Safer Surgery part 41 ppsx

Stress Measurement Our model comprises stress measurement by continuous ergospirometry, analyses of cortisol and alpha-amylase in saliva and a brief post-stress questionnaire.. Analysis

exposed to highly standardized conditions However, if complications occur, the candidates are entitled to leave the algorithms for RSI classic and RSI controlled and act as they would do in clinical reality

Observation of unsafe Actions and Critical events

The observation of unsafe actions and critical events is well established for human factor research using simulator environments (Gaba 1992, Gaba and Howard

2002, Howard et al 2003, Overly et al 2007) In this study we aim to evaluate a clinical guideline, applied to paediatric simulation; we are venturing into virtually unexplored territory We record unsafe actions and critical events using a checklist

Figure 22.2 Flow chart for simulated scenario and stress measurement

Time

[min]

-10 1st saliva sample (pre-stress value)

Start of ergospirometry

5 min rest Briefing of scenario

Pre-oxygenation

+10 2nd saliva sample (first stress value)

3 min rest End of ergospirometry +20 3rd saliva sample (second stress value)

+40

4th saliva sample (post-stress value)

Questionnaire End of trial

Simulator-Based Evaluation of Clinical Guidelines in Acute Medicine 375 These are defined as follows: oxygen saturation (SpO2) < 90 percent, heart rate <

80 beats per min, forced mask ventilation with airway pressure (PAW) > 20 cm H2O, esophageal or endobronchial intubation, and more than one intubation attempt

Stress Measurement

Our model comprises stress measurement by continuous ergospirometry, analyses

of cortisol and alpha-amylase in saliva and a brief post-stress questionnaire

Ergospirometry

We measure cardiorespiratory stress by ergospirometry, using a Cortex Metamax 3

B™ (Cortex Biophysik) (see Figures 22.3 and 22.4) This portable ergospirometry device with face mask comes combined with a Polar T 41™ (Polar Electro) heart rate meter The following parameters are collected: respiratory rate (RR), minute volume (MV), oxygen consumption (VO2), carbon dioxide production (VCO2) and heart rate (HR) VO2 measurement is performed at STPD-conditions (Standard Temperature, Pressure, Dry)

Figure 22.3 MetaMax 3B ™

The portability of the ergospirometry device enables measurement of cardiorespiratory strain or stress under realistic working conditions with only minimal discomfort due to face mask, tubing and device It allows virtually full range of motion for the candidate

Cortex Metamax 3B™ uses a breath-by-breath technique During ergospirometry, the candidate wears a breathing mask strapped to his face, breathing through a turbine-equipped volume sensor with a range of 0.05 to 20 l/sec, a sensitivity of 7

ml, and a precision of 2 percent The oxygen analyser contains an electrochemical cell, allowing a measurement range from 0 to 35 percent The infrared carbon dioxide sensor measures values from 0 to 13 percent (accuracy 0.1 Vol percent) Both sensors have a measurement kinetic of 100 ms

Figure 22.4 Candidate with mobile and wireless ergospirometry device

attached

Simulator-Based Evaluation of Clinical Guidelines in Acute Medicine 377

Ergospirometry data are wirelessly transmitted via telemetry with a maximum range of 1000 m All parameters are continuously visualized and recorded with Windows™-based software (MetaSoft 3.3™, Cortex Biophysik) which allows for processing of the ergospirometry data and which is also compatible with other data-processing software such as Windows Excel™

Before each trial (scenario), one-point calibration is performed before the ergospirometry device is attached to the candidates They are then asked to sit in

a comfortable arm chair in a shaded room for five minutes to relax, to get used

to the face mask and to reach their individual cardiorespiratory baseline values

on rest This procedure is repeated after the scenario The candidates are further advised to talk as little as possible in order to minimize any potential impact on spirometry This requirement is quite easy to meet as both RSI procedures are highly standardized

After this tuning phase, the candidate is informed about the scenario and the anaesthesia induction technique to be performed (RSI classic or RSI controlled) Then the scenario starts Finally ergospirometry and recording are discontinued after the five-minute rest after the scenario

Analysis of Cortisol and Alpha-amylase in Saliva

The second column of stress measurement consists of analyses of cortisol and alpha-amylase in saliva These have been proved to be valid and reliable markers

of adrenergic stress response in previous studies (Nater et al 2006, Müller 2007, Yamaguchi et al 2006)

Cortisol Physical and mental stress is a stimulus for increased cortisol secretion

Cortisol levels can be determined either in serum, plasma or saliva, the latter reflecting its biologically effective fraction (Kirschbaum and Hellhammer 1994) Highest concentrations in saliva are seen approximately 20 minutes after the beginning of exposure to stress (Kirschbaum et al 1995b) (see Figure 22.5)

In addition, cortisol follows a circadian rhythm with highest concentrations in the morning and lowest in the afternoon (Table 22.1) Hence we execute all trials

in the afternoon between 2 and 6 pm

Gender also has an impact on cortisol levels During the follicle phase of the female cycle, cortisol values become significantly lower (Kirschbaum et al 1995a) To rule out any impact of the female cycle on cortisol levels, we restricted the study to male candidates only Furthermore, chronic nicotine consumption (e.g., inhalation of cigarette smoke) increases basal cortisol levels but diminishes stress response values whereas age does not have an influence on cortisol secretion (Kirschbaum and Hellhammer 1994)

Alpha-amylase Apart from olfactory and gustatory trigger vegetative (ß2-adrenergic) stimuli provide the main pathway of secretion of alpha-amylase during acute stress response (Chatterton et al 1996, Nater et al 2006) This

relation has been validated with volunteers undergoing the Trier Social Stress Test (TSST) This study showed that stress induced increase of salivary alpha-amylase was related to heart rate, blood pressure and plasma-noradrenaline levels (Rohleder et al 2004, Nater et al 2006) Furthermore, van Stegeren et al (2006) could demonstrate that secretion of salivary alpha-amylase is suppressed by

