Table 5.
Synthetic oxytocin dose regimens, maternal levels and total dose calculations
| Synthetic oxytocin (SOT): Infusion rate (mU/min) OR Intramuscular injection in International Units (IU) OR Controls (Sampling details) |
Maternal oxytocin levels (mean, pg/mL) | Calculated total SOT (IU) per hour | Calculated total SOT (IU) if dose given over 8 hours (unless stated) | Comments |
|---|---|---|---|---|
| Intrapartum | ||||
| Data from Fuchs (1983) n = 15 labour induction, n = 17 spontaneous labour | ||||
| Basal levels pre-labour | 17.4 | Nil | Nil |
Doubling infusion rate approx doubled oxytocin levels Oxytocin levels below 10 mU/min are within range of levels in women with no SOT (See Table 3 for details) |
| Spontaneous 1st stage | 45.4 | Nil | Nil | |
| SOT: 1–3 mU/min | 21.1 | 0.06–0.18 | 0.5–1.4 | |
| 4–6 mU/min | 49.1 | 0.24–0.36 | 1.9–2.9 | |
| 7–9 mU/min | 58.8 | 0.42–0.54 | 3.4–4.3 | |
| 10–16 mU/min | 110 | 0.6–0.96 | 4.8–7.7 | |
| Data from Furuya (1988) n = 5 labour induction (Data estimated from Fig. 7) | ||||
| Basal levels pre-labour | 2 |
No control group without SOT Doubling infusion rate approx tripled oxytocin levels |
||
| SOT: 12 mU/min | 8 | 0.6 IU | 4.8 | |
| 16 mU/min | 17 | 0.9 | 7.2 | |
| 20 mU/min | 19 | 1.2 | 9.6 | |
| 24 mU/min | 38 | 1.4 | 11.2 | |
| 32 mU/min (n = 3) | 55 | 1.9 | 15.2 | |
| Postpartum (vaginal birth) | ||||
|
Data from Thornton (1988) n = 25 postpartum SOT, n = 15 no postpartum SOT Sampled every 30 sec for 15 min, starting just before birth | ||||
| No SOT: | Nil | Nil |
Standard postpartum intramuscular injection (5 IU SOT with 0.5 mg ergometrine) Peak oxytocin levels 3-fold higher than peak physiological levels, as measured in this postpartum study Total dose: 5 IU SOT |
|
| before birth | 3.2 | |||
| at 5–15 min | 6.4 | |||
| mean peak | 11.6 | |||
| 5 IU intramuscular (IM) SOT at birth of anterior shoulder: | 5 | 5 (single dose) | ||
| before birth | 3.1 | |||
| at 5–15 min | 15.9 | |||
| mean peak | 30.5 | |||
|
Data from Gibbens (1972) n = 10 postpartum SOT IM; n = 14 postpartum SOT IV bolus Sampled frequently for 60 min, starting just before birth (Data estimated from Fig. 1) | ||||
| SOT IM: | Nil | Nil |
Standard postpartum injection (5 IU SOT with 0.5 mg ergometrine) given IM/IV at birth of anterior shoulder Total dose: 5 IU SOT Rapid high peak following IV bolus, peaking at 1 min Gradual lowering but prolonged peak following IM |
|
| before birth | < 1.2 | |||
| at 1 min | 40 | |||
| at 3 min | 50 | |||
| at 6 min | 45 | |||
| at 30 mins | 18 | |||
| SOT IV: | 5 | 5 IU (single dose) | ||
| before birth | < 1.5 | |||
| at 30 sec | 330 | |||
| at 1 min | 550 | |||
| at 3 min | 280 | |||
| at 6 min | 100 | |||
| at 30 min | 20 | |||
|
Data from Fuchs (1982) n = 10 postpartum SOT, n = 10 no postpartum SOT Sampled just before birth and 5 min, 30 min, 2 hours postpartum | ||||
| No SOT: | Nil | Nil |
Postpartum infusion dose relatively high compared to labour Oxytocin levels 8–10-fold higher than physiological levels, as measured in this postpartum study Total dose: 12-18 IU SOT |
|
| at 5 min | 41.1 | |||
| at 30 min | 29.1 | |||
| at 120 min | 29.4 | |||
| SOT infusion at 100–150 mU/min, reduced over 2 hours | 6–9 | 12–18 (over 2 hours) | ||
| at 5 min | 93.4 | |||
| at 30 min | 275 | |||
| at 120 min | 127 | |||
Units: IU: international units; mU: milliUnits; pg: picograms; mL: millilitres
Oxytocin conversions: 1 IU = 1000 mU; 1 mU = 1000 μU; 1 mg = 1000 μg; 1 μg = 1000 ng; 1 ng = 1000 pg; 1 IU = 1.67 μg; 1 mU = 1.67 ng; 1 μg = 0.6 IU; 1 ng = 0.60 mU; 1 pg/mL = 1 pmol/L = 1pM
Abbreviations: approx approximately, IM intramuscular, IV intravenous, min minutes, sec seconds, SOT synthetic oxytocin
See Table 3 for full details of studies