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Original Articles – Regional

An ergonomic task analysis of spinal anaesthesia

Ajmal, Muhammada; Power, Susanb; Smith, Timc; Shorten, George Da

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European Journal of Anaesthesiology: December 2009 - Volume 26 - Issue 12 - p 1037-1042
doi: 10.1097/EJA.0b013e3283317dc9



Ergonomics is the study of physical interaction between humans and their working environment and ‘human factors engineering’ is the study of the underlying psychological (cognitive) element responsible for such interaction. Analysis of the ‘interactive triangle’ which describes everyday vocational activity has demonstrated that two components of this triangle (body mechanics and nature of work) are almost similar across a group of workers performing a task. However, the third component, ‘work habits’, is characterized by great interindividual variation. In this context, the goal of ergonomics is to create a uniform working style, which ensures physical and mental well being in a specific group of workers.

The application of ergonomics is essential in the healthcare industry, in particular to those who perform physically and technically difficult procedures [1–5]. This includes anaesthetists who perform procedures such as spinal anaesthesia particularly on patients undergoing lower limb trauma surgery [6]. Because of painful limited mobility, these patients cannot respond to anaesthetists' demands to compensate deficiencies in the optimal posture and position required for successful advancement of a needle close to their spinal cord [7]. Only a few studies [8,9] have been performed to evaluate postural behaviour of anaesthetists and are limited to the procedure ‘laryngoscopy’ in a simulated environment. Some methodologies [10,11] have also been described to assess anaesthetists' work habits. How anaesthetists perform their routine procedures in terms of ergonomics is still open to question. In this study, we selected spinal anaesthesia for examination because it entails several elements that are vulnerable to poor ergonomics performance; namely, the safety and efficacy of the procedure depends on both visual and haptic information, the arrangement of several physical components requires the attention of the operator during the procedure and an effective team of at least three healthcare workers is required. The principal objective of this study was to characterize the performance of spinal anaesthesia in a busy acute hospital setting using ergonomic task analysis.


With approval of the Clinical Research Ethics Committee for Cork Teaching Hospitals, Cork, Ireland, and having obtained written informed consent from each participating patient or anaesthetist, a prospective observational study was performed in a busy orthopaedic operating room of an acute care hospital setting. In this setting, spinal anaesthesia is frequently performed on patients undergoing lower limb trauma surgery.

Task analysis has been used previously in studying critical incidences in anaesthesia [6]. In ergonomic task analysis of spinal anaesthesia, intervention was through a data capture sheet and a questionnaire. The sheet was based on basic ergonomic principles and professional standards applicable to the practice of spinal anaesthesia [1,12]. The sheet was developed using a series of multidisciplinary (anaesthetists, occupational health physician and ergonomist) discussions. Patient, operator and heterogeneous environmental factors were the domains of assessment parameters included in the sheet. For example, height and distance of skin puncture (relative to the operator) are the patient factors studied to evaluate the impact on the ergonomic performance. The position of the operator (sitting or standing) and the vertical height of the dominant shoulder tip (side on which the spinal needle was held for the spinal procedure) in neutral posture (relative to the skin puncture point) are examples of the operator factors that will affect the performance. The operator's sequence of performing the component steps (opening of the instrument kit, positioning of the patient, gown and gloves, drawing of the drugs into syringes, sterilization of the skin and draping the patient and identifying the skin puncture point) of the procedure was also observed. Heterogeneous environmental factors included all the factors other than patient and operator factors which could have affected the ergonomic performance of the procedure (e.g. ambient temperature, intensity of light during the procedure, training of assistants who help in positioning the patients, position of the ‘patient monitor’ screen and impediment of operators due to obstacles in their vicinity). A preliminary sheet was piloted on five procedures. This sheet was then reviewed and modified using input from all three disciplines. For instance, handedness of the operator was not included in the preliminary version of sheet and was added to the final. The final version of this sheet was then applied to 24 proposed spinal anaesthesia procedures to acquire data. All the applicable assessment parameters were included in the data capture sheet.

