Meal & Correction Bolus
Carb Entries - You can input a new meal entry by tapping the leftmost icon (as seen below in the toolbar) in Loop:
This will bring up the "Add Carb Entry" menu where you can enter the number of carbs consumed, specify the time/date of the meal, and absorption time (more on this below).
Carb Absorption Time
Unlike traditional pumps, Loop asks you to specify how long you expect it takes for the carbohydrates in your meal to absorb (and therefore continue to raise your blood glucose). You can change the absorption time of your meal entry by either tapping one of the icons for Food Type, or by modifying the time listed for Absorption Time. By default, this is set at 3 hours (the taco icon); meanwhile, the lollipop is meant to simulate fast absorbing (high glycemic) foods at 2 hours, while the pizza is meant to simulate slow absorbing (low glycemic, or meals containing more fats & proteins) foods at 4 hours. If you are unsure if your meal is likely to be fast, medium, or slow absorbing, you can tap the rightmost plate icon to bring up icons of common foods that fit into each category and let that help you decide. More advanced users may find that some mixed meals contain a combination of carbs that absorb quickly and some that absorb more slowly (e.g. Chinese food) - in these cases, you could consider logging components of the meal as separate entries (e.g. the sauce and rice as fast absorbing, the protein and fats as slow absorbing).
Fortunately, Loop’s developers know that carb absorption varies widely in the real world, so since Loop v1.4.0, the algorithm uses a dynamic carb absorption model that adapts whenever actual carb absorption doesn't match well with what you entered. That means you don’t have to worry about getting the carb absorption exactly right - know that Loop is forgiving and only uses that information as a guide!
Extended Bolus for Complex Meals
Importantly, Loop cannot perform extended boluses (square or dual wave) in the traditional sense - instead, it will use the information from your carb entry (including carb absorption time) to calculate how much of the bolus to give you upfront, then will plan to deliver the remainder of the bolus through higher temporary basal adjustments later on (which is similar to what an extended bolus achieves). You can therefore essentially specify an extended bolus by inputting a longer carb absorption time, since this tells Loop to anticipate glucose to rise more slowly over the next couple hours - accordingly, it will make sure the initial bolus doesn’t drop your glucose below your suspend threshold in the short term, then start to increase your temporary basal rates as it predicts glucose to rise over time.
You can let Loop know that you intend to pre-bolus by tapping and adjusting the date/time of the meal entry (defaults to the current time, or now) forward into the future, by the amount of time you want to give the bolus in advance of the meal. For example, if it’s exactly noon and you want to bolus now for a meal that you will have in 15 minutes (i.e. a 15 minute prebolus), you would tap and change the time to be 12:15pm. Once you save your meal entry, Loop will open up its bolus tool to provide a recommended bolus if it deems it appropriate.
Alternatively, another way to pre-bolus is to enable your pre-meal override by tapping the second from left icon in the toolbar:
This will direct Loop to target the lower blood glucose range that you specified in settings, with the goal of delivering a little more insulin in advance of the meal to help preempt and minimize the spike from that meal. Remember that the pre-meal override will remain in effect until either it is turned off, one hour elapses, or carbs are entered.
Once you save your carb entry, Loop will bring up its bolus tool with a recommended bolus amount. You can tap the recommended units of insulin to copy that amount to the bolus line, or you can manually enter your own dose (which we generally don’t recommend, for reasons stated previously), then tap Deliver to initiate that bolus. This will take you back to the main screen, where you can see a "Starting Bolus" notification near the top.
Note that the bolus tool will not appear if Loop predicts that your current insulin-on-board will cover the additional carbs you just entered, if your predicted glucose is already expected to drop below your specified suspend threshold, or it doesn't have updated blood glucose data.
Edit Carb Entries
Tapping the Carbohydrate section on Loop's main status screen will open up the carb entry history, where you can modify or delete prior entries:
As previously discussed, Loop actually uses your carb entries not just to calculate a recommended bolus, but also tries to account for their glucose-raising effects in its glucose predictions into the future. Therefore, if you put in a carb entry and don’t actually eat that meal, remember to go in and delete accidental entries by swiping left (otherwise Loop will still think you ate that meal and potentially try to increase your temporary basal rates to address a predicted rise in glucose). Meanwhile, if you ever end up eating more or less than what you expected, or decide to eat a different time, you can also go in and modify this information after the fact - this will allow Loop to adjust its glucose prediction to more closely simulate what actually happened!
When your blood glucose is persistently high or trending high, you can tap the bolus entry tool to check if Loop might recommend a correction bolus:
In cases where Loop calculates that it will not be able to stay within the correction range even with maximal basal adjustments, it will offer a correction bolus that you can then choose to enact. Know that Loop will not notify you when a correction bolus is being offered, and will never automatically deliver this bolus without your approval. Fortunately, correction boluses should not be frequently needed with accurate settings and reasonable carb counting.
Keep in mind, we would recommend that you use correction boluses only in a limited manner. At any given point in time, Loop’s prediction may be in error. For example, if you were rising and at a peak, but the system had been increasing temporary basal rates, you will eventually plateau and and reach your blood glucose correction range with basal modulation alone. Basal modulation can change over time but if you bolus before the plateau, you will likely get more insulin than you need.
Overrides allow you to inform Loop that you anticipate your insulin needs to change for a period of time (during situations such as exercise or hormone cycles), without having to modify all of your settings individually. These adjustments will temporarily change your overall insulin needs (increasing or decreasing all of your basal, bolus, and correction doses proportionately) and the target range for the duration of time specified, according to how the preset was created and modified in Settings.
These override presets (created and modified in settings) can be accessed and activated by tapping the workout icon in Loop's toolbar: