The selection of anaesthetic protocols and peri-operative processes for the Caesarean section should be aimed at maximising the survival of the dam and neonates, deliver offspring with good vigour and high Apgar scores, with a comfortable dam willing to suckle and bond with her offspring immediately following surgery (see the Caesarean Section Survival Guide. Part 1: Physiology and Pre-anaesthetic Considerations).
Selection of Anaesthetic Protocols
Plan the C-section anaesthetic to:
- Minimise time from induction to delivery of neonates
- Allow rapid recovery of dam
- Provide efficacious maternal analgesia
- Ensure high neonate Apgar scores
- Allow early suckling and bonding with neonates
Multimodal anaesthesia, including local/regional anaesthesia should therefore be considered.
The majority of drugs that cross the blood-brain barrier e.g. sedatives, tranquillisers, analgesics, induction and maintenance agents, will also cross the placenta to potentially affect the neonate.1,2 Therefore, in order to reduce the CNS depressant effects of drugs on both the dam and the offspring the following should be considered when selecting anaesthetic protocols for the Caesarean patient3:
- Select drugs with a short duration of action
- Choose drugs with minimal physiological effects
- Use drugs that can be antagonised wherever possible
- Reduce doses of anaesthetic related drugs by 25-40%. The dose requirements in pregnant patients can be considerably lower than in non-pregnant animals, therefore reduce the dose accordingly (see Caesarean Section Survival Guide. Part 1: Physiology and Pre-anaesthetic Considerations)
- Use the lowest possible dose
- Administer to effect wherever possible
Premedication & pre-anaesthetic analgesia
As for anaesthetic procedures in non-pregnant patients, the use of premedicants may reduce the dose requirements of other CNS depressant drugs e.g. induction and maintenance agents, and reduce anxiety in the patient allowing an increased tolerance for intravenous catheterisation & pre-oxygenation. However, as most premedicants cross the placenta to potentially affect the neonate, the necessity for premedication should be carefully considered following assessment of the physical status of the dam and her amenability to handling.2 Any choice of premedication, if used, is therefore at the discretion, and is the responsibility, of the attending veterinary surgeon.
Possible Premedication Protocols
Not administering a premedicant to the dam eliminates the concerns regarding the effects of the drug on the neonates. What has to be considered however is that the dam will not have received an analgesic prior to induction & there will be no premedicant dose sparing effects.
The majority of studies performed on C-section patients used no premedication, with analgesia, in the form of an opioid, being administered following delivery of the last neonate.4 Indeed, many premedicants commonly used in the non-pregnant animal are not specifically licenced for use in gravid dams, and some e.g. buprenorphine, are specifically contraindicated during pregnancy prior to delivery of the neonates.1 The precise wording of SPCs regarding use in pregnancy and during lactation should be carefully assessed.
The Caesarean section is major surgery and analgesia should not be withheld. Once the last neonate has been successfully delivered the dam is, in effect, no longer pregnant and many anaesthetists would administer analgesics at this point (see later under “Analgesia”).1,4
No premedication is the protocol of choice of many anaesthetists and general practitioners.4
PREMEDICATION WITH FULL MU OPIOID ONLY
Full mu agonist opioids will provide preoperative sedation and peri-operative analgesia to the dam, with minimal cardiovascular depression, and be dose sparing for other CNS depressants e.g. inhalation agents, resulting in more stable haemodynamic parameters.1 However, respiratory depression may occur and ventilatory support should be provided if necessary.3 Following full mu opioid administration the effects on the physiology of the dam, and therefore the unborn neonates, should be considered: hypoxia of the unborn foetus can be a consequence of drug-induced maternal respiratory depression3 in an animal that already has a compromised respiratory function (20% decrease in FRC) as a result of the physiological changes of pregnancy (see Caesarean Section Survival Guide. Part 1: Physiology and Pre-anaesthetic Considerations).4
Opioids have the advantage that antagonism is possible with naloxone in both the dam and the delivered neonates.5 If it is necessary to administer naloxone the period of effect of both the opioid and naloxone should be assessed e.g. the duration of action of naloxone is less than 1 hour, whereas methadone has an average duration of effect of 2-4 hours.6 Repeat dosing of naloxone may therefore be necessary.7 It should be remembered that antagonization of undesirable opioid side-effects with naloxone will also antagonise the analgesic effects and alternative forms of pain relief should be considered.
