**3.1 Cardiorespiratory stability**

SA is considered the best-tolerated anesthetic method for cardiovascular unstable NBs. In preterm and ex-preterm with congenital heart disease, SA has shown good stability in systolic, diastolic, and mean arterial pressure, due to the absence of arterial hypotension secondary to sympathetic blockade as observed in adults. The same occurs with the management of respiratory diseases such as BPD. Most NBs show a very low incidence of postoperative complications. Even those weakened NBs are able to maintain spontaneous breathing during surgery, avoiding intubation of the trachea and subsequent mechanical ventilation [5].

#### **3.2 Hemodynamic stability**

Spinal anesthesia produces a thoracic and lumbar sympathetic block and therefore vasodilation below the level of the block. However, due to the incomplete sympathetic innervation in children under eight years of age, SA is characterized by excellent hemodynamic stability that does not require prior administration of intravenous fluids or the use of vasopressors. The blood volume in the capacitance vessels of the lower limbs is less. However, when SA is administered with GA, hemodynamic stability is considerably modified due to the pharmacological action of general anesthetics. In the newborn with congenital heart disease, SA is preferred over GA, which produces minimal cardiovascular changes [6].

#### **3.3 Short stay in the post-anesthesia care unit**

Respiratory complications in the post-anesthesia care unit (PACU) are more common with the use of inhaled anesthetics, intravenous or opioids, concerning SA, especially in preterm or ex-preterm patients who are susceptible to relatively frequent periods of apnea and respiratory depression. GA and opioids are

considered predictors of a longer stay in the PACU. SA has been the most important factor that has reduced the length of stay in the PACU [7].
