ANESTHESIA TECHNIQUES: (GOALS)

•  Monitored anesthesia care (MAC):  Anxiolysis, sedation, analgesia & monitoring by anesthesia personnel able to anticipate and react to changes in pt status & anesthetic state/requirements

•  General anesthesia: Pt unresponsive to significant stimulation; often requires airway, ventilatory, and/or cardiovascular support

•  Neuraxial techniques: Spinal/epidural alone or combined with above techniques for intraop & postop analgesia to chest, abdomen, & lower extremity

•  Peripheral nerve block: Minimal physiologic effects make these techniques useful, especially in a pt with significant comorbidities.

MONITORED ANESTHESIA CARE VS. GENERAL ANESTHESIA: ASA DEFINITIONS

•  MAC: Anesthesia service that involves varying depths of sedation, analgesia, & anxiolysis but, most importantly, requires that provider is “prepared & qualified to convert to general anesthesia when necessary.”

•  General anesthesia: State when “patient loses consciousness & the ability to respond purposefully … irrespective of whether airway instrumentation is required”

FLUMAZENIL (FOR ANTAGONISM OF BENZODIAZEPINE EFFECTS)

•  Initial recommended dose = 0.2 mg

•  If desired level of consciousness not achieved in 45 sec, repeat 0.2 mg dose

•  0.2 mg dose may need to be repeated q60sec to max of 1 mg

•  Note: Be aware of potential for resedation due to short half-life

INHALATIONAL INDUCTION

•  Allows induction without IV access, as IV placement can be anxiety-provoking

•  Onset of anesthesia faster in children than in adults (ratio of alveolar ventilation to FRC is in inverse proportion to body size; i.e., infants & children have increased ratio of alveolar ventilation to FRC)

Pediatric Technique

•  For infants & children who tolerate a mask:

• Start with 70% nitrous oxide in mask on pt

• Introduce volatile agent only after 3 to 5 min of N₂O/O₂

• Cut back N₂O and increase O₂ percentage as potent agent is added

•  For anxious children—rapid induction (in as few as 4 breaths):

• Often requires involvement of multiple personnel and/or parents

• Prime circuit with 70% N₂O, O₂ & 8% sevoflurane

• Place mask firmly on pt while monitoring airway throughout

• With loss of consciousness, increase percentage of O₂ & decrease N₂O

• Decrease sevoflurane conc over next few minutes as agent equilibrates

• Support ventilation as needed

• Place IV (often with an assistant to assure appropriate attention to airway)

Note: Sevoflurane induction has been associated with bradycardia, especially in patients with Down’s syndrome [J Clin Anesth. (22):8, Dec 2010, 592–597]

Adult Inhalational Induction

•  Consider for adults in whom IV placement is extremely anxiety-provoking/difficult

•  Disadvantages: May cause ↑ cough, hiccups, & possibly ↑ risk of nausea/vomiting

•  Prime circuit with 8% sevoflurane & 70% N₂O (usually requires 3 fill/empty cycles of an occluded anesthesia circuit)

•  Instruct pt to exhale completely & then inhale from mask to vital capacity & hold

•  If still conscious & unable to hold breath any longer, instruct pt to take additional deep breaths

INTRAMUSCULAR INDUCTION

•  May be useful technique for:

• Uncooperative pts in whom IV placement/inhalation induction impossible

• Loss of control of pt and/or airway during attempted inhalation induction

• Agitation/disinhibition with premedication

• Need for rapid sequence induction without venous access

•  Typical IM dosing:

• Ketamine 6.5–10 mg/kg, 10% solution

• Atropine 0.02 mg/kg, to reduce secretions

• Succinylcholine 3–4 mg/kg, included for rapid sequence induction

Note: Atropine & succinylcholine may be combined in same syringe; administer midazolam after IV placement to prevent ketamine emergence delirium

RECTAL INDUCTION

Characteristics

•  Convenient for healthy children old enough to have separation anxiety but still not mature enough to cooperate (8 mos to 5 yrs/o)

•  Parents & child familiar with rectal route for other medications (i.e., acetaminophen)

•  Avoids needle for IM/IV induction & struggle involved with inhalational induction

