Pulmonary hypertension

Cite this article as:
Marc Anders. Pulmonary hypertension, Don't Forget the Bubbles, 2013. Available at:
https://doi.org/10.31440/DFTB.3731

Definition: systolic PAP >35 mmHg or mean PAP >25 mmHg, clinically if systolic PAP:systolic BP <0.5

WHO Classification
I. Pulmonary arterial hypertension
I.1 Idiopathic
I.2 Familial
I.3 Associated with collagen vascular disease, portal hypertension, HIV, drugs & toxins, congenital systemic-pulmonary shunts, others
I.4 Persistent PHT in the Newborn
I.5 Pulmonary veno-occlusive disease
II. Pulmonary hypertension w/ left heart disease:left sided atrial, valvular or ventricular disease (TAPVR, MS, AS, Coarctation)
III. PHT associated with disorders of the respiratory system: COPD, sleep apnea, central hypoventilation Syndrome, high altitude, CLD
IV. PHT due to chronic thrombotic or embolic events
V. Miscs: sarcoidosis, histiocytosis, others

Diagnosis:

  • PA pressure: most reliable, invasive line
  • LA pressure: differential diagnosis – LV dysfunction
  • Echocardiography: measurement of TR jet velocity (modified Bernoulli equation: RVSP = 4 * v2 + RAP), movement of the interventricular septum, identify anatomical problems
  • Cardiac catheterisation: right heart catheter (mPAP >25 mmHg or PVR >3 Wood units/m2) → vasodilator therapy challenge to guide further therapy
  • Cardiac MRI: RV structure and function (limited in neonates)
  • High resolution chest CT with contrast: parenchymal lung disease, thromboembolism, others

Physiology:

Increase in RV afterload → RV volume and pressure increase → RV systolic dysfunction (→ TR) and diastolic dysfunction (→ RV diastolic HTN → increased right to left shunt if exists → hypoxia) → reduced RV output → reduced LV filling → reduced CO and reduced coronary artery perfusion pressure → RV ischemia and ventricular interdependence → RV systolic dysfunction


Neonatal PHT:

Incidence 2:1000, most common due to MAS, RDS, pneumonia, also idiopathic or in congenital diaphragmatic hernia


Postoperative PHT:

  • Preoperative predisposition: increased PVR, increased PBF, increased PVR and PBF, increased pulmonary venous pressure, lesion related (TAPVD, AVSD, VSD, IAA, truncus, shunt ops)
  • Cardiopulmonary bypass: decreased NO production, ischaemia-reperfusion injury, attendant inflammatory response (thromboxane, microemboli, leucosequestration, HPV)
  • Standard cardiovascular monitoring: early signs are tachycardia and hypotension; hypoxia occurs early only due to intracardiac shunts or as a late sign

Prophylaxis for postoperative PHT:

Maintain adequate analgesia and sedation (fentanyl 1 mcg/kg IV before painful stimuli), consider paralysis, normothermia, normal pH, aim paCO2 30-35 mmHg, paO2>75 mmHg in non-cyanotic lesion, prevent hyper- and hypoinflation, minimise intrathoracic pressures, consider milrinone infusion, consider iNO


Therapy for acute PHT crisis:

  • Increase FiO2 to 1.0: O2 is the best pulmonary vasodilator
  • Support cardiac output:resuscitation if required, dopamine (5-10 mcg/kg/min), dobutamine (5-10 mcg/kg/min), adrenaline (0.02-0.1 mcg/kg/min), milrinone (0.25-0.75 mcg/kg/min) as a PDE3 inhibitor increases cAMP → PVR vasodilation
  • NO donator: increased cGMP → vasodilation: commence NO 20 ppm, SNP (0.5-4 mcg/kg/min), GTN (0.5-5 mcg/kg/min)
  • Prostacyclin (= prostaglandin I2 = epoprostenol): increased cAMP → vasodilation, commence infusion (5-15 ng/kg/min), or nebulised; half-life: 3 min., can increase PBF and promote pulmonary oedema
  • Surfactant in neonates: promotes lung expansion, commence stat dose of poractant alpha (200 mg/kg)
  • Consider HFO: promotes lung expansion, avoid hyperinflation
  • Consider ECMO

