General Surgery (Board Review Series) 1st Edition
1
Anesthesiology
Robert D. Sullivan
Lisa M. Sullivan
- Initial Assessment and Monitoring
- Preoperative assessment of the surgical patient
- The American Society of Anesthesiologists (ASA) Classification
- is part of the physical evaluation of the patient (Table 1-1).
- The classification system
- is graded as classes 1–6 in order of increasing risk of mortality.
- Blood pressure
- Noninvasive blood pressure monitoring
- An appropriate size cuff
- is most often placed on the arm, avoiding limbs with arterial-venous shunts or intravenous (IV) sites.
- A cuff that is too narrow
- relative to patient size may give a falsely elevated blood pressure.
- Intra-arterial blood pressure monitoring
- Indications for intra-arterial monitoring include
- elective hypotension.
- anticipation of wide blood pressure variation.
- the need for frequent blood sampling.
- The most common sites of measurement
- are the radial and femoral arteries.
- Electrocardiogram (ECG)
- The ECG is used for detection of
- cardiac dysrhythmias.
- myocardial ischemia.
P.4
- electrolyte abnormalities, which are not uncommon under anesthesia.
- Leads V2 and V5
- together can detect 95%of intraoperative ischemia, allowing for early intervention.
Table 1-1. American Society of Anesthesiologists (ASA) Physical Status Classification
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Class 1: Healthy
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Class 2: Mild systemic disease without functional limitation
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Class 3: Moderate to severe systemic disease with functional limitation
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Class 4: Severe systemic disease that is constantly life-threatening and functionally incapacitating
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Class 5: Not expected to survive 24 hours with or without surgery
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Class 6: Organ donor
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E: Added to classification if procedure is an emergency
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- Pulse oximetry
- An oximeter
- is placed on any perfused tissuethat can be transilluminated.
- This provides
- an estimate of the level of oxygen binding by hemoglobinin the blood, providing an early warning of hypoxia.
- Arterial oxygen saturation (SaO2)
- of 70%, 80%, and 90%corresponds to arterial oxygen tensions (PaO2) of 40, 50, and 60, respectively.
- In the presence of severe anemia
- oximeter readings may be normal even when tissue hypoxia is present.
- Temperature
- Monitoring sites include
- esophagus.
- nasal pharynx.
- axilla.
- bladder.
- Maintenance of normothermia
- can improve tissue perfusion and limit coagulopathies.
- Elective hypothermia
- is used to decrease tissue oxygen demand, particularly for some cardiac and neurosurgical procedures.
- Urine output (UOP)
- Monitoring UOP
- via a Foley catheter provides an estimate of end-organ perfusion and fluid status.
P.5
- This is generally used
- for all surgeries over 2 hours.
- to decompress the bladderto avoid injury during laparoscopic procedures and cesarean sections.
- Swan-Ganz catheter
- The tip of this catheter
- lies in the pulmonary arterial system.
- The pressure changes
- observed during initial placement of a Swan-Ganz catheter are demonstrated in Figure 1.1.
- This catheter is used to monitor
- left ventricular filling pressures.
- cardiac output.
- systemic vascular resistance.
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Figure 1.1. Swan-Ganz catheter placement. A pressure tracing during passage of a Swan-Ganz catheter from the right atrium (RA) to the point where the catheter tip is wedged within a branch of the pulmonary artery (PCWP). Passage into the right ventricle (RV) is marked by a sudden increase in systolic pressure, the pulmonary artery (PA) by an increase in diastolic pressure, and PCWP by a decrease in pressure. (Reprinted with permission from Morgan E, Mikhail N: Clinical Anesthesiology, 2nd ed. Stamford, CT, Appleton & Lange, 1996, p 89.)
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- Capnography
- This method
- provides measurement of end-tidal carbon dioxide (CO2) tension.
- confirms adequacy of ventilation and thus endotracheal tube (ETT) placement.
- This measurement is an estimate of PaCO2
- The same device also measuresinspiratory and expiratory anesthetic gas concentrations, confirming anesthetic gas delivery.
