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Measurement of pulmonary gas exchange in the ICU. Stephen Rees Center for Model-based Medical Measurement of pulmonary gas exchange in the ICU. Stephen Rees Center for Model-based Medical Decision Support, Department of Health Science and Technology, Aalborg University. Disclosure: Board- member and minority share holder of Mermaid Care, who produce the ALPE system.

Our goal: To see if well know physiological models can be useful in clinical Our goal: To see if well know physiological models can be useful in clinical practice. • Poor ventilator therapy increases mortality (ARDSNet. Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome. NEJM 2000; 342. ) • Standardization helps, if used. Young et al. Ventilation of patients with acute lung injury and acute respiratory distress syndrome: has new evidence changed current practice? Crit. Care Med 2004; 32: 1260 -5. Esteban et al. Evolution of mechanical ventilation in response to clinical research. Am J Respir Crit Care Med 2008; 177: 170 -8. • Automation can achieve standardization • Current automated mechanical ventilator tools do not apply physiological models.

INVENT approach – physiological models INVENT approach – physiological models

INVENT approach – physiological models Find me the ventilator settings for this individual giving INVENT approach – physiological models Find me the ventilator settings for this individual giving simulations which clinically preferred.

Why was this path interesting to pursue? • How is pulmonary gas exchange measured Why was this path interesting to pursue? • How is pulmonary gas exchange measured today? • How could pulmonary gas exchange be measured? • How might these measurements be used in clinical practice?

• How is pulmonary gas exchange measured today? • How could pulmonary gas • How is pulmonary gas exchange measured today? • How could pulmonary gas exchange be measured? • How might these measurements be used in clinical practice?

How is pulmonary gas exchange measured today? Clinical The Pa. O 2/Fi. O 2 How is pulmonary gas exchange measured today? Clinical The Pa. O 2/Fi. O 2 ratio • Used in the definition of ALI, ARDS • Sensitive to changes in Fi. O 2 30% of the patients change disease classification. • Poor quantification of gas exchange D S Karbing et al. Variation in the Pa. O 2/Fi. O 2 ratio with Fi. O 2: Mathematical and experimental description, and clinical relevance. Critical Care. 2007; 11(6): R 118.

How is pulmonary gas exchange measured today? Clinical Experimental The Pa. O 2/Fi. O How is pulmonary gas exchange measured today? Clinical Experimental The Pa. O 2/Fi. O 2 ratio The Multiple Inert Gas Elimination Technique (MIGET) • Used in the definition of ALI, ARDS. • Sensitive to changes in Fi. O 2 30% of the patients change disease classification. • The basis of our understanding of ventilation/perfusion distribution in the lungs. • Complex – requiring tracer gases and gas chromatography. • Poor quantification of gas exchange. D S Karbing et al. Variation in the Pa. O 2/Fi. O 2 ratio with Fi. O 2: Mathematical and experimental description, and clinical relevance. Critical Care. 2007; 11(6): R 118. Wagner PD, Saltzman HA, West JB. Measurement of continuous distributions of ventilation-perfusion ratios: theory. J Appl Physiol. 1974 May; 36(5): 588 -99

Data analysed using a 50 compartment model. To give ventilation and perfusion distributions. Data analysed using a 50 compartment model. To give ventilation and perfusion distributions.

Is there an effective, useful, compromise in measurement of pulmonary gas exchange. CLINICAL STANDARD Is there an effective, useful, compromise in measurement of pulmonary gas exchange. CLINICAL STANDARD Arterial Pa. O 2, Pa. O 2/ Fi. O 2 ratio, Effective shunt. EXPERIMENTAL STANDARD MIGET ”Simple measures lack discrimination while complex measurements are infeasible in clinical care…. (the authors)… seek a middle ground” Assessment of gas exchange in lung disease: balancing accuracy against feasibility. Wagner PD. Critical Care. 2007; 11(6): 182.

is • How is pulmonary gas exchange measured today? • How can pulmonary gas is • How is pulmonary gas exchange measured today? • How can pulmonary gas exchange be measured using the ALPE technology? • How might these measurements be used in clinical practice?

