Final answer:
Arterial blood gas analysis is the most direct method of assessing the effectiveness of treatment in a patient with acute respiratory failure on mechanical ventilation, as it measures essential blood gases and gives insight into pulmonary function.
Step-by-step explanation:
The best method for a nurse to determine the effectiveness of the current treatment regimen for a client in acute respiratory failure receiving mechanical ventilation would be A) Arterial blood gas analysis. This test measures the levels of oxygen, carbon dioxide, and other important parameters in the patient's blood, giving a direct indication of how well the lungs are functioning in exchanging gases.
It is an essential tool in managing ventilator settings and assessing a patient's response to treatment. While other options such as B) Heart rate measurement, C) Urine output monitoring, and D) Oxygen saturation monitoring provide useful information about the patient's overall status, they do not give as direct an assessment of pulmonary function as an arterial blood gas analysis does.