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Each year pneumonia causes more than 3 million deaths in children under 5 years of age (including neonates) and results in 11-20 million hospitalisations. 1 2 Some 98% of deaths from pneumonia in children occur in developing countries. 3 Hypoxaemia is a significant risk factor for mortality 4 - 6 and a strong predictor of radiographic pneumonia. 5 7 8 The recognition of hypoxaemia among children with pneumonia is crucial in management, may assist in diagnosis and helps determine prognosis.
Currently the World Health Organization (WHO) sets out the clinical signs which should guide the starting and stopping of oxygen therapy. Where pulse oximetry is available, WHO recommends an arterial oxygen saturation measured by pulse oximetry (Sp o 2 ) of 90% as the threshold for oxygen administration. 9 However, such an approach may only be possible in settings where oxygen supplies are not limited. At high altitudes, where normal oxygen saturation levels are lower than at sea level, a threshold of 90% may be less relevant. A clearer definition of the lower limit of normal Sp o 2 among children at different altitudes would enable protocols for oxygen therapy to be adapted to local conditions, and enable resources to be appropriately applied.
To assist in the identification and management of hypoxaemia, this study aimed to use the published literature to define normal values of Sp o 2 in children and to propose a model for defining hypoxaemia at varying altitudes.
METHODOLOGY
Search strategy and inclusion criteria
A review was conducted using OVID Medline (1950-August week 2 2007) and Embase (1980-2007 week 33), according to the search strategy described in box 1. The abstracts of potentially relevant publications were reviewed, and the complete texts of studies addressing the inclusion criteria (outlined below) were obtained. References cited by these articles, as well as the link option "Find similar" in OVID and Embase were then used to widen the search.
Studies were included if they reported the Sp o 2 of healthy, awake children aged 1 week to 12 years and permanently residing in the study location. In order to ensure that study data used in the analysis provide a reasonable estimate of the normal Sp o 2 of the populations they represent, we set the...