A 6-year-old girl presents to the operating room for an open reduction and internal fixation of a fractured femur. The patient is extremely anxious and uncooperative. How would you induce anesthesia?

An inhalation induction uses a volatile anesthetic to induce anesthesia and can be accomplished without intravenous access.

Inhaled (volatile) Anesthetics

•Usually used to maintain anesthesia

•May also be used to induce anesthesia

•Dosage is expressed in percent concentration of inhaled gas

•All inhaled (volatile) anesthetics cause some degree of vasodilatation and myocardial depression

•Nitrous oxide has the most hemodynamically stable pharmacodynamics

•Choice of volatile anesthetic

•Titratability

•Desflurane is the most titratable, followed by sevoflurane

•Airway irritability

•Sevoflurane causes the least airway irritation and is readily used for the induction of anesthesia

•Desflurane is associated with the most airway irritability

•Effect on closed air spaces

•Nitrous oxide readily diffuses from the blood to closed air spaces, causing either expansion or an increase in pressure

•Nitrous oxide should be avoided in situations where an increase in volume or pressure of an enclosed air space should be avoided, such as middle ear surgery, bowel obstruction, a closed pneumothorax, or the presence of intravascular gas.

Minimum Alveolar Concentration

•Defined as the partial pressure of inhaled anesthetic that prevents movement in response to a surgical incision in 50% of the population

•Used to determine the appropriate dosage and to compare potencies of volatile anesthetics

•The concept of Minimum Alveolar Concentration (MAC) is additive. Certain factors reduce or increase the MAC of a given inhalational anesthetic agent. Examples include:

•Potency of a volatile agent

•Age

•Patient temperature

•Concurrent drug administration

•Ethanol and illicit substance use

•Pregnancy

A 33-year-old healthy woman is about to undergo an emergent abdominal laparoscopy for ovarian torsion. The patient last ate a full meal 3 hours prior to presentation in the operating room. What strategy should be used for induction and intubation?

Adults who have eaten within 6 to 8 hours of general anesthesia are at increased risk for aspiration. When an operation is urgent or emergent, a rapid-sequence induction with propofol and succinylcholine can be used. The anesthesiologist compares the potential risk of aspiration with the potential risk of delaying surgery.

Rapid Sequence Induction

•Used to decrease the risk of aspiration prior to intubation

•A mask with 100% oxygen is placed over the patient’s mouth and nose

•Replaces the gas in the patient’s lungs with oxygen (denitrogenation)

•The patient is then given an intravenous induction agent (e.g., propofol, etomidate, thiopental, ketamine) along with succinylcholine, providing rapid onset of anesthesia and muscle paralysis

•A rapidly acting non-depolarizing muscle relaxant (such as rocuronium) may be used if succinylcholine is contraindicated

•Cricoid pressure is applied prior to induction

•The cricoid cartilage is a circumferential ring, and applying pressure compresses the esophagus posterior to it

•Cricoid pressure reduces the likelihood of passive regurgitation/aspiration of gastric contents

•Cricoid pressure can also improve visualization of vocal cords, although this is best achieved by applying pressure to the thyroid cartilage

•Once fasciculations from the succinylcholine are seen, the patient is intubated and the airway secured

•Positive pressure mask ventilation is avoided to prevent delivering air into the stomach, which would increase the risk for aspiration

A 29-year-old construction worker who presented after a fall from a ladder with paraplegia and multiple fractures is going to the OR for revision of his external fixation. It is 6 days after his fall. What paralytic should you avoid in this patient?

Succinylcholine. Due to his spinal trauma, there is upregulation of his acetylcholine receptors. Succinylcholine administration would likely result in hyperkalemia.

Succinylcholine

•Rapid onset and offset of action

•Binds, depolarizes, and non-competitively inhibits acetylcholine receptors at the neuromuscular junction (NMJ)

•Metabolized by plasma pseudocholinesterases

•An extended clinical effect is seen in patients with atypical plasma pseudocholinesterases

•Fasciculations usually occur and can cause postoperative myalgias

•Causes an acute transient increase in plasma potassium level

•Increase in plasma potassium level is related to the number of acetylcholine receptors at the NMJ

•Patients with increased receptors at the NMJ are at increased risk for hyperkalemia

•Spinal cord injury

•Burns

•Immobility

•Neuromuscular disorder such as muscular dystrophy

•However, succinylcholine may be given to patients in renal failure with normal potassium levels

Non-Depolarizing Neuromuscular Blockers

•Act by competitively antagonizing the acetylcholine receptor at the NMJ

•Each depolarizing neuromuscular blockers (NMB) has its own unique profile based on

•Onset of action

•Rocuronium has a fast onset

•Duration of action

•Hemodynamic effects

•Pancuronium causes tachycardia by vagolysis

•Metabolism

•Most non-depolarizing NMBs are metabolized by the liver and/or kidney

•Cisatracurium degrades spontaneously in plasma and is useful in patients with liver and kidney failure

Monitoring Effects of Non-Depolarizing Neuromuscular Blockers

•An electric current is placed over a peripheral nerve, and the corresponding muscle is observed

•The standard is to administer four pulses of current at a set frequency (train-of-four)

•The fewer the number of twitches, the greater the neuromuscular blockade

Reversal of Non-Depolarizing Neuromuscular Blockers

•Non-depolarizing NMBs act by competitive inhibition

•By increasing the concentration of acetylcholine in the NMJ, it is possible to clinically reverse the effects of the NMB

•The patient must have at least one visible twitch when testing the train-of-four

•An acetylcholinesterase inhibitor is used

•Acetylcholinesterase inhibitors can increase the amount of acetylcholine at muscarinic receptors as well, resulting in bradycardia

•An anticholinergic agent (i.e., atropine or glycopyrrolate) must be given with the acetylcholinesterase inhibitor (i.e., neostigmine or edrophonium) to prevent this bradycardia

A 28-year-old male presents to the operating room for elective shoulder surgery. The anesthesiologist recommends performing an interscalene block for postoperative pain control. 30 cc of 0.5% ropivacaine is injected around the brachial plexus via the interscalene groove in the patient’s neck. Shortly after injection, the patient comments on a ringing sound in his ears and begins to seize. What should you do next?

The patient’s seizure is due to local anesthetic toxicity. Treatment includes monitoring and maintaining the patient’s airway, oxygenation, ventilation, and circulation. Administer a benzodiazepine, barbiturate, or propofol to stop the seizure.

Mechanism of Local Anesthetics

•Prevent propagation of nerve impulses by blocking sodium channels

•Act by entering neurons in the neutral uncharged form and then block sodium channels from within the cell

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