Impact of the mobile intensive care unit

SUMMARY

Interhospital transfer of critically ill patients is associated with hemodynamic and pulmonary deterioration. In order to minimize additional risks of transport, a mobile intensive care unit with a specialized retrieval team (MICU) service was established at our tertiary referral center in 2009. To evaluate the effects of this new transporting mode, we performed a prospective audit to investigate the quality of interhospital transfers to our university affiliated ICU.

We evaluated transfers performed by MICU from March 2009 until December 2009. Data on fourteen vital variables were collected at the moment of departure, arrival and 24h after admission. Variables before and after transfer were compared using the Paired-Sample Test. Major deterioration was expressed as a variable beyond a predefined critical threshold. Results were compared to the data of our previous study concerning interhospital transfer performed by ambulance (1).

74 transfers over a 10-month period were evaluated: 84 percent of all patients were mechanically ventilated and 53 percent were on vasoactive agents. At arrival, systolic blood pressure, glucose and haemoglobin were significantly different compared to departure, although major deterioration never achieved significant values. 38 percent showed an increase of total number of variables beyond threshold at arrival, 32 percent exhibited a decrease of one or more variables beyond threshold and thirty percent had an even number. There was no correlation with the duration of transfer or severity of disease with patient status at arrival. ICU mortality was 28%.

Compared to the transfers performed in 2005, there were far less incidents in the current situation: 12.5% vs. 34%. In the current study, all incidents were due to technical problems. Although mean APACHE II score was significantly higher, patients transferred by MICU showed less deterioration in pulmonary parameters compared to the patients transferred by ambulance.

Conclusion

Transfer by MICU appears to be well prepared and imposes minimal risk to the critically ill patient when compared to transfer performed by ambulance. The implementation of a transport protocol with a mobile Intensive Care Unit and a specialized retrieval team has therefore led to an improvement in quality of (critical) care.

INTRODUCTION

Interhospital transfer of critically ill patients is regulated by a national guideline, prescribing a coordinating role for tertiary ICUs in diverse regions. The national gradation of ICUs into three levels is based on the availability of an intensivist, volume, total number of days of treatment and ventilatory support/year and other organizational characteristics*. The emphasis of this ICU-guideline is coordination and consultation; in some cases it is preferred to transport the patient to a high intensity medical staffed ICU in order to facilitate a higher intensity of care or to give appropriate therapy.

Interhospital transport is associated with limited monitoring capabilities and less staffed guidance during transfer than in the ICU environment and imposes important risks to the critically ill (1-4). In the Dutch setting, former transfer of the critical ill was performed in a standard ambulance requiring at least an ambulance nurse and a chauffeur, and was occasionally accompanied by an Intensive Care nurse or a physician.

Transferring critically ill patients can be necessary because of limited possibilities of advanced therapeutic interventions in rural hospitals. To find out whether interhospital transfer leads to an improvement in outcome, Westfall et al performed an analysis of 51,530 transferred patients with myocardial infarction (5). Baseline characteristics like age and severity of illness were not evenly distributed in both patient groups, but the mortality advantage in transferred patients still existed after adjustment for patient and hospital characteristics as well as therapy (O.R. for 30-day mortality = 0.80, 95% C.I. 0.76-0.84).

The benefits for critically ill patients treated in tertiary ICUs compared to patients treated in rural ICUs have been well investigated in countries abroad, like in the United States. However, there is not much knowledge about the volume-associated mortality in Dutch ICUs, which have a different organization compared to American ICUs. One study has been performed in the Dutch setting to investigate the effect of volume on patient mortality. Peelen et al found a slightly beneficial 3% concerning hospital mortality in patients with severe sepsis in high volume ICUs compared to small volume ICUs (6). The fact that this is the only publication which describes the national situation, the Dutch guideline is therefore mostly based on foreign literature. The most important article probably is the systemic review of Pronovost (7), in which 27 studies have been included. Data analysis showed -in the presence of a higher intensity of ICU staffing (e.g. intensivist)- a reduction in hospital mortality as well as a reduced ICU and hospital length of stay.

