Automatic tube compensation (ATC) is a recent alternative method that is used during ventilator-assisted breathing (VAB) to cover up for the pressure decrease within the endotracheal tube (ETT). Despite some benefits associated with this method, it is yet to be used to determine the possibility of safely removing the ETT from the mechanical ventilation after weaning. During VAB, the ETT has used boost the resistant force that facilitates the reduction in pressure because the reduction in pressure is indirectly proportional to the rate of flow making it impossible to compensate it using constant ventilatory support. Various proposals have been projected on how to compensate for tube resistance, but studies on ETT characteristic have suggested that specific constant pressure support can only cover up for ETT resistant force at a specific rate of flow. In this study, the hypothesis is that ATC should be able to predict the ability of the patient breathes in the absence of ventilatory and artificial airway support.
Methods
The study was carried out for two years (July 1996 to July 1998) in Basel and involved 90 patients 32 and 58 women and men respectively with age ranging from 43 to 71 years. Out of these patients, 54 received assist-controlled ventilation, and 15 received pressure-controlled ventilation and the remaining received both assist-control and pressure-control ventilation. The inclusion criteria were based on patient improvement in or recovery from the underlying cause of the ARF. Patients who met the criteria were subjected to the T-tube through their airways. The measurement of the tidal volume and the respiratory frequency was done using a spirometer during the first 3 minutes, and this was continued for not less than 15 minutes. The ventilatory mode was put on to the appropriate mode for those who had a lower respiratory frequency of 35 b.p.m and tidal volume of more than 5ml/kg b.w. Any patient who presented with signs of decompensation had the trial terminated by the physician in charge. Those patients who presented with signs of poor tolerance in the course of the trial had the previous ventilator support reinstated while the trial tube was removed for those who went through the 2-hour trial without any problem. They are then provided with oxygen using a facemask. Either reintubation or non-invasive ventilator support was considered for those who did not have successful extubation.
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Those who had an unsuccessful trial were randomly subjected to the remaining two modes to determine if they could be extubated. Those who went through the 2-hour trial successfully were extubated.
Statistical Analysis
Kruskal-Wallis test and Chi-square test were used to compare continuous variables and categorical data respectively. Based on a two-way table, the Chi-square was used to analyze the accuracy of prediction. Calculations showed that each group required 38 patients to enable detection at a power of 80%, a difference in extubation outcome of 30%, with a two-tailed alpha error of 0.05.
Results
All the three groups of the patients shared a similarity in the important aspect of the study and all the 90 patients who were included in the study successfully went through the pre-test at T-tube and were subjected to the assigned ventilatory mode in the trial. Differences were observed in respiratory rate, tidal volume and respiratory rate to tidal volume ratio. The respiratory rate and tidal volume were lower and larger for those on ATC in comparison to those with the T-tube and PSV. No difference observed for other respiratory parameters and minute ventilation. Out of the 90 patients, 78 representing 87% of the patients passed the 2-hour trial and were to be extubated. The extubation of 62 of these 78 patients was successful while extubation of the remaining 16 was unsuccessful. Five of them required non-invasive ventilator support, two required reintubation, and nine required both. For those who could not pass the initial trial, the ETT was left.
Discussion and Interpretation
As seen from this study the ATC is a safe option that can be adopted in the final stage or phase of weaning. Extubation failure took into account patients who required reintubation, patients who required non-invasive ventilator support and cases of unjustified withholding of extubation. The findings of this study regarding extubation failure are similar to those from other studies.
As demonstrated in this study the use of ATC provides a reliable option for that can be utilized in spontaneous breathing trial before the removal of the endotracheal tube. Through this study, one gets to learn that over assistance may lead to unsuccessful extubation while under assistance may bring about poor tolerance that may lead to the withholding of the extubation process.
References
Perkins, G. D., Mistry, D., Gates, S., Gao, F., Snelson, C., Hart, N., ... & Hoddell, B. (2018). Effect of Protocolized Weaning With Early Extubation to Noninvasive Ventilation vs. Invasive Weaning on Time to Liberation From Mechanical Ventilation Among Patients With Respiratory Failure: The Breathe Randomized Clinical Trial. Jama , 320 (18), 1881-1888.