P.6
- Unexpected severe hypercapnia can also be a sensitive indicator of malignant hyperthermia.
- Transesophageal echocardiogram (TEE)
- may be used to monitor cardiac function, particularly during cardiac or aortic procedures.
- Induction of Anesthesia
- Methods
- IV or mask induction
- of general anesthesiamay be used.
- Childrenfrequently undergo a mask induction with volatile anesthetic gas before placement of an IV, whereas adults most often undergo an IV induction.
- A variable combination of agentsis based on patient characteristics and the surgical procedure.
- These include an amnestic, analgesic, hypnotic, muscle relaxant, and volatile agent.
- A “rapid sequence” induction
- is performed by sequential IV administration of fast-acting agents with rapid endotracheal intubation.
- Pre-oxygenation with 100% oxygen
- allows de-nitrogenation of the patient's functional residual volume.
- provides extra time for airway management before arterial oxygen desaturation occurs.
- Indications for rapid sequence induction include
- recent oral intake.
- symptomatic gastroesophageal reflux disease (GERD).
- delayed gastric emptying (e.g., gastroparesis) or previous gastrectomy.
- pregnancy.
- bowel obstruction.
- Analgesic agents
- Analgesic agents are generally administered
- in boluses at induction and before surgical incision, then in maintenance doses as needed.
- Additional doses may be administered
- based upon signs of the sympathetic response to pain, such as increasing heart rate and blood pressure.
- Fentanyl
P.7
- has an onset of action in 2 minutes and peak effect in 5 minutes.
- This drug is metabolized
- Airway reflexes are bluntedwith minimal cardiac depression.
- Like other narcotics, this may induce respiratory arrest.
- Morphine sulfate
- is a narcotic.
- has a 5-minute onset of action and 20 minutes to peak effect.
- The active metabolites are cleared by the kidney.
- Therefore morphine should be used cautiously in patients with impaired renal function.
- This may cause histamine release
- and associated mild hypotension.
- Alfentanil, sufentanil, and remifentanil
- are synthetic narcotics.
- have very fast onset and progressively shorter durations of action.
- Ketamine
- is a phencyclidine (PCP) analog.
- This drug provides intense
- analgesia.
- amnesia.
- dissociative anesthesia.
- It also
- generally increases heart rate and blood pressure.
- maintains spontaneous ventilation.
- is an excellent bronchodilator.
- Illusions and dysphoria are common
- but can be limited by premedicating with a benzodiazepine.
- Ketamine
- is not a respiratory depressant.
- may be given as the sole anesthetic agent.
- is one of several agents used for induction of anesthesia (Table 1-2).
- Sedative–hypnotic agents
- Sodium thiopental(see Table 1-2)
- is a barbiturate.
- induces unconsciousness within 30 seconds without providing analgesia.
- reduces cerebral oxygen demand and is an excellent anticonvulsant.
- After a single dose, drug redistribution into muscle may result in rapid awakening.
- Therefore frequent repeated dosing is necessary.
- Side effects include
P.8
- hypotensionthat may be profound in the setting of hypovolemia.
- heart failure.
- beta-blockade.
- Thiopental may also cause
Table 1-2. Anesthetic Induction Agents
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Agent
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Blood Pressure
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Metabolism
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Analgesia
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Onset
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Actions and Effects
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Ketamine
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Stable
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Liver
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Potent
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Fast
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Illusions and dysphoria
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Sodium thiopental
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Decreased
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Liver
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None
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Fast
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Antiseizure
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Propofol
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Decreased
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Liver and plasma esterases
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Mild
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Fast
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Antiseizure, infusions
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Etomidate
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Stable
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Liver and plasma esterases
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None
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Fast
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Adrenocortico depressant
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- Propofol(see Table 1-2)
- is also a fast-acting agent.
- does not produce a “hangover” effect, thus it is ideal for outpatient surgeries.
- possesses antipyretic and antiemetic properties.
- Rapid metabolism
- occurs via the liverand plasma esterases.
- Side effects include
- hypotension.
