The effects of uterine and umbilical blood flows on the transfer of propofol across the human placenta during in vitro perfusion

Propofol Pharmacokinetics and Estimation of Fetal Propofol Exposure during Mid-Gestational Fetal Surgery: A Maternal-Fetal Sheep Model

BACKGROUND

Measuring fetal drug concentrations is extremely difficult in humans. We conducted a study in pregnant sheep to simultaneously describe maternal and fetal concentrations of propofol, a common intravenous anesthetic agent used in humans. Compared to inhalational anesthesia, propofol supplemented anesthesia lowered the dose of desflurane required to provide adequate uterine relaxation during open fetal surgery. This resulted in better intraoperative fetal cardiac outcome. This study describes maternal and fetal propofol pharmacokinetics (PK) using a chronically instrumented maternal-fetal sheep model.

METHODS

Fetal and maternal blood samples were simultaneously collected from eight mid-gestational pregnant ewes during general anesthesia with propofol, remifentanil and desflurane. Nonlinear mixed-effects modeling was performed by using NONMEM software. Total body weight, gestational age and hemodynamic parameters were tested in the covariate analysis. The final model was validated by bootstrapping and visual predictive check.

RESULTS

A total of 160 propofol samples were collected. A 2-compartment maternal PK model with a third fetal compartment appropriately described the data. Mean population parameter estimates for maternal propofol clearance and central volume of distribution were 4.17 L/min and 37.7 L, respectively, in a typical ewe with a median heart rate of 135 beats/min. Increase in maternal heart rate significantly correlated with increase in propofol clearance. The estimated population maternal-fetal inter-compartment clearance was 0.0138 L/min and the volume of distribution of propofol in the fetus was 0.144 L. Fetal propofol clearance was found to be almost negligible compared to maternal clearance and could not be robustly estimated.

CONCLUSIONS

For the first time, a maternal-fetal PK model of propofol in pregnant ewes was successfully developed. This study narrows the gap in our knowledge in maternal-fetal PK model in human. Our study confirms that maternal heart rate has an important influence on the pharmacokinetics of propofol during pregnancy. Much lower propofol concentration in the fetus compared to maternal concentrations explain limited placental transfer in in-vivo paired model, and less direct fetal cardiac depression we observed earlier with propofol supplemented inhalational anesthesia compared to higher dose inhalational anesthesia in humans and sheep.

Effect of decreased fetal perfusion on placental clearance of volatile anesthetics in a dual perfused human placental cotyledon model

Placental transfer of volatile anesthetics is a critical issue in managing fetal distress during cesarean section under general anesthesia. Using dual perfused human placental cotyledons obtained from parturients undergoing elective cesarean section (n = 5), we investigated the effect of decreased fetal perfusion on placental clearance of sevoflurane and isoflurane. Keeping the maternal flow rate fixed, fetal flow rate was consecutively decreased from 3 ml/min (control perfusion) to 2 ml/min (intermediate perfusion) and to 1 ml/min (hypoperfusion). Placental transfer was assessed by the clearance of anesthetics by the placenta, defined by the ratio of anesthetic concentration in fetal vein and maternal artery, multiplied by fetal flow rate. Placental clearance was compared between different fetal perfusion states and anesthetics. Hypoperfusion resulted in a lower clearance of sevoflurane and isoflurane compared with control (P = 0.002, P < 0.001) and intermediate (P = 0.04, P = 0.018) perfusion. Clearances of sevoflurane and isoflurane were comparable during control perfusion (P = 0.93), intermediate perfusion (P = 1.00), and hypoperfusion (P = 0.88). Thus, maintenance of volatile anesthetics at a marginally low concentration may not be necessary when fetal distress is observed during emergency cesarean delivery because placental transfer of volatile anesthetics decreases with decreasing fetal perfusion.

