Monitoring During Transport

Guidelines for Transport

Despite the frequency of inter- and intrahospital transport, there are only a small number of guidelines relevant to a wide patient population.^13-15 Specific guidelines for disease states (eg, head injury, stroke, myocardial infarction) are available, but this review focuses primarily on the transport of patients with respiratory failure. The available guidelines are mostly over a decade old and likely require revision.

The American College of Critical Care Medicine (ACCM) guidelines were last updated in 2004. Expert opinion and research published from 1986 through 2001 were used to construct these guidelines. The ACCM’s approach was based on the following framework: (1) pretransport coordination and communication; (2) personnel; (3) equipment; (4) monitoring; and (5) documentation. The main emphasis was patient safety through careful preparation, appropriate personnel, and required technology.¹³

The ACCM guidelines include alphabetical lists of recommended transport equipment (65 items) and transport medications (39 items). Devices for monitoring include pulse oximeter, capnograph, noninvasive blood pressure monitor, electrocardiogram (ECG) monitor with vascular pressure monitoring capabilities, and a stethoscope. Of note, the list specifies end-tidal CO₂ monitors, which could include colorimetric devices. Monitoring is implied to be continuous with the exception of noninvasive blood pressure.

The Australian and New Zealand College of Anaesthetists (ANZCA) published guidelines for transport in 2015.¹⁴ This group’s guidelines encompass recommendations for prehospital, interhospital, and intrahospital transport. The ANZCA’s list of monitoring equipment includes pulse oximeter, ECG monitor, capnograph, temperature monitor, vascular pressure monitor, and a blood pressure cuff. Proposed monitoring includes routinely assessing the patient’s breathing frequency, , capnography (for both ventilated and sedated patients), continuous ECG, blood pressure, and in select circumstances point-of-care arterial blood gas analysis.

The ANZCA guidelines note some caveats regarding monitoring: “Monitoring of certain physiological variables should be carried out during transport. Some or all of these basic recommendations will need to be exceeded routinely depending on the physical status of the patient. Clearly any monitoring method may fail to detect unfavourable clinical developments, and monitoring does not guarantee any specific patient outcome.”¹⁴ This is a cogent reminder that, despite best practice and technology, careful eyes-on monitoring by personnel remains critical.

The AARC guidelines specifically address the mechanically ventilated patient during transport. The list of recommended monitoring activities includes integral monitoring of pressure, checking volume and flow values from the portable ventilator, pulse oximetry, ECG, monitoring vascular pressure, and use of a stethoscope and a hand-held spirometer. The spirometer was recommended to verify ventilator volumes or record spontaneous breathing. Re-commended routine monitoring includes continuous ECG monitoring, continuous or intermittent blood pressure monitoring, intermittent recording of breathing frequency, continuous monitoring of airway pressure and volume, intermittent breath sounds, and . A comparison of these guidelines is shown in Table 1.

Guidelines for transport are forced to cover such a wide-ranging class of patients and environments that it is difficult to create a document to cover every eventuality. Monitoring standards are based on expert opinion and common-sense application. Transport without pulse oximetry might seem unthinkable, yet nothing in the literature points to improved outcomes from monitoring . It is interesting that the AARC guidelines do not include capnography, which may be due to the time of the writing (2003) and the cost and size of capnography devices of that time. Capnography may play an important role in monitoring spontaneously breathing patients as a method to detect apnea and in ventilated patients to assure adequacy of ventilation and airway position. Current guidelines require updating.

Adverse Events as a Guide to Required Monitoring

Adverse events are frequent during transport due to the stresses of moving a patient and the patient’s underlying pathophysiology. However, these physiologic perturbations are often reported in studies of patient movement when the important events to capture are serious adverse events. Mishaps or incidents during transport are often overreported, leading to the concern about the risks of transport. Coupled with the memory bias that allows most clinicians to remember “the catastrophe in radiology,” an overestimation of transport risks is likely. Undoubtedly, serious adverse events occur during patient movement, but these should be compared to events commonly observed in stationary patients in the ICU setting.^16-19 Serious adverse events or critical incidents can often be defined as changes in patient condition that require an intervention (eg, change in ventilator settings, change in vasoactive medications, cardioversion, etc.). A list of common physiologic perturbations (ie, adverse events) compared to serious adverse events during transport are shown in Table 2.

Adverse Events During Intrahospital Transport

A number of studies in the late 1980s and early 1990s provided a basis for understanding the risks of transport and the frequency of adverse events.^16,17,20,21 Changes in technology and practice allow this data to be viewed in light of more recent publications. Pertinent studies on adverse events during intrahospital transport are reviewed here.

