Hyperventilation can be a manifestation of anxiety that involves abnormally fast breathing (tachypnea) and an elevated minute ventilation that exceeds metabolic demand. This report describes a case of hyperventilation-induced hypocapnia resulting in tetany in a 16-year-old girl undergoing orthodontic extractions under intravenous conscious sedation. Pulse oximetry is the gold standard respiratory-related index in conscious sedation. Although the parameter has great utility in determining oxygen desaturation, it provides no additional information on respiratory function, including, for example, respiratory rate. In this case, we found capnography to be a very useful aid to monitor respiration in this patient and also to treat the hypocapnia.
Trousseau sign demonstrating flexure of the fingers and thumb.
Capnography monitor demonstrating respiratory waveform (upper panel) and rate (89 breaths/min), oxygen saturation (SpO2; 98%), end-tidal carbon dioxide (ETCO2; 11), and pulse rate (129 beats/min). This illustrates hyperventilation with resultant low ETCO2; SpO2 is normal and alone would not serve as an index of respiratory disturbance.
A trend graph based on mean values for end-tidal carbon dioxide (ETCO2) and respiratory rate calculated every 5 seconds after the first infusion. The graph shows the progressive fall in ETCO2 from baseline, following induction of sedation, as a result of hyperventilation. Note the gradual recovery of ETCO2 as respiratory rate returns towards normal.
Nasal cannula and oral extension to capture expired CO2.
Method used to have patient rebreathe expired air in an effort to increase arterial CO2.
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