CPB with AP Collateral

Date
September 13, 2025
URL
https://x.com/withascalpel/status/1966835261457002876?s=46
Categories
CPBTOFSingle Ventricle

CPB with AP Collateral

Definition and why they matter

Aortopulmonary (AP) collaterals are systemic-to-pulmonary vessels that enlarge in chronically cyanotic lesions (e.g., TOF/PA, MAPCAs, complex arch disease). On CPB, they behave as a low-resistance parallel circuit that diverts arterial pump flow to the lungs (“collateral steal”). This shifts the circuit’s operating point, raises the perfusion pressure required to maintain systemic delivery, and risks under-perfusion of the lower body and kidneys. Continuous collateral runoff sustains pulmonary venous return, so the heart may remain full despite “full” bypass, predisposing to LV distension and suboptimal cardioplegia.

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Characteristic intraoperative physiology

  • Collateral steal: A portion of pump output disappears into the lung bed. Systemic adequacy must be inferred from somatic NIRS, arterial pressure profile, urine output, and lactate rather than nominal pump flow alone.
  • Persistent filling and residual ejection: Ongoing pulmonary venous return keeps LV/RV volumes high; native ejection may persist unless venous drainage and venting are optimized.
  • During cross-clamp: Bronchial/AP collateral backflow into the main PA often obscures the field and interferes with myocardial protection unless actively managed.

Pre-CPB planning

  • Anticipate the steal and upsize the circuit. When unifocalization or flow-study–guided repair is planned, many programs cool to ~25 °C, run flows around ~100 mL/kg/min with pH-stat, and use an upsized circuit (oxygenator, reservoir, cannulae, vent, tubing) with capability to perform both intraoperative pulmonary flow studies and residual collateral flow measurement [1].
  • Vent strategy ready. Prepare an LV vent (via RSPV/LA or transaortic) and a PA/LA sump.
  • Gas strategy. Consider mild permissive hypercarbia early in bypass to raise PVR and temper collateral runoff; titrate toward normocarbia as systemic delivery stabilizes.
  • If available/feasible: coil or temporarily occlude large discrete collaterals pre-op or intra-op (selective snaring/clip) before long ischemic intervals.

Conduct of bypass: actionable tactics

  1. Perfusion objectives
  • Aim for adequate systemic DO₂, recognizing that arterial line pressure will often be higher than usual for a given flow.
  • Avoid excessive vasodilation (worsens steal) and avoid extreme vasoconstriction (afterload-induced LV distension). Small, frequent vasoactive adjustments are preferable to large swings.
  • Reassess adequacy every few minutes using a bundle: somatic NIRS + U/O + lactate trajectory + acid–base. Escalate if any diverge.
  1. Drainage and decompression
  • Maximize venous return: optimize height, use VAVD judiciously, and add a secondary venous cannula if needed.
  • Vent early and liberally. LA/LV vent to prevent distension; confirm decompression with TEE (closed aortic valve and rising LVEDP are red flags).
  • If residual native ejection persists, confirm ACT/anticoagulation and check for inadequate drainage or occult obstruction.
  1. Managing the AXC period
  • Expect PA backflow from bronchial/AP sources. Options (often combined):
    • Snare or clamp the main PA (or branch PA) during critical steps.
    • Place a PA sump or sucker; keep cardiotomy suction effective and blood–air exposure minimal.
    • Deepen hypothermia or shorten ischemic intervals if visualization or cardioplegia efficacy is compromised.
  1. Gas and temperature management
  • Start with slightly lower FiO₂ and mild hypercarbia to counter runaway pulmonary flow; retitrate as systemic markers improve.
  • Use moderate hypothermia to widen safety margins when backflow is heavy or surgical times are prolonged.

Quantifying collateral runoff (useful numbers to anchor management)

  • After MAPCA harvesting, residual collateral flow averages ~5.5 mL/kg/min but varies widely (~0.8–15.2 mL/kg/min). Patients at the higher end may require higher pump flows to sustain systemic delivery [2].
  • Intraoperative pulmonary flow studies (after unifocalization) often perfuse the reconstructed PA tree at 3 L/min/m²; the mean PA pressure at this flow correlates with post-repair RV pressure and RV:Ao ratio, helping determine feasibility of complete repair [3].

Weaning and early postoperative care

  • Persistent volume load. Until collaterals are definitively addressed, the LV may face increased preload; employ careful afterload control, diuresis, and ventilatory strategies that avoid excessive pulmonary overcirculation.
  • Pulmonary hypertension vigilance. Collateral flow plus reperfusion can raise pulmonary pressures; be ready with ventilation optimization, sedation, and selective pulmonary vasodilators if indicated.
  • Renal protection. Because steal disproportionately threatens the lower body, continue close surveillance of urine output, creatinine, and somatic NIRS after separation from bypass.
  • Definitive collateral management. Plan postoperative imaging and coil/plug embolization for significant residual collaterals once hemodynamics allow. In neonates after arterial switch, hemodynamically important MAPCAs are uncommon but can cause pulmonary hemorrhage or heart failure; percutaneous coil occlusion in the early postoperative period is often effective [5].

Longer-term hemodynamics (what success looks like)

Following complete repair and at subsequent conduit change several years later, patients typically maintain low RV:Ao pressure ratios (~0.36–0.39), supporting the durability of the reconstructed pulmonary vascular bed when initial intraoperative targets are met [4].

At-a-glance checklist (for the pump run)

  • Expect higher arterial pressures at a given flow; judge success by delivery surrogates (somatic NIRS, U/O, lactate), not by flow alone.
  • Augment venous drainage and vent the LV/LA early; verify decompression with TEE.
  • During AXC, control PA backflow (snare/vent/sucker); consider more cooling or shorter ischemic windows if protection or visualization suffer.
  • After CPB, manage ongoing volume load and screen for diastolic dysfunction and pulmonary hypertension; arrange definitive collateral closure when feasible.

References

[1] Margetson TD, Sleasman J, Kollmann S, McCarthy PJ, Jahadi O, Sheff D, Shuttleworth P, Mainwaring RD, Hanley FL. Perfusion Methods and Modifications to the Cardiopulmonary Bypass Circuit for Midline Unifocalization Procedures. J Extra Corpor Technol. 2019;51(3):147-152.

[2] Mainwaring RD, Margetson TD, McCarthy P, Sleasman J, Jahadi O, Shuttleworth P, Sheff D, Kollmann S, Patrick WL, Hanley FL. Measurement of Residual Collateral Flow in Pulmonary Atresia With Major Aortopulmonary Collaterals. Ann Thorac Surg. 2019;108(1):154-159.

[3] Goodman A, Ma M, Zhang Y, Ryan KR, Jahadi O, Wise-Faberowski L, Hanley FL, McElhinney DB. Mid-Term Outcomes After Unifocalization Guided by Intraoperative Pulmonary Flow Study. World J Pediatr Congenit Heart Surg. 2021;12(1):76-83.

[4] Mainwaring RD, Reddy VM, Peng L, Kuan C, Palmon M, Hanley FL. Hemodynamic assessment after complete repair of pulmonary atresia with major aortopulmonary collaterals. Ann Thorac Surg. 2013;95(4):1397-1402.

[5] Doulamis IP, Marathe SP, Oh NA, Saeed MY, Muter A, Del Nido PJ, Nathan M. Major Aortopulmonary Collateral Arteries Requiring Percutaneous Intervention Following the Arterial Switch Operation: A Case Series and Systematic Review. World J Pediatr Congenit Heart Surg. 2022;13(2):146-154.