Buprenorphine is contraindicated prior to delivery of pups.
Other Premedicants - Considerations
This group of sedatives are not a suitable choice for C-section premedication. Acepromazine has a long onset time following both intravenous and intramuscular administration (10-15 minutes and 30-40 minutes respectively).3,8 Acepromazine is also associated with a prolonged, non-antagonisable, duration of action and produces vasodilation and hypotension in an animal that may already be dehydrated, susceptible to haemorrhage and/or experiencing positional hypotension (see Caesarean Section Survival Guide. Part 1: Physiology and Pre-anaesthetic Considerations).1,3,6 Bradycardia may occur.6 Peripheral vasodilation and resetting of the thermoregulatory centre disrupt temperature control in both the dam and the neonate. Additionally, the neonatal liver has a limited capacity to metabolise this group of drugs.3
Despite the issues associated with phenothiazines if a degree of maternal sedation is necessary prior to C-section some authors suggest they may be cautiously administered at very low doses following a risk-benefit assessment.7,9,10,11
All alpha-2 agonists cause profound, dose related sedation and (shorter-lived) analgesia. Following administration there is peripheral vasoconstriction, with subsequent hypertension, a reduction in cardiac output (by up to 50%) and bradycardia. These effects are likely to negatively affect both the dam and neonates as alpha-2 agonists readily cross the placenta.1,4 One of the originally marketed alpha-2 agonists, xylazine, was specifically identified as risk factor for increased neonatal mortality in a study examining peri-operative risk factors for puppies delivered by C-section.4,9
“Reversal” of the sedative and unwanted side effects of alpha-2 agonists will also antagonise the analgesia effects and therefore other pain relief should be administered to the dam prior to recovery.
If, following a risk-benefit analysis, it is determined that alpha-2 agonists have to be administered prior to C-section e.g. to the genuinely difficult patient, then a low dose should be selected, and the effects antagonised once the animal is anaesthetised.1
Benzodiazepines e.g. midazolam & diazepam, rapidly transfer across the placenta and are readily absorbed by the foetus. The immature neonatal liver does not however possess the mature hepatic enzyme systems required for efficient metabolism.3 In humans, maternal benzodiazepine administration has been associated with low infant Apgar scores, spells of apnoea, cyanosis, sedation and reduced suckling (“floppy infant syndrome”).12,13 Neurological depression has been observed in puppies delivered following midazolam/ketamine anaesthesia.11
The benzodiazepines should therefore be avoided or used very cautiously following a risk-benefit analysis.
Local anaesthetic techniques reduce discomfort in the dam during recovery allowing early nursing and bonding with the offspring.1 Additionally, as part of a multimodal approach to anaesthesia, they can reduce maintenance agent requirements therefore decreasing exposure to the possible cardiovascular and respiratory depressant effects of the drugs.
Line blocks at the incision site prior to laparotomy, as part of balanced anaesthetic techniques, assist in minimising the unconscious response to pain and potentially allow lower levels of volatile maintenance agent to be administered in order to maintain a suitable depth of anaesthesia.3 High levels of volatile agent are known to cause hypotension and reduced uterine blood flow therefore minimising exposure of the dam to these agents will minimise foetal acidosis.7
Splash blocks at the incision site at the time of closure will provide a degree of maternal analgesia during recovery but will not provide analgesia during the procedure itself.
