Early acute respiratory failure due to severe tetanus: evidence for intrapulmonary shunting of blood

ABSTRACT

Early acute respiratory failure is a common presenting manifestation of severe tetanus, yet the underlying mechanism is not well understood. Our purpose was to clarify the issue by testing the contribution of various cardiopulmonary factors in the genesis of respiratory failure. We performed cardiac catheterization and pulmonary angiogram on 14 consecutive cases of severe tetanus with acute respiratory failure, Shunt fraction and alveolar-arterial oxygen difference were calculated in all patients after being ventilated with 100% oxygen for over 20 minutes. All patients had severe hypoxemia and hypocapnia at the time of presentation while receiving nasal oxygen. Cardiac catheterization and oximetric studies revealed normal mean pulmonary capillary wedge and left ventricular end diastolic pressures with no evidence of intracardiac shunting of blood. Pulmonary angiograms showed no evidence of pulmonary emboli or arteriovenous communication. Ventilation with 100% oxygen failed to correct hypoxemia. Calculated shunt fraction ranged from 27.3 to 38.1%. The alveolar-arterial oxygen difference was more than 450 mm Hg in all of the cases. Our results indicate that intrapulmonary shunting of blood is the underlying mechanism for the early acute respiratory failure seen in these patients