Mechanical ventilation of the critically ill patient is best practiced in the safe confines of the intensive care unit (ICU). Transport of ventilated patients, however, remains a frequent challenge. Successful transport requires effective communication, appropriate planning, key personnel, and compact, rugged equipment. Clinicians should be aware of the physiologic effects of transport, frequency of adverse events, and methods to prevent complications.

Mechanically ventilated patients are moved frequently within the hospital. The most common destinations for patients transported from the ICU are computed tomography (CT) and the operating room with other radiologic modalities also being common.1–15 Most transports between the ICU and non–operating room destinations last 40 to 90 minutes.2,5–7,10,12–14 More recently, portable scanners have been used to perform CT scans in patients with traumatic brain injury to reduce the uncertainties of transport.

Magnetic resonance imaging is an increasingly common destination for the critically ill ventilated patient. Safe transport is more challenging in this setting because of limited patient access and the need for nonferrous equipment.

Interfacility transport has increased in recent years owing to the regionalization of specialty care in neonatology, respiratory failure, trauma, transplantation, stroke, and cardiac disorders. The growth of hospital systems with acute and chronic care facilities represents another reason for interhospital transport as patients travel back and forth based on acuity. The current military operations in Iraq and Afghanistan have generated thousands of long distance interhospital transports requiring mechanical ventilation.

Interhospital transport can be accomplished using ground or air transport. Ground transport is the most readily available and least expensive, while also the least influenced by weather. There are few restrictions on weight and patient access can be quite good. Helicopters offer a significant improvement in speed but are expensive to operate. Patient care is made more difficult by weight limitations and a cramped, noisy cabin. Fixed-wing transport is the only viable option when critical patients must be moved over long distances.

The American College of Critical Care Medicine suggests that all hospitals have a formalized plan addressing pretransport coordination and communication, composition of transport team, transport equipment, monitoring during transport, and documentation.16 Many adverse events associated with transport can be avoided with preparation and communication.14,15,17–21 Patients having to wait at their destination can be particularly problematic and can be avoided with proper coordination.8

An experienced critical care nurse and respiratory therapist should accompany all mechanically ventilated patients during transport.16,22 The need for physician presence has been evaluated in pediatric transports but has not been clearly elucidated.23–25 The American College of Critical Care Medicine recommends a physician competent in airway management, advanced cardiac life support, and critical care medicine accompany all unstable patients.16 The American Association for Respiratory Care does not opine on physician presence, but does suggest that team members be skilled in airway equipment operation and troubleshooting.22

Considerable effort has been expended to catalog the risks of transport.3–8,10–15,17,18,26,27 The costs associated with transport include transport equipment, personnel, and managing complications of transport. Benefits may include discovering new pathology that changes treatment, intervention to address disease processes, or, in the case of interhospital transport, receiving care not available at the sending facility. Several investigations have noted that in two-thirds of transports to radiology, the patient’s treatment course is unaltered.5,6 Head CT is least likely to result in a change in therapy, whereas abdominal CT is most likely to result in new findings and guide intervention.

Transporting ventilated patients requires transitioning to portable equipment, repositioning the patient, and transfer from the ICU bed. Patients are often transported in the supine position, which changes respiratory mechanics and may alter hemodynamics. Many intrahospital destinations are distant from the ICU, located in facilities never designed to house critically ill patients. Both remote locations and poor physical plants may contribute to complications and untoward outcomes. Complications of intrahospital transport are frequently recalled as “the catastrophe in radiology.” During interhospital transport, patients must be cared for in the suboptimal confines of a transport vehicle. Transport complications range from minor changes in heart rate to cardiac arrest. Table 27-1 lists common complications. The true complication rate is difficult to ascertain because of inconsistent definitions in existing studies.

Cardiovascular Complications

Cardiovascular events are the most frequent complication during intrahospital and interhospital transport, and are reported in up to 50% of cases.4–7,11,13,14,17,28–33 An increase in heart rate is seen frequently as a result of anxiety, pain, and activity. Arrhythmias are common during the transport of high-risk cardiac patients, a finding complicated by the fact that routine lead II monitoring may be unable to detect early changes.34,35 Acute respiratory alkalosis resulting from hyperventilation alters myocardial irritability, leading to dysrhythmias.4,36–39 This finding commonly is associated with unmonitored manual ventilation but can occur with a ventilator when minute ventilation is unreliable.39

Hypotension during transport may result from loss of intravenous access, interruption of vasoactive agents, pneumothorax, or bleeding. Alkalemia associated with hyperventilation likewise can cause hypotension.4,39,40 Excessive hyperventilation is associated with increased intrathoracic pressure, reduced venous return, and reduced cardiac output. During cardiopulmonary resuscitation, excessive ventilation reduces the efficiency of cardiopulmonary resuscitation and is referred to as “death by ventilation.” Hypertension can result from stress and anxiety, as well as from patient movement that encounters “bumps” in the transport path and jostling of patients that causes pain.3,5,6,41 Cardiac arrest has been reported during transport, but patient movement per se has not been directly implicated.17,31,32

