Respiratory syncytial virus (RSV) is a virus that can cause severe pulmonary infections in infants. The effects of this, especially in the still developing lungs after birth, can take a long time from which to recover. However, you have a special circumstance that complicates things: you live at significant altitude. The relative lack of oxygen at that altitude can lead to elevated blood pressure across the lungs, which is called pulmonary hypertension. Studies from The Children’s Hospital in Denver show that infants and children living at altitude are at greater risk to have pulmonary hypertension, with need for more supplemental oxygen, or even other therapies. This can be variable, though, based on genetics. Therefore, the pediatric cardiologist will want to assess for evidence of elevated blood pressure on the right side of the heart. This can be done with a combination of the physical examination, electrocardiogram (ECG), and an echocardiogram (cardiac ultrasound). The echocardiogram would also look for other structural defects in the heart that may be contributing to your child’s decreased oxygen saturations, especially one called pulmonary atresia with ventricular septal defect, a congenital defect that can be missed early on and still progress to worsening cyanosis. Therefore, it is not unreasonable that your son be evaluated by not only a pulmonary specialist but also by a cardiologist in this case.
To add more specificity--- his last overnight study was 1 week ago and he spent 85% of the time at o2 sats between 90-93, and 14% of the time between 80-89%, but all of that time was actually spent between 80-85 and 1% of the time below 80%. This is consistent with his other 3 studies and his hospital overnight. I have an older child with significant chronic lung disease and asthma so I'm well-versed in using pulse-ox machines for accurate results on wiggly infants.