monitoring anesthetic depth and recovery Flashcards
what are the stages of anethesia
- analgesia
- delirium
- surgical stage (light, moderate, moderate/deep, deep)
- respiratory paralysis
light anesthetic plane
imedes procedure from being performed
moderate anesthetic plane
surgical plane
deep anesthetic plane
patient at risk due to magnitude of undesirable side effects
EEG indication of anesthetic depth
supplement not suplant - need to use other skills to asses depth
how to measure response to noxious stimuli
somatic response
- sensory - pain
- motor - movement
autonomic reponse
- cardiovascular - increase ABP and HR
- respiratory - increase RR and TV
- sudomotor - sweating, tearing
- ocular - pupil dilation
- hormonal - stress response
what does response to noxious stimuli depend on
stimulus intensity
- larger intensity = greater response
anesthetic depth
- relative anesthetic quantity within CNS
- lighter anesthetic depth = greater response
motor indicators: movement
- movement = somatic response to noxious stimuli
- light plane: movement
- moderate to deep plane: no movement
- relatively objective - purposeful movement vs muscle fasciculation or reflex movement
motor indicators: tone
- MOST anesthetic maintenance agents: anesthetic dept = skeletal muscle relaxation; EXCEPTION: ketamine
- extra-ocular muscles (ocular globe rotation, nystagmus)
- masticatory muscles (jaw tone)
eye positon - light plane
central eye position (no rotation)
eye position - moderate plane
species variability
- dog, cats, pigs: ventromedial rotation
- cattle: ventral rotation
- horse: minimal and unpredictable
- small ruminants and camelids: no rotation
eye position - deep plane
central eye position
eye position exception
ketamine - central eye position at all planes
nystagmus
- most useful in horses
- light plane: large rapid nystagmus
- moderate to deep plane: absent
jaw tone - light plane
strong
jaw tone - moderate to deep
loose
jaw tone less useful in patients with:
- narrow TMJ range of motion (horses, ruminants, rabbits, pigs)
- TMJ disorders
- well developed masticatory muscles (horses. ruminants. rabbits)
- large mandibular mass (horses, large ruminants)
reflexes
- anesthetic depth = loss of reflexes
- palpebral reflex commonly used (species dependent, light - present, moderate/deep - absent)
- protective airway reflexes also lost under general anesthesia (gag reflexes, swallowing, coughing)
palpebral reflex exceptions
species exceptions: horses and camelids
- light and moderate: present
- deep: absent
agent exception: ketamine
- light and modetate: present (all species)
- deep: absent (all species)
cardiovascular indicators
anesthetic depth = cardiovascular depression
- decreased contractility and systemuc vascular resistance
- arterial blood pressure as an anesthetic depth indicator
- low blood pressure suggests TOO deep anesthetic plane
autonomic response to noxious stimuli
cardio indicators
- measurable as increased ABP and HR
- autonomic responses as an anesthetic depth indicator
blood pressure confounding factors
- choice of anesthetic technique and drugs
- hypoventilation, hypoxemia
- anemia, hemorrhage
- cardiovascular disease
respiratory indicators
anesthetic depth = respiratory depression
- minute ventilation = RR x TV
- objective assessment (PaCO2 as depth indicator, severe hypoventilation suggests TOO deep)
- subjective assessment (visual est. - unreliable)
autonomic response to noxious stimuli
respiratory indicators
- measurable as increased RR
- autonomic responses as an anesthetic depth indicator
respiratory confounding factors
- noxious stimuli
- hypercapnia, hypoxemia, hyperthermia
- agent dependent
- mechanical ventilation
response to noxious stimuli during light plane
summary
- movement (CAUTION)
- severe tachycardia and hypertension
- erratic respiratory pattern (patient-ventilator dyssynchrony if on ventilator)
- sweating and tearing (HORSES0
- pupil dilation
response to noxious stimuli during moderate plane
summary
- NO movement
- mild to moderate increase in BP, HR, RR
- relative myosis
response to noxious stimuli during deep plane
summary
- NO movement
- minimal to absent changes in ABP, HR, RR
- pupil dilation
inhaled anesthetics
- anesthetic depth = PCNS (partial pressure in CNS) = PA (partial pressure in alveoli)
- end-respiratory gases closely represent that of alveolar gas (end-tidal concentration)
minimum alveolar concentration
measure of relative potency of inhaled anesthetics
limitations of MAC as a reference point
- inter-individual (& intra-individual) variability
- age, systemic disease, pregnancy
- premedication, body temp
when does the recovery period begin
when the procedure is finished and all anesthetic drugs have been discontinued
steps of recovery
- discontinue all anesthetic drugs
- move the animal to a dedicated area
- position the animal in sternal recumbency when possible to facilitate breathing
- increase O2 flow to prevent hypoxia and facilitate wash-out
- reversal?