- blunting of airway reflexes facilitating intubation.
- respiratory arrest.
- This drug may be used
- to maintain anesthesia.
- in the intensive care unit to provide sedation.
- Propofol
- is suspended in a 10% lipid solution providing 1.1 kCal/mL.
- Etomidate(see Table 1-2)
- is a fast-acting hypnotic agent.
- is commonly used for induction when hypotension must be minimized.
- Rapid metabolism
- is via the liver and plasma esterases.
- Continuous infusions
- are avoided because of the risk of adrenocortical suppression.
- Other side effects
- Benzodiazepines
. These drugs provide
P.9
- anxiolysis.
- hypnosis.
- amnesia.
- anticonvulsant effects.
- some skeletal muscle relaxation.
- They do not provide
- The most commonly used benzodiazepine
- is the short-acting agent, midazolam.
- These agents
- are hepatically metabolized.
- may have prolonged activity in geriatric patients and patients with liver failure.
- Morphine agents may cause
- respiratory arrest, especially when combined with a narcotic.
- Flumazenilis a benzodiazepine antagonist used to treat overdoses.
- However, this agent may be associated with seizure development.
- Muscle relaxants (Table 1-3)
Table 1-3. Neuromuscular Blocking Agents
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Agent
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Depolarizing Blockade Fasiculations
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Metabolism
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Increased Serum Potassium
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Activity
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Succinylcholine
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+
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Pseudocholin-esterase
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+
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Fastest onset and shortest duration
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Rocuronium
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–
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Liver
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–
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Fastest onset of nonde-polarizers
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Pancuronium
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–
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Renal
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–
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Longest acting
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Cis-atracurium
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–
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Nonenzymatic breakdown
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–
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Action not prolonged in renal or liver disease
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Mivacurium
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–
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Pseudocholin-esterase
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–
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Brief duration
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- Muscle relaxation is often used
- to facilitate endotracheal intubation.
- during abdominal surgery.
- when movement could be devastating (neurosurgery).
- These drugs do not posses properties of analgesia, hypnosis, or amnesia.
- Patients are paralyzed, but will still feel and remember the surgery.
- Relaxantsare divided into depolarizing and nondepolarizing agents.
- Depolarizingagents cause an initial transient muscle fiber activation before relaxation occurs.
- Succinylcholine
P.10
- provides rapid depolarizingneuromuscular blockade.
- This agent
- mimics acetylcholine.
- has a rapid onset of 30 seconds.
- has a short duration of action (5–10 minutes).
- It is rapidly metabolized
- by plasma pseudocholinesterase.
- Patients with abnormal pseudocholinesterase
- may have prolonged paralysis after administration of succinylcholine.
- About 1 in 3000 patients are homozygous for this trait.
- The onset of this effect is heralded by muscle fasciculations.
- Cellular potassium release from initial muscle fiber activation causes an increase in serum potassiumthat can be dangerous in some patients.
- Patients with the potential for a greatly exaggerated increase in serum potassium are at risk for hyperkalemic cardiac arrest.
- Conditions where this agent is contraindicated include
- denervation injuries(e.g., stroke).
- myopathy.
- major burn injuries.
- severe trauma.
- potentially undiagnosed myopathy (i.e., children).
- bedridden states.
- Malignant hyperthermia
- is a rare complication associated with succinylcholine administration.
- is an autosomal dominant hypermetabolic disorder of skeletal muscle.
- The combination
- of volatile anesthetics and succinylcholine most frequently triggers this disorder.
- Manifestationsmay include
- acidosis.
- trismus/masseter muscle spasm.
- hypercapnia.
- tachycardia.
- rapid temperature elevation.
- hypertension.
- arrhythmias.
- hypoxemia.
- hyperkalemia.
- myoglobinuria.
- Treatmentinvolves
- discontinuing the volatile agent.
P.11
- cooling the patient.
- IV dantrolene.
- The nondepolarizing neuromuscular blocking agentsinclude
- rocuronium.
- pancuronium.
- vecuronium.
- atracurium.
- mivacurium.
