Final answer:
An elderly smoker with low sodium and no signs of heart failure may have SIADH, likely related to pulmonary issues. Treatment involves managing fluid intake and underlying conditions, with a focus on smoking cessation to prevent recurrence.
Step-by-step explanation:
The presentation of an old smoker with hyponatremia (Na = 125), moist mucus membranes, and absence of jugular venous distention (JVD) suggests a potential case of syndrome of inappropriate antidiuretic hormone secretion (SIADH) or possibly another etiology for the hyponatremia that could be Pneumonia related. In the absence of JVD, it is less likely to be a case of congestive heart failure or severe volume overload. The treatment for SIADH typically involves fluid restriction in mild cases, and in more severe cases or symptomatic patients, may include administration of hypertonic saline and drugs like vasopressin antagonists. It's critical to address the underlying cause, such as pneumonia often seen in smokers or other lung diseases, eventually smoking cessation intervention would also be an integral part of the management.
The patient's presentation is suggestive of SIADH, possibly secondary to pulmonary complications like pneumonia associated with smoking. Treatment should consist of careful fluid management, correction of electrolyte imbalances, and addressing any underlying pulmonary condition, including support for smoking cessation.