Twenty-four anaesthetists from all employment grades (consultants, senior registrars, specialist registrars and basic trainees) with variable estimated previous spinal anaesthesia experience and 24 patients of various ASA anaesthesia risk grades, those who were otherwise scheduled to receive spinal anaesthesia, were recruited for this study. The recruitment started in December 2008 and ended in April 2009. During this period, the equipment, patient processing and staff active in this operating theatre were substantially similar. The patients' recruitment was not consecutive but depended on the presence of an anaesthetist who had not previously participated and the availability of the dedicated investigator. Each of the 24 anaesthetists was directly observed while performing spinal anaesthesia in a dedicated orthopaedic trauma operating theatre in a routine environment by a single investigator. Patients were also observed for any kind of distress present prior to or at commencement of positioning. The period of observation started immediately before commencement of positioning the patient and ended upon completion of intrathecal injection of local anaesthetic (or takeover by a supervising anaesthetist). Photographs and video clips were used to substantiate direct observations, a measuring tape was used to measure length and height and a central control system was used to record ambient temperature [13]. Microsoft Office Excel 2003 was used to calculate the mean ± SD (range).

The range of rotational movements were an estimate of the investigator's direct observations substantiated by photographs and video clips [14,15]. The training level of assistants (specific for assisting in spinals) who helped in positioning a patient for spinal anaesthesia was ascertained by direct questioning.

A questionnaire was distributed at the end of each procedure and was applied to acquire demographics and assess operators' sequence of performing component steps of the procedure. The purpose was to compare the claimed and observed sequence of performance. For instance, ‘Was operator observed positioning the patient prior to putting on sterilized gown and gloves as claimed by the operator in the response to questionnaire’? This was a pilot study; the reliability of the questionnaire was not separately assessed.


Twenty-four anaesthetists (operators), of whom four were consultants, five senior registrars, nine specialist registrars and six basic specialist trainees, were observed performing spinal anaesthesia in an orthopaedic trauma operating room. Lifetime-estimated spinal anaesthesia experience of these anaesthetists was 10, 50, 100 and 150 procedures for one, four, one and 18 anaesthetists, respectively. Eleven male and 13 female patients age 74.6 ± 14 years (38–95) [mean ± SD (range)] were recruited. Of the 24 recruited patients, six were graded ASA-I, 14 ASA-II and four as ASA-III anaesthesia risk status and required surgery on their hip, femur, ankle and knee in 19, two, two and one patient, respectively for treatment of fractures.

In the ergonomic performance of observed spinal anaesthesia procedures, the interaction between the patient, operator and environmental factors was such that two operators were unsuccessful in performing the lumbar puncture and the procedure was completed by a senior colleague. Of the 22 procedures completed by the initial operator, one was converted to general anaesthesia due to inadequacy of the block achieved. The position of 10 patients needed to be readjusted due to involuntary withdrawal at the application of antiseptic solution to their backs. On direct observation, 10 out of 24 operators who claimed otherwise in the questionnaire, gowned and gloved prior to positioning and patients were positioned only by the assistants. Six anaesthetists changed their position from sitting to standing and then sitting again at least twice during the procedure. Sixteen anaesthetists demonstrated an excessive degree (estimated >90°) of lumbar, thoracic or cervical spine rotation at some point during the procedure. Eleven anaesthetists demonstrated a marked degree of flexion (estimated ≥60°) of the lumbar, thoracic or cervical spine at some point during the procedure. Ten operators performed with lateral shoulder tilt. At the point of skin puncture, the ratio of vertical height of the dominant shoulder tip of anaesthetists in neutral posture to vertical height of the skin puncture point varied greatly [1.26 ± 0.13 (1.02–1.74), mean ± SD (range)]. Seven anaesthetists brought their dominant hand to their nondominant side (≥180°) to pick up required instruments during the procedure. All operators filled at least one syringe with local anaesthetic by pointing needles towards assistants who held ampoules containing local anaesthetic. Nine operators did not continuously monitor patients' vital parameters while performing the procedure. The individual patient, operator and environmental factors are described in the following sections.

Patient factors

None of the 24 patients studied had an obvious spinal deformity or was in obvious distress before positioning. Twenty-two patients were placed in the lateral and two in the sitting position to facilitate administration of spinal anaesthesia. Fifteen out of the 22 patients who were placed in the lateral position had their operative (injured) side up (nondependent) and seven had their operative side down (dependent). Six of the 24 patients were in mild to moderate distress during positioning to facilitate spinal anaesthesia. Considering the posture of the posterior aspect of patients' backs in the lateral position, the angle between the coronal and the horizontal plane was more than 90° (i.e. tilted away from the operator) in 10 cases, less than 90° (i.e. tilted towards the operator) in one case and approximately 90° (neutral) in 11 cases during the procedure. Patients were positioned on the operating table such that the horizontal distance of the skin puncture point to the vertical plane that contained the edge of the operating table and vertical height of the patient's skin puncture point was 12.3 ± 9.3 cm (2–41) and 94 ± 11 cm (47–105) [mean ± SD (range)], respectively. Patient-related variables are summarized in Table 1.

