What is the relationship between near infrared spectroscopic regional mixed arterio-venous oxygen saturation and

jugular bulb venous saturation during core cooling and bilateral selective antegrade

cerebral perfusion?

Vamsidhar B Dronavalli, Ashvini Menon, Ishtiaq Rahman, David Green, Timothy Jones, Jorge Mascaro, Robert S Bonser

Department of Cardiothoracic Surgery, University Hospital Birmingham NHS Foundation Trust, Queen

Elizabeth Hospital, Birmingham, UK.

Conflict of interest - none

Aim

• To assess near infrared spectroscopy (NIRS) as a regional index of mixed arterio-venous cortical saturation (rSO2 ) in managing patients during core cooling (CC)

Introduction

• Increasing jugular bulb venous oxygen saturation(SjO2) during CC correlates with reducing brain O2 consumption and guides safe commencement of hypothermic circulatory arrest (HCA).

• NIRS a regional index of rSO2 has been advocated as a surrogate of SjO2.

Methodology

• 9 patients undergoing CC

• Utilising NIRS, rSO2 was measured – At 35oC, 30oC, 25oC and 15oC during CC– At 5, 15 ,30 and 45 mins of SACP– At 15oC, 20oC, 25oC ,30oC and 35oC during warming

• Utilising a jugular bulb line venous oxygen saturation, SjO2 was measured at similar time points

• Standardised anaesthetic and bypass protocol

The patients

15 patients

Procedures

7x Ascending aorta + arch + elephant trunk ± Aortic valve replacement

2x Ascending aorta+ arch replacement

5x Ascending aortic aneurysm and arch aneurysm

2x Mega aortic syndrome

1X chronic type A dissection

1x Pseudo aneurysm of distal arch and proximal descendingDiagnosis

Mean age=55

Results

TempoC rSO2 SjO2

Core cooling 35 57±13% 77±25%

30 61±13 91±11%,

25 59±14 97±3

20 67±9 99±0.7

15 75±10% 99±0.5%

SACP at 15oC 5min 78±6 97±3

15 min 72±13 97±4

30 min 71±15 96±3

End Re-warming phase

35 87±15 64±12%

Both rSO2 and SjO2 increased with cooling p<0.01 and p=0.03 repectively

rSO2 and SjO2 vs temperature change

Scatter plot of SjO2% vs rSO2%

Conclusion

• NIRS rSO2 assessment during CC underestimates SjO2 for reasons that remain unclear.

• Regional SO2 is paradoxically lower than SjO2 during CC and our data raises questions of what each index of oxygen extraction is actually measuring.