Maternal and fetal arterial blood gas data during general anaesthesia for caesarean delivery of preterm twin lambs

Isoflurane increases the activity of the vascular matrix metalloproteinase-2 in non-pregnant rats and increases the nitric oxide metabolites in pregnancy

Surgeries that require general anesthesia occur in 1.5-2% of gestations. Isoflurane is frequently used because of its lower possibility of affecting fetal growth. Therefore, we examined the isoflurane anesthesia-induced effects on maternal hemodynamic and vascular changes. We hypothesized that isoflurane would enhance endothelium-dependent vasodilation as a consequence of increased nitric oxide and decreased metalloproteinases (MMPs). Female rats (n=28) were randomized into 4 groups (7 rats/group): conscious (non-anesthetized) non-pregnant group, non-pregnant anesthetized group, conscious pregnant group, and pregnant anesthetized group. Anesthesia was performed on the 20th pregnancy day, and hemodynamic parameters were monitored. Nitric oxide metabolites, gelatinolytic activity of MMP-2 and MMP-9, and the vascular function were assessed. Isoflurane caused no significant hemodynamic changes in pregnant compared with non-pregnant anesthetized group. Impaired acetylcholine-induced relaxations were observed only in conscious non-pregnant group (by approximately 62%) versus 81% for other groups. Phenylephrine-induced contractions were greater in endothelium-removed aorta segments of both pregnant groups (with or without isoflurane) compared with non-pregnant groups. Higher nitric oxide metabolites were observed in anesthetized pregnant in comparison with the other groups. Reductions in the 75 kDa activity and concomitant increases in 64 kDa MMP-2 isoforms were observed in aortas of pregnant anesthetized (or not) groups compared with conscious non-pregnant group. Isoflurane anesthesia shows stable effects on hemodynamic parameters and normal MMP-2 activation in pregnancy. Furthermore, there were increases in nitric oxide bioavailability, suggesting that isoflurane provides protective actions to the endothelium in pregnancy.

Anaemia and Hypoproteinaemia in Pregnant Sheep during Anaesthesia

Simple Summary

Anaemia during pregnancy is commonly reported in humans and is considered a significant health issue as it is associated with adverse neonatal outcomes including low birth weight, preterm birth and possible perinatal mortality. Pregnant sheep are a common model for research investigating the causes and consequences of preterm birth, but the incidence and significance of anaemia during pregnancy is not known. However, intraoperative anaemia in pregnant sheep has been reported previously. In addition, it has been demonstrated that the cause of intraoperative anaemia is not pregnancy alone as pregnant sheep in a farm environment did not develop anaemia. The aim of this study was to document the red blood cell and protein content of maternal blood before, during and after anaesthesia and surgery to elucidate the cause and duration of intraoperative anaemia in pregnant sheep in a research context. The concentration of red blood cells and protein decreased during anaesthesia and were attributed to the use of anaesthetic drugs and fluids as opposed to the pregnancy status of the sheep.

Abstract

The aim of this study was to document the packed cell volume (PCV), haemoglobin concentration and total protein concentration of maternal blood before, during and after anaesthesia. Six singleton Merino-cross pregnant ewes at 116-117 days of gestation were premedicated with intramuscular acepromazine (0.02 mg/kg) and buprenorphine (0.01 mg/kg), and anaesthesia was induced with intravenous midazolam and ketamine. Anaesthesia was maintained with isoflurane in 100% oxygen. Serial blood samples were collected the day before anaesthesia (baseline), immediately prior to induction of anaesthesia (pre-op), at the end of the procedure (intra-op) and the following day (post-op). There was a significant change in the PCV during the study (p = 0.003) with an initial decrease of 12.5% from the baseline (0.36 (0.36–0.4) to 0.315 (0.29–0.34), p = 0.044), a further intraoperative decrease of 41.7% from the baseline (0.21 (0.195–0.245), p = 0.002) and an increase the day afterwards (0.3 (0.285–0.35), p > 0.99 compared with baseline). The haemoglobin concentration also changed (p < 0.0001) (baseline: 114 (111.8–123); pre-op: 97 (77.25–104.5), 14.9% decrease, p = 0.022; intra-op: 70 (61.5–83.25), 38.5% decrease, p = 0.0009; post-op: 101.5 (96.25–114) g/L, p > 0.99). Likewise the change in total protein during the study was significant (p = 0.0003) and decreased from the baseline [70 (67.25–70.75) g/L] prior to anaesthesia (61 (58.25–64.5) g/L, 12.9% decrease, p = 0.0437) and further during anaesthesia (55.5 (53.75–63.25) g/L, 20.7% decrease, p = 0.0021) with an increase [63 (61.25–67) g/L, p > 0.99] on the first post-op day. In conclusion, intraoperative anaemia and hypoproteinaemia occurred in this study. These alterations are attributed to a combination of the side effects of acepromazine and haemodilution.

