BJA Advance Access published online on August 18, 2008
British Journal of Anaesthesia, doi:10.1093/bja/aen239
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Influence of resident training on anaesthesia induction times
1 Department of Anaesthesiology, University Hospital Hamburg-Eppendorf, Hamburg, Germany
2 Department of Anaesthesiology and Intensive Care, Charité-Universitätsmedizin Berlin, Campus Charité Mitte and Campus Virchow Klinikum, Charitéplatz 1, 10117 Berlin, Germany
* Corresponding author. E-mail: martin.schuster{at}charite.de
Accepted for publication June 25, 2008.
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Abstract |
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Background: The effect of resident training in anaesthesiology on operating room (OR) economics is an issue of debate. Comparisons of anaesthesia process times between residents and consultants might be systematically skewed by interactions of anaesthesia technique and patient factors.
Methods: In this prospective, observational study, we analysed anaesthesia process times in 599 cases performed for four different surgical services in a University hospital. The following factors were recorded for each case and used in multivariate analyses of process times: age, American Society of Anesthesiologist (ASA) status, BMI, emergency status, the educational level of the anaesthetist, and the anaesthesia technique.
Results: In the non-adjusted comparison, only for two of seven anaesthetic techniques did resident cases have statistically significant longer induction times than consultant cases: general anaesthesia with placement of a central venous catheter [mean (SD) anaesthesia time for resident cases 38.2 (17.0) vs 22.3 (10.0) min for consultant cases, P=0.001] and general anaesthesia with a laryngeal mask airway [resident cases 11.3 (5.5) vs consultant cases 7.3 (5.0) min, P=0.003]. Anaesthetic technique had the greatest effect on anaesthesia induction time. Educational level of the anaesthetist and age of the patients had small, but significant effects.
Conclusions: Anaesthesia cases performed by residents have in some, but not in all, anaesthesia techniques increased process times compared with cases performed by consultants. This limits a possible negative impact on OR economics by resident education. Patient-based factors including ASA status, BMI, and emergency status have minimal or no effect on anaesthesia process times.
Keywords: anaesthetic techniques, induction; education; OR economics; OR efficiency; resident training
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Introduction |
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The drive for operating room (OR) efficiency has led to increased interest in the time taken by resident training in the OR. Several studies have been published regarding the impact of surgical resident training on surgical times;1–6 however, the results are conflicting and seem to be dependent on the specific type of operation performed.1 Regarding anaesthesia resident training, the main focus has been on anaesthesia induction times and the preincisional time period. The assumption is that training of anaesthesia residents might increase the anaesthesia process times and thereby negatively influence OR efficiency and increase waiting time for surgeons.7 In a recent study, Eappen and colleagues8 investigated retrospectively the effect of the introduction of new anaesthesia residents on anaesthesia process times. The authors found a significant, but very small effect of resident teaching on induction, emergence, or turnover times. Davis and colleagues,9 using a prospective study design, reported an increase of the anaesthesia induction time by a mean (SD) of approximately 4.5 (3.2) min for teaching cases.
A major challenge in comparing anaesthesia induction times between residents and consultants is the complex interactions of technique, provider, and patient. For example, patients with higher ASA classes might have increased process times not only because they are medically more complex, but also because they are more likely to receive invasive monitoring [placement of central venous catheters (CVC) and arterial lines] which leads to increased induction times.10 On the basis of our experience, we also assumed that other patient-related factors might increase the anaesthesia process times, including obesity, age, or emergency status of patients. In many instances, the more difficult cases will be performed by anaesthesia consultants themselves. But if residents predominantly do uncomplicated cases, an unadjusted comparison of anaesthesia induction times between consultants and residents might be systematically skewed. We therefore studied process times of anaesthesia cases of residents and consultants for different anaesthetic techniques and recorded and adjusted for possible patient-related factors.
