The study objectives were to determine the frequency of AE during transport, the elements that predict the risk of IHT of critically ill patients, and the improvements to be put in place in our ICU.
Incidence of adverse events
In our cohort of 262 IHT, we showed that AE occurred during 45.8% of IHT. Twenty-six percent of these IHT resulted in patient-related AE. Sixty-four percent of these patient-related AE were major (16.8% of transports) requiring medical intervention during transport.
Our cohort is one of the largest cohorts of IHT of patients on mechanical ventilation (262 IHT). Only two published series are larger: Lahner studied a cohort of 452 IHT of adults and children [9], and Kue recently published a retrospective study of 3,358 IHT [14]. This last study reported few AE (59 events, 1.7%) but only very serious patient AE were recorded. In our study, we identified a higher number of AE during IHT. This is however similar to the incidence reported in the literature: up to 68% of transports depending on the series [8–11, 14, 16, 19–21]. The definition of AE is the most important confounding factor. In this study, we followed the most common definitions of AE [13]. Thus, our high incidence of AE despite respect of the protocol and practical training of junior physicians may be explained by the thorough recording of AE. Certainly some of these incidents (including “line, tube, and drain” incidents) can occur independently of IHT, but this AE incidence is lower than the incidence of AE during IHT. Many are preventable through proper preparation [22, 23]. Thus, the team carrying the patient must be prepared for the occurrence of these incidents [24].
Equipment-related incidents represented the majority of incidents, but AE with an impact on the patient still occurred in 26% of IHT, which is similar to literature data (17-33% of transports) [9–11, 19]. Our series includes only one accidental extubation and no cardiac arrest during IHT, unlike other studies [8–11, 16, 20]. This low percentage of very severe AE may be due to the presence of an experienced porter and perhaps also to more care and attention being paid to transport modalities under the study conditions.
No coordination problem with the radiology department was noted with specific daily time slots reserved for ICU patients. Synchronization with the radiology department is organized by our porters. Thus, our ICU patients wait a minimum of time in the radiology department during IHT.
Risk factors of these AE
We have shown that AE occurred in 45.8% of IHT. Risk factors were fluid challenge for IHT, PEEP > 6 cmH2O, and sedation before transport. Twenty-six percent of these IHT resulted in patient-related AE. Risk factors specific for these patient-related AE were PEEP > 6 cmH2O before transport and treatment modification for transport. Sixty-four percent of these patient-related AE were major (16.8% of transports) with catecholamine administration and treatment modification for transport identified as predictive factors. In our study, AE during transport did not increase the risk of ventilator-associated pneumonia, ICU length of stay, or time spent on MV.
The male to female ratio was 2:3 (men = 129, women = 55) comparable to the proportions usually found in our ICU. Patient’s sex was not a risk factor for the occurrence of an AE during IHT. The repetition of IHT for the same patient was not a risk factor for AE during IHT. Each transport of the same patient is associated with a similar level of risk.
We conducted our study only for one type of transport (to CT scan) to exclude risk factors related to the radiology procedures and to identify risk factors related to the patient (and not to diseases or invasive techniques). Few IHT were performed after working hours. The time of day or day of the week had no influence on AE during IHT. The severity of patients and invasive devices are not predictive of AE during IHT. Even if this was assumed in other studies [11], it has not yet been demonstrated. We found sedation of the patient before transport, PEEP > 6 cmH2O, and the need for fluid infusion for transport to be risk factors for any AE during IHT. Sedation of the patient as high PEEP is a known risk factor in the literature [8–11, 16, 20] but not treatment modification identified in our study as a risk factor for patient-related AE. It is possible that transport was undertaken too early after treatment modification with insufficient time for stabilization, leading to a direct risk to the patient. Treatment modifications were primarily increase in sedation or fluid challenge, which should perhaps change our attitude. However, patient severity was not associated with AE during IHT. The number of infusion pumps was predictive of AE during IHT in univariate but not multivariate analysis, which also was shown by Doring [19]. This may be related to the fact that we limit the number of infusion pumps during transport in our protocol. We listed many equipment-related incidents during transport, which were usually battery problems or improperly set alarms (high pressure on ventilator). We used second- and third-generation respirators as recommended for these types of IHT [25]. Third-generation respirator was used preferentially if the patient was treated for ARDS or if ventilatory mode of the patient before IHT was PSV. The material used does not explain AE (no statistical difference). Experienced or anaesthetist junior physicians had fewer equipment-related incidents than the other junior physicians, because they are more familiar with the equipment used and may better anticipate potential problems with these devices. Most of these equipment-related incidents appear to be preventable, particularly those affecting the transport ventilators. They should be avoided by proper preparation and checks before IHT. Good coordination between the radiology team and the ICU is essential, because duration of transport also is associated with patient-related AE, a point already shown in other studies, such as those by Lahner or Smith [9, 26].
AE during transport were not significantly associated with a higher risk of ventilator-associated pneumonia compared with patients transported without AE, perhaps because of a too small number of patients included in our study. This result differs from that of the study by Bercault, which compared patients with and without IHT [15]. Bercault’s study included all IHT, including IHT to MRI, coronary angiography, and arteriography (33/158 transports) with a much longer length of transport and a more systematic strict supine positioning. In this study, the risk of ventilator-associated pneumonia was associated with IHT [15]. However, this association is particularly difficult to interpret, because patients who require IHT have been shown to be more serious and to have a longer ICU and hospital length of stay, which are well-known risk factors of ventilator-associated pneumonia [27, 28]. This reason also explains why we chose an observational design for our study. Using a randomized, control design or matching between patients with or without IHT to study these parameters would have explored more the consequence of the procedure than the effect of IHT. Of course, AE as recorded in our study can occur when a patient remains in his ICU room. Comparison in AE frequency during these two periods requires further study.
Finally, AE during IHT had little impact on patient outcomes; we did not find that an AE during the IHT entailed consequences for time spent on MV or ICU length of stay.
Consequences for our practices
Our study had a direct impact on our practices. It allowed us to identify most common AE, to overcome the most frequent errors, to check the equipment (replacement of batteries for example), and to implement a reproducible protocol for IHT, with training of junior physicians, but also of nurses [29–31]. Particular attention should be paid to the risk factors that were found in our study. Our single-center study can probably be extrapolated to other centers, because our protocol was performed in accordance with the widely used guidelines of Warren et al. [4]. Our conclusions may be useful to other ICUs because they are consistent with recent guidelines [13], and the points highlighted are probably encountered in other services. The main consequence we have drawn from our study is to increase the size of the transport team, including an ICU nurse to help the junior physician to deal with the complexity of ICU patient. Using such a three-person transport team has recently been recommended by Fanara [13]. However, the beneficial effect of such a three-person transport team in reducing AE during IHT should be evaluated by a further study.
Study limitations
Several limitations of this study should be noted. The main bias of our study is the fact that some patients in need of a procedure requiring transport may have had their transport denied by senior physicians because it was estimated to be too dangerous given the severity of the patient. Some data have not been included in our study, such as the reasons for CT scan. These data would have allowed more detailed analyses regarding “urgent” or “routine” CT scan and the relevance of the CT scan and therefore transport. Our study may not be extrapolated to all ICUs, because some diseases (such as neurosurgical disease) or certain types of invasive techniques (such as the measurement of intracranial pressure) are poorly represented in our study.
Our study has focused on patients and their immediate environment. Because the healthcare delivery is very complex, both provider and systems (two major components beyond patients in healthcare delivery) need to be modified to reach good outcome for both patients and organizations [32]. A more systematic approach would perhaps show other risk factors that are accessible to improvement.
