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Ann Thorac Surg 2006;82:323-325
© 2006 The Society of Thoracic Surgeons

Case report

Detection of Lower Torso Ischemia by Near-Infrared Spectroscopy During Cardiopulmonary Bypass in a 6.8-Kg Infant With Complex Aortic Anatomy

Mathias Redlin, MD a , Wolfgang Boettcher, ECCP b , Michael Huebler, MD c , Felix Berger, MD d , Roland Hetzer, MD c , Andreas Koster, MD a , * , Wolfgang M. Kuebler, MD a , e

a Department of Anesthesia, Deutsches Herzzentrum Berlin, Germany
b Department of Perfusion, Deutsches Herzzentrum Berlin, Germany
c Department of Cardiothoracic and Vascular Surgery, Deutsches Herzzentrum Berlin, Germany
d Department of Congenital Heart Disease, Deutsches Herzzentrum Berlin, Berlin, Germany
e Institute of Physiology, Charité-Universitätsmedizin, Berlin, Germany

Accepted for publication September 1, 2005.

* Address correspondence to Dr Koster, Department of Anesthesia, Deutsches Herzzentrum Berlin, Augustenburger Platz 1, D-13353 Berlin (Email: koster{at}dhzb.de).


   Abstract
Top
 Abstract
Introduction
 Comment
 Acknowledgments
 References
 
Neonates and small infants with congenital heart disease and complex cardiac and vascular anatomy are particularly prone to episodes of complete or incomplete regional ischemia during cardiopulmonary bypass. These episodes may result either from inhomogeneous distribution of arterial blood flow via the aortic cannula or from impaired drainage of blood via the venous cannulae. However, techniques for continuous routine monitoring of regional perfusion in neonates or small infants undergoing cardiopulmonary bypass are extremely limited. Over recent years, transcranial near-infrared spectroscopy has become established as a useful technique for the non-invasive monitoring of cerebral oxygenation. Here we present a case in which simultaneous near-infrared spectroscopic monitoring of the oxygenation status in the brain and the right upper thigh revealed lower torso ischemia due to accidental cross-clamping of a hypoplastic descending aorta which would otherwise have been unnoticed. This shows that parallel near-infrared spectroscopy of the brain and the lower extremities may represent a novel non-invasive monitoring technique to ensure adequate cerebral and extracerebral perfusion during cardiopulmonary bypass.


   Introduction
Top
 Abstract
 Introduction
Comment
 Acknowledgments
 References
 
Monitoring of adequate tissue perfusion and oxygenation is of critical relevance in neonates and infants undergoing cardiac surgery with cardiopulmonary bypass (CPB) since the complex cardiovascular anatomy and the small operative situs increase the risk for inhomogeneous distribution of arterial blood or impaired drainage of venous blood. Yet, the intraoperative possibilities for non-invasive monitoring are extremely limited in this patient group. Near-infrared spectroscopy (NIRS) has evolved into a powerful optical technique to measure hemoglobin concentration and oxygenation in tissue, but its application in pediatric cardiac surgery has so far been limited to cerebral monitoring [1]. We have extended the use of NIRS to simultaneous measurement of oxygenation in brain and thigh skeletal muscles on a routine basis. We present a case in which, using this strategy, we were able to detect intraoperative acute arterial malperfusion of the lower torso after aortic clamping in an infant with congenital heart disease and complex aortic anatomy.

A 15-month-old infant (body weight: 6.8 kg; height: 70 cm) had previously undergone surgical correction of a type A interrupted aortic arch and a ventricular septal defect. Subsequent development of a stenosis of the distal aortic anastomosis required multiple interventions and stent implantation in this region. Now, the infant was scheduled for the resection of a membranous subaortic stenosis with a pressure gradient of 70 mmHg, as diagnosed by echocardiography. Since the child had bilateral femoral artery thrombosis, no cardiac angiography was performed before the operation.

