Background: Capnography provides insight into the management of many emergencies. It reflects the factors affecting perfusion and metabolism, and it is used for continuous monitoring of mechanically-ventilated patients.Objectives: To investigate the correlation between the partial pressure of end tidal carbon dioxide (PetCO₂) and arterial blood carbon dioxide (PaCO₂), and to investigate the accuracy of the change of capnographic curve in diagnosis of special pathological situations. Patients and Methods: A total of 100 patients (1 day to 15 years), mechanically-ventilated due to various clinical causes were monitored by PetCO2, and arterial blood gas (ABG) concomitant with assessment of PetCO2. Results: Significant correlation was found between PaCO₂ and PetCO₂, and abnormal PaCO₂-PetCO₂ gradient was found to be correlated well with the duration of mechanical ventilation. Various PetCO₂ waveforms were recorded. Conclusion: Capnography should be used for monitoring of critically ill patients and for confirmation of endotracheal intubation. It should be applied during cardio pulmonary resuscitation (CPR) and to monitor the quality of CPR. It is used to monitor the integrity of patient ventilator interface, identification of ventilated patients in need for additional sedation or neuromuscular blockage, and readjustment of ventilator parameters.