Page 20 - ANZCP Gazette APRIL 2022
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Enrolled patients had preoperative transcranial doppler (TCD) evaluations to assess the quality of the temporal window (bilateral) for insonation of the middle cerebral arteries (MCAs). Patients without adequate temporal window were excluded. Other exclusion criteria included: patient refusal; emergency surgery; pregnancy; redo procedures; abnormal pre-operative neurological examination; ejection fraction of less than 40%; existing cerebrovascular disease; a history of transient ischemic attack or stroke; and pre- existing carotid disease.
In accordance with routine practice at the Auckland District Health Board Perfusion Department, CPB circuits were deployed on a Stockert S5 heart lung machine (Sorin Group, Munich, Germany), using the SMARxTTM polyvinyl chloride tubing (COBE, Cardiovascular, Arvada, CO), a Sorin Inspire 6M hard-shell venous reservoir and oxygenator (Sorin Group, Mirandola, Italy), Pall AL20 arterial line filter (Pall Corp, Portsmouth, UK), silicone replacement pump raceway tubing (Natvar, City of Industry, Los Angeles, CA) and a CSC14 cardioplegia delivery system (Sorin Group, Munich, Germany).
All circuits were flushed with CO2 through the arterial line filter for approximately five minutes at 1L/min before priming with Plasmalyte-148 (Baxter International Corporation, NSW, Australia). Cephazolin (1g), heparin (100 IU.kg) and tranexamic acid (500mg) were added and circulated before initiation of bypass. Institutional clinical practice guidelines for the conduct of CPB were followed. These include mean arterial pressure (MAP) ≥ 50mmg, PaO2 20-30kPa, venous saturations >70%, non-pulsatile flow (2.0-3.0L/m2/min), a target haematocrit of >0.22 during CPB and oxygen delivery index (DO2i)> 270mL/min/m2, active or passive cooling to mild hypothermia (32-34 °C), -stat acid/base management, and activated clotting time (ACT)> 480 seconds.
The arterial line filter was continuously purged during CPB via a connection to the venous inlet port. The minimum level sensor level on the hard-shell venous reservoir was set at 150-200mL as per manufacturers recommended
guidelines for minimum volume. Cannulation techniques involved ascending aortic and two-stage venous cannulation for all patients. Anaesthetic management similarly followed institutional norms without the use of nitrous oxide.
The heart was deaired through aortic root venting, through a combined dual lumen “Y” antegrade cardioplegia and venting needle. The aortic root vent was utilised after the removal of the aortic cross clamp and before application of the PASC. Deairing techniques for some surgeons also included evacuation of the aortic root air through the proximal anastomotic site before the last stitch and release of the PASC. In the rare case of remaining visible air when using the transoesophageal echocardiogram, the aortic root vent was reinserted or continued after termination of CPB for prolonged deairing. The aortic root vent and venous cannula were decannulated before the administration of protamine. Decannulation of the aortic cannula took place after protamine administration was complete and the patient was haemodynamically stable.
Continuous emboli count in the right and left MCAs were recorded using two 2.25MHz transducers fitted on a DiaMon head brace (DWL/Compumedics Germany GmbH, Singen, Germany). The head brace was placed on the patients head once the patient was fully anaesthetized. The depth of the insonation on the TCD transducers was varied between 35-65mm until bilateral representative spectral MAA flow was identified. High- intensity transient signals (HITS) representing emboli were defined as short-duration, High intensity signals equal to or greater than 4dB above as background noise. Emboli were automatically counted and differentiated into artefact, gaseous (bubbles) or solid in real time by the DWL Doppler X TCD device’s integrated differentiation software (DWL/ Compumedics Germany GmbH, Singen, Germany).
Emboli counts (with subdivision into differentiation of gaseous and solid emboli) were measured from the initiation of CPB to the termination of CPB. Our phase of interest for this study was the period involving aortic cross clamp removal, partial clamp application and removal (if used), to termination of bypass (Figure 1). We expected to have similar emboli counts up to the cross clamp removal between the two groups, and to see some differences after this period.
17 APRIL 2022 | www.anzcp.org
