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Does adding milk to tea delay gastric emptying?
British Journal of Anaesthesia 112 (1): 66–71 (2014) Advance Access publication 19 August 2013 . doi:10.1093/bja/aet261
CLINICAL PRACTICE
Does adding milk to tea delay gastric emptying? S. Hillyard1,2*, S. Cowman 2, R. Ramasundaram2, P. T. Seed 3 and G. O’Sullivan 2 1
Department of Anaesthesia, Rockingham General Hospital, Elanora Drive, Rockingham, WA 6168, Australia Department of Anaesthesia, Guy’s and St Thomas’ NHS Foundation Trust, St Thomas’ Hospital, Westminster Bridge Rd, London SE1 7EH, UK 3 Division of Women’s Health, King’s College London, Women’s Health Academic Centre, King’s Health Partners, Westminster Bridge Rd, London SE1 7EH, UK 2
* Corresponding author. E-mail: [email protected]
Editor’s key points † Current preoperative fasting guidelines assume that gastric emptying is delayed after ingestion of fluids containing milk. † This study in healthy adults compared gastric emptying after drinking tea with or without milk. † There was no difference in gastric emptying times determined by paracetamol absorption or ultrasound. † This suggests that adding up to 50 ml milk to a hot drink does not delay gastric emptying. † Further studies are required in patients undergoing surgery.
Background. Many preoperative fasting guidelines suggest that hot tea or coffee with milk added should be considered similar to solid food, allowing an interval of 6 h before commencing anaesthesia. There is little evidence to support these instructions, with recent guidelines undecided on the issue. This study aimed to establish whether there was a clinically significant delay in gastric emptying associated with adding a modest amount of milk to tea. Methods. This randomized controlled crossover study was conducted in 10 healthy volunteers. The paracetamol absorption technique and real-time ultrasound measurement of the cross-sectional area of the gastric antrum were used to assess gastric emptying after ingestion of 300 ml of black tea or 300 ml of tea with milk (250 ml black tea plus 50 ml of full fat milk). Results. The mean difference in the time to reach the peak paracetamol concentration (tmax) was 28 min [95% confidence interval (CI) 223.1 to 7] in favour of tea with milk. Ultrasound assessment indicated that the geometric mean of the half-time to gastric emptying (T1/2) after tea without milk was 22.7 (95% CI 12.7–40.9) min and after tea with milk 23.6 (95% CI 13.5–41.0) min (ratio 1.04) (95% CI 0.47–2.29). Conclusions. This study demonstrated no difference in gastric emptying times when a modest amount of milk was added to tea. These findings suggest that it may be acceptable to allow patients to add a small quantity of milk to their tea or coffee and follow the same fasting restrictions applied to clear fluids. Keywords: gastric emptying; paracetamol; preoperative care; ultrasound Accepted for publication: 30 May 2013
The aim of preoperative fasting is to ensure a relatively empty stomach, thereby minimizing the risk of aspiration of gastric contents during induction and emergence from general anaesthesia.1 Pulmonary aspiration of gastric contents is now rare, a consequence not onlyof preoperative fasting but also of modern anaesthetic techniques. Preoperative fasting regimens have therefore become increasingly liberal, such that the ingestion of clear fluids is now encouraged until 2 h before elective surgery.2 3 Enhanced recovery programmes similarly encourage strategies such as preoperative nutrition and hydration.4 The currently acceptable preoperative clear fluids include water, black tea/coffee, and pulpless fruit juices. The traditional 2 h fast, to allow clear fluids to empty from the stomach, is relatively conservative as 250–300 ml of water should leave the stomach in ,30–60 min.5 In the UK, 165 million cups of tea are drunk each day, 98% of which are drunk with milk,6 suggesting that tea with milk is generally preferable than black tea.
However, no studies have defined a safe volume of milk that can be added to hot drinks consumed before an operation. Hence, when the European guidelines on preoperative fasting were published in 2011, no clear advice could be given on this issue.2 We postulated that the addition of a volume of milk, similar to that typically added to hot clear drinks such as tea or coffee, would not hinder gastric emptying. If confirmed, current preoperative fasting guidelines could then be extended to allow patients to consume tea/coffee with milk before an operation. In this study, gastric emptying was measured by the paracetamol absorption technique and by serial real-time ultrasound (RUS) measurements of the gastric antral cross-sectional area.
Methods This trial is registered with ClinicalTrials.gov (ref: NCT01809938), received ethical approval from the South East London Research
& The Author [2013]. Published by Oxford University Press on behalf of the British Journal of Anaesthesia. All rights reserved. For Permissions, please email: [email protected]
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Does adding milk to tea delay gastric emptying?
Ethics Committee 2, and was conducted between November 2011 and January 2012. After completion of written informed consent, 10 healthy volunteers were entered into this randomized controlled crossover trial. Exclusion criteria included: medical conditions with a predisposition to delayed gastric emptying (e.g. diabetes or gastric disease), ingestion of paracetamol within the previous 24 h, ingestion of solids or non-clear liquids in the previous 6 h, and ingestion of clear liquids in the previous 2 h. Each participant took part in both arms of the trial, drinking black tea and tea with milk, the order of which was determined by a computerized random number generator and concealed from the investigators by opaque brown paper envelopes. In each arm of the study, the procedure was as follows. The subject sat in a semi-reclined position at a 458 angle, a 16 g i.v. cannula was sited in an upper limb, and baseline blood samples were obtained. The initial cross-sectional area of the gastric antrum was then measured by ultrasound (MicroMaxx C60e/5-2 MHz Probe, Sonosite, Inc., Bothel, Washington, DC, USA). The investigating anaesthetist then left the room, the subject opened their randomization envelope and drank, as directed, either 300 ml of black tea or 300 ml of tea with milk (250 ml black tea plus 50 ml of full fat milk) over 3 min, followed by 1.5 g of dispersible paracetamol dissolved in 30 ml of water. Venous blood samples were obtained every 10 min for the first hour, then every 30 min until 150 min had elapsed. Each sample was obtained after aspirating and discarding a 5–10 ml waste blank. Paracetamol concentrations in each sample were measured using an enzymatic assay on the ADVIA 2400 analyser (Siemens Healthcare Diagnostic, Frimley, Surrey, UK), which had a sensitivity of 1 mg litre21 and a daily coefficient variation of ,5%. The peak paracetamol concentration (Cmax) and time to peak concentration (tmax) were thus determined. Values were plotted against time to calculate the area under the curve (AUC) at 60, 90, 120, and 150 min; and to infinity by the cubic spline method. The cross-sectional surface area (CSA) of the gastric antrum was measured by ultrasound in RUS at baseline, every 10 min for 60 min and then at 30 min intervals for 150 min. These measurements were performed by two of the investigators who had been trained by a radiologist specializing in abdominal ultrasound. The CSAwas calculated as described previously,7 by determining the maximal anteroposterior (D1) and longitudinal diameter (D2) in the sagittal plane. For every time point, three measurements were taken of D1 and D2 and the average values used in the following formula to calculate the antral CSA. Antral CSA = p × D1 ×
