【Pediatric anesthesia】Pediatric PAH

Pediatric PAH

1.
How to diagnose pediatric PAH

As in adults, pediatric PAH is defined as mean pulmonary artery pressure above 25 mmHg at rest but normal capillary wedge pressure, or greater than 30 mmHg
during exercise.

Clinically, PAH should be considered when children have a history of respiratory complications or cardiac malformations, hypoxia, do not respond significantly to oxygen therapy and alveolar remanoeuvre measures, or when the oxygen gradient before and after the catheter in the neonatal exceeds 20 mmHg
.
Suspicious diagnosis can be made
by tricuspid regurgitation on echocardiography or by direct measurement of lung pressure through cardiac catheterization.

2.
Precipitating factors for increased pulmonary artery pressure

In pediatrics and adults with congenital heart disease, pulmonary hypertension is an independent predictor
of morbidity during noncardiac surgery.
Moreover, the incidence of pulmonary hypertension crisis and cardiac arrest increases markedly in children with PAH undergoing noncardiac surgery or cardiac catheterization and may occur
suddenly without any obvious signs.
Physiological disorders such as hypoxia, hypercapnia, acidosis, and increased sympathetic tone can lead to a sudden and significant increase
in pulmonary vascular resistance (PVR).
Increased PVR leads to increased right ventricular pressure, increased right-to-left shunt in the heart, and decreased myocardial oxygen supply, which will further reduce cardiac output, exacerbate hypoxia, hypercapnia, further increase PVR, and finally lead to cardiac arrest
.

PAH can be further divided into responsive and non-responsive to drugs or oxygen, which correlates significantly with
patient outcomes.

3.
Choice of anesthetic for patients with PAH

No adverse events were found to be significantly associated
with any specific anesthetic medications, anesthesia procedures, or airway management.
When planning anesthesia for patients with pulmonary hypertension, it is most important to avoid sudden increases
in pulmonary artery pressure due to sympathetic stimulation.

Sedatives are beneficial in reducing sympathetic tone and avoiding increased oxygen consumption and arrhythmias
.
However, the combined application of benzodiazepines and narcotic analgesics can cause hypotension, which in turn causes an increase in sympathetic tone reactivity, which has the opposite effect
.
Similarly, inhalation anesthetics can cause dose-dependent systemic vascular resistance and decreased myocardial contractility, which leads to increased
sympathetic tone.
However, isoflurane and sevoflurane have been shown to promote pulmonary vasodilation, but nitrous oxide has little effect
on pulmonary artery hemodynamics in children with PAH.

Opioids are beneficial for PAH because they have less effect on pulmonary and systemic hemodynamics and increase PVR caused by inhibition of harmful stimuli
.
Propofol has also been successfully used in children
with PAH.
However, care must be taken when using it, as repeated single doses of propofol may cause dramatic changes
in cardiac output and systemic resistance.
Etomidate maintains hemodynamic stability
during anesthesia induction.
It exhibits a relaxing effect
on the pulmonary arteries in normally oxygenated mice.
In any case, opioids should still be used in combination with etomidate to inhibit elevated sympathetic tone, as during endotracheal intubation
.
In contrast, ketamine is not very common in pediatric PAH patients because it is thought to increase sympathetic tone and PVR
.
In mechanically ventilated patients, ketamine is not a problem
if hypoxia and hypercapnia can be avoided.

4.
Pulmonary vasodilator drugs

Pulmonary vasodilators can be used intravenously and inhaled
.
Intravenous vasodilators such as topazoline, prostacyclin, phenbenzamine, phentolamine, and nitrovasodilators have been used to reduce pulmonary artery pressure
.
These drugs are generally not selective for systemic and pulmonary circulation, carry a risk of hypotension, and sometimes do more harm than good
, especially in patients undergoing cardiac surgery.
Drugs that work by the inhaled route are inhaled nitric oxide (iNO) or inhaled prostacyclin
.
iNO improves right ventricular systolic function by reducing right ventricular load, while increasing left ventricular preload, restoring aortic blood pressure and coronary perfusion
.
However, if left heart dysfunction is present, iNO should be used with caution, as increased left ventricular preload can worsen cardiac function
.
In 1993, Wessel et al.
found that pulmonary vascular endothelial cell dysfunction occurred after extracorporeal bypass, and the response to acetylcholine was weakened, while the response to iNO was still maintained
.
The authors speculate that endothelial cell dysfunction, with decreased endogenous NO release, may be the cause of
postoperative pulmonary hypertension.
Journois and collaborators then discovered that iNO can be used to treat pulmonary hypertension crises that do not respond to traditional treatments
.
Miller et al.
suggest that even low doses of iNO (2ppm) still have therapeutic effects
in these patients.
Beghetti et al.
have shown that treatment with low-dose iNO for several days not only still has a therapeutic effect, but also carries a small
risk of toxic reactions.
Several different types of congenital heart surgery, such as mitral stenosis correction, complete pulmonary venous ectopic drainage correction, bidirectional Glenn surgery, and Fontan circulation surgery, can be complicated by increased pulmonary vascular resistance, and have been successful
with iNO.
In addition, iNO appears to be effective
for pulmonary hypertension after heart transplantation and/or lung transplantation.
When implanted with a left heart assist device, iNO improves right heart function, possibly by increasing pulmonary venous return and left atrial pressure to facilitate pump flow
.
For patients who rely on iNO therapy and develop pulmonary hypertension "rebound" after evacuation, the treatment strategy is to switch to sildenafil
at evacuation.
Inhaled prostacyclin only needs to be administered through a nebulizer, unlike NO, which requires a special drug delivery device, so its use is increasing
.
The use of two prostacyclins, epoprostenol or iloprost, has been reported, and prospective studies are ongoing
.
The main problem with this class of drugs is that the dose has not yet been determined, and the exact dose is unknown
for mechanically ventilated patients.
When vasodilators cannot be used, it is more advantageous to use antivasoconstrictors
.
Endothelin is the most promising site of action
.
Currently, selective or non-selective endothelial receptor blockers are being investigated
in animal experiments and pre-human trials.
In addition, research focusing on protective strategies during extracorporeal circulation is also underway, which may provide new therapeutic ideas
for preventing endothelial dysfunction.

5.
Pulmonary hypertension (PHC) crisis treatment strategies?

Avoidance: Avoid factors that promote increased PVR, such as hypoxia, hypercapnia, acidosis, systemic hypotension, and increased
sympathetic tone.
Treatment: Rapid diagnosis and treatment of PHC is key to
successful resuscitation.
First, 100% oxygen inhalation is given, hyperventilation is used to treat hypercapnia, and sodium bicarbonate is given to alkalinize the blood
.
When there is a marked decrease in cardiac output and signs of cardiac arrest, chest compressions and epinephrine
are promptly used.
Muscle relaxants may help control breathing
.
Remove any noxious stimuli and consider giving narcotic analgesics
.
Increased preload with fluid infusions and increased cardiac output with inotropes, such as dobutamine or milrinone, also reduce PVR; Or dopamine, which maintains SVR and improves coronary perfusion
.
Use of pulmonary vasodilators
.