NIRS & Optical Topography Studies on the Paediatric Cardiothoracic Intensive Care Unit

The risk of neurological injury for infants and children with cardiac and/or acute respiratory defects undergoing surgical procedures is considerable. This can be attributed to the fact that the specific surgical procedures are inevitably accompanied by periods of hypoxia/ischemia. Therefore, the application of specific monitoring to detect cerebral hypoxic conditions associated with neurological injury would both allow intervention on individual patients and drive refinements in strategies to reduce risk. Our studies are focused on children with intractable cardio-respiratory failure whose heart and lungs are supported on extracorporeal membrane oxygenation (ECMO). Establishing ECMO involves cannulation of the major vessels in the neck-internal jugular vein and carotid artery-maintaining and weaning from ECMO requires manipulation of ECMO flows, which can affect cerebral blood flow and potentially lead to neurologic complications.

The long-term aim of the studies is to use an optical topography system to investigate topographic cerebral oxygenation changes in patients undergoing ECMO. However initially we are monitoring regional cerebral and peripheral tissue oxygenation using a dual channel system, with the aim of investigating the relationship between brain and peripheral tissue oxygenation during changes in ECMO related variables.

We have used a dual channel near infrared system to measure changes in oxy-(HbO2) and deoxy-(HHb) haemoglobin concentrations, and tissue oxygenation index (TOI) on the forehead (cerebral) and calf (peripheral) of ECMO patients undergoing flow manipulations in the ECMO circuit. Power spectral density (PSD) and coherence analysis were performed on the HbO2 signal recorded at the two measurement sides in order to extract vasomotion, respiratory and cardiac oscillations [1].

Figure 1: Dual channel near infrared system (NIRO 200) in use on an ECMO patient.

Figure 2: Changes in HbO2 and HHb concentrations and TOI in the brain and leg for Patient 1 during reduction in the ECMO circuit flow.

Figure 3: PSDs for Patient 1 at 100%, 90%, 80% and 70% ECMO circuit flow, showing respiratory rate (RR) with its first harmonic and a peak at twice the ECMO pump frequency (2f_pump)

Multichannel Near Infrared Spectroscopy (Optical Topography) to investigate regional cerebral oxygenation in infants supported on extracorporeal circulation

In the current era of advanced cardiac surgery and extracorporeal membrane oxygenation (ECMO), there are serious limitations with inadequate and/or misleading neuromonitoring especially in the setting of haemodilution and non-pulsatile flow. The implications of neurological monitoring with relevance to neurodevelopmental outcome have not been clearly delineated.

To date most NIRS studies have used optodes placed on the forehead which monitor only a small area of the anterior cerebrum. We have developed a novel multichannel NIRS protocol for providing regional measures of cerebral oxygenation and haemodynamics for use in cardiac theatres and intensive care [2]. As ECMO in the cardiac intensive care could be a surrogate model similar to a patient undergoing cardiac surgery on cardiopulmonary bypass, we have carried out preliminary studies on patients on ECMO during manipulations in the ECMO circuit blood flows [3].

Figure 4. (a) Schematic of the source-detector array and channel configuration. The photograph shows the UCL designed neonatal cap in use with each source (S) and detector (D) annotated. (b) HbO2, HHb and HbT concentration changes from 12 channels during ECMO circuit flow changes. The vertical dotted lines represent the time at which a change in flow was induced so that each section in the plots corresponds to a specific flow, as annotated on channel 1 (a-baseline (100% flow), b=90% flow, c=80% flow, d=70% flow, e=80% flow, f=90% flow, g=baseline).

References

1. Papademetriou M.D., Tachtsidis I., Leung T.S., Elliott M.J., Hoskote A., Elwell C.E., “Cerebral and Peripheral Tissue Oxygenation in Children supported on ECMO for Cardio-Respiratory failure.” Advances in Experimental Medicine and Biology (2010) 662:447-453. [URL]
2. Papademetriou M.D., Tachtsidis I., Banaji M., Elliott M.J., Hoskote A., Elwell C.E., "Regional cerebral oxygenation measured by multichannel near infrared spectroscopy (optical topography) in an infant supported on venoarterial extracorporeal membrane oxygenation." Journal of Thoracic and Cardiovascular Surgery (2011) 141(5):e31-e33 [URL]
3. Papademetriou M.D., Tachtsidis I., Banaji M., Elliott M.J., Hoskote A., Elwell C.E., "Optical topography to measure variations in regional cerebral oxygenation in an infant supported on venoarterial extracorporeal membrane oxygenation. Advances in Experimental Medicine and Biology (2012) 737:71-76 [URL]