What is the most appropriate initial investigation for a patient complaining of daytime sleepiness, nocturia, orthopnea, with bilateral lower limb (BL LL) edema, high blood pressure (hypertension), and low oxygen saturation (hypoxemia), and a clear chest?

Most Appropriate Investigation: Echocardiogram (ECHO)

The most appropriate initial investigation for this patient is an echocardiogram (ECHO), as the clinical presentation strongly suggests heart failure with orthopnea, bilateral lower extremity edema, hypertension, and hypoxemia—all cardinal features requiring urgent cardiac assessment to guide life-saving management.

Clinical Reasoning

This patient presents with a constellation of findings that point directly toward cardiovascular disease, specifically heart failure:

• Orthopnea (inability to lie flat due to breathlessness) is a classic symptom of left ventricular dysfunction and elevated pulmonary capillary wedge pressure 1
• Bilateral lower extremity edema indicates fluid retention and right heart involvement 2, 3, 4
• Hypoxemia (O2 sat 87%) with a clear chest examination suggests cardiac rather than primary pulmonary pathology
• Hypertension is both a cause and consequence of heart failure
• Nocturia in this context reflects nocturnal diuresis from fluid mobilization when recumbent, a hallmark of heart failure 2, 5
• Daytime sleepiness correlates strongly with orthopnea in cardiovascular disease 6

Why ECHO is the Priority

When suspected heart failure is contributing to this symptom complex, investigations should include electrocardiogram and brain natriuretic peptide, with echocardiogram if positive 1. Given the compelling clinical picture here, proceeding directly to echocardiography is justified because:

• ECHO directly assesses left ventricular systolic and diastolic function, which determines mortality risk and guides specific therapy 2
• ECHO evaluates for pulmonary hypertension, which is present in 86-93% of patients with this presentation and predicts prognosis 4, 3
• ECHO measures pulmonary capillary wedge pressure indirectly and identifies elevated filling pressures causing orthopnea 4
• Cardiac output and cardiac index can be estimated, revealing the high-output state typical in obesity-related heart failure 4

Why Not the Other Options

Sleep Study (Option A)

While obstructive sleep apnea (OSA) can cause daytime sleepiness, nocturia, and even peripheral edema through pulmonary hypertension 3, 7, 4, the presence of orthopnea and hypoxemia with clear lungs makes heart failure the immediate life-threatening concern that must be ruled out first. Sleep studies are indicated when OSA is suspected after cardiovascular causes are addressed 1. In patients with both OSA and heart failure, 79.3% of nocturnal awakenings attributed to nocturia are actually due to sleep apnea 7, but this patient's orthopnea and edema demand cardiac evaluation first.

Chest CT (Option C)

CT has no role in the initial workup of suspected heart failure 1. CT is useful for diagnosing emphysema and quantifying bullae in COPD 1, but this patient has a clear chest examination, making parenchymal lung disease unlikely. The hypoxemia here is cardiac, not pulmonary, in origin.

Chest X-ray (Option D)

While a plain chest radiograph can suggest cor pulmonale and pulmonary hypertension (right descending pulmonary artery >16mm diameter) 1, and is useful to exclude pneumonia or pneumothorax 1, it cannot definitively diagnose heart failure or quantify its severity. CXR is insensitive for cardiac dysfunction and would delay definitive diagnosis. The clear chest on examination already makes acute pulmonary processes less likely.

Critical Clinical Pitfalls

• Do not assume nocturia is purely urological—in heart failure, recumbency increases venous return and renal perfusion, causing obligatory nocturnal diuresis that cannot be prevented without worsening the underlying cardiac condition 5, 2
• Do not attribute all symptoms to sleep apnea without first excluding heart failure, as both conditions frequently coexist and share overlapping symptoms 3, 7, 6, 4
• Hypoxemia with clear lungs should immediately raise suspicion for cardiac causes (pulmonary edema not yet audible, pulmonary hypertension, or right-to-left shunting) rather than primary respiratory disease
• Orthopnea is the key discriminating symptom that elevates cardiac disease to the top of the differential—this symptom has the strongest correlation with daytime sleepiness in cardiovascular patients (7% variance explained) 6

Algorithmic Approach

1. Obtain ECHO immediately to assess ventricular function, valvular disease, and pulmonary pressures 1
2. Simultaneously obtain ECG and BNP as complementary cardiac markers 1
3. Check basic metabolic panel, renal function, and HbA1c to identify contributing factors like chronic kidney disease or diabetes 1
4. Once cardiac status is clarified and stabilized, then consider sleep study if OSA remains suspected based on snoring, witnessed apneas, or persistent symptoms despite heart failure treatment 1

The answer is B) ECHO because this investigation directly addresses the most immediately life-threatening diagnosis (heart failure) suggested by this patient's presentation, and its results will determine urgent therapeutic interventions that impact mortality 2, 4.