- These agents
- competitively inhibit acetylcholineat the neuromuscular junction.
- These agents do not cause
- fasciculations.
- an increase in serum potassium.
- Rocuronium
- has the fastest onset (45–60 seconds).
- is often substituted for rapid sequence induction when succinylcholine is contraindicated.
- Pancuronium
- is inexpensive and used when prolonged paralysis is needed.
- This agent blocks autonomic ganglia, resulting in a mild tachycardia.
- Clearance is dramatically prolonged in renal failure.
- Atracurium
- undergoes esterase elimination.
- does not require the kidney or liver for metabolism.
- Mivacuriummetabolism is dependent on pseudocholinesterase.
- All agents are potentiated by
- hypokalemia.
- hypocalcemia.
- hypermagnesemia.
- The degree of neuromuscular blockade
- can be monitored by peripheral nerve stimulation.
- To reverse neuromuscular blockade
- acetylcholinesterase inhibitors(e.g., neostigmine) given with an anticholinergic (e.g., glycopyrrolate) to counteract bradycardia are often administered at the end of a surgery.
III. Airway
- Mask ventilation
- is used at the time of induction.
- can be the sole means of airway management in a patient with minimal risk of aspiration.
P.12
- The head and jaw
- must be positioned appropriately to open the airway and to avoid collapse of soft tissues.
- Ventilation can also be facilitated
- by either an oral or a nasal airway device (Figure 1.2).
- Oral airway devices
- prevent the tongue from obstructing the oropharynx.
- Insertion of nasal airway devices
- may be tolerated by an awake patient.
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Figure 1.2. Interventions providing airway patency without endotracheal intubation. All of these measures alleviate obstruction often caused by the tongue allowing for ventilation, but these do not protect against aspiration. (A) Mask ventilation with jaw thrust. (B) Oropharyngeal airway device. (C) Nasopharyngeal airway device. (Adapted with permission from Dorsch JA, Dorsch SE: Understanding Anesthesia Equipment: Construction, Care, and Complications. Baltimore, Williams & Wilkins, 1994, p 371.)
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- A laryngeal mask airway (LMA) device
- is designed to lodge in the hypopharynx superior to the larynx.
P.13
- prevents soft tissue obstruction of the airway.
- The LMA can be used
- to ventilate a patient with up to 20 cm H20 pressure (the competency of the upper esophageal sphincter).
- This device is contraindicated
- in patients at risk for aspiration.
- in cases where paralysis, controlled ventilation, or both, are necessary.
- Endotracheal intubation
- involves placement of a tube through the vocal cords into the trachea under direct visualization.
- Placement of an ETT allows for
- ventilatory support.
- oxygenation.
- relative protection of the airway from aspiration.
- Tube position may be confirmed by
- observing bilateral chest rising with ventilation.
- looking for condensation of breaths within the ETT.
- Continuous measurement of end-tidal CO2
- may also confirm appropriate placement of the tube within the trachea.
- If a patient appears difficult to intubate
- the safest option is to allow for spontaneous ventilation and intubate with topical airway anesthetics and minimal sedation.
- Fiberoptic laryngoscopy
- can aid in the intubation of the difficult airway, especially in patients with head and neck injuries.
- Inhalational Anesthetics
- After induction
- anesthesia is maintained with a volatile anesthetic.
- The volatile anesthetics provide
- hypnosis.
- amnesia.
- some degree of analgesia and muscle relaxation.
- The agents differ in
- blood solubility.
- potency.
- side effect profiles.
P.14
- The minimum alveolar concentration (MAC)
- is the smallest concentration of anesthetic at which 50% of patients will not move in response to surgical incision.
- The MAC of the agents
- are generally additive, while the side effects are not.
- Combining different agents to optimize the MAC while minimizing potential side effects is referred to as balanced anesthesia.
- The solubility of the agent
- within the blood correlates with speed of induction.
- Thus insoluble agentsprovide the quickest onset.
- The volatile agents commonly used today include
- halothane.
- isoflurane.
- sevoflurane.
- desflurane(Table 1-4).