D2 4
A consistently reproducible position for scanning the gastric antrum was achieved using the abdominal aorta and left lobe of the liver as anatomical landmarks, as detailed in earlier studies.8 9 Antral CSA was plotted against time and gastric emptying expressed as half-time to gastric emptying (T1/2). This was defined as the time from baseline to the time the gastric antrum returns to half the maximal value (CSA1/2 max),7
with CSA 1/2 max calculated as below: CSA1/2 max = CSAmax −
CSAmax − CSAbaseline 2
Statistics The primary outcome was tmax. Previous studies have shown the mean or median tmax values for paracetamol to vary from 25 to 60 min after ingestion of clear fluids, with standard deviation up to 38 min.10 11 In this study, we considered that a delay of gastric emptying of under 60 min would not be clinically important; and that we would be able to declare that the two regimes were equivalent if the (two sided) 95% confidence interval (CI) for the mean difference (MD) in tmax, between black tea and tea with milk included only times ,60 min. Using these assumptions and taking (pessimistically) a correlation between repeated measurements of 0.0, power analysis12 determined nine participants would be required (with 90% power) to show equivalence. Power will be greater if there is a positive correlation. A 95% CI for the MD in tmax that lay entirely within 60 min of no effect would confirm the hypothesis that tea with milk was clinically equivalent to black tea. For each subject, the AUC of the paracetamol concentration was estimated as the weighted average of all measurements up to 150 min, following standard procedures.13 Since this time point was somewhat arbitrary, sensitivityanalysis also considered AUCvalues calculated for all measurements up to 60, 90, and 120 min, and linear extrapolation of the curve to final elimination, to confirm that changing the basis of the test did not change the result. The AUC of the drug concentration is a standard summary score used in many circumstances. A single value is calculated for each subject under each condition across all time points, as described by Matthews and colleagues.14 Treatment effects for all continuous outcomes were estimated using linear regression, correcting for the order of presentation; standard errors were adjusted for repeated observations using robust standard errors.15 Analysis was conducted using Stata (StataCorp, College Station, TX, USA), version 11.2. The secondary outcome was the RUS-determined T1/2. For this, no clinically important difference was pre-specified.
Results Ten participants (five males, five females) consented to, enrolled, and completed the study; their characteristics are given in Table 1. It was possible to measure the CSA of the gastric antrum in both arms of the study in nine of the subjects.
Table 1 Participants’ characteristics Median (inter-quartile range) Gender (male/female) Age (yr) Height (cm)
5/5 (not applicable) 36 (30 – 36) 170 (170 –174)
Weight (kg)
74 (73 – 81)
Body mass index (kg m22)
25 (24 – 29)
67
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Hillyard et al.
A
B
Liver
Liver
Gastric Antrum
Gastric Antrum
It was difficult to visualize the gastric antrum in one participant after drinking both black tea and tea with milk; this subject was therefore excluded in the final analysis of the US data. Figure 1 illustrates a typical image generated during the study. The interval between the two test days ranged from 1 to 42 days. All 10 subjects were able to provide a complete data set for assessment of paracetamol levels. Figure 2 shows the results of the mean plasma paracetamol concentrations plotted against time, indicating that there was little difference in gastric emptying after drinking either black tea or tea with milk. Further analysis of these data (Table 2) yielded a MD in tmax in favour of tea with milk, of 28 min (95% CI of 223.1 to 7.1), demonstrating non-inferiority of gastric emptying for tea with milk when compared with black tea. The result remains essentially the same if the basis of comparison is only the first 60, 90, or 120 min; or if the curve is extrapolated to infinity. The difference in the gastric emptying times assessed using RUS was not significant. The geometric mean T1/2 after drinking black tea was 22.7 (95% CI 12.7 –40.9) min and after tea with milk 23.6 (95% CI 13.5 –41.0) min (ratio 1.04) (95% CI 0.47 – 2.29). After drinking black tea or tea with milk, the mean antral CSA returned to below baseline values within 90 min, as shown in Figure 3.
Discussion The current ASA preoperative fasting guidelines state that ‘It is appropriate to fast from intake of a light meal or nonhuman milk 6 h or more before elective procedures requiring general anesthesia, regional anesthesia, or sedation/analgesia (i.e., monitored anesthesia care)’. ‘Because nonhuman milk is similar to solids in gastric emptying time, the amount ingested must be considered when determining an appropriate fasting period’.3 The recent ESA guidelines did not reach a firm conclusion about the addition of milk to tea/coffee, noting that no
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Plasma paracetamol concentration (µg ml–1)
Fig 1 Ultrasound images in subject number 1, demonstrating the cross-sectional area of the gastric antrum in the sagittal plane after ingesting tea with milk at T0 (A) and at T10 (B).
25 22 20 18 16 14 12 10 8 6 4 2 0
Black tea Tea with milk
0
20
40
60 80 100 Time (min)
120
140
160
Fig 2 Plasma paracetamol concentrations plotted against time after drinking 300 ml of tea with milk or 300 ml of black tea. The data are mean (SD) (n¼10 in each group).
studies had examined this practice specifically.2 Milky drinks have traditionally been discouraged because of their high fat and protein content, which can delay gastric emptying.16 The main practical and clinical issue is the need to differentiate between a drink containing a modest quantity of milk (15 – 20% of the total volume) and a drink consisting almost exclusively of milk. Unfortunately, the current situation is such that surgery is often postponed or even cancelled because the patient admitted to drinking tea/coffee with some milk. Ironically, enhanced recovery programmes are now followed by many surgical disciplines, in particular colorectal surgery, where high carbohydrate drinks are consumed within 2 h of surgery, the aim being to mitigate the patient’s metabolic response to surgery. While allowing tea/coffee with milk to be consumed before an operation is unlikely to alter the metabolic
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Does adding milk to tea delay gastric emptying?
