TECHNIQUES




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 practitioner
When 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 doamount 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/kinked
Disconnections & 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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Jul 4, 2016 | Posted by in ANESTHESIA | Comments Off on TECHNIQUES

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