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
(Pointer activation)
Good afternoon…today I will introduce a new method for detecting inferior vena cava compression in term parturients using diagnostic ultrasound.
This is a collaborative study between CUHK and the HKPU.
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
Aortocaval compression in pregnancy is caused by the compression of the abdominal aorta and inferior vena cava by the heavy gravid uterus… Thus it is important to position the patient laterally to prevent this. 2

3. Effects of inferior vena cava compression
Compression of IVC by gravid uterus
Venous return to heart
Right atrial pressure / Preload / CO / SV
The consequences of ACC can be deleterious to both mother and the baby.
[click] IVC compression decreases the venous return to the heart, resulting in a lower CO and SV.
[click] and this in turn will reduce uterine blood flow, causing fetal compromise.
[click] When this occurs, the body will initially try to compensate the changes by increasing maternal HR and SVR, or by diversion of blood through the azygous vein, vertebral plexus and the epidural venous plexus.
Uterine blood flow
Fetal compromise
Compensatory mechanisms:
Maternal Heart rate
Systemic vascular resistance
Collateral circulation: azygous vein, vertebral plexus & epidural venous plexus 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
According to published literatures, there are numerous methods to diagnose and detect ACC in term parturients.
[click] In the old days direct invasive methods such as contrast angiography or venography were used.
[click] Subsequently MRI, CT and abdominal ultrasound provided much clearer and slightly less invasive methods for the detection of the problem. 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)
Others, indirectly inferred ACC by detecting a gradient in arterial pressure of the femoral and brachial arteries, and usually the drop in femoral BP when ACC occurs is much greater than the brachial BP.
[click] Another way is to observe for haemodynamic disturbance when compression occurs, such as a drop in cardiac output or effects of compensatory mechanisms such as an increase in 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
[click] However, all the above methods required sophisticated equipment and complicated setups… and no bedside technique exists to detect ACC in these patients. 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.
In our study… we aim to develop an easier bedside method for detecting IVC compression in pregnant women, and
[click] 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 pregnant women. 7

8. Venous phasicity test - Principles
The theory of the venous phasicity test is that if we have a continuous column of blood, [click] then any changes in the pressure of the thorax will be transmitted to the femoral vessel to change the flow… [click] resulting in a phasic flow in response to respiration, which can be detected with ultrasound.
Theoretically it is possible to apply this principle for detecting IVC compression in parturients...although this has never been described in any literature.
Presence of phasicity 8

9. Venous phasicity test - Principles
[click] if there is compression in the IVC this column of fluid will be broken then [click] there will be cessation of phasic flow…
This test has been widely accepted for detecting venous obstruction in non-pregnant patients by sonographers…for example in patients with hepatic venous obstruction, DVT… and it was recommended for us to try in parturients.
Absence of phasicity 9

10. Methods Clinical Research Ethics Committee Approval
Informed written consent
10 ASA I-II term parturients
Before elective Caesarean section
With the approval of clinical ethics committee, informed, written consent were sought from patients on the day before surgery. 10 ASA I or ASA II healthy women were recruited and the study was performed before anaesthesia. 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)
[click] We used a Philips HDI-3000 ultrasound unit installed with a curvilinear probe.
[click] We made use of colour flow US to directly insonate the abdominal aorta and IVC, and colour spectral Doppler to investigate the flow pattern of the femoral vein with the respiratory phasicity tests.
[click] All investigations were performed with patients lying supine on a tilting table at 0, left 7.5 degrees and 15 degrees respectively. 11

12. Aortic/IVC Compression
Dinamap
NIBP (Right arm)
Datex
NIBP (Right calf)
USCOM
Cardiac Output
Colour-flow US
Aortic/IVC Compression
Doppler US
Femoral vein
Finometer
NIBP & CO
Portapres
Detects aortic compression
In addition to standard monitoring devices, we used a variety of monitors to enable us to detect aortocaval compression. ……
[CLICK] On the finger is a Finometer which provides a continuous arterial pressure measurement…A second cuff was placed on the toe and this is how we detect aortic compression.
[CLICK] In addition, we also have two NIBP cuffs on the R arm and the R calf….working on the same principle…
[CLICK] We use the USCOM for intermittent CO measurement…Haemodynamic changes usually accompany IVC compression and this is what we detected with the USCOM and the Finometer…
[CLICK] With ultrasound we image for the aorta, IVC and together with the femoral vein, and flow pattern were assessed…
Patients were kept tilted at each position for at least 3 minutes to equilibrate before each study.
Femoral vein US Image 12

