A nurse is caring for a 6-week-old infant who has hypertrophic pyloric stenosis (HPS). Which of the following clinical manifestations should the nurse expect?

A. Alertness as such weight loss is not expected: This response may unnecessarily alarm the mother when, in fact, some weight loss in the early days is normal.

B. Reassurance as this is a normal weight loss.

It is normal for newborns to lose some weight during the first few days of life. The loss is often related to fluid loss, changes in feeding patterns, and initial adjustment to life outside the womb. A loss of one-half pound in a 2-day-old neonate is generally considered within the normal range. It's important for the nurse to reassure the new mother that this weight loss is expected and not a cause for alarm. Newborns typically start to regain their birth weight within a week or two. This reassurance can help ease the mother's distress and anxiety.

C. Alarm as this is a drastic weight loss: Characterizing this weight loss as "drastic" is not accurate or helpful and would likely increase the mother's anxiety.

D. Concern as this may be an indicator of inadequate nutrition: Jumping to the conclusion of inadequate nutrition without further assessment and evidence is premature and may unnecessarily worry the mother. It's important to start with reassurance and then investigate if there are concerns about nutrition.

Option A (Place the infant in reverse Trendelenburg position) and option B (Place the infant in the knee to chest position) are not the immediate actions to address this situation. While these positions might be used in specific situations, assessing blood pressure is more appropriate in this context to evaluate for potential vascular issues.

Option C. Take the infant's blood pressure in all extremities.

In an infant with weaker femoral pulses compared to the brachial and radial pulses, there might be a concern about coarctation of the aorta (a narrowing of the aorta), which can affect blood flow to the lower extremities. To confirm this and assess for potential issues, taking blood pressure measurements in all four extremities is crucial. This comparison can help identify pressure differentials between the upper and lower extremities, which is a hallmark sign of coarctation of the aorta.

Option D (Notify the Physician) is generally a good step, but taking the blood pressure in all extremities should be done first to provide comprehensive information for the physician when discussing the infant's condition.