What intervention is warranted when the patient exhibits vital signs of temperature 40°C and SpO2 of 81%?

The correct choice is to initiate intravenous fluid challenge when a patient presents with a high temperature of 40°C and a significantly low SpO2 level of 81%. This combination of vital signs indicates potential infection or sepsis and suggests that the patient may be experiencing a significant physiological stress response, which can lead to dehydration and impaired oxygenation.

Administering intravenous fluids can help to restore intravascular volume, improve circulation, and enhance oxygen delivery to tissues by increasing blood pressure and cardiac output. In cases of elevated temperature, there is often increased metabolic demand, leading to further fluid loss and potential compromise of organ function. Providing fluids can also support the respiratory system and may improve oxygenation levels, addressing the low SpO2.

The other options, while they may be appropriate in specific contexts, do not directly address the urgent need to stabilize the patient's hemodynamic status and ensure adequate oxygen delivery. Antimicrobial therapy is important but typically follows fluid resuscitation in cases of suspected infection. Changing from a non-rebreather mask to a nasal cannula would not be advisable given the low oxygen saturation, as this would decrease the amount of supplemental oxygen the patient receives. Chest physiotherapy is generally used to facilitate airway clearance but would not address