Inclusion Criteria:  Age: 18 - 65 years Confirmed diagnosis (COVID-19) - positive PCR Tachypnoea (Respiratory rate> 30/min) Ability to provide informed consent and perform all study procedures  Exclusion Criteria:  History of allergy or adverse reaction to fentanyl or other opioids Pregnancy Active neuromuscular or musculoskeletal disease. Active malignancy Morbid obesity (Body mass index >40) Use of opioids in the previous 4 weeks. Inability to provide informed consent and perform all study procedures.