Page 31 - ANZCP Gazette APRIL 2022

would be substantial and likely necessitate a number of blood transfusions. In practice, the total amount of cardioplegia may not need scavenging as the potassium level may be sufficiently low, however if the baseline serum potassium levels are high and the operation is long, Del Nido cardioplegia could be a very useful tool in the control of potassium levels. Liu et al (40) reported the use of Del Nido cardioplegia in 22 cardiac operations on pregnant patients at their institution finding it to be a safe method of arresting the heart. As a note of precaution, the protective effect of cold cardioplegia may be reduced slightly due to the higher than normal CPB temperature for pregnant patients. The anaesthetist could give insulin to control potassium levels, so cardioplegia scavenging may not be necessary. Insulin is a safe drug to use as it does not cross the placenta. The use of frusemide or thiazide is not recommended to increase urine output and remove excess potassium; these drugs cross the placenta and can be harmful to the fetus.
During the case haematocrit stayed between 37.5 and 31.8%. Mahli, Izdes and Coskun (18) suggest that haematocrit should be kept above 25%, with other authors suggesting a minimum of 28% (41)(36). Glucose stayed between 6.9 and 9.4 mmol/L. It is important to avoid maternal hypoglycemia as it can lead to fetal bradycardia (41). The aortic valve was replaced using a 25 mm On-x mechanical valve and straight aortic graft conduit. The patient was slowly rewarmed, due to the added risk to the fetus at this stage, and the procedure completed with no issues. Total bypass time was 155 minutes and a cross-clamp time of 109 minutes. The patient was transferred to ICU, where an ultrasound of the fetus displayed no adverse effects from the procedure or signs of fetal distress. The mother gave birth to a healthy baby at full term.
Summary
The following recommendations and considerations are made after review of the literature and experience gained from the case at WRH:
• It is ideal to time surgery for the 2nd trimester if required pre-delivery
• Use fetal and uterine monitoring if the gestational age is appropriate and the expertise is available
• Consider the use of tocolytics
• Use a 150 left lateral recumbent position if the gestational age is 20 weeks or more
• Avoid femoral cannulation if the situation allows
• Heparin dosing may need to be higher than normal with more frequent monitoring
• Discontinue RAP if the patient becomes at any moment haemodynamically unstable
• Have an empty volume bag attached to the circuit upon initiation of CPB due to the increased patient circulating volume
• CPB flow of at least 3.0 L/min/m2
• Primarily use flow to raise MAP, then vasoconstrictors if unsuccessful
• Pulsatile flow may be beneficial
• Keep MAP at or above 70 mmHg (higher if uterine contractions are present)
• Use alpha stat pH management
• If feasible, limit cooling to 340C and rewarm slowly
• Keep potassium levels below 5 mmol/L (ZBUF, scavenge cardioplegia, Del Nido cardioplegia, insulin)
• Maintain a Hct of at least 25% • Avoid hypoglycemia
References
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