The principle and procedure • Variation of FIO 2 and measurement of ventilatory flow, The principle and procedure • Variation of FIO 2 and measurement of ventilatory flow, gasses, Sp. O 2 plus a single blood gas, can be used to calculate pulmonary shunt, low V/Q and high V/Q. • Three to five step changes in FIO 2, each to steady state. • Model analysis and parameter estimation.

high V/Q low V/Q high V/Q low V/Q

high V/Q Well oxygenated Venous oxygenation low V/Q Poorly oxygenated high V/Q Well oxygenated Venous oxygenation low V/Q Poorly oxygenated

high V/Q low V/Q Well oxygenated Poorly oxygenated Oxygen responsive Venous oxygenation Not oxygen high V/Q low V/Q Well oxygenated Poorly oxygenated Oxygen responsive Venous oxygenation Not oxygen responsive

Oxygen loss = PAO 2 - Pc. O 2 high V/Q low V/Q Oxygen Oxygen loss = PAO 2 - Pc. O 2 high V/Q low V/Q Oxygen responsive Not oxygen responsive

Oxygen loss = PAO 2 - Pc. O 2 high V/Q low V/Q Oxygen Oxygen loss = PAO 2 - Pc. O 2 high V/Q low V/Q Oxygen responsive Not oxygen responsive

Clinical values of ‘shunt’ and ‘O 2 loss’ Pre-op patient (x) Shunt = 1% Clinical values of ‘shunt’ and ‘O 2 loss’ Pre-op patient (x) Shunt = 1% O 2 loss = 2 % Post- op CABG patient (*) Shunt = 12% O 2 loss = 3% aa ICU patient (ARDS) (+) Shunt = 21% O 2 loss = 17% Kjærgaard S, Rees S, Malczynski J, Nielsen JA, Thorgaard P, Toft E, Andreassen S. Non-invasive estimation of shunt and ventilation-perfusion mismatch. Intensive Care Medicine 2003 May; 29(5): 72734.

Clinical values of ‘shunt’ and ‘O 2 loss’ What does this mean clinically? Shunt Clinical values of ‘shunt’ and ‘O 2 loss’ What does this mean clinically? Shunt Pre-op patient (x) Shunt = 1% O 2 loss = 2 % Post- op CABG patient (*) Shunt = 12% O 2 loss = 3% aa O 2 loss (Low V/Q) ICU patient (ARDS) (+) Shunt = 21% O 2 loss = 17 % Kjærgaard S, Rees S, Malczynski J, Nielsen JA, Thorgaard P, Toft E, Andreassen S. Non-invasive estimation of shunt and ventilation-perfusion mismatch. Intensive Care Medicine 2003 May; 29(5): 727 -34.

Clinical values of ‘shunt’ and ‘O 2 loss’ What does this mean clinically? Shunt Clinical values of ‘shunt’ and ‘O 2 loss’ What does this mean clinically? Shunt Pre-op patient (x) Shunt = 1% O 2 loss = 2 % Post- op CABG patient (*) Shunt = 12% O 2 loss = 3% aa O 2 loss (Low V/Q) ICU patient (ARDS) (+) Shunt = 21% O 2 loss = 17 % Kjærgaard S, Rees S, Malczynski J, Nielsen JA, Thorgaard P, Toft E, Andreassen S. Non-invasive estimation of shunt and ventilation-perfusion mismatch. Intensive Care Medicine 2003 May; 29(5): 727 -34.