Transplacental transfer of medetomidine and ketamine in pregnant ewes

The extent of placental transfer of medetomidine and ketamine is unknown in pregnant ewes. Date-mated singleton (n = 8) and twin (n = 8) pregnant merino cross ewes were anaesthetized for Caesarean delivery of preterm lamb fetuses. A combination of medetomidine (20 μg/kg) and ketamine (10 mg/kg) was administered by intravenous injection and surgery performed immediately thereafter. Blood samples were collected from the ewe at one, five and 10 min after intravenous injection and from the umbilical vein of the fetus at delivery. Non-pregnant ewes were also anaesthetized (n = 8). There was no difference in the plasma concentration of medetomidine or ketamine when comparing singleton and twin ewes or pregnant and non-pregnant ewes for the short duration of the study. Fetal plasma concentrations of each drug were comparable to the maternal concentrations at the same time. We conclude that both drugs cross the placenta readily and provide anaesthesia and analgesia for the fetus when it is delivered.

The human placental perfusion model: a systematic review and development of a model to predict in vivo transfer of therapeutic drugs

Dual perfusion of a single placental lobule is the only experimental model to study human placental transfer of substances in organized placental tissue. To date, there has not been any attempt at a systematic evaluation of this model. The aim of this study was to systematically evaluate the perfusion model in predicting placental drug transfer and to develop a pharmacokinetic model to account for nonplacental pharmacokinetic parameters in the perfusion results. In general, the fetal-to-maternal drug concentration ratios matched well between placental perfusion experiments and in vivo samples taken at the time of delivery of the infant. After modeling for differences in maternal and fetal/neonatal protein binding and blood pH, the perfusion results were able to accurately predict in vivo transfer at steady state (R² = 0.85, P < 0.0001). Placental perfusion experiments can be used to predict placental drug transfer when adjusting for extra parameters and can be useful for assessing drug therapy risks and benefits in pregnancy.

Propofol inhibits potassium chloride induced contractions of isolated human umbilical vessels

BACKGROUND AND OBJECTIVE

We have evaluated the effects of propofol and its relationship with K+ channels on human isolated umbilical vessels.

METHODS

Umbilical vessel rings were suspended in isolated organ baths containing Krebs-Ringer solution. In the first series of experiments the effect of propofol (10(-9)-10(-4) M) was examined in a concentration-dependent manner on umbilical vessels precontracted with KCl (60 mmol). In the second series, these effects were studied in the presence of tetraethylammonium.

RESULTS

A mild contraction was produced by low dose propofol in both precontracted umbilical artery and umbilical vein segments. 10(-4) M propofol caused significant relaxation in both umbilical artery and umbilical vein. The relaxation response was significantly reduced by the addition of 10(-1) M tetraethylammonium.

CONCLUSION

These results suggested that the responses of propofol on KCl-induced contractions of both umbilical artery and vein were dose dependent, and this effect involved Ca2+ activated K+ channels.

Anthracyclines during pregnancy: embryo–fetal outcome in 160 patients

BACKGROUND

Anthracyclines are essential for the treatment of malignancies observed in pregnant patients. Knowledge of the potential side-effects of chemotherapy on the developing fetus is essential for patient counseling.

PATIENTS AND METHODS

We collected information concerning patients treated with anthracyclines during pregnancy from a review of literature between 1976 and 2001 and our experience. The events analyzed were malformations, fetal death and spontaneous abortion. A chi(2) test with a Yates correction was used to compare the distribution of severe events.

RESULTS

A total of 160 patient pregnancies were analyzed. The fetal outcome was frequently normal (73%). Abnormalities included malformations (3%), fetal death (9%), spontaneous abortion (3%), fetal complications (8%) and prematurity (6%). Fetal death was often directly consecutive to maternal death (40%). Unfavorable fetal outcome was significantly more frequent in leukemia patients (P = 0.001). In patients with solid tumors, the first trimester was significantly associated with more complications (P = 0.029). The risk of severe fetal toxicity was increased 30-fold when the dose of doxorubicin per cycle exceeded 70 mg/m(2) (P = 0.037).

CONCLUSIONS

Anthracyclines may induce embryo-fetal toxicity. Nevertheless the risk seems low, especially after the first trimester and using doses of doxorubicin below 70 mg/m(2).

The influences of maternal albumin concentrations on the placental transfer of propofol in human dually perfused cotyledon in vitro

IMPLICATIONS

These results indicate that fetal exposure to propofol can vary considerably depending on maternal plasma albumin concentration. A fractional change in the maternal protein binding of propofol can result in a relatively large difference in fetal exposure.