FRCA Notes

Congnital Diaphragmatic Hernia

The curriculum asks us to 'explain the implications of paediatric medical and surgical problems including major congenital abnormalities e.g. diaphragmatic hernia'.

Resources

  • Congenital diaphragmatic hernia arise owing to a defect in the diaphragm, which allows abdominal organs to protrude into the thoracic cavity
  • It is potentially life-threatening due to the associated lung hypoplasia and pulmonary hypertension
  • Affects 1 in 3,000 - 5,000 live births
  • Majority left-sided; only 20% right-sided and bilateral herniae rare
  • Survival >75% although still an appreciable mortality (25-30%) especially if untreated

  • Less than 2% are familial

  • 10-15% have genetic or chromosomal abnormalities
    • Trisomy 13, 18 or 21
    • Fryns syndrome
    • Cornelia de Lange syndrome
    • Beckwith-Wiedemann syndrome
    • CHARGE syndrome

  • 30% have ≥1 structural abnormality
    • Cardiovascular (14%)
      • VSD (29%)
      • ASD (26%)
      • Coarctation (8%)
      • Hypoplastic left heart (7%)
    • Genitourinary (7%)
    • Limb (5%)
    • CNS (5%)
    • Palatal (2%)

By type

  1. Bochdalek (95%)
    • Failure of fusion of the pleuroperitoneal folds
    • Postolateral herniation through the Foramen of Bochdalek
    • Mostly left-sided but can be right-sided or bilateral (2%)

  2. Morgagni (5%)
    • Herniation through the foramen of Morgagni; a small defect within the septum transversum
    • Retrosternal or parasternal herniation
    • Usually smaller herniation and right-sided in 90% of cases
    • Associated with better outcome

By defect size

  1. Small defect surrounded entirely by muscle (survival ∽95%)
  2. <50% chest wall with absent diaphragmatic tissue
  3. >50% chest wall with absent diaphragmatic tissue
  4. Complete absence of hemidiaphragm (survival ∽57%)

By prognosis

  • Can be stratified into low (<10%) vs. intermediate (∽25%) vs. high (∽50%)
  • Risk factors for increased mortality include:
    • Birth weight <1.5kg
    • Apgar score <7 at 5mins
    • Presence of chromosomal abnormality
    • Presence of major cardiac abnormality
    • Supra-systemic pulmonary hypertension on TTE
    • Higher plasma concentrations of endothelin-1

  • Other poor prognostic factors include low gestational age at diagnosis, small contralateral lung, bilateral CDH, predicted lung volume <15%, total lung volume <20ml, or observed:expected lung-to-head ratio <25%

  • The most reliable antenatal predictor of survival is the absence of liver herniation

  • Some suggestion that pulmonary hypoplasia may be the primary disturbance due to genetic and environmental factors, rather than a consequence
  • This hampers formation of the (hemi-)diaphragm, allowing abdominal contents into the thoracic cavity, further hindering lung development on the affected side(s)
  • Vascular remodelling and pulmonary hypertension ensues ± LV hypoplasia

Embryology

  • On day 22 of embryonic development the septum transversum extends from the anterior aspect of the body cavity
  • From week 5 pleuro-peritoneal folds then originate from the lateral sides of the body cavity
  • From week 7 the septum transversum and pleuro-peritoneal folds extend inwards, fuse with each other and the oesophageal mesentery to form the initial diaphragmatic structure
  • By week 16 the muscular component of the diaphragm begins to develop

Lung parenchyma

  • Abnormal differentiation of type 2 pneumocytes
  • Decreased branching of terminal bronchioles leads to under-developed airways
  • Severely hypoplastic lungs

Pulmonary vasculature

  • Thickening of intra-pulmonary arteries → pulmonary hypertension
  • Exaggerated response to vasoactive substances, e.g. endothelin-1, which exacerbates pulmonary hypertension
  • Persistent pulmonary hypertension of the newborn ensues

Diagnosis

  • 50%-60% are diagnosed antenatally as a result of routine ultrasound screening
    • Right-sided herniae are more difficult to diagnose
    • Diagnosis is easier with advancing gestation, the presence of other abnormalities and increased ultrasonographer experience
  • Foetal MRI can confirm a diagnosis
  • Once identified, high-resolution ultrasound allows severity grading and selection of those who may benefit from intra-uterine intervention

Foetal surgery

  • Foetoscopic endoluminal tracheal occlusion (FETO)
    • An experimental therapy (TOTAL Trial) which occludes the trachea with a balloon to prevent efflux of pulmonary fluid, stretch the lung parenchyma and accelerate growth
    • Improves short-term mortality in those with a poor prognosis

Diagnosis

  • Usually apparent soon after birth due t severe respiratory distress: tachypnoea | cyanosis | 'scaphoid' abdomen [inward concavity of the anterior abdominal wall]
  • CXR typically shows abdominal organs in the thoracic cavity

Immediate management

  • I&V is performed immediately after delivery, taking care to avoid high-pressure BVM ventilation
  • NGT insertion to decompress stomach ± NG on suction
  • Venous access (consider umbilical line)
  • Arterial access; pre- and post-ductal
  • Pre-/post-ductal saturations monitoring

  • Early TTE will reveal:
    • Degree of cardiac impairment
    • Presence of concurrent structural cardiac abnormalities
    • Degree of pulmonary hypertension
    • Presence of right-to-left shunting

  • Ultrasound of head and kidneys should take place to check for other abnormalities

Ongoing ICU management

  1. Optimising gas exchange
    • Target pre-ductal SpO2 >92% and post-ductal SpO2 80-95%
    • Pressure-limited ventilation to limit barotrauma to the hypoplastic lung
    • Peak pressure <25cmH2O
    • PEEP 3-5cmH2O
    • Permissive hypercapnoea

