C Sections Flashcards
Anticholinergics
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
ACP
Long DOA: no indications for routine use, restrict to markedly excited animals only
ACP: significant maternal, fetal depression at low dozes
BDZ
Benzodiazepines: midaz, diazepam – induce neonatal depression immediately following birth
Lower doses: reduce risk
Antagonism: flumazenil
a2s
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
Xylazine
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
Detomidine
appears well tolerated by pregnant mares, drug of choice in ruminants
Opioids
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
Thiopental
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
Propofol
Rapidly crosses placenta, rapidly cleared from neonatal circulation
Longer term CRI may result in fetal depression
Etomidate
–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
Saffan
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
Alfaxan CD
Cyclodextran carrier devoid of histamine‐releasing properties
Short‐acting, minimal CV depression, few AEs
Improved Apgar scores vs propofol
Dissociatives
Increased uterine contraction
Low doses may be used for induction
Retrospective study: ketamine use associated with respiratory depression, apnea, decreased vocalization, increased mortality
Inhalants
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
NMBA
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
Guaifenesin: horses, cattle, small ruminants:
transplacental transfer minimal based on vigor of newborn
LAs
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
NSAIDS
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
C Sections in Dogs, Cats
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?
Recognition of Fetal Distress in SA
Fetal HR slows with hypoxia
* <180bpm: fetal distress
* <160bpm: EMERGENCY
Foals
Foals must be delivered within 20-30’ of chorioallantoic membrane rupture
>40’: EMERGENCY
Advantages of GA for C section
Speed, easy of induction
Reliability, control with optimum operating conditions
Route for maternal O2 administration
Intubation: protection of airway
Disadvantages of GA for C Section
Greater neonatal depression
Inadequate ax plane = maternal catecholamine release
Aspiration
When would GA be more appropriate than locoregional anesthesia for a c section?
Hypovolemia
Prolonged dystocia
Stressed Fetus
Maternal cardiac failure
Morbid obesity
Upper airway resistance (Brachycephalic)
What are the three parturition stages of horses?
Stage I: positioning of fetus, several hours
Stage II: rupture of chorioallantois, 10-20’ – MUST BE <30’
Stage III: passage of placenta, <3hr
Horses and C Sections
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
Most important feature of an equine c section?
RAPID SPEED - GET THE FOAL OUT
Recoveries following equine c sections
- Mares may be exhausted - prone to difficult recovery, consider H/T ropes
Oxygen Support
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
What is the effect of hypoventilation on uterine BF?
decreases uterine blood flow
What are some challenges associated with c sections in ruminants?
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
Effect of pregnancy on LA requirements?
PREGNANCY WILL DECREASE LA DOSE REQUIRED
Absolute contraindications to epidural anesthesia?
coagulopathies, septicemia, infection in area of needle insertion, uncorrected hypotension, lumbosacral pathology
Relative contraindications to epidural anesthesia?
bacteremia, neurologic disease aggravated by epidural drug administration
Changes to Epidural Space with Pregnancy
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
Advantages of Locoregional Techniques with C Sections
Simplicity
Minimal exposure of fetus to drugs
Less intraoperative bleeding
Less risk of aspiration while awake
Excellent muscle relaxation/analgesia
Disadvantages of Locoregional Techniques with C sections
sympathetic blockade, treat with IVF or ephedrine
Spinal Cord Ends
Spinal cord terminates at L6 for dogs, L7/mid sacrum for cats
* Terminates mid sacrum in swine, ruminants
Epidurals in SR, Pigs
- Epidurals well established, not difficult - L6/S1
- If not under GA/intubated: caution with extension of head, neck –> soft palate may occlude airway
Epidurals in Pigs
*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
Rastabi et al VAA 2020 - duration of motor/sensory blockade with saline vs phentolamine
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
Elane et al JAVMA 2022 - intrathecal lidocaine for goat c sections
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
Epidurals in Cattle
Sacrococcygeal space usually ossified in adult
Coccygeal epidural will facilitate vaginal delivery, decreases Ferguson’s reflux
Proximal Paravertebral Block
o Proximal: proximity to spine
Nerves blocked: T13, L1, L2, +/- L3
Landmarks: L1-L3, +/- L4
Blocked adjacent to verbebrate, parallel (needles pointed ventral)
Distal Paravertebral Block
distance from spine
Dorsal, ventral br T13, L1-L3
Needle pointing medial, toward midline
Inverted L/7 block
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
Infiltration Block
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
When give NSAIDS during a c section?
AFTER fetus separated from placenta- reduces fetal prostaglandin concentration, premature DA closure
