Answer:

The ABG values should be determined immediately. In a severe, prolonged asthmatic attack, there will be combined respiratory and metabolic acidosis resulting from CO₂ retention and lactic acidosis from tissue hypoxia. Hypercarbia, hypoxemia, and acidemia promote arrhythmias and impair the response to bronchodilator therapy. Sodium bicarbonate (NaHCO₃) should be given to correct the acidosis because -agonists are not effective in severe acidosis. At the same time, bronchodilator therapy should be continued or increased.

A patient with severe, refractory bronchospasm may require ventilation with a ventilator equipped to generate very high inspiratory pressures. An ICU ventilator can generate inspiratory pressures as high as 120 cm H₂O. Most anesthesia machines cannot deliver adequate alveolar ventilation because the circuit has too much compressible volume (tubing compliance) and the ventilator does not have sufficient driving power. The major disadvantage of an ICU ventilator is its inability to use inhalational anesthetics. Some newer anesthesia machines incorporate an ICU-type ventilator with vaporizers and oxygen mixers. They may be ideal for this situation.

Heliox is a helium/oxygen mixture that, secondary to its lower density to air, can permit higher flow rates at lower pressures, theoretically improving delivery of oxygen during bronchospasm. A major limitation is that heliox mixtures can only provide 21% to 30% oxygen. Also, although heliox facilitates ventilation, it does not reverse the underlying bronchospasm. Reports on the perioperative use of heliox remain limited.

Finally, although not available at all centers, venovenous extracorporeal membrane oxygenation (VV-ECMO) may be established in order to adequately oxygenate the blood when all other measures have failed. ECMO is expensive, requires specially trained personnel, and is an invasive treatment modality associated with a number of potential complications. However, it is a potentially lifesaving measure that should be considered in select cases of severe, refractory hypoxemia secondary to respiratory disease.