In digestion, a bolus (from Latin bolus, \"ball\") is a ball-like mixture of food and saliva that forms in the mouth during the process of chewing (which is largely an adaptation for plant-eating mammals). It has the same color as the food being eaten, and the saliva gives it an alkaline pH.
The placement of the bolus dose depends on the systemic levels of the contents desired throughout the body. An intramuscular injection of vaccines allows for a slow release of the antigen to stimulate the body's immune system and to allow time for developing antibodies. Subcutaneous injections are used by heroin addicts (called 'skin popping', referring to the bump formed by the bolus of heroin), to sustain a slow release that staves off withdrawal symptoms without producing euphoria.
A bolus delivered directly to the veins through an intravenous drip allows a much faster delivery which quickly raises the concentration of the substance in the blood to an effective level. This is typically done at the beginning of a treatment or after a removal of medicine from blood (e.g. through dialysis).
Diabetics and health care professionals use bolus to refer to a dosage of fast-acting insulin with a meal (as opposed to basal rate, which is a dose of slow-acting insulin or the continuous pumping of a small quantity of fast-acting insulin to cover the glucose output of the liver).
In veterinary medicine a bolus is a large time-release tablet that stays in the rumen of cattle, goats, and sheep. It can also refer to a dose of liquid injected subcutaneously with a hypodermic needle, such as saline solution administered either to counteract dehydration or especially to mitigate kidney failure, a common ailment in domestic cats. Before it is fully absorbed, which can take several minutes or longer, the liquid remains in the form of a bolus, a ball or lump under the animal's skin.
A bolus is a single, large dose of medicine. For a person with diabetes, a bolus is a dose of insulin taken to handle a rise in blood glucose (a type of sugar), like the one that happens during eating. A bolus is given as a shot or through an insulin pump.
Intervention: Intervention group: intravenous slow 5 IU oxytocin bolus over 1 minute and additional 40 IU oxytocin infusion in 500 mL of 0.9% saline solution over 4 hours (bolus and infusion). Placebo group: 5 IU oxytocin bolus over 1 minute and 500 mL of 0.9% saline solution over 4 hours (placebo infusion) (bolus only). Main outcomes Major obstetric haemorrhage (blood loss >1000 mL) and need for an additional uterotonic agent.
Results: We found no difference in the occurrence of major obstetric haemorrhage between the groups (bolus and infusion 15.7% (158/1007) v bolus only 16.0% (159/994), adjusted odds ratio 0.98, 95% confidence intervals 0.77 to 1.25, P=0.86). The need for an additional uterotonic agent in the bolus and infusion group was lower than that in the bolus only group (12.2% (126/1033) v 18.4% (189/1025), 0.61, 0.48 to 0.78, P
Methods: We randomly assigned children with severe febrile illness and impaired perfusion to receive boluses of 20 to 40 ml of 5% albumin solution (albumin-bolus group) or 0.9% saline solution (saline-bolus group) per kilogram of body weight or no bolus (control group) at the time of admission to a hospital in Uganda, Kenya, or Tanzania (stratum A); children with severe hypotension were randomly assigned to one of the bolus groups only (stratum B). All children received appropriate antimicrobial treatment, intravenous maintenance fluids, and supportive care, according to guidelines. Children with malnutrition or gastroenteritis were excluded. The primary end point was 48-hour mortality; secondary end points included pulmonary edema, increased intracranial pressure, and mortality or neurologic sequelae at 4 weeks.
Results: The data and safety monitoring committee recommended halting recruitment after 3141 of the projected 3600 children in stratum A were enrolled. Malaria status (57% overall) and clinical severity were similar across groups. The 48-hour mortality was 10.6% (111 of 1050 children), 10.5% (110 of 1047 children), and 7.3% (76 of 1044 children) in the albumin-bolus, saline-bolus, and control groups, respectively (relative risk for saline bolus vs. control, 1.44; 95% confidence interval [CI], 1.09 to 1.90; P=0.01; relative risk for albumin bolus vs. saline bolus, 1.01; 95% CI, 0.78 to 1.29; P=0.96; and relative risk for any bolus vs. control, 1.45; 95% CI, 1.13 to 1.86; P=0.003). The 4-week mortality was 12.2%, 12.0%, and 8.7% in the three groups, respectively (P=0.004 for the comparison of bolus with control). Neurologic sequelae occurred in 2.2%, 1.9%, and 2.0% of the children in the respective groups (P=0.92), and pulmonary edema or increased intracranial pressure occurred in 2.6%, 2.2%, and 1.7% (P=0.17), respectively. In stratum B, 69% of the children (9 of 13) in the albumin-bolus group and 56% (9 of 16) in the saline-bolus group died (P=0.45). The results were consistent across centers and across subgroups according to the severity of shock and status with respect to malaria, coma, sepsis, acidosis, and severe anemia.
