Anesthesia: Exam 1 Intro Lecture & Anesthesia Machines/Equipment

therapeutic index

Anesthesia has a low _____ _____; balancing act between too much & too little medication.

Anesthesiology

Study & discipline of the use of anesthetic agents & production of the state of anesthesia

Anesthesia

Reversible loss of sensation to all or part of the body

*Drug induced depression of CNS & PNS

Spinal cord

Primary site where anesthetics act to inhibit purposeful responses

General

Anesthesia that's drug-induced with controlled, reversible loss of consciousness & sensation

*Either injectable/inhalational agents/combo

No

With general anesthesia, is the patient arousable by physical stimulation?

Tranquilization

A state of tranquility & calmness in which the animal is awake, relaxed, and unconcerned about its surroundings

-Animal is easily arousable & will respond to painful stimuli

Sedation

CNS depression in which the animal is awake, sleepy, but still able to be aroused by stimulation

-Minor manipulations can be performed, & aggressive animals may be easier to handle

Sedation

Is tranquilization or sedation a more significant/stronger CNS depression?

No, yes, yes

Is an animal under general anesthesia arousable by physical stimuli? Under tranquilization? Under sedation?

Dissociative anesthesia

General anesthesia where the animal is unaware of external stimuli with some muscle rigidity (catalepsy), open eyes with palpebral reflexes, & somewhat intact swallowing reflexes

thalamocortical, limbic

Dissociative anesthetic agents interrupt neurotransmission between the _____________ and _________ areas of the CNS

Yes

Do animals under dissociative anesthesia have palpebral & swallowing reflexes?

No

Is an animal unconscious under local anesthesia?

Regional anesthesia

Local anesthesia in which specific nerve blocks are performed to desensitize a certain part of the body

Local anesthesia

Administration of a local anesthetic agent to desensitize part of the body

-Chemical/manual restraint is necessary to perform this technique

Conscious, unconcious

Analgesia:

- Patient has diminished pain perception if _____.

-Patient has reduced autonomic responses to noxious stimuli if ______.

Preventive analgesia

Use of analgesic drugs & techniques before, during, & after pain begins

-Administering pre-medications before surgery allows less drugs to be used overall (& therefore less side effects)

-Prevents plastic wind up of pain pathways

Nociception

Activation of nociceptors by a noxious stimuli

Nociceptors

Specialized sensory nerves that detect & transmit noxious sensations to higher centers in the spinal cord & brain

Pain

Unpleasant sensory & emotional experience associated with actual/potential tissue damage

Conscious, nociception

Pain is a _____ awareness & response to _____.

Unconsciousness

Loss of individual awareness which occurs when the brain's ability to integrate info is blocked/disrupted

-Block interactions between brain regions & reduce cortical activity patterns

Spontaneous righting reflex

What reflex is lost to indicate that an animal is unconscious?

*In humans: loss of response to spoken command

Amnesia, Analgesia

5 Components of the Anesthetic State:

- Unconsciousness

- _____ = loss of memories

- _____ (more accurately, antinociception)

- Immobility (dose dependent)

-Attenuation of autonomic responses to noxious stimuli

False (consciousness = subjective experience/awareness, responsiveness = spontaneous/goal directed movement)

True or False: Unresponsiveness is the same thing as unconsciousness.

Ligand gated ion

Most anesthetics work on a subcellular target/receptor with a synaptic function via ___ ____ ___ channels.

NMDA (N-methyl-D-aspartate) antagonists, GABA (Gamma aminobutyric acid) agonists

Subcellular Receptors:

-____ = receptor that dissociatives (Ex: ketamine) act on

-______ = receptor that inhalants & most hypnotic injectables act on

ECG (evaluates brain electrical activity)

What diagnostic tool can be used to define loss of consciousness?

Awake

Based on this ECG, is the patient awake or deeply anesthetized?

-Low voltage amplitude, many high frequency components (fast), "desynchronized"

Deeply anesthetized

Based on this ECG, is the patient awake or deeply anesthetized?

-High voltage, slow oscillations, "synchronized", dose dependent

spinal activity

Non-purposeful movement during anesthesia is due to ____________, not consciousness.

Memory & awareness in the patient is lost at < ___% of the anesthesia concentration that it takes to cease movement.

Amnesia

Does anesthesia first cause amnesia or analgesia?

True (at the level of the brainstem or spinal cord, cerebral cortex connection NOT required)

True or false: Unconscious animals can produce complex movements

Yes (respond autonomically & reflexively to noxious stimuli but they are not feeling the pain)

Will an anesthetized animal respond to noxious stimuli?

Cerebral cortex

Where in the brain does conscious integration of nociceptor input have to occur in order to create the sensation of pain?

