June 2012 669

Ventilators The Support System

Continuous capnography from intubation to extubation offers several benefits, including confirming tracheal intubation, monitoring the integrity of the endotracheal tube (ETT) and ventilatory circuit, assisting with the titration of mechanical ventilatory support, assessing pulmonary capillary blood flow, and monitoring for extubation readiness. The technology required to perform capnography on expired gas is not new, although recent advances have greatly improved the reliability and clinical applicability. From the start it must be noted that capnography has been considered a basic standard of care in anesthetic monitoring by the American Society for Anesthesiologist.

Pressure Control VentilationVentilator determines inspiratory time – no patient participationParameters
• Triggered by time
• Limited by pressure
• Affects inspiration onlyDisadvantages
• Requires frequent adjustments to maintain adequate VE
• Pt with noncompliant lungs may require alterations in inspiratory times to achieve adequate TV

Mechanical ventilation is associated with numerous life-threatening complications, and should be discontinued at the earliest possible time in the course of a patient’s illness. Weaning patients from a ventilator is one of the most challenging problems faced by physicians working in an intensive care unit (ICU), and accounts for a huge portion of the clinical workload in this setting. Management of the weaning process has fallen within the realm of clinical judgement, but studies now indicate that an empirical approach can prolong the duration of mechanical ventilation

Spontaneous breathing trials

The best way to determine suitability for discontinuation of mechanical ventilation is to perform a spontaneous breathing trial. There are three ways to do this: putting the patient  on a minimum pressure support and PEEP (for example 5-7cmH2O PS/5cmH2O PEEP performing mechanics and extubating), using a T-piece.

A T-piece trial involves the patient breathing through a T-piece plus a flow of oxygen-air and no ventilatory assistance) for a set period of time. The work of breathing is higher than through a normal airway (although this simulates laryngeal edema or airway narrowing). If tolerated, the chances of successful extubation are high. If not reattachment to a ventilator is simple. An alternative variant to this is the use of a CPAP circuit, which overcomes some of the work of breathing through the ett and prevents airway collapse.

Need for Tracheostomy Prolonged intubation may injure airway and cause airway edemaAdvantages
• Issue of airway stability can be separated from issue of readiness for extubation
• May quicken decision to extubate
• Decreased work of breathing
• Avoid continued vocal cord injury
• Improved bronchopulmonary hygiene
• Improved pt communicationDisadvantages
• Long term risk of tracheal stenosis
• Procedure-related complication rate (4 percent – 36 percent)

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