Rationale: Respiratory muscle strength in children can be assessed by maximal inspiratory pressures (MIP), maximal expiratory pressures (MEP), and sniff nasal inspiratory pressures (SNIP). However, previous studies involved small cohorts of healthy children and reported wide reference ranges.

Objectives: To perform a systematic review to summarize existing reference ranges for MIP, MEP, and SNIP tests in healthy children and to conduct a meta-analysis to develop comprehensive prediction equations.

Data Sources: Five databases were searched for relevant studies from database inception to May 29, 2017.

Data Extraction: Study inclusion was limited to publications that evaluated MIP, MEP, and SNIP values in healthy children aged 18 years or younger. Studies were also excluded if testing methodology differed greatly from the 2002 American Thoracic Society Statement on Respiratory Muscle Testing. Requests for raw data were made to authors via e-mail.

Synthesis: A total of 18 studies including 3,509 children were systematically reviewed. Diagnostic accuracy of the included studies was assessed using the QUADAS-2 tool, which revealed a high risk of bias for flow and timing and for applicability that may influence the generalizability of our findings. All 18 studies evaluated respiratory pressures in children in seated position. MIP tests were conducted from residual volume, MEP tests from total lung capacity, and SNIP tests from functional residual capacity. The MIP and MEP values in three age groups for boys and girls were summarized using meta-analysis based on individual participant data from five studies containing 1,709 healthy children. Further analyses showed that MIP and MEP were significantly greater in boys than in girls (P < 0.0001). In both sexes, MEP values were always greater than MIP values (P < 0.05). Multivariable random effects models were then performed to establish sex-specific prediction equations. These equations found age, height, and weight to be significant predictor variables. Only two studies with SNIP values from healthy children were included in the review, but they were not part of the meta-analysis.

Conclusions: We summarized the available reference ranges for MIP, MEP, and SNIP tests based on existing literature, especially for three age groups, and developed prediction equations that can be used in pulmonary function laboratories to aid clinicians. Existing literature on SNIP tests is limited, and future studies are encouraged to explore their use in children.