After the induction of anesthesia, arterial and central venous pressure were continuously monitored via catheters introduced into the left radial artery and the vena cava via the right jugular vein, respectively. A first pair of NIRS optodes (NIRO-200, Hamamatsu Photonics K.K.T., Japan) was positioned non-invasively on the infant's forehead with an estimated optical pathlength of 20 cm between emitter and detector. A second optode pair was placed on the right thigh with an estimated pathlength of 18 cm [2]. The emitter optodes were connected to the pulsed laser diodes of the spectrometer NIRO-200, whereas the sensor optodes, which collect the backscattered light from the tissue, were connected to a photomultiplier tube. From light attenuation in tissue measured at different wavelengths in the near-infrared range, the following parameters were calculated: (i) concentration changes of oxyhemoglobin, deoxyhemoglobin and total hemoglobin according to the modified Lambert-Beer law and hemoglobin absorption spectra; (ii) tissue oxygenation index (TOI) as hemoglobin oxygen saturation and (iii) tissue hemoglobin index (THI) as relative hemoglobin concentration within the scanned tissue section according to the principle of spatially resolved reflectance spectroscopy [3].

CPB was performed via an 8 F aortic cannula with single venous drainage using a 16 F cannula. A left ventricular vent was placed via the right upper pulmonary vein. When CPB was established, TOI determined in the cerebral compartment was 75% and in the right thigh 67%. However, immediately after cross-clamping of the ascending aorta, a rapid drop of the TOI at the right thigh down to approximately 20% was noted, indicating ischemia of the lower extremity (Fig 1). The simultaneous decrease in THI and oxyhemoglobin concentration revealed that tissue ischemia was caused by inadequate arterial inflow, and not by impaired venous drainage. Yet the TOI in the cerebral compartment remained unchanged, indicating a regional rather than a systemic perfusion deficit. This notion was also supported by measurements of mean arterial pressure and arterial perfusion pressure, which did not differ from values recorded before aortic cross-clamping.


Figure 1
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  		Fig 1. Near-infrared spectroscopy measurement during the critical period. O2Hb = change in oxygenated hemoglobin (µmol/l). cHb = change in total hemoglobin (µmol/l). HHb = change in deoxygenated hemoglobin (µmol/l). TOI = Tissue Oxygenation Index (relation of oxygenated hemoglobin to total hemoglobin) (%). THI = Tissue Hemoglobin Index (relative value of total hemoglobin). nTHI = Normalized THI (change in total hemoglobin in relation to base-level hemoglobin).

 
Instantaneous re-assessment of the cross-clamp position by the surgeon revealed that the descending aorta, which was hypoplastic and ran right behind the ascending aorta, had been included in the cross-clamping. The cross-clamp was repositioned, resulting in an increase of TOI, THI and oxyhemoglobin concentration in the right lower extremity to baseline levels (Fig 1). The subsequent operation and the postoperative course of the patient were uneventful and the infant was discharged from the hospital on day 7.


   Comment
Top
 Abstract
 Introduction
 Comment
Acknowledgments
 References
 
We report a case in which non-invasive monitoring of tissue oxygenation at two different sites, the forehead and the right thigh, revealed major lower torso ischemia during cardiopulmonary bypass which would have remained undetected by conventional hemodynamic monitoring techniques.

Over the past years, NIRS has become established as a versatile technique for non-invasive monitoring of cerebral oxygenation in neonates and small infants during cardiothoracic surgery [4–6]. The TOI reflects changes in cerebral oxygenation with a high degree of sensitivity and specificity [3], and may even be used in pediatric cardiac surgery patients to indicate trends in mixed venous oxygen saturation due to the positive correlation of the two parameters [7]. Approximately 70% of the obtained signal is derived from the venous compartment, whereas capillaries and arterioles contribute 20% and 10%, respectively [8]. On the other hand, transcutaneous NIRS of the thigh or calf has been used extensively in sports medicine to monitor skeletal muscle oxygenation [9]. Although measurements at these sites may yield important additional information on lower torso oxygenation during cardiopulmonary bypass, NIRS monitoring of extracerebral tissue has not yet been implemented in cardiac surgery.

At our institution, we have performed simultaneous NIRS monitoring of cerebral oxygenation and skeletal muscle oxygenation at the thigh for the past 2 years as standard monitoring practice in neonates and small infants undergoing cardiovascular surgery with CPB. This strategy was introduced to obtain additional information on oxygenation and perfusion status of the brain and lower torso in this specific patient subgroup, for which monitoring techniques other than those using systemic perfusion pressures are not routinely available and in which the small operative situs bears an increased risk for complete or incomplete organ ischemia during CPB.

