Ebook Monitoring tissue perfusion in shock: Part 2
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Ebook Monitoring tissue perfusion in shock: Part 2
Cneck *or upfMetiCentral and Mixed Venous o2 Saturation: A Physiological AppraisalGuillermo Gutierrez7.1Historical PerspectiveThe oxygen saturation of Ebook Monitoring tissue perfusion in shock: Part 2f mixed venous, and that of central venous blood, have been used widely to monitor tissue oxygenation and also as markers of adequate resuscitation in critically ill patients [1,2]. The development of these techniques paralleled rapid advances in physiology that occurred during the past century. Ado Ebook Monitoring tissue perfusion in shock: Part 2lf Eugen Fick (1821 — 1901) first proposed the idea that blood flow to an organ could be estimated as the ratio of the organ’s 02 uptake to the o2 conEbook Monitoring tissue perfusion in shock: Part 2
centration difference of arterial and venous blood [3]. When applied to cardiac output. Fick’s principle becomesCardiac output = (VO2)sys/([O2]a -[o,]Cneck *or upfMetiCentral and Mixed Venous o2 Saturation: A Physiological AppraisalGuillermo Gutierrez7.1Historical PerspectiveThe oxygen saturation of Ebook Monitoring tissue perfusion in shock: Part 2s of arterial and pulmonary artery blood are needed to calculate (O2]a and [O2]mv as the sum of 02 bound to hemoglobin and that dissolved in plasma:[O,] = 13.9xSO,x[Hb] + 0.031xPO, mL L"'-7.2where [Hb| is the hemoglobin concentration (g- dL“’). so2 is the fractional hemoglobin o> saturation, and PO2 Ebook Monitoring tissue perfusion in shock: Part 2 is the plasma o2 partial pressure (mmHg). The units of [O2] are mL o2 per liter of blood.Many years would pass before Fick's principle could be appliEbook Monitoring tissue perfusion in shock: Part 2
ed to measure cardiac output in humans. The delay may be partly attributed to technical difficulties inherent in sampling pulmonary artery blood, but Cneck *or upfMetiCentral and Mixed Venous o2 Saturation: A Physiological AppraisalGuillermo Gutierrez7.1Historical PerspectiveThe oxygen saturation of Ebook Monitoring tissue perfusion in shock: Part 2Washington, DC. USAe-mail: ggutierrez@mfa.gwu.edu© Springer International Publishing AG. part of springer Nature 201893A. A. Pinto Lima. E. Silva (eds.). Monitoring Tissue Perfusion in Shock.httnv/AIrti rtrư/m 1007/078-A-A1 0-dA l¥L? 794G. Gutierrezthai passing a catheter into the heart would prove Ebook Monitoring tissue perfusion in shock: Part 2fatal. Instead, cardiac output was estimated by measuring the co2 concentration of expired gases and arterial blood [4]. This cumbersome and error-proEbook Monitoring tissue perfusion in shock: Part 2
ne technique was particularly unreliable in patients with diseased lungs [5].In 1929. while working in a clinic in Eberswalde. Germany. Werner ForssmaCneck *or upfMetiCentral and Mixed Venous o2 Saturation: A Physiological AppraisalGuillermo Gutierrez7.1Historical PerspectiveThe oxygen saturation of Ebook Monitoring tissue perfusion in shock: Part 2med its placement w ith fluoroscopy. Once satisfied of the safety of the procedure, he inserted an atrial catheter in a terminally ill woman, instilling a preparation of epinephrine and digitalis aiming at improving the heart’s contractility [6]. A year later, working in Prague. Otto Klein (1881 — 1 Ebook Monitoring tissue perfusion in shock: Part 2968) performed 30 heart catheterizations using Forssmann’s technique and measured cardiac output by Fick’s principle [7]. He presented his findings atEbook Monitoring tissue perfusion in shock: Part 2
a meeting in Boston but was ignored by the medical community. A decade later. Andre' Cournand (1895-1988) and Dickinson Richards (1895-1973). while aCneck *or upfMetiCentral and Mixed Venous o2 Saturation: A Physiological AppraisalGuillermo Gutierrez7.1Historical PerspectiveThe oxygen saturation of Ebook Monitoring tissue perfusion in shock: Part 2 place for an extended time with no harm to the patient [9|. Forssmann, Courtland. and Richards shared the 1956 Nobel Prize in Physiology or Medicine for “their discoveries concerning heart catheterization and pathological changes in the circulatory system." The reason why the Nobel Prize Committee Ebook Monitoring tissue perfusion in shock: Part 2failed to likewise honor Professor Klein remains a mystery.The need for fluoroscopic guidance limited the use of right heart catheterization to a fewEbook Monitoring tissue perfusion in shock: Part 2