References • Classifying and monitoring ICU patients • • D S Karbing, et al. References • Classifying and monitoring ICU patients • • D S Karbing, et al. Variation in the Pa. O 2/Fi. O 2 ratio with Fi. O 2: Mathematical and experimental description, and clinical relevance. Critical Care. 2007; 11(6): R 118. S Kjærgaard, et al. Non-invasive estimation of shunt and ventilation-perfusion mismatch. Intensive Care Medicine 2003 May; 29(5): 727 -34. • Assessment of respiratory function, before during and after surgical intervention • • Kjærgaard S et al. Modelling of hypoxaemia after gynaecological laparotomy. Acta Anaesthesiol. Scand. 2001 Mar; 45(3): 349 -356 Kjærgaard S et al. Hypoxaemia after cardiac surgery: Clinical application of a model of pulmonary gas exchange. EJA. 2004 Apr; 21(4): 296 -301. Rasmussen BS et al. Oxygenation within the first 120 h following coronary artery bypass grafting. Influence of systemic hypothermia (32 degrees C) or normothermia (36 degrees C) during the cardiopulmonary bypass: a randomized clinical trial. Acta Anaesthesiol. Scand. 2006 Jan; 50(1): 64 -71. Rasmussen BS et al. Oxygenation and release of inflammatory mediators after off-pump compared to after onpump coronary artery bypass surgery. Acta Anaesthesiol. Scand. 2007, 51(9): 1202 -10. • Standardising and optimising ventilator therapy • • • Karbing DS, et al. Retrospective evaluation of a decision support system for control of mechanical ventilation. Med Biol Eng Comput. 2011 Nov 22. [Epub ahead of print] Karbing DS, et al. Prospective evaluation of a decision support system for setting inspired oxygen in intensive care patients. J. Crit Care, 2010, 25(3): 367 -74. C Allerød, et al. A Decision Support System for suggesting ventilator settings: Retrospective evaluation in cardiac surgery patients ventilated in the ICU. Comput. Meth Prog. Biomed 2008, vol. 92, nr. 2, s. 205 -212

Comparison to MIGET – We showed • The ALPE model adequately describes MIGET data Comparison to MIGET – We showed • The ALPE model adequately describes MIGET data in a physiological situation analogous to acute lung injury, and gives similar parameter values to the MIGET model Rees S. E, et al. , J Appl Physiol. 101(3), 826 -32, (2006). • The ALPE model gives accurate predictions of Pa. O 2 across a range of PEEP, Inspiratory : Expiratory (IE) ratio, and FIO 2 settings compatible with clinical treatment of acute lung injury Rees SE. Intensive Care Med. 36(12), 2117 -24. (2010). We did not show, or try to show that • The ALPE adequately describes injury similar to mature ARDS or other more complex situations. • Fi. O 2 v Sa. O 2 curves give V/Q distributions similar to MIGET.

• How is pulmonary gas exchange measured today? • How can pulmonary gas • How is pulmonary gas exchange measured today? • How can pulmonary gas exchange be measured using the ALPE technology? • How might these measurements be used in clinical practice?

How might these measurements be used in clinical practice? • Appropriate setting of FIO How might these measurements be used in clinical practice? • Appropriate setting of FIO 2 • Monitoring the effects of PEEP

How might these measurements improve clinical practice? • Appropriate setting of FIO 2 – How might these measurements improve clinical practice? • Appropriate setting of FIO 2 – How might one use these parameters “shunt” and “Oxygen loss” to set FIO 2. • Monitoring the effects of PEEP

An ICU case – shunt = 15 %, O 2 loss = 9 % An ICU case – shunt = 15 %, O 2 loss = 9 %

An ICU case – shunt = 15 %, O 2 loss = 9 % An ICU case – shunt = 15 %, O 2 loss = 9 % Shunt O 2 loss (Low V/Q)

An ICU case – shunt = 15 %, O 2 loss = 9 % An ICU case – shunt = 15 %, O 2 loss = 9 % Shunt What FIO 2 should they have? O 2 loss = 9 % FIO 2 = 21% + 9% O 2 loss (Low V/Q)

