O2, CO2, Ventilation & Perfusion Logan & Jason

Haemoglobin Curve Which of the following environments would NOT shift the haemoglobin dissociation curve to the right? Muscle capillaries during exercise Metabolic alkalosis Hyperthermia A patient with SIRS A patient with type II respiratory failure

O2 CO2 Storage location Bound to haemoglobin (Dissolved) Chemoreceptor (Molecular weight) (Solubility) Speed of Diffusion Net Flux Partial pressure controlled by Bound to haemoglobin (Dissolved in plasma) Peripheral ↓ Big gradient, big flux Perfusion limited (rest) Diffusion limited (exercise) (Dissolved) (Bound to αα) (Bound to haemoglobin) As bicarbonate Peripheral Central (as H+) ↑ ↑ ↑ 21x faster than O2 Small gradient, small flux Diffusion/ventilation limited Receptors- NB what receptors for pH? COPD Big, slows it down, but very soluble, balance is faster O2 NOT vent limited- sats probe- 98%, what happens if hyperventilate? O2 20 to 6, whereas Co2 is 6.5 to 5.3 NB Diffusion is ↑ by pressure gradient/ventilation eg 100% O2, ↓ by thicker alveolar walls eg fibrosis, oedema

Ventilation: Perfusion Ratio Is there more ventilation at the base or apex of the lung? APEX BASE Perfusion Ventilation V/P or V/Q “aeration” Ventilation and perfusion are both greatest at the BASE, but their ratio is most favourable at the APEX (V/Q>1), which is where most gas exchange happens “good aeration”.

Case 1 A 57 year old woman presents with a 3 day history of a productive cough, fever and rib pain on inspiration. What is your most likely diagnosis? Pneumonia (RLL) Is the V/Q ratio changed initially? Perfusion normal, ventilation and diffusion reduced in RLL initially, so V/Q decreased Therefore what would you expect to happen to the PaO2 and PaCO2 in an ABG? V/Q=0 so decreased O2 (diffusion) and mildly elevated CO2 How does it change with time? Lung shunts blood away from RLL, decreasing Q, therefore increasing V/Q overall Best immediate treatment? 100% O2, ABx

Case 2 A 42 year old male presents with a swollen right calf, chest pain and shortness of breath, tachypnoea What is your most likely diagnosis? Pulmonary embolus (from DVT) Is the V/Q ratio changed initially? Perfusion REDUCED, ventilation and diffusion NORMAL, so V/Q increased Therefore what would you expect to happen to the PaO2 and PaCO2 in an ABG? Hyperventilation REDUCES PACO2 (blow off), but poor perfusion means that PAO2 is REDUCED Best immediate treatment? 100% O2, thrombolyse (ie dissolve clot)

Case 3 A 70 year old male, long term smoker, is brought into A&E via ambulance after falling at home. On examination he is short of breath, cyanosed and is noted to have a hyper-resonant chest. What is the most likely cause of the examination findings? COPD (emphysema+ chronic bronchitis) Why is he cyanosed? Elastic destroyed, so REDUCED ventilation LOW O2 (and HIGH CO2) Would you give supplementary oxygen? Yes in an emergency setting. (hypoxia kills before hypoxic drive). Aim for sats 88-92%.

Case 4 A 42 year old male potter presents with worsening shortness of breath over the last 6 months. What is the most likely diagnosis? Silicosis/pulmonary fibrosis In a healthy lung what limits oxygen transport into the blood? Perfusion limitied In this case, what is limiting transport? Thickening of the alveolar walls, so diffusion limited. Hb saturation not achieved by the end of the capillary Will the transport be worse or better with exercise? Worse, because Hb has even less time in capillary to uptake O2

Case 5 Patient presents with pale complexion, shortness of breath on exertion, dizziness, palpitations. What is your most likely diagnosis? Anaemia You give 100% O2 through a mask to help with shortness of breath. What will this do to the O2 content of the blood? Very little, since Hb is already saturated, and only a small amount can dissolve