Conclusions: Fluid boluses significantly increased 48-hour mortality in critically ill children with impaired perfusion in these resource-limited settings in Africa. (Funded by the Medical Research Council, United Kingdom; FEAST Current Controlled Trials number, ISRCTN69856593.).
Hence, determining the oxytocin concentration for cesarean section is important. However, since the activity of oxytocin varies from individual to individual  and an appropriate dose has not been established, 5-20 IU is intravenously injected based on experience [11,12]. There is a recent assertion that bolus intravenous injection or bolus-continuous parallel intravenous injection of oxytocin is more effective than continuous intravenous injection in cesarean section [13,14]. There is also a report that a great quantity of bolus intravenous injection requires caution because it causes hemodynamic changes related to hypotension [1,2]. Therefore, research is necessary on the method of oxytocin injection and the effective minimum concentration for cesarean section to induce uterine contraction without side effects.
The subjects were randomly divided into three groups, 20 subjects per group. For the oxytocin injection, 5 ml of bolus diluted with normal saline and 40 ml of infusion solution were prepared in advance by a nurse who did not participate in the study. In Group 1, bolus intravenous injection was done for about five seconds with 5 ml of normal saline and then continuous intravenous injection of 20 IU oxytocin diluted with 40 ml of normal saline was done at a rate of 0.5 IU/min for 40 minutes with a syringe pump. In groups 2 and 3, bolus intravenous injection of 2 IU and 5 IU of oxytocin diluted with 5 ml of normal saline was done at a rate of 1 ml/sec, and then continuous intravenous injection of 10 IU of oxytocin diluted with 40 ml of normal saline was done at a rate of 0.25 IU/min for 40 minutes with a syringe pump. The epidemiological data did not show a difference in the age, height, weight, and gestation period of the patients among the groups (Table 1). The obstetrician evaluated the degree of uterine contraction on a LAS in which the grade was determined from a grade of o to 10 (0 = completely atonic, 10 = fully contracted)  at five-minute intervals during the operation for 25 minutes from the time just after the newborn was delivered. In the cases where the uterine contraction was considered as insufficient during the operation, intravenously injection of 0.2 mg of methylergonovine was done by the request of the obstetrician, diluting it with normal saline and slowly injecting it over one to two minutes with careful monitoring of the blood pressure. The blood loss was estimated by measuring the weight of the suction bottle and gauze excluding the amniotic fluid.
Change of maternal mean arterial pressure (MAP) after oxytocin injection during Cesarean delivery. Oxytocin was injected in the following doses; Group 1: 0.5 IU/min continuous injection, Group 2: 2 IU bolus-continuous injection, Group 3: 5 IU boluscontinuous injection. *P < 0.05 compared with each group after oxytocin injection.
According to many recent studies, oxytocin bolus injection was reported to be more effective than infusion by intravenous injection to reduce blood loss by inducing the appropriate uterine contraction , and thus, the minimum bolus dose has been discussed [19-21]. A suggested method to reduce hemodynamic changes is the repeated intravenous injections of a small quantity of a bolus dose and bolus-continuous parallel intravenous injection [14,22]. Svanstrom et al.  stated that attention is required because a bolus injection of 10 IU oxytocin may cause temporary hypotension and tachycardia as well as myocardial ischemia, apart from the operation, pregnancy, and autonomic blocking by spinal anesthesia. Pinder et al.  recommended 5 IU as the bolus dose since 10 IU of bolus intravenous injection caused severe hemodynamic changes, but they stated that the dose might not be considered as safe, either. On the contrary, Butwick et al.  asserted that a dose of more than 5 IU might not be necessary because appropriate uterine contraction occurred even with a bolus dose of 0.5-3 IU. Sartain et al.  injected 2 IU and 5 IU of bolus doses, which are the same doses for groups 2 and 3 in our experiment and reported that the use of 2 IU was more effective because the hemodynamic changes were more severe in the 5 IU group even though the uterine contraction were similar in the two groups. These results were similar to our results and the hemodynamic changes were always temporary.
Change of heart rate (HR) after oxytocin injection during Cesarean delivery. Oxytocin was injected in the following doses; Group 1: 0.5 IU/min continuous injection, Group 2: 2