Fanara et al¹ performed a systematic review of intrahospital transport of critically ill subjects based on publications from 1998 to 2009. They identified 8 papers that focused on adverse events, of which 6 were prospective trials and 2 were retrospective trials.^18,22-28 These publications included 35 to 290 subjects, of whom two thirds received mechanical ventilation. The analysis specifically addressed clinical problems including cardiovascular incidents, respiratory incidents, and materiel incidences (eg, staff error or equipment failure).¹ Importantly, the authors identified global adverse events separately from severe adverse events.

The global adverse event incidence was > 50% in each of the studies, whereas important incidents occurred in only 0–30% of transports. Doring et al²³ reported severe hypotension in 2% and hypoxemia in 30% of neurosurgical subjects. Shirley and Stott²⁷ reported a global adverse events rate of 59% but no cardiovascular or respiratory events. In this trial, equipment failure and human error accounted for the majority of incidents.²⁷ In a prospective trial of subjects moved from the emergency department to the ICU, Lovell et al²⁶ reported cardiovascular clinical problems in 31% of subjects and reported 1 death after cardiac arrest.

Beckmann and colleagues²⁸ studied 176 patients transported from the ICU and reported severe hypotension in 3%, cardiac arrest in 3% and hypoxemia in 11%. As with other trials, the rate of equipment and human failures far exceeded physiologic insults.²⁸ Damm et al²² prospectively studied 64 ICU subjects transported for diagnostic or therapeutic procedures, reporting an average of 2 incidents per transport. This included 2 cardiac arrests, 11 hypoxemic events, and 19 instances of hypotension. A striking finding in this study was ventilator failure in 21% of transports, which was categorized as oxygen or battery failure in 10 cases and disconnection from the oxygen source in 7 cases. The paper by Damm et al²² is also the first paper to identify patient–ventilator asynchrony as a common problem (26%) during transport. This may be related to sedation, pain during movement, or the inability of portable ventilators to match the performance ICU ventilators. The authors also observed that patient incidents were more commonly associated with sedated subjects, subjects undergoing diagnostic procedures, and use of a turbine ventilator, with the latter likely being an issue with high gas consumption of ventilators utilizing a bias flow during expiration.²² The authors concluded, in disagreement with other studies, that transport of mechanically ventilated critically ill patients, was a high-risk procedure associated with potentially severe complications.²²

In the remaining 3 trials,^18,24,25 serious adverse events occurred in < 10% of cases, with cardiac arrest and hypotension being the most common serious adverse events. Two of these trials involved transport from the emergency department to the ICU, and incidents were > 1 per transport in all 3 studies. The study by Papson et al¹⁸ is the only one to report occurrence of a pneumothorax during movement. Instances of equipment failure ranged from 9% to 46%, and hypoxemia was uncommon.

A multi-center cohort study from the OUTCOMEREA trial group (12 ICUs in France) evaluated 1,782 mechanically ventilated subjects undergoing 3,006 transports (1–17 per subject). Unique to this trial was the evaluation of not only adverse events during transport, but also posttransport complications. After adjustment for propensity score and confounding factors in the 24 h prior to transport, transport subjects had a higher risk of complications (odds ratio 1.9, 95% CI 1.7–2.2). The need for intrahospital transport was associated with a longer duration of ICU stay but had no impact on mortality. Reported complications included pneumothorax, atelectasis, ventilator-associated pneumonia (VAP), and electrolyte disturbances.¹⁸ Of note, the increase in VAP rate within 4 d of transport is consistent with data reported by Kollef et al²⁹ and Bercault et al.³⁰ The etiology for an increased rate of VAP following transport may be secondary to changes in patient position, breaking the ventilator circuit, or changes in endotracheal tube cuff pressures. Monitoring cuff pressure or continuous control of cuff pressure might be useful in preventing this complication.

A recent systematic review specifically addresses adverse events during intrahospital transport of critically ill children.³¹ This review included 24 studies with a total of 4,104 transports. In this group of pediatric subjects, respiratory and airway events were the most common adverse events, and the risk of an adverse event increased as the severity of underlying illness and the degree of respiratory support increased. The authors concluded that use of a ventilator was superior to manual ventilation and that most adverse events were preventable and could potentially be mitigated by the use of checklists and redundancy. Table 3 lists the reported respiratory events from 15 studies evaluating pediatric transport. Many of these studies were conducted with mechanically ventilated subjects, but others involved subjects with native airway.

