Final answer:
The nurse should initiate oxygen therapy as the first action when caring for a client with bilateral pneumonia and low oxygen saturation levels. This will help improve the oxygen levels in the blood and relieve respiratory distress.
Step-by-step explanation:
The nurse should take the action of initiating oxygen therapy as the first priority. With a SaO₂ level of 85% and the client experiencing dyspnea and using accessory muscles to breathe, it indicates a significant decrease in oxygen saturation. Oxygen therapy will help improve the oxygen levels in the client's blood and relieve their respiratory distress.
Administering a bronchodilator may be appropriate in the case of bronchospasm or if there is evidence of reversible airway obstruction, but it is not the first action to take in addressing the low oxygen saturation levels.
Providing chest physiotherapy may be beneficial in clearing mucus and improving lung function, but again, it is not the priority in this case.
Administering an antibiotic may be indicated if there is evidence of a bacterial infection causing the pneumonia, but it does not address the immediate concern of low oxygen levels.