Answer: You are absolutely correct. If it is felt that acute pulmonary edema is the likely cause for a patient’s respiratory distress, then CPAP would be indicated along with Nitroglycerin (NTG) as per the Acute Pulmonary Edema Medical Directive.
Again you are correct that it has been our teaching at SWORBHP that if a patient with pulmonary edema is improving with CPAP, there is no need to keep removing the mask to administer NTG especially given the physical difficulty of administering a spray of NTG sublingually when high flow oxygen is also being applied.
To answer your question in terms of clinical improvement and how best to define it, as long as your patient is in respiratory distress (as evidenced by a paramedic clinical judgment and a significantly elevated respiratory rate, accessory muscle use etc.) and the oxygen saturation is < 92%, paramedics should titrate the CPAP pressure and FIO2 as per the Medical Directive.
Specifically, the Medical Directive calls for paramedics to consider increasing the FIO2 if the patient SAO2 is < 92% despite treatment and/or 10cmH2O pressure or equivalent flow rate of device as per BH direction.
The directive also lists the titration interval of 2.5cm H2O every 5min to a maximum setting of 15cm H2O and a maximum FIO2 of 100%.