The decision of Dutch intensivists whether to transport a critically ill patient to another hospital was assessed by van Lieshout (8). The most important determinants in the decision whether to transport a critically ill patient were the level of escorting personnel and the transfer facilities rather than patient's characteristics or the intensity of the supportive care. The results of this study reflect the value and importance of a well established transporting device. The implementation of a MICU or a specialist retrieval team has shown to be effective in reducing risks in other countries (9;10).

In our tertiary center, about hundred transfers per year are accepted from other ICUs. From March 2009 on, all transfers concerning critically ill patients have been accomplished by MICU. In order to find out to which extent incidents and adverse events happen during or shortly after this new way of transport, we performed a prospective observational study, including all transfers performed by MICU from March until December 2009. In this audit, we tried to find an answer to the following questions: what is the relative frequency of incidents during transfer? Which proportion of incidents is due to technical failure and/or to staff management? What is the influence of transfer and incidents on the condition of the critically ill patient; e.g. did vital variables, documented before transport pass any critical threshold during transfer? What is the 24 hours ICU mortality of our study population and were there any significant factors that could predict such an outcome?

Another goal of this study was to objectify if transfer of the critically ill by MICU is safer than transfer by ambulance. In 2005, transfer of critical ill patients has been evaluated in much the same way this study is conducted. At the time, transfer was performed by ambulance with guidance of mostly ambulance personnel instead of intensive care staff. In order to evaluate the possible benefits of the MICU service, we compared our results to the data from the hundred transfers done by standard ambulance transport in 2005.

MATERIAL AND METHODS

A stratified protocol clarification was sent to all referring ICUs in our region, thereby explaining the procedure of transfer. Transfer by MICU concerns a planned transport, and all transports are being performed from Monday till Sunday from 8.00-0.00. In order to accomplish the transfer, the referring intensivist has to consult the MICU-coordinator, in which a MICU transport form about patient's characteristics has to be completed. After registration of the (to be transferred) patient and authorization of the transfer by the MICU-physician and the supervising staff member of the accepting ICU, the MICU sets out to transfer the critically ill patient.

When the MICU-team arrives in the referring ICU, the critically ill patient is being stabilized and prepared for transfer; if a complication such as respiratory insufficiency in a non-intubated patient during transfer is to be expected, the patient undergoes intubation. In this way, it is tried to prevent acute deterioration of the patient as much as possible. During transport, the MICU-nurse or physician completes forms describing haemodynamic and ventilatory variables.

Although responsible for all performed transfers with MICU in the Northern region of the Netherlands, our university-based ICU is not always the ICU of destiny. In this study, we only included performed transfers to our tertiary ICU and to the ICU of the Scheper Hospital in Emmen. Total study population counted 74 patients; table 1 shows the diagnosis at transfer. Characteristics of the transferred patients are summarized in table 2.

Statistics

We performed a Paired-Sample T test to evaluate if the variables before and after transport were statistically different. This test is used to determine the equality of means of two related groups. Performing this analysis, each parameter could be tested whether significant changes occurred within the period of transportation. Before comparison, 'critical thresholds' were predefined. In order to see whether the distribution of a variable passing a critical threshold differed in time (indicating major deterioration), we performed the McNemar test. This test is used to compare dichotomous variables in a repeated measures situation (where subjects are assessed before and after an intervention). Each variable (whether beyond threshold or not) at departure and arrival could be analyzed this way.

For each variable, the percentage of patients in whom the critical threshold was reached was calculated. This is defined as a variable within the normal range before transfer but values beyond threshold at arrival, indicating a deterioration in the patient's status.

These mentioned critical thresholds are regarded as clinically relevant deteriorations. For instance, the haemoglobin threshold of 4.4mmol/L (7 g per deciliter) is being cited in the study by Hbert, in which a restrictive strategy of red cell transfusion within the critical care is recommended (11). The threshold of the mean arterial pressure (MAP below 60mmHg) is associated by an increased risk of death in early septic patients (12). Thresholds concerning body temperature are also being cited in literature(13;14). Remaining thresholds are based on thresholds as used in clinical practice in The Netherlands.