Lidocaine is a suitable local anaesthetic for local infiltration in the C-section patient due to its rapid onset of action. However, the maximum lidocaine dose for line and splash blocks should be considered in order to reduce potential toxicity. The ceiling dose varies between authors: Dukes-Novakovski (2016) recommends 3mg/kg maximum diluted to provide a suitable volume for infiltration; and Robertson (2016) suggests a maximum dose of 2mg/kg lidocaine.
EPIDURAL (EXTRADURAL) ANAESTHESIA
Extradural anaesthesia can be used as an adjunct to general anaesthesia. However, it may take a considerable length of time to administer, potentially negatively affecting the outcome of the C-section, and requires experience & expertise to perform successfully.
If an epidural is to be administered, lidocaine is the preferred agent1,3,5 and the total volume should be reduced compared to non-pregnant animals due to engorgement of the vertebral vessels in the gravid dam. 2-3mg/kg of 2% lidocaine, with a maximum volume of 6ml will induce spinal anaesthesia rapidly but with a relatively short duration of action.1,3
Opioid administration via the epidural route will minimise hypotension and the temporary paraplegia associated with lidocaine, but opioid epidurals do not provide a suitable level of incisional anaesthesia if used without general anaesthesia.6
Extradural anaesthesia is not without issue: Hypotension and hypoperfusion of the uterus & placenta, due to spinal sympathetic nerve blockade, may occur. If the blockade extends cranially to the cervical region respiratory compromise or arrest are possible.3,5
Epidural anaesthesia should be avoided if the patient is hypovolaemic or septic.5
General anaesthesia of the C-section patient has several advantages over conscious extradural anaesthesia:
- General anaesthesia reduces the potential for maternal catecholamines release in response to stress or discomfort. This provides a degree of protection from the associated hypertension of the dam and placental hypoperfusion, and therefore protection from deterioration of cardiovascular function7
- General anaesthesia is reliable
- General anaesthesia provides control of the maternal airway and protection from aspiration (if the animal is rapidly intubated following induction)3,5,7
- Oxygen can be delivered efficiently to an intubated dam and therefore the neonates
- Depth of anaesthesia and associated physiological parameters can be managed
- The animal is immobile during the procedure
- Intermittent positive pressure ventilation (IPPV) can be initiated if necessary
Induction should ideally occur in a theatre, with all personnel and equipment prepared and ready for the procedure. The dam should have been stabilised, had an intravenous catheter placed and be receiving IV fluids, been pre-clipped, had an initial surgical prep, and and be receiving oxygen (see the Caesarean Section Survival Guide. Part 1: Physiology and Pre-anaesthetic Considerations article).
Regardless of the route selected for induction of anaesthesia it should be noted that the physiological changes that occur in the dam during pregnancy, possible dehydration, sepsis and exhaustion can all affect the dose of the chosen drug. During pregnancy anaesthetic drug requirements are generally reduced by 25-40% (up to 60%).3 The lowest possible dose should therefore be administered, ideally to effect, and the patient very closely monitored.
The changes in hormone levels and other neuroinhibitors e.g. beta-endorphins, can significantly reduce the anaesthetic requirements of the pregnant animal. The minimum alveolar concentration (MAC) of all volatiles is reduced.1,7
Although traditionally used for inducing anaesthesia in the C-section patient, mask induction has been associated with increased mortality in dogs when compared to intravenous induction and inhalation maintenance.14
Patients induced with inhaled volatile agents will almost always experience stage II excitement and may struggle.6 This will increase oxygen demand in a patient already experiencing an increased metabolic rate and requirement for oxygen as a result of the pregnancy. The stage II excitement can therefore, potentially lead to maternal and foetal hypoxia.
Mask inductions tend to be slower than when intravenous drug administration is used. There is an increased risk of aspiration and intubation should, therefore, be rapid.6 Additionally, the effects of volatile induction can be unpredictable due to the cardiorespiratory changes associated with pregnancy.1 Dugdale (2010) reports that inhalation anaesthetics readily cross the placenta causing a degree of depression in the foetus proportional to the depth of anaesthesia in the dam with deep anaesthesia causing reductions in blood flow to the uterus, and subsequent foetal acidosis, within 15 minutes of first administration.
