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Oxygen Transport Calculations - …

Oxygen Transport Calculations M. L. Cheatham, MD, FACS, FCCM. Oxygen Transport IN REVIEW . Calculations . There are four primary monitoring questions Is intravascular volume or preload adequate? Is blood flow adequate? Is vascular resistance appropriate? S. Supply l Demand Is Oxygen Transport balance appropriate? Volumetric assessment of preload status is superior to pressure- pressure-based measurements Michael L. Cheatham, MD, FACS, FCCM Continuous hemodynamic monitoring provides an Director, Surgical Intensive Care Units improved understanding of patient illness and Orlando Regional Medical Center response to therapy Orlando, Florida Oxygen Transport BALANCE Oxygen Transport BALANCE.

Oxygen Transport Calculations – M . L. Cheatham, MD, FACS, FCCM Revised 01/14/2009 1 OXYGEN TRANSPORT CALCULATIONS SlDemand Michael L. Cheatham, MD, FACS, FCCM

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Transcription of Oxygen Transport Calculations - …

1 Oxygen Transport Calculations M. L. Cheatham, MD, FACS, FCCM. Oxygen Transport IN REVIEW . Calculations . There are four primary monitoring questions Is intravascular volume or preload adequate? Is blood flow adequate? Is vascular resistance appropriate? S. Supply l Demand Is Oxygen Transport balance appropriate? Volumetric assessment of preload status is superior to pressure- pressure-based measurements Michael L. Cheatham, MD, FACS, FCCM Continuous hemodynamic monitoring provides an Director, Surgical Intensive Care Units improved understanding of patient illness and Orlando Regional Medical Center response to therapy Orlando, Florida Oxygen Transport BALANCE Oxygen Transport BALANCE.

2 The foremost question in critical care is not: Failure to provide sufficient Oxygen to meet cellular a) What is the perfect PAOP or EDVI? demands leads to b) What cardiac output ensures patient survival? Cellular ischemia c) What systemic vascular resistance is optimal? Bacterial translocation Sepsis S i The ultimate question is: Worsening shock d) Is tissue Oxygen delivery sufficient to meet Organ dysfunction cellular Oxygen demand? Multiple system organ failure Death DEFINITIONS ASSESSING Oxygen Transport . Oxygen delivery (DO2) To assess the adequacy of a patient's Oxygen The amount of Oxygen pumped to the tissues by Transport balance, four more questions must be the heart considered Does Oxygen delivery meet the patient's needs?

3 Yg consumption Oxygen p (VO. ( 2) Is cardiac output adequate for consumption? The amount of Oxygen consumed by the tissues Is Oxygen consumption adequate for demand? Oxygen demand Is the patient's hypoxemia due to a pulmonary problem or to a low flow state? The amount of Oxygen required by the tissues to function aerobically May exceed both Oxygen delivery and consumption during critical illness Revised 01/14/2009 1. Oxygen Transport Calculations M. L. Cheatham, MD, FACS, FCCM. Oxygen Transport BALANCE Oxygen Transport BALANCE.)

4 If Oxygen delivery and Oxygen consumption are If Oxygen demand exceeds delivery, shock is present balanced Cellular Oxygen is deficient Supply equals demand Energy is produced via anaerobic metabolism with The cellular requirements of the body are met lactic acid (lactate) as a byproduct Normal N l metabolic t b li processes proceed d uninhibited i hibit d Lactate L t t cannott be b reutilized tili d and d accumulates l t Anaerobic metabolism is minimized leading to: Metabolic acidosis A Happy Pea Monster Cellular injury The well- well-known fable of the Pea Cellular death Monster will be used to illustrate the key concepts of Oxygen Transport balance A Sick Pea Monster.