Adverse Events During Interhospital Transport

Interhospital transport typically involves moving patients between hospitals for specialized or higher echelons of care.³ Fan et al³ undertook a systematic review of interhospital transport in 2006. Relying on 5 studies (n = 245 subjects) in which two thirds of subjects were transported by air and one third by ground, the authors reported a wide range of adverse event reporting.^45-51 Only 2 of these studies were prospective, and they included just 25 subjects. In 3 studies, a physician was in attendance for all transports. Only the report by Barillo et al⁴⁷ identified a common adverse event, respiratory alkalosis (19% of subjects), in subjects ventilated at altitude using pressure control ventilation. In another study, these authors reported similar rates of respiratory alkalosis during aeromedical evacuation using high-frequency percussive ventilation.⁵² These results can be explained by the use of ventilators that lack altitude compensation and thus deliver a larger volume when used higher altitude.⁵³ These results suggest that the presence of point-of-care arterial blood gas analysis could play a role in preventing these adverse effects.

Singh and colleagues⁵⁴ studied the use of mechanical ventilation during interfacility transport and reported that the most common adverse event was new-onset hypotension. In this retrospective study, frequent and repeated sedation was provided in > 70% of cases and neuromuscular blockade in 22%. Hypotension was transient and was most often associated with administration of sedation.⁵⁴ The same authors performed a retrospective review of land-based interfacility transports occurring over a 5-y time frame. They observed 333 (6.5%) critical adverse events in 5,144 transports, which breaks down to 1 in 15 patient movements. New hypotension was the most frequent adverse event, whereas respiratory events were seen in only 1.3% of cases. Emergency intubation was performed in 4 instances (0.08%), and hypoxemia was observed in 65 cases (1.3%).

Hypobarism during aeromedical transport would logically increase the likelihood of hypoxemia during interfacility transfer,⁵⁵ yet studies by Wilcox et al⁴ and Barnes et al⁵⁶ did not report hypoxemia in ventilated subjects with respiratory failure. In fact, hyperoxemia is more likely. These results are likely secondary to the use of continuous oximetry and the practice of providing additional oxygen to protect against hypoxemic events.⁵⁷

Several studies from the United States military evacuation of casualties from the conflicts in Iraq and Afghanistan provide some insight into adverse events.^58,59 These trials included mechanically ventilated subjects in cases of non-battle injuries (20%) and battle injuries (60%). In the latter group, subjects were frequently ventilated at settings that did not comply with the ARDSNet tidal volume and PEEP/ tables. However, the mean difference in tidal volume between groups was 30 mL. Subjects with noncompliant ventilator settings had more frequent inflight events. The most frequent inflight events were respiratory events, which occurred in 35–43% of all subjects and in 47% of subjects ventilated outside the desired settings. These subjects were monitored with pulse oximetry, capnography, ECG, blood pressure, and heart rate, and the mean was 99%. These data suggest that, even with continuous multimodal monitoring, adverse events are common. Perhaps an early warning system is needed.⁶⁰

In one of the few studies involving subjects who were not mechanically ventilated, our group evaluated during aeromedical evacuation of the walking wounded.⁶¹ Our study included 61 subjects who were not receiving supplemental oxygen and could walk (also known as the walking wounded). A mean decrease in of 4% was seen in all subjects upon achievement of cruising altitude (ie, barometric pressure of 564 mm Hg). < 90% were seen in 90% (55 of 61) of subjects, and < 85% (34 of 61) were seen in 56% of subjects. The mean duration of hypoxemia at < 90% was > 44 min, and the mean duration of hypoxemia at < 85% was 12 min. The longest period of hypoxemia at < 85% was 44 min. Figure 1 depicts the incidence and duration of hypoxemia. The long-term effects of these hypoxemic events are speculative but could have an impact in patients with head injuries, lung injury, and infections.^62,63

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Fig. 1.

Incidence of hypoxemia in aeromedical evacuation of casualties not receiving oxygen. The total sample was 61 subjects; only 6 subjects had no events with < 90%. Of those 55 hypoxemic subjects, 21 subjects had of 85–90%. The duration of hypoxemia was < 10 min in 20 subjects and > 10 min in 14 subjects.

This review of adverse events during transport demonstrates the frequency and severity of cardiovascular and respiratory compromise seen during transport. Although none of these trials evaluated monitoring, each provides a list of undesirable outcomes, around which monitoring can be designed. Routine use of oximetry, capnography, ECG, blood pressure monitoring, and values provided by the ventilator (eg, airway pressures, volumes, and flows) appear to be required elements for the ventilated patient. In the nonventilated patient, continuous oximetry, heart rate, and breathing frequency seem to be prudent measures. New systems that monitor breathing frequency and volume by acoustics or chest wall movement should be studied. The use of systems that can warn of impending failure should be evaluated. As in many instances, an ounce of prevention is worth a pound of cure.

Capnography During Transport

Despite the paucity of data on use of monitoring during transport aside from the reports of current practice, capnography has been studied as a method to facilitate ventilation during transport. This includes use in prehospital care and during inter and intrahospital transport. In some of these studies, end-tidal carbon dioxide pressure () is used as a target, whereas in others the resultant arterial partial pressure of carbon dioxide () is reported.

