research in physiology – the forgotten ‘basic science’
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Research in physiology – the forgotten ‘basic science’. Rob Ross Russell Consultant Paediatrician Cambridge. My background. Trained in paediatrics since 1983 Worked in PICU or respiratory throughout Moved to Cambridge as consultant in PICU in 1992 NHS post - PowerPoint PPT PresentationTRANSCRIPT
University of
Cambridge
Research in physiology – the forgotten ‘basic
science’Rob Ross Russell
Consultant Paediatrician Cambridge
University of
Cambridge
My background
• Trained in paediatrics since 1983• Worked in PICU or respiratory
throughout• Moved to Cambridge as consultant in
PICU in 1992• NHS post• Associate lecturer at University• Director of Studies at Peterhouse
University of
Cambridge
Jenny is a known asthmatic of 7 years of age.
She presents to the ED with a 2 days history of URI and increasing wheeze
Her blood gases show: pH 7.5pCO2 3.6 kPapO2 6.4 kPa, sat 87%BE -3.6HCO3 21 mmol/L
Three cases
John is an ex 25/40 gestation baby.
He was ventilated for 4 weeks and in oxygen until 4 months of age
He is now 5½ months old, with an URI
His gas shows: pH 7.4pCO2 9.6 kPapO2 6.4 kPa, sat 87%BE +12HCO3 32 mmol/L
Jude is a 5 month old with Fallot’s TetralogyAlthough he has been clinically well he is still awaiting
surgery
His blood gases show: pH 7.42pCO2 4.8 kPapO2 6.4 kPa, sat 87%BE 0HCO3 25 mmol/L
University of
Cambridge
Jenny is a known asthmatic of 7 years of age.
She presents to the ED with a 2 days history of URI and increasing wheeze
Her blood gases show: pH 7.5pCO2 3.6 kPapO2 6.4 kPa, sat 87%BE -3.6HCO3 21 mmol/L
Three cases
Jude is a 5 month old with Fallot’s TetralogyAlthough he has been clinically well he is still
awaiting surgery
His blood gases show: pH 7.42pCO2 4.8 kPapO2 6.4 kPaBE 0HCO3 25 mmol/L
John is an ex 25/40 gestation baby.
He was ventilated for 4 weeks and in oxygen until 4 months of age
He is now 5½ months old, with an URI
His gas shows: pH 7.4pCO2 9.6 kPapO2 6.4 kPa, sat 87%BE +12HCO3 32 mmol/L
University of
Cambridge
Three cases
Jude is a 5 month old with Fallot’s TetralogyAlthough he has been clinically well he is still
awaiting surgery
His blood gases show: pH 7.42pCO2 4.8 kPapO2 6.4 kPaBE 0HCO3 25 mmol/L
John is an ex 25/40 gestation baby.
He was ventilated for 4 weeks and in oxygen until 4 months of age
He is now 5½ months old, with an URI
His gas shows: pH 7.4pCO2 9.6 kPapO2 6.4 kPaBE +12HCO3 32 mmol/L
Jenny is a known asthmatic of 7 years of age.
She presents to the ED with a 2 days history of URI and increasing wheeze
Her blood gases show: pH 7.5pCO2 3.6 kPapO2 6.4 kPa, sat 87%BE -3.6HCO3 21 mmol/L
University of
Cambridge
• All three children have hypoxia (paO2 6.4 kPa, saturation 87%), but very different pathology
• All three children have more than enough surface area to their lungs to allow entirely normal oxygenation
• So.. What is happening?
University of
Cambridge
Graph showing ventilation at different levels in the lung
University of
Cambridge
Graph showing ventilation (red) and perfusion (blue) at different levels in the lung
University of
Cambridge
Low VQ ratio
High VQ ratio
pO2 89 132pCO2 42 28VQ 0.63 3.3
Graph showing ventilation (red) and perfusion (blue) at different levels in the lung
University of
Cambridge
VQ ratios
University of
Cambridge
University of
Cambridge
Measuring VQ and shunt
University of
Cambridge
University of
Cambridge
University of
Cambridge
University of
Cambridge
Measuring oxygenation in infantsInitial results and analysis
T. DassiosCambridge, January 2014
University of
Cambridge
Regression: V/Q vs. CGA
University of
Cambridge
Shift and FiO2 requirement
University of
Cambridge
So what about SSCs??
• To do these studies we need to make patients hypoxic (sats<90%)
• If this does not happen in air, we need to reduce FiO2
• Hypoxic gas mixes are expensive and inflexible
University of
Cambridge
ACE Venturi to the rescue…
Venturis are used widely in ED. They work by taking a driver gas (usually oxygen) in through a narrow inlet, then changing to a wide bore. This causes a drop in pressure in the driver gas, which draws air through the portholes, giving a fixed concentration of oxygen.
University of
Cambridge
ACE Venturi to the rescue…
Different colours have different sized portholes, and so deliver different concentrations of oxygen from 24% to 60%..
University of
Cambridge
The SSCs
Jenny Wilson• Took the question ‘Can we use nitrogen
as a driver gas and deliver a reliable (hypoxic) concentration of oxygen?’
University of
Cambridge
Answer
• Yes…
• But…
University of
Cambridge
Answer
• Yes… Nitrogen reliably delivers a flow independent FiO2 of between 19% and 10.5% oxygen
• But… you can’t add a reservoir to the system without altering the FiO2
University of
Cambridge
SSC 2
Amelia Robinson• Looked at the repeatability of the
results • Studied a group of children with
scoliosis – dropping their FiO2 to 10.5% (‘top of Mt Blanc’ levels!)
University of
Cambridge
Answer
• The technique is reliable and repeatable, but hyperventilation affects the gas concentration
• Scoliosis does not affect VQ in idiopathic disease
University of
Cambridge
What next?
• We found that the reason we could not develop a reservoir was due to the effect of downstream resistance on the characteristics of the Venturi
• So what happens when you put a tight face mask on patients in ED???
University of
Cambridge
Hannah Fox• Currently evaluating the effect
of face mask application on the FiO2 delivered with a Venturi.
• Watch this space…
University of
Cambridge
Summary
• We have developed a mathematical model of gas exchange in the lung that allows measurement of shunt and VQ.
• Several SSC projects have helped with the process and methodology, but have also raised important clinical questions about an everyday technique in ED
University of
Cambridge
Acknowledgements
• Prof Gareth Jones• Dr David Sapsford
• Joan Lasenby• Nick Fung• Dr Ben Stenson
• Prof Colin Morley
University of
Cambridge
Thank you