Breastfeeding after Anesthesia

©G.M. Woerlee, 2005–2023

Some breastfeeding women undergo surgical procedures. They nearly all ask whether it is safe to continue breastfeeding their infant after having undergone anesthesia. According to popular belief, anesthetic drugs are powerful and dangerous, and their presence in breast milk may well adversely affect the health of any baby fed such milk. Accordingly, women are usually advised to cease breastfeeding for 24 hours after surgery, and to dispose of their milk during this time ("pump and dump"). But is this correct advice? Is breastfeeding after anesthesia and surgery safe?

What determines breast milk drug content?

Fat solubility and the amount of milk per feed determine the total dose of any drug ingested by a suckling infant. Women never feed their infants while unconscious under general anesthesia - they are always conscious when feeding their infants. Most anesthetic drugs causing sedation and respiratory arrest are fat-soluble sedatives, hypnotics and opiates. This means that the concentrations of these drugs in tissues and fluids with a high fat content is higher than that in blood, which has a relatively low fat content. So what is the fat content of various organs?

Whole blood, total fats (including cell membranes etc) = 0.37%
Human milk, total fats in liquid milk = 4.75%
Human brain, total fats as percentage wet weight of brain = 10-12%

A person is awake and conscious after awakening from general anesthesia. The fat content of the brain is higher than that of human milk, and so the brain concentration of any drug is lower in breast milk than in the brain of the mother. In other words, the amount of any drug is lower in breast milk than in the brain. The relative concentrations of some drugs in breast milk relative to the concentration in blood, (actually plasma), is given in the table below as a ratio of the concentration in milk relative to blood plasma.

Drug name	Milk/Plasma ratio (M/P ratio)	Reference
Lidocaine	0.17-0.35	Giuliani 2001
Aspirin	0.033-0.05	Findlay 1981
Paracetamol	1.0	Notarianni 1987
Naproxen	0.01	Spigset 2000
Ibuprofen	0.008-0.06	Spigset 2000
Indomethacin	0.01-1.48	Spigset 2000
Codeine	2.16-2.46	Spigset 2000
Morphine	2.45	Spigset 2000
Pethidine	0.68-1.59	Spigset 2000
Fentanyl	2.10	Spigset 2000
Halothane	1.0	Cote 1976
Thiopentone	1.0	Anderson 1987
Propofol	1.0	Schmitt 1987
Midazolam	0.15	Matheson 1990
Nitrazepam	0.27	Matheson 1990

Total dose of any drug ingested by an infant

The volume of milk produced by a lactating mother in the first few months after delivery is up to 500 ml per day. This together with the knowledge of the M/P ratios makes it possible to calculate the total dose of a drug present in the mother ingested by a suckling infant with the following formula.

Dose = C x (M/P) x V

Dose = Total dose of drug ingested by infant (mg)
C = maternal plasma concentration of drug during suckling (mg/l)
(M/P) = milk/plasma concentration ratio
V = volume of milk ingested by the infant (liters)

This equation is simple. But what plasma drug concentrations of anesthetic drugs can one expect? A woman who breastfeeds her infant is conscious and breathing, which means that anesthetic drug concentrations are lower than those required to induce unconsciousness and cause breathing to stop. Moreover, a woman who breastfeeds her baby is always alert and not heavily sedated, which means even lower anesthetic drug concentrations. Anesthetic drug concentrations causing sedation and unconsciousness are listed in the appendix of the book Gerry's Real World Guide to Pharmacokinetics & Other Things. These data together with the M/P ratios above make the above equation usable. Calculations using the equation above are very instructive - they reveal that the total dose of any anesthetic drug ingested by a suckling infant is negligible. Furthermore, any drug ingested by a suckling infant is absorbed through the intestines of the infant. Such absorption is slow and inefficient, resulting in only an insignificant amount of any anesthetic drug present in a mother actually being absorbed into the blood a breastfeeding infant (Nitsun 2006).

Conclusion - continue breastfeeding after anesthesia

Anesthetic drugs are administered for a short period of nearly always less than two hours, and analgesic drugs to relieve the pain of surgery are administered for only a few days. The total doses of these drugs ingested by an infant is negligable, and intestinal absorption of these drugs by suckling infant is also negligible, which is why the advice of all experts is simply to continue breastfeeding after any operation (Howie 2006, Lang 2003). If a woman feels she is capable of breastfeeding her baby after an operation, she may do so in full knowledge that any anesthetic and analgesic drugs present in her blood will not affect her child.