Dystocia and neonatal resuscitation Flashcards
What is the normal length of gestation (measured from mating) in
a) Dogs
b) Cats
a) Dogs: 57 – 72 days
b) Cats: 52 – 74 days
Explain why there is a variability in gestation length in dogs. Measurement of which hormones may be helpful in closer estimation of parturition date?
Causes for variation in expected parturition date include the variable time at which a bitch may stand to be mated relative to time of ovulation, prolonged life of the oocyte and the length of time spermatozoa can survive in the reproductive tract of the bitch (sperm can survive up to 7 days in utero).
Parturition typically occurs 65 days after a peak in LH. At the time of ovulation, progesterone concentration typically measures 4–10 ng/mL. Parturition occurs 63 days (+/−1) following the date of ovulation.
Describe hormonal and physiological changes required for induction of parturition
The signal for parturition is thought to be fetal.
Maturation of the foetal adrenal cortices results in cortisol release from the fetal adrenal gland.
↑ oestrogen secretion by ovarian tissue through day 45–60 of pregnancy.
Estrogen stimulates the upregulation of genes encoding myometrial contraction-associated proteins, and promotes prostaglandin release from the uteroplacental complex (now thought to be primarily trophoblastic cells).
Prostaglandin E2 (PGE2) produced is luteolytic, resulting in corpus luteum regression and a reduction in circulating progesterone.
As a result of the luteolytic effect of PGE2, progesterone concentration rapidly drops from a range of 4–10 ng/mL to approximately 2 ng/mL over a 12–24-hour period toward the end of pregnancy.
Falling progesterone is believed to cause a rise in circulating prolactin, and subsequently lactation.
Parturition occurs 24–48 hours following the rapid decline in circulating progesterone.
Prostaglandin F2-alpha plays a key role in increasing the sensitivity of the myometrium to oxytocin.
This in turn facilitates smooth muscle contraction, and softening of the cervix.
Oxytocin also plays a role in parturition.
Oxytocin is secreted via the posterior pituitary gland in response to increased pressure placed upon the cervix.
Oxytocin release results in activation of a sensory pathway that ultimately terminates in the proventricular nucleus of the hypothalamus. Neural impulses are then sent to the posterior pituitary resulting in the release of oxytocin.
Oxytocin in turn increases myometrial contractility.
The following graph shows hormonal changes occurring in a bitch. Label the graph with the following:
a) Progesterone
b) Oestrogen
c) Ovulation
d) Follicular stimulating hormone
e) Luteinising hormone
Additionally, label the graph with the following phases of oestrus (draw a horizontal line to indicate the approximate length of each phase):
o Anoestrus
o Proestrus
o Oestrus
Anestrus -20 to -10 days: FSH up then down
E2 increases end of anestrus and over proestrus
Estrus LH peak, E2 start decreasing, ovulation mid estrus, progesterone increases
a) Anoestrus considered to be “obligate” lasting a minimum of 7 weeks after progesterone declines below 1–2 ng/ml, and averages 18–20 weeks (2 to >9mths Romangoli)
b) Proestrus average 9 days (up to 4 wks)
c) Oestrus average 9 days (5-10 days Concannon, 4-24 days Romangoli)
Ref. Concannon 2011, Ettinger (chapter by Romangoli) 2017, Wisconsin Uni http://www.ansci.wisc.edu/jjp1/ansci_repro/lec/lec_25_dog_cat/lec25out.htm
Describe physiological, behavioural and hormonal changes occurring during different stages of normal parturition. Indicate approximate length of each stage.