RESULTS

From March until December 2009, 74 transfers were performed to our university-based ICU and the ICU of the Scheper Hospital Emmen. All transfers were from 14 regional hospitals in the north eastern region of the Netherlands. Two ICUs transferred 10 patients or more, four ICUs transferred between 5 and 9 patients and eight ICUs transferred less than 5 patients. Main indication for transfer was the need for higher intensity of care or advanced therapy, for example the indication of renal replacement therapy. Main diagnosis at transfer was respiratory failure (27%), followed by sepsis (17.6%) and multi organ failure (10.8%).

Incidents

Primary aim of this study was to evaluate the safety of the transportation protocol for critically ill patients. The incidents that were noted during transfer are noted in table 3. In summary, nine incidents were recorded; all of them due to technical failure. As a consequence, two transfers had to be performed by an ambulance without changing the escorting personnel.

Adverse events

In three transfers, a leakage of compressed air was present without indication of shortage of compressed air. In these transfers was a modest decline in saturation at arrival (92% vs. 96%). During the transfer in which the heater broke down, body temperature of the transferred patient declined from 37.8 to 34.8C.

Arrival in the referral ICU

Within 24 hours of admission four patients died (5%) and another three patients (4%) were already transported to a normal care unit. Mean number of passed critical thresholds of the deceased patients before transfer was 2.3, at arrival this was increased to 3. One patient had one less variable beyond threshold after transfer, three patients showed an increase of respectively 1 and 2 variables beyond threshold. Mean APACHE II score was higher in group of deceased patients compared to the remaining patients, although the difference did not achieve significance (34.7 vs. 19.8, p=0.13 by Independent-Sample T test; one APACHE-score missing). One patient died because of a newly diagnosed ruptured thoracic-abdominal aortic aneurysm, one patient died during asystole in which resuscitation was not successful, the two other patients were abstained because of no therapeutic options in severely diffuse brain ischemia and severe metabolic acidosis refractory to therapy. ICU mortality was 28%.

Comparison previous study 2005

As reported earlier, a comparable study is conducted in 2005. Data from these patients (transferred by ambulance) enables comparison of the incidents and adverse events of the transferred patients from our study population.

Situation 2005: incidents during transfer by ambulance

In 2005, incidents were recorded in 34% (n=34) of all transfers, in which 30 percent was estimated to be related to technical failure. The remaining 70 percent of all incidents could have been prevented by better preparation prior to transfer. Although significant differences between variables before and after transfer were absent, deterioration in pulmonary status -whether due to transfer, incidents or the severity of illness- was prominent: about ten patients were respiratory insufficient at arrival of whom five required imminent mechanical ventilation.

Situation 2009: incidents during transfer by MICU

We found a relative frequency of incidents of 12.5% (n=9). Table 3 shows all events occurred during transfer by MICU, all of them due to technical failure. Major deterioration expressed as an increase in number of variables beyond a critical threshold did not achieve significance. More important, no immediate action during transfer or upon arrival had to be performed in order to stabilize the transferred patient.

Deterioration during transfer: MICU vs. ambulance

We also wanted to compare changes in hemodynamic parameters during transfer. Assuming serious deterioration of the transferred critically ill would now be less frequent compared to the transfers performed in 2005, we compared individual differences in variables during transfer. Since respiratory variables showed marked deterioration in 2005, we focused on these parameters.

Distribution of differences during transfer in 2005 and 2009 showed significant difference for the vital variables pH, paO2 and paCO2, using the Independent-Samples T test (a<0.05). Distribution of these differences is displayed in figure 3 a-d.

DISCUSSION

Assessing the safety of the transport of critically ill patients, primary endpoints in this study were clinical parameters, interventions and incidents occurring during interhospital transfer.

