INTRODUCTION: Mechanical ventilation (MV) is a life-supporting modality that is used
in a significant proportion of patients in intensive care units , the term
mechanical ventilation refers to various artificial means used to support
ventilation and oxygenation1, 2
Mechanical ventilation is commonly delivered in intensive care by
positive pressure ventilation. Positive pressure ventilation modes are defined
by inspiratory events. Expiration is treated as an independent entity. The
primary expiratory parameter, positive end expiratory pressure (PEEP) can
be applied to any of the ventilator modes. VENTILATOR MODES: The various modes of ventilation are classified based on the types of
breaths that are selected. The modes most commonly used in pediatric
practice are discussed here. VOLUME TARGETED MODES : 1. Controlled Mechanical Ventilation (CMV): In this mode, the ventilator
controls all the ventilation while patient has minimal or no respiratory effort.
This is the mode used at the initiation of mechanical ventilation. 2. Assisted Mechanical Ventilation (AMV): All breaths are triggered when
the patient’s inspiratory effort exceeds the preset sensitivity threshold of
negative pressure. In all other respects, it is similar to controlled mechanical
ventilation.
3. Assist Control Ventilation (ACV): ACV is a combination of AMV and
CMV. In this mode, the patient initiates the breathing as in AMV. However,
if the patients fails to initiate the breathing within a prescribed time the
ventilator triggers the breathing and provides a controlled breath as in CMV,
thus ensuring a guaranteed minute ventilation.
4. Intermittent Mandatory Ventilation (IMV): It is essentially a combination
of spontaneous breathing and CMV. A modified circuit provides a
continuous gas flow that allows the patient to breathe spontaneously with
minimal work of breathing, At a predetermined frequency, the ventilator
provides a positive pressure breath to the patient.
5. Synchronized Intermittent Mandatory Ventilation (SIMV): SIMV allows
the patient to trigger a mandatory breath in the assist mode thereby
synchronizing it with the patient’s respiratory effort. However, if the patient
does not trigger a breath within an allotted time; the ventilator delivers a
conventional breath. AIM OF THE STUDY: To assess the effectiveness of the 3 standard methods of weaning from
mechanical ventilators namely T – tube weaning, synchronized intermittent
mandatory ventilation (SIMV) , continuous positive airway pressure /
pressure support ( CPAP/PSV) ventilation in terms of successful weaning, to
assess the incidence of weaning failure and duration of weaning with each
and also the duration of hospital stay and outcome of these patients so that
the best of the weaning procedure can be followed for successful weaning in
future. DISCUSSION: In this randomized control trial of comparing the three methods of
weaning ( T – piece trial , CPAP / PSV & SIMV ) from mechanical
ventilators in children aged 1 month to 12 years , the results were analysed
using appropriate statistical tests. In our study weaning was successful as
well as duration of weaning was shorter in T – Piece technique than the
other two.
Intermittent Mandatory Ventilation
Several advantages have been claimed for intermittent mandatory
ventilation as a weaning technique: it is supposed to prevent a patient from
“fighting” the ventilator, reduce respiratory-muscle fatigue, and expedite
weaning. However, there are few data to support these claims24,26Intermittent
mandatory ventilation is usually delivered in a synchronized manner with
demand- valve circuitry, which increases the work of breathing. The
intermittent nature of assistance also poses a problem. It was previously
assumed that the degree of respiratory-muscle rest was proportional to the
level of machine assistance. However, recent evidence indicates that
respiratory-sensor output does not adjust to breath-to-breath changes in
respiratory load, and intermittent mandatory ventilation may therefore contribute to the development of respiratory muscle fatigue or prevent
recovery from it.
Studies of the efficacy of intermittent mandatory ventilation in weaning
have serious limitations. Schachtern et al44. compared it with conventional
ventilation & noted no difference between the two techniques in the duration
of ventilator support. Their study suffers from a retrospective design
nonuniform study groups, and inadequate description of the protocol.
Esteban etal24 compared it with single daily and multiple daily spontaneous
breathing trials with t- piece and pressure ventilation and found SIMV as the
poorest method of weaning. On comparison with single daily T – piece trial
P value was < 0.006. In our study P value was 0.000. SUMMARY AND CONCLUSION: A randomized trial of comparing three methods of weaning from
mechanical ventilators was completed in 88 children.
From this study we conclude that,
1. Spontaneous extubation during weaning was least with T – piece trial.
2. Duration of weaning & number of trials needed for weaning was least
with T - piece trial.
3. Weaning was ~ 6 times faster with T – piece than with CPAP/PSV
and ~ 8 times faster than with SIMV.
4. Weaning success was also highest with T – piece trial.
5. Duration of weaning was not significantly different between
CPAP/PSV & SIMV group
6. T – piece trial as a technique for weaning of children from mechanical
ventilators is the best as far as duration and success of weaning is
concerned. This is independent of age or sex or etiology or duration of
ventilation prior to weaning or presence of shock or use of inotropes
or the underlying disease process
