In hyperventilation the EtCO2 value will decrease. Increases ETCO2 is seen in thyrotoxicosis, fever (increased CO2production) and high spinal anesthesia (alveolar hypoventilation). Factors affecting ETCO2 Increased ETCO2 Decreased ETCO2 Metabolism Hypehermia Fever Thyrotoxicosis Pain Shivering Metabolism Hypothermia Metabolic acidosis Respiratory Hypoventilation Respiratory depression COPD Paial airway obstruction Rebreathing Respiratory Hyperventilation Total airway obstruction Extubation Circulatory Increased cardiac output (ROSC after cardiac arrest) Hypeension Circulatory Hypotension Cardiac arrest Pulmonary emboli Apparatus malfunction Exhausted CO2 absorber Inadequate fresh gas flow Ventilatory malfunction Apparatus malfunction Circuit disconnection Leak in sampling Ventilatory malfunction