Table 1
Table 1:
Patient characteristics and position (n = 24)

Operator factors

No anaesthetist marked the patient's skin to demonstrate the position of anatomical landmarks. All anaesthetists palpated the patients' back to localize an interspinous space before needle insertion and nine out of 24 operators palpated the nondependent iliac crest to identify the level for needle insertion. Seven of the 24 anaesthetists positioned the instrument tray on their nondominant side prior to commencing the procedure. Six of the 22 anaesthetists who started the procedure in a sitting position changed their position to standing, then sitting and then standing again to complete the procedure (i.e. lumber puncture was done when sitting, and intrathecal injection was completed when standing, and a dressing on the spinal puncture wound was applied when sitting and the patient's drape was removed when standing or the first attempt for lumber puncture was done when sitting and the second when standing). Three anaesthetists did not adhere to standard aseptic practice for the procedure and used sterilized gloves but not gowns; two of these operators were consultants (clinical experience ≥10 years) and one a registrar (5-year clinical experience). Data collected by the application of the questionnaire suggested that all the operators followed a specific predefined order (sequence) while performing the component steps of the procedure. Eighteen operators seemed to follow this order with a specific motive (rationale) and six as a matter of routine. The vertical height of the anaesthetist's dominant shoulder tip in neutral before spinal needle insertion was 118 ± 17.4 cm (50–155) [mean ± SD (range)]. Operator-related parameters are summarized in Table 2.

Table 2
Table 2:
Operator factors (n = 24)

Environmental factors

All 24 patients were directly exposed to an ambient (room) temperature of 17.5 ± 1 °C (16–20.7) [mean ± SD (range)] for at least a part of the procedure. The backs of all these patients were cleaned with antiseptic solution at ambient temperature.

Nine of 24 anaesthetists were positioned such that the patient monitor screen (DATEX Ohmeda AS/3, Wisconsin, USA; noninvasive blood pressure, SpO2 and ECG) was not visible to them during the procedure. None of the operators used a dedicated operating light for the procedure. Seventeen of 24 anaesthetists had assistance available from another anaesthetist during the procedure. All anaesthetists had dedicated nursing and porter assistance available for positioning the patient. None of these assistants were specifically trained in positioning patients for this procedure. The movements of four out of 24 operators were impeded during the procedure due to physical obstacles in their vicinity (e.g. operating table attachments). None of the anaesthetists had a comprehensive (all in one) procedure kit available to them.


It appears that ergonomic performance of anaesthetists was clearly suboptimal while performing spinal anaesthesia on patients undergoing lower limb trauma surgery. Although there was a display of tense body postures, extreme degree of rotational movements of the spine, overreaching for objects, suboptimal arrangement of procedural trays, lack of consistency in the ‘set up’ used and conducting the procedure in an uncomfortable range of temperature and light intensity, but solely the operators cannot be blamed for this. Patient and environmental factors played a significant role in this underperformance. However, the operators who took over at the failure of initial operators were successful just by adjusting the height and distance of skin puncture relative to the operator and improving the posture of the patient's back in the lateral position. Although many environmental factors are not under the immediate control of operators, improvements will not come unless end-users (operators) are conscious about these [16].

Musculoskeletal disorders are a significant occupational hazard for healthcare providers, and ergonomic problems faced by surgical teams have recently increased due to advances in technology (e.g. video endoscopic surgery) [17]. Evidence exists that even simple surgical procedures have associated occupational hazards if ergonomic principles are overlooked [18].