Table 1-4. Inhalational Anesthetic Agents
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Agent*
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Blood Pressure
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Muscle Relaxation
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Broncho-dilatation
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Expands Air Cavities
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Misc.
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Halothane
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Decreased cardiac output
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+
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+
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-
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Rarely causes hepatitis
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Isoflurane
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Decreased vascular resistance
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+
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+
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-
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Used in cardiac and CNS
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Sevoflurane
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Decreased vascular resistance
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+
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+
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-
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Used in mask inductions
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Desflurane
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Decreased vascular resistance
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+
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+
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-
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Irritating to airway
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Nitrous oxide (N2O)
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Stable
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-
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-
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+
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Mask analgesia
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CNS = central nervous system.
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*The agents are listed in order of decreasing blood solubility (faster induction and emergence) and also in order of decreasing potency (higher percentage of inhaled gas required for effect).
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- Side effects
- Cardiovascular
- All of these agents cause hypotension
- either through depression of myocardial contractility (e.g., halothane) or via vasodilation.
- These agents, particularly halothane
- tend to be arrhythmogenic, an effect potentiated in many cases by epinephrine.
- Isoflurane is often preferred
- for patients with cardiac disease because it causes the least cardiac depression and the most coronary artery dilation.
P.15
- Respiratory
- Volatile agents cause
- rapid shallow breathing, resulting in a net decrease in minute ventilation.
- bronchodilation.
- All agents severely blunt hypoxic drive
- and to a lesser degree, blunt hypercapnic drive, in subanesthetic concentrations.
- Central nervous system
- These agents
- impair cerebral autoregulation, or the ability of the brain vasculature to control blood flow over a wide range of blood pressures.
- Isoflurane
- used in conjunction with hyperventilation minimizes the impaired autoregulation.
- is used in patients with increased intracranial pressure.
- Halothane
- can rarely cause a chemical hepatitis.
- All volatile agents cause
- significant muscle relaxationindependent of paralytic agents.
- Nitrous oxide (N2O)
- requires high inhalational concentrations (not potent).
- is insoluble in blood.
- Cardiac effects
- N20 causes minimal cardiac depression.
- It generally does not alter blood pressure.
- Respiratory effects
- This agent shares many of the respiratory effects of the volatile agents.
- However, it is not bronchodilatory and causes an increase in pulmonary vascular resistance.
- This agent does not
- provide muscle relaxation.
- Administration of N20 may expand air cavities
- by diffusing in faster than nitrogen diffuses out.
- This agent should be avoided in patients with
- a pneumothorax.
- intracranial air.
- intestinal obstruction.
- middle ear occlusion.
P.16
- Regional Anesthesia
- Overview
- Many surgeries can be successfully performed
- with neuraxial or peripheral application of local anesthetics.
- Regional anesthesia may also be used
- for postoperative pain relief.
- Upper extremity regional blocksinclude
- intrascalene.
- supraclavicular.
- axillary nerve blocks.
- A femoral nerve blockcan be used for lower extremity anesthesia.
- A Bier blockinvolves IV injection of local anesthetic for upper and occasionally lower extremity anesthesia.
- Before IV injection of anesthetic into the designated extremity, the venous system is emptied by compression with elastic wraps and a tourniquet is placed to block arterial inflow.
- Neuraxial blockadeinvolves
- injection of anesthetic into either the epidural or subarachnoid spaces.
- Contraindications shared by the Bier and neuraxial blocksinclude
- local or systemic infection.
- coagulopathy.
- hypotension.
- Complicationsinclude
- headache.
- urinary retention.
- rarely, epidural or intraspinal hematomas or infection.
- Postpuncture dural headaches
- are positional, being much worse when the patient is upright.
- Treatment of these headachesincludes
- bedrest.
- hydration.
- analgesics.
- caffeine.
- epidural blood patching.
- For an epidural blood patch, peripherally drawn blood is injected into the epidural space at the dural puncture site to seal the injured dura.