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Setting of the study
With approval of the ethics committee of the Chamber of Physicians, Hamburg, we prospectively studied anaesthesia process times in cases undertaken from April to June, 2006, during regular OR hours (7 a.m. to 8 p.m.) in the main surgical suite with nine ORs in a university hospital in Germany. The surgical services studied were: cardiothoracic surgery, including paediatric cardiothoracic surgery, general surgery, including paediatric general surgery, and urology and hepatobiliary surgery, including a transplant service. Most cases were performed on inpatients; however, a few outpatient procedures were also performed. Cases performed by surgeons using local anaesthesia with an anaesthetist monitoring the patient or performed without involvement of the department of anaesthesia were excluded from the analysis. We also excluded the cases when patients came to the OR from the intensive care units or the emergency department already intubated.
Anaesthesia process time predictors recorded
On the basis of the previous work done by our group,11 the following possible influencing factors for anaesthesia induction time were recorded for each patient: anaesthesia technique, age, BMI, American Society of Anesthesiologist (ASA) physical status, and emergency status. For reasons of group sizes and to ensure dichotomous values for statistical analysis, we separated healthy patients and patients without severe systemic disease (ASA I/ASA II) from patients with severe systemic disease (ASA III, ASA IV, and ASA V). The age groups used were: below 12, 12–70, and >70 yr. Because of the anatomical, physiological, and pharmacological changes that have occurred by puberty, the standard operating procedures for anaesthesia for older children are more similar to those in adults than in younger children. For example, for older children, we use i.v. instead of inhalation induction and the process of separation from the parents is in general shorter than for younger children. There is variability both concerning the development of individual children and the providers approach to children around puberty. Since we had to draw a definite line for the purpose of analysis, we used 12 yr as the upper limit of the paediatric age group. Obesity was defined as the presence of a BMI of above 30; for patients under the age of 18, the age-adjusted 90th-percentile was used as upper limit of normal weight. Emergency cases were defined as cases which had to be performed within 4 h after first OR registration.
For this study, we classified the educational level of residents on the basis of the presence or non-presence of board certification. In Germany, there is a 5 yr anaesthesia residency programme with a 1 yr of mandatory intensive care unit experience which in our institution is always in the final year. During the study period, the department had 56 consultants and 45 residents. In order to undertake a more detailed review of the effect of training, we undertook a subgroup analysis of the residents involved in the study. The residents with 1 or 2 and the residents with 3 or 4 yr experience were grouped together and compared with each other and the consultant group.
We defined as primary treating physician the anaesthetist or anaesthesia resident who intubated the patient or who placed the regional anaesthesia technique. Inductions performed by residents were, in general, supervised by consultants. However, the extent to which the consultant influenced the resident case varied depending on the experience of the resident and the clinical situation. Since we wanted to study the clinical reality, we did not influence this interaction between resident and consultant; however, if the case was planned and started with a resident as primary treating physician, the case remained in the resident group, even if the consultant helped the resident, for example, with line placement or took over because of problems or complications.
Anaesthesia techniques studied
In the final analysis, we included only those anaesthetic techniques which were performed in at least five different cases both by consultants and by residents. Therefore, data from the following anaesthetic techniques were included: general anaesthesia with oral intubation (T); general anaesthesia with intubation and placement of a CVC (TC); general anaesthesia with intubation, placement of a CVC and arterial line (TCA); general anaesthesia with intubation, placement of a CVC and arterial line and epidural catheter (TCAEC); general anaesthesia with laryngeal mask airway (LMA); spinal anaesthesia (SP); and spinal anaesthesia with laryngeal mask airway (SP/LMA).
A total of 828 surgical cases were performed during the study period; however, 229 cases were excluded from the analysis for one of the following reasons: cases performed using local anaesthesia with (5 cases) or without (29 cases) involvement of the anaesthesia department, patients already intubated before the OR (26 cases), or anaesthesia techniques with fewer than five cases performed both by consultants and by residents (169 cases). This last group included cases with general anaesthesia and placement of arterial line, but no CVC, placement of pulmonary artery catheter, or placement of double lumen tube and cases with fibreoptic intubation. A total of 599 cases were therefore included in the final analysis.