A normal person – shunt = 15 %, O 2 loss = 9 % A normal person – shunt = 15 %, O 2 loss = 9 % FIO 2 = 21+9 = 30 % ≈ 30 k. Pa ≈ 225 mm. Hg FEO 2 = 14+9 = 23 % ≈ 23 k. Pa ≈ 173 mm. Hg O 2 loss = 9 % ≈ 9 k. Pa ≈ 67 mm. Hg Pc. O 2 ≈ 23 -9 =14 k. Pa ≈ 105 mm. Hg Sc. O 2 ≈ 98 % Sv. O 2 ≈ 70% shunt = 15 % Sa. O 2 ≈ 94% Pa. O 2 ≈ 9. 5 k. Pa ≈ 71 mm. Hg

An ICU case – shunt = 15 %, O 2 loss = 9 % An ICU case – shunt = 15 %, O 2 loss = 9 % FIO 2 = 30 % Sa. O 2 = 94 % Normal oxygenation of that which is “oxygen responsive”

ALPE control of Fi. O 2 Baseline Clinician System Karbing DS, Allerød C, Thorgaard ALPE control of Fi. O 2 Baseline Clinician System Karbing DS, Allerød C, Thorgaard P, Carius AM, Frilev L, Andreassen S, Kjærgaard S, Rees SE. Prospective evaluation of a decision support system for setting inspired oxygen in intensive care patients. Journal of Critical Care, 2010, 25(3): 367 -74.

How might these measurements improve clinical practice? • Appropriate setting of FIO 2 • How might these measurements improve clinical practice? • Appropriate setting of FIO 2 • Monitoring the effects of PEEP

Physiological rational for PEEP monitoring with gas exchange • Most PEEP monitoring techniques based Physiological rational for PEEP monitoring with gas exchange • Most PEEP monitoring techniques based upon mechanical rather than functional measurements. • Opening may not be the same a improving functionality, and the functionality is the gas exchange. • We know from MIGET that changing PEEP modifies the V/Q distribution in the lung. Dantzker DR, et al. Ventilation-Perfusion distributions in the Adult Respiratory Distress Syndrome. Am Rev Resp Dis. 1979, 120: 1039 -52.

Case 1 – no response to PEEP increase. • Support ventilation, 6 days in Case 1 – no response to PEEP increase. • Support ventilation, 6 days in the ICU. • FIO 2 = 60 %, PEEP 6 cm H 2 O. • Shunt = 10 %, O 2 loss = 11%

Case 1 – no response to PEEP increase. • Support ventilation, 6 days in Case 1 – no response to PEEP increase. • Support ventilation, 6 days in the ICU. • FIO 2 = 60 % to 45 % PEEP = 6 cm H 2 O to 12 cm. H 2 O. • Shunt = 9 %, O 2 loss = 13%

Case 2 – response to PEEP increase. FIO 2 40 %, PEEP 15 cm Case 2 – response to PEEP increase. FIO 2 40 %, PEEP 15 cm H 2 O Shunt 10 %, O 2 loss 5 % Controlled ventilation, 1 day in the ICU. FIO 2 40 %, PEEP 5 cm H 2 O Shunt 20%, O 2 loss 2%

Case 2 – response to PEEP increase. FIO 2 40 %, PEEP 15 cm Case 2 – response to PEEP increase. FIO 2 40 %, PEEP 15 cm H 2 O Shunt 10 %, O 2 loss 5 % PEEP = 10 cm H 2 O FIO 2 40 %, PEEP 5 cm H 2 O Shunt 20%, O 2 loss 2%

Conclusions • We are trying to find a balance, bringing well known physiology into Conclusions • We are trying to find a balance, bringing well known physiology into clinical tools. • Goals – Provide a physiological description of gas exchange – Help find appropriate FIO 2 – Help monitor the functional effects of PEEP

Future and thoughts • Comparison with CT scans in ARDS • Comparison with HRCT Future and thoughts • Comparison with CT scans in ARDS • Comparison with HRCT in COPD patients • Tidying up assumptions – HPV, steady state conditions, etc. • A thought, oxygen is also used as a tracer to estimate EELV. These could be combined.