Pediatric Anesthesiology: Research Report
The bidirectional Glenn (BDG) shunt or superior cavopulmonary connection directs systemic venous blood from the superior vena cava (SVC) directly to the pulmonary artery (Fig. 1). In children with single ventricle physiology being staged to a Fontan procedure, the BDG is normally performed at 3–6 mo of age. The Fontan procedure or total cavopulmonary connection creates a one-ventricle series circulation, and is generally performed at 2–3 yr of age.
Use of a hand-held ultrasound probe to obtain two-dimensional images of the internal jugular vein (IJV) significantly facilitates IJV cannulation in infants and children (1–3), and is routinely used by the attending physicians on the Cardiac Anesthesia Service at our institution for this purpose. In addition, Trendelenburg position and enhancement maneuvers, such as manual liver compression and a simulated Valsalva maneuver, can be used in children with normal cardiac anatomy to increase the size of the IJV and further facilitate cannulation (4,5). We compared the effects of these maneuvers on the size of the right internal jugular vein (RIJV) in patients with a BDG shunt presenting for a Fontan procedure.
The protocol was approved by the Clinical Investigations Committee of Children's Hospital Boston and written parental informed consent was obtained for each patient. Twenty-one consecutive patients with a BDG shunt (Fig. 1) scheduled to undergo an elective Fontan procedure (total cavopulmonary connection) were studied. Patients with bilateral BDG shunts and patients with a patent azygous vein to the SVC connection were excluded.
Premedication and anesthesia induction was at the discretion of the attending anesthesiologist. After endotracheal intubation and institution of mechanical ventilation, placement of IV catheters and an arterial catheter, the patients were positioned in the supine position (S) with the neck slightly extended on a rolled towel placed under the shoulders. The head was then turned 45° to the left. The RIJV was imaged in the center of the screen with a two-dimensional 5 MHz ultrasound transducer system (SonoSite® TITAN) by an investigator. In each patient, imaging of the RIJV was accomplished with the ultrasound probe held perpendicular to the skin at the level of the cricoid cartilage. The transducer was applied with minimal pressure to ensure the vein was not compressed. Liver compression (L) was achieved with manual compression, whereby the dorsum of an assistant's hand was kept parallel to the posterior aspect of the patient's 12th rib for 10 s. The simulated Valsalva maneuver (V) was achieved by applying a positive inspiratory pressure of 20 cm H2O for 10 s. For the Trendelenburg position (T), the operating table was tilted down to a 15° angle.
Ultrasound images of the RIJV were captured during each of the following eight maneuvers: 1) baseline S, 2) S in combination with L, 3) S in combination with V, 4) S in combination with L and V, 5) T, 6) T in combination with L, 7) T in combination with V, and 8) T in combination with L and V.
All RIJV measurements, except those involving V, were made at end-expiration. After freezing the image on the screen the cross-sectional area (CSA; in cm2) of the RIJV was measured by a second investigator using planimetry software.
RIJV CSA data, as well as percent change in CSA from baseline (S) data, were analyzed using one-way analysis of variance with repeated measures and with Tukey post hoc pairwise comparisons of the mean responses to the different treatments. Statistical analyses were performed with JMP 6 software for Macintosh (SAS, Cary, NC). Data are reported as mean ± sd. A P < 0.05 was considered significant.
Complete data were collected from all patients. Demographic data are presented in Table 1. All patients except one underwent the planned Fontan procedure. This one patient, with a mildly hypoplastic left ventricle, underwent takedown of the BDG and conversion to a two-ventricle repair. There were no significant differences in RIJV CSA with position change or enhancing maneuvers. RIJV mean CSA data are presented in Table 2. Individual patient RIJV CSA at each measurement interval is presented in Figure 2. There were no significant differences in mean percent change in RIJV CSA from baseline (S) with position change or enhancing maneuvers. In 23.8% (5 of 21) of patients one or more position change or enhancing maneuvers produced a 25% or more increase in RIJV CSA. In 28.6% (6 of 21) of patients, one or more position change or enhancing maneuvers produced a 10% or more decrease in RIJV CSA. Percent change in RIJV CSA data is presented in Table 3. Individual patient percent change in RIJV CSA at each measurement interval is presented in Figure 3.