Technique

•  Cut 14-Fr suction catheter to 10 cm & lubricate

•  Place catheter in pt’s rectum & administer medication through syringe

•  Follow medication with air bolus to purge remaining drug from catheter lumen

•  Instruct parent/caregiver to hold buttocks together for at least 2 min

•  Anticipate defecation & provide caregiver with waterproof mat

•  Harmless hiccupping may occur

•  Constant monitoring by anesthesia personnel required throughout

•  Pt should be taken to procedure area as soon as sufficient sedation achieved

•  Maintain primary attention on supporting pt’s airway

COMPONENTS OF ANESTHESIA

•  An anesthetic may contain any or all of the following components: Anxiolysis, analgesia, hypnosis, amnesia, paralysis

•  Inhalational & IV agents provide anxiolysis & hypnosis, little or no analgesia (except for ketamine and nitrous oxide) (Anesthesiology 2008;109(4):707–722)

•  Narcotics provide analgesia, little or no hypnosis/sedation

“BALANCED ANESTHETIC” TECHNIQUE

•  A technique of general anesthesia based on the concept that administration of a mixture of small amounts of several neuronal depressants summates the advantages but not the disadvantages of the individual components of the mixture

A “balance” of virtues of different agents allows less of each to be used

•  Allows for faster emergence & less risk of cardiovascular collapse

•  Use of muscle relaxants may increase risk of intraoperative awareness

MONITORING OF NEUROMUSCULAR BLOCKADE/PARALYSIS

Technique

Peripheral nerve stimulator (PNS) electrically stimulates motor nerve adductor pollicis (ulnar n.), obicularis oculi (facial n.), posterior tibial n., peroneal n.

Train of Four

Four stimuli given at a frequency of 2 Hz every 5 sec

→ Potentially eliciting 4 twitches (T1–T4)

→ TOF ratio T4:T1 indicates degree of neuromuscular block

→ Nondepolarizing agents:Produce progressive reduction in magnitude of T1–T4; number of elicited twitches indicates degree of blockade with recovery, twitches appear in reverse order

→ Depolarizing agents (succinylcholine):Produce equal but reduced twitches (no fade)

Tetanic Stimulation

Tetanic stimulation: Concept that acetylcholine is depleted by successive stimulations; 50 Hz for 5 continuous seconds produces detectable fade in muscle contraction

→ The extent of fade is related to the degree of neuromuscular block

→ No fade = no neuromuscular block

→ Sustained response to tetanus present when TOF ratio is >0.7

Double-Burst Stimulation

•  Two bursts of three stimuli at 50 Hz with each triple burst separated by 750 ms

•  Decrease in second response indicates residual block

•  Ratio is related to TOF ratio but easier to interpret reliably

Post-Tetanic Count

•  50 Hz tetanic stimulus given for 5 sec, followed by stimulus at 1.0 Hz 3 sec later

•  No. of responses detectable predicts time for spontaneous recovery

•  Fade response appears earlier than train of four

•  Can be used under deep paralysis to estimate time to recovery and potential for use of reversal agents.

Phase II Blockade with Succinylcholine

•  Postjunctional membranes repolarized, but still not responding to acetylcholine

•  Resembles blockade by nondepolarizing agents (get TOF fade, tetanic stim)

•  Mechanism unknown, occurs when succinylcholine dose exceeds 3–5 mg/kg IV

•  Reversal agents (neostigmine) may or may not antagonize phase II blockade

AWARENESS

•  Complication where pt regains consciousness during general anesthetic & can recall events afterward. Important to distinguish goals of General Anesthesia from that of Monitored Anesthesia Care.

•  Pts experience ranges from benign recall of conversation to posttraumatic stress disorder (PTSD) involving disturbed sleep, nightmares, flashbacks, & general anxiety

•  Negative psychologic consequences can last for years after the event

•  If awareness occurs, pts often respond favorably to a complete explanation, apology, & reassurance that they are not crazy. Psychology consult should be considered early if patient is in favor

Frequency of Awareness (from prospective study of 11,785 general anesthetics)

•  0.15% of all cases

•  0.18% with paralysis

•  0.10% without paralysis

BRAIN FUNCTION MONITORING, DEPTH OF ANESTHESIA, AND AWARENESS

•  Brain function monitors analyze EEG signals & translate them into a number between 0 and 100 that corresponds to anesthetic depth

•  Two devices currently available (BIS from Aspect, SEDLine from Masimo)

