Neonatal brain oxygenation during thoracoscopic correction of esophageal atresia

Guidelines and procedures for this investigation were reviewed and approved by the institutional Medical Ethics Committee of the University Medical Center Utrecht. Parents were informed about the study design and procedures, and informed parental consent was obtained from both parents of each participating neonate. This study was performed in compliance with the principles established in the Helsinki Declaration (version Fortaleza, October 19, 2013). NIRS monitoring is already used as a standard clinical monitoring tool in the NICU of the Wilhelmina Children’s Hospital.

Fifteen patients with type C EA (with distal TEF) had complete data registration and were eligible for analysis. Table 1 presents demographics and clinical characteristics of the patients in this study. Eight patients had associated comorbidities, of which two patients had a right descending aorta and two patients had non-cyanotic cardiac malformations that required surgical correction at a later stage; one patient with dextrocardia and partial anomalous pulmonary venous connection (PAPVC) and one patient with a malaligned ventricular septal defect with overriding aorta. All patients had an overall uneventful thoracoscopic correction of EA. Median time in the OR was 211 [126–387] min, and the median time of PT was 130 [74–260] min.

The aim of this study was to investigate the effects of the installation of a CO₂ PT on the hemodynamics and cerebral oxygenation of neonates receiving thoracoscopic correction of EA. We observed that surgery with an intrathoracic pressure of 5 mmHg can be performed, while the MABP remains within normal limits. Application of the PT initially lowers SaO₂, raises paCO₂, and lowers arterial pH levels. These parameters were corrected through the course of surgery by changes in the ventilation. Under these conditions, cerebral saturation remained within the safety range during the whole procedure. Furthermore, in the postoperative phase cerebral oxygenation and all other monitored parameters remained within normal limits. Our results suggest that a thoracoscopic procedure with a CO₂ PT set at a pressure of 5 mmHg and flow of 1 L/min can be performed under conditions that allow for reversible arterial blood gas disturbances, with cerebral NIRS values that are elevated during anesthesia induction but that remain stable during and after the PT application.

A large number of pediatric surgical indications can be successfully managed by minimally invasive techniques [18], especially for cases involving treatment of EA. In an increasing number of pediatric surgical centers, these atresias are managed by thoracoscopic interventions [19]. Although benefits of either open or thoracoscopic approach to EA surgery remain to be proven in randomized studies [20], the thoracoscopic approach favors advantages supportive of less postoperative pain, shorter hospital stay [21], less scoliosis caused by rib fusion, decreased respiratory impairment, and improved overall cosmetic result [3, 22, 23].

Despite plausible clinical advantages favoring thoracoscopic EA surgery, concerns have been raised regarding the safety of these thoracoscopic interventions in neonates. These concerns focus mostly on the impact of the applied pressurized CO₂ PT on neonatal hemodynamics and organ perfusion [3, 4, 20, 24, 25]. Intrathoracic CO₂ insufflation collapses the lung, which adversely affects the O₂ and CO₂ exchange causing hypoxia and hypercarbia. Another factor that causes hypercarbia is the excess systemic CO₂ load that is absorbed from the thoracic cavity during the PT CO₂ gas insufflation [5]. Hypoxia and especially hypercarbia with a lowered pH cause vasodilatation of the cerebral vessels in the neonate [26‐28]. When lower arterial oxygen saturation causes lower cerebral oxygen supply, the hypercarbia-induced vasodilatation can compensate for the reduced cerebral oxygen supply if blood pressure remains adequate. Diminished perioperative cerebral oxygen saturation during neonatal cardiothoracic surgery is correlated with poor neurodevelopment outcomes [6, 7] and brain magnetic resonance imaging abnormalities at 1 year [8]. Recently, Bishay et al. [5] reported that severe perioperative hypercarbia, acidosis, and decreased cerebral oxygenation were seen in neonates that underwent thoracoscopic surgery for EA and congenital diaphragmatic hernia. It is proclaimed that the reduction in the cerebral oxygenation lingered for up to 24 h postoperatively. However, in the paper by Bishay et al. [5] the rScO₂ value at the start of operation of 87 % was very high, possibly due to initial hyper-oxygenation. It decreased to 75 % at the end of operation. Also in the postoperative phase, cerebral oxygenation levels remained within reference range.

Furthermore, in the published series on neonatal thoracoscopic interventions [5, 20] that describe the negative impact of CO₂ application, PT pressures of up to 10 mmHg were applied. A recent experimental study in piglets showed that 10 mmHg PT pressures caused severe hemodynamic instability and decreased cerebral perfusion, whereas these conditions remained stable with PT pressures of 5 mmHg [29]. The results from this piglet study suggest that the applied pressure of 5 mmHg, as used routinely in our clinic, has no severe adverse effects and seems safe to use in thoracoscopic procedures.

In response to the concerns about thoracoscopic EA surgery, Conforti et al. [30] concluded that cerebral oxygenation remains stable during open EA correction. The results of our present study show that this conclusion is not exclusively reserved for open EA correction but that it is also possible during thoracoscopic surgery. We believe that close monitoring and a close collaboration between neonatologists, anesthesiologists, and pediatric surgeons is essential for achieving stable physiological conditions with sustained brain oxygenation levels. According to the anesthesia protocol, fluid expansion and inotropes were applied to prevent blood pressure from declining below physiological limits during the thoracoscopic procedure. Moreover, in the present study we observed that in the initial phase of surgery, installation of the PT caused arterial saturation to drop. To allow adequate ventilation, CO₂ PT insufflation was then stopped until the patient had recovered. If reinstallation of CO₂ PT persisted in causing low oxygen saturation, insufflation pressures were not increased but an additional trocar was introduced to gently move the lung away from the operating field-of-view. Initial hypercarbia and consequent acidosis was alleviated during the operation by continuous adjustment of ventilator settings. Acceptable limits of perioperative CO₂ blood gas values are as yet not known [2, 31]. However, to ascertain CO₂ and pH levels stayed within acceptable range, adequacy of ventilation is confirmed by arterial blood gas analysis at 30-min intervals [20, 30].

Whether the initial hypercapnia, which can have strong vasoactive effects [2, 26‐28] and the acidosis, recorded in our study, could be detrimental for the developing neonatal brain is unknown [31, 32]. These blood gas results are comparable though to those seen during open EA surgery. In our study the initial paCO₂ during the pneumothorax was 54 mmHg. It was 56 mmHg in a series of patients that were operated via (open) thoracotomy in the study by Bishay et al. [20]. Also, the resulting acidosis in our series with a pH of 7.25 is comparable to a pH of 7.26 in the study of Bishay et al. [20]. In our study, cerebral oxygenation remained stable and not jeopardized during or after the thoracoscopic procedure. The initial increased cerebral NIRS values prior to the surgical procedure are also described in other studies of open or thoracoscopic neonatal surgery [5, 30]. This could be a consequence of an increased supply of oxygen at the phase of anesthesia induction. Also in our study the highest median FiO₂ was recorded at this time (0.68 ± 0.24).

In conclusion, thoracoscopic EA repair can be performed without the need for conversion or extended procedural times with CO₂-insufflation pressures that are sustained around 5 mmHg. Cerebral oxygenation was stable within the normal range during and after the procedure. Close perioperative monitoring of neonatal brain oxygenation and close collaboration between surgeons, anesthesiologists and neonatologists will remain part of our operative protocol for patients undergoing thoracoscopic reconstruction of EA. Future studies in our institution will focus on the long-term effects of these types of surgery in neonates and the aim of understanding and avoiding impact on the neonatal brain with adverse neurodevelopmental outcomes.