Minimal clinically important differences in nasal peak inspiratory flow.

Introduction: Acoustic Rhinometry, Rhinomanometry, Nasal Spirometry and Nasal Peak Inspiratory flow (NPIF) all measure subtly different constructs of nasal function. All have limitations but NPIF is simple and quick to integrate into clinical practice. The minimum clinically important difference (MCID) for an outcome measure is an estimate of the smallest change that is experienced by a patient or group as being significant. Studies, particularly with large samples, may generate results that while statistically significant, have limited clinical effect. Defining MCID allows an assessment of the clinical impact of an intervention. This study defines the MCID for NPIF.

Methods: Prospective study of patients from a tertiary clinic undergoing open septorhinoplasty. Nasal obstruction scores and NPIF were recorded before and after surgery. Global function and nasal obstruction scores were used to assess subjective change. Statistical based and patient anchored techniques were used to define MCID.

Results: 51 patients with a mean age 36 +- 13 yrs (75% female) were recruited. All had open rhinoplasty, septal reconstruction, spreader grafts and turbinate reduction. Baseline NPIF was 101 +- 35 L/min. The statistically derived MCID (half standard deviation) was 18 L/min, the patient anchored approaches were 20 L/min and 20-25 L/min.

Discussion: Although NPIF is effort dependant with the potential for poor test-retest reliability, it is simple, quick and a reliable technique can be quickly learnt. An MCID of 20L/min is recommended when NPIF is used as an outcome tool. Understanding the MCID is critical for assessing the impact of nasal surgery.