Monitoreo gráfico pulmonar en tiempo real

Noviembre 2007

 

 

Real-Time Pulmonary Graphic Monitoring

 

Michael A. Becker,

 

Clin Perinatol 34 (2007) 1–17

 

 

Until recently, the use of nonatal bedside real-time graphic monitoring was either nonexistent or tedious at best. For a quarter of a century, the mainstay of neonatal mechanical ventilation was continuous flow, timecycled, pressure-limited ventilation without patient synchronization of the ventilator breaths. Primary parameter adjustments with this modality included the mandatory respiratory rate, peak inspiratory pressure (PIP), positive end expiratory pressure (PEEP), inspiratory time, and circuit flow rate. The assessment of the appropriateness of these parameters was determined subjectively by noting color, observing chest excursions, and listening to breath sounds, and objectively by intermittent assessment of gas exchange and radiography. The advent of transcutaneous PO2 and PCO2 monitoring, as well as pulse oximetry, provided evidence that the management of neonatal respiratory failure is a dynamic process requiring much more intensive surveillance than the intermittent assessments.

In the late 1980s, pulmonary mechanics technology was finally made available in the neonatal intensive care unit (NICU). This portable equipment was brought to the bedside and used by specially trained individuals. The objective was to be able to assess diseases, evaluate medication treatments such as bronchodilators, and to adjust the ventilator parameters to achieve optimal ventilation and oxygenation. The principle device used to obtain the bedside pulmonary mechanics was a pneumotachograph.

 

However, it needed to be disassembled, cleaned, and reassembled between patients. This process was long and tedious and if not done correctly could affect the accuracy of the measurements. Testing also required disconnecting and reconnecting the patient from the ventilator, which often disturbed the baby and changed the pattern of breathing. The pneumotachograph was heavy and bulky and if not supported appropriately could change the position of the endotracheal tube in small infants. It added significant deadspace to the ventilator circuit and increased the work of breathing. The values obtained were basic; they were generally tidal volume, compliance, and resistance. Although probably reasonably accurate, the values supplied the practitioner with limited information, which was merely a ‘‘snapshot’’ of the patient’s pulmonary status and interaction with the ventilator. The information was generally not useful in determining events that occurred either before or after the study.

 

Today, real-time bedside pulmonary graphics have become a standard of care in mostdif not alldNICUs. Most of the new generation of mechanical ventilators incorporate proximal airway sensors, also referred to as transducers, that are positioned between the ventilator circuit and the endotracheal tube. They are extremely light and introduce minimal additional deadspace. This microprocessor-based technology is integral to the intended function of the ventilator. The more common sensor technologies fall into one of two categories: thermal or differential pressure type. The sensor detects either flow or pressure and converts the signal to a clinically useful analog value.

 

For example, the flow signal can be integrated to obtain a volume measurement. The sensor also is used to detect patient effort to facilitate or ‘‘trigger’’ synchrony between the patient’s own effort and the delivery of a mechanical breath by the ventilator. The information is presented in real-time and is a continuous display, not the snapshot of the previous pulmonary function technology but more similar to a ‘‘motion picture’’ of each individual breath as well as trends of measured values over an extended period of time.

 

Graphic monitoring assists the clinician at the bedside in several ways. It can be helpful in fine-tuning or adjusting ventilator parameters. For instance, one can track and determine the progress of a disease such as respiratory distress syndrome by following compliance measurements. Graphic monitoring may help to determine the patient’s response to pharmacologic agents such as surfactant, diuretics, or bronchodilators. The clinician also has the ability to trend monitored events over a prolonged period of time. The understanding of graphic monitoring may at times be considered complex. There are many clinical situations that may be identified at the bedside. Each patient is different and provides unique learning experiences. This being said, if the clinician becomes comfortable with identifying a small number of common situations, it may greatly enhance clinical expertise.