End-Tidal Capnography Findings in Inhalation Poisoning
In patients with inhalation poisoning, nasal end-tidal capnography (ETCO2) would typically show abnormal waveforms and values that reflect respiratory compromise, with patterns dependent on the specific toxin and severity of exposure.
Characteristic ETCO2 Findings in Inhalation Poisoning
Increased ETCO2 values (>50 mmHg) may be observed in patients with respiratory depression from inhalation poisoning, indicating hypoventilation and potential respiratory compromise 1
Absent waveform on capnography may indicate severe respiratory depression or apnea in patients with significant inhalation toxicity 1
Absolute change from baseline ETCO2 greater than 10 mmHg is a significant finding that can indicate respiratory depression before oxygen desaturation occurs 1
Abnormal capnographic waveform patterns may be present, reflecting alterations in ventilation-perfusion matching due to toxic inhalation effects 1
Clinical Significance of ETCO2 Monitoring in Poisoned Patients
ETCO2 monitoring can detect respiratory depression earlier than pulse oximetry alone, as changes in ETCO2 often precede oxygen desaturation in inhalation poisoning cases 2, 3
Capnography provides nearly continuous (99% of monitoring time) reliable measurement of ventilatory function in sedated, non-intubated poisoned patients 2
Changes in capnography preceded 70% of hypoxic episodes detected by pulse oximetry in patients with sedative overdose, suggesting its value in early detection of respiratory compromise 2
ETCO2 monitoring can help detect hypoventilation before clinical signs become apparent, as an increase in ETCO2 might be the only early clue to potential respiratory compromise 1
Limitations and Considerations
A single elevated ETCO2 reading (≥50 mmHg) has limited predictive value for complications in deliberate drug poisoning, with sensitivity of only 46% and specificity of 80% 4
The correlation between ETCO2 and arterial PCO2 may be affected in patients with significant lung injury from inhalation toxins, limiting its accuracy as a substitute for arterial blood gas measurement 5
Mouth breathing or nasal cannula occlusion can impair the ability of end-tidal PCO2 monitoring to accurately detect respiratory patterns in poisoned patients 1
For optimal monitoring in inhalation poisoning, vital capacity maneuver ETCO2 measurements correlate better with arterial PCO2 than tidal volume measurements (r=0.91 vs. lower correlation) 5
Specific Patterns Based on Poisoning Type
Decreased ETCO2 values may be observed in cases where the toxin causes hyperventilation or in early stages of toxicity 6, 7
Fluctuating ETCO2 patterns may be seen in patients with seizure activity related to certain inhalation toxins, with post-ictal hyperventilation causing temporary decreases in ETCO2 7
Progressive increases in ETCO2 over time may indicate worsening respiratory depression and need for more aggressive intervention 1, 3
Monitoring Recommendations
Continuous capnography monitoring is essential for early detection of respiratory changes in patients with inhalation poisoning 6, 3
When monitoring poisoned patients, document trends in ETCO2 values rather than relying on isolated readings, as dynamic changes may be more predictive of complications than static measurements 7, 4
For patients with inhalation poisoning, an ETCO2 greater than 50 mmHg, an absent waveform, or an absolute change from baseline in ETCO2 greater than 10 mmHg should prompt immediate clinical reassessment 1