C Sections

Question 1

Anticholinergics

Answer 1

Decrease salivation, inhibit excessive vagal efferent activity from traction on uterus
o Benefits vary with species – greatest with dogs, cats
o Glyco increases gastric pH –> may decrease severity of chemical pneumonitis
o Glyco may be more appropriate, does not cross BBB/BPB

Question 2

ACP

Answer 2

Long DOA: no indications for routine use, restrict to markedly excited animals only

ACP: significant maternal, fetal depression at low dozes

Question 3

BDZ

Answer 3

Benzodiazepines: midaz, diazepam – induce neonatal depression immediately following birth
 Lower doses: reduce risk
 Antagonism: flumazenil

Question 4

a2s

Answer 4

presynaptic a2A R in LC – inhibition of NE release, reduce post-synaptic membrane excitability
 Inhibits cortical arousal response = conscious sedation effect
 Neonates rousable with physiologic stimulus  cry after birth, respond to sensory input

Question 5

Xylazine

Answer 5

rapidly crosses placenta, fetal/material depressant effects – resp, CV
 Caution or avoid in ruminants – spontaneous abortion
 +ketamine: life-threatening CP changes in dogs, decreased tissue perfusion – do not use in SA

Question 6

Detomidine

Answer 6

appears well tolerated by pregnant mares, drug of choice in ruminants

Question 7

Opioids

Answer 7

o Rapidly cross placenta, cause neonatal respiratory/CNS depression
o Fetal elimination may require 2–6 days
o Agonist–antagonist or partial agonist (butorphanol and buprenorphine) reportedly induce less respiratory depression
o Opioids can be antagonized

Question 8

Thiopental

Answer 8

 Rapidly crosses placenta, rapidly cleared from neonatal circulation
* Fetal metabolism may contribute to its rapid clearance in utero
 Neonatal respiratory depression, sleepiness, decreased activity
 Suckling activity decreased, reported depressed for 4d, less with lower doses <4mg/kg

Question 9

Propofol

Answer 9

 Rapidly crosses placenta, rapidly cleared from neonatal circulation
 Longer term CRI may result in fetal depression

Question 10

Etomidate

Answer 10

–Fetal tissue perfusion well maintained
–Rapid initiation of neonatal spontaneous breathing, greater fetal vitality at delivery than with thiopental
–Plasma esterase metabolism
* LJ Chp 16: severe neonatal depression

Question 11

Saffan

Answer 11

 Two progesterone‐like steroids (alfaxalone 9mg/mL; alfadolone 3mg/mL)
 Induction = smooth, rapid
 CV depression proportionate to dose, similar to TP or methohexital
 Less respiratory depression than barbiturates
 Use in dogs not recommended: solubilizing agent (cremaphore) causes severe histamine release unless pretreated with antihistamines

Question 12

Alfaxan CD

Answer 12

 Cyclodextran carrier devoid of histamine‐releasing properties
 Short‐acting, minimal CV depression, few AEs
 Improved Apgar scores vs propofol

Question 13

Dissociatives

Answer 13

Increased uterine contraction

Low doses may be used for induction

Retrospective study: ketamine use associated with respiratory depression, apnea, decreased vocalization, increased mortality

Question 14

Inhalants

Answer 14

Readily cross the placenta with rapid equilibration
 Isoflurane, sevoflurane, desflurane preferred: induction, recovery more rapid

Deep levels of anesthesia: maternal hypotension, decreased UBF, fetal acidosis
o N2O can potentiate effect, <60%: fetal depression minimal, diffusion hypoxia does not occur upon delivery

Question 15

NMBA

Answer 15

Cross placenta to a limited extent, little effect on neonates at clinical doses
o Succinylcholine: traditional choice when combined with an ultrashort‐acting barbiturate or propofol for induction

–Avoid panc, dox - DT long DOA
–Can consider mivacurium (15-20’), atra, vec

Reverse non-depolarizing, use PPV

Question 16

Guaifenesin: horses, cattle, small ruminants:

Answer 16

transplacental transfer minimal based on vigor of newborn

Question 17

LAs

Answer 17

Ester (procaine or tetracaine)
 Metabolized by maternal, fetal pseudocholinesterase; little accumulation

Amide
–Metabolized by hepatic microsomal enzymes
–Potentially increased metabolism of lidocaine DT increased hepatic BF
–Neonatal plasma concentrations greater then 3mcg/mL lido/mep = neonatal depression, rarely occur after epidural
* Mepivacaine: not metabolized well by fetus/neonates

Sympathetic blockade: decreases uteroplacental perfusion

Question 18

NSAIDS

Answer 18

Exposure during the first trimester = higher rate of miscarriage in women

Exposure during second trimester = altered organogenesis of brain, kidneys, lungs, bones, GIT, CV system

Exposure in late 3rd trimester = premature closure of DA

Question 19

C Sections in Dogs, Cats

Answer 19

Fetal death rises rapidly with prolonged stage II labor
 Fetal death with 1-4.5hr of labor = 5.4%
 Fetal death with 5-24hr of labor = 13.7%
 Are fetuses in distress?

Question 20

Recognition of Fetal Distress in SA

Answer 20

Fetal HR slows with hypoxia
* <180bpm: fetal distress
* <160bpm: EMERGENCY

Question 21

Foals

Answer 21

Foals must be delivered within 20-30’ of chorioallantoic membrane rupture
 >40’: EMERGENCY

Question 22

Advantages of GA for C section

Answer 22

Speed, easy of induction
Reliability, control with optimum operating conditions
Route for maternal O2 administration
Intubation: protection of airway

Question 23

Disadvantages of GA for C Section

Answer 23

Greater neonatal depression
Inadequate ax plane = maternal catecholamine release
Aspiration

Question 24

When would GA be more appropriate than locoregional anesthesia for a c section?

