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PubMed This is a summary of 18 peer-reviewed journal articles Updated
Pediatric Cardiology

The Critical Interstage Period

At a Glance

The interstage period between a baby’s first Norwood or Hybrid surgery and the Glenn is especially vulnerable. Daily checks of oxygen, weight, feeding, and wet diapers can reveal problems early, but your cardiac team’s individualized emergency plan always takes priority.

The “Interstage” period is the time between your baby’s first surgery (the Norwood or Hybrid) and their second (the Glenn). While it is a joyful time to have your baby at home, it is widely considered the most vulnerable phase of the single ventricle journey [1][2].

During this time, the single ventricle is performing “double duty,” pumping blood to both the lungs and the body simultaneously [3]. This “parallel circulation” is fragile: if too much blood goes to the lungs, the rest of the body may not get enough, and if the tiny shunt or conduit becomes narrow, the baby’s oxygen can drop dangerously fast [2][4].

Your Role: The Home Monitoring Program

Because changes in a baby’s condition can be subtle, your cardiac team will likely enroll you in a Home Monitoring Program [5]. Structured programs can help detect deterioration early and require a rapid team response, though they do not eliminate all risks [6][7].

You will typically be asked to track three things every day:

  1. Oxygen Saturation: Using a home pulse oximeter, you will check how much oxygen is in the blood. Important: Wiggling, cold hands, or a poorly placed probe can give false readings. Always wait for a steady waveform. Your team will give you a specific, individualized target range (for example, 75-85%, but this varies strictly by anatomy and shunt type) [8].
  2. Daily Weight: You will use a specialized infant scale to weigh your baby. Even a few ounces of weight loss or a “flat” weight trend (stagnant growth) can be an early sign that the heart is working too hard [9][10].
  3. Feeding and Intake: You will record exactly how many ounces your baby drinks and how many wet diapers they have [5].

Recognizing Red Flags: When to Act

You are the expert on your baby. If you feel something is “off,” or your baby looks severely ill, trust your instincts and call for emergency help regardless of what the numbers on the monitor say [11]. Your center should provide a printable, individualized emergency plan.

Action Level Symptoms to Watch For
Emergency (Call 911) Collapse or unresponsiveness; skin that looks grey, severely blue, or mottled; extreme difficulty breathing (skin pulling in deeply around ribs); or a seizure. Do not delay emergency care to repeat an oxygen reading [1][8].
Call Cardiac Team Immediately Oxygen saturation drops below your center’s explicit emergency threshold (e.g., <70%, but follow your specific plan); a sudden, persistent drop from your baby’s usual baseline; “fussiness” that cannot be calmed; or breathing that is faster or harder than usual [8][1].
Call Team Today Stagnant weight or weight loss; taking less than their usual amount of formula/milk; persistent vomiting or diarrhea; or fewer wet diapers than usual [8][9].

Nutrition: The “Fuel” for Surgery

Babies with a single ventricle burn calories at a much higher rate than other infants because their heart is working so hard [12]. To ensure your baby is strong enough for the Stage 2 Glenn surgery, the team focuses intensely on growth [9].

  • Fortified Feeding: Adding extra calories to breast milk or formula. Critical: You must use the exact recipe prescribed by your cardiac dietitian. Mixing errors can cause dangerous dehydration or electrolyte imbalances. [12]
  • Feeding Tubes: Many interstage babies use a Nasogastric (NG) tube (a small tube through the nose) or a Gastrostomy (G) tube (a tube through the stomach wall) [13]. These are tools, not failures; they allow the baby to get the calories they need without the exhausting “work” of sucking and swallowing [7]. Ask your team what to do if an NG or G-tube problem occurs at home.

Common Interstage Medications

Your baby may come home on a combination of medications, though the exact regimen is highly individualized based on their specific anatomy, blood pressure, and kidney function. Never start, stop, or repeat a dose without your team’s guidance. Ask your team exactly what to do if your baby misses or vomits a dose.

Examples of medications your team might consider include:

  • Aspirin: An antiplatelet drug sometimes used to prevent tiny clots from forming in the shunt or conduit [14].
  • Digoxin: Sometimes used to help the heart squeeze and manage certain rhythms. It requires careful monitoring for toxicity [15][16].
  • Diuretics (like Furosemide): “Water pills” that help the body get rid of extra fluid. They must be monitored to avoid dehydration [17].
  • ACE Inhibitors: Used selectively (not universally) in certain patients to relax blood vessels [18].