13. Direct Abdominal scan of aorta / IVC
Inferior vena cava
Abdominal aorta
With direct abdominal scan, the IVC and aorta could be seen in the US image… although not always as clear as this, and sometimes with considerable difficulty.
Spine 13

14. Direct abdominal scan of aorta / IVC
This is an example of what we could see, on the left with the patient with the compression of the IVC in the supine position... and the right with 15 degrees tilt there is relief of compression... You can see the difference in the size and the colour-filling of the vessel.
Supine position degrees tilt
Difference in size /colour-filling of vessel 14

15. 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)
Loss of phasicity  Presence of IVC compression
[click] The phasicity test of the femoral vein was performed following direct insonation of the abdominal aorta and IVC.
[click] For each angles of tilt, we performed the respiratory phasicity test of the femoral vein with spectral Doppler.
Patient was requested to perform quiet and deep breathing and then a valsalva by blowing onto a closed PEEP valve for 3 seconds.
[click] The pattern of loss of phasicity was analyzed in relation to whether IVC compression was detected using conventional methods. 15

16. Quiet breathing Supine position 15 degrees tilt
The above diagrams illustrate the results during quiet breathing:
In this case in the supine position there is no respiratory phasicity, but restored at 15 degrees tilt… you can see the significant difference in the pattern of the waveform.
Supine position degrees tilt
Difference in respiratory phasicity at different tilts 16

17. Forced breathing Absence of phasicity (IVC obstruction)
The one on the left illustrates the waveform pattern in the presence of IVC obstruction during forced breathing… And on the right … without obstruction respiratory fluctuation can be clearly seen in the Doppler waveform.
Absence of phasicity (IVC obstruction)
Presence of phasicity (No obstruction) 17

18. Valsalva Manoeuvre
If NO IVC obstruction occurs when the patient was asked to perform a valsalva… [click] a normal waveform shows a cessation of flow followed by [click] a surge in flow upon expiration. 18

19. Results:     = /  = /  Pos CO HR/SVR IVC NB FB VAL Status
Position
Haemodynamics
Patency / Phasicity test
IVC status
Pos CO
HR/SVR
IVC NB FB
VAL
Status
Supine (n=3)
  
IVC compression
Lt 7.5º (n=3) 
IVC partial compression
Supine (n=27)
= / 
= / 
IVC patent
Lt 15º (n=30)
This table summarizes the changes observed, including parameters such as the CO, HR and SVR, the patency of IVC and the phasicity test with different respiratory modes.
These icons show you the patency of IVC, and these indicate the presence and absence of phasicity…
For each patient… we performed studies at 3 positions… hence we have a total of 30 positions… This is what we have found:
[click] In terms of the venous phasicity test, 3 patients out of 10 were detected with fairly severe IVC compression when lying supine. In these patients no phasicity were observed for all respiratory modes. Direct scanning found that IVC compression occurred at level of T6/T7… [click] At 7.5 degrees laterally, phasicity was restored with deep breathing and valsalva and direct abdominal scan showed improved IVC patency…
[click] By tilting to 15 degrees, enhanced respiratory phasicity were observed during quiet and deep breathing. 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
As a summary …
[click] In patients with partial IVC compression, there was loss of venous phasicity during quiet breathing, but restored during forced respiration and valsalva. There was minimal haemodynamic disturbance and with increasing tilt to 15 degrees respiratory phasicity was improved.
[click] And in patients with complete obstruction, there were loss of phasicity for all respiratory modes… and we could see more severe haemodynamic effects.
[click] With increased lateral tilts, phasicity restored and direct abdominal scan showed 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
[click] In conclusion…We have described the venous phasicity test for detecting IVC compression.
[click] It appears that the changes observed can be used in place of the more established but complicated methods...such as direct scanning of the abdomen.
[click] There are several limitations with direct scanning: It is time consuming and difficult to perform as the view can be obstructed by the gravid uterus…… Even If the view was not obstructed the depth of penetration of the US can be a problem for obese patients. Seeing an open vessel does not always mean that flow is present…. and we had to perform Doppler studies ...which is even more difficult at such depth. 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
[click] The advantage of venous phasicity test is that it is non-invasive, reproducible and convenient to perform… it also takes into account the efficiency of collateral circulations which may be present… Many anaesthetists are familiar with the anatomy and have scanned this area for insertion of femoral catheters.
We have performed this preliminary investigation to show its feasibility, but require further study to improve and modify it to confirm its clinical utility. 22

23. Annual Scientific Meeting in Anaesthesiology 2006
- 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