FIGURE 1: A schematic block diagram of an IDSS/controller for mechanical ventilation
Patient & ventilator data
Input from clinician
Input Data Analyzer, Data Validator,
Artifact Detector, Noise Remover, Data Smoother.
Alarm Unit
Information processing & control unit
Graphic display
outputs to clinicians/ ventilator
Output generator
Alarm to clinician
from mechanical injury. This important concept led to employing volume targeted ventilation in the NICU. Volume targeted techniques for neonatal ventilation include volume guarantee or volume limited ventilation, and to a much lesser extent, volume controlled ventilation. Volume guarantee, which adjusts PIP to limit the tidal volume delivered per breath, combined with synchronized intermittent mandatory ventilation (SIMV) has been reported to decrease the number of high volume mechanical breaths and the peak inspiratory pressure of triggered ventilator breaths. Volume targeted ventilation also decreased the periods of hypocapnea, which can cause brain injury in the preterm infant. A clinical surrogate for low tidal volume ventilation in preterm infants is permissive hypercapnia (defined as PaCO2 between 50 and 60 mmHg). Permissive hypercapnea and targeting a pulse oximetry saturation (SpO2) less than 95 % help in decreasing volutrauma and barotrauma. Employing a ventilation strategy that is individualized according to the specific infant’s lung disease is another important aspect of mechanical ventilation. The use of open lung strategy to prevent atelectasis and the use of low tidal volume (4-6 ml/kg) to prevent volutrauma in the newborn infant are being employed now in many NICUs.
Preterm infant born at 24 weeks gestation on mechanical ventilation.
FUTURE DIRECTIONS Improving synchronization between ventilator and patient Neurally Adjusted Ventilatory Assist (NAVA) is a relatively new concept in mechanical ventilation, where the patient’s respiratory drive – measured from the diaphragm electrical activity (EAdi) - controls the timing and the magnitude of pressure delivered. It requires the insertion of a special orogastric tube. One advantage of NAVA over synchronization methods, which rely on changes of flow or pressure of the gas in the ventilator circuit, is that it is not affected by ET tube leaks. ET tube leaks are common in preterm infants. Since it is not affected by leaks, it can also be used for synchronization in Non-Invasive Ventilation (NIV-NAVA). However, so far NAVA has not been shown to have better patients’ outcome than current methods of synchronization.
the positive pressure breath in synchrony with the end of spontaneous
inspiration or when lung inflation is completed. Respiratory signals used for synchronization have included abdominal wall motion, esophageal pressure, thoracic impedance, airway pressure, and gas flow. The latter is also used to terminate the mechanical breath in a modality known as flow cycling. Measuring gas flow also permits tidal volume (VT
)
monitoring, which is available now in most neonatal ventilators. Another advantage of the ventilator’s ability to measure gas flow to
the patient is that it could present flow waves and loops as a graphical presentation, which reflects the pulmonary function of the baby. This ability provides the clinician with valuable information about the lung condition and changes that take place over the course of the infant’s illness. Many trials of short-term physiological measurements suggested
synchronized ventilation had potential benefits. This evidence led to several prospective randomized comparisons of synchronized versus conventional ventilation. Synchronization facilitated weaning and led to a shorter duration of mechanical ventilation. However, these trials did not demonstrate consistent beneficial effects on survival, IVH, air leaks, or BPD. One of the most significant changes in mechanical ventilation of
newborns in the last decade came from animal studies and clinical trials, which showed that large tidal volumes are damaging to the lungs. Volutrauma in addition to Barotrauma are now targets for preventative ventilation strategies. It was shown in animal and adult human studies that the use of small tidal volumes (4-8 ml/kg) may protect the lung
014 ARAB HEALTH MAGAZINE ISSUE 2 2012
Dead space reduction techniques Preterm infants have a relatively large anatomical dead space in comparison to their tidal volume. Instrumental dead space can further reduce alveolar ventilation. This can lead to hypercapnia, resulting in higher ventilator settings and delayed weaning. Continuous tracheal gas insufflation (CTGI) consists of gas insufflation to the distal end of the ET via built-in capillaries. This produces a washout of the ET tube and flow sensor. In one study in preterm infants, CTGI reduced PaCO2 under constant ventilator settings or maintained a constant PaCO2 when settings were lowered. Its use in a randomized trial resulted in more rapid weaning from the ventilator.
Closed Loop System Intelligent decision support systems (IDSSs) for mechanical ventilation have been developed. While advanced ventilators have many added features and offer different outputs to respond to patients’ needs, they have mostly remained open loop devices. The clinician determines the action based on or regardless of the information received. An IDSS would be a practical tool to help the clinician integrate the available data and make the right choice for the patient. Despite the apparent need for these systems and development of many technologies to address this need, IDSSs have not been commonly used in mechanical ventilation. Figure 1 shows an example of a closed loop system in mechanical ventilation.
CONCLUSION Mechanical ventilation of the newborn has undergone through major changes over the last decade and benefited from many technological advances. It is expected to continue to evolve even at a faster pace with new technologies and smaller, more challenging premature babies.
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84