The trauma group from Seattle published a series of papers on CO₂ monitoring during prehospital and emergency department ventilation.^64-66 The first study evaluated intubated trauma patients presenting to the emergency department and receiving mostly manual ventilation. In a retrospective study of almost 600 subjects, the authors reported that hyperventilation and severe hypocapnea was common (18%).⁶⁴ Hypercapnia was seen in subjects with higher injury severity scores, and these subjects were more likely to be hypoxic and acidodic. Those subjects with normocapnea had better outcomes, particularly in traumatic brain injury.⁶⁴ Their second retrospective study focused on traumatic brain injury, and they reported improved outcomes in subjects with being 30–39 mm Hg (mortality rate of 21% vs 33%).⁶⁵ Despite the use of the term “targeted ,” the authors reported the resultant during ventilation.

This group’s third trial was a prospective observational study comparing and in 180 subjects over a 9-month observation period.⁶⁶ They reported a poor correlation between the variables, with hypercapnia a common finding when was in the target range of 35–40 mm Hg. They concluded that should not be used to guide prehospital emergency department ventilatory support.⁶⁶ These findings are important given the relationship between adequate ventilation and outcomes in traumatic brain injury.⁶⁷

Helm et al⁶⁸ evaluated the use of capnography to control prehospital ventilation in trauma subjects. All subjects were monitored with capnography and transported by helicopter, but the capnographic results were only visible to caregivers in half of subjects.⁶⁸ The subjects with monitoring were normocapnic 3 times more often and were less likely to be hypoventilated.⁶⁸ The authors concluded that prehospital monitoring was valuable.⁶⁸ As with any discussion of capnography, the impact of cardiac output and dead space must be considered. The relationship of and is often widely disparate for reasons unrelated to minute ventilation.

Palmon et al⁶⁹ studied the use of capnography to control manual ventilation during intrahospital transport. Studying 50 subjects moved from the operating room to the ICU, the authors reported no advantage of capnography in these extremely short transport times.⁶⁹ In a small study (n = 12) utilizing capnography, Tobias and colleagues⁴⁰ reported that unintentional hyperventilation was common in children during intrahospital transport.

Transcutaneous CO₂ Monitoring During Transport

Transcutaneous monitoring represents another avenue for monitoring ventilation during transport. Maheshwari and Luig⁷⁰ retrospectively reviewed data on 43 neonates during transport, and they reported no benefit of monitoring transcutaneous CO₂ to prevent hypocarbia or hypercarbia. Tingay et al⁷¹ compared and transcutaneous CO₂ during neonatal transport in 21 neonates during transport and concluded that transcutaneous CO₂ was preferable to for monitoring ventilation; this study did not address outcomes. Hinkelbein et al⁷² compared to and transcutaneous CO₂ during ground transport of critically ill mechanically ventilated adults. Comparing 170 data sets from 34 subjects, the authors concluded that a combination of capnography and point-of-care arterial blood gas analysis might provide the best monitoring.⁷²

Early Warning Systems

The use of early warning systems to predict impending respiratory compromise and need for life-saving interventions has been evaluated by a number of groups.^60,73-79 The use of the National Early Warning Score, National Early Warning Score 2, Hamilton Early Warning Score, R to R variability on ECG, /, and the ScoreO₂ have all been described as methods to predict poor outcomes in hospitalized patients. To date, none of these systems have been applied to patients during transport. Given the data in this review, monitoring is prevalent, yet adverse events remain a concern, so the ability to stratify risk on the basis of these scores could prove a fruitful avenue of research.

Checklists

Two recent papers have highlighted the role of documentation and checklists in safety during transport.^80,81 Although documentation and checklists are within the scope of monitoring, this paper has attempted to review devices for monitoring and those events that monitoring is designed to avoid. Nonetheless, documentation regarding patient transport deserves some mention. In both studies, the use of a checklist or transport tool is described and the impact on safety is reviewed.^80,81 This includes the provision of adequate staffing, adequate equipment, and monitoring. These systems are intended to improve continuity, mitigate risks, prevent mishaps, and document the process of transport.

Summary

Monitoring respiratory and cardiac function during transport is routinely done during prehospital, intrahospital, and interhospital transport. Current guidelines provide a framework for required monitoring, but they need to be updated. In the mechanically ventilated patient, oximetry, ECG, blood pressure, capnography, and monitors integral to the ventilator are standards of care. Monitoring the nonintubated patient has been rarely studied during transport and requires urgent study. The use of early warning systems should be explored as methods to reduces adverse events and improve patient outcomes.