Arterial blood gas changes following nasal packing in dogs

Previous clinical studies pertaining to blood gas changes following nasal packing have agreed that the packing is frequently followed by hypoxia but have found differing responses in arterial PCO2 to nasal packing. This is of more than incidental importance, because the mechanisms by which hypoxia develops should determine the method by which the hypoxia is treated. The various causes of hypoxia are reviewed, and a method of instituting an indwelling systemic arterial catheter for the purpose of drawing sequential blood samples for gas determinations is described. Using the indwelling arterial catheters, arterial blood was sampled from a series of awake, unsedated dogs before, during, and after the dogs were subjected to anterior and posterior nasal packing. Blood gas determinations showed significant depressions of PO2 and elevations of PCO2 during the period when the packing was in place. The altered blood gas values quickly returned to essentially normal (control) values after the packing was removed. In order to help assess the degree of lower airway response to an upper airway stimulus as a cause of these blood gas changes, the protocol was repeated in previously laryngectomized dogs. In these animals no consistently significant change occurred in either the PO2 or PCO2 following either the packing or its removal. Our findings suggest that airway obstruction (and hypoventilation) rather than increased bronchomotor tone is the main cause of hypoxia in awake dogs with anterior and posterior packing. Because of the likelihood of hypoventilation and significant hypercarbia in patients in whom nasal packing is employed, we discourage the routine usage of oxygen, unless blood gas levels are checked prior to the institution of oxygen therapy.