Evaluating clinical variables before and after transfer, systolic blood pressure (and mean arterial pressure), haemoglobin and glucose were significantly different at the moment of arrival. The increase in systolic blood pressure (121.2 to 131.1 mmHg, p= 0.00), however, may indicate an altered hemodynamic circulation rather than a major deterioration. Blood glucose level increased from 7.0 to 7.6 mmol/L (p=0.03) as the haemoglobin concentration declined from 6.6 to 6.3 mmol/L (p=0.04). Although these variables are significant, the clinical relevance seems dubious. We therefore searched for the presence of major deterioration during transfer, expressing it as the distribution of each variable beyond critical threshold. Using the McNemar test, we did not find significant major deterioration in any of the variables.

In order to objectify the effects of transfer further, we also looked at individual data. Expressing deterioration as total number of variables beyond threshold, 38% of all patients showed an increase of total number of variables beyond threshold after transfer, of which 5% had an increase of three or more variables. This degree of deterioration was not related to transportation time nor with severity of illness (expressed as the APACHE II score).

Risk of mortality is predicted on the severity of disease, expressed as an APACHE II score which is calculated within the first 24 hours after admission. As most patients are transferred from other ICUs, our APACHE II scores are secondary scores. Prior stabilization in referring ICUs may therefore underestimate recorded APACHE II scores in our university affiliated ICU. Mean APACHE II score of our study population was significantly higher than the APACHE II score of our total ICU population: 20.0 vs. 14.5 (p<0.001 by One-Sample T Test). ICU mortality was 28% in our patient population, which is by far higher compared to the mortality of our total ICU population of 11.2% (excluding cardiac surgery patients).

Comparing our data with the data from the study in 2005, there are several improvements. The frequency of incidents is far less in the present situation (34% vs. 12.5%), as is the impact of the occurred incidents. Few adverse events are recorded during or shortly after incidents and unlike 2005, no interventions have been necessary during transfer by MICU in order to stabilize the transferred patient. Moreover, spread of individual differences in pulmonary parameters show less deterioration compared to the transferred patients in 2005, although APACHE II score is significantly higher in the present study (20.0 vs. 12.6, p=0.00 by Independent Sample T-test).

The evaluation of the interhospital transfers performed in our university affiliated medical ICU in 2005 showed major deterioration of some patients during transport. 70 percent of all incidents were estimated to be 'preventable', which describes the lack of preparation before transfer. The frequent absence of guiding intensive care physicians during transfer reflects the importance of a strict transportation protocol for critically ill patients.

The safety of a specialist retrieval team with or without a Mobile Intensive Care Unit is founded in the article of Bellingan (9). They compared patient transport with a specialist retrieval team with the current way of transporting critically ill (by ambulance) and found that patients transferred with a MICU were less severely acidotic and hypotensive upon arrival than patients transferred with a regular ambulance. It must be noted though that it is very hard making comparative patient groups because of case-mix and co-morbidity, and can therefore give an unjustified conclusion. Although in the article it is being stated that the admission diagnoses are not significantly different, this can be due to wide spreading diagnostic categories in a relative small patient population.

There are more studies that emphasize the importance of a well established transfer protocol or device such as a MICU. Uusaro evaluated long-distance transfer in critically ill patients with severely, unstable respiratory and circulatory failure. Expressing major complications as life-threatening deterioration in the clinical status of the patient, they did not have any major complication during transfer (15).

Similar to these studies, we do not have any data of patients who were not transported. It is therefore not possible to state that transfer is beneficial to patient survival. However, transferred patients had a higher APACHE II score than our general ICU population, which gives the impression that the way of selecting patients for referral is adequate. When looking at patients' data, transfer by MICU appears to be safe despite the higher degree of severity of disease. We therefore conclude that the safety of the current way of transporting critically ill is warranted and that the MICU sets a major improvement in quality of caring for the critically ill.

CONCLUSIONS

Initiating interhospital transport involves deliberation of various determinants such as patient's status, transfer indication, escort and transport facilities. Associated risks in interhospital transport have to be weighed against its possible advantage for each critically ill patient. In order to facilitate the choice of interhospital transfer, transfer itself must be as 'safe' as possible, e.g. additional risks for the patient must be minimized.

