable. These results suggest that IVC diameters at the measured site may not be reflective of the aorto-caval compression in term pregnant women.
References:1)Circulation 2010;122(18 Suppl3:S829-61;2)Resuscitation 2010;81:1400–1433;3) Resuscitation 2013;84:304-8;4)Ann Emerg Med 2010;55:290–5.