Lecture 30: Anesthesia for Cesarean Sections, Neonates, and Geriatrics

changes in pregnancy

increases:

increased cardiac outout due to increased heart rate and stroke volume

blood and plasma volume

minute ventilation due to increased resp rate

oxygen consumption (around 20%)

intragastric pressure

GFR

changes in pregnancy

decrease

Hb and PCV

plasma protein

PaCO2

tidal volume, functional residual capacity and total lung capacty

total pulmonary resistance and peripheral vascular resistance

GI motility, gastric emptying, and gastric pH

BUN and creatinine

potential complications in dam

venous return may be decreased when placed dorsally due to compression of vena cava by gravid uterus —> resulting in what effects on the heart?

relative anemia

• maternal blood volume increases by around 20 %, with larger increase in plasma volume

• PCV within the normal range may mean the bitch is actually dehydrated

hypocalcemia in small breed dogs, large litters, or with uterine inertia

• ionized calcium preferred test —> why?

increased myocardial work and reduced cardiac reserve

increase in alveolar ventilation —> rapid response to inhalant anesthesia

prone to hypoxemia

increased risk of regurgitation, if possible —> plan for surgery

elevated renal values may indicate dehydration or underlying kidney disease

emeregency vs. planned c-section

emergency:

• paatient has been in active labor for >1 hour with no fetus delivered

• may be in a compromised metabolic state

• viability of puppies a concern

planned

• gestation length known

• during “normal” hours… plenty of help

• patient is fasted

most common cause of dystocia?

assessment of patient:

signalment: brachycephalic breeds are common

history: other medical conditions; any current meds

how long bitch has been in labor and if any puppies have been delivered (dead or alive)

PE: abdominal ultrasound (more sensitive in detecting fetal viability) or radiographs to determine number, size, and position

fetal heart rate of 150-200 bpm = healthy; 100-150 bpm = fetal stress

bloodwork:

PCV, T.S., BUN, calcium, glucose, and electrolytes

what bpm is fetal stress?

100-150 bpm

stabilization and patient prep prior to surgery

correct fluid deficits and electrolyte imbalances prior to surgery if possible, otherwise during surgery

± blood type and cross match patient since blood transfusion may be needed if blood loss is severe during surgery

shave abdomen and dirty scrub prior to induction if possible

induce in the OR and have surgeon scrubbed and gown/gloves on —> goal is to have puppies/kittens out within 5-10 mins of induction

personnel devoted to anesthesia, surgery, puppies based on availability

increased gastric acid and decreased lower esophageal tone —>

esophageal reflux

maropitant and ondansetron help with nauseea/vomiting, but not:

Regurgitation

observe and treat —> injectable PPI —> suction and lavage —>

sucralfate after recovery

preoxygenation:

• rapid eeoxygenation at induction, decreased lung expansion

• maternal hypoxemia = fetal hypoxemia and acidosis

• preoxygenate with 100% oxygen for minimum of 5 mins before induction —> don’t oxygenate the room!

• be prepared for rapid intubation!

how is preoxygenation accomplished?

premedications:

premeds will affect the fetus, move quickly!

opioids are useful —> pure mu agonists = reversible!

treat early with anti-emetics

most drugs cross the placenta, so short-acting drugs that can be antagonized are preferred

drugs that are highly protein bound do not readily cross the placenta - buprenorphine (highly protein bound but hard to reverse and not as much analgesia)

how do you make buprenorphine work?

benzodiazepines as premed

mild sedation and skeletal muscle relaxation

Dr. Wilson avoids because it decreases fetal viability

fetal livers do not metbolize due to immature enzyme systems, so you get prolonged sedation

can antagonize flumazenil after delivery

phenothiazines

cause maternal hypotension and leads to fetal hypoxemia

acepromazine has a long duration and cannot be reversed; requres hepatic metabolism

decreases ability of neonate to thermoregulate

NOT recommended for c-sections!!!

alpha2-agonists

increased chance of puppy mortality?

CV effects include bradycardia, arrythmias, decreased contractility and initial hypertension followed by hypotension

xylazine has an oxytocin-like effect on uterus

consider low doses after puppies removed

low doses may be beneficial at other times also

induction:

swiftly securing airway reduces the risk of aspiration. Have suction available. Keepe P in sternal and head above stomach

injectable technique recommended over inhalent induction. Disadvantages of “masking down” include:

• takes longer than injectable

• inhalation induction is more rapid in pregnant animals because of decreased functional reserve and increased minute volume, so this could lead to overdose compared to non-prenant p

• stress and catecholamine release = fetal stress

• hypoxemia in dam and fetuses

• risk of regurgitation and aspiration from unprotected airway

do NOT mask anything down!!!

injectable induction agent:

propofol

dose 2-6 mg/kg, IV to effect, higher dose if alone - lower dose if with other drugs

metabolized in liver and crosses placenta

may cause hypotension due to vasodilation

respiratory depression may necessitate IPPV

provides no analgesia

not cumulative

this is a great induction agent in c-sections

injectable induction agent:

alfaxalone

1-2 mg/kg, IV for c-section in the dog and similar puppy survival rates to propofol and was associated with better neonatal vitality during first 60 minutes after birht

Alfaxalone CRI has been compared to maintenance with iso - slower recovery and lower APGAR scores, but no difference in survival

injectable induction agents NOT to use during c-sections:

ketamine + modazolam should not be used in c-sections

• ketamine —> significant depressant effects in neonates

• decreased likelihood of puppies breathing spontaneously at birth with use of ketamine

inhalent anesthesia for c-section maintenance

all inhalants cross the placenta because lipid solubility and low molecular weight

