Neonates Anesthesia

What is considered a neonate in veterinary medicine?

a patient less than 3 months of age

By how many weeks are the major organs well developed in neonates?

12 weeks

What is special about neonates?

They’re major organ systems are under developed

• Cardiovascular

• Pulmonary

• Thermoregulatory

• Renal

• Hepatic

What is different in the neonatal cardiovascular system from the adult cardiovascular system?

• Heart rate dependent for cardiac output (CO)

• Less functional contractile tissue

  • Adult = contractility up to 300%

  • Neonate = only up to 30%

• Very little cardiac reserve

  • Caution for excess IV fluid administration

What is the key to anesthetizing a neonatal patient?

• Maintaining HR

• Maintaining body temperature by short surgical and anesthesia time

• Reduce drug doses

What is different about the neonate respiratory system than the adult respiratory system?

• Higher resting respiratory rate (increased oxygen demand)

• Small airways

• Pliable rib cage

• Gentle constant ventilation is required during anesthesia

What are some of the consequences of neonates having small airways?

• Obstruction

• Closing volume (volume where alveoli collapse) is much smaller)

• Increased potential for hypoxia

What other organ systems should we be concerned with for neonates?

• Immature sympathetic nervous system

• Decreased ability to respond to stress of anesthesia

• Hepatic microsomal enzymes are deficient (prolonged metabolism and and elimination and effect of drugs)

• Glycogen stores are low (fasting time = 4 hours)

• Renal function (prolonged drug effect)

Why are neonates more likely to experience hypothermia?

• Typically less body fat

• Immature thermoregulatory control

• Large ratio of surface area to body mass

What are some common neonate anesthetic procedures and what kind of drugs should be used?

• Tail docking

• Dew claw amputation

• Reduce dose

• Use of local anesthetics/opioids

How do neonates react to drugs?

• Immature blood-brain barrier

• High volume of distribution because of large extracellular fluid volume

• Decreased protein binding of drugs

• Decreased metabolism

What are some common pre-meds for neonates?

• Low dose opioids/ benzodiazepines

• anticholinergics

What drugs are best avoided in neonates and why?

Acepromazine

• significant hypotension

• heat lost due to vasodilation

• hepatic metabolism and renal clearance - longer drug effect

Dexmedetomidine and other alpha -2 agonist drugs

• severe bradyarrhythmias

• Extensive hepatic metabolism and renal clearance - longer drug effect

What is the most common anesthetic induction for neonates?

• Inhalant via face mask

What are some good anesthetic induction drugs for neonates and how should they be given?

• Propofol, alfaxalone, or etomidate

• Should be given slowly

• Titrate to effect

• Lower dose

What are the advantages and disadvantages of the non-rebreathing circuit for neonates?

Advantages

• less resistance - reduce the work of breathing

Disadvantage

• Poor at maintaining body temp due to high O2 flow rates

• Increase risk of barotrauma more quickly

Why are injectable anesthetics not recommended for neonates?

• Requires great care due to extensive metabolism required to excrete these drugs

• It is easier and safer to use general anesthesia to protect airway and to have an IV catheter

Colloids can be used for —

IV boluses, rarely CRIs

Hypertonic saline for —-

IV boluses (rapid need for large volumes, head trauma)

Hypotonic fluids NEVER for—-

IV boluses, infusions to fix Na disorders or maintenance in patients who can’t tolerate lots of Na

All animals over the age of — years are considered geriatric, regardless of species, breed, or current heath

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When is a dog/cat considered geriatric?

• Not single definition for “geriatric” in dogs and cats

• When it reaches 75% to 80% of its anticipated life expectancy

What is once thing that generally occurs with geriatric patients?

• Most organs have decreased reserved functions

  • Cardiovascular

  • Pulmonary

  • Thermoregulatory

  • Renal

  • Hepatic

• Common to have actual concurrent disease

Organ reserve

the ability of organs to withstand significant, sometimes life-threatening, physiological stress

What are some geriatric-related cardiovascular changes?

• Susceptible to HYPOTENSION (decreased blood volume, CO, baroreceptor activity)

• Maybe prone to cardiac arrhythmias

• Not uncommon to have cardiac disease

• Produce severe reduction in cardiac reserve capacity

How can a geriatric patient’s reduction in cardiac reserve capacity be a danger when under anesthesia?