Table 2 Paracetamol pharmacokinetics. Data are mean (SD) and as MD, between tea with milk and black tea (95% CI). AUC150, area under the curve from 0 to 150 min; Cmax, maximum plasma concentration; tmax, time to maximum plasma concentration. *The AUC is the weighted average of all measured paracetamol concentrations during the 150 min of observation; the weightings depending on the spacing between observations
AUC150 (mg min ml Cmax (mg ml21) tmax (min)
21
)*
Tea with milk (n510)
Black tea (n510)
MD (95% CI)
P-value
1886 (309)
1779 (355)
107 (2127 to 341)
0.32
21.4 (5.0)
19.5 (4.5)
1.9 (22.8 to 6.6)
0.39
28 (223.1 to 7.1)
0.26
30 (17.6)
8
Mean antral CSA (cm2)
7 6
Black tea Tea with milk
5 4 3 2 1 0
0 10 20 30 40 50 60 70 80 90 100110120130140150 Time (min)
Fig 3 Change in antral CSA over time after drinking 300 ml of tea with milk or 300 ml of black tea. The data are mean (SD) (n¼9 in each group).
response, it might improve patient satisfaction and wellbeing and reduce unnecessary cancellations of surgery. The physiology and time scale of gastric emptying of solids mandates a preoperative fasting time of at least 6 h. The same is not true forclear liquids, which leave the stomach exponentially with 90% of the ingested volume being emptied within 1 h.17 18 It is uncertain why a long period of fasting from liquids was ever introduced into clinical practice. However, at a time when pulmonary aspiration was one of the leading causes of anaesthetic mortality, a publication suggesting that a gastric volume of .0.4 ml kg21 with a pH ,2.5 placed patients at a greater risk of pulmonary aspiration became widely accepted.18 This claim was later found to be based on an experiment in one rhesus monkey in whom acid had been instilled into the right bronchus,19 but later studies indicated that larger volumes were required to produce a significant pneumonitis.20 Subsequent studies on preoperative fasting found no difference in gastric residual volume and pH in patients (adults and children) who had been fasted from midnight or only for 2–3 h before to surgery.21 22 Many of these studies on preoperative fasting were performed in Canada. Communication with one of the authors of these studies (R. Maltby) revealed that they did examine the addition of milk to tea/coffee and found no statistical difference in residual gastric volume between the milk and no milk groups. However, these results were omitted in their
38 (23.9)
publications on gastric fluid volume and pH in elective patients receiving preoperative oral fluids, because the numbers were small and patients had not been randomized to these subgroups.23 24 A further study, in which patients fasted overnight or were given a breakfast of tea/coffee with milk and buttered toast 2–4 h before surgery, demonstrated no difference in pH and volume of the gastric contents aspirated through a nasogastric tube.25 Arguably, it might have been difficult to aspirate toast through a nasogastric tube, but the results will have been valid for the emptying of the liquid phase of the meal. In the context of this study, it is not surprising therefore that we failed to demonstrate a difference between gastric emptying of black tea or tea with a modest quantity of milk. The severity of pulmonary aspiration correlates with gastric volume, pH, and the presence of particles in the aspirate.26 Neither the volume nor the pH of the gastric contents was measured in this study. However, it can be presumed that the stomach would be relatively empty after an overnight fast. Since this study demonstrated that the stomach had returned to a similar size 60–120 min after consuming black tea or tea with milk, it can be assumed that the stomach was again relatively empty by that time. These results could possibly be extended to obese patients as healthy, fasting, obese subjects have a similar gastric volume and pH to lean subjects.27 28 While the situation in obstetrics might be considered to be more complex, Wong and colleagues10 29 demonstrated that the gastric emptying of both 50 and 300 ml of water is not delayed in either normal or obese parturients at term. Therefore, it is likely that the emptying of tea with milk would not be delayed at term. Both gastroenterologists and anaesthetists use the paracetamol absorption technique to evaluate gastric emptying of liquids. The technique is based on the assumption that, as paracetamol is absorbed almost exclusively from the small intestine, its rate of appearance in the systemic circulation will reflect the rate of gastric emptying. The safety and simplicity of the technique make it acceptable to patients/volunteers when they are asked to take part in a study. The reliability of the paracetamol absorption technique is also well established and has been shown to correlate significantly with scintigraphically measured gastric emptying time, the acknowledged ‘gold standard technique’ for measuring gastric emptying.30 31 The indices used for measuring gastric emptying include pharmacokinetic parameters such as the maximum concentration (Cmax), the time it occurs (tmax), and the area under the time concentration curve (AUCt). It is known that there is significant between-subject variation in the absorption, distribution, and
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BJA elimination of paracetamol, whereas the intra-subject variation is minimal. Therefore, crossover studies, such as the present one, are useful to minimize the inter-subject variation in absorption, distribution, and elimination.32 The frequency of blood sampling is important with this technique and a higher sampling frequency has been shown to result in a significantly higher Cmax and an earlier identification of the start of the elimination phase. Sampling every 10 min for the first hour is needed to identify the initial phase of emptying. Reassuringly, the results of the measured parameters in our study are similar to those in other studies of a similar design.10 11 One participant had a baseline paracetamol concentration of 3 mg ml21 on the first occasion. When questioned after the assay results were available, she agreed that she had taken a headache remedy the evening before the study, which she had not thought to contain paracetamol. As the level was extremely low and a significant time had elapsed since ingestion, we considered it appropriate to include her results in the final analysis. In the studies that lead to the liberalization of preoperative fasting, gastric volume was usually determined by measuring the volume of aspirated gastric contents shortly after the induction of general anaesthesia. In a study in which the emptying of a caloric liquid meal was evaluated with the paracetamol absorption technique, the total contents of the stomach were aspirated after 45 min, the estimated time point at which most subjects would have emptied between 40% and 60% of the meal.33 This estimation proved to be correct as the median percentage emptied at 45 min was close to 50%. This study demonstrated both the accuracy of the paracetamol absorption technique for measuring gastric emptying and in addition highlighted the importance of ongoing gastric secretion, as the volume ingested and the volume aspirated after 45 min were similar. This suggests that assessing the rate of emptying by changes in gastric volume, for example, by RUS may not give an entirely accurate picture of the gastric volume/secretion/ emptying interaction. Thus, using two methods to estimate gastric emptying should improve overall assessment of the process of gastric emptying. RUS is another very useful non-invasive technique for measuring gastric emptying. Its advantage is that it is relatively easy to perform, is acceptable to patients, and avoids both gastric intubation and exposure to radiation. It has been shown that for volumes up to 300 ml, measurements of the CSA of a single section of the gastric antrum reflect the intragastric volume.34 The accuracy of RUS has been validated against gold standard techniques such as scintigraphy.16 35 In one early study comparing scintigraphy and RUS, they were equally effective in evaluating liquid gastric emptying, demonstrating that saline emptied significantly faster than semi-skimmed milk (1.8% fat).16 More recently, it has been suggested that twodimensional ultrasonography is sufficiently sensitive to be used as a bedside test to determine gastric content and volume before emergency surgery.36 This observational study in 183 patients, undergoing either elective or emergency surgery, measured the antral CSA immediately before induction of anaesthesia. After tracheal intubation, an 18 Fr multiorifice Salem tube was inserted into the stomach and the
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contents were aspirated during the ensuing 15 min. There was a significant positive correlation between the antral CSA and the aspirated gastric volume. The correlation coefficient was 0.72 (P,0.0001). However, in our study, the relatively wide CI for the effect of the intervention on the half-life for stomach emptying demonstrates the difficulty of accurately estimating this quantity, particularly given the relatively small changes in stomach volume involved. Position is known to affect the rate of gastric emptying, in particular the left lateral position has been shown to delay gastric emptying relative to the right.37 These studies were performed in the semi-upright position as necessitated by RUS measurements and is the position in which oral fluids are normally consumed. The results of this study in healthy volunteers support our hypothesis that the addition of a small to moderate volume of full fat milk to tea/coffee would not significantly delay gastric emptying. There was no significant difference in the mean maximum concentration of paracetamol (Cmax) and mean time maximum concentration (tmax) between black tea and tea with milk. In addition, RUS measurements showed that at 60 min, the stomach had returned to a size similar to that before the drink was consumed. This suggests that current preoperative fasting guidelines, which recommend only black tea/ coffee before surgery, could be altered to allow patients to add a modest quantity of milk (up to 50 ml) to these drinks. Full fat (4%) milk was used in this study, but in today’s health conscious world, it is likely that most people drink tea/coffee with semiskimmed milk (1.8–2% fat) and that the emptying profile of tea with semi-skimmed/skimmed milk will be similar to that seen in this study. Limitations of this study are that it was performed in healthy volunteers with presumed normal gastric emptying. None were obese and the presumed anxiety that may accompany the wait for surgery was not an issue. Therefore, further observational studies are required to verify the safety of allowing patients to consume tea/coffee with milk before elective surgery.