Common questions in this guide

What is the interstage period for a baby with a single-ventricle heart defect?
It is the time at home between the first staged heart operation, such as a Norwood or Hybrid procedure, and the Glenn operation. It is considered especially vulnerable because the single ventricle sends blood to both the lungs and the body.
What should I check every day during the interstage period?
Most home monitoring plans track oxygen saturation with a pulse oximeter, daily weight, how much the baby drinks, and wet diapers. Use the target range and instructions given by your cardiac team because normal values vary by the baby’s anatomy and shunt or conduit.
When should I call 911 for a single-ventricle baby?
Call 911 for collapse or unresponsiveness, grey or very blue or mottled skin, severe trouble breathing with deep pulling at the ribs, or a seizure. Do not delay emergency care to repeat an oxygen reading, and seek help if the baby looks severely ill even when monitor numbers do not seem alarming.
What oxygen saturation change should prompt a call to the cardiac team?
Use the emergency threshold in your child’s individualized plan; a value below that threshold or a sudden, persistent fall from the usual baseline requires immediate contact. A sample threshold such as below 70% is not universal, so do not substitute a general number for your center’s instructions.
How can I support my baby’s growth before the Glenn operation?
Your team may prescribe extra calories in breast milk or formula, and some babies need an NG or G tube to receive enough nutrition without tiring during feeds. Follow the dietitian’s exact recipe because incorrect mixing can cause dehydration or electrolyte problems.
What should I do if my baby vomits or misses a heart medicine dose?
Do not repeat, stop, or change a dose unless your cardiac team tells you to do so. Ask in advance what to do for a missed or vomited dose of aspirin, digoxin, a diuretic, or any other prescribed medicine.
Could a shunt or conduit problem cause warning signs besides low oxygen?
It may be associated with a sudden or persistent oxygen drop, faster or harder breathing, unusual fussiness, or another change from your baby’s usual condition. Because warning signs can vary, use your center’s emergency plan and call the cardiac team immediately when your baby is not acting normally.

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Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.What is the individualized 'normal' baseline range for my baby's oxygen saturation, and at exactly what number should I call the emergency line?
  2. 2.Who is our primary contact person for daily monitoring questions, and how do we reach them after hours or on weekends?
  3. 3.If my baby is not meeting their weight gain goals, what is the exact recipe for fortifying milk, and who should I contact for adjustments?
  4. 4.Are there specific signs of shunt or conduit narrowing that I should be looking for beyond just a drop in oxygen levels?
  5. 5.What exact steps should I take if my baby misses or vomits a dose of aspirin, digoxin, or any other prescribed medication?

References

References (18)
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    Characteristics of Interstage Death After Discharge from Stage I Palliation.

    Ahmed H, Anderson JB, Bates KE, et al.

    Pediatric cardiology 2021; (42(6)):1372-1378 doi:10.1007/s00246-021-02621-1.

    PMID: 33948710
  2. 2

    Hypoplastic Left Heart Syndrome: Definition, Morphology, and Classification.

    Jacobs JP

    World journal for pediatric & congenital heart surgery 2022; (13(5)):559-564 doi:10.1177/21501351221114770.

    PMID: 36053108
  3. 3

    Computational Modeling of Oxygen Delivery in Norwood Physiology: Differential Effects of Systemic and Pulmonary Vasodilator Conditions.

    Savorgnan F, Shah V, Turner E, et al.

    Journal of cardiovascular development and disease 2026; (13(8)) doi:10.3390/jcdd13080347.

    PMID: 42645818
  4. 4

    Cobra-Head Cuffed Vascular Graft as Right Ventricle-to-Pulmonary Artery Shunt in Norwood Procedure.

    Januszewska K, Lehner A, Schmidt C, et al.

    The Annals of thoracic surgery 2021; (112(1)):156-161 doi:10.1016/j.athoracsur.2020.05.050.

    PMID: 32599049
  5. 5

    Interstage Home Monitoring After Newborn First-Stage Palliation for Hypoplastic Left Heart Syndrome: Family Education Strategies.

    Nieves JA, Uzark K, Rudd NA, et al.

    Critical care nurse 2017; (37(2)):72-88 doi:10.4037/ccn2017763.

    PMID: 28365652
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    Home Monitoring Program Reduces Mortality in High-Risk Sociodemographic Single-Ventricle Patients.