Stage 1:
- nesting behaviour
- relaxation and dilation of cervix
- foetus adopts birth posture
- uterine contraction commences
- chorioallantois enters vagina
- duration 6-12h (up to 36h)
- peak prolactin + drop in progesterone 12-24h prior parturition and increase in PGF2α
Stage 2:
- uterine contraction continues
- foetus enters birth canal
- overt abdominal contraction commences
- amnion enters vagina
- foetus expelled
- duration 2-12h (rarely 24h in bitch, but normal for queen to last up to 24h)
- increase in oxytocin levels
Intervals between pups 30min up to several hours (BSAVA Manual 4h)
Stage 3:
- placental circulation lost
- placental dehiscence and separation occurs
- uterine and abdominal contractions continue
- placenta is expelled
- lochia for up to 3 weeks, uterine involution 12-15 weeks
- endometrium secretes pulses of PGF2α, oxytocin causes uterus to contract to disrupt contact between uterus and foetal membranes
Define dystocia and 4 clinical categories of small animal dystocia
Dystocia is defined as an inability to expel the foetus(es) from the uterus or birth canal
Failure to begin stage 2 labor
Cessation of stage 2 labor before completion
Prolonged unproductive stage 2 labor
Apparently normal stage 2 labor with foetal distress
List at least 7 indicators for clinical examination in a bitch/queen in labour
● Client concern
● Signs of systemic illness
● Decline in body temperature, followed by return to
normal temperature with no progression into labor
● Stage 1 labor extends beyond 12 hours with no
evidence of progression
● No puppy within 2 hours of entering stage 2 labor (or
no kitten within 1 hour)
● Forceful abdominal contractions and no fetus within a
30-minute period
● Intermittent abdominal contractions with no fetus
delivered within a 2-hour period
● If pregnancy extends beyond 72 days with no
progression into labor
● Stillborn fetuses are passed
● Uteroverdin in vaginal discharge but no puppy or
kitten passed within 2 hours
- List at least 3 maternal and 3 foetal factors that might contribute to dystocia
Maternal Physiologic Primary uterine inertia Hereditary Stress/environmental disturbances Old age Obesity Systemic disease Uterine overdistention (eg, large litter size, fetuses too big) Uterine underdistention (eg, small litter size, inadequate fetal fluids) Estrogen/progesterone balance Calcium/magnesium balance Inadequate oxytocin secretion Prematurity Secondary uterine inertia Morphologic Primary (eg, birth canal too small) Secondary (eg, abnormal influence on or within birth canal) Pelvic fractures Uterine torsion Uterine rupture Uterine herniation Uterine prolapse Mass-like lesions of pelvic canal, uterus, vagina, or vulva (eg, hyperplasia, neoplasia, hematoma, abscess) Fibrosis of uterus, cervix, or vagina Vaginal septum
Fetal Malpresentation Oversize (eg, single fetus pregnancy) Fetal death Fetal malformations
Name and briefly describe 4 neonatal reflexes that help to assess vigor
Dorsal stimulation
A neonate is rubbed strongly over the dorsal lumbar area and should move vigorously and/or squeal in response
Righting reflex
The neonate is placed on its back and should then immediately turn itself over into ventral recumbency
Suckling reflex
A finger, bottle or the dam’s nipple is offered to the neonate that should then begin suckling
Rooting reflex Response
The neonate should push its muzzle into a cupped hand or against its mother’s mammaries in search of milk
- True or false?
a) Normal heart rate at birth for neonatal puppies is 160-180bpm and for kittens 200-220bpm.
b) Doxapram is a central respiratory stimulant which is unlikely to improve hypoxaemia associated with hypoventilation.
c) Normal body temperature in puppies and kittens is 35.2-37°C at birth and normalises to adult values at 4 weeks of age.
d) Mean arterial pressure in neonatal puppies is lower at birth (49mmHg) but normalises by 1 month of age (94mmHg).
- True or false?
a) Normal heart rate at birth for neonatal puppies is 160-180bpm and for kittens 200-220bpm. False – for both kittens and puppies it’s 200-220bpm.
b) Doxapram is a central respiratory stimulant which is unlikely to improve hypoxaemia associated with hypoventilation. True
c) Normal body temperature in puppies and kittens is 35.2-37°C at birth and normalises to adult values at 4 weeks of age. True
d) Mean arterial pressure in neonatal puppies is lower at birth (49mmHg) but normalises by 1 month of age (94mmHg). False – it remains that low for first several months and normalises at 9mths of age.
