Dosing

The dose of a general anesthetic will be different for different patients. Your doctor will decide on the right amount for you. The dose will depend on:

• Your age;
• Your general physical condition;
• The kind of surgery or other procedure you are having; and
• Other medicines you are taking or will receive before and during surgery.

In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For general anesthetics, the following should be considered:

Allergies Tell your doctor if you have ever had any unusual or allergic reaction to barbiturates or general anesthetics. Also tell your health care professional if you are allergic to any other substances, such as foods, preservatives, or dyes.

Pregnancy

• For barbiturate anesthetics (methohexital and thiopental) Methohexital has not been studied in pregnant women. However, it has not been shown to cause birth defects or other problems in animal studies. Studies on effects in pregnancy with thiopental have not been done in either humans or animals. However, use of barbiturate anesthetics during pregnancy may affect the nervous system in the fetus.
• For etomidate Etomidate has not been studied in pregnant women. Although studies in animals have not shown etomidate to cause birth defects, it has been shown to cause other unwanted effects in the animal fetus when given in doses usually many times the human dose.
• For inhalation anesthetics (enflurane, halothane, isoflurane, methoxyflurane, and nitrous oxide) Enflurane, halothane, isoflurane, methoxyflurane, and nitrous oxide have not been studied in pregnant women. However, studies in animals have shown that inhalation anesthetics may cause birth defects or other harm to the fetus.When used as an anesthetic for an abortion, enflurane, halothane, or isoflurane may cause increased bleeding.When used in small doses to relieve pain during labor and delivery, halothane may slow delivery and increase bleeding in the mother after the baby is born. These effects do not occur with small doses of enflurane, isoflurane, or methoxyflurane. However, they may occur with large doses of these anesthetics.
• For ketamine Ketamine has not been studied in pregnant women. Studies in animals have not shown that ketamine causes birth defects, but it has caused damage to certain tissues when given in large amounts for a long period of time.
• For propofol Propofol has not been studied in pregnant women. Although studies in animals have not shown propofol to cause birth defects, it has been shown to cause deaths in nursing mothers and their offspring when given in doses usually many times the human dose.

General anesthetics may cause unwanted effects, such as drowsiness, in the newborn baby if large amounts are given to the mother during labor and delivery.

Breast-feeding Barbiturate anesthetics (methohexital and thiopental), halothane, and propofol pass into the breast milk. However, general anesthetics have not been reported to cause problems in nursing babies.

Children Anesthetics given by inhalation and ketamine have been tested in children and have not been shown to cause different side effects or problems in children than they do in adults.

Although there is no specific information comparing use of etomidate in children with use in other age groups, this medicine is not expected to cause different side effects or problems in children than it does in adults.

Although there is no specific information comparing use of thiopental administered intravenously in children with use in other age groups, using thiopental intravenously in children is not expected to cause different side effects or problems in children than it does in adults.

Propofol has been tested in children to produce loss of consciousness before and during surgery. It has not been shown to cause different side effects or problems in children than it does in adults. Propofol should not be used in critically ill children to help the children withstand the stress of being in the intensive care unit. Some critically ill children have developed problems with their body chemistries after receiving propofol, and a few children have died as a result of this. It is not known if propofol or the severe illnesses of the children caused this problem.

Older adults Elderly people are especially sensitive to the effects of the barbiturate anesthetics (methohexital and thiopental), etomidate, propofol, and anesthetics given by inhalation. This may increase the chance of side effects.

Ketamine has not been shown to cause different side effects or problems in older people than it does in younger adults.

Other medicines Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. When you are receiving general anesthetics, it is especially important that your health care professional know if you are taking any other medicine, including any of the following:

• Street drugs, such as amphetamines (uppers), barbiturates (downers), cocaine, marijuana, phencyclidine (PCP or angel dust), and heroin or other narcotics Serious, possibly fatal, side effects may occur if your medical doctor or dentist gives you an anesthetic without knowing that you have taken another medicine

• Malignant hyperthermia, during or shortly after receiving an anesthetic (history of, or family history of). Signs of malignant hyperthermia include very high fever, fast and irregular heartbeat, muscle spasms or tightness, and breathing problems This side effect may occur again