- Spinal anesthesia (Figure 1.3)
P.17
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Figure 1-3. Lumbar spinal versus epidural anesthesia. (Reprinted with permission from Morgan E, Mikhail N: Clinical Anesthesiology, 2nd ed. Stamford, CT, Appleton & Lange, 1996, p 222.)
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- A small gauge needle (e.g., < 22 gauge)
- designed to minimize dural trauma is usually inserted midline in the L3–L4 interspace.
- Free flow of cerebrospinal fluid (CSF)
- confirms subarachnoid placement where local anesthetic is injected.
- Anesthesia
- onset occurs within minutes.
- can last up to 2 hoursdepending on the agent and dosage.
- The level of sympathetic blockade
- is typically higherthan the level of sensory block.
- This is, in turn, above the level of motor block.
- These differences are caused by variations in nerve size and myelination.
- Sympathetic blockade results in hypotensionthat may be profound.
- Excessively high spinal anesthesiamay cause respiratory depression.
- Motor functiontypically recovers before sensation.
- Small doses of narcotics
- can also be injected intrathecally to provide analgesia or to augment local anesthetic action.
- A “saddle block”
- provides anesthesia to the perineum by using hyperbaric solutions (solutions more dense than CSF) to block the sacral dermatomes.
P.18
- Epidural anesthesia
- A catheter
- may be placedin the epidural space, allowing for continuous infusion of anesthetic agent to relieve perioperative pain or labor pain.
- Dilute concentrations of anesthetic
- allow for sparing of motor function.
- The final level of sensory blockade
- is related to the volume injected, which is in contrast to spinal anesthesia, where it is related to dosage.
- The onset of blockade
- occurs more slowly than with spinal anesthesia.
- A caudal block
- involves placement of anesthetic into the epidural space through the sacral hiatus.
- Local anesthetics
- may be infiltrated in a wound to provide local pain relief.
- The most common agents are
- lidocaine.
- ropivacaine.
- bupivacaine.
- These agents may be associated with
- seizures and severe refractory arrhythmiasif injected intravascularly, particularly bupivacaine.
- Early manifestations may include
- perioral numbness.
- visual and hearing disturbances.
- sedation.
- Epinephrine-induced local vasoconstrictionmay prolong the anesthetic effects of these agents.
- Epinephrine with local anesthetics should be used cautiously in patients with cardiac disease, uncontrolled hypertension, or when infiltrating tissues with minimal collateral blood flow (e.g., digits, ears, nose, penis).
- Pain Management
- Patient controlled analgesia (PCA)
- is often used for postoperative pain relief.
- Narcotics
- are self-administered by the patient through a device that allows a selected doseto be delivered at specific time intervals to a preset maximum.
- The pump can also be set
P.19
- to deliver a basal rate of medication per hour.
- PCA is designed to
- provide better pain control.
- avoid over-medication of the patient.
- Pain management clinics
- specialize in the treatment of chronic pain.
- Components of treatment of chronic pain
- routinely include psychological evaluation and therapy.
- Narcotics are avoided when possible in favor of other agents including
- nonsteroidal anti-inflammatory agents.
- antiseizure medications (e.g., gabapentin).
- antidepressant medications (e.g., amitriptyline).
- Regional anesthetic techniques
- are also frequently used.
P.20
Review Test
Directions: Each of the numbered items or incomplete statements in this section is followed by answers or by completions of the statement. Select the ONE lettered answer or completion that is BEST in each case.
- At emergence from an uncomplicated general anesthetic for a laparoscopic appendectomy, an otherwise healthy 19-year-old male smoker develops a severe cough. Intravenous lidocaine is administered and the endotracheal tube is pulled before the patient is responsive to verbal commands. The patient becomes cyanotic and the SaO2is 75%. The anesthesiologist is unable to administer positive pressure mask ventilation. What is the most appropriate initial step in the management of this patient?