Authors’ contributions S.H. assisted in the study design, collected data, and drafted the manuscript. S.C. assisted in study design and gained the ethical approval. R.R. collected data. P.S. was the trial statistician and assisted in drafting the manuscript. G.O. was the principal investigator, conceived this study, and assisted in drafting the manuscript.
Acknowledgements The authors thank Dr R. Maltby for providing further information on his gastric emptying studies and Prof. F. Reynolds for her advice given on the manuscript. The paracetamol assay was performed by Dr R. Sherwood and Ms T. Dew (Department of Clinical Biochemistry, Kings College London, UK).
Declaration of interest G.O’S. was an unpaid member of the task force involved in producing the European Society of Anaesthesiology’s guidelines
Does adding milk to tea delay gastric emptying?
on perioperative fasting established in June 2009, published in the European Journal of Anaesthesiology 2011.
Funding This study was funded by a grant from Guy’s and St Thomas’ Charitable Foundation. P.T.S. is partly funded by Tommy’s the Baby Charity (Registered charity no. 1060508).
References 1 Mendelson CL. The aspiration of stomach contents into the lungs during obstetric anesthesia. Am J Obstet Gynecol 1946; 52: 191–205 2 Smith I, Kranke P, Murat I, et al. Perioperative fasting in adults and children: guidelines from the European Society of Anaesthesiology. Eur J Anaesthesiol 2011; 28: 556– 69 3 Practice guidelines for preoperative fasting and the use of pharmacologic agents to reduce the risk of pulmonary aspiration: application to healthy patients undergoing elective procedures: an updated report by the American Society of Anesthesiologists Committee on Standards and Practice Parameters. Anesthesiology 2011; 114: 495– 511 4 Henriksen MG, Hessov I, Dela F, Hansen HV, Haraldsted V, Rodt SA. Effects of preoperative oral carbohydrates and peptides on postoperative endocrine response, mobilization, nutrition and muscle function in abdominal surgery. Acta Anaesthesiol Scand 2003; 47: 191–9 5 O’Sullivan GM, Sutton AJ, Thompson SA, Carrie LE, Bullingham RE. Noninvasive measurement of gastric emptying in obstetric patients. Anesth Analg 1987; 66: 505– 11 6 United Kingdom Tea Council. Tea Facts: Facts about Tea That Everyone Should Know, 2012. Available from http://www.tea.co.uk (accessed 23 September 2012) 7 Irvine EJ, Tougas G, Lappalainen R, Bathurst NC. Reliability and interobserver variability of ultrasonographic measurement of gastric emptying rate. Dig Dis Sci 1993; 38: 803–10 8 Bolondi L, Bortolotti M, Santi V, Calletti T, Gaiani S, Labo G. Measurement of gastric emptying time by real-time ultrasonography. Gastroenterology 1985; 89: 752– 9 9 Darwiche G, Almer LO, Bjorgell O, Cederholm C, Nilsson P. Measurement of gastric emptying by standardized real-time ultrasonography in healthy subjects and diabetic patients. J Ultrasound Med 1999; 18: 673– 82 10 Wong CA, Loffredi M, Ganchiff JN, Zhao J, Wang Z, Avram MJ. Gastric emptying of water in term pregnancy. Anesthesiology 2002; 96: 1395– 400 11 Iirola T, Vilo S, Aantaa R, et al. Dexmedetomidine inhibits gastric emptying and oro-caecal transit in healthy volunteers. Br J Anaesth 2011; 106: 522–7 12 Jones B, Jarvis P, Lewis JA, Ebbutt AF. Trials to assess equivalence: the importance of rigorous methods. Br Med J 1996; 313: 36– 9 13 Chou SC, Liu JP, eds. Design and Analysis of Bioavailabilityand Bioequivalence Studies. Boca Raton, FL: Chapman & Hall/CRC Press, 2009 14 Matthews JN, Altman DG, Campbell MJ, Royston P. Analysis of serial measurements in medical research. Br Med J 1990; 300: 230–5 15 Rogers WH. Regression standard errors in clustered samples. Stata Tech Bull 1993; 13: 19– 23 16 Marzio L, Giacobbe A, Conoscitore P, Facciorusso D, Frusciante V, Modoni S. Evaluation of the use of ultrasonography in the study of liquid gastric emptying. Am J Gastroenterol 1989; 84: 496–500 17 Sandhar BK, Elliott RH, Windram I, Rowbotham DJ. Peripartum changes in gastric emptying. Anaesthesia 1992; 47: 196–8
BJA 18 Roberts RB, Shirley MA. Reducing the risk of acid aspiration during cesarean section. Anesth Analg 1974; 53: 859– 68 19 Roberts RB, Shirley MA. Antacid therapy in obstetrics. Anesthesiology 1980; 53: 83 20 Raidoo DM, Rocke DA, Brock-Utne JG, Marszalek A, Engelbrecht HE. Critical volume for pulmonary acid aspiration: reappraisal in a primate model. Br J Anaesth 1990; 65: 248–50 21 Phillips S, Hutchinson S, Davidson T. Preoperative drinking does not affect gastric contents. Br J Anaesth 1993; 70: 6– 9 22 Crawford M, Lerman J, Christensen S, Farrow-Gillespie A. Effects of duration of fasting on gastric fluid pH and volume in healthy children. Anesth Analg 1990; 71: 400– 3 23 Hutchinson A, Maltby JR, Reid CR. Gastric fluid volume and pH in elective inpatients. Part I: coffee or orange juice versus overnight fast. Can J Anaesth 1988; 35: 12 –5 24 Maltby JR, Reid CR, Hutchinson A. Gastric fluid volume and pH in elective inpatients. Part II: coffee or orange juice with ranitidine. Can J Anaesth 1988; 35: 16– 9 25 Miller M, Wishart HY, Nimmo WS. Gastric contents at induction of anaesthesia. Is a 4-hour fast necessary? Br J Anaesth 1983; 55: 1185– 8 26 Schwartz DJ, Wynne JW, Gibbs CP, Hood CI, Kuck EJ. The pulmonary consequences of aspiration of gastric contents at pH values greater than 2.5. Am Rev Respir Dis 1980; 121: 119 – 26 27 Harter RL, Kelly WB, Kramer MG, Perez CE, Dzwonczyk RR. A comparison of the volume and pH of gastric contents of obese and lean surgical patients. Anesth Analg 1998; 86: 147–52 28 Maltby