The provision of intensive care during transport to and from the intensive care unit (ICU) presents a major challenge. Available data suggest that critical care transport is becoming increasingly common, driven by the centralization of specialties and an expanding number of diagnostic and therapeutic options outside of the ICU. The bulk of critical care transports happen within the hospital itself. Observational data suggest that critical care transport is a high-risk but worthwhile activity and that this risk can be minimized by adequate planning, proper equipment, and appropriate staffing. Prehospital transport of the critically ill patient presents more problems because prior planning is more difficult.
Clinical data on transport of the critically ill patient are derived mainly from cohort trials and can provide guidelines in terms of personnel (physicians, nurses, and paramedics), mode of transport (air or road), and specific treatments (prehospital tracheal intubation and advanced life support).
Intrahospital Transport of the Critically Ill
Adverse Effects
Several observational studies suggest that significant physiologic disturbances (large variations in heart rate, blood pressure [BP], or oxygen saturation) occur during 53% to 68% of intrahospital transports. Physiologic variability is also common in stationary critically ill patients, occurring in 60% of such patients in a study by Hurst and colleagues compared with 66% in transported patients. Many of these physiologic changes can be safely managed by an appropriately trained transport team, but serious adverse events do occur. Prospective observational studies have found an adverse event rate of 36% to 45.8%. A large multicenter cohort study showed an odds ratio (OR) for the occurrence of adverse events in intrahospital transports of 1.9. These events included pneumothorax, ventilator-associated pneumonia, and atelectasis. Increased length of stay was noted in the same study but not a difference in mortality Damm and colleagues found a cardiac arrest rate of 1.6% in a prospective observational study of 123 intrahospital transports. Waydhas and colleagues found that a reduction in the Pa o 2 /F io 2 (partial pressure of oxygen, arterial/fraction of inspired oxygen) ratio occurred in 83.7% of patients when transported with a transport ventilator and that this was severe (>20% reduction from baseline) in 42.8%. Furthermore, the changes persisted for more than 24 hours in 20.4% of transports. Two large cohort studies in which logistic regression analysis was used found out-of-unit transport to be an independent risk factor for ventilator-associated pneumonia (ORs of 3.1 and 3.8 ). Intrahospital transport is also one of the factors associated with unplanned extubation.
When compared with APACHE (Acute Physiology and Chronic Health Evaluation) II and III matched controls, patients requiring intrahospital transport were found to have a higher mortality (28.6% vs 11.4%) and a longer ICU length of stay. None of the excess mortality was directly attributable to complications of the transport, and the authors concluded that the findings reflected a higher severity of illness in patients who required transportation. However, serious adverse events did occur in 5.9% of transports.
Predicting Adverse Events during Intrahospital Transport
Factors associated with an increased risk for adverse events during transport include pretransport secondary insults in head-injured patients, high injury severity score, and high Therapeutic Interventions Severity Score (TISS) but not APACHE II score. Age older than 43 years and an F io 2 higher than 0.5 are predictive of respiratory deterioration on transport.
The number of intravenous pumps and infusions, as well as the time spent outside of the unit, has been shown to correlate with the number of technical mishaps. The Australian ICU Incident Monitoring study found that 39% of transport problems were related to equipment, with 61% relating to patient or staff management issues. Factors limiting harm were rechecking of the patient and equipment, skilled assistance, and prior experience.
Hemodynamic variability is more frequent in patients being transferred to the ICU from the operating room than in those transported for diagnostic procedures outside of the ICU. This is probably related to emergence from anesthesia.
Risk-to-Benefit Ratio of Intrahospital Transport
Observational studies suggest that the therapeutic yield for intrahospital transport is high. Hurst and colleagues found that the results of diagnostic testing facilitated by the transport resulted in a change in treatment in 39% of patients. Out-of-unit radiologic studies in ICU patients tend to be high yield. For instance, computed tomography scanning of the thorax has been shown in observational studies to change the clinical course in 26% to 57% of cases.
Management of the Transport
A cohort study has found that transport ventilators reduce variability in blood gas parameters when compared with manual bagging. Although several older studies found manual ventilation to be as good or better than use of a transport ventilator, the performance characteristics of transport ventilators has improved significantly over time, and the performance of many modern transport ventilators is comparable to that of ICU ventilators. Changes in blood gas parameters have been shown to correlate with hemodynamic disturbances (arrhythmias, hypotension).
Capnometry (end tidal carbon dioxide [ETCO 2 ]) monitoring reduces the variability Pa co 2 (partial pressure of CO 2 , arterial) in adults. In children, manual ventilation without ETCO 2 monitoring resulted in only 31% of readings falling within the intended range.
A single randomized controlled trial (RCT) found that hypothermia was common in trauma patients undergoing intrahospital transport (average temperature on return to the unit was 34.7° C) and that this was prevented by active warming during transport.
