One of managing steps in respiratory failure is high flow nasal cannula (HFNC), but the exact time to turn to invasive machine ventilation (IMV) is necessarily being determined. Respiratory rate and oxygenation (ROX) index, defined as the ratio of oxygen saturation as measured by pulse oximetry (SO2)/ FiO2 to respiratory rate (RR), is used to determine when to intubate the patients who are on HFNC and prevent the delayed intubation. Modified Respiratory rate and oxygenation (mROX), defined as (PaO2/ FiO2) / respiratory rate, is also used to point the time of intubation in case HFNC of patients with respiratory failure . The diagnostic and prognostic accuracy of both parameters are reported in previous papers, but the preference of them is under research. In this study, we aim to observe and compare the diagnostic accuracy between ROX and mROX in determine the time of invasive mechanical ventilation.

Respiratory Failure (RF) is a condition where there's insufficient oxygenation in the body tissue, whether acute, chronic or acute on chronic; occurring due to decreased oxygen or excessive carbon-dioxide in the blood . There are four types of respiratory failure; Hypoxemic respiratory failure (Type1), hypercapnic respiratory failure (Type2), ) . Causes of RF are varied and accounted for any abnormality related upper respiratory tract, lower respiratory tract, central and peripheral nervous system or muscles of respiration . However, in the last three decades, the most common causes of RF is acute myocardial infarction (AMI), acute respiratory distress syndrome (ARDS), RF related to corona virus (Covid-19) and acute exacerbation of chronic obstructive lung disease (COPD).

Inclusion Criteria:

• Adult patients of both sex aged between 18 to 80 years
• Patient diagnosed with acute type 1or 2 or chronic type 1or 2 respiratory failure.
• Patient for chest ICU admission
• Patient for HFNC and/ or Noninvasive mechanical ventilation.

Exclusion Criteria:

• Pediatric patients
• Pregnant females
• Patients who are for intubation on ICU admissionc.

Patient diagnosed with acute type 1or 2 or chronic type 1or 2 respiratory failure.