Pregnant sheep develop hypoxaemia during short-term anaesthesia for caesarean delivery

Short-term anaesthesia of the pregnant ewe may be required for caesarean delivery of a preterm foetus within a research protocol. The aim of this study was to evaluate and compare the acid-base and haematological status of the ewe and foetus at the time of surgical delivery by collecting maternal and foetal arterial blood samples. Fifteen date-mated singleton-pregnant merino cross ewes at 122.0 (±0.5) days of gestation were anaesthetised with a combination of midazolam (0.5 mg/kg) and ketamine (10 mg/kg) by intravenous injection. A subarachnoid injection of lidocaine (60 mg) was given to desensitise the caudal abdomen. Supplemental oxygen was not provided, and an endotracheal tube was not placed in the ewe's trachea. The development of maternal respiratory acidosis (hypercapnia) and hypoxaemia was anticipated. Samples of arterial blood for blood gas analyses were collected simultaneously from the radial artery of the ewe and the umbilical artery of the foetus immediately after delivery. The results from the maternal blood samples were within the normal range for pH, partial pressure of carbon dioxide in arterial blood (PaCO₂), base excess, glucose, lactate, haematocrit and haemoglobin concentration. The maternal partial pressure of oxygen in arterial blood (PaO₂) revealed hypoxaemia: 45.2 (41.1-53.4) mmHg. Foetal arterial blood gas analysis revealed hypoxaemia (15.0 ± 3.1 mmHg) and hypoglycaemia (0.1 (0.1-1.1) mmol/L). The benefit of providing supplemental oxygen and/or placing an endotracheal tube must be carefully weighed against the benefit of saving time when prompt delivery of the foetus is planned. In this study the pregnant ewe developed severe hypoxaemia, and this abnormality may have contributed to a low foetal PaO₂.

Sedation of sheep following the administration of acepromazine with buprenorphine or morphine is similar

The aim of this study was to compare sedation of sheep with acepromazine and buprenorphine or morphine. Twenty merino sheep received acepromazine (0.03mg/kg) with buprenorphine (0.02mg/kg, AB, n=10) or morphine (0.3mg/kg, AM, n=10) by intramuscular injection. Sedation was scored (SS) on a scale from 0 (no sedation) to 10 (heavy sedation). Response to restraint was scored (RS) on a scale from 0 (agitated) to 4 (relaxed). Three independent blinded observers and a single blinded observer determined the SS and RS, respectively. The SSs were summed (maximum 30). Data were compared using a t-test. Data is mean±SD (95% confidence interval). Each group comprised 2 wethers and 8 ewes. There was no difference between the AB and AM groups: weight 44±3.1kg and 44.7±3kg (p=0.58); SS 4.6±3.2 (2.4-6.9) and 6.6±3.5 (4.1-9.1) (p=0.21); and RS 1.6±1.3 (0.5-2.7) and 2±1.5 (0.7-3.3) (p=0.6). No adverse effects of the drugs were observed. Sedation with AB or AM at these doses is similar in sheep without observed adverse effects.

Pregnant Sheep in a Farm Environment Did Not Develop Anaemia

Simple Summary

Anaemia refers to a low red blood cell count and is common during pregnancy in women. Anaemia has been reported in sheep undergoing surgery during pregnancy for biomedical research projects. The incidence and severity of anaemia during pregnancy in sheep is unknown. Three groups of sheep were established: non-pregnant; pregnant with a single lamb; and pregnant with twin lambs. The stage of pregnancy was known as the sheep were mated on a known date and pregnancy was confirmed 50 days later by ultrasound examination. During pregnancy, blood samples were collected to measure red cells in the blood and protein levels. Samples were also collected to ensure that the sheep did not have any risk factors for anaemia, such as nutritional deficiency and internal parasites. Anaemia did not occur in any sheep during the study. Anaemia did not develop during pregnancy and red cell counts and protein levels were similar between each group. All the sheep lambed as expected, except for one that was expecting twins delivered a single lamb.

Abstract

The aim of this study was to document the haematological profile of pregnant ewes throughout gestation. Sheep were divided into three groups (n = 8 per group): non-pregnant, singleton, or twin pregnancy. Blood samples were collected every 14 days from day 55 of gestation for haemoglobin concentration; packed cell volume; total protein; and albumin concentration. On days 55 and 125 of gestation blood was collected for trace element estimation: soluble copper and zinc; glutathione peroxidase (GSHPx); and methylmalonic acid (MMA). Pooled faecal samples were collected on days 55, 97, and 139 of gestation. Pasture cuts were collected on days 97 and 153 of gestation. The haematology and protein concentrations were not different between groups throughout the study. Copper concentration increased in all animals during the study (p < 0.0001). Zinc concentration was lowest in the singleton and twin pregnant sheep on day 55 of gestation (p = 0.04). GSHPx was not different between groups during the study. MMA decreased in all animals during the study (p < 0.0001), but was not different between groups. Faecal samples were consistently negative for strongyle and nematode eggs, and coccidian oocysts. The pasture was good quality. Pregnant sheep in a farm environment with normal trace element status, no parasites, and an adequate diet, did not develop anaemia (PCV < 0.27).