Who should accompany the critically ill patient during transport? Specialized transport teams have been found to have a lower rate of complications than historic controls. Interestingly, physician attendance was not clearly correlated with a reduced risk for mishap in an observational study of 125 transports. The implementation of a pretransport checklist has been found to reduce the rate of serious adverse events from 9.1% to 5.2%
Interhospital Transfer
The number of interhospital transfers of critically ill patients is increasing because of a reduction in the number of hospitals, centralization of specialist services, and reconfiguration of health-care services between acute and elective medicine. Approximately 4.5% of critical care stays are associated with an interhospital transfer. The benefits of transport to the patient need to be weighed against the not inconsiderable risks of the transport process. There are few RCTs on this subject, and conclusions have to be drawn from nonrandomized, cohort, or uncontrolled studies.
Adverse Effects
Various published audits and descriptive studies have shown that the interhospital transport of critically ill patients is associated with an increased morbidity and mortality during and after the journey. Even with specialist mobile intensive care teams, mortality before and during transport is substantial (2.5%) despite a low incidence of preventable deaths during transport (0.02% to 0.04%). Singh and colleagues reported an in-transit mortality of 0.1% among 19,228 interhospital transfers in Canada. Other authors have reported higher interhospital transport mortality and have found that 24% to 70% of incidents are avoidable.
Critical events occur in 4% to 17.1% of interhospital transfers. In adults, these events are mainly cardiovascular (e.g., new hypotension, arrhythmia, hypertension) or respiratory (e.g., arterial desaturation, inadvertent extubation, respiratory arrest). The most common complications observed during pediatric and neonatal transportation are hypothermia, respiratory complications, and loss of intravenous access.
Does Interhospital Transport Contribute to Mortality?
The long-term outlook for critically ill patients who require interhospital transport is worse than for those who do not require transport. Four cohort studies have found that transported patients have a higher ICU mortality and longer ICU stays than controls. In three of these four studies, this difference in mortality was not significant after adjustment for severity of illness. A systematic review of the impact of transfer on outcome for trauma patients found no significant association between transfer status and in-hospital mortality.
Prediction of Adverse Events
The APACHE II, TISS, and Rapid Acute Physiology scoring systems do not correlate with critical events during transport in adults, and the PRISM (Pediatric Risk of Mortality) score has proved to be similarly unreliable in children. Independent predictors of critical events during transport include female sex, older age, higher F io 2, multiple injury, assisted ventilation, hemodynamic instability, inadequate stabilization before transport, transport in a fixed-wing aircraft, and increased duration of transport. Patients undergoing interhospital transport after cardiac arrest have a re-arrest rate of 6% during the transfer.
Planning of the Transport
The importance of planning and preparing for interhospital transport cannot be overstated because poor planning has been shown to lead to an increased incidence of adverse events and mortality. In an audit of transfers to a neurosurgical center, 43% were found to have inadequate injury assessment, and 24% received inadequate resuscitation. Deficiencies in assessment and resuscitation before transfer were identified in all patients who died. Guidelines have been developed to address this issue in many jurisdictions, but inadequate assessment and resuscitation remain as problems. Price and colleagues found that the development of national guidelines led to only modest improvements in patient care.
Selection of Personnel
It is recommended that a minimum of two people, in addition to the vehicle operators, accompany a critically ill patient during transport. The team leader can be a nurse or physician depending on clinical and local circumstances. It is imperative that the team leader has adequate training in transport medicine and advanced life support. Adequately trained nurses have been shown to be as safe at transporting critically ill children as doctors. Appropriately staffed and equipped specialist retrieval teams have been shown to be superior to occasional teams at transferring critically ill adults and children. In an observational study, Vos and colleagues demonstrated an 80% reduction in critical incidents during pediatric interhospital transport undertaken by a specialist retrieval team.
In a cohort study, Orr and colleagues found an increase in mortality (23% vs 9%) among children transported by a nonspecialized team. This difference remained after adjustment for severity of illness.
Mode of Transport
The choice between the three options of road, helicopter, and fixed-wing transport are affected by three main factors: distance, patient status, and weather conditions. Three observational studies have addressed the effect of air versus road transfer on mortality. A retrospective review of 1234 adult transfers has shown no difference in mortality or morbidity between patients transferred by air versus road, whereas the other two studies found an increase in survival in patients transported by air. Brown and colleagues conducted a logistic regression analysis on 74,779 patient transfers and found an OR for survival of 1.09 among patients with a TISS greater than 15 who were transferred by air. A prospective cohort study has demonstrated that air transport is faster than ground transport, and for transfers of less than 225 km, helicopter transport is faster than fixed-wing transport.
Equipment and Monitoring
Comprehensive lists of equipment and medications needed for transport of critically ill patients are available elsewhere and are beyond the scope of this chapter. It is generally accepted that the standard of organ support and monitoring available in the ICU should be continued during the transport to the greatest extent possible. An RCT of near-continuous noninvasive BP monitoring compared with intermittent BP monitoring during interhospital transport of critically ill children found less organ dysfunction and a shorter ICU stay in the intervention group. Uncontrolled observational studies have shown that point-of-care blood gas analysis during interhospital transfer allows early identification and treatment of changes in gas exchange and metabolic parameters. Interfacility transport of patients receiving extracorporeal membrane oxygenation has been shown to be feasible and safe with good survival outcomes. A retrospective study of transports of infants being transferred for therapeutic hypothermia has found that the use of a purpose-built cooling machine was associated with better temperature control and faster time to achieving target temperature than passive cooling.