Roberston (2016) does not recommend mask inductions.
INTRAVENOUS INDUCTION AGENTS
Intravenous agents will provide a controlled induction and early management of the maternal airway via intubation. This will permit efficient oxygen administration and control of anaesthetic depth with volatile agents. With good planning (see the Caesarean Section Survival Guide. Part 1: Physiology and Pre-anaesthetic Considerations) intravenous inductions can permit rapid surgical delivery of the neonates.
The two most common intravenous induction agents administered to C-section patients in the UK are alfaxalone and propofol. Alfaxalone, with its minimal cardiorespiratory effects, smooth, controlled induction and maintenance, rapid and predictable elimination, excellent neonate vigour and early maternal recovery, is the induction drug of choice of many anaesthetists.1
Alfaxalone (Alfaxan, Jurox UK) is a neuroactive steroid molecule licenced for induction of anaesthesia prior to delivery of neonates by C-section in the canine patient.
Alfaxalone is solubilised in an inert cyclodextrin carrier, has a neutral pH, does not cause discomfort on injection and does not irritate tissues if inadvertently administered perivascularly. Alfaxalone acts at the GABAA receptor causing hyperpolarisation with resultant unconsciousness and muscle relaxation.
Smooth, unrushed induction with minimal excitation are observed following alfaxalone administration. If given slowly there is a low incidence of apnoea.19 However, preoxygenation should always be performed where possible in the C-section patient.
Minimal depression of the cardiovascular system with marginal changes to blood pressure (the baroreceptor reflex is not depressed) follow administration and a compensatory increase in heart rate are frequently observed.
Alfaxalone has a wide safety margin and is rapidly, and predictably, eliminated via hepatic metabolism and excretion of inactive compounds in the bile and urine. Following a single induction dose anaesthesia of sufficient depth to allow intubation persists for 8-12 minutes in the dog and 20-25 minutes in the cat.
Alfaxan SPC section on C-sections:
Propofol is not universally licenced for induction of anaesthesia in the C-section patient therefore the specific propofol SPC should be referred to.
Propofol is an alkyl phenol that modulates the GABAA receptor of the central nervous system. It is insoluble in aqueous solutions and is therefore formulated in an oil-water phospholipid emulsion containing soya bean oil, egg phosphatide and glycerol. The unpreserved formulation has been shown to support bacterial growth.18 Preserved versions commonly contain benzyl alcohol (which has been associated with preterm neonatal fatalities in humans - see SPC). It has a pH of approximately 7.
Metabolism is hepatic (and possibly in the lungs,19 kidneys & gastrointestinal tract) via glucuronidation and hydroxylation. Recovery is due to redistribution and metabolism.
Propofol should be administered slowly and to effect. Some animals may demonstrate discomfort on intravenous injection. Hypotension, with reduced systemic vascular resistance and cardiac output, is the most prominent haemodynamic effect of propofol. The baroreceptor reflex is thought to be depressed resulting in depression of the normal reflex increase in heart rate. Hypotension may be profound and careful monitoring is vital, especially in hypovolaemic or already hypotensive patients.3,6
Apnoea is a commonly encountered side-effect, particularly after rapid administration of propofol, therefore prompt intubation should be performed.
Some authors suggest delaying delivery of the neonates for 20 minutes after propofol induction in the bitch. This is to allow redistribution of the propofol from the undelivered foetuses back to the dam.16,20 However, if the neonates are in distress e.g. following placental detachment, this delay could potentially lead to increases in morbidity or mortality.
ALFAXALONE VS PROPOFOL FOR C-SECTIONS: PUBLISHED STUDIES
There have been several studies comparing the effects of alfaxalone and propofol in the C-section patient.
