Journal of Medical and Surgical Intensive Care Medicine 2012 , Vol 3, Issue 2
Prediction of Extubation Success in Myasthenic Crisis Using Bedside Functional Residual Capacity Measurement: A Prospective Feasibility Study
Mehmet Akif Topçuoğlu 1 , Ethem Murat Arsava 1 , Tijen Cankurtaran 2 , Erhan Akpınar 2
1Department of Neurology, Faculty of Medicine, Hacettepe University, Ankara, Turkey
2Department of Radiology, Faculty of Medicine, Hacettepe University, Ankara, Turkey
DOI : 10.5152/dcbybd.2012.09

Aim: Extubation failure often complicates the recovery phase of a myasthenic crisis (MC). Bedside functional residual capacity (FRC) is a relatively new technique shown to be promising in the improvement of ventilation management in the intensive care unit (ICU), and may have a role in the estimation of extubation success. Since the prediction of extubation success is difficult due to the absence of formally evaluated disease-specific criteria, the appropriateness of any strategy described for non-neuromuscular conditions should be validated for specific neuromuscular diseases such as MC. In accordance, we designed a pilot study to determine the feasibility of bedside FRC measurement in the prediction of extubation success in MC and to determine its yield when added to the conventional parameters.

Material and Methods: We prospectively studied the additive value of bedside FRC measurements to predict extubation outcome in 11 MC episodes. The area under the receiver operating characteristic curve (ROC AUC), sensitivity and specificity of all weaning and extubation indices that passed exploratory analysis were determined.

Results: The frequency of extubation failure, defined as the need for reinstitution of ventilatory support within 72 hours of planned endotracheal tube removal, was 55% in this study population, in which all patients met the standard weaning indices indicating safety of extubation. The risk of extubation failure was connected to higher airway pressures (peak inspiratory and plato pressures; PIP and Pplato; ROC AUCs: 0.933 and 0.917), increased gradient of end-tidal CO2 to arterial CO2 (CO2 gradient; ROC AUC:0.900) and total airway care score (ACS; ROC AUC:0.983), but not to FRC, the simplified acute physiology score (SAPS-II) and the traditional weaning criteria such as the rapid shallow breathing index (RSBI) and mouth occlusion pressure (P0.1). Although perhaps useful when measurable, the utility of maximal inspiratory/expiratory mouth pressures (MIP and MEP) was also low due to the inability of MC patients to perform the maneuvers required to obtain these parameters. In contrast, FRC measurement was easily attainable at the bedside, with zero risk to the patient and correlated well to the aerated lung volume measured by chest CT (r=0.717).

Conclusion: This preliminary study suggests that bedside FRC measurement is safe and feasible for long-term monitoring of intubated myasthenic patients. Its utility in determining weaning and extubation outcomes requires further studies with larger samples. Standard weaning parameters may not be accurate enough in the prediction of extubation outcome in MC, probably reflecting differences in the pathophysiology of failure of extubation and weaning. As a new semi-objective measurement of pulmonary secretion status, ACS can be helpful in the identification of the risk of extubation failure. 

Keywords : Myasthenic crisis, maximum expiratory pressure, maximum inspiratory pressure, atelectasis, recruitment