Most Appropriate Investigation: Echocardiography
The most appropriate initial investigation for this patient is echocardiography (ECHO), not a sleep study. While the patient has daytime sleepiness and nocturia that could suggest sleep-disordered breathing, the clinical presentation is dominated by signs of acute decompensated heart failure requiring immediate cardiac evaluation.
Clinical Reasoning
Why ECHO Takes Priority
The patient presents with a constellation of heart failure symptoms: orthopnea, bilateral lower extremity edema, hypertension, and critically low oxygen saturation (87%) 1.
Two-dimensional echocardiography with Doppler should be performed during initial evaluation of patients presenting with heart failure to assess left ventricular ejection fraction, left ventricular size, wall thickness, and valve function 1.
The combination of orthopnea (inability to lie flat due to pulmonary congestion), bilateral leg edema (volume overload), and hypoxemia with clear lungs suggests heart failure rather than primary pulmonary pathology 1.
Initial examination should include assessment of volume status and oxygen saturation, with echocardiography as the definitive test to establish cardiac function 1.
Why Not Sleep Study First
While nocturia and daytime sleepiness can indicate obstructive sleep apnea, screening for sleep-disordered breathing is reasonable in selected patients who present with heart failure, but only after cardiac evaluation is complete 1.
Sleep studies are indicated when coexisting obstructive sleep apnea is suspected after initial cardiac workup, not as the first-line investigation in a patient with clear signs of volume overload and hypoxemia 1.
The patient's nocturia is more likely secondary to heart failure-related fluid redistribution when supine rather than primary sleep apnea, as nocturia is independently associated with cardiovascular disease even after adjusting for sleep-disordered breathing 2.
Most awakenings attributed to nocturia in patients with cardiac disease are actually due to the underlying cardiac condition rather than bladder pressure 3, 4.
Critical Clinical Context
Immediate Concerns
Oxygen saturation of 87% requires urgent evaluation and supplemental oxygen to maintain SpO2 >90% 1.
The clear chest examination does not rule out heart failure, as early decompensation may present without overt pulmonary crackles, particularly if the patient has been upright 1.
High blood pressure in the setting of heart failure symptoms suggests hypertensive heart disease with possible diastolic dysfunction 1.
Diagnostic Algorithm
Perform echocardiography immediately to assess:
- Left ventricular systolic and diastolic function
- Right ventricular function and pulmonary pressures
- Valvular abnormalities
- Chamber sizes and wall thickness 1
Obtain chest radiograph (posterior-anterior and lateral) to evaluate for cardiomegaly, pulmonary congestion, and pleural effusions that may not be apparent on physical examination 1.
Check BNP or NT-proBNP levels to support the diagnosis of heart failure and assess severity 1.
Only after cardiac evaluation is complete, consider sleep study if symptoms persist despite optimal heart failure management, as sleep-disordered breathing screening is reasonable in selected heart failure patients but is not the initial diagnostic priority 1.
Common Pitfalls
Do not attribute all symptoms to sleep apnea without thoroughly excluding cardiac causes, especially in patients with multiple cardiovascular risk factors and objective signs of volume overload 5, 6.
Clear lung fields do not exclude heart failure, particularly in chronic compensated states or early decompensation 1.
Nocturia in cardiac patients is often misattributed to urological or sleep disorders when it actually reflects nocturnal fluid mobilization from peripheral edema 2, 3, 4.
The hypoxemia (87%) is severe enough to warrant immediate investigation of cardiac causes before pursuing sleep studies, as pulse oximeter oxygen saturation <90% requires urgent evaluation and oxygen supplementation 1.