JR, Pytka S, Watson NC, Cowan RA, Fick GH. Drinking 300 mL of clear fluid two hours before surgery has no effect on gastric fluid volume and pH in fasting and non-fasting obese patients. Can J Anaesth 2004; 51: 111–5 29 Wong CA, McCarthy RJ, Fitzgerald PC, Raikoff K, Avram MJ. Gastric emptying of water in obese pregnant women at term. Anesth Analg 2007; 105: 751– 5 30 Willems M, Quartero AO, Numans ME. How useful is paracetamol absorption as a marker of gastric emptying? A systematic literature study. Dig Dis Sci 2001; 46: 2256–62 31 Glerup H, Bluhme H, Villadsen GE, Rasmussen K, Ejskjaer N, Dahlerup JF. Gastric emptying: a comparison of three methods. Scand J Gastroenterol 2007; 42: 1182–6 32 Sanaka M, Kuyama Y, Yamanaka M. Guide for judicious use of the paracetamol absorption technique in a study of gastric emptying rate of liquids. J Gastroenterol 1998; 33: 785– 91 33 Medhus AW, Lofthus CM, Bredesen J, Husebye E. Gastric emptying: the validity of the paracetamol absorption test adjusted for individual pharmacokinetics. Neurogastroenterol Motil 2001; 13: 179 – 85 34 Perlas A, Chan VW, Lupu CM, Mitsakakis N, Hanbidge A. Ultrasound assessment of gastric content and volume. Anesthesiology 2009; 111: 82– 9 35 Holt S, Cervantes J, Wilkinson AA, Wallace JH. Measurement of gastric emptying rate in humans by real-time ultrasound. Gastroenterology 1986; 90: 918– 23 36 Bouvet L, Mazoit JX, Chassard D, Allaouchiche B, Boselli E, Benhamou D. Clinical assessment of the ultrasonographic measurement of antral area for estimating preoperative gastric content and volume. Anesthesiology 2011; 114: 1086–92 37 Nimmo WS, Prescott LF. The influence of posture on paracetamol absorption. Br J Clin Pharmacol 1978; 5: 348–9
Handling editor: J. P. Thompson
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CLINICAL PRACTICE
Does adding milk to tea delay gastric emptying? S. Hillyard1,2*, S. Cowman 2, R. Ramasundaram2, P. T. Seed 3 and G. O’Sullivan 2 1
Department of Anaesthesia, Rockingham General Hospital, Elanora Drive, Rockingham, WA 6168, Australia Department of Anaesthesia, Guy’s and St Thomas’ NHS Foundation Trust, St Thomas’ Hospital, Westminster Bridge Rd, London SE1 7EH, UK 3 Division of Women’s Health, King’s College London, Women’s Health Academic Centre, King’s Health Partners, Westminster Bridge Rd, London SE1 7EH, UK 2
* Corresponding author. E-mail: [email protected]
Editor’s key points † Current preoperative fasting guidelines assume that gastric emptying is delayed after ingestion of fluids containing milk. † This study in healthy adults compared gastric emptying after drinking tea with or without milk. † There was no difference in gastric emptying times determined by paracetamol absorption or ultrasound. † This suggests that adding up to 50 ml milk to a hot drink does not delay gastric emptying. † Further studies are required in patients undergoing surgery.
Background. Many preoperative fasting guidelines suggest that hot tea or coffee with milk added should be considered similar to solid food, allowing an interval of 6 h before commencing anaesthesia. There is little evidence to support these instructions, with recent guidelines undecided on the issue. This study aimed to establish whether there was a clinically significant delay in gastric emptying associated with adding a modest amount of milk to tea. Methods. This randomized controlled crossover study was conducted in 10 healthy volunteers. The paracetamol absorption technique and real-time ultrasound measurement of the cross-sectional area of the gastric antrum were used to assess gastric emptying after ingestion of 300 ml of black tea or 300 ml of tea with milk (250 ml black tea plus 50 ml of full fat milk). Results. The mean difference in the time to reach the peak paracetamol concentration (tmax) was 28 min [95% confidence interval (CI) 223.1 to 7] in favour of tea with milk. Ultrasound assessment indicated that the geometric mean of the half-time to gastric emptying (T1/2) after tea without milk was 22.7 (95% CI 12.7–40.9) min and after tea with milk 23.6 (95% CI 13.5–41.0) min (ratio 1.04) (95% CI 0.47–2.29). Conclusions. This study demonstrated no difference in gastric emptying times when a modest amount of milk was added to tea. These findings suggest that it may be acceptable to allow patients to add a small quantity of milk to their tea or coffee and follow the same fasting restrictions applied to clear fluids. Keywords: gastric emptying; paracetamol; preoperative care; ultrasound Accepted for publication: 30 May 2013
The aim of preoperative fasting is to ensure a relatively empty stomach, thereby minimizing the risk of aspiration of gastric contents during induction and emergence from general anaesthesia.1 Pulmonary aspiration of gastric contents is now rare, a consequence not onlyof preoperative fasting but also of modern anaesthetic techniques. Preoperative fasting regimens have therefore become increasingly liberal, such that the ingestion of clear fluids is now encouraged until 2 h before elective surgery.2 3 Enhanced recovery programmes similarly encourage strategies such as preoperative nutrition and hydration.4 The currently acceptable preoperative clear fluids include water, black tea/coffee, and pulpless fruit juices. The traditional 2 h fast, to allow clear fluids to empty from the stomach, is relatively conservative as 250–300 ml of water should leave the stomach in ,30–60 min.5 In the UK, 165 million cups of tea are drunk each day, 98% of which are drunk with milk,6 suggesting that tea with milk is generally preferable than black tea.