This study demonstrates that Trendelenburg position and enhancement maneuvers have no effect on the CSA of the RIJV in children with a BDG shunt when they present for the Fontan procedure. In addition, there was no effect of these interventions on the percent change in RIJV CSA from the supine position. A mean increase of 25% or more in CSA is generally considered to be clinically significant in terms of facilitating RIJV cannulation in children (4).
The mean RIJV CSA in the supine position in our patients with a mean age of 31.9 ± 9.3 mo was 0.58 ± 0.18 cm2. This RIJV CSA is identical to the supine RIJV CSA of 0.58 ± 0.22 cm2 found in a study of children without cardiac disease with a mean age of 34.5 ± 18.3 mo (4). In contradistinction to our patients, these same investigators found all combinations of position and enhancement maneuvers increased RIJV CSA by 25% or more except for 15° Trendelenburg position alone and liver compression alone in the supine position (4). They found the combination of 15° Trendelenburg position, 10 s of an inspiratory hold at 25 cm H2O, and liver compression to be most effective, increasing the CSA of the RIJV by 66% (4). Contrary to their findings in children, no combination of position or enhancement maneuvers was effective in increasing RIJV CSA by 25% or more in healthy infants in the same study (4). In a mixed group of infants and children (age 6 mo to 8 yr) without cardiac disease, 10 s of inspiratory hold at 20 cm H2O was demonstrated to be more effective than 20° Trendelenburg position in increasing the CSA of both the RIJV and the left IJV (5). This simulated Valsalva maneuver increased the CSA of the right and left IJV by 38% and 29% respectively (5).
In patients with a BDG shunt the inferior vena cava (IVC) is not in continuity with the SVC. IVC blood returns to a common atrium and mixes with pulmonary venous blood; this mixed blood is then delivered to the single systemic ventricle. When the SVC and IVC are in continuity maneuvers that enhance return of IVC blood to the central circulation, such as Trendelenburg position or liver compression, would be expected to increase SVC and IJV size. Such an increase would not be expected in BDG shunt patients.
The increased intrathoracic pressure that accompanies a simulated Valsalva maneuver in patients without a BDG shunt increases the size of the IJV (extrathoracic vein) while obstructing and decreasing the size of the SVC (intrathoracic vein) (6,7). A simulated Valsalva maneuver increases alveolar pressure as well as intrathoracic pressure. In patients with a BDG shunt, RIJV and SVC pressures are increased (10–15 mm Hg) and are equal to mean pulmonary artery pressure. It could be anticipated that a simulated Valsalva maneuver would increase SVC and RIJV size, as there will be direct transmission of alveolar pressure to these vessels in the absence of an intervening atria or ventricle. In this circulation, there will be rapid equilibration of alveolar, mean pulmonary artery, SVC, and IJV pressures. However, it is unlikely that a simulated Valsalva maneuver at 20 cm H2O (14.7 mm Hg) is capable of substantially increasing RIJV pressure and CSA in a BDG shunt patient with an increased SVC pressure at rest. In addition, the SVC and RIJV are likely to be less compliant at the elevated pressures seen in BDG shunt patients with little expected increase in CSA seen for a given increase in transmural pressure. We chose not to use a higher inspiratory hold pressure based on our clinical experience that higher airway pressures significantly reduce pulmonary blood flow leading to hypoxemia in these patients.
In summary, Trendelenburg position and enhancement maneuvers are unlikely to increase the RIJV CSA to an extent that facilitates RIJV cannulation in BDG shunt patients presenting for the Fontan procedure. In addition, in some BDG shunt patients, these maneuvers may significantly reduce RIJV CSA. Thus, the routine use of provocative maneuvers to facilitate cannulation of the RIJV in children with a BDG shunt does not appear warranted.
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© 2007 International Anesthesia Research Society
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