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Ann Thorac Surg 1997;64:1820-1822
© 1997 The Society of Thoracic Surgeons

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Case Report

Cerebral Effects in Superior Vena Caval Cannula Obstruction: The Role of Brain Monitoring

Division of Cardiovascular Surgery, Department of Surgery, and Department of Anaesthesia, Children's Hospital of Eastern Ontario and University of Ottawa, Ottawa, Ontario, Canada

Accepted for publication July 14, 1997.

	Abstract

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A pediatric cardiac case of transient obstruction of the superior vena cava by the venous cannula before cardiopulmonary bypass is presented. With venous obstruction and increase in central venous pressure, reduced cerebral blood flow velocities and absence of diastolic Doppler flow were detected. This was followed by regional cerebral venous oxygen desaturation and global electroencephalographic slowing. Reposition of the venous cannula led to the recovery of these physiologic indicators and a noncomplicated clinical outcome.

	Introduction

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Insertion of a cannula into the superior vena cava (SVC) may decrease venous return [1] and potentially reduce cardiac output. This has been related to the use of relatively large, stiff venous cannulas that distort these very pliable great veins [2]. Furthermore, a malpositioned SVC cannula impairs cerebral venous drainage [1], increasing intracranial pressure and compromising cerebral blood flow.

Transcranial Doppler echography, electroencephalography (EEG), and regional cerebral venous oxygen saturation (rCVOS) by near-infrared spectroscopy have been used for detection of brain dysfunction during adult cardiac operations [3], but their utility in the pediatric cardiac surgery population is not established. We report a pediatric case in which the risk of brain dysfunction was detected by transcranial Doppler echography, EEG, and rCVOS during SVC obstruction by the venous cannula. The immediate reposition of the cannula led to the recovery of the physiologic indicators of brain dysfunction.

A 3-year-old, 13-kg female child underwent surgical closure of a secundum atrial septal defect. Anesthetic maintenance was primarily opioid (sufentanil) supplemented by isoflurane (expired concentration, 0.2% to 0.6%). A 2-MHz pediatric Doppler probe (Medasonics, Fremont, CA) was placed on the temporal window for monitoring the peak, mean, and end-diastolic values of the cerebral blood flow velocities (CBFVs) from the right middle cerebral artery at the level of the bifurcation (depth, 45 mm). Electroencephalographic activity was recorded using scalp-surface electrodes through eight bipolar derivations from homologous frontotemporal, frontocentral, centrooccipital and temporooccipital locations. A 16-channel Grass machine (Grass, Quincy, MA) filtered (bandpass, 1 to 70 Hz) and printed the EEG. Continuous recordings started from before cannulations (baseline) to initial bypass. A persistent increase (>50%) in slow delta EEG activity (1 to 3.5 Hz) relative to the baseline not associated with anesthetic management was considered EEG slowing. The rCVOS was monitored by an Invos 3100 Cerebral Oximeter (Somanetics, Troy, MI) using a near-infrared light patch with two receivers (30 and 40 mm) placed on the right forehead outside the external limits of the sagittal sinus. In addition to brain monitoring, the mean arterial pressure, heart rate, systemic arterial oxygen saturation, right internal jugular central venous pressure (CVP), end-tidal CO₂, and inspired oxygen fraction were all continuously monitored.

The peak, mean, and diastolic CBFVs measured at the precannulation baseline were 64, 41, and 23 cm/s, respectively (mean arterial pressure, 55 mm Hg; hematocrit, 0.35%; heart rate, 150 beats/min). The rCVOS and systemic arterial oxygen saturation were 77% and 99%, respectively (inspired oxygen fraction, 0.39; arterial carbon dioxide tension, 33 mm Hg). The EEG before aortic cannulation showed a mixture of high-frequency and low-frequency activity, particularly with high frequencies distributed on bifrontal derivations (Fig 1). These findings reflected the effects of both the opioid and halogenated anesthetic agent on brain electrical activity.

View larger version (23K): [in this window] [in a new window]   Fig 1. . Electroencephalogram (EEG) recorded during a transient episode of obstruction in the superior vena cava (SVC) by the venous cannula. The "faster" EEG activity from before (A) is substituted by large-amplitude "slow" delta waves distributed in all derivations during the obstruction (B). Release of the obstruction (C) gradually returned the high-frequency components of the EEG and decreased the proportion of low-frequency activity.