Metcalfe et al (2014) reported that Alfaxan was an effective induction agent for C-section with an excellent safety profile. The incidence and duration of apnoea in the dam were less with Alfaxan than with propofol and the scores for puppy vigour were numerically superior with Alfaxan compared to propofol.
Doebeli et al (Theriogenology 2013) concluded that the neonate Apgar scores were greater in the alfaxalone group than the propofol group and that alfaxalone induction was associated with better neonatal vitality during the first 60 minutes after delivery.
Doebeli A et al (J Repro Biol. 2013) demonstrated that dams induced with alfaxalone had a significantly shorter recovery times than those induced with propofol (mean 10 vs 26 minutes respectively). Puppies from both the alfaxalone and propofol induction groups had similar survival rates and that there was no statistical difference between groups in the number of puppies delivered.
Summaries of these papers may be viewed here.
Ketamine inductions have been associated with neonatal neurological and respiratory depression, apnoea, decreased vocalisation necessitating intensive resuscitation.1,7,15 Increased neonatal mortality has been observed.10,11,16
Ketamine should be avoided or used with caution.1,3
Maintenance of Anaesthesia and Monitoring
Following induction, a secure airway should be achieved as soon as possible to reduce the possibility of aspiration. Transition to maintenance should be performed smoothly with the lowest possible concentration of volatile necessary to achieve a suitable depth for the surgical procedure.
If local anaesthesia is being administered to the patient this should be performed as soon as possible to reduce the time from induction to delivery of the neonates.
Inhalation maintenance is the preferred choice6 and will reduce to potential for prolonged recoveries in both the dam and the neonates.4 Isoflurane and sevoflurane in oxygen are both suitable.
The 20% reduction in functional residual capacity (FRC) and 40% increase in tidal volume mean that changes to anaesthetic depth can occur quickly.3,6 In addition, the hormonal alterations associated with pregnancy reduce anaesthetic requirements resulting in a lower volatile minimal alveolar concentration (MAC) when compared to the non-pregnant animal (reductions of 30-40 % are possible).1,3,4 Depth of anaesthesia should therefore be monitored frequently and very closely.
Volatile agents rapidly cross the placenta to the foetus and the degree of foetal depression is proportional to the depth of anaesthesia in the dam.7 Hypotension, as a consequence of vasodilation and reduced cardiac output, is a common side effect of volatile agent administration3 and this must be considered in the C-section patient. Deep maternal anaesthesia can result in significant hypotension, reduced placental blood flow, and foetal hypoxia & acidosis.7 Therefore, the delivery of volatile agent should be minimised as far as possible via balanced anaesthetic techniques e.g. the use of local anaesthesia.
The positioning of the dam should be considered carefully. In women, dorsal recumbency can cause mechanical compression of the aorta and caudal vena cava resulting in a reduced venous return and cardiac output, with a consequential decrease in blood flow to the placenta and foetus.23 In addition, the pressure of the gravid uterus on the diaphragm reduces the FRC. Therefore raising the dam into a slight “head up” position will assist in relieving some of this pressure and reduce the potential for ventilation:perfusion mismatching.
Accurate, frequent, and continuous monitoring of cardiovascular and respiratory parameters, temperature, and depth of anaesthesia are essential.1
Anaesthetic depth should be assessed using the normal observations of eye position, reflexes, response to surgical stimulation, jaw tone etc.
Pulse oximeter measurements will give an indication of the pulse rate and oxygenation status of the dam. Pulse oximeters measure only peripheral oxygen saturation (SpO2) and not arterial oxygen saturation (SaO2). In the anaesthetised patient large changes in SaO2 can occur before any discernible change in SpO2 are observed. Therefore other forms of patient monitoring should be used, if available, in addition to observation and pulse oximetry.
Capnography is the gold standard for anaesthetic monitoring. Not only does it provide information on ventilation but also on the metabolic rate and circulatory status of the patient.