In the present case this strategy proved to be of particular value because it was the only detectable indicator of lower torso ischemia. Neither blood pressure measured via the left radial artery nor arterial line pressure monitored by the CPB system indicated that the cross-clamp had also interrupted the flow in the descending aorta. Parallel NIRS measurements at the forehead and the thigh showed rapid hemoglobin deoxygenation in the thigh skeletal muscle but not in the brain, indicating regional ischemia. Concomitant changes in THI and oxyhemoglobin concentration revealed an arterial inflow problem, since venous outflow occlusion increases oxyhemoglobin and total hemoglobin concentration in resting skeletal muscle [5]. This information facilitated the immediate correction of the cross-clamp position and prevented prolonged lower torso ischemia which might have had detrimental local and systemic effects [10]. Although the current report presents a case of rare and complex aortic anatomy, it demonstrates that simultaneous near-infrared spectroscopy of the brain and the lower torso is a useful and potentially crucial monitoring technique to ensure adequate tissue perfusion and oxygenation in neonates and small infants undergoing cardiovascular surgery with CPB. Further studies are required to assess the usefulness of this approach as an additional standard routine procedure, to determine its sensitivity and specificity for the detection of regional ischemia or tissue hypoxia during CPB, and to evaluate potential thresholds for intervention.


   Acknowledgments
Top
 Abstract
 Introduction
 Comment
 Acknowledgments
References
 
We thank Anne M. Gale, Editor in the Life Sciences, for editorial assistance.


   References
Top
 Abstract
 Introduction
 Comment
 Acknowledgments
 References
 

  1. Saidi N, Murkin JM. Applied neuromonitoring in cardiac surgerypatient specific management. Semin Cardiothorac Vasc Anesth 2005;9:17-23.[Abstract/Free Full Text]
  2. van der Zee P, Cope M, Arridge SR, et al. Experimentally measured optical pathlengths for the adult head, calf and forearm and the head of the newborn infant as a function of inter optode spacing Adv Exp Med Biol 1992;316:143-153.[Medline]
  3. Al Rawi PG, Smielewski P, Kirkpatrick PJ. Evaluation of a near-infrared spectrometer (NIRO 300) for the detection of intracranial oxygenation changes in the adult head Stroke 2001;32:2492-2500.[Abstract/Free Full Text]
  4. Jöbsis FF. Noninvasive, infrared monitoring of cerebral and myocardial oxygen sufficiency and circulatory parameters Science 1977;198:1264-1267.[Abstract/Free Full Text]
  5. Hayashida M, Kin M, Tomioka T, et al. Cerebral ischemia during cardiac surgery in children detected by combined monitoring of BIS and near-infrared spectroscopy Br J Anesth 2004;92:662-669.[Abstract/Free Full Text]
  6. Nollert G, Jonas RA, Reichert B. Optimized cerebral oxygenation during cardiac surgerya review of experimental and clinical investigations with near-infrared spectrophotometry. Thorac Cardiovasc Surg 2000;48:247-253.[Medline]
  7. Tortoriello TA, Stayer SA, Mott AR, et al. A noninvasive estimation of mixed oxygen saturation using near-infrared spectroscopy by cerebral oximetry in pediatric cardiac surgery patients Paediatr Anaesth 2005;15:495-503.[Medline]
  8. Boushel R, Langberg H, Olesen J, et al. Monitoring tissue oxygenation with near-infrared spectroscopy (NIRS) in health and disease Scand J Med Sci Sports 2001;11:213-222.[Medline]
  9. Van Beekvelt MCP, Colier WNJM, Wevers RA, van Engelen BGM. Performance of near infrared spectroscopy in measuring local O2 consumption and blood flow in skeletal muscle J Appl Physiol 2001;90:511-519.[Abstract/Free Full Text]
  10. Shahani R, Marshall JG, Rubin BB, Li RK, Walker PM, Lindsay TF. Role of TNF-alpha in myocardial dysfunction after hemorrhagic shock and lower-torso ischemia Am J Physiol Heart Circ Physiol 2000;278:H942-H950.[Abstract/Free Full Text]



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