• Limits the patient’s ability to compensate for cardiovascular changes that occur during anesthesia

What should we avoid in the anesthetic management of geriatric patients regarding cardio?

• Bradycardia or tachycardia

• Sudden changes in blood pressure

• Hypotension or hypertension

• Increased vascular resistance

If a patient has myocardia disease what consequence could that cause for a patient going under anesthesia?

• Increase the chance to develop cardiac arrhythmias while under general anesthesia

  • 2nd degree heart block

  • Bundle branch block

  • Ventricular premature contractions (VPC)

  • Atrial fibrillation

• Common existing arrhythmias or exaggerated from anesthesia or surgery

What drugs should we avoid or use conservatively for a myocardial disease patient?

• Xylazine or dexmedetomidine

  • Bradycardia, 2nd degree heart block

• Ketamine

  • Increase HR and BP

What else can we do to support the cardiovascular system for a geriatric patient or a patient with myocardial disease?

• Intravenous access and fluid therapy

• Blood pressure measurement

• Continuous ECG

What are some age-related respiratory changes?

• Decreased vital capacity

  • Weakened respiratory muscle

  • Loss/decrease of elastic tissue

  • Pulmonary fibrosis

  • Tidal volume

• Decreased respiratory functional reserve

• Predisposed to atelectasis with anesthesia and/or prolonged recumbency

• Increased susceptibility to respiratory infections

What are some drugs that we should avoid or use with caution with geriatric patients that have decreased respiratory functional reserve?

Propofol, alfaxalone, etomidate, or inhalant anesthetics

• Mild to moderate respiratory depression

• results in marked hypoxia and hypercapnia

What should we do to help a respiratory disease patient?

• Anesthetic management should avoid any respiratory depression

• Caution with intermittent positive pressure ventilation!! Never ventilate with pressure over 20 cm H2O

What are some common pathologic lung lesions?

• Pulmonary fibrosis

• Pulmonary neoplasia

• Pneumonia

• Pulmonary cyst, bullae, or blebs

What should we do for the respiratory disease patient?

• Pre-oxygenation before induction

• Monitor closely pulse oximetry, capnography, and blood gas analysis

• Airway control, patency, and oxygen supplementation

What does the reduction in liver function for geriatric patients mean for anesthesia?

• Prolonged metabolism and excretion of drugs

• Prolonged recovery

What drugs should be avoided to account for age-related hepatic changes?

• Drugs that have a long duration of action

• Drugs that rely heavily on hepatic metabolism

• Drugs that cannot be reversed

Reduced hepatic function may lead to…

• Hypoprotenemia

• Impaired clotting function

• a greater susceptibility to hypothermia and hypoglycemia

• Hypotension

What is important to do before anesthesia to account for age-related hepatic changes?

• Preanesthetic hematology - CBC. serum chem, clotting profile

What does a decrease in renal functional reserve mean for a patient?

• Less tolerant of dehydration or acute hemorrhage during surgery

• But…over hydration due to excessive fluid administration will lead to pulmonary edema due to limited respiratory functional reserve

Reduction of renal blood flow can lead to?

• Hypovolemia

• Hypotension

• Hypoxia

• Hypercapnia

What should you monitor for anesthesia to check for renal function?

• Monitor urine production

• 1-2 ml/kg/hr normal urine production during anesthesia

For geriatric patients choose drugs with…

• short duration

• reversible drugs

• less hepatic/renal depending metabolism/elimination

• choose cardio friendly drugs and reduce dosage

Why should the use of NSAIDs be avoided in geriatric patients?

• Liver dysfunction

• Renal dysfunction

• GI dysfunction

• Platelets dysfunctio

What are some good choices for induction drugs for geriatric patients

• Propofol, alfaxalone, or etomidate

  • rapid induction and relatively complete recoveries

  • cardiopulmonary effect

  • respiration depression

  • preoxygenate for 5 minutes

Why is acepromazine often avoided for geriatric patients?

• metabolized in liver

• not reversible

• prolonged recovery

• Hypotension due to vasodilation

Why are anticholinergic agents often avoided for geriatric patients?

• may precipitate sinus tachycardia

What are some anesthetic pre-meds recommended for geriatric patients?

• Benzodiazepines

• Opioids

What pre-meds should be avoided with geriatric patients?

• Alpha-2 agonists

• Anti-cholinergics

• Acepromazine