(A) Intravenous naloxone
(B) Deepen anesthetic depth
(C) Re-intubate the patient
(D) Intravenous succinylcholine
(E) Intravenous fentanyl
1–D. The anesthesiologist is probably unable to ventilate the patient because the patient is in laryngospasm. Intravenous (IV) lidocaine is effective at preventing and treating laryngospasm but smokers have particularly reactive airways that predispose to coughing and laryngospasm at emergence. IV or intramuscular succinylcholine can rapidly relieve the spasm. Partial laryngospasm (stridor) often responds to gentle positive pressure ventilation, deepening the anesthetic volatile agent, or both. An initial attempt at intubation would likely be unsuccessful and can worsen the spasm. Neither naloxone nor fentanyl is likely to have much effect. Healthy adults can generate enough negative intrathoracic pressure against a closed glottis that they can suffer postobstructive pulmonary edema.
- A 27-year-old woman with gastroesophageal reflux disease (GERD) undergoes a rapid sequence anesthetic induction for an anterior cruciate ligament repair. She is pre-oxygenated with 100% oxygen (4 deep breaths) and induced with propofol, lidocaine, and fentanyl. Succinylcholine is administered and cricoid pressure applied. The endotracheal tube (ETT) is placed with direct laryngoscopy to 20 cm at the teeth and the SaO2is 100%. What is the most reliable indication of ETT placement in the trachea?
(A) Persistent ETCO2 measurement with ventilation
(B) Bilateral breath sounds with ventilation
(C) Breath condensation in the ETT
(D) Absence of sound over the epigastrium with ventilation
(E) SaO2 of 100% immediately after intubation
2–A. Esophageal intubation is only a disaster if unrecognized. Ideally, the endotracheal tube (ETT) is placed through the vocal cords under direct vision. Bilateral breath sounds and ETT condensation can sometimes occur with esophageal intubation. Persistent ETCO2 tracings with ventilation confirms tube placement in the trachea. Tracheal breath sounds can radiate to the epigastrium. One-sided breath sounds represent mainstem intubation, usually right-sided. With optimal pre-oxygenation a healthy individual can take over 5 minutes to desaturate.
- A 40-year-old woman with Type I diabetes mellitus and end-stage renal disease is scheduled for an arteriovenous fistula repair. She refuses a regional anesthetic technique (axillary block). She undergoes a rapid-sequence induction with cricoid pressure to lessen the chance of gastric content aspiration, and after much difficulty an endotracheal tube is correctly placed and the cuff inflated. Two hours after an uneventful anesthetic the patient remains somnolent and intubated in the postanesthetic care unit with a respiration rate of 10/min. An arterial blood gas reveals hypercapnia (PaCO2of 65) and an acidosis (pH 7.2). What anesthetic agent is most likely responsible for this patient's prolonged anesthesia?
(A) Pancuronium
(B) Morphine
(C) Fentanyl
(D) Isoflurane
(E) Midazolam
3–B. The metabolites of morphine accumulate in renal failure and can produce prolonged narcosis, evidenced by somnolence, a slow respiratory rate, hypercapnia, and a corresponding respiratory acidosis. Pancuronium clearance is also prolonged in renal failure but does not produce somnolence. Fentanyl and midazolam provide analgesia and sedation, respectively, but do not accumulate in renal failure. Isoflurane elimination is dependent on ventilation.
- A surgeon is performing a laparoscopic cholecystectomy on an obese 35-year-old woman under general anesthesia with endotracheal intubation. The anesthetic is maintained with isoflurane, fentanyl, and rocuronium. The surgeon repetitively asks for more “relaxation” to better visualize the field. The patient has no response to peripheral nerve stimulation and is hemodynamically stable. Which of the following may provide additional relaxation in this setting?
(A) Additional fentanyl
(B) Adding nitrous oxide to anesthetic
(C) Increasing isoflurane concentration
(D) Additional rocuronium
(E) Administering intravenous thiopental
4–C. Additional paralytic agents provide no further clinical relaxation effect after abolishing neuromuscular stimulation, but do make reversal of paralysis impossible until a response returns as the paralytic agent is eliminated. The volatile agents (isoflurane), unlike nitrous oxide, barbiturate (thiopental), or narcotics (fentanyl), do provide muscle relaxation independently of neuromuscular blockers (rocuronium), but it is unclear if they would have much additional effect in this scenario.