5 Oxygen Transport BALANCE Oxygen Transport BALANCE. Oxygen consumption may just meet Oxygen demand Patient survival is improved by optimizing Oxygen Requires a high extraction of Oxygen from blood delivery to ensure that . Places patient at risk for rapid decompensation Little physiologic reserve is present 1) Oxygen demand is met at baseline Organs with high baseline Oxygen extraction, such as the heart, are at high risk for ischemia AND. 2) There is an adequate physiologic Oxygen reserve to cope with acute increases in Oxygen demand An Unhappy Pea Monster.

6 Oxygen Calculations MEASURED PARAMETERS. Knowledge of the Oxygen Transport equations is Arterial Oxygen tension (PaO2). essential to understanding the pathophysiology Arterial carbon dioxide tension (PaCO2). and appropriate treatment for the various shock states Arterial Oxygen saturation (SaO2 or SpO2). Pulmonary artery and central venous oximetry Mixed venous Oxygen saturation (SvO2). catheters provide the ability to monitor Oxygen Transport balance at the bedside Central venous Oxygen saturation (ScvO2). Continuous mixed venous oximetry (SvO2) Venous Oxygen tension (PvO2).

7 Continuous central venous oximetry (ScvO2) Hemoglobin (Hgb). Intermittent calculation of Oxygen delivery (DO2I) and Oxygen consumption (VO2I) Cardiac output (CO). Revised 01/14/2009 2. Oxygen Transport Calculations M. L. Cheatham, MD, FACS, FCCM. CALCULATED PARAMETERS VASCULAR CIRCUIT. Cardiac index (CI) Central to any assessment Pulmonary capillary Oxygen content (CcO2) of Oxygen Transport is the PULMONARY. ability to calculate the CcO2. Arterial Oxygen content (CaO2) amount of Oxygen in the PAO2. Venous Oxygen content (CvO2) blood at any yppoint in the RIGHT LEFT.

8 Body VENTRICLE VENTRICLE. Arterial Arterial--venous Oxygen content difference (Ca- (Ca-vO2). Oxygen utilization coefficient (OUC) Such Calculations are CvO2. Ca-vO2. CaO2. OUC. dependent upon both the PvO 2 PaO2. SaO2. Oxygen delivery index (DO2I) measured Oxygen tension SvO 2 SYSTEMIC. Oxygen consumption index (VO2I) and Oxygen saturation at each point Intrapulmonary shunt (Qsp/Qt). CALCULATING Oxygen CONTENT Oxygen CONTENT. To calculate the Oxygen content of blood, one must Oxygen content recognize that: = Oxygen bound to Hgb + Oxygen dissolved in plasma 1.)

9 Oxygen can be either bound or unbound . Oxygen bound 2. Each gram of Hgb can carry up to mL of Oxygen = Hgb conc x Oxygen Hgb can carry x Hgb saturation This Thi number b varies i from f species i tot species i 3. The solubility of Oxygen in blood is mL. mL//dL Oxygen dissolved 4. The amount of Oxygen carried by Hgb depends upon = Oxygen tension x solubility coefficient of Oxygen its saturation This varies depending upon the patient's inspired C O. O2 = ( x Hgb x S O. S O2) + (P O. (P O2 x ). Oxygen fraction (FiO2) and the presence of any mixed, unoxygenated blood where signifies the location of the blood Also known as intrapulmonary shunt ( c for end end--capillary, a for arterial, or v for venous).)

10 CALCULATING Oxygen CONTENT ALVEOLAR Oxygen TENSION (PAO2). To calculate the Oxygen content of Assuming an FiO2 of > ( , SAO2= ). blood as it leaves the alveolus (CcO2), remember that: PULMONARY. PAO2 = FiO2 x [(PB-PH20)-(PaCO2/RQ)]. CcO2. 1. Hgb should be fully saturated PAO2. SAO2 where PB = barometric pressure, PH2O = water vapor ( , (i e SAO2=1 0 if FiO2 > ). 0 21) as pressure RQ = respiratory quotient pressure, RIGHT LEFT. it leaves the alveolus VENTRICLE VENTRICLE. 2. The alveolar Oxygen tension Ca-vO2. CaO2. PAO2 = x [(760 torr - 47 torr).]


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