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Delayed Sternal Closure Neonatal operations with a long cardiopulmonary bypass time can result in diastolic dysfunction, and sternal approximation may result in cardiac compression with decreased diastolic filling and a critical reduction of cardiac output.123 An open sternum and subsequent delayed sternal closure is a frequently used strategy to ameliorate poor cardiac output and allow for the resolution of inflammation and edema of the myocardium and lungs It may be used in patients with incomplete hemostasis to help prevent cardiac tamponade.124–126 Because diastolic dysfunction predictably worsens in the first 24 hours following surgery, delayed sternal closure is sometimes applied to all neonates following complex operations Alternatively, it can be applied selectively, but universal criteria do not exist Typically closure of the open sternum is undertaken when mobilization of the third space fluid begins and vasoactive support has been reduced Delayed sternal closure is associated with a prolonged CICU course, prolongation of intubation, and an increased risk of infection.127 This association is likely the result of delayed sternal closure being applied to higher-risk patients, but it suggests that elective use of delayed sternal closure should be used with caution Assessment of Systemic Oxygen Delivery Assessment of DO2 in those at risk for shock or in shock is the primary tenet in the care of critically ill patients As discussed earlier, it is important to appreciate the limitations of “standard” hemodynamic parameters and the perfusion examination in determining the adequacy of Qs and DO2 in critically ill patients and even more so in those with a multidistribution circulation An effective construct for managing critically ill patients is to think of the determinants of VO2 and DO2 and relationship between them The use of venous and NIRS oximetry is a useful adjunct to the conventional approach of monitoring standard clinical parameters See the detailed discussion offered earlier as well as that in Chapter 70, as the principles are similar in the postoperative period Mechanical Ventilation and Transitioning to Spontaneous Ventilation In addition to determining whether adequate ventilation and oxygenation are present on minimal ventilatory support (low mandatory rate and pressure support, end-expiratory pressure and FiO2), consideration should be given to the fact that PPV may have a profound impact on cardiovascular function, as described above The following conditions may delay extubation: ventricular diastolic and systolic dysfunction, the former compounded by and the latter assisted by PPV; residual lesions; arrhythmias; parenchymal and pleural disease; lack of hemostasis; and renal dysfunction with associated fluid imbalance A useful paradigm for considering extubation readiness, particularly in those that have been on PPV for a protracted period of time, is consideration to the following determinants of ventilatory capacity: respiratory muscle energetics (VO2/DO2), an important factor in those with a limited Qs/DO2 and elevated work of breathing; respiratory muscle loading conditions, including airway resistance and total respiratory compliance, the latter consisting of lung and chest wall elastance (thoracic cage and diaphragm [affected by abdominal disease]); and neuromuscular competency, including an assessment of respiratory control and drive, ensuring adequate clearance of sedatives and analgesics; and the extent to which disuse atrophy of the respiratory muscles is present It is also important to consider the fact that neonates have considerably less respiratory reserve than infants and children This is primarily the result of a highly compliant thoracic cage that does not become completely ossified until about 1 year of age Relative to infants and children, the functional residual capacity is reduced, predisposing the neonate to developing atelectasis and impaired oxygenation In addition, the highly compliant chest wall provides less structural support in the face of exaggerated negative-pressure breathing, which leads to energy being wasted in distorting the chest wall (retractions) In addition, the neonatal diaphragm contains less fatigue-resistant fibers and the subglottic space has a reduced cross-sectional area, rendering it more susceptible to postextubation laryngeal edema and swelling One strategy that may be used during transition to spontaneous breathing is the empiric use of noninvasive positive airway pressure following extubation: continuous positive airway pressure (CPAP) for lung volume and oxygenation or biphasic positive airway pressure (BiPAP) for lung volume and ventilatory assistance Following extubation, upper airway disease may be the result of postextubation laryngeal edema and inflammation, vocal cord paresis from injury to the recurrent laryngeal nerve, unmasking of upper airway disease, such as laryngomalacia and inadequate upper airway tone due to oversedation Evaluation and Monitoring of the Central Nervous System Short-, mid-, and longer-term outcome studies have revealed significant neurodevelopmental impairment in approximately half of all survivors of neonatal surgery for complex congenital heart disease (see also Chapter 76).128 Numerous mechanisms—including inadequate DO2 in the fetus, postnatal hypoperfusion, hypoxemia, thromboembolism, and underlying cerebral vasculopathy—have been implicated as some mechanisms leading to brain injury.129 Additionally, the brains of neonates with complex congenital heart disease are immature at the time of birth, with significantly altered metabolism, making them selectively vulnerable to ischemic insults; therefore in many centers the evaluation and monitoring of the central nervous system has become a routine part of perioperative care of neonates with fUVH and other complex congenital heart defects (Table 71.6).130–132 The modalities outlined in Table 71.6 are not mutually exclusive and are part of a multimodal evaluation of the central nervous system in postoperative neonates Table 71.6 Modalities for Evaluation and Monitoring of the Central Nervous System Modality Near infrared spectroscopy Timing Advantages Preoperative, Easy bedside interpretation, easily accessible intraoperative, postoperative Postoperative Detection of subclinical seizures, assessment of cortical function by assessment of background Continuous video encephalography Ultrasonography Preoperative, postoperative Magnetic resonance imaging Preoperative, postoperative Disadvantages Poor reproducibility, poor intersubject reliability Resource-intense, requires specialist interpretation Detection of structural abnormalities, periventricular leukomalacia, large intracranial hemorrhages, hydrocephalus, easily accessible, performed at the bedside Insensitive for stroke detection, high false-positive rate for hemorrhages Detection of structural abnormalities, stroke, hemorrhages, white matter injury, thrombosis, others Not available at bedside, requires sedation in some (short studies can be done, as with swaddling) Near Infrared Spectroscopy NIRS is the most widely used continuous neuromonitoring strategy in