Figure 22.5 Salivary cortisol levels during stress (Trier Social Stress Test,

TSST) and rest conditions (nater et al 2006)

Reference intervals

Plasma

a.m. 62- 195 µg/L (171- 536 nmol/L)

Saliva

Source: Methods Sheet Cortisol, version 10, Roche Diagnostics (2005)

Table 22.1 Reference intervals for plasma and salivary cortisol

Simulator-Based Evaluation of Clinical Guidelines in Acute Medicine 379

non-selective beta-blocker propanolol However, it remains unknown whether salivary alpha-amylase directly reflects noradrenaline release and would hence allow the replacement of the invasive measurement of plasma noradrenaline Peaks of salivary alpha-amylase are measured approximately 10 to 20 minutes after beginning of stress input and returns rapidly to baseline values (Nater and Rohleder 2005) (Figure 22.6)

Lowest salivary concentrations of alpha-amylase are found in the morning immediately after getting up and highest in the evening (Nater et al 2007b) There are no well-defined reference intervals for salivary alpha-amylase but as we are interested in changes from baseline values only, this should not affect measurements and data interpretation Salivary flow rate does not have an impact on alpha-amylase concentration in saliva and hence need not be calculated when cotton-wool Salivettes™ are used (Rohleder et al 2006) In summary, salivary cortisol and alpha-amylase are valid and reliable parameters to determine adrenergic stress response Saliva analyses are non-invasive and relatively easy to perform which make them popular for proband studies However, their slow kinetics do not allow

to measure rapid changes but rather peak levels of stress

Saliva Sampling The candidates are advised not to eat, drink or smoke two hours

before beginning of the study For each trial (simulated scenario), we obtain four saliva samples: –10, +10, +20 and +40 minutes from the beginning of the scenario,

Figure 22.6 Salivary alpha-amylase and norepinephrine (noradrenaline) in

response to stress (Trier Social Stress Test, TSST) (Rohleder et

al 2004)

representing pre-stress, stress (two samples), and post-stress conditions (Figure 22.2) As cortisol and alpha-amylase have slightly different peak times we obtain two samples at 10 and 20 minutes

To gain saliva samples, the candidates have to rinse their mouth with water twice before they chew on a cotton roll (Salivette™, Sarstedt) for two minutes The loaded Salivettes™ are centrifuged at 3000 rpm for five minutes and then immediately cooled to 5°C All analyses are performed within 24 hours of collection

at the Department for Clinical Chemistry at University Medical Centre Göttingen According to previous studies, centrifuged salivary cortisol and alpha-amylase samples are stable at 5–8°C for up to five days (Kirschbaum and Hellhammer

1994, Nater forthcoming) Alpha-amylase in saliva is analysed with a Cobas Integra 800™ kit (Roche Diagnostics) which is based on an enzymatic extinction test Salivary cortisol is determined with an immunoassay using a Cobas Modular Analytics E 170™ system (Roche Diagnostics)

Post-stress Questionnaire Most simulator-based studies include some kind of

self-assessment Though much debated for its scientific validity, this methodology may help to identify individually perceived attitudes and behaviour (Gaba et al 1998, Howard et al 2003) In our study we compare perceived stress and safety levels with objectively measured values After having obtained the fourth saliva sample, all candidates are asked to fill in a brief post-stress questionnaire which consists of two ratings and one open question: ‘How was your perceived subjective stress level (scale 1–10)? How safe did you feel with the used RSI technique (1–10)? Which unsafe actions or critical events did you notice during the scenario?’

Statistical Analysis All data from demography, observation, ergospirometry,

saliva analyses and self-assessment are put into purpose-designed data templates (Excel™) All nine stress values obtained from ergospirometry, saliva analyses and self-assessment, such as respiratory rate, respiratory minute volume, oxygen consumption, carbon dioxide production, heart rate, salivary cortisol and alpha-amylase, stress and safety perception) are defined as dependent variables (DV) These DV will be tested for their dependence on method (RSI technique), professional experience (years in anaesthesiology) and interaction of both We also aim to correlate stress (measurements and self-perception) with unsafe actions and critical incidents (observation) as well as the three methods of stress measurement (ergospirometry, salivary analyses and perception) with each other Statistical analyses will be performed with SPSS Version 14 P-values lower than 0.05 will

be regarded as significant

Preliminary Results

At time of writing, our pilot study has just started So far the key features of the model work reliably, including function of the infant simulator with its standardized

Simulator-Based Evaluation of Clinical Guidelines in Acute Medicine 381

scenario and trends, observation of unsafe actions and critical incidents, mobile ergospirometry, saliva analyses and self-assessment (questionnaire) Marked physical and mental stress has been induced hitherto in all candidates in the course

of the scenarios, indicating an adequate level of suspension of disbelief This is regarded to be an essential pre-requisite of simulator-based training, assessment and research So far the scenarios have lasted about four to seven minutes The main increase in respiratory rate, respiratory minute volume, oxygen consumption, carbon dioxide production and heart rate occur towards intubation of the infant mannequin Salivary cortisol and alpha-amylase peaks are detected at 10 or 20 minutes and return towards baseline at 40 minutes after start of the scenario

Summary

Our model of a simulator-based evaluation of clinical guidelines is methodologically feasible, using a combination of observation, stress measurement (ergospirometry and salivary cortisol and alpha-amylase) and self-assessment Our preliminary data suggest that this evaluation method could endorse future developments of guidelines in acute medicine in order to produce less stress, less unsafe actions and critical incidents, and subsequently increase patient safety

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