•  ASA position: BIS not routinely indicated & decision to use should be made on a case-by-case basis by individual practitionerWhen compared to monitoring of the end-tidal anesthetic-agent concentration (ETAC), BIS does not appear to reduce the incidence of intraoperative awareness (N Engl J Med 2011;365:591–600, August 18, 2011)

BRAIN FUNCTION MONITORING & ANALGESIA

•  Number correlates best with hypnotic component of anesthetic provided by benzodiazepines, propofol, & potent volatile agents

•  N₂O, low-dose narcotics & neuraxial/peripheral nerve blocks have little effect on the number (These agents do ↓ amount of additional hypnotic needed to keep the number constant when pts are exposed noxious stimuli)

•  Ketamine confounds the number & contraindicates its use. Use of Nitrous Oxide (alone) may result in inaccurate correlation of BIS and level of sedation and hypnosis (A & A August 2006 vol. 103 no. 2 385–389).

TOTAL INTRAVENOUS ANESTHESIA (TIVA)

•  TIVA anesthetics usually include hypnotic (propofol) + analgesic (remifentanil)

•  IV infusion drugs should be connected as closely as possible to pt’s IV catheter (Minimize dead space where infusion meds can accumulate)

•  TIVA may be more susceptible to dosing errors

•  Must always monitor for: IV lines that are infiltrated/kinkedDisconnections & dosing errors

Advantages of  TIVA over Inhalation Induction & Maintenance

•  Smooth induction with minimal coughing/hiccupping

•  Easier control of anesthetic depth

•  More rapid, predictable emergence

•  Lower incidence of PONV

•  Ideal operating conditions for neurologic surgery with reduced cerebral blood flow & cerebral metabolic rate; allows intraoperative neuromonitoring

•  ↓ organ toxicity & atmospheric pollution

•  Avoids N₂O side effects (expansion of closed airspaces & bone marrow suppression)

Common Indications for  TIVA

•  Anesthesia for airway endoscopies, laryngeal & tracheal surgeries

•  Anesthesia in remote locations or during transport

•  Malignant hyperthermia–susceptible patients

•  History of significant PONV

Advantages of Continuous Infusions Compared with Intermittent Bolus Dosing

•  Avoid oscillations in drug concentration

•  Minimize relative over- or underdosing

•  Provide stable depth of anesthesia

•  Reduce incidence of side effects (hemodynamic instability)

•  Shorten recovery times

•  ↓ total drug requirements by 25–30%

Titration of Maintenance Infusions

•  Titrate to anticipated intensity of observed responses to surgical stimulus

•  Drug requirements are highest during endotracheal intubation

•  Requirements ↓ during surgical prep & draping

•  Infusion rates should be ↑’d a few minutes before skin incision

•  Pt movement & changes in hemodynamics should guide infusions titration

•  After start of surgery: If no response for 10–15 min, ↓ infusion rate by 20%if response, administer bolus & ↑ infusion rate

•  Opioid should be administered to achieve analgesia

•  Hypnotic should be titrated to individual requirements & surgical stimulus

•  Infusion rates need to be titrated down to restore spontaneous respiration at surgery’s end

GUIDELINES FOR USING PROPOFOL

Induction of General Anesthesia

•  2–3 mg/kg IV (reduced in pts given opioids/other premeds, aged >50)

Maintenance of General Anesthesia

•  80–150 mcg/kg/min IV combined with N₂O or an opiate

•  120–200 mcg/kg/min IV if sole agent

•  Consider reducing dose after 2 hr (propofol accumulates)

•  Turn off infusion 5–10 min prior to desired time of emergence (can give 1–2 mL boluses as needed to keep pt asleep until emergence)

Sedation

•  10–50 mcg/kg/min IV

EXTUBATION & EMERGENCE

Common Extubation Criteria

•  Regular respiratory rate

•  Stable SpO₂

•  Adequate paralysis reversal (sustained head/leg lift for 5 sec); able to protect airway

•  Tidal volumes >4 mL/kg

•  Return of consciousness (following commands)

•  Stable end-tidal CO₂ at physiologic levels

Indications for Continued Postop Intubation

•  Epiglottitis

•  Localized upper airway edema secondary to surgery or trauma

•  Surgery causing injury to recurrent laryngeal nerves

•  Upper airway edema from massive intraoperative volume infusion (especially combined with prolonged Trendelenburg or prone positioning)

•  Unstable hemodynamics or continued bleeding

•  Neurologic compromise (GCS <8)

Deep Extubation

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