There is a paucity of published data on ergonomics applied to anaesthetic practice and none that examines patient, operator and environmental factors (and their interaction) simultaneously. Matthews et al. [9] in their study ‘Body posture during simulated tracheal intubation’ and Walker [8] in ‘Posture used by anaesthetists during laryngoscopy’ analysed the postural behaviour of anaesthetists in a simulated environment. In these two identical simulated studies, authors linked the bad posture with immediate outcome of the procedure and its aesthetic appreciation. Long-term physical consequences such as injury to the operator's back remained unmentioned. Further to this, the authors concluded that postures of novices were bad when compared with experienced anaesthetists, and ‘formal instructions’ were advocated as a remedial measure. However, it is unclear whether good performance by the experienced group resulted from formal instructions or developed due to progressive experience [19]. We elected to observe procedures in a ‘real world’ clinical setting on the assumptions that certain additional obstacles to optimal ergonomic performance would apply and any deficiencies identified would have greater external validity. We did not take immediate success as an outcome measure of the performance. We believe that immediate success at the cost of a long-term consequence to operators is not a fair deal [17,18]. Contrary to the above-mentioned studies, in fact, our results highlight the real need for formal instructions in a scenario in which only experience does not seem to work. A multidisciplinary team of experts (anaesthetists, occupational health physician and ergonomist) participated in both the design of the assessment sheet and interpretation of the data.

This study has certain limitations. For example, participating anaesthetists were aware of the purpose of the study and may have altered their behaviour as a result. We believe that the effect of this ‘nonblinding’ is that our results may underestimate the true extent of ergonomic underperformance. No attempt was made to ‘standardize’ the preparation for the procedure in order to isolate those factors that were within the immediate control of the operator. We did not use any sophisticated devices to measure the range of body movements. The study was performed in a single clinical location (nonmulticentral) and all the participants had recent experience of training or practising in the same hospital. This raises the possibility that at least some of the deficiencies observed are specific to this setting. In our opinion, these results justify performance of a large multicentre study of ergonomic performance in a variety of different settings not only on spinal but also on other anaesthesia procedures. In this preliminary study, no attempt has been made to differentiate ‘cognitive (human factors)’ and ‘physical (ergonomic)’ performance, a hierarchical task analysis for spinal anaesthesia or to apply a specialized valid ‘human factor’ tool such as human error identification or the Systematic Human Error Reduction and Prediction Approach [20–22]. We undertook to determine whether common ergonomic deficiencies exist for a representative anaesthetic procedure and setting. These and other tools will be of greatest value in addressing specific elements of the deficiencies we have identified.

Our findings indicate that spinal anaesthesia is usually performed (at least in the setting described) without application of basic ergonomic principles. We believe that this finding, if confirmed, justifies inclusion of formal instruction in ergonomic principles as part of basic anaesthesia training. This training would improve performance of anaesthetic procedures such as spinal anaesthesia [23]. Educating medical practitioners on the correct method of patient handling would decrease the incidence of soft tissue injury to the practitioner. Establishing a standardized ‘set up’ and arrangement of procedural trays would also tend to decrease human error. Those who carry out such procedures would do so using a consistent approach based on simple ergonomic principles. Hospital administrators should provide specific training to all healthcare workers who assist with spinal anaesthetic and other surgical and medical procedures. All staff assisting in the procedures should have an up-to-date patient-handling course. Equipment should be positioned so that the operator can easily access it, that is, clearly visualize the patient monitors at all times. Ultimately, it is the responsibility of the operator to ensure that the procedure is performed safely and effectively.


In the setting described, there seems to be no agreement among anaesthetists on the ergonomic performance of spinal anaesthesia at least on patients undergoing lower limb trauma surgery. The ergonomic performance of operators was clearly suboptimal in the majority of the procedures and substantial deficiencies were observed in the performance of anaesthetists of all levels of experience. Other than patient and operator factors, environmental factors contributed significantly to this underperformance. This underrecognized problem should be further investigated not only in spinal but also in other anaesthesia procedures. After evaluation, the problem should be addressed through formal instructions in basic anaesthesia training and improvements in the settings of anaesthesia and operating rooms.


The authors extend their thanks to the nurses: Paula Fleming, Esther Keame, Gilish O' Shea; porters: Patrick McCarthy, Frank O'Donovan, Sean Hennessy, Dennis Moss, Finbar Buckley, Kevin O'Flynn, Jason Sexton, orthopaedic surgeons: Dr A. Mitra, Dr M. Maqbool working in Operating Theatre 2 at Cork University Hospital, Ireland; and the patients who participated for their help and cooperation in conducting this study.

There are no conflicts of interest in this study.


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ergonomic task analysis; performance of anaesthetists; spinal anaesthesia

© 2009 European Society of Anaesthesiology