However, no studies have defined a safe volume of milk that can be added to hot drinks consumed before an operation. Hence, when the European guidelines on preoperative fasting were published in 2011, no clear advice could be given on this issue.2 We postulated that the addition of a volume of milk, similar to that typically added to hot clear drinks such as tea or coffee, would not hinder gastric emptying. If confirmed, current preoperative fasting guidelines could then be extended to allow patients to consume tea/coffee with milk before an operation. In this study, gastric emptying was measured by the paracetamol absorption technique and by serial real-time ultrasound (RUS) measurements of the gastric antral cross-sectional area.
Methods This trial is registered with ClinicalTrials.gov (ref: NCT01809938), received ethical approval from the South East London Research
& The Author [2013]. Published by Oxford University Press on behalf of the British Journal of Anaesthesia. All rights reserved. For Permissions, please email: [email protected]
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Does adding milk to tea delay gastric emptying?
Ethics Committee 2, and was conducted between November 2011 and January 2012. After completion of written informed consent, 10 healthy volunteers were entered into this randomized controlled crossover trial. Exclusion criteria included: medical conditions with a predisposition to delayed gastric emptying (e.g. diabetes or gastric disease), ingestion of paracetamol within the previous 24 h, ingestion of solids or non-clear liquids in the previous 6 h, and ingestion of clear liquids in the previous 2 h. Each participant took part in both arms of the trial, drinking black tea and tea with milk, the order of which was determined by a computerized random number generator and concealed from the investigators by opaque brown paper envelopes. In each arm of the study, the procedure was as follows. The subject sat in a semi-reclined position at a 458 angle, a 16 g i.v. cannula was sited in an upper limb, and baseline blood samples were obtained. The initial cross-sectional area of the gastric antrum was then measured by ultrasound (MicroMaxx C60e/5-2 MHz Probe, Sonosite, Inc., Bothel, Washington, DC, USA). The investigating anaesthetist then left the room, the subject opened their randomization envelope and drank, as directed, either 300 ml of black tea or 300 ml of tea with milk (250 ml black tea plus 50 ml of full fat milk) over 3 min, followed by 1.5 g of dispersible paracetamol dissolved in 30 ml of water. Venous blood samples were obtained every 10 min for the first hour, then every 30 min until 150 min had elapsed. Each sample was obtained after aspirating and discarding a 5–10 ml waste blank. Paracetamol concentrations in each sample were measured using an enzymatic assay on the ADVIA 2400 analyser (Siemens Healthcare Diagnostic, Frimley, Surrey, UK), which had a sensitivity of 1 mg litre21 and a daily coefficient variation of ,5%. The peak paracetamol concentration (Cmax) and time to peak concentration (tmax) were thus determined. Values were plotted against time to calculate the area under the curve (AUC) at 60, 90, 120, and 150 min; and to infinity by the cubic spline method. The cross-sectional surface area (CSA) of the gastric antrum was measured by ultrasound in RUS at baseline, every 10 min for 60 min and then at 30 min intervals for 150 min. These measurements were performed by two of the investigators who had been trained by a radiologist specializing in abdominal ultrasound. The CSAwas calculated as described previously,7 by determining the maximal anteroposterior (D1) and longitudinal diameter (D2) in the sagittal plane. For every time point, three measurements were taken of D1 and D2 and the average values used in the following formula to calculate the antral CSA. Antral CSA = p × D1 ×
D2 4
A consistently reproducible position for scanning the gastric antrum was achieved using the abdominal aorta and left lobe of the liver as anatomical landmarks, as detailed in earlier studies.8 9 Antral CSA was plotted against time and gastric emptying expressed as half-time to gastric emptying (T1/2). This was defined as the time from baseline to the time the gastric antrum returns to half the maximal value (CSA1/2 max),7
with CSA 1/2 max calculated as below: CSA1/2 max = CSAmax −
CSAmax − CSAbaseline 2
Statistics The primary outcome was tmax. Previous studies have shown the mean or median tmax values for paracetamol to vary from 25 to 60 min after ingestion of clear fluids, with standard deviation up to 38 min.10 11 In this study, we considered that a delay of gastric emptying of under 60 min would not be clinically important; and that we would be able to declare that the two regimes were equivalent if the (two sided) 95% confidence interval (CI) for the mean difference (MD) in tmax, between black tea and tea with milk included only times ,60 min. Using these assumptions and taking (pessimistically) a correlation between repeated measurements of 0.0, power analysis12 determined nine participants would be required (with 90% power) to show equivalence. Power will be greater if there is a positive correlation. A 95% CI for the MD in tmax that lay entirely within 60 min of no effect would confirm the hypothesis that tea with milk was clinically equivalent to black tea. For each subject, the AUC of the paracetamol concentration was estimated as the weighted average of all measurements up to 150 min, following standard procedures.13 Since this time point was somewhat arbitrary, sensitivityanalysis also considered AUCvalues calculated for all measurements up to 60, 90, and 120 min, and linear extrapolation of the curve to final elimination, to confirm that changing the basis of the test did not change the result. The AUC of the drug concentration is a standard summary score used in many circumstances. A single value is calculated for each subject under each condition across all time points, as described by Matthews and colleagues.14 Treatment effects for all continuous outcomes were estimated using linear regression, correcting for the order of presentation; standard errors were adjusted for repeated observations using robust standard errors.15 Analysis was conducted using Stata (StataCorp, College Station, TX, USA), version 11.2. The secondary outcome was the RUS-determined T1/2. For this, no clinically important difference was pre-specified.
Results Ten participants (five males, five females) consented to, enrolled, and completed the study; their characteristics are given in Table 1. It was possible to measure the CSA of the gastric antrum in both arms of the study in nine of the subjects.
Table 1 Participants’ characteristics Median (inter-quartile range) Gender (male/female) Age (yr) Height (cm)
5/5 (not applicable) 36 (30 – 36) 170 (170 –174)
Weight (kg)
74 (73 – 81)
Body mass index (kg m22)
25 (24 – 29)
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Hillyard et al.