Data collection and time definitions
The anaesthesia preparation and induction times were recorded manually in minutes for each case by independent observers. The observers were medical students trained by one of the authors (M.S.) in recording perioperative process times. The observers were not involved in patient care and did not influence the clinical setting. The data used for this study were a subset from a larger data set for a research project on OR simulation; however, the study design and the planned analysis were finalized before the start of the study. Studying human behaviour always carries the risk that the fact of being observed changes in the behaviour of the subject (so-called Hawthorne effect).12 To minimize this risk, we did not disclose the planned analyses regarding the effect of educational level on preparation and induction times to the residents and consultants. They were only aware of the aforementioned simulation project. We did not record the name of the treating physician, but only the educational level to avoid any possible conflict regarding this data sampling.
Anaesthesia preparation time was defined as the time from the beginning of presence of the anaesthetist to the beginning of anaesthetic induction. In this time, the anaesthetist prepares the case and places the i.v. cannula. For regional techniques, the patient is positioned during this time and the site for any planned regional technique is inspected and prepared. Anaesthetic induction time was defined as the time from the injection of anaesthetic drug to the end of induction, after placement of all catheters, when the patient was ready to be positioned by the surgeon. In the case of regional anaesthesia, the penetration of the skin with the needle was used for the anaesthetic start time and the end of induction was when the anaesthetist released the patient for surgical positioning. In cases where an arterial line was placed by the anaesthetist in the awake patient immediately before induction, the induction time started with the start of placement of the arterial line.
Since anaesthesia preparation, including the placement of i.v. cannulae can be time-consuming and might possibly be performed better by experienced consultants, we analysed two process times: (i) the pure anaesthetic induction time and (ii) the anaesthetic induction time plus the anaesthesia preparation time.
Data analysis
The data were analysed in Microsoft Excel 2002 (Microsoft, Redmond, WA, USA) and SPSS 13.0 (SPSS, Chicago, IL, USA). If not otherwise stated, values are given as mean (SD). Comparisons of the induction times used the Mann–Whitney test. For comparisons with more than two groups, the Kruskal–Wallis test was used. If a significant difference between the groups was present, the groups were tested against each other using the Mann–Whitney test. For multivariate analysis of different predictors, a multiple linear regression model with a stepwise forward approach was used. The data used for the multiple linear regression models with the dependent variable anaesthetic induction time were checked for normal distribution using the normal plots. All above-specified influencing factors were included. Anaesthetic techniques and age groups were included in the multivariate analysis in blocks. To evaluate the appropriateness of the regression model, it was verified that the residuals showed an approximate normal distribution. A P-value of 0.05 or less was considered to be significant.
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The patient characteristics and the distribution among the anaesthesia techniques and the surgical disciplines can be found in Table 1. Of the 599 cases included, 200 were performed by residents. The effect of patient-related factors on induction times are displayed in Table 2. For each technique, only those variables are included for which at least five cases were present for each category. Emergency status and obesity did not have a significant effect on the process time of any anaesthetic technique. Compared with the other two age groups, paediatric patients did not have longer process times for anaesthesia with intubation, but when placement of CVCs and arterial lines was necessary, the paediatric group had significantly longer process times than the other age groups.
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Obesity was defined as a BMI of above 30; for patients under the age of 18, the age-adjusted 90th-percentile was used as upper limit of normal weight. 