View larger version (31K): [in this window] [in a new window]   Fig 2. . Transcranial Doppler waveforms before (A) and during superior vena caval (SVC) obstruction and cannula reposition (B). An arrow indicates the change in flow velocity pattern in the middle cerebral artery due to the release of the obstruction. Absence of diastolic flow is the first sign of transient obstruction detected before the reposition of the cannula (B).

	Comment

Top Footnotes Abstract Introduction Comment Acknowledgments References

The differential diagnosis of changes in end-diastolic CBFV during pediatric cardiac operations should include other conditions in which cerebrovascular resistance increases (eg, increased intracranial pressure) or cases in which the cerebral hemodynamics are altered by the presence of a patent ductus arteriosus or as a consequence of aortic valve incompetence [5]. Although variations in transducer position may affect CBFV, the use of other simultaneous hemodynamic and electrophysiologic indicators helps to define the clinical significance of any transcranial Doppler echographic changes.

In this case, brain monitoring permitted the evaluation of the cerebral effects of a surgical intervention. Transcranial Doppler echography offers a noninvasive means of assessing changes in brain circulation [5], and EEG allows one to detect signs of neuronal dysfunction secondary to cortical ischemia [6]. The rCVOS assesses cerebral vascular oxygenation during the operation [3], and this has been related to jugular bulb measurements in pediatric cardiac patients [7]. Although additional investigations with this technique are necessary in children, individual trends as in this case may be useful when used with other indicators of brain dysfunction. Brain monitoring may be of even greater utility during bypass when CVP catheters may not be functional, or in situations where a CVP catheter is impractical or undesirable.

	Acknowledgments

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Doctor Rodriguez is recipient of the Popham Fellowship Award. The cerebral oximetry monitor was provided by Somanetics, Inc (Troy, MI).

	Footnotes

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Address reprint requests to Dr Rodriguez, Division of Cardiovascular Surgery, Children's Hospital of Eastern Ontario, 401 Smyth, Ottawa, ON, K1H 8L1, Canada.

	References

Top Footnotes Abstract Introduction Comment Acknowledgments References

 

1. Kern FH, Hickey PR. The effects of cardiopulmonary bypass on the brain. In: Jonas RA, Elliott MJ, eds. Cardiopulmonary bypass in neonates, infants and young children. Oxford: Butterworth-Heinemann Ltd, 1994:263–81.
2. Friesen RH, Thieme R. Changes in anterior fontanel pressure during cardiopulmonary bypass and hypothermic circulatory arrest in infants. Anesth Analg 1987;66:94–6.[Abstract/Free Full Text]
3. Edmonds HL Jr, Rodriguez RA, Audenaert SM, Austin EH III, Pollock SB, Ganzel BL. The role of neuromonitoring in cardiovascular surgery. J Cardiothorac Vasc Anesth 1996;10:15–23.[Medline]
4. Rodriguez RA, Splinter WM, Cornel G, Roberts D, Reid C. Effects of aorto-venous cannulation for cardiopulmonary bypass (CPB) on cerebral blood flow velocities (CBFV) and electroencephalogram (EEG) in children [Abstract]. Anesth Analg 1997;84:S126.
5. Bode H, Eden A. Transcranial Doppler sonography in children. J Child Neurol 1989;4:S68–76.[Abstract/Free Full Text]
6. Edmonds HL Jr, Griffiths LK, van der Laken J, Slater AD, Shields CB. Quantitative electroencephalographic monitoring during myocardial revascularization predicts postoperative disorientation and improves outcome. J Thorac Cardiovasc Surg 1992;103:555–63.[Abstract]
7. Daubeney PEF, Pilkington SN, Janke E, Charlton GA, Smith DC, Webber SA. Cerebral oxygenation measured by near-infrared spectroscopy: comparison with jugular bulb oximetry. Ann Thorac Surg 1996;61:930–4.[Abstract/Free Full Text]

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This Article Abstract Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Rosendo A. Rodriguez Garry Cornel Lloyd Semelhago Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Rodriguez, R. A. Articles by Weerasena, N. A. Search for Related Content PubMed PubMed Citation Articles by Rodriguez, R. A. Articles by Weerasena, N. A.