Chapter 37: Mobilization and Portable Ventilation

In recent years, there has been increasing interest in mobilization and ambulation of mechanically ventilated patients. This therapy requires the use of a portable ventilator. Portable ventilators are also used for intra- and inter-hospital transport. This chapter covers aspects of mobilization and ambulation of mechanically ventilated patients, as well as the use of portable ventilators for transport.

Survivors of critical illness who have been mechanically ventilated can have muscle wasting and fatigue. Survivors of acute respiratory distress syndrome (ARDS) may have persistent physical disability for years after ICU (intensive care unit) discharge. The consequences of these acquired deficits may lead to disability, social isolation, institutionalization, and a significant economic burden for society. A variety of factors are responsible for these physical deficits, including severity of illness, acute inflammation, corticosteroid administration, and use of neuromuscular blockers. Perhaps the most important risk factor is prolonged bed rest.

Daily awakening and spontaneous breathing trials lead to fewer ventilator days, and there is accumulating evidence supporting early physical activity for mechanically ventilated patients. The ABCDE bundle is an evidence-based organizational approach for the management of critically ill mechanically ventilated patients: awakening and breathing coordination of daily sedation and spontaneous breathing trials, choice of sedative or analgesic agents, delirium monitoring, and early mobility and exercise.

Approaches to Mobilization and Ambulation of the Mechanically Ventilated Patient

Prior to ambulation, there are specific factors that need to be considered. It is important to consider the amount of sedation the patient is receiving. In addition to having a more alert and responsive patient, less sedation also frequently allows the patient to be extubated sooner. The patient also needs to be hemodynamically stable. While it may be tempting to move quickly to full ambulation, patients should be allowed to progress more slowly, first sitting up and dangling their legs from the bed, then standing and then taking a few steps at the bedside and moving into a chair before progressing to more ambitious goals.

When considering mobilizing and ambulating patients who are mechanically ventilated, it is important to remember that with respiratory compromise, the patient's ventilatory status and reserve can limit their exercise capacity. This means that, in some cases, respiratory support may need to be increased in order to improve the patient's ability to mobilize and ambulate. Also, because exercise demands an increase in oxygen requirement of the respiratory muscles, it can steal oxygen from other skeletal muscles, causing additional limitation of mobility and ambulation. This effect can be addressed by increasing the amount of support during mobility and ambulation, to allow increased ventilation without increased oxygen demand by the respiratory muscles.

Despite concerns that have been raised about the safety of mobilizing and ambulating patients with critical illness, few serious adverse events have been reported. For early mobilization and ambulation to be a success, there also must be a collaborative consensus that ambulation can proceed safely, and that consensus should include collaboration among all the members of the patient's team, including physicians, nurses, and physical and respiratory therapists. The level of ventilator support should not be a limiting factor. Patients who are on high Fio₂ and a high level of positive end-expiratory pressure (PEEP) can be ambulated safely. The limiting factor is the amount of sedation the patient is receiving, not the settings on the ventilator.

The success of early mobilization and ambulation programs requires significant multidisciplinary teamwork and coordination from all staff members, from attending physicians, residents and fellows, to nurses, physical therapists, respiratory therapists, and critical care technicians. Typically, the nurse manages the catheters and monitor, the physical therapist manages the patient's activity, the respiratory therapist manages the ventilator, and a critical care technician assists as needed.

For successful ambulation, the ventilator must have a sufficient amount of battery power. Most of the portable ventilators that are commercially available have hours of internal battery power, and those batteries must be kept fully charged. Lacking a sufficient battery, a long extension cord may be used when necessary, but caution to avoid tripping over the cord or accidentally unplugging it must be exercised. It is important to use modes of ventilation that promote synchrony. When a patient begins ambulation, the team should consider whether changes need to be made on the ventilator settings so that the patient will be synchronous with the ventilator during that activity.

In addition to a walker, it is important to have the ventilator and oxygen cylinders on a movable wheelbase, and to have a ventilator circuit with sufficient length to allow for movement. There are a number of commercially available portable ventilators designed for patient transport that can be used for ambulation of patients. A pulse oximeter is also important to monitor the patient's oxygen saturation and titrate the ventilator settings accordingly, and to monitor the patient's heart rate.

For patients who are too unstable to be awakened for active mobilization, passive range-of-motion and positioning exercises are important to minimize the development of joint contractures. Neuromuscular electrical stimulation and passive cycling are modalities that may be increasingly available in the future.

Critically ill patients commonly require diagnostic tests and therapeutic procedures that cannot be performed at the bedside. When the critically ill patient requires transport, every effort should be made to take the ICU with the patient. For the mechanically ventilated patient, that means personnel who are familiar with the patient, monitoring equipment, airway equipment, and a means of providing ventilation (Table 37-1). Ventilation during transport can be provided by using either a manual ventilator or a portable ventilator. Use of a portable ventilator is superior to manual ventilation because it provides a more consistent level of ventilation and frees a clinician to perform other tasks.

Characteristics of a Portable Ventilator

There are available very sophisticated microprocessor-controlled portable ventilators. Ideally, the ventilator should be capable of providing modes that are commonly used in the ICU. There should be separate controls for respiratory rate and tidal volume. The ventilator should be able to provide either volume- or pressure-controlled ventilation. It should be possible to control the Fio₂. PEEP must be available, and the trigger sensitivity must be PEEP-compensated. High pressure and disconnect alarms should be provided.

A major consideration is portability. The ventilator should be lightweight. The ventilator's dimensions should make it easy to transport with the patient (eg, place on the bed). Transport ventilators may be either pneumatically or electronically powered. A major disadvantage of pneumatically controlled transport ventilators is that they consume gas for operation, thus depleting the gas source very quickly. Microprocessor-controlled portable ventilators typically provide more precise control settings, are affected less by fluctuations in source-gas pressure, and do not consume as much gas for their operation. Battery-operated ventilators should have a battery life of at least 4 hours and the battery should recharge quickly.

A unique challenge occurs when mechanically ventilated patients require transport for magnetic resonance imaging. Operation of the magnetic resonance imager creates a strong magnetic field. Thus, devices (including ventilators) that have ferromagnetic components cannot be used. Patients can be ventilated using either a manual ventilator, or a ventilator specifically designed for use during magnetic resonance imaging. Also, aluminum oxygen cylinders and aluminum regulators are necessary for oxygen delivery.