Emergency cases were defined as cases which had to be performed within 4 h after first OR registration. Numbers may not add up to 100% due to rounding
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0.05 was considered to be significant. For case numbers in each group, see Table The analyses of process times according to education level are displayed in Figure 1. In Figure 1A, the anaesthetic induction time alone is shown; in Figure 1B, the anaesthetic induction time plus the anaesthesia preparation time is shown. For all techniques except simple intubation, resident cases had longer induction times. However, the differences were small and only reached statistical significance for cases with intubation and CVC insertion, but no arterial line and for cases with using the LMA. Analyses of preparation times for cases of spinal anaesthesia and spinal anaesthesia combined with laryngeal mask airway also revealed statistically significant longer process times for the resident groups. The subgroup analyses (Fig. 2A and B) showed that in many, but not all techniques, the more senior residents performed almost as fast as consultants.
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Using a stepwise forward approach, the predictor with the largest impact on the induction time, the anaesthesia technique, was entered in the multivariate regression model first. Anaesthesia techniques were included in the multivariate analysis as a block. The predictive value of the model (adjusted R2) reached 0.554. That is to say 55.4% of the variability of induction times observed in the study is explained by the different anaesthesia techniques. The influence of the remaining predictors was then recalculated and the information about age group was added next to the model, since it resulted in the best improvement of the predictive value of the model. The resulting adjusted R2 of the model was then 0.575. Finally, the information about the educational level of the anaesthetist further statistically significantly increased the predictive value of the model; however, this increase was small (change in adjusted R2 of model of 0.010). The results of the final multivariate regression model are displayed in Table 3. Information about the ASA, emergency, or obesity status of the patient did not further increase the predictive value of the model and these were not included in the final regression model. The variability of induction times observed in the data set was not influenced by these factors when the abovementioned predictors (anaesthesia technique, age group, and educational level) were already included in the model.
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Discussion |
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There is an ongoing debate regarding the consequences of reduced working hours following the European Work Time Directive which might lead to reduced experience and skills in newly qualified anaesthetists.13 14 The second major threat to resident education is increased pressure from hospital administrators to improve operating process times which could lead to a reduction in practical training of residents, transferring more workload on to the presumably faster anaesthesia consultants. Therefore, several studies have been undertaken to examine the impact of anaesthesia resident training on OR economics. Eappen and colleagues8 examined the effect of the introduction of new anaesthesia residents to the OR using retrospective data from more than 3000 anaesthesia cases performed in a large academic medical centre. The authors examined anaesthetic induction, emergence, and turnover time, and found a small, but statistically significant increase of about 3 min when comparing cases of new anaesthetic residents with cases performed by consultants alone. Davis and colleagues9 found an overall increase of approximately 5 min for teaching cases, but no increase in process times for placement of CVCs or arterial lines in a prospective study of 1558 cases performed in an academic medical centre.
In our study, examining for the first time a range of different anaesthetic techniques, we found increased induction times and anaesthesia preparation time plus induction times for resident cases in certain, but not all anaesthetic techniques. In the multivariate analysis, the effect of resident training was significant but small, explaining only approximately 1% of anaesthetic induction time variability. The reasons for this limited effect might be that resident education implies supervision. The degree to which residents perform their cases manually or intellectually alone might differ, but the consultant is available not only in the case of unexpected complications but also to improve workflow. This can be seen in our data from the TC and TCA cases. In TC cases, the consultants performed much faster than residents but in TCA cases, they did not. Though we did not record every process step independently, we observed that in most resident TCA cases consultants placed the arterial line, whereas the residents intubated the patient and placed the CVC. This division of labour was possible due to the extra manpower provided for education. This is often neglected when the effect of teaching on process times is considered. In contrast, in consultant TCA cases, the placement of the arterial line had to wait until the end of the CVC placement or was done before the CVC placement, but always sequentially, which led to increased induction times compared with consultants TC cases. The results of our study were not profoundly changed when we used the total preincisional time period (anaesthesia preparation time plus induction time) instead of the anaesthetic induction alone; however, there was a trend that the anaesthesia preparation was performed faster by consultants.
Compared with the previous work, an advantage of our study is that we analysed different anaesthetic techniques separately. Therefore, we did not have to rely on a surgical case mix index to estimate case complexity, which might not adequately represent anaesthesia case complexity. Furthermore, we prospectively collected for each patient's risk factors which might be associated with increased process times, including age, obesity, ASA, and emergency status. This adjustment for risk factors diminishes possible bias due to consultants treating more complex cases.