The MICU has gained a role in the national guideline concerning interhospital transfer of critically ill patients. This observing study of all transfers performed in our university-based ICU shows that transfer by MICU is not associated with major deterioration in the patient's status. Our conclusion is that implementation of a transport protocol with a mobile Intensive Care Unit has led to an improvement in quality of care on the road, compared to the former way of transfer by ambulance.

SAMENVATTING

Kwaliteit van zorg binnen de Intensive Care wordt zoveel mogelijk gewaarborgd door de nationale CBO-richtlijn voor volwassen IC-patinten. Deze richtlijn deelt Nederlandse IC's op in drie niveaus op basis van IC-grootte, aantal beademingsdagen per jaar, de aanwezigheid van een intensivist (uitgedrukt in fte) en andere organisatorische criteria. Vanuit de richtlijn is per regio een cordinerende functie verbonden aan de IC van het hoogste niveau (niveau 3); kleine regionale IC's dienen de patinten te overleggen bij wie de verwachte behandelduur bij opname meer dan 72 uur bedraagt.

In sommige gevallen leidt dit tot een overname van de IC-patint door de cordinerende IC. Daarnaast kan interhospitaal transport gewenst zijn wegens logistieke redenen of beperkte therapeutische mogelijkheden in de regionale IC's. Hoewel overplaatsing het doel heeft om de overlevingskansen van de betreffende patint te verbeteren, is transport geassocieerd met hemodynamische en respiratoire instabiliteit van de IC-patient. Om het risico van verslechtering gedurende het transport te minimaliseren, bestaat er sinds 2001 een CBO-richtlijn* betreffende het transport van de IC-patint. Hierin wordt het belang van het gebruik van een MICU in combinatie met de inzet van gespecialiseerde begeleiding (IC-verpleegkundigen en intensivisten) benadrukt. Dit vervoersprotocol is in 2009 wettelijk geaccordeerd.

Sinds maart 2009 worden in de regio Groningen alle IC-transporten per MICU gereden. Om de veiligheid van dit transportprotocol vast te stellen, is een prospectieve, observationale studie verricht ter evaluatie van de gereden transporten. Eindpunten hierbij waren het aantal incidenten, status van de patint uitgedrukt in veertien variabelen en eventuele interventies onderweg. De resultaten van dit onderzoek zijn vervolgens vergeleken met de data en resultaten van de evaluatie van IC-transport per ambulance (verricht in 2005).

Het percentage incidenten gedurende het MICU-transport bedroeg 12.5% t.o.v. 34% in 2005. Alle incidenten waren in 2009 gerelateerd aan technisch falen, in tegenstelling tot de gerapporteerde incidenten in 2005 waar naar schatting 70% gerelateerd was aan een inadequate voorbereiding van de IC-patint alvorens transport en de resterende 30% technische mankementen betrof.

In deze studie is geen sprake geweest van een significant ernstige verslechtering van de patinten gedurende het transport. De patinten met een toename van het aantal overschreden variabelen (variabelen die de vooraf vastgestelde grenswaarden gepasseerd waren) gedurende het transport, hadden daarnaast geen significant langere transporttijd of hogere APACHE II scores (een score die de ernst van ziekte weergeeft). Deze resultaten zijn vergelijkbaar met de resultaten uit 2005. Op individueel niveau is een gunstig effect van het nieuwe vervoersprotocol zichtbaar: de verslechtering van respiratoire parameters gedurende het transport is significant kleiner t.o.v. 2005 en het aantal verrichte spoedintubaties bij aankomst in het overnemende ziekenhuis is teruggebracht tot nul.

Op basis van deze studie kan worden geconcludeerd dat de huidige manier van IC-transport beter is dan het reguliere vervoer per ambulance. Transport per MICU lijkt derhalve een veilige manier om een ernstig zieke patint te vervoeren.

REFERENCES

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