A
B
Liver
Liver
Gastric Antrum
Gastric Antrum
It was difficult to visualize the gastric antrum in one participant after drinking both black tea and tea with milk; this subject was therefore excluded in the final analysis of the US data. Figure 1 illustrates a typical image generated during the study. The interval between the two test days ranged from 1 to 42 days. All 10 subjects were able to provide a complete data set for assessment of paracetamol levels. Figure 2 shows the results of the mean plasma paracetamol concentrations plotted against time, indicating that there was little difference in gastric emptying after drinking either black tea or tea with milk. Further analysis of these data (Table 2) yielded a MD in tmax in favour of tea with milk, of 28 min (95% CI of 223.1 to 7.1), demonstrating non-inferiority of gastric emptying for tea with milk when compared with black tea. The result remains essentially the same if the basis of comparison is only the first 60, 90, or 120 min; or if the curve is extrapolated to infinity. The difference in the gastric emptying times assessed using RUS was not significant. The geometric mean T1/2 after drinking black tea was 22.7 (95% CI 12.7 –40.9) min and after tea with milk 23.6 (95% CI 13.5 –41.0) min (ratio 1.04) (95% CI 0.47 – 2.29). After drinking black tea or tea with milk, the mean antral CSA returned to below baseline values within 90 min, as shown in Figure 3.
Discussion The current ASA preoperative fasting guidelines state that ‘It is appropriate to fast from intake of a light meal or nonhuman milk 6 h or more before elective procedures requiring general anesthesia, regional anesthesia, or sedation/analgesia (i.e., monitored anesthesia care)’. ‘Because nonhuman milk is similar to solids in gastric emptying time, the amount ingested must be considered when determining an appropriate fasting period’.3 The recent ESA guidelines did not reach a firm conclusion about the addition of milk to tea/coffee, noting that no
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Plasma paracetamol concentration (µg ml–1)
Fig 1 Ultrasound images in subject number 1, demonstrating the cross-sectional area of the gastric antrum in the sagittal plane after ingesting tea with milk at T0 (A) and at T10 (B).
25 22 20 18 16 14 12 10 8 6 4 2 0
Black tea Tea with milk
0
20
40
60 80 100 Time (min)
120
140
160
Fig 2 Plasma paracetamol concentrations plotted against time after drinking 300 ml of tea with milk or 300 ml of black tea. The data are mean (SD) (n¼10 in each group).
studies had examined this practice specifically.2 Milky drinks have traditionally been discouraged because of their high fat and protein content, which can delay gastric emptying.16 The main practical and clinical issue is the need to differentiate between a drink containing a modest quantity of milk (15 – 20% of the total volume) and a drink consisting almost exclusively of milk. Unfortunately, the current situation is such that surgery is often postponed or even cancelled because the patient admitted to drinking tea/coffee with some milk. Ironically, enhanced recovery programmes are now followed by many surgical disciplines, in particular colorectal surgery, where high carbohydrate drinks are consumed within 2 h of surgery, the aim being to mitigate the patient’s metabolic response to surgery. While allowing tea/coffee with milk to be consumed before an operation is unlikely to alter the metabolic
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Does adding milk to tea delay gastric emptying?
Table 2 Paracetamol pharmacokinetics. Data are mean (SD) and as MD, between tea with milk and black tea (95% CI). AUC150, area under the curve from 0 to 150 min; Cmax, maximum plasma concentration; tmax, time to maximum plasma concentration. *The AUC is the weighted average of all measured paracetamol concentrations during the 150 min of observation; the weightings depending on the spacing between observations
AUC150 (mg min ml Cmax (mg ml21) tmax (min)
21
)*
Tea with milk (n510)
Black tea (n510)
MD (95% CI)
P-value
1886 (309)
1779 (355)
107 (2127 to 341)
0.32
21.4 (5.0)
19.5 (4.5)
1.9 (22.8 to 6.6)
0.39
28 (223.1 to 7.1)
0.26
30 (17.6)
8
Mean antral CSA (cm2)
7 6
Black tea Tea with milk
5 4 3 2 1 0
0 10 20 30 40 50 60 70 80 90 100110120130140150 Time (min)
Fig 3 Change in antral CSA over time after drinking 300 ml of tea with milk or 300 ml of black tea. The data are mean (SD) (n¼9 in each group).
response, it might improve patient satisfaction and wellbeing and reduce unnecessary cancellations of surgery. The physiology and time scale of gastric emptying of solids mandates a preoperative fasting time of at least 6 h. The same is not true forclear liquids, which leave the stomach exponentially with 90% of the ingested volume being emptied within 1 h.17 18 It is uncertain why a long period of fasting from liquids was ever introduced into clinical practice. However, at a time when pulmonary aspiration was one of the leading causes of anaesthetic mortality, a publication suggesting that a gastric volume of .0.4 ml kg21 with a pH ,2.5 placed patients at a greater risk of pulmonary aspiration became widely accepted.18 This claim was later found to be based on an experiment in one rhesus monkey in whom acid had been instilled into the right bronchus,19 but later studies indicated that larger volumes were required to produce a significant pneumonitis.20 Subsequent studies on preoperative fasting found no difference in gastric residual volume and pH in patients (adults and children) who had been fasted from midnight or only for 2–3 h before to surgery.21 22 Many of these studies on preoperative fasting were performed in Canada. Communication with one of the authors of these studies (R. Maltby) revealed that they did examine the addition of milk to tea/coffee and found no statistical difference in residual gastric volume between the milk and no milk groups. However, these results were omitted in their
38 (23.9)
publications on gastric fluid volume and pH in elective patients receiving preoperative oral fluids, because the numbers were small and patients had not been randomized to these subgroups.23 24 A further study, in which patients fasted overnight or were given a breakfast of tea/coffee with milk and buttered toast 2–4 h before surgery, demonstrated no difference in pH and volume of the gastric contents aspirated through a nasogastric tube.25 Arguably, it might have been difficult to aspirate toast through a nasogastric tube, but the results will have been valid for the emptying of the liquid phase of the meal. In the context of this study, it is not surprising therefore that we failed to demonstrate a difference between gastric emptying of black tea or tea with a modest quantity of milk. The severity of pulmonary aspiration correlates with gastric volume, pH, and the presence of particles in the aspirate.26 Neither the volume nor the pH of the gastric contents was measured in this study. However, it can be presumed that the stomach would be relatively empty after an overnight fast. Since this study demonstrated that the stomach had returned to a similar size 60–120 min after consuming black tea or tea with milk, it can be assumed that the stomach was again relatively empty by that time. These results could possibly be extended to obese patients as healthy, fasting, obese subjects have a similar gastric volume and pH to lean subjects.27 28 While the situation in obstetrics might be considered to be more complex, Wong and colleagues10 29 demonstrated that the gastric emptying of both 50 and 300 ml of water is not delayed in either normal or obese parturients at term. Therefore, it is likely that the emptying of tea with milk would not be delayed at term. Both gastroenterologists and anaesthetists use the paracetamol absorption technique to evaluate gastric emptying of liquids. The technique is based on the assumption that, as paracetamol is absorbed almost exclusively from the small intestine, its rate of appearance in the systemic circulation will reflect the rate of gastric emptying. The safety and simplicity of the technique make it acceptable to patients/volunteers when they are asked to take part in a study. The reliability of the paracetamol absorption technique is also well established and has been shown to correlate significantly with scintigraphically measured gastric emptying time, the acknowledged ‘gold standard technique’ for measuring gastric emptying.30 31 The indices used for measuring gastric emptying include pharmacokinetic parameters such as the maximum concentration (Cmax), the time it occurs (tmax), and the area under the time concentration curve (AUCt). It is known that there is significant between-subject variation in the absorption, distribution, and
