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Surgical and minimally-invasive procedures, including cardiac and radiological, have high-stake patient outcomes. Working pressures, altering shift rotas, and ever-increasing demands have led to worsening sleep patterns for surgeons and allied professionals. Sleep deprivation alone has harmful consequences in relation to clinical outcomes and the physical and mental health of the surgeon, and to offset fatigue, some surgeons use legal stimulants such as caffeine and energy drinks. This stimulant use, however, may come at the cost of negative effects on cognitive and physical function. We aimed to explore evidence behind the use of caffeine, and its consequences on technical performance and clinical outcomes.
Haluza et al showed that following two consecutive 12-hour night shifts, clinical staff would need at least three days off work to avoid prolonged fatigue.
However, with service demands and problems with understaffing this is difficult to achieve. Some surgeons regularly use stimulants such as caffeine and “energy drinks” to offset fatigue and the concentration problems caused by poor or inadequate sleep.
Commercial stimulants play a significant role in the workplace, with coffee being one of the most commonly consumed beverages worldwide (Fig. 1).
Caffeine’s function as a psychostimulant has been recognised in The Queensland Health Fatigue Management Strategy, which states that the use of 400 mg caffeine induces wakefulness.
Caffeine, however, does not only affect the state of wakefulness, but can also influence psychomotor performance. High doses can impair dexterity, whereas moderate doses can reduce the time taken to complete motor tasks,
and it is difficult to achieve the balance of caffeine intake that works entirely in one’s favour without experiencing unwanted side effects. Some surgeons individually consume varying quantities of caffeine to combat inadequate sleep and fatigue, and there is little uniformity in their intake levels. Besides, caffeine, most commonly in the form of coffee and tea, is undoubtedly enjoyed independent of any stimulant effect.
Fig. 1Coffee beans contain a high level of caffeine.
Significant evidence exists on the effects of coffee on wakefulness in other workers, such as truck-drivers, and studies have shown that after coffee, night-time performance is similar to that of daytime in 75%.
These data may be extrapolated to provide information regarding the impact of caffeine on a surgeon’s ability to work effectively whilst sleep deprived.
Over the last two decades the use of an increasing range of caffeinated energy drinks has emerged.
These drinks can deliver caffeine in a concentrated form and are produced to taste attractive, but they can easily add to caffeine consumption, used alone or in addition to other caffeine intake. They may also contain other stimulants such as taurine and there are health concerns about them, for example, related to the cardiovascular, neurological, and renal systems.
Caffeine is also available in other forms with various uses, and tablets (designed to deliver it at concentrated levels) to increase wakefulness have doses of up to 100 mg/tablet. At levels of 180 mg/capsule, caffeine is found in some weight loss, “fat burner” products, and it sometimes forms part of the ingredients of commonly used cold and flu preparations at amounts between 25 mg and 50 mg/dose.
Caffeine is effective for inducing wakefulness and restoring cognitive performance in sleep-deprived individuals
Caffeine is the most widely consumed neuro-stimulant in the world, and caffeinated drinks are consumed in a quantity second only to water.
Three mechanisms of action are suggested for caffeine, with the neuro-cognitive effects most widely associated with its antagonistic action on adenosine. By inhibiting adenosine, it indirectly increases activity in the locus coeruleus, basal forebrain, and hypothalamus, and in turn induces wakefulness. The critical centre of activity responsible for this effect has been proposed to be the brainstem via the basal forebrain.
Most studies on its effects look at individuals with controlled sleep deprivation followed by the administration of caffeine. Subjective and objective wakefulness are then measured. Study aims have been to induce wakefulness to that of rested individuals,
These effects will vary amongst individuals, with key influences including the amount of sleep deprivation, the delivery method/dose of caffeine, and numerous metabolic factors.
Multiple studies demonstrate that low doses (from 0.18 mg/kg) are sufficient to achieve these benefits, and cognitive responses often follow a flat dose-response curve thereafter.
These qualities are desirable in a physically demanding role, but translating these effects into the surgical or interventional field would have limitations, as fine motor function can be diminished by caffeine. Whilst refined motor control may not be important in many sports, it is to the surgeon.
Caffeine’s negative effect on dexterity is dose-dependent. A moderate intake of 2.5 mg/kg may induce fine hand tremor, while 5 mg/kg leads to worsened dexterity.
These effects, however, could be partially mitigated through tolerance, so caffeine has a mixed effect on psychomotor performance and may increase speed at the expense of dexterity.