The respiratory centre of the pregnant animal becomes more sensitive to carbon dioxide and, combined with the increase in tidal volume and respiratory rate, the normal end tidal carbon dioxide (PaCO2) may be as low as 30-33mm Hg.24
Oxygen desaturation occurs readily in the pregnant patient as a result of decreased FRC and increased respiratory rate at a time of higher oxygen demand. It is important however, to not over ventilate. As the arterial pressure of carbon dioxide (PaCO2) falls (indirectly reflected in end tidal carbon dioxide – ETCO2) following hyperventilation the placental blood flow reduces and there is an increased risk of foetal hypoxia. It has been suggested by Robertson (2016) that ETCO2 values are maintained at 35mm Hg or higher.
Hypotension is a concern in the C-section patient. The physiological changes that occur during pregnancy (increased cardiac output and cardiac contractility), the potential for dehydration, sepsis, supine positioning during surgery, administration cardio-depressive drugs, and the attenuated baroreceptor reflex, can all contribute to the development of hypotension. Additionally, there is no autoregulation of foetal blood flow, and uteroplacental perfusion is pressure dependent.24 Careful monitoring of blood pressure is therefore essential and intravenous fluid therapy should be instigated prior to anaesthesia.3
Maternal hypothermia can be significant during C-sections and attention should be paid to regular and consistent monitoring and the maintenance of core temperature.
Ultimately, the peri-parturient dam is under the influence of several physiological changes which will influence anaesthesia – AND the anaesthetic itself will have effects.
Many anaesthetists recommend the administration of an opioid analgesic e.g. methadone, buprenorphine (please refer to the SPCs for further details), once the last neonate has been delivered. This technique will provide analgesia, which will be effective at the time of maternal recovery, will assist in smoothing the recovery but won’t over sedate the dam, allowing her to bond with, and suckle, her offspring.3 There may be concerns about the presence of opioid in the milk, although the levels have been found to be very low (1-2% of the maternal dose).25 In humans the amount of opioid received by the infant had no clinical effect.26 Therefore, pain relief in the dam should not be withheld.
If there is any concern about neonatal depression following opioid administration the antagonist naloxone can be given directly to the neonates.
NON-STEROIDAL ANTI-INFLAMMATORY DRUGS (NSAIDS)
Intraoperative hypotension is not uncommon in the C-section patient, and this could be exacerbated by significant haemorrhage, leading to the maternal and foetal issues described above. In addition, maternal renal perfusion may be affected by the hypotension. Lascelles et al (1998) recommended waiting until the end of the surgical procedure before administering NSAIDs.
Once delivered any membranes should be removed from the head of the neonate and, if necessary, fluid carefully suctioned from the nose.3,4 Swinging the neonate to clear fluids is not effective. Evidence suggests swinging may actually be harmful and this technique should therefore be avoided.3 Stimulation of the umbilicus, anogenital region or the nasal philtrum may also encourage respiration. If necessary endotracheal intubation with a soft cannula or small diameter tube will permit very carefully controlled positive pressure ventilation.3 Moon et al (2000) demonstrated that neonates that breathed and vocalised within 1 minute of delivery had an increased survival.
Low neonatal heart rates may indicate hypoxia and oxygen therapy should be instigated.3
Opioid induced neonatal depression may be antagonised with naloxone into the umbilical vein, intramuscularly or sublingually. Naloxone is unlikely to of value if the neonate is hypoxic due to hypoventilation.3
Neonates are unable to thermoregulate and they should be dried quickly following delivery. The rubbing of a towel will stimulate them to breathe and vocalise. Warmth should be provided, although care should be taken as some devices can lead to overheating or even burns. Regular monitoring of neonate temperature is vital.
A downloadable summary of the information presented in this article may be downloaded here and should be used in conjunction with the material described in the Caesarean Section Survival Guide. Part 1: Physiology and Pre-anaesthetic Considerations.