What is the relevance of our findings for practical OR management purpose? Are the observed differences clinically or economically relevant? It has been argued that small increases in process times are unlikely to affect OR efficiency and that there are much more important levers to optimize OR economics than possible reduction in teaching could accomplish.7 15 However, the politics of OR management can be difficult, and discussions between surgeons and anaesthetists about assumed delays and waiting times in the OR because of resident teaching can be very unpleasant for all parties involved.16 In order to establish an objective basis for such discussions, we believe it is important to know the process times of one's own department and the effects of teaching. In most cases, teaching has only little effect on overall anaesthetic workflow efficiency.
Another application of our study results is the fine tuning of planning processes in the OR. Overlapping anaesthetic induction has been proposed as major step to enhance throughput in the OR. The concept is based on the idea of parallel processing and necessitates additional induction rooms. In order to minimize unused OR time, anaesthetic induction is started before finishing the previous surgical case. In two recent studies, it has been shown that overlapping anaesthetic induction can allow to perform additional cases in orthopaedic and general surgical OR suites.17 18 However, this concept will improve OR throughput only under certain circumstances19 and requires additional anaesthetic teams. A major issue for overlapping processes is the necessity to have exact information about the expected duration of anaesthetic induction. Factors that may influence this are important. If anaesthetic induction is completed too early, it results in an undesirable extension of anaesthetic time for the patient and wasted time for the anaesthetist. If the induction is completed too late, the benefit of the overlapping induction is reduced. Our study suggests that the main predictor for anaesthetic induction time is the anaesthetic technique, and for some techniques also young patient age and resident training. Other factors seem to be of minor importance. The overriding importance of anaesthetic technique might seem to be trivial. However, in daily practice, all too often this information regarding the planned anaesthetic technique is not available to the OR manager when planning OR workflow. But, based on our study, we could argue that this is the only anaesthetic- related information needed to define reasonable estimates regarding expected anaesthetic process times. This might help to optimize case sequencing and define the time, when the patients and anaesthetists should be available in the OR.
Some limitations of our study have to be noted. The partition of cases according to the different anaesthetic techniques led in some instances to rather small groups. This reduces the statistical power to detect differences. In most techniques, we saw a trend to shorter process times in consultant cases; however, the difference did not reach statistical significance.
Furthermore, we were not able to include several complex techniques like fibreoptic intubation or cases in which pulmonary artery catheters were placed, since too few cases were performed by residents. Furthermore, we cannot exclude that anaesthetists might have performed differently because they were being observed. However, as far as possible, the anaesthetists were blinded regarding the real reason for data collection and any bias should have applied to both residents and consultants.
It is important to note that changes in the process times are only a part of the economic impact of resident training. Other factors to be noted are the possible increase of critical incidents or complications and the necessity for escalation of care including more invasive monitoring, longer stay in the post-anaesthesia care unit, or unplanned admission to the intensive care unit. A recent study by Posner and Freund20 using data from a quality management database showed that residents in the second year might have a higher incidence of adverse outcomes compared with first or third year residents. Costs for residents are lower than for consultants. On the other hand, consultants are needed in order to ensure proper training13 and for crisis management.21 Even though stochastic simulation models might help to define the best workforce mix, modelling the financial effect of different staffing solutions for the hospital administration remains complex.
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The study was funded by departmental resources.
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During the study period, Dr Schuster was engaged in research collaboration with Dräger Medical, Lübeck, Germany, on operating room workflow optimization. We wish to thank Christiane Buckl and Lisa Wicha for assistance during the study.
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References |
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21 Paoletti X, Marty J. Consequences of running more operating theatres than anaesthetists to staff them: a stochastic simulation study. Br J Anaesth (2007) 98:462–9.
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