False

True or false: Anesthetized animals feel pain

Stages 1-3

What stages of anesthesia can be demonstrated in both induction to anesthesia & during recovery?

Amnesia, voluntary movement, analgesia (at deeper levels)

What are the 3 characteristics of Stage 1 of Anesthesia?

*Hint: AVMA is #1

Delirium or involuntary excitement

What characterizes Stage 2 of Anesthesia?

*Want to quickly induce & get out of this stage ASAP & stay in stage 3 for as long as possible

Surgical anesthesia

What is Stage 3 of Anesthesia?

cardiovascular/pulmonary collapse

What is Stage 4 of Anesthesia?

Preanesthetic, maintenance

Sequence of the Perianesthetic Period:

1) _____ = patient eval (history, PE, labwork, patient ID), prep, & medication

2) Induction of anesthesia = transition from consciousness to anesthetized

3) Anesthetic _____ (during surgery)

4) Recovery period (24 hrs)

24

The recovery phase is a ___ hour period after awakening from general anesthesia

Evaluation, preparation

An anesthetic care plan consists of patient ____ & patient _____.

Patient evaluation

Assesses patient demeanor & baseline health status

-Includes PE, patient identification (body weight, signalment), history, & any laboratory date

Patient preparation

Part of the anesthetic care plan that includes:

-1) the nature of the procedure to be performed

-2) a means to monitor the patient

-3) knowledge of potential complications associated with both the procedure & anesthetic procedure

-4) a means to treat any complications which arise

False (these tests fail to uncover pathologic conditions/abnormalities that don't necessarily improve patient care/outcome)

True or false: Extensive pre-anesthetic lab screening has been shown to improve patient outcome.

physical exam, history

Pre-anesthetic lab tests should be chosen based on ___________ _____ & patient ______

PCV (packed cell volume), TP (total protein)

What is the minimum lab work that should be done pre-surgery for a young, healthy animal that will be anesthetized for an elective procedure?

ASA (American Society of Anesthesiologists) classification system

System created to assess risk of anesthesia before anesthetizing the animal

-Based on patient physical status (PE, history, signalment)

No systemic disease (normal, healthy patient)

What is ASA class 1?

Class 1 (healthy animal + elective procedures = class 1)

A healthy dog is coming in for a spay. What ASA class is this?

Mild compensated systemic disease

What is ASA class 2?

-Ex: Uncomplicated orthopedic injury, localized/controlled infection, mild obesity, mild airway problems

Class 2

What ASA status do all brachiocephalic dogs automatically fall under?

Moderate/severe systemic disease that's ongoing but compensated (stable vital signs)

What is ASA class 3?

-Some functional limitations exist that increase anesthesia risk

*Ex: Animal with significant fractures/hemorrhage, CHG with clinical signs of reduced cardiac reserve, moderate hypovolemia, azotemia, diabetes mellitus, severe obesity

Serious, decompensated systemic disease

What is ASA class 4?

-Disease is a constant threat to life = High anesthetic risk because vital body systems are involved (Heart, lungs, CNS)

*Ex: Acute GDV, life threatening hemorrhage, severe toxemia/icterus, severe colic

Moribund, requires intensive life support

What is ASA class 5?

-Patient not expected to live > 24 hrs with or without surgery

-Ex: Colic, torsions, sometimes GDVs

Brain dead

What is ASA class 6 (used on in human medicine for donor purposes)?

Emergency (surgery must be done regardless of physical status)

What is the E component of ASA?

*can be added to any of the 5 ASA classes

False (Age in the absence of disease is not an adequate reason, should not assume that geriatric patients are automatically higher risk)

True or False: Age alone is an adequate reason to increase anesthetic risk assignment.

2 (mild systemic disease, well compensated)

A dog comes in with a torn ACL and mild obesity; this is ASA class __

2 (brachycephalic = mild systemic disease, well compensated)

A bulldog comes in for surgery; this is ASA class __

3 (moderate systemic disease that is ongoing but compensated)

A dog comes in with controlled diabetes; this is ASA class __

3 (moderate systemic disease that is ongoing but compensated)

A dog comes in with congestive heart failure with minor clinical signs of reduced cardiac reserve; this is ASA class __

4 (severe systemic disease that is a constant threat to life, uncompensated disease, or vital body system involved)

A hit by car dog comes in with severe hemorrhage and needs a blood transfusion; this is ASA class __

4 (severe systemic disease that is a constant threat to life, uncompensated disease, or vital body system involved)

A dog comes in with acute gastric dilation volvulus (GDV); this is ASA class __

5

A horse comes in with severe colic and is not expected to live 24 hours with or without surgery; this is ASA risk __

True

True or False: Fasting prior to surgery has been shown to decrease aspiration risk, improve abdominal access, & improve ventilatory function.

