Does Adding Milk to Tea Delay Gastric Emptying?
Condition: Gastric Emptying
Study type: Interventional

Summary: 
      Most pre-operative fasting regimes dictate that if there is any milk added to tea or coffee,
      the preoperative fasting time should be extended from 2 to 6 hours. The purpose of this study
      is to demonstrate whether there is really a delay in gastric emptying time associated with
      the inclusion of milk in a cup of tea.
    

Detailed description: 
      This was a randomised controlled crossover study conducted in ten healthy volunteers. The
      paracetamol absorption technique and real-time ultrasound measurement of the cross-sectional
      area (CSA) of the gastric antrum were used to assess gastric emptying following ingestion of
      300ml of black tea or 300ml of tea with milk (250ml black tea plus 50ml of full fat milk)

      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 computerised 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 45 angle, a 16g intravenous cannula was sited in an upper limb and baseline
      blood samples taken. The initial cross-sectional area of the gastric antrum was then measured
      by ultrasound.

      The investigating anaesthetist then left the room, the subject opened their randomisation
      envelope and drank, as directed, either 300ml of black tea or 300ml of tea with milk (250ml
      black tea plus 50ml of full fat milk) over 3 minutes, followed by 1.5 g of dispersible
      paracetamol dissolved in 30ml of water.

      Blood samples were taken every 10 minutes for the first hour, then every 30 minutes until 150
      minutes had elapsed. Paracetamol concentrations in each sample were measured using an
      enzymatic assay. Time to peak concentration (tmax) was thus determined.

      The CSA of the gastric antrum was measured by ultrasound in real-time (RUS) at baseline,
      every ten minutes for 60 minutes and then at 30-minute intervals for 150 minutes. Antral CSA
      was plotted against time and gastric emptying expressed as half-time to gastric emptying
      (T½). This was defined as the time from baseline to the time the gastric antrum returns to
      half the maximal value.

      The primary outcome was tmax. Previous studies have shown mean or median tmax values for
      paracetamol to vary from 25 to 60 minutes following ingestion of clear fluids, with standard
      deviation up to 38 minutes. In this study we considered that a delay of gastric emptying of
      under 60 minutes 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 for the mean
      difference in tmax, between black tea and tea with milk included only times less than 60
      minutes. Using these assumptions and taking (pessimistically) a correlation between repeated
      measurements of 0.0, power analysis determined nine participants would be required (with 90%
      power) to show equivalence.

      A 95% confidence interval for the mean difference in tmax that lay entirely within 60 minutes
      of no effect would confirm the hypothesis that tea with milk was clinically equivalent to
      black tea.
    

Intervention name(s): Black tea; Tea with milk
Intervention type(s): Other; Other
Intervention description(s): 300ml of tea without milk; 250ml of black tea with 50ml of full fat milk
Allocation: Randomized
Intervention model: Crossover Assignment
Masking: Single (Investigator)
Primary purpose: Basic Science
Keywords: Gastrointestinal tract emptying; Pre-operative fasting; Ultrasound; Paracetamol Absorption