Therapy for chronic PHT:

  • Sildenafil: (PDE5 inhibitor → increased cGMP), test dose 0.1 mg/kg, then increase slowly to maximum 2 mg/kg q4hr. FDA recommends against the use in sildenafil in chronic PHT in children, as lower doses were not effective, higher doses increased mortality. The implication its use in PICU is unclear.
  • Prostacyclin
  • Bosentan (1 mg/kg BD, increase to 2 mg/kg BD after 4 weeks)
  • Lung transplantation

References:

[1] Pediatr Crit Care Med. 2010 Mar;11(2 Suppl):S79-84: Steinhorn: Neonatal pulmonary hypertension

[2] Pediatr Crit Care Med. 2010 Mar;11(2 Suppl):S27-9: Taylor et al: Fundamentals of management of acute postoperative pulmonary hypertension

[3] Pediatr Crit Care Med. 2010 Mar;11(2 Suppl):S23-6: Mullen: Diagnostic strategies for acute presentation of pulmonary hypertension in children: particular focus on use of echocardiography, cardiac catheterization, magnetic resonance imaging, chest computed tomography, and lung biopsy

[4] Pediatr Crit Care Med. 2010 Mar;11(2 Suppl):S15-22: Bronicki et al: Pathophysiology of right ventricular failure in pulmonary hypertension

[5] Pediatr Crit Care Med. 2010 Mar;11(2 Suppl):S30-6: Barr et al: Inhaled nitric oxide and related therapies

[6] Pediatr Crit Care Med. 2010 Mar;11(2 Suppl):S41-5: Ivy: Prostacyclin in the intensive care setting

[7] Pharmacotherapy. 2010 Jul;30(7):728-40: Buckley et al: Inhaled epoprostenol for the treatment of pulmonary arterial hypertension in critically ill adults


All Marc’s PICU cardiology FOAM can be found on PICU Doctor and can be downloaded as a handy app for free on iPhone or AndroidA list of contributors can be seen here.

Pacing

Cite this article as:
Marc Anders. Pacing, Don't Forget the Bubbles, 2013. Available at:
https://doi.org/10.31440/DFTB.3715

NBG Code

I II III IV V
Paced Sensed Mode Modulation Multi-site
0-none 0-none 0-none 0 -none
A-Atrium A-Atrium T-triggered R-rate modulated A-Atrium
V-Ventricle V-Ventricle I-inhibited
D-dual D-dual D-dual

 

Modes of Pacing

Description Indication Limitation
AOO asynchronous atrial Bradycardia w/ intact AV, poor atrial sensing vulnerable Phase → AF
VOO asynchronous ventricular Bradycardia w/ conduction problems and poor ventricular sensing vulnerable Phase → VF
AAI demand atrial Bradycardia w/ intact AV not possible in Atrial Tachycardia
VVI demand ventricular Bradycardia w/ conduction problems / SSS / AF / Overdrive no atrial seqeuential mode
DOO asynchronous AV sequential Bradycardia, which benefits w/ sequential vulnerable Phase → AF or VF
DVI ventricular inhibited, AV sequential Desire for dual chamber pacing with poor atrial sensing risk of AF
DDI dual sensing, AV sequential all possible
DDD AV universal all possible, except atrial tachyarrhythmia not in atrial tachycardia

 


Specific indications:

  • AVRT: Consider overdrive pacing in AAI
  • AF: VVI
  • Overdrive pacing: when JET rate controlled, pacing 10% faster in AAI or DDD to regain atrial kick with AV conduction
  • Pace termination of reentry tachycardia (either atrial or AVRT): pace AAI 10-20% faster than atrial rate for short burst. If rapid reinitiation after successful capture, try gradually slowing pacing rate after reversion (risk of atrial fibrillation)
  • Atrial ECG: bipolar – attach atrial wire to right arm and left arm lead (atrial ECG prominent in I),;unipolar – attach atrial wire to V1 and V2 (atria ECG prominent in V1 and V2)

