In this case, pericardium traction, one of the common procedures during MICS, triggered a decrease in rSO2 that alerted us to the risk of cerebral ischemia. The change in rSO2 was sufficient to cause us to speculate that cerebral ischemia might have occurred in the patient.
Recently, a smaller incision during median sternotomy has become an alternative technique during cardiac surgeries for simple congenital heart deformities, such as closure of VSD and atrial septum defects [3, 5]. The smaller incision in pediatric MICS forces the surgeon to pull up the pericardium more strongly to secure a field of view, which can subsequently deform the aorta or the branch (Fig. 2B), which would possibly lead to cerebral ischemia. Additionally, it is extremely difficult to visualize such a physical deformity of arteries by TEE in pediatric MICS. Hence, monitoring of cerebral saturation by near-infrared spectroscopy (NIRS) is becoming an alternative for avoiding such an unforeseen emergency. Some groups have reported that the decrease in rSO2 was related to the surgical procedure in cardiac surgery [8, 9], whereas few reports have shown that simple traction of the pericardium can affect rSO2 values as we experienced.
Accumulating studies show that the rSO2 values measured by NIRS are trustworthy physiological indicators during pediatric cardiovascular surgeries [6, 7]. An interventional algorithm to prevent cerebral desaturation using NIRS has been introduced as a feasible strategy in clinical situations [7, 10, 11]. Following that algorithm, we concluded that arterial malperfusion was plausible because of the following observations: (1) the RRBP and rSO2 values dropped simultaneously, (2) SpO2 on the left hand remained unchanged, (3) the RFBP was maintained, (4) there was no apparent hemorrhage, (5) the CVP did not change, and (6) the patient’s heart rate and body temperature remained stable. Our decision to insert two artery catheters at the right radial artery and right femoral artery and monitor SpO2 at the left hand and foot may have been excessive. However, we aimed to monitor the blood flow at all the extremities during pediatric MICS in order to be alert to any signs indicating obstruction of blood flow. It ultimately gave us more clues to understand what happened in this emergent situation and for future reference.
There are limitations to the use of NIRS devices for monitoring of cerebral saturation. In the present case, we chose the INVOS sensor that reflects a mixture of Hb saturation in venous, capillary, and arterial blood [7]. Alternatively, NIRO®, another device for monitoring cerebral saturation, can give us detailed information from each source [12]. Another issue to be considered is that we used an adult sensor to measure the rSO2 value. Although standard values of rSO2 vary depending on the type of sensor used [13, 14], they are enough to be trustworthy [6, 7]. In this case, we did not check bilateral brain saturation, but monitoring of RRBP and SpO2 on the left hand provided us enough information. A carotid artery ultrasound and/or Transcranial Doppler ultrasound may be preferable for detecting cerebral malperfusions.
In conclusion, we experienced a pediatric case of MICS in which pericardium traction, one of the common procedures in MICS, caused a decrease in rSO2, but we were able to prevent cerebral ischemia during the surgery with useful monitoring including rSO2, arterial blood pressure, and SpO2 at extremities. To achieve better quality of life after congenital heart surgery, we should be aware that pericardium traction during MICS can lead to cerebral ischemia that is preventable by cautious observation of the patient.