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BJA elimination of paracetamol, whereas the intra-subject variation is minimal. Therefore, crossover studies, such as the present one, are useful to minimize the inter-subject variation in absorption, distribution, and elimination.32 The frequency of blood sampling is important with this technique and a higher sampling frequency has been shown to result in a significantly higher Cmax and an earlier identification of the start of the elimination phase. Sampling every 10 min for the first hour is needed to identify the initial phase of emptying. Reassuringly, the results of the measured parameters in our study are similar to those in other studies of a similar design.10 11 One participant had a baseline paracetamol concentration of 3 mg ml21 on the first occasion. When questioned after the assay results were available, she agreed that she had taken a headache remedy the evening before the study, which she had not thought to contain paracetamol. As the level was extremely low and a significant time had elapsed since ingestion, we considered it appropriate to include her results in the final analysis. In the studies that lead to the liberalization of preoperative fasting, gastric volume was usually determined by measuring the volume of aspirated gastric contents shortly after the induction of general anaesthesia. In a study in which the emptying of a caloric liquid meal was evaluated with the paracetamol absorption technique, the total contents of the stomach were aspirated after 45 min, the estimated time point at which most subjects would have emptied between 40% and 60% of the meal.33 This estimation proved to be correct as the median percentage emptied at 45 min was close to 50%. This study demonstrated both the accuracy of the paracetamol absorption technique for measuring gastric emptying and in addition highlighted the importance of ongoing gastric secretion, as the volume ingested and the volume aspirated after 45 min were similar. This suggests that assessing the rate of emptying by changes in gastric volume, for example, by RUS may not give an entirely accurate picture of the gastric volume/secretion/ emptying interaction. Thus, using two methods to estimate gastric emptying should improve overall assessment of the process of gastric emptying. RUS is another very useful non-invasive technique for measuring gastric emptying. Its advantage is that it is relatively easy to perform, is acceptable to patients, and avoids both gastric intubation and exposure to radiation. It has been shown that for volumes up to 300 ml, measurements of the CSA of a single section of the gastric antrum reflect the intragastric volume.34 The accuracy of RUS has been validated against gold standard techniques such as scintigraphy.16 35 In one early study comparing scintigraphy and RUS, they were equally effective in evaluating liquid gastric emptying, demonstrating that saline emptied significantly faster than semi-skimmed milk (1.8% fat).16 More recently, it has been suggested that twodimensional ultrasonography is sufficiently sensitive to be used as a bedside test to determine gastric content and volume before emergency surgery.36 This observational study in 183 patients, undergoing either elective or emergency surgery, measured the antral CSA immediately before induction of anaesthesia. After tracheal intubation, an 18 Fr multiorifice Salem tube was inserted into the stomach and the
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contents were aspirated during the ensuing 15 min. There was a significant positive correlation between the antral CSA and the aspirated gastric volume. The correlation coefficient was 0.72 (P,0.0001). However, in our study, the relatively wide CI for the effect of the intervention on the half-life for stomach emptying demonstrates the difficulty of accurately estimating this quantity, particularly given the relatively small changes in stomach volume involved. Position is known to affect the rate of gastric emptying, in particular the left lateral position has been shown to delay gastric emptying relative to the right.37 These studies were performed in the semi-upright position as necessitated by RUS measurements and is the position in which oral fluids are normally consumed. The results of this study in healthy volunteers support our hypothesis that the addition of a small to moderate volume of full fat milk to tea/coffee would not significantly delay gastric emptying. There was no significant difference in the mean maximum concentration of paracetamol (Cmax) and mean time maximum concentration (tmax) between black tea and tea with milk. In addition, RUS measurements showed that at 60 min, the stomach had returned to a size similar to that before the drink was consumed. This suggests that current preoperative fasting guidelines, which recommend only black tea/ coffee before surgery, could be altered to allow patients to add a modest quantity of milk (up to 50 ml) to these drinks. Full fat (4%) milk was used in this study, but in today’s health conscious world, it is likely that most people drink tea/coffee with semiskimmed milk (1.8–2% fat) and that the emptying profile of tea with semi-skimmed/skimmed milk will be similar to that seen in this study. Limitations of this study are that it was performed in healthy volunteers with presumed normal gastric emptying. None were obese and the presumed anxiety that may accompany the wait for surgery was not an issue. Therefore, further observational studies are required to verify the safety of allowing patients to consume tea/coffee with milk before elective surgery.
Authors’ contributions S.H. assisted in the study design, collected data, and drafted the manuscript. S.C. assisted in study design and gained the ethical approval. R.R. collected data. P.S. was the trial statistician and assisted in drafting the manuscript. G.O. was the principal investigator, conceived this study, and assisted in drafting the manuscript.
Acknowledgements The authors thank Dr R. Maltby for providing further information on his gastric emptying studies and Prof. F. Reynolds for her advice given on the manuscript. The paracetamol assay was performed by Dr R. Sherwood and Ms T. Dew (Department of Clinical Biochemistry, Kings College London, UK).
Declaration of interest G.O’S. was an unpaid member of the task force involved in producing the European Society of Anaesthesiology’s guidelines
Does adding milk to tea delay gastric emptying?
on perioperative fasting established in June 2009, published in the European Journal of Anaesthesiology 2011.
Funding This study was funded by a grant from Guy’s and St Thomas’ Charitable Foundation. P.T.S. is partly funded by Tommy’s the Baby Charity (Registered charity no. 1060508).
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