- During intubation, a 21-year-old paraplegic patient is given succinylcholine. The patient demonstrates fasciculations and the vocal cords are easily visualized with a laryngoscope with subsequent placement of the endotracheal tube. Peaked T waves and intermittent ectopy are then noted on the electrocardiogram. What is the most appropriate first step in this patient's management?
(A) Administration of a beta-agonist
(B) Administration of insulin and glucose
(C) Oral exchange resin
(D) Administration of calcium chloride
(E) Administration of sodium bicarbonate
5–D. Calcium is thought to play a cardioprotective role in the event of hyperkalemia by preventing life-threatening arrhythmias. Additionally, hyperventilation can be started immediately if the patient is intubated because the respiratory alkalosis will lower serum potassium. The other agents listed should also be administered as quickly as possible to decrease serum potassium, however, none of them provide the immediate cardioprotective effect seen with calcium.
- A 40-year-old man with epiglottitis is intubated at an outside hospital and sent to the emergency room for evaluation. The transport team states that the patient became combative during the trip and was given more “sedative” and strapped more securely to the stretcher. During your examination you notice that the patient can blink his eyes to command but is unable to move any extremities nor make respiratory effort. He blinks affirmatively to your query if he is in pain. You administer a narcotic and a benzodiazapine. What is the most likely cause of paralysis?
(A) A C2 cord lesion
(B) Meningitis
(C) Guillain-Barré syndrome
(D) Subarachnoid hemorrhage
(E) Muscle relaxant
6–E. Muscle relaxants are successful in making a restless patient remain still, and thus are mistakenly thought by some to possess sedative or analgesic properties. They do not impair consciousness or memory, and most importantly, they do not provide any analgesia. The history and initial physical findings are inconsistent with a C2 cord lesion or a subarachnoid hemorrhage. Meningitis is unlikely to be associated with such paralysis without significant depression of the level of consciousness. Guillain-Barré syndrome would not present in such an acute fashion.
Questions 7–8
A 24-year-old man is transported to the emergency room after a motor vehicle accident. He is alert and hemodynamically stable, but has an obvious right femur fracture. He is brought to the operating room for an open reduction of the fracture. He undergoes a rapid sequence induction with sodium thiopental, fentanyl, and succinylcholine; the anesthetic is maintained with nitrous oxide and isoflurane. During surgery the ventilation pressures begin to rise while the blood pressure begins to fall. Auscultation reveals decreased breath sounds on the right. A right thoracostomy tube is placed, relieving a tension pneumothorax.
- Which agent most likely contributed to the pneumothorax?
(A) Fentanyl
(B) Sodium thiopental
(C) Nitrous oxide
(D) Isoflurane
(E) Succinylcholine
7–C. Nitrous oxide (N20) diffuses into air cavities faster than nitrogen can diffuse out. Therefore, expansion of such potential spaces will continue until the concentration of N20 in the cavity approaches the inspired N20 concentration. Other volatile anesthetic agents such as isoflurane and the other agents mentioned are not associated with expansion of air cavities.
- The N20 is discontinued, the isoflurane inspired concentration increased, and the newly inserted chest tube is left to water seal while the patient continues to receive positive pressure ventilation. The surgery continues and the femoral artery is found to be lacerated. The patient suffers severe hemorrhage and becomes hypotensive. Isoflurane is discontinued and a small dose of midazolam is given for amnesia. Which of the following is the most appropriate muscle relaxant to administer at this time to avoid excessive hypotension?
(A) Pancuronium
(B) Succinylcholine
(C) Atracurium
(D) Rocuronium
(E) Mivacurium
8–A. Pancuronium provides a mild vasoconstrictive effect that is useful when the patient is initially hypotensive and thus prone to worsening hypotension with many other anesthetics. In addition, pancuronium also provides long-lasting muscle relaxation that is important for preventing sudden movement in response to surgical stimulation during long delicate operations. The other agents listed may augment the hypotension.
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