    • HFOV as a rescue strategy; may require NMBA which are otherwise avoided if possible

    • ECMO as a rescue therapy prior to surgical correction, potentially indicated by:
      • PIP >28cmH2O to achieve sats target
      • PaCO2 >9kPa despite optimised ventilation
      • Pre-/post-ductal saturations consistently ≤80% or 70% respectively
      • Lactate >5mmol/L
      • Refractory hypotension despite optimised fluid and vasoactive therapy, with a UO <0.5ml/kg/hr

    • Consider surfactant

  2. Optimising PVR/minimising pulmonary hypertension
    • Avoid excessive hypercarbia (PCO2 <6kPa)
    • Adequate oxygenation (PO2 >7.5kPa)
    • Normal acid/base status
    • Nitric oxide, although may not improve outcome and response should be assessed using TTE and if no significant improvement therapy should be ceased
    • Intravenous pulmonary vasodilators e.g. sildenafil, prostacyclin

  3. Maintaining organ perfusion in the face of cardiac dysfunction e.g. use of milrinone, noradrenaline, dobutamine or dopamine as deemed appropriate based on TTE findings
    • E.g. MAP >45mmHg or age-appropriate MAP

  • CDH repair is not a surgical emergency; repair should only take place once haemodynamic and ventilatory stability has been achieved
  • Abdominal organs are returned to the abdominal cavity, and the diaphragmatic defect is either closed by primary repair (i.e. sutured) or by a patch repair

Approaches

  • Open surgery involves a subcostal incision and is often necessary for larger defects, those with liver herniation or on higher levels of cardiorespiratory suppor

  • Thoracosocpic surgery
Advantages Disadvantages
↓ post-operative pain Surgery takes longer
↓ ventilation time Results in ↑ PaCO2 and ↓pH
Earlier feeding ↓ cerebral oxygenation saturations
Shorter hospitalisation Higher ventilatory pressures needed
Better cosmesis Higher rates of recurrence

Timing of surgery

  • The historical strategy of emergency (early) repair has been replaced by an approach aimed at optimising the patient as best possible before proceeding
  • Surgery only occurs after adequate resuscitation and identification/optimisation of comorbidities, which is typically ∽48hrs but may be longer in comorbid children
  • Aim for the following physiological parameters to have been met before surgery:
    • MAP normal for gestation
    • Pre-ductal SpO2 consistently 85-95% on an FiO2 of <0.5
    • Lactate <3mmol/L
    • UO >1ml/kgh/hr
  • Alternatively, surgical repair on ECMO can take place although there are high risks inc. bleeding, and a divided literature on timing of surgery on ECMO (early vs. delayed repair)

Perioperative considerations in the child undergoing repair of a congenital diaphragmatic hernia


Decision to operate

  • Little consensus on best time to operate, but it is not an emergency procedure
  • Decision to operate should involve an MDT of anaesthetists, surgeons, NICU, paediatricians and parents
  • There should be stable cardiorespiratory function and evidence of resolving pulmonary hypertension
  • Parameters indicating suitable stability for repair include:
Factor Target
SpO2 >92% on FiO2<0.5
MAP >45mmHg (or normal for gestational age)
Vasoactive drugs <0.05mcg/kg/min NAd/Adr
Lactate <3mmol/L
UO >1ml/kg/hr
Pulmonary artery pressure <2/3rds systemic pressure
iNO dose Weaning, and <10ppm
Hb >100g/L
TTE Good RV function

Pre-assessment

  • Ante-natal and peri-natal history
  1. ETT size, position and method of securing
    • Intubation grade

  2. Current ventilatory settings and trends in support
    • ABG results
    • Pre- and post-ductal saturations
    • Previous or ongoing need for HFOV or ECMO

  3. Assessment of adequacy of venous and arterial access
    • Pharmacotherapy; vasoactive drugs, pulmonary vasodilators and their trends
    • Current fluid management
    • Blood results and availability of blood products
    • Up-to-date TTE looking at RV function and PA pressures in particular

  4. Cranial ultrasound results
    • Sedation strategy
    • Need for or most recent use of NMBA

  5. Glucose management
    • Haemoglobin, platelet and clotting levels
    • Urine output
    • Renal function and electrolytes

  • Close communication between surgical and anaesthetic teams as surgical manipulation can directly impact physiology

Ventilation

  • The most common issue intra-operatively is the inability to control PCO2, especially in thoracoscopic repair
  • Aim to:
    • Accurately measure CO2 by considering transcutaneous monitoring
    • Minimise circuit dead space as much as possible
    • Consider periods of manual hyperventilation using a T-piece to reduce hypercapnoea and assess lung compliance
  • A strategy using pressure control ventilation (to reduce risk of barotrauma) and zero PEEP (to reduce end-expiratory compression of alveolar capillaries and raised PVR) may be preferable

Pulmonary hypertension

  • If concerns over worsening PVR:
    • Increase FiO2, reduce PCO2, manage acidosis
    • Ensure adequately warmed
    • Provide adequate analgesia
    • Consider nitric oxide
  • Continue or maintain vasoactive infusions to maintain organ perfusion, manage intra-operative shunting

  • Return to NICU ventilated
  • Anticipate deterioration in lung compliance and gas exchange immediately post-op.
  • Pulmonary hypertension may persist
  • Monitor for complications:
    • Bleeding
    • Chylothorax
    • Early recurrence
    • Patch infection

  • Mortality approaching 30%
  • Long-term morbidity in 87%
    • Recurrent LRTI (34%)
    • Chest deformity (40%)
    • GORD (30%)
    • Failure to thrive (20%)
    • Sensorineural hearing loss (50%)
    • Cognitive impairment (up to 70%)
    • Lateral scoliosis