THE ROLE OF REGIONALOXYGEN SATURATION

Using near infrared spectroscopy during low outputsyndrome in pediatric cardiac surgery

a cura diVladimiro L. Vida

Jose L. ZuluetaDemetrio Pittarello

Giovanni Stellin

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ISBN: 978-88-6292-304-0Prima edizione: novembre 2012

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Contents

LIST OF CONTRIBUTORS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

CHAPTER 1Commonly used abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

CHAPTER 2Near Infra-Red Spectroscopy (NIRS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.1 Principles of Physics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92.2 The equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122.3 Scientifi c validation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132.4 Clinical Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

a) Cerebral perfusion in newborn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15b) Cerebral perfusion in congenital heart disease . . . . . . . . . . . . . . . . . . . . . 16c) Systemic Perfusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17d) Other applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19NIRS “trends” in pediatric cardiac surgery . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

2.5 Limitations of NIRS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212.6 Spatial resolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212.7 Distribution of cerebral arterial-venous blood fl ow . . . . . . . . . . . . . . . . . . . 222.8 The extra-cerebral tissues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222.9 Tissue chromophores not containing haematin . . . . . . . . . . . . . . . . . . . . . 232.10 Metabolically inactive tissues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232.11 Cardiac output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Methods of cardiac output measurement . . . . . . . . . . . . . . . . . . . . . . . . . . 24Fick’s method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Contents The role of regional oxygen saturation

4

Dilution indicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25Indirect calorimetry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25Analysis of alveolar gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26CO2 re-breathing techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26Bio-impedance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27Arterial waveform and Doppler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27The SvO2: venous oxygen saturation monitoring . . . . . . . . . . . . . . . . . . . . . . 27

2.12 Low cardiac output syndrome (LCOS) . . . . . . . . . . . . . . . . . . . . . . . . . . . 29Peri-operative low cardiac output state . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

CHAPTER 3Original Contribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31

3.1 Aim and methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313.2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 353.3 Comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .47

APPENDIX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .57

LIST OF CONTRIBUTORS

Maddalena Padrini, MD – Pediatric Cadiology Unit, Dept. of Pediatrics, University of Padua, Italy

Demetrio Pittarello, MD – Chief Cardiac Anesthesiologist, Institute of Anesthesia and Intensive Care, Department of Medicine, University of Padua, Italy

Giovanni Stellin, MD – Professor of Cardiac Surgery, Director of the Pediatric and Congenital Cardiac Surgery Unit, Dept. of Cardiac, Th oracic and Vascular Sciences, University of Padua, Italy

Vladimiro L. Vida, MD, PhD – Staff Pediatric Cardiac Surgeon, Pediatric and Congenital Cardiac Surgery Unit, Dept. of Cardiac, Th oracic and Vascular Sciences, University of Padua, Italy

Jose L. Zulueta, MD – Staff Cardiac Anesthesiologist, Institute of Anesthesia and Intensive Care, Department of Medicine, University of Padua, Italy

CHAPTER 1Commonly used abbreviations

ACT: activated clotting timeARDS: acute respiratory distress syndromeBMI: body mass indexBSA: body surface areaCaO2: arterial oxygen contentCAVC: complete atrio-ventricular canalCBF: cerebral blood fl owCBV: cerebral blood volumeCPBP: cardiopulmonary by-passCI: cardiac indexCO: cardiac outputCVC: central venous catheterCvO2: venous oxygen contentCVVH: continuos veno-venous hemofi ltration DHCA: deep hypothermic circulatory arrestVSD: ventricular septal defectDO2: availability of oxygenDO2I: indexed availability of oxygen DORV: double outlet right ventricleD-TGA: transposition of the great arteriesEC: units of packed red blood cellsECLS: extra corporeal life supportECMO: extra corporeal membrane oxygenationERO2: extraction of oxygenHR: heart rateFDA: food and drug administration