Problems & troubleshooting:

  • Daily pacemaker check: underlying rhythm, sensing and capture threshold (set threshold twice as measured)
  • Failure to pace: causes and treatment: threshold (increase output), ischaemia, electrolyte-disturbance (correct), post DC, lead malfunction, medication (flecainide, sotalol, propafenone, lignocaine, procainamide), cross-talk inhibition (reduce sensitivity, reduce output), oversensing (increase sensitivity), can also try to reverse polarity, or addition of skin lead
  • Failure to capture: threshold (increase output), ischaemia, electrolyte disturbance (correct), post DC, medication (flecainide, sotalol, propafenone, lignocaine, procainamide) – can also try to reverse polarity
  • Failure to sense: causes and treatment – sensing threshold (decrease sensing threshold)
  • Pacemaker-mediated tachycardia: change mode to DDI, adjust post ventricular atrial refractory period
  • Failure to track in DDD mode: adjust PVARP, AV interval and upper track rate

Checking and testing the pacemaker:

Patient non-pacing dependent

  • Start setup: atrial & ventricular leads connected to pacemaker (PM) cables, cables unplugged from PM, PM off
  • Turn PM on: default settings appear (DDD, rate 80, atrial (A) output 10 mA, ventricular (V) output 10 mA, A sensing threshold 0.5 mV, V sensing threshold 2 mV

 

Testing the sensing thresholds:

  • Set rate at least 20% below patient’s rate
  • Turn A and V outputs to 0.1 mA
  • Turn A and V sensing to ‘asynchronous’
  • Slowly increase V sensing by decreasing the number on scale, and observe the V red light
  • Record measured V sensing threshold (?? red light blinking)
  • Set V sensing to default 2 mV
  • Slowly increase A sensing by decreasing number on scale, and observe the A red light
  • Record measured A sensing threshold (?? red light blinking)
  • Set A sensing threshold to default 0.5 mV

 

Testing the output thresholds:

  • Set rate at least 20% above patient’s rate
  • Slowly increase A output by increasing the number on the scale, and observe ECG for distinct rate change
  • Record measured A capturing threshold
  • Turn A output threshold back to 0.1 mA
  • Slowly increase V output by increasing the number on the scale, and observe ECG for distinct rate and QRS shape change
  • Record measured V capturing threshold
  • Turn V output threshold back to 0.1 mA
  • Turn rate back down to at least 20% below patient’s rate

 

Final PM setting in backup mode:

  • Check V sensing on 2 mV and V light blinking red
  • Check A sensing on 0.5 mV and A light blinking red
  • Set pacing rate at acceptable backup rate below patient’s own rate
  • Turn A output up to 2x measured A output threshold
  • Turn V output up to 2x measured V output threshold

References:

[1] Anaesthesia. 2007 Apr;62(4):364-73: Reade: Temporary epicardial pacing after cardiac surgery: a practical review. Part 2: Selection of epicardial pacing modes and troubleshooting

[2] Pediatr Crit Care Med 2010 Vol. 11, No. 1: Skippen et al: Pacemaker therapy of postoperative arrhythmias after pediatric cardiac surgery


 All Marc’s PICU cardiology FOAM can be found on PICU Doctor and can be downloaded as a handy app for free on iPhone or AndroidA list of contributors can be seen here.

Blalock-Taussig Shunt

Blalock-Taussig Shunt

Cite this article as:
Marc Anders. Blalock-Taussig Shunt, Don't Forget the Bubbles, 2013. Available at:
https://doi.org/10.31440/DFTB.3598

Definition: Modified Blalock-Taussig shunt: Gortex graft from subclavian or innominate artery to the ipsilateral PA to augment PBF. Blalock-Taussig shunt: direct anastomosis between the transected subclavian artery (or the innominate artery) and the pulmonary artery.