Which of the following laboratory values are expected to be markedly elevated in neonates when compared with adult dogs and cats?
a) HCT
b) USG
c) ALP
d) Bilirubin
Which of the following laboratory values are expected to be markedly elevated in neonates when compared with adult dogs and cats?
a) HCT – Incorrect. HCT decreases from 47.5% at birth to 30% by day 28 in puppies
b) USG – Incorrect. Urine is isosthenuric as ability to concentrate or dilute urine is limited
c) ALP – Correct! As high as 3845 IU/l in puppies, 3x fold increase in kittens
d) Bilirubin – Incorrect. Only mild increase observed
Explain how drug absorption differ in neonates when compared with adults.
Drug absorption
Oral absorption of drugs in the neonate is often different from that in the adult due to:
- Slower transit time as a result of delayed/slowed gastric emptying
- Increased volume of mucus within the stomach
- Higher stomach pH
PO route of administration should be avoided during first 72h of life because absorption is significantly higher due to increased GI permeability.
Intestinal flora is also very sensitive to disruption by oral antimicrobial agents.
IV and IO route of administration is the most predictable and is preferred over IM or SC administration.
Explain how drug distribution differ in neonates when compared with adults.
Drug distribution
The distribution of drugs is quantified by the volume of distribution. For water-soluble drugs, the volume of distribution is increased in the neonate because it has a greater body water content than an adult.
· For lipid-soluble drugs the volume of distribution is decreased owing to the lower body fat content. There is also decreased binding to plasma proteins and a lower concentration of albumin in neonates.
· The blood–brain barrier is not complete in very young neonates; therefore, there is increased permeability to lipid-soluble drugs and higher concentrations of drugs that are normally removed by p-glycoprotein. This may lead to increased effects of anaesthetics and raised concentrations of avermectins and digoxin in the brain (thus, avoid them).
Explain how drug metabolism and excretion differ in neonates when compared with adults.
Drug metabolism and excretion
It accounts for most of the differences in neonatal physiology and thus greatly influences drug disposition.
· Renal clearance of drugs is decreased in neonates and renal excretion of many drugs (e.g. diazepam, digoxin) is diminished, which increases the half-life of the drug in circulation.
· Drugs requiring activation via hepatic metabolism will have lower plasma concentrations, and drugs requiring metabolism for excretion will have higher plasma concentrations.
· Antibiotics that are safe in neonates include penicillins and cephalosporins but the dosing interval should be increased to every 12hours rather than q8h. Tetracyclines should be avoided because of enamel hypoplasia and tooth discoloration, and chloramphenicol because of possible bone marrow toxicity. Metronidazole is a preferred drug for giardiasis and anaerobic infections but the dose and/or frequency should be decreased in neonates.
· Dosages of CV drugs (adrenaline, dopamine, dobutamine etc.) can be difficult to determine due to variable maturity of the autonomic nervous system. Response to atropine and lidocaine is decreased in the neonate.
· Phenothiazine tranquillizers should be used with caution because they induce hypothermia and hypotension as a result of vasodilation which, in the neonate, is not compensated for by an increase in heart rate. Midazolam is probably a better choice of drug for this purpose.
· For analgesia, opiates are very safe in neonates when given at the correct dosage but the animal must be monitored closely because of the propensity of these drugs to depress HR and RR.
Name at least 4 risk factors for increased neonatal mortality.
Low birth weight (most significant factor).
Obese dams, singleton litters, being the first neonate born in a litter.
Extended or difficult labour.
Poor prepartum condition of the dam, prematurity, congenital malformations, genetic defects, injury, environmental exposure, malnutrition, parasitism, and infectious disease all contribute to neonatal morbidity and mortality.
