Brachiocephalic hypertension with reduced lower limb blood pressure measurements in coarctation is a common finding. However, in the presence of large patent ductus arteriosus (PDA) or co-existing collaterals, little or no difference in systolic pressures of the upper and lower limbs is observed. We present a case and a plausible explanation to findings contrary to above.
A 6-week-old, 2.8 kg, male infant presented to us with feeding difficulty, diaphoresis and tachypnoea with chest recessions. All four peripheral pulses were well felt with oxygen saturations of 90% in each. Transthoracic echocardiography documented double outlet right ventricle (L-malposed aorta) with subaortic conus, non-routable inlet ventricular septal defect with muscular extension, large PDA, hypoplastic distal transverse arch and isthmus with preductal coarctation and severe pulmonary artery hypertension. Lack of difference in upper and lower limb non-invasive blood pressure monitoring was attributed to large PDA. CT angiography was performed to aide precise arch delineation. Distal transverse arch reconstruction and coarctoplasty by left thoracotomy with pulmonary artery banding (PAB) via midline sternotomy in a single setting planned after counselling the family about single ventricle staged approach.
After standard ASA monitoring, anaesthesia was induced with sevoflurane and oxygen and maintained with isoflurane and oxygen-air mixture. Fentanyl (2 mcg/kg) and pancuronium (0.1 mg/kg) were used for intubation. Methylprednisolone (30 mg/kg) was administered and ambient temperature maintained at 32-34° C for spinal cord protection. Somatic and cerebral NIRS monitoring were used to assess adequacy of flow. Right internal jugular central venous line, right radial and right femoral arterial were secured after induction. Blood pressure in right radial artery measured 85/41 (62) and 119/32 (61) was measured in right femoral artery. Oxygen saturations in upper and lower extremity were 92%. Distal arch repair was done utilizing left reversed subclavian flap. This was followed by ductal division, coarctectomy and extended end to end anastomosis. After the repair, radial artery pressures measured 70/40 (60) and femoral artery measured 80/40 (52). As planned patient was moved to supine position for midline PA banding. Thereafter the child was shifted to the ICU for recovery.
The plausible explanation for the “paradox” of high arterial pressures in lower extremity: low pulmonary vascular resistance led to preferential flow from right ventricle across the pulmonary valve vis-à -vis the aortic. This was further accentuated by the distal aortic obstruction. The large bolus of blood in the descending aorta fed by the large PDA caused higher systolic pressures (119 mm Hg). During diastole, the extreme run-off into the branch pulmonary arteries caused reversal from the PDA leading to low diastolic pressures (32 mm Hg). The mean arterial pressure therefore remained consistent in both the extremities (61 and 62 mm of Hg).
This index case highlights a strange finding with a possible insight into its cause helping the perioperative physician to understand the physiology better.
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