Background: Acid base disorders are frequently present in critically ill patients. Metabolic acidosis is 
associated with increased mortality, but it is unclear whether as a marker of the severity of the disease 
process or as a direct effector. The understanding of the metabolic component of acid base 
derangements has evolved over time, and several theories and models for precise quantification and 
interpretation have been postulated during the last century. Unmeasured anions are the footprints of 
dissociated fixed acids and may be responsible for a significant component of metabolic acidosis. 
Their nature, origin, and prognostic value are incompletely understood. This review provides a 
historical overview of how the understanding of the metabolic component of acid base disorders has 
evolved over time and describes the theoretical models and their corresponding tools applicable to 
clinical practice, with an emphasis on the role of ABG in general and several specific settings.
Objectives: Aim of the study : to determine the value of ABG on mortality and morbidity in 
Pediatric Intensive Care Unit in minia university hospital. Methods: This was a retrospective study 
done over 2 years. There were total 653 patients (1 month to18 years), who were divided into 
survivals and non survivals groups. All data were collected and analyzed retrospectively including:
Name, Age, sex, , length of stay in PICU, underlying etiology, cause of admission, and requirement 
for mechanical ventilation. laboratory investigations; from the patients' records, we obtained the 
results of routine blood samples on patients' admission to PICU which were immediately transported 
to the central laboratory in the hospital. These samples were arterial blood gases, Data retrieved from 
the medical files and statistically analyzed after permission from the ethical committee. Results:
There were significant difference in the outcome of patients admitted to the PICU regarding the age 
group, sex, length of stay in PICU, requiring mechanical ventilation, respiratory failure P-value were 
(<0.001, <0.001, 0.007, <0.001, and <0.001 respectively). Conculsion:. There is no consensus 
regarding preferred methodology for the evaluation of acidebase derangements in critically ill 
patients. The physicalechemical approach by Stewart does not have a clear advantage over the 
traditional bicarbonate-based method. Both should be regarded as complementary for optimal 
understanding of acidebase disorders.