Comparison of three oxygen monitors in detecting endobronchial intubation

Detection of endobronchial intubation by monitoring the CO2 level above the endotracheal cuff

Early detection of accidental endobronchial intubation (EBI) is still an unsolved problem in anesthesia and critical care daily practice. The aim of this study was to evaluate the ability of monitoring above cuff CO2 to detect EBI (the working hypothesis was that the origin of CO2 is from the unventilated, but still perfused, lung). Six goats were intubated under general anesthesia and the ETT positioning was verified by a flexible bronchoscope. The AnapnoGuard system, already successfully used to detect air leak around the ETT cuff, was used for continuous monitoring of above-the-cuff CO2 level. When the ETT distal tip was located in the trachea, with an average cuff pressure of 15 mmHg, absence of CO2 above the cuff was observed. The ETT was then deliberately advanced into one of the main bronchi under flexible bronchoscopic vision. In all six cases the immediate presence of CO2 above the cuff was identified. Further automatic inflation of the cuff, up to a level of 27 mmHg, did not affect the above-the-cuff measured CO2 level. Withdrawal of the ETT and repositioning of its distal tip in mid-trachea caused the disappearance of CO2 above the cuff in a maximum of 3 min, confirming the absence of air leak and the correct positioning of the ETT. Our results suggest that measurement of the above-the-cuff CO2 level could offer a reliable, on-line solution for early identification of accidental EBI. Further studies are planned to validate the efficacy of the method in a clinical setup.

Continuous Monitoring of Dynamic Pulmonary Compliance Enables Detection of Endobronchial Intubation in Infants and Children

BACKGROUND

Auscultation of breath sounds is used routinely to confirm tracheal placement of endotracheal tubes (ETT). In infants and children, this method is limited by the conduction of breath sounds bilaterally, despite endobronchial intubation. Although several methods of detecting endobronchial intubation have been described, none is both simple and reliable. In this investigation, we determined whether changes in pulmonary compliance and airway pressures, measured using continuous side stream spirometry, can reliably detect endobronchial intubation in pediatric patients.

METHODS

Forty patients aged 1 month to 6 years were included. After endotracheal intubation the ETT was incrementally advanced as two observers monitored breath sounds and spirometry (Pressure-Volume Loops). Changes in pulmonary compliance, peak inspiratory pressure, or auscultation were reported, at which point ETT position was confirmed by fiberoptic bronchoscopy.

RESULTS

Endobronchial intubation decreased measured pulmonary compliance by 45 +/- 11% (mean +/- sd; P < 0.001, Range 26%-66%) and increased peak airway pressures by 26 +/- 17% (mean +/- sd; P < 0.001, Range 0-87). Changes in peak airway pressures were smaller and more variable when compared to changes in compliance. Breath-sound auscultation failed to detect endobronchial intubation in 7.5% of cases.

CONCLUSIONS

Pulmonary compliance changes are a sensitive and an accurate indicator of endobronchial intubation in infants and children. Both increased peak airway pressures and changes in breath sounds are less sensitive indicators of endobronchial intubation.

Model-Based Detection of Endobronchial Intubation

To detect endobronchial intubation (EBI) noninvasively in real time, we developed a novel, automated, lumped model-based approach. The model uses routinely monitored airway pressure and flow as inputs. The specificity of the method in detecting EBI was determined by testing events of stiff chest wall (SCW) in the absence of EBI. EBI was induced in 10 anesthetized, paralyzed, and mechanically ventilated mongrel dogs (19-45 kg) by advancing the endotracheal tube into the right mainstem bronchus. The event of SCW was created by wrapping a pressure cuff around the chest. Airway pressure and flow were continuously recorded at the mouth, and respiratory impedance was estimated from these signals. Model parameters were iteratively identified until the root mean square error between the respiratory and model-predicted impedance was minimum. The change in model parameters during EBI from baseline was analyzed. In nine of 10 cases, it was determined that during EBI, the model's compliance element (C1) decreased > or =50% and model's resistance element (R2) changed < or =10-fold from baseline. Testing this rule on 40 cases of SCW, four false positives were obtained. During SCW, R1 and R2 increased, whereas C2 decreased significantly from baseline. This preliminary study is a promising step toward noninvasive, real-time detection of EBI to aid clinicians in decision making.

Pulse oximetry

The pulse oximeter, a widely used noninvasive monitor of arterial oxygen saturation, has numerous applications in anesthesiology and critical care. Although pulse oximetry is considered sufficiently accurate for many clinical purposes, there are significant limitations on the accuracy and availability of pulse oximetry data. This article reviews both the clinical uses of the pulse oximeter and the limitations on its performance. The pulse oximeter is generally acknowledged to be one of the most important advances in the history of clinical monitoring.