    Castellanos DA, Herrington C, Adler S, et al.

    Pediatric cardiology 2016; (37(8)):1575-1580 doi:10.1007/s00246-016-1472-x.

    PMID: 27554255
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    Role of Home Monitoring in Reducing Disparities in the Interstage Mortality of Infants with Single Ventricle.

    El-Magharbel Y, Goldberg CS, Yu S, et al.

    The Journal of pediatrics 2026; (296()):115186 doi:10.1016/j.jpeds.2026.115186.

    PMID: 42250746
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    Impact of home monitoring program on interstage mortality after the Norwood procedure.

    Staehler H, Schaeffer T, Wasner J, et al.

    Frontiers in cardiovascular medicine 2023; (10()):1239477 doi:10.3389/fcvm.2023.1239477.

    PMID: 37900558
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    Interstage Weight Gain Is Associated With Survival After First-Stage Single-Ventricle Palliation.

    Evans CF, Sorkin JD, Abraham DS, et al.

    The Annals of thoracic surgery 2017; (104(2)):674-680 doi:10.1016/j.athoracsur.2016.12.031.

    PMID: 28347534
  10. 10

    Association of Interstage Home Monitoring With Mortality, Readmissions, and Weight Gain: A Multicenter Study from the National Pediatric Cardiology Quality Improvement Collaborative.

    Oster ME, Ehrlich A, King E, et al.

    Circulation 2015; (132(6)):502-8 doi:10.1161/CIRCULATIONAHA.114.014107.

    PMID: 26260497
  11. 11

    Acceptability of a parental early warning tool for parents of infants with complex congenital heart disease: a qualitative feasibility study.

    Gaskin KL, Wray J, Barron DJ

    Archives of disease in childhood 2018; (103(9)):880-886 doi:10.1136/archdischild-2017-313227.

    PMID: 29567664
  12. 12

    Power of a Learning Network in Congenital Heart Disease.

    Anderson JB, Brown DW, Lihn S, et al.

    World journal for pediatric & congenital heart surgery 2019; (10(1)):66-71 doi:10.1177/2150135118815023.

    PMID: 30799702
  13. 13

    Impact of Home Monitoring Program and Early Gastrostomy Tube on Interstage Outcomes following Stage 1 Norwood Palliation.

    Matthews CR, Hartman D, Farrell AG, et al.

    Pediatric cardiology 2023; (44(1)):124-131 doi:10.1007/s00246-022-02947-4.

    PMID: 35727331
  14. 14

    Variability of antithrombotics use in patients with hypoplastic left heart syndrome and its variants following first- and second-stage palliation surgery: a national report using the National Pediatric Cardiology Quality Improvement Collaborative registry.

    Ramachandran P, King E, Nebbia A, et al.

    Cardiology in the young 2017; (27(4)):731-738 doi:10.1017/S1047951116001189.

    PMID: 27981915
  15. 15

    Attributable mortality benefit of digoxin treatment in hypoplastic left heart syndrome after the Norwood operation: An instrumental variable-based analysis using data from the Pediatric Health Information Systems Database.

    O'Byrne ML, Song L, Huang J, et al.

    American heart journal 2023; (263()):35-45 doi:10.1016/j.ahj.2023.05.005.

    PMID: 37169122
  16. 16

    Impact of Digoxin Use on Interstage Outcomes of Single Ventricle Heart Disease (From a NPC-QIC Registry Analysis).

    Klausner RE, Parra D, Kohl K, et al.

    The American journal of cardiology 2021; (154()):99-105 doi:10.1016/j.amjcard.2021.05.048.

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    Trends in Discharge Prescription of Digoxin After Norwood Operation: An Analysis of Data from the Pediatric Health Information System (PHIS) Database.

    O'Byrne ML, Song L, Huang J, et al.

    Pediatric cardiology 2021; (42(4)):793-803 doi:10.1007/s00246-021-02543-y.

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  18. 18

    Angiotensin-Converting Enzyme Inhibitor Prescription for Patients With Single Ventricle Physiology Enrolled in the NPC-QIC Registry.

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    Journal of the American Heart Association 2020; (9(10)):e014823 doi:10.1161/JAHA.119.014823.

    PMID: 32384002

This page is for informational purposes only and does not constitute medical advice. Your baby’s cardiac team should set oxygen targets, medication instructions, feeding plans, and emergency steps for your child.