when the most common time for small animals (and rabbits) to die
the recovery period
what are the goals of anesthetic recovery
- creating a safe and quiet environment
- maintaining cardiovascular function
- maintaining ventilatory function
- restoring or maintaining normal temperature
- providing additional analgesia
recovery environment
depends on:
- species
- location
- caseload
safe:
- temperature
- protection
recovery equipment
- oxygen supplementation
- thermal support
- induction agents
- monitoring (adequately trained personnel, patient assessment)
patient assessment in recovery
- cardiovascular
- respiratory
- temperature
- pain
monitoring cardiovascular function
- mucous membrane color and CRT
- heart rate (ECG, palpate pulses)
- blood pressure (doppler monitoring, monitoring, invasive BP)
- lactate
how to support cardiovascular function
- IV fluids
- positive inotropes (dobutamine, dopamine)
- vasopressors (dopamine, phenylephrine, norepinephrine)
respiratory monitoring
ventilation
- respiratory pattern and effort
- capnography
- air flow
- thoracic ausculation
- arterial blood gas
oxygenation
- pulse oximetry
- arterial blood gas
ready to extubate - dogs
- risk of aspiration
- swallowing consistently-ready to extubate
ready to extubate - cats
- risk of laryngospasm and tracheal trauma
- one swallow or movement
ready to extubate - horses
- obligate nasal breathers risk of obstruction is recovery
- extubate when standing
ready to extubate - ruminants
- extreme risk aspiration
- extubate when chewing and swallowing vigorously
procedure and patient considerations
- tracheal collapse
- pneumonia
- ventral slot
- thoracotomy
- neuromuscular blocking agents
- upper airway obstruction
brachycephalic breeds
- maintain ET tube until totally awake
- pre/post O2
- ready to re-intubate
- increased vagal tone
oxygen supplemenation
- young healthy small animals for routine procedures usually don’t need supplemental O2 (hypothermia - shivering - increased O2 consumption)
- horses may supplement for increased oxygen consumption during recovery
- if N2O used during anesthesia, wash out system w/ 100% O2 for 5-10 min to prevent diffusion hypoxia
dysphoria/emergence delirium
- high doses of opioids (dysphoria)
- older animals
- predisposed breeds
- quick improvement w/ 1-3 mcg/kg naloxone or 0.05-0.1 mg/kg butorphanol
pain
- suspicion of insufficient analgesia
- improves with further analgesia
- high ABP, fR, and HR: non-specific, elevated in fear, stress, shock, during recovery from anesthesia
- VAS/DIVAS and composite pain scales
if no signs of pain at surgical site, consider the other sources of discomfort:
- full bladder
- constipation
- bandage pain
- joint pain from positioning during surgery
- other pre-existing source of pain (OA, pancreatitis, etc)
prevention and treatment of dysphoria
prevention
- minimize stimuli
treatment
- time
- consider reversal (benzodiazepines, opioids)
- consider sedation (alpha 2 agonists, ace)
prolonged recovery
- clearance of inhalant anesthetics (ventilation, duration of anesthesia)
- clearance of injectable anesthetics (hepatic function, renal function)
- hypothermia
- metabolic abnormalities (hypoglycemia, electrolyte disturbances)
- neurologic abnormalities
prolonged recovery treatment
rule out:
- hypothermia
- hypoglycemia
- abnormal electrolytes
consider reversing
- alpha-2 agonist: atipamezole, tolazoline, yohimbine
- benzodiazepines: flumazenil
- opioids: butorphanol, nalozone, naltrexone, nalbuphine
transfer
- patient signalment and medical condition
- anesthetic procedure
- all medications
- complications
- current status
- catheter management
- contact information
