A new method for detecting inferior vena cava compression in term parturients

1. A new method for detecting inferior vena cava compression in term parturients Shara WY Lee, Kim S Khaw, Warwick D Ngan Kee Michael TC Ying, Stella SY Ho Department of Anaesthesia & Intensive Care Department of Diagnostic Radiology & Organ Imaging The Chinese University of Hong Kong Department of Health Technology & Informatics The Hong Kong Polytechnic University Annual Scientific Meeting in Anaesthesiology 2006 – 18th ~ 19th November 2006 (HKCEC) 1

2. Aortocaval Compression in Pregnancy • Compression of abdominal aorta & inferior vena cava by the gravid uterus • Positioning of parturient – to minimize haemodynamic disturbance 2

3. Compression of IVCby gravid uterus Venous return to heart Right atrial pressure / Preload / CO / SV Uterine blood flow Fetal compromise Compensatory mechanisms: Maternal Heart rate Systemic vascular resistance Collateral circulation: azygous vein, vertebral plexus & epidural venous plexus Effects of inferior vena cava compression 3

4. Established methods to detect ACC Directly: • Angiography to visualize aortic compression • Venography - Presence of collateral circulations • Azygous vein, vertebral plexus & epidural venous plexus • Less invasive modalities • MRI, CT • Abdominal US scan 4

5. Established methods to detect ACC Indirectly: • Detection of femoral / brachial hypotension • Gradient of BP femoral artery vs. BP brachial artery • BP femoral artery > BP brachial artery • Haemodynamic disturbance • Cardiac Output • Compensatory mechanisms ( Heart rate and SVR) 5

6. Established methods to detect ACC All the methods required complicated setups No convenient and non-invasive bedside technique available to detect aortocaval compression 6

7. Study Objective To develop an easier bedside method for detecting inferior vena cava compression in parturients We hypothesize that: Observing for phasic blood flow in the femoral vein using ultrasound can be used to detect inferior vena cava compression in term parturients. 7

8. Venous phasicity test - Principles Presence of phasicity 8

9. Venous phasicity test - Principles Absence of phasicity 9

10. Methods • Clinical Research Ethics Committee Approval • Informed written consent • 10 ASA I-II term parturients • Before elective Caesarean section 10

11. Materials and Methods • Philips HDI-3000 ultrasound unit (3-5MHz curvilinear probe) • Step 1: Direct insonation of abdominal aorta & IVC • Colour-flow ultrasound • Step 2: Respiratory phasicity test of the femoral vein • Colour spectral Doppler ultrasound • Patient positioned on tilting table (0º, left 7.5º & 15º) 11

12. Dinamap NIBP (Right arm) USCOM Cardiac Output Colour-flow US Aortic/IVC Compression Finometer NIBP & CO Datex NIBP (Right calf) Doppler US Femoral vein Portapres Detects aortic compression Femoral vein US Image 12

13. Direct Abdominal scan of aorta / IVC Inferior vena cava Abdominal aorta Spine 13

14. Direct abdominal scan of aorta / IVC Supine position15 degrees tilt Difference in size /colour-filling of vessel 14

15. Loss of phasicity  Presence of IVC compression Phasicity test of femoral vein • To study the changes after direct abdominal insonation of IVC • Respiratory phasicity test (Spectral Doppler US) • Quiet breathing • Deep breathing • Valsalva manoeuvre (15 cmH2O PEEP valve) 15

16. Quiet breathing Supine position15 degrees tilt Difference in respiratory phasicity at different tilts 16

17. Forced breathing Absence of phasicity (IVC obstruction) Presence of phasicity (No obstruction) 17

18. Valsalva Manoeuvre 18

19. Results: Position Haemodynamics Patency / Phasicity test IVC status 19

20. Summary: Venous phasicity of femoral vein • In patients with partial IVC compression • Loss of phasicity during - Quiet breathing • Phasicity restored - Deep breathing & Valsalva • Minimal haemodynamic disturbance • Increased respiratory phasicity at 15º • In patients with complete IVC compression • Loss of phasicity during - Quiet / Deep breathing & Valsalva • More severe haemodynamic disturbance • Effects of lateral tilts • Phasicity restored during quiet breathing at 15º • Direct abdominal scan at ~T9 – Improved IVC patency 20

21. Conclusions • Venous phasicity test – Detection of IVC compression • ? Superseed abdominal scan • Limitations of direct abdominal scan: • Time consuming • View obstructed by fetus (Fetal orientation) • Inadequate penetration (Gravid uterus increases depth of IVC) • Open vessel ≠ Presence of flow 21

22. Conclusions • Venous phasicity test: • Non-invasive, reproducible and convenient • Includes functional collateral circulation • Familiar anatomy – femoral catheters • Preliminary investigation shows feasibility • Further study to improve and modify present methodology and confirm clinical utility 22

23. - The End - Annual Scientific Meeting in Anaesthesiology 2006 Shara WY Lee, Kim S Khaw, Warwick D Ngan Kee Michael TC Ying, Stella SY Ho Department of Anaesthesia & Intensive Care Department of Diagnostic Radiology & Organ Imaging The Chinese University of Hong Kong Department of Health Technology & Informatics The Hong Kong Polytechnic University 23