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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

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research in physiology the forgotten basic science

Research in physiology – the forgotten ‘basic science’

Rob Ross Russell

Consultant Paediatrician

Cambridge

my background
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
three cases

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 7.5

pCO2 3.6 kPa

pO2 6.4 kPa, sat 87%

BE -3.6

HCO3 21 mmol/L

Three cases

Jude is a 5 month old with Fallot’s Tetralogy

Although he has been clinically well he is still awaiting surgery

His blood gases show: pH 7.42

pCO2 4.8 kPa

pO2 6.4 kPa, sat 87%

BE 0

HCO3 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 7.4

pCO2 9.6 kPa

pO2 6.4 kPa, sat 87%

BE +12

HCO3 32 mmol/L

three cases1

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 7.5

pCO2 3.6 kPa

pO2 6.4 kPa, sat 87%

BE -3.6

HCO3 21 mmol/L

Three cases

Jude is a 5 month old with Fallot’sTetralogy

Although he has been clinically well he is still awaiting surgery

His blood gases show: pH 7.42

pCO2 4.8 kPa

pO2 6.4 kPa

BE 0

HCO3 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 7.4

pCO2 9.6 kPa

pO2 6.4 kPa, sat 87%

BE +12

HCO3 32 mmol/L

three cases2
Three cases

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 7.5

pCO2 3.6 kPa

pO2 6.4 kPa, sat 87%

BE -3.6

HCO3 21 mmol/L

Jude is a 5 month old with Fallot’sTetralogy

Although he has been clinically well he is still awaiting surgery

His blood gases show: pH 7.42

pCO2 4.8 kPa

pO2 6.4 kPa

BE 0

HCO3 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 7.4

pCO2 9.6 kPa

pO2 6.4 kPa

BE +12

HCO3 32 mmol/L

slide6

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?
slide9

Low VQ ratio

High VQ ratio

Graph showing ventilation (red) and perfusion (blue) at different levels in the lung

so what about sscs
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
ace venturi to the rescue
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.

ace venturi to the rescue1
ACE Venturi to the rescue…

Different colours have different sized portholes, and so deliver different concentrations of oxygen from 24% to 60%..

the sscs
The SSCs

Jenny Wilson

  • Took the question ‘Can we use nitrogen as a driver gas and deliver a reliable (hypoxic) concentration of oxygen?’
answer
Answer
  • Yes…
  • But…
answer1
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
ssc 2
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!)
answer2
Answer
  • The technique is reliable and repeatable, but hyperventilation affects the gas concentration
  • Scoliosis does not affect VQ in idiopathic disease
what next
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???
slide28

Hannah Fox

  • Currently evaluating the effect of face mask application on the FiO2 delivered with a Venturi.
  • Watch this space…
s ummary
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
acknowledgements
Acknowledgements
  • Prof Gareth Jones
  • Dr David Sapsford
  • Joan Lasenby
  • Nick Fung
  • Dr Ben Stenson
  • Prof Colin Morley