4-6 hours

How long should monogastric animals be fasted prior to surgery per recent studies?

> 12 hours

Fasting for longer than ____ hours has been shown to decrease stomach pH & increase gastric volume/risk of regurgitation.

Pocket pets (tiny dogs, birds, pediatrics), horses

What animals have the shortest recommended fasting period (0-4 hrs) prior to anesthesia?

Dogs/cats

What animals should be fasted for 4-6 hours prior to anesthesia but withholding water is not necessary?

24-48 hours

How long should Ruminants be fasted before surgery?

Analgesics +/- tranquilizers

What medications are typically used for pre-anesthetic pain control?

*AKA what meds are used as premeds

Autonomic response (patient is unconscious and cannot feel pain BUT can still have autonomic responses to nociception)

Your surgery dog has been stable under general anesthesia. When the ovarian pedicle is stretched, your dog's HR and RR increases. Is this a sign of pain or an autonomic response?

Depends on the pain of the procedure (Sedated animals are awake, sleepy, and able to be aroused by noxious stimuli)

Medicine wishes to "sedate" a dog for percutaneous liver biopsy. Will sedation be sufficient to perform this procedure? Why or why not?

General anesthesia

You want a dog to be unconscious, relaxed, analgesic, and nonresponsive to surgical stimulation for a percutaneous liver biopsy. What term would best describe this?

Blood, electrolyte, & fluid deficits (*BEF = before anesthetics)

What types of deficits should be corrected prior to the administration of anesthetic drugs?

All of the above

Which of the following are the minimum PE findings that the anesthetist should be familiar with before administering anesthetic drugs?

A) Auscultate heart/lungs & note any abnormal cardiac rhythms/murmurs and lung sounds

B) Palpate pulses

C) Record HR, RR, MM color, CRT, & hydration status

D) Observe mentation/behavior

All of the above

Which of the following information is necessary to formulate an anesthetic care plan?

A) Patient ID

B) Patient history

C) Physical exam findings

D) Laboratory data

E) Physical status classification (ASA)

No (patient has lost consciousness)

Is an animal in Stage 2 of anesthesia consciously aware of its environment?

Pipelines

Central gas supply that transports carrier gases (O2, nitrous oxide, or air) from 1 part of the hospital to the anesthesia machine

*Different adaptors & colored hoses prevent giving the patient the wrong gas

Cylinders

Portable, compressed gas containers

*Can be used as a gas source in anesthesia machines instead of central (pipeline) sources

*Different colors depict different gases (Nitrous oxide = Blue, CO2 = Grey)

Green

What color are the oxygen cylinders in the US?

-White in Canada, Europe, & Australia

Counterclockwise (to the left)

What direction do you turn the cylinder wrench to open the cylinder?

Crack valve briefly

What should you do to a gas cylinder prior to mounting it on the yoke to clear debris?

Flowmeter

Measures the flow of gases into the patient breathing circuit

-Units: Liters/min

Vaporizer

Converts liquid anesthetic agents (Ex: isoflurane) into a gas mixture in a controlled manner

Latent heat of vaporization

Amount of heated needed to convert liquid anesthetic agents into a vapor at a constant temperature

Copper, stainless steel

Overtime, temperature & thus anesthetic vapor pressure will decrease in vaporizers. What substances with high specific heat & thermal conductivity are added to help vaporizers with this problem?

Precision vaporizer

Delivers a precise concentration of anesthetic to the patient

-Temperature & flow compensated

-High resistance & agent specific

*Can be manual or automatic

O2 flush valve

What valve bypasses the vaporizer to deliver large volumes of pure O2 to the breathing circuit (35-75 L/min)?

Barotrauma, death (always disconnect patient 1st)

What can happen if you push the O2 flush valve while it is connected to your patient?

Rebreathing systems

AKA circle systems, breathing circuit for adults, pediatrics, & large animals

-Unidirectional gas flow with 1 way valves

Rebreathing systems

Do rebreathing or nonrebreathing systems use less gas & cause slower changes in the anesthetic plane?

-Can be used in all patients > 5kg

Nonrebreathing systems

Breathing system that provides high O2 flow to minimize rebreathing of CO2 in small patients (< 5 kg)

-Bypasses 1 way valves & CO2 absorbent canisters to minimize resistance in circuit

Bain circuit (modified mapleson D)

Nonrebreathing system with an inner tube that delivers fresh gas & an outer tube that carries away exhaled gases to the scavenger

Rebreathing/reservoir bag

Rubber bag that supplies peak inspiratory demands in both types of breathing systems

-Can ventilate patient & monitor ventilation rate with it