10/1/1999

Transporting the critically ill, mechanically ventilated patient has become common place in this era of advanced diagnostic techniques and treatments. Trauma patients routinely travel to computed tomography (CT) and the angiography suite for both diagnosis and therapy. Patients from the medical intensive care unit (ICU), likewise require trips outside the ICU for important tests and definitive care.

Whenever a transport is considered, an analysis of the cost-benefit and risk-benefit must be undertaken. Studies have demonstrated that many transports outside the ICU fail to result in any change in patient management. (1,2) Similarly complications related to transport are well recognized and most therapists can recall a favorite story of cardiac arrest in radiology or hyperbaric medicine. And while some authors have suggested that complications during transport are frequent (3-5) others have shown that critically ill patients frequently have complications, regardless of their environment. (2) In fact, the frequent 2:1 or 3:1 care afforded during transport may help reduce complications due to increased vigilance. (2,6)

Most therapists have heard or participated in the conversation related to the patient too sick to transport. This may include the patient with hemodynamic instability (multiple vasopressor infusions) or the patient requiring high levels of ventilatory support (pressure control ventilation, high positive and expiratory pressure). In the latter case, manual ventilation may be unwise and current transport ventilators may not provide the features necessary (pressure support) for transport of this kind of patient.

The following case report represents a case of transporting the sickest of the sick mechanically ventilated patient, where transport was considered difficult and ventilatory support was of greatest concern.

A 56-year-old man was admitted to the intensive care unit suffering from a necrotizing pneumonia which quickly advanced to acute respiratory distress syndrome (ARDS). He was ventilated in the pressure control, assist control mode with a pressure of 38 cmH2O, a PEEP of 18 cmH2O, and an inspired oxygen concentration (FIO2) of 0.80. His respiratory frequency was 14 breaths per minute, inspiratory time was 1.6 seconds, and I:E ration was 1:1.5. This level of support provided only marginal blood gases, with a pH of 7.30, PaCO2 of 62 mm Hg, and a PaO2 of 72 mm Hg. When he was disconnected from the ventilator and manually ventilated, he became bradycardic and his pulse oximetry saturation (SpO2) fell below 90%. The patient required transport to CT for evaluation of an intra-abdominal process. Despite risks of transport, the attending physicians determined that the identification of a potential new source of infection was important to defining further care. The clinical staff agreed that a method of ventilation which closely mimicked the ICU ventilator was a must. The current transport ventilators used in the hospital did not provide pressure control. After some discussion, a trial of the transport was attempted using a new ventilator, the LTV1000 (Pulmonetic Systems, Inc., Colton, CA).

The LTV1000 was chosen because of the ability to provide both flow triggering and pressure control ventilation. The patient required pressure control to maintain oxygenation and prevent high pressures which might result in barotrauma/volutrauma. Previous attempts at manual ventilation and switching the patient to volume control ventilation for even short periods ended in poor gas exchange and/or cardiovascular compromise.

Prior to transport, the monitoring equipment, oxygen cylinder, and ventilator were assembled. An emergency airway kit and drug box were placed in the bed and a respiratory therapist, nurse and resident were all gathered to travel with the patient to CT. Prior to leaving the ICU, the patient was placed on the LTV1000 at ventilator settings equivalent to those used one the ICU ventilator. After a stabilization period of 10 minutes, SpO2 remained above 90% and the patient's cardiovascular status was unchanged. Following this initial positive sign, the transport was begun.

The patient was transported to the elevator and down six floors to the radiology suite. In the CT scanner, the patient was lifted to the CT tabled without incident. The abdominal CT was accomplished with and without contrast and a sizeable sub-phrenic abcess was identified. This fluid collection was drained percutaneously and the exudate sent for culture. The patient was returned to ICU without difficulty, the entire transport time lasting approximately 3 hours.

Arterial blood gases were drawn prior to switching the patient to the LTV1000 and at the end of the transport, just prior to returning the patient to the ICU ventilator. The results of these samples are shown in the table below.

Transporting the critically ill patient always requires an analysis of the risk/benefit and cost/benefit ratio. Adequate preparation, appropriate staffing, and the right tools are paramount to successful transport. In this instance, the LTV1000 proved invaluable in transporting a critically ill patient requiring pressure control ventilation, a mode not available in other transport ventilators. The LTV1000 is unique for a ventilator of its size (12 lbs.). It includes a blower to provide an air source, has a blender which allows FIO2 from 0.21 - 1.0, monitors tidal volume, provides pressure support, pressure control, and allows for flow triggering. In this case, the features of the LTV1000 made it possible to transport this patient.