Retrieval Systems
The following are the four main infrastructural factors that have been addressed in clinical studies:
- 1.
Mode of transport
- 2.
Prehospital personnel
- 3.
Prehospital time
- 4.
Receiving care facility
Mode of Transport
The comparison between road and helicopter transport has been the focus of several large cohort studies in recent years. Four of these five studies demonstrated a survival advantage for severely injured patients transported by helicopter with an OR of death of 0.41 to 0.68. The reason for the survival advantage is less clear. In one study, a survival advantage was demonstrated despite longer transport times in the helicopter group, but patients in the helicopter group were more intensively managed in the prehospital phase. It has been suggested that patients retrieved by helicopter may be more likely to be brought to a level I or II trauma center, and this may partly explain the survival advantage.
Prehospital Personnel
One RCT and a systematic review of controlled nonrandomized studies have addressed the issue of physician- versus paramedic-delivered prehospital care. The RCT found a 35% reduction in mortality in the physician-treated group. In the systematic review, 9 of 19 studies involving trauma patients and 4 of 5 studies involving patients who experienced out-of-hospital cardiac arrest also demonstrated a reduction in mortality in the physician-treated group. The largest of these controlled studies involved 14,702 trauma patients and showed an OR for death of 0.7 in the physician-treated group. The evidence indicates that physicians tend to treat patients more aggressively and have fewer prehospital tracheal intubation failures than paramedics.
Prehospital Time
Severely injured patients have been shown in cohort trials to have an increased mortality, length of stay, and complications with prehospital times of more than 60 minutes. Time from injury to arrival at definitive care may not be as important in highly developed trauma systems with the capability to provide aggressive care in the prehospital phase.
Receiving Care Facility
Several large cohort studies have found a reduction in mortality for severely injured trauma patients when they are transferred directly to a level I trauma center. The largest of these included more than 6000 patients from 15 regions in the United States. Patients treated primarily in level I trauma centers had a lower in-hospital (OR, 0.8; confidence interval [CI], 0.66 to 0.98) and 1-year mortality (OR, 0.75; CI, 0.60 to 0.95). Subgroup analysis suggested that the mortality benefit was primarily confined to more severely injured patients.
Specific Interventions in the Prehospital Setting
Whether advanced life support (ALS) measures (e.g., endotracheal intubation, intravenous cannulation, and fluid and drug administration) delivered at the scene and in transit are of benefit to patients when compared with basic life support (BLS) is unclear. Three before and after studies of ALS compared with BLS (the Ontario Prehospital Advanced Life Support studies) looked at the effect of the institution of ALS in prehospital care in patients with out-of-hospital cardiac arrest, respiratory distress, and major trauma. No improvement in mortality was observed among the patients with cardiac arrest or trauma, and among trauma patients with a Glasgow Coma Scale (GCS) less than 9, mortality was increased in the ALS phase. There was a small mortality benefit in patients with respiratory distress.
Similarly, a meta-analysis of 15 observational and cohort studies comparing ALS with BLS for trauma patients demonstrated an increased mortality in ALS patients (OR, 2.59). The same authors subsequently published a large observational study comparing different prehospital systems in Canada. After correction for confounders using logistic regression analysis, they found a 21% increase in mortality for patients treated with onsite ALS ( P = 0.01).
One RCT and several observational studies have looked specifically at the effect of prehospital tracheal intubation on outcome. The RCT compared prehospital rapid sequence induction (RSI) by intensive care paramedics versus intubation in hospital for patients (n = 312) with traumatic brain injury (GCS < 9). The authors found an improvement in neurologic outcome at 6 months (risk ratio for good outcome of 1.28 in the intervention group). In contrast, several observational studies have found an increase in mortality with prehospital intubation.
A prospective observational study of 1320 trauma patients who underwent airway interventions by an anesthesiologist on arrival in a level I trauma center found that 31% of those who had undergone tracheal intubation met the criteria for failed intubation, with 12% having unrecognized esophageal intubation on arrival. A prospective observational study found a decrease in the rate of unrecognized misplaced intubations from 9% to 0% after the introduction of continuous ETCO 2 monitoring in the prehospital setting. A meta-analysis of the success rate of prehospital tracheal intubation has found that physicians have a better success rate than nonphysicians (success rate, 0.991 vs 0.849) but that the success rate of nonphysicians is better (0.967) if muscle relaxants are available. Prehospital tracheal intubation is a complex intervention and its value is likely related to many factors, including the skill of the provider, patient population, access to drugs to facilitate the intervention, and other aspects of the prehospital trauma system.
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