Aggarwal et al studied the effects of sleep deprivation and caffeine on the ability of subjects to perform tasks with a laparoscopic simulator. The performance parameters measured included time taken to complete the task, economy of movement, and reaction time.
Caffeine given to sleep-deprived individuals successfully restored the time taken to complete the task to the baseline value (measured whilst rested), but had no significant effect on the higher error rate of sleep-deprived individuals.
This may lead sleep-deprived individuals consuming caffeine to have false confidence to perform procedures safely.
Moderate-to-high doses of caffeine can lead to deleterious effects on function and wellbeing
Caffeine is used worldwide, and in most countries there are few regulations as to how it is advertised, marketed, and sold. Doses of more than 4 mg/kg often lead to nervousness, irritability, anxiety, insomnia, tremor, tachycardia, and palpitations.
One can receive a high dose by consuming anything over a single energy drink or by combining energy drinks with coffee or tea. Using other preparations containing caffeine, for example, some cold remedies and weight-loss products, may lead to the inadvertent ingestion of high levels, especially if combined with caffeine-containing drinks.
Energy drinks have been shown to have a higher risk of adverse side effects when with more traditional methods of caffeine consumption.
Their use has been noted to have a negative association with wellbeing and has been shown to increase damaging health behaviours such as smoking and increased alcohol consumption.
Regular users of caffeine may develop a dependence that can result in withdrawal symptoms if the intake is lowered or stopped; cognitive performance has been posited to be adversely affected by acute caffeine withdrawal.
In these cases, where apparent, caffeine can be used to prevent further deterioration. This method of amelioration is described by the withdrawal-symptom reversal theory.
Therefore there is a wide variability in serum peak times and in the metabolic removal of caffeine. The daily limit of intake should be <400 mg. Serious side effects are apparent at 1 g intake/day.
The effect of caffeine extends beyond that of neuro-stimulation and includes the inhibition of phosphodiesterase enzymes to increase cyclic adenosine monophosphate (cAMP), the mobilisation of intracellular calcium, and antagonism of benzodiazepine receptors.
Institute of Medicine (US) Committee on Military Nutrition Research. Pharmacology of caffeine - caffeine for the sustainment of mental task performance. National Academies Press (US), 2001. Available from URL: https://www.ncbi.nlm.nih.gov/books/NBK223808/ (last accessed 23 February 2023).
At very high doses it is these mechanisms that have been proposed to be the cause of its toxic and rarely fatal effects.
Optimal consumption is difficult to predict due to the wide range of the plasma mean half-life of caffeine and the varying time to reach peak serum levels. The half-life depends on variations amongst individuals and factors that affect metabolism, for example, smoking, body mass index (BMI), and oral contraceptives.
Institute of Medicine (US) Committee on Military Nutrition Research. Pharmacology of caffeine - caffeine for the sustainment of mental task performance. National Academies Press (US), 2001. Available from URL: https://www.ncbi.nlm.nih.gov/books/NBK223808/ (last accessed 23 February 2023).
To receive the optimal effects and avoid the unwanted and potentially dangerous ones, surgeons and colleagues who undertake minimally-invasive procedures should aim to monitor their caffeine intake. There is a multitude of considerations to achieve this, for example, the extent of sleep deprivation, delivery method/dose of caffeine, and metabolic, health, and environmental factors.
The varying amounts of caffeine in different brands of coffee, tea, and energy drinks also make it difficult to accurately estimate the caffeine content that is consumed.
Caffeine may have a role in restoring a degree of cognitive function to that of rested levels, but there is little evidence to support its regular use to improve a clinician’s performance. Regular caffeine consumption is concerning due to its long-term effects on the user’s health and wellbeing. Caffeine tolerance may also occur, leading to overall increased consumption, and there is also a risk of withdrawal symptoms. The outcomes of surgical and invasive procedures may suffer, as evidence shows that caffeine quickens surgical tasks but diminishes dexterity, and has no positive impact on error rate.
Caffeine may be perceived as attractive in a competitive environment like surgery where the expectations of patients, health organisations, and “self” are high. Possible risks to the caffeine consumer may add to the already high rates of anxiety, depression, and burnout amongst clinicians,
Institute of Medicine (US) Committee on Military Nutrition Research. Pharmacology of caffeine - caffeine for the sustainment of mental task performance. National Academies Press (US), 2001. Available from URL: https://www.ncbi.nlm.nih.gov/books/NBK223808/ (last accessed 23 February 2023).
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