Respiratory Complications

Hypoxemia is a well-documented transport complication.2,4–6,14,30,32,33,40,42,43 It may result from loss of positive end-expiratory pressure (PEEP), changes in patient position, impaired secretion removal, equipment malfunction, and failure to reproduce ventilator settings adequately. During transport of adult patients, high inspired oxygen concentrations (FIO2) are used commonly as a matter of convenience.18,44 Elevated FIO2, however, may mask deterioration in lung function and contribute to absorption atelectasis. Patients requiring PEEP of more than 10 cm H2O are vulnerable to deterioration in oxygenation during transport that lasts up to 24 hours.3

Hyperventilation is frequent with manual ventilation4,39,42,45 and with poor control of minute ventilation by portable ventilators.42 Sudden respiratory alkalosis can result in changes in cardiovascular function. Hyperventilation increases intrathoracic pressure, produces air trapping, reduces cardiac output, shifts the oxyhemoglobin dissociation curve to the left (hindering oxygen unloading), and causes cerebral and myocardial vasoconstriction. These combined effects may adversely affect patient outcome.46

Hypoventilation is reported less frequently and generally is better tolerated.3–6,8,10–13,26,27 Decreased tidal volume contributes to atelectasis and acute respiratory acidosis, which may compromise cardiac function. Sedation and neuromuscular blocking agents may also contribute to hypoventilation.

Unplanned extubation is an infrequent but potentially catastrophic complication.17,30 Inability to establish an adequate airway is associated with hypoxemia and poor outcome in head-injured patients.19,47 Unintubated patients with marginal airway control may benefit from intubation before transport. Radiologic procedures requiring the patient to remain supine may compromise the tenuous airway.

Other Complications

Increases in intracranial pressure have been reported during transport and are associated with supine positioning, changes in ventilation, airway compromise, and hypoxemia.3,19,47

Hypothermia during transport occurs because hallways, examination areas, and transport vehicles have imprecise environmental controls.10 Exposure of skin surfaces for adequate radiologic examinations and use of skin preparations for procedures further contribute to temperature loss. Blood loss has been reported during movement of patients with unstable fractures.10 Transport from the ICU is an independent predictor for the development of pneumonia, although a causative role cannot be definitively established.9,48 Table 27-2 lists studies evaluating complications of transport.

Air transport subjects patients to altitude-induced physiologic alterations. Fixed-wing aircraft commonly pressurize to a cabin altitude of 8000 feet (barometric pressure of 565 mm Hg). Rotor-wing aircraft do not have pressurized cabins, leaving the patients and crew exposed to ambient barometric pressure. Flight altitudes are typically much lower in fixed-wing flight, but may reach physiologic significance when flying over high terrain.

The most relevant alterations in the hypobaric environment are hypoxemic hypoxia and expansion of gases. A change in altitude from sea level to 8000 feet is associated with hypoxemia in patients with normal and abnormal pulmonary function.49,50 At similar altitude changes, gases expand in volume by 30%. This may cause injurious pressure increases in endotracheal tube cuffs during ascent.51–53 Inconsequential volumes of trapped gases at sea level may cause significant physiologic effects at altitude, most dramatically in the setting of untreated pneumothorax. Less severe, but important, effects for patient comfort include ear pain secondary to pressure changes and expansion of gas in the gastrointestinal tract.

Ventilator performance can be adversely affected by changes in barometric pressure. Pneumatically operated devices will have alterations in tidal volume, frequency, and inspiratory time as altitude increases. Even sophisticated transport ventilators may deliver excessive tidal volumes in hypobaric environments.54 Some newer ventilators automatically compensate for hypobaric effects on gas density.

There are few absolute contraindications to transport. Transport of the ventilated patient is best considered as transferring the ICU with the patient, not transferring the patient from the ICU. Patients occasionally are deemed too sick to transport. The specific contraindications to transport are (a) inability to maintain acceptable hemodynamic status, (b) inability to establish an adequate airway, (c) inadequate personnel, (d) inability to maintain adequate gas exchange, and (e) inability to monitor patient status effectively. Rescue therapies for acute respiratory distress syndrome are a relative contraindication to transport. If transport is required for potentially lifesaving therapy, then it should be considered. Safe transport with aggressive rescue therapies, including inhaled nitric oxide, prone ventilation, inhaled prostacyclin, and high-frequency percussive ventilation, has been described.55–59

Appropriate equipment and monitoring are important to maintaining homeostasis and ensuring safety (Table 27-3). Monitoring during transport should emulate the ICU. Minimum requirements include electrocardiographic monitoring of heart rhythm and rate, invasive or noninvasive blood pressure monitoring, and pulse oximetry. Continuous capnography greatly enhances safety by immediately detecting inadvertent extubation, circuit disconnection, or ventilator failure. Its importance cannot be overstated. Monitoring should adapt to the needs of the patient and include additional pressure monitoring if intracranial pressure or central venous pressure catheters are present. Battery-powered intravenous pumps for medication delivery also are required.