Answer 24

 Hypovolemia
 Prolonged dystocia
 Stressed Fetus
 Maternal cardiac failure
 Morbid obesity
 Upper airway resistance (Brachycephalic)

Question 25

What are the three parturition stages of horses?

Answer 25

 Stage I: positioning of fetus, several hours
 Stage II: rupture of chorioallantois, 10-20’ – MUST BE <30’
 Stage III: passage of placenta, <3hr

Question 26

Horses and C Sections

Answer 26

o Induction of parturition not recommended DT problems with surfactant production, skeletal m maturation
o Dystocia: profound effects on the survival of foals
o Normally delivered within 20-30 mins after chorioallantoic membrane rupture
 Few survive after 40mins, almost none at 90 mins

Question 27

Most important feature of an equine c section?

Answer 27

RAPID SPEED - GET THE FOAL OUT

Question 28

Recoveries following equine c sections

Answer 28

• Mares may be exhausted - prone to difficult recovery, consider H/T ropes

Question 29

Oxygen Support

Answer 29

o Supplemental oxygen can increase fetal oxygen content, viability
o Fetal blood has lower 2,3-DPG – more O2 content with lower O2 tension
 Higher HGB saturation at lower O2 tension
 Umbilical vein PO = 30mmHg

Question 30

What is the effect of hypoventilation on uterine BF?

Answer 30

decreases uterine blood flow

Question 31

What are some challenges associated with c sections in ruminants?

Answer 31

not fasted, predisposed to regurgitation, aspiration, bloat/ruminal tympany

Normal ruminant things PLUS gravid uterus - very predisposed to VQ mismatch, hypoventilation, hypoxemia - consider performing under locoregional/standing

Question 32

Effect of pregnancy on LA requirements?

Answer 32

PREGNANCY WILL DECREASE LA DOSE REQUIRED

Question 33

Absolute contraindications to epidural anesthesia?

Answer 33

coagulopathies, septicemia, infection in area of needle insertion, uncorrected hypotension, lumbosacral pathology

Question 34

Relative contraindications to epidural anesthesia?

Answer 34

bacteremia, neurologic disease aggravated by epidural drug administration

Question 35

Changes to Epidural Space with Pregnancy

Answer 35

o Pregnancy associated with increased blood volume, increased shunting of abdominal blood to epidural tissues, increased epidural fat stores
 Increases volume of epidural blood vessels, fat –> decreases potential volume of epidural space
 Volume of epidural injected in pregnant animal at term migrates more rostrally than same volume injected in non-pregnant animal of similar size

Dose, vol of LA for epidural or spinal anesthesia reduced by ~1/3

Question 36

Advantages of Locoregional Techniques with C Sections

Answer 36

 Simplicity
 Minimal exposure of fetus to drugs
 Less intraoperative bleeding
 Less risk of aspiration while awake
 Excellent muscle relaxation/analgesia

Question 37

Disadvantages of Locoregional Techniques with C sections

Answer 37

sympathetic blockade, treat with IVF or ephedrine

Question 38

Spinal Cord Ends

Answer 38

Spinal cord terminates at L6 for dogs, L7/mid sacrum for cats
* Terminates mid sacrum in swine, ruminants

Question 39

Epidurals in SR, Pigs

Answer 39

• Epidurals well established, not difficult - L6/S1
• If not under GA/intubated: caution with extension of head, neck –> soft palate may occlude airway

Question 40

Epidurals in Pigs

Answer 40

*Pigs: 10mL/100kg, 15mL for 200kg, up to 20mL in large pigs
o Alternatively: one 1mL lido injected for first 40cm of distance from base of tail to occipital protuberance plus 1.5mL for each additional 10cm of back length

Question 41

Rastabi et al VAA 2020 - duration of motor/sensory blockade with saline vs phentolamine

Answer 41

epidural administration of 5mL normal saline after epidural injection of lidocaine-epinephrine reduced duration of sensory but not motor block in sheep
o Epidural administration of phentolamine diluted to final volume of 5mL diminished both duration of sensory, motor block in sheep administered epidural lidocaine + epinephrine

Question 42

Elane et al JAVMA 2022 - intrathecal lidocaine for goat c sections

Answer 42

intrathecal lidocaine at 1mg/kg at LS space provided adequate analgesia for C sections in goats
o Minimal complications, quicker return to hind limb motor function post operatively than historically reported for epidurals
o Bupivacaine traditionally reported to interfere with motor for 11hr, lidocaine for 3hr – goats stood at ~3+/-1hr

Question 43

Epidurals in Cattle

Answer 43

Sacrococcygeal space usually ossified in adult

Coccygeal epidural will facilitate vaginal delivery, decreases Ferguson’s reflux

Question 44

Proximal Paravertebral Block

Answer 44

o Proximal: proximity to spine
 Nerves blocked: T13, L1, L2, +/- L3
 Landmarks: L1-L3, +/- L4

Blocked adjacent to verbebrate, parallel (needles pointed ventral)

Question 45

Distal Paravertebral Block

Answer 45

distance from spine
 Dorsal, ventral br T13, L1-L3

Needle pointing medial, toward midline

Question 46

Inverted L/7 block

Answer 46

o Inject LA along caudal border of last rib, along lumbar transverse processes
o +: easy to perform, out of the surgical field
o -: large amount of local anesthetic required, peritoneum not blocked

Question 47

Infiltration Block

Answer 47

o Inject anesthetic along surgical margins
o +: easy to perform
o -: large amount of local required, distorts anatomy, bleeding at surgical site, could cause fetal depression

Question 48

When give NSAIDS during a c section?

Answer 48

AFTER fetus separated from placenta- reduces fetal prostaglandin concentration, premature DA closure