What laboratory and imaging studies should be ordered in a patient with smoke inhalation?

Tests to Order in Smoke Inhalation

All patients with suspected smoke inhalation should immediately receive arterial blood gas analysis with co-oximetry to measure carboxyhemoglobin (COHb) levels, serum lactate, and pH to assess for carbon monoxide poisoning and metabolic acidosis suggestive of cyanide toxicity. 1

Essential Laboratory Tests

Immediate Blood Work

• Arterial blood gas (ABG) with co-oximetry to measure COHb levels, pH, and oxygenation status 1, 2
• Serum lactate level - values ≥10 mmol/L suggest cyanide poisoning, particularly if the CO source was a house fire 1
• Complete blood count (CBC) with differential and platelets to assess baseline hematologic status 3
• Basic metabolic panel including electrolytes, BUN, and creatinine 3
• Liver function tests (LFTs) to evaluate for systemic toxicity 3

Critical Interpretation Points

• Severe metabolic acidosis with pH <7.20 correlates with 30-50% short-term mortality in CO-poisoned patients and strongly suggests concomitant cyanide poisoning if the source was a house fire 1
• COHb levels alone do not correlate well with clinical severity - patients may be critically ill with relatively low COHb levels, especially if significant time has elapsed since exposure 4

Toxicology Screening

• Blood alcohol level and toxicology screen should be obtained if intentional CO exposure is suspected, as 44% of intentional poisoning patients have coingestions, with 66% involving ethanol 1
• Consider expanded toxicology panel if mental status changes seem disproportionate to reported exposure 1

Imaging Studies

Chest Imaging

• Chest radiograph (CXR) should be obtained in all patients to establish baseline and identify early pulmonary complications 3, 2
• Chest CT with IV contrast may be considered for patients with severe respiratory symptoms or suspected parenchymal injury, though not routinely required initially 3

Airway Assessment

Fiberoptic Bronchoscopy

• Direct laryngoscopy or fiberoptic bronchoscopy is the gold standard for diagnosing upper and lower airway injury and should be performed when inhalation injury is suspected 2, 5, 6
• Bronchoscopy can identify pharyngeal burns, edema, carbonaceous deposits, mucosal erythema, and airway obstruction that may not be clinically apparent 6
• This is the only method to recognize or exclude upper respiratory tract obstruction with certainty 6

Pulmonary Function Assessment

Spirometry

• Forced expiratory volume in 1 second (FEV1) and forced vital capacity (FVC) should be measured when feasible, as reduced values indicate lower respiratory tract injury 6
• These measurements help quantify the degree of airway obstruction from bronchoconstriction 3

Clinical Assessment Parameters

Vital Signs and Physical Findings to Document

• Respiratory rate, oxygen saturation, and work of breathing 3
• Presence of stridor, hoarseness, dysphagia - these suggest upper airway thermal injury 2, 6
• Facial burns, singed nasal hairs, carbonaceous sputum - clinical indicators of inhalation injury 2, 4
• Wheezing, dyspnea, chest tightness - suggest lower respiratory tract involvement 6

Common Pitfalls to Avoid

• Do not rely solely on COHb levels to determine severity or guide treatment decisions, as clinical presentation may be worse than laboratory values suggest 4
• Do not delay intubation in patients with signs of upper airway compromise (stridor, hoarseness, oropharyngeal edema, deep facial/neck burns), as airway edema is progressive 2, 4
• Do not overlook cyanide toxicity in house fire victims with severe metabolic acidosis (pH <7.20) or lactate ≥10 mmol/L, even if COHb levels are not dramatically elevated 1
• Do not assume normal initial chest radiograph excludes significant injury, as pulmonary complications often develop over 24-48 hours 3

Follow-Up Testing

• Repeat ABG and lactate should be obtained after initiating 100% oxygen therapy to assess response and guide duration of treatment 1, 2
• Serial chest radiographs are warranted for hospitalized patients to monitor for development of pulmonary edema, pneumonia, or acute respiratory distress syndrome 3
• Clinical follow-up at 1-2 months with neuropsychological evaluation if cognitive symptoms develop, as delayed neurological sequelae can occur even after acute treatment 1