Chapter 1 The role of regional oxygen saturation

8

FiO2: percentage of inspired oxygenHb: hemoglobin (deoxygenated)HbO2: oxygenated hemoglobinHLHS: hypoplastic left heart syndromeIAA: aortic arch interruptionICU: intensive care unitLAP: left atrial pressureLCS: low output stateNIRS: near-infrared spectroscopyPaCO2: arterial tension of carbon dioxideDBP: diastolic blood pressureMAP: mean arterial pressurePaO2: arterial oxygen tensionFFP: fresh frozen plasmaPM: pacemakerPNX: pneumothoraxCPV: central venous pressureRCP: regional cerebral perfusionrSO2: regional oxygen saturationSaO2: arterial oxygen saturationO2 saturation: trans-cutaneous oxygen saturationSV: stroke volumeSvO2: central venous saturationSVR: systemic vascular resistancesSVRI: indexed systemic vascular resistancesT: central temperatureTOF: tetralogy of fallotVAD: ventricular assist deviceVO2: oxygen consumptionVO2I: indexed oxygen consumption

CHAPTER 2Near Infra-Red Spectroscopy (NIRS)

2.1 Principles of Physics

Th e NIRS technique, fi rst introduced by Jobsis (1) in 1977, is a noninvasive optical method, for in vivo continuous tissue oxygenation monitoring. Th e fi rst NIRS application in the pediatric patients dates back to 1985 when Brazy and Lewis (2) monitored cerebral oxygenation in preterm infants.

Th e NIRS is nowadays a common practice for clinical monitoring of both pediatric and adult patients in many medical fi elds (3).

NIRS instrumentation is similar to that for the UV-visible and mid infra-red ranges. Th ere is a source, a detector, and a dispersive element. Light Emitting Diodes (LEDs), which produce light in the spectrum of near-infrared, are used as radiation source Th e light travels through optical fi bers back and forth between the spectrophotometer and the distal end, called optode. Th e optode contains the dispersive element, a prism, which spatially separates light by wavelength. NIRS is based on the following physical principles: 1) biological tissues are relatively transparent to light in the spectrum of near infrared (700-1000 nm wavelength). Such low absorption coeffi cient permits high penetration depth, up to 8 cm of tissue, in contrast with the higher absorption coeffi cient of visible light (400-700 nm spectrum) permitting no more than 1 cm tissue penetration; 2) the Lambert-Beer’s law, (Figure 1) which relates the absorption of light to the properties of the material through which the light is travelling. Th e law states that there is a logarithmic dependence between the transmission of light trough a substance and the product of the concentration of the absorbent molecules, or chromophores, dispersed in the solution, the distance the light travels through the material and the molar extinction coeffi cient of the material, as expressed by the following equation:

Chapter 2 The role of regional oxygen saturation

10

A = (εx bx c)

A= absorbance (no units, A = log10 P0 / P ), where Po is the initial light power and P is the power of light aft er it passes through the sample

e= molar absorptivity or extinction coeffi cient (L mol-1 cm-1) b= path length of the sample (cm) c= concentration of the compound in solution (mol L-1)

Figure 1. explaining the Lambert-Beer law

Th e Lambert-Beer’s law allows to calculate the concentration of one or more substances dissolved in a solvent, if the size of the container is known, measuring the intensity of the incident and transmitted light. When more than one substance is dispersed in the solution, diff erent wavelength radiations are used (each one specifi c for its absorbent). Th e total attenuation of light is the sum of that of all the absorbers:

A = (ε1 x b x c1) + (ε2 x b x c2) + …

Th at is the case of biological tissues, where many compounds concur to the overall absorption of light (water, lipids, melanin, myoglobin, oxygenated hemoglobin and deoxygenated, cytochromes, etc), each one having a diff erent absorption spectrum.

Since the spectrum of absorption of the hemoglobin depends on its oxygenation state, the NIRS method is utilized to measure the quantity of oxygen bound to the hemoglobin present in a tissue or the regional oxygen saturation (rSO2).