well-equipped medical centers. This state of affairs changed dramatically in 1970 with the invention of the flow-directed pulmonary artery catheter (PCneck *or upfMetiCentral and Mixed Venous o2 Saturation: A Physiological AppraisalGuillermo Gutierrez7.1Historical PerspectiveThe oxygen saturation of Ebook Monitoring tissue perfusion in shock: Part 2c guidance [10] allow ing continuous monitoring of pulmonary artery and central venous pressures. as well as providing ready access to mixed venous blood. Technical improvements to the PAC followed in rapid order, including the thermodilution indicator technique to measure cardiac output directly 11 Ebook Monitoring tissue perfusion in shock: Part 21] and infrared reflection spectrometry to monitor mixed venous blood o2 saturation (SmvO2) continuously (12, 13]. The direct measurement of cardiac oEbook Monitoring tissue perfusion in shock: Part 2
utput by thermodilution superseded Fick's principle and the need to measure SmvO2.The unhindered access to pulmonary artery blood provided by the PAC Cneck *or upfMetiCentral and Mixed Venous o2 Saturation: A Physiological AppraisalGuillermo Gutierrez7.1Historical PerspectiveThe oxygen saturation of Ebook Monitoring tissue perfusion in shock: Part 2nce of smvo2. and that of its surrogate, central venous 02 saturation (SCVO2). remains a topic of intense and continuing debate [ 14. 15]. At various times. smvo2 has been endorsed as an indicator of cardiac output [16]. as a marker of peripheral tissue oxygenation [17]. and as a predictor of morbid Ebook Monitoring tissue perfusion in shock: Part 2ity and mortality [18, 19]. Particularly during the past decade. SCVO2 also has been touted as a reliable guide to resuscitation in sepsis [20]. The vEbook Monitoring tissue perfusion in shock: Part 2
alidity, or lack thereof, of these claims is best explored by reviewing the physiological foundations of SmvO2 and SCVO2.7 Central and Mixed Venous OjCneck *or upfMetiCentral and Mixed Venous o2 Saturation: A Physiological AppraisalGuillermo Gutierrez7.1Historical PerspectiveThe oxygen saturation of Ebook Monitoring tissue perfusion in shock: Part 2y the expired gases method ( V O2)Exp is equivalent to systemic 02 consumption, (V 02)Sys. The timed collection of expired air into a Douglas bag represents the “gold standard” in measuring (V02)exP:(Vo.) = Vh(l-F1.C0,-F1,0,)/(l-F,0,) inLmin 1-7.3In this expression. VE refers to the expired gas volu Ebook Monitoring tissue perfusion in shock: Part 2me collected in the bag over a finite period of time: FEC02 and FE02 are the volumetric fractions of co2 and o2 in expired gas. respectively: and FịO2Ebook Monitoring tissue perfusion in shock: Part 2
is the inspired 02 fraction or 0.21 for room air. Given the nature of the denominator. (V O2)exp cannot be calculated for F|O2 = 1.0, and becomes cliCneck *or upfMetiCentral and Mixed Venous o2 Saturation: A Physiological AppraisalGuillermo Gutierrez7.1Historical PerspectiveThe oxygen saturation of Ebook Monitoring tissue perfusion in shock: Part 2 analyzers. Due to the small differences in 02 concentration between the inspired and expired gases at high F|O2. the reliability of this method also deteriorates for F|O2 > 0.60 [22].In clinical ICƯ practice. (V o2)sys is most commonly estimated as the product of cardiac output (0 measured by therm Ebook Monitoring tissue perfusion in shock: Part 2odilution and the 02 content difference between arterial and mixed venous blood (the “reverse” Fick's method):(VoX.=e([°-’L -[°=L) ,11Lmin 1-7.4It shoEbook Monitoring tissue perfusion in shock: Part 2
uld be noted that Eq. 7.4 does not account for pulmonary 02 consumption, since the deep bronchial veins drain on the left side of the circulatory systCneck *or upfMetiCentral and Mixed Venous o2 Saturation: A Physiological AppraisalGuillermo Gutierrez7.1Historical PerspectiveThe oxygen saturation of Ebook Monitoring tissue perfusion in shock: Part 2ssociated with substantial pulmonary 02 consumption, such as pneumonia [23 J or acute lung injury [24. 25].7.3smvo2 as a Measure of 02 Extraction RatioThe efficiency of 02 uptake by the tissues is characterized by the 02 extraction ratio (ERO2)syt:(ERO5)s>,-(VO2)S)i/(DO2)syi-7.5 Ebook Monitoring tissue perfusion in shock: Part 2Cneck *or upfMetiCentral and Mixed Venous o2 Saturation: A Physiological AppraisalGuillermo Gutierrez7.1Historical PerspectiveThe oxygen saturation ofGọi ngay
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