CV and resp depression

keep % as low as possible to avoid neonatal resp depression

MAC is decrased during prenancy by 16-40% for iso

manual or mechanical ventilation

may be needed due to pressure on diaphragm from uterus

avoid hyperventilation —> decreased uterine and umbilical blood flow —> fetal hypoxemia

comparison of protocols

• use of propofol, alfaxalone, and isoflurane was associated with a lower puppy mortality rate

• use of xylazine associated with an increased puppy mortality rate

• use of ketamine, or inhalation anesthetics was associated with decreased puppy vigor, mortality?

use of local anesthesia in c-sections

line block with lidocaine (2 mg/kg) or bupivicaine (1 mg/kg) prior to surgery and after, block the layers as you close

Nocita - liposome encapsulated bupvacaine works extremely well as pre and post line block for extended analgesia

epidural anesthesia

decrease volume by 25% because of decreased epidural space due to increased collateral circulation

epidural lidocaine (2%; 2-3 mg/kg up to 6m) provides good regional anesthsia and muscle relaxation

use lidocaine instead of bupivacaine because shorter onset (5-10 mins) and duration (60-90 mins)

can combine with morophine (0.1 mg/kg) to prolong anesthesia

epidural block

complications during anesthesia

hypotension

• hemorrhage and increased intra-abdominal pressure decrease cardiac return

• treat if MAP below 60 mm Hg or sysstolic below 80 mmHg

  • decrease anesthetic depth —> PIVA

  • crystalloid fluid bolus (5-10 mL/kg)

  • ± colloid therapy (Vetstarch or 5mL/kg IV bolus over 15 mins)

  • opioid bolus or alpha-2 agonist if fetus(es) out

  • atropine to treat bradycardia and improve CO

  • vasopressor and chronotropic drugs

    • less effectve during pregnancy… thought to be due to downregulation of alpha and beta receptors and increases in prostaglandin leading to vasodilation —> vasopressin?

positive inotropes

ephedrine (0.03-0.1 mg/kg IV bolus)

• improves BP without decreasing uterine blood flow

dobutamine and dopamine

• improve maternal BP but decrease uterine blood flow

• aggressive fluids if able!

management of newborns:

fetal oropharyngeal cavities must be cleaned/suctioned to avoid upper airway obstruction

if bradycardic (HR should be >180 bpm) —> supplement with oxygen, make sure able to breathe and oxygenate

supplies to gather for management of newborns?

rules for puppies:

deliver as quickly as possible

rub the newborn vigorously to stimulate breathing and movement

• do not swing them! Risk cerebral contusion and hemorrhage ):

supplement with O2 using face mask or in oxygen chamber

• may be able to intubate with an IVC

Acupuncture at GV-26 stimulates what?

breathing! 25 g needle

what can you give under tongue of newborns to stim breathing?

epinephrine

what do you place a drop or two of under the tongue of newborns if dam was given opioids to remove fetuses?

naloxone - readily absorbed by mucous membranes

summary for c-section cases

stabilize/prep with IV fluid therapy, gastroprotectants, and preoxygenetion

formulate a protocol based on patient’s ASA status

• premed: make them work for you

• induction: propofol or alfaxalone ± CRI for maintenance

• local anesthesia

• minimize time under GA

• return dam to puppies as soon as she has revocered and send home to decrease stress/encourage bonding

• post-op meds to consider

  • NSAIDs and line block for dam, can consider acetaminophen as well

  • may consider dose of opioid (e.g. buprenorphine at 10-20 mcg/kg)

  • stay tuned for info on longer acting buprenorphine formulations for dogs…

  • cats - zorbium —> transdermal buprenorphine

  • gaba may be added

anesthesia for neonatal and pedes patients

cardiac output is mostly heart rate dependent, so avoid bradycardia!!

airway obstruction, hypoventilation, and hypoxemia can occur; tissue oxygen demand is 2-3 x greater

hepatic and renal systems not fully functional until about 6-8 weeks, so avoid drugs with extensive metabolism or reduce dose

hypoglycemia can occur from fasting and minimal glycogen stores, so add dextrose to IV fluids. avoid high fluid rates!

• no fasting

many drugs have a greater effect due to lower plasma proteins and higher free drug fraction to cross BBB

poor thermoregulatory ability, so have warming devices ready

age of neonate:

up to 4-6 weeks

age of pediatric =

6 - 12 weeks

considerations for premends in neonates and pedes cases

obtain accurate weight, use smaller syringes and dilute drugs for accurate dosing

avoid acepromazine and a2-agonists in pedes patients

• younger p’s do not tolerate bradycardia like adults

midazolam is a great choice for some, but requires liver metabolism and lead to excitement

opioids may cause bradycardia, so consider anticholinergic

have naloxone available for reversal if needed

• some young animals will be sedated well enough from opioid alone

glycopyyrolate lasts longer and less likely to produce sinus tachycardai than atropine

geriatric patients:

gather hx, PE!! other tests as indicated

BP… activity hx and stress test

lower drug dosages and use of short-acting drugs that can be antagonized. Balanced anesthesia plan ideal

careful titration of IV fluids before, during, and after anesthesia

decreasing mental status may mean prolonged recoveries in some

remember…

AGE IS NOT A DISEASE!