Originally published: Thursday, 27th September 2018
- Robertson S (2016). Anaesthetic management for caesarean sections in dogs and cats. In Practice 38, 327-339
- Von Heimendahl A & Cariou M (2009). Normal parturition and management of dystocia in dogs and cats. In Practice. 31, 254-261
- Duke-Novakovski et al (2016). BSAVA Manual of Canine and Feline Anaesthesia & Analgesia. 3rd Edition.
- Clarke K, Trim C & Hall LW (2013). Veterinary Anaesthesia. 11th edition. Saunders Ltd
- Kushnir Y & Epstein A (2012). Anaesthesia for the pregnant cat and dog. Israel J Vet Med. 67, 19-23
- Dugdale A (2010). Veterinary Anaesthesia: Principles to Practice.
- Grimm KA (editor) (2015) Lumb & Jones Veterinary Anaesthesia and Analgesia. Wiley & Sons.
- Murrell J (2007). Choice of premedicants in cats and dogs. In Practice. 29,100-106
- Moon PF et al (2000). Perioperative risk factors for puppies delivered by caesarean section in the United States and Canada. JAVMA 36, 359-368
- Moon-Massat PF & Erb HN (2002). Perioperative factors associated with puppy vigour after delivery by Caesarean section. J Am Anim Hosp Assoc. 38, 90-96
- Luna SPL et al (2004). Effects of four anaesthetic protocols on the neurological and cardiorespiratory variables of puppies born by Caesarean section. Vet Rec 154, 387-389
- Celleno D et al (1993). Which induction drug for Caesarean section? A comparison of thiopental sodium, propofol and midazolam. J Clin Anaesth. 5, 284-288
- McElhatton PR (1994). The effects of benzodiazepine use during pregnancy and lactation. Repro Toxicol. 8, 461-475
- Broadbelt DC et al (2008). The risk of death: The Confidential Enquiry into Perioperative Small Animal Fatalities. Veterinary Anaesthesia & Analgesia 35, 365-373
- Pascoe PJ & Moon PF (2001). Periparturient and neonatal anaesthesia. Vet Clin North Am: Small Anim Prac. 21, 315-341
- Funkquist PME et al (1997). Use of propofol-isoflurane as an anaesthetic regimen for caesarean section in dogs. JAVMA. 211, 313-317
- Grint N et al (2008). Clinical evaluation of alfaxalone in cyclodextrin for the induction of anaesthesia in rabbits. Vet Rec 163, 395-396
- Strachan FA et al (2008). A comparison of bacterial growth in alfaxalone, propofol and thiopental. JSAP 49 186-190
- Matot I et al (1993). Pulmonary uptake of propofol in cats. Effect of fentanyl and halothane. Anaesthesiology 78, 1157-1165
- Metcalfe S et al (2014). Multicentre, randomised clinical trial evaluating the efficacy and safety of alfaxalone administered to bitches for induction of anaesthesia prior to caesarean section. Aus Vet J. 92, 333-337
- Doebeli A et al (2013). Apgar scores after induction of anaesthesia for canine caesarean section with alfaxalone versus propofol. Theriogenology. 80, 850-954
- Doebeli A et al (2013). Induction of anaesthesia for canine caesarean section with alfaxalone. Repro Biol. 22-64
- Tan EK & Tan EL (2013). Alterations in physiology and anatomy during pregnancy. Best Practice & Res: Clinical Obs & Gynae. 27, 791-802
- Ryan SD & Wagner AE (2006). Caesarean section in dogs: Physiology and perioperative considerations. Compendium. 34-43
- Spigset O & Hagg S (2000). Analgesics and breast feeding: safety considerations. Paediatric Drugs 2, 223-238
- Bloor M et al (2012). Tramadol in pregnancy and lactation. Int J Obs Anaesth. 21, 163-167
- Lascelles BD et al (1998). Efficacy and kinetics of carprofen, administered preoperatively or postoperatively, for the prevention of pain in dogs undergoing ovariohysterectomy. Vet Surg. 27, 568-582
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