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Annals of Cardiac Anaesthesia Annals of Cardiac Anaesthesia Annals of Cardiac Anaesthesia
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INVITED COMMENTARY  
Year : 2014  |  Volume : 17  |  Issue : 1  |  Page : 15-16
Modes of ventilation, cerebral oximetry, and bidirectional Glenn procedure


Director (Academic), Chief Consultant & Professor, Narayana Hrudayalaya Hospitals, Bangalore, Karnataka, India; Professor of International Health, University of Minnesota, USA

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Date of Web Publication2-Jan-2014
 

How to cite this article:
Kanchi M. Modes of ventilation, cerebral oximetry, and bidirectional Glenn procedure. Ann Card Anaesth 2014;17:15-6

How to cite this URL:
Kanchi M. Modes of ventilation, cerebral oximetry, and bidirectional Glenn procedure. Ann Card Anaesth [serial online] 2014 [cited 2019 Nov 14];17:15-6. Available from: http://www.annals.in/text.asp?2014/17/1/15/124125


Bidirectional Glenn (BDG) is a palliative procedure performed to bypass the right ventricle (RV) in certain children with complex congenital heart disease who are not amenable to total surgical correction or as a first-stage operation for patients scheduled for Fontan procedure later. The superior vena cava (SVC) is transected and an end-to-side anastomosis to the right pulmonary artery is performed whereby the venous return from the SVC is committed bidirectionally to the pulmonary circulation. The pulmonary blood flow (PBF) after BDG depends on the SVC pressure to overcome the pulmonary vascular resistance (PVR); the adequacy of PBF depends on the transpulmonary pressure gradient which is the pressure difference between SVC and the left atrium (LA) / right atrium as the two atria are connected via an existing or iatrogenic large atrial septal defect. However, increases in the SVC pressure can impede the cerebral venous return and are potentially detrimental. In addition, positive intrathoracic pressure can decrease the PBF after a BDG or Fontan procedure. Based on hemodynamic tenets, spontaneous ventilation is preferred in a Fontan physiology because of the philosophy that negative intrathoracic pressure augments PBF. Penny et al. have demonstrated that mechanical ventilatory support using external oscillatory device with a mean negative chamber pressure is advantageous from a hemodynamic point of view in patients after Fontan operation. [1] It has been assumed that spontaneous ventilation is ideal for these patients to reduce the intrathoracic pressure and enhance the forward flow of blood into the pulmonary circuit; however, a strong evidence for this is lacking. Using Doppler flow velocity measurement, Peterson et al. showed that there is no significant change in PBF with a variety of manipulations during spontaneous and controlled ventilation. [2],[3],[4]

In this issue of Annals of Cardiac Anaesthesia, Turkoz et al. demonstrate the beneficial effects of continuous positive airway pressure ventilation + pressure support ventilation (CPAP + PSV) and spontaneous ventilation on regional cerebral oxygen saturation, hemodynamic status, and lactate levels in 20 patients undergoing BDG, as compared to intermittent positive pressure ventilation (IPPV) and synchronized intermittent mandatory ventilation (SIMV). [5] Based on the finding, the authors conclude that CPAP + PSV improves cerebral oxygen saturation and hemodynamic parameters. The factors that influence the cerebral oxygen saturation are PaCO 2 , mean arterial pressure, and SaO 2 . Analysis of the data provided by the authors showed that the changes associated with institution of CPAP + PSV were: a significant (a) increase in systolic arterial pressure (SAP), (b) increase in diastolic arterial pressure (DAP), (c) increase in mean arterial pressure (MAP), (d) decrease in mean airway pressure, (e) decrease in mean pulmonary rtery pressure (mPAP ), and (f) decrease in inotropic score. As there was no significant increase in the PaCO 2 and SpO 2 after institution of CPAP + PSV, the increase in cerebral oxygen saturation may be attributable purely to the increase in MAP as a result of awakening and imposition of spontaneous respiration. Without objective measurements of PBF (e.g. with Doppler echocardiography, measurement of transpulmonary pressure gradient, and/or demonstration of stroke volume/cardiac index), it is rather difficult to pinpoint the reason for improvement in cerebral oximetry in these patients. Furthermore, it is puzzling to note that in two patients, the postoperative cerebral oximetry levels were higher than the SpO2 (this is physiologically not possible!). However, high SpO2 is often observed in cyanotic patients using some pulse oximetry monitors.

The term cerebral tissue oxygen monitoring is a technique based on O 2 -sensitive electrode that is placed on the cerebral white matter and I would rather use the term cerebral oximetry which involves the use of near infra-red light technology. This is purely to avoid confusion of the terminology.

 
   References Top

1.Penny DJ, Hayek Z, Rawle P, Michael L. Rigby and Andrew N. Redington Ventilation with external high frequency oscillation around a negative baseline increases pulmonary blood flow after the Fontan operation. Cardiol Young 1992;2:277-80.  Back to cited text no. 1
    
2.Peterson KL, DeCampli WM, Pike NA, Robbins RC, Reitz BA. A report of two hundred twenty cases of regional anesthesia in pediatric cardiac surgery. Anesth Analg 2000;90:1014-9.  Back to cited text no. 2
[PUBMED]    
3.Fyfe DA, Kline CH, Sade RM, Greene CA, Gillette PC. The utility of transesophageal echocardiography during and after Fontan operations in small children. Am Heart J 1991;122:1403-15.  Back to cited text no. 3
[PUBMED]    
4.Penny DJ, Redington AN. Doppler echocardiographic evaluation of pulmonary blood flow after Fontan operation: the role of the lungs. Br Heart J 1991;66:372-4.  Back to cited text no. 4
[PUBMED]    
5.Turkoz A, Balci ST, Gonen H, Cinar O, Ozker E, Turkoz R. The effects of different ventilator modes on cerebral tissue oxygen saturation in patients with bidirectional superior cavopulmonary connection. Ann Card Anaesth 2014;17:10-5.  Back to cited text no. 5
    

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Correspondence Address:
Muralidhar Kanchi
Narayana Hrudayalaya Hospitals, Bangalore, Karnataka, India

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Source of Support: None, Conflict of Interest: None


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