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118 Cards in this Set

  • Front
  • Back

Pathways of Oxygen in Anesthesia Machine (5)

• Flow to the fresh gas flowmeters
• Powers the oxygen flush valve
• Activates the fail-safe mechanisms
• Activates the oxygen low-pressure alarm
• Compresses the bellows of the ventilator

Components of the High Pressure System (3)

• Cylinder/tanks and the pressure within them 45-50psi (2200 psi or 650L)
• PISS from cylinders to machine
• Regulator - reduces pressure suitable for use in the machine (first stage)

Components of the Intermediate Pressure System (6)

• Pneumatic part of the master switch
• Pipeline sources→ oxygen, nitrous and air (DISS) 50-55psi
• Pressure regulators (second stage)
• Oxygen pressure failure device→ O2 pressure falls, will turn off N2O
• Oxygen flush valve
• Flowmeter control valves

Components of the Low Pressure System (6)

• Flow meter tubes
• Hypoxia prevention safety device (proportioning link)
• Unidirectional valves (Outlet Check Valve)
• Common gas outlet
• Pressure relief devices
• Vaporizers/Vaporizer Manifold



Pressure is slightly above atmospheric pressure (760mmHg)

Advantages of Piston Ventilators (4)

• No PEEP (2-3 cm H2O are mandatory on standing bellows ventilators due to the design of the ventilator spill valve)
• Greater precision in delivered tidal volume due to compliance and leak compensation, fresh gas decoupling and the rigid piston design
• Measuring compliance and leaks with a transducer near the piston eliminates a bulky, costly sensor close to the patient’s airway
• Electricity is the driving force for the piston→ if hospital O2 supply dies, only use cylinder O2 for FiO2 and not to be driving gas for bellows

Disadvantages of Piston Ventilators (3)

• Loss of familiar visible behavior of a standing bellows during disconnects, or when patient is breathing over and above the ventilator settings
• Quiet→ less easy to hear regular cycling
• Can entrain air and continue to deliver tidal volumes with less oxygen concentration

ICU vents VS Anesthesia vents

• ICU ventilators are more powerful allowing for greater inspiratory pressure and tidal volumes
• CO2 absorber is absent in ICU vents
• ICU vents support more modes of ventilation
• Gas supplied by ICU vent directly ventilates the patient
• Anesthesia driving gas never reaches the patient
• Bellows are essential in anesthesia vents (except for piston types)

Volume Control Ventilation:

What we set: TV, RR, I:E


How breath is delivered: set TV over insp. time


Initiated by: time (RR), independent of pt effort


Limited by: volume


Flow rate: fixed throughout inspiration


Indications: most common in OR

Pressure Control Ventilation:

What we set: inspiratory pressure, RR


How breath is delivered: until set airway pressure is reached


Initiated by: time (RR), independent of pt effort


Limited by: pressure


Flow rate: decreases as airway pressure rises; ceases when set pressure is reached


Indication: anytime pressure should be low - neonates, preemies

Intermittent Mandatory Ventilation (IMV):

What we set: RR, TV


How breath is delivered: either set TV (main gas flow) or patient's resp. effort (demand gas flow)


Initiated by: time (RR) (patient can demand breaths but vent does not assist)


Limited by: volume


Flow rate: two sources of flow; one for delivered breaths, one for demand breaths


Indication: weaning

Synchonized Intermittent Mandatory Ventilation (SIMV):

What we set: TV?


How breath is delivered: assisting patient's respiratory effort


Initiated by: patient effort


Limited by: volume?


Flow rate: same as volume control


Indication: waking up patient in OR

AC-Intermittent Mode Ventilation:

What we set: RR, TV


How breath is delivered: as TV or pressure


Initiated by: patient effort, with RR as backup


Limited by: volume


Flow rate: depends on TV or pressure mode


Indication: ?

Pressure Support Ventilation:

What we set: inspiratory airway pressure


How breath is delivered: support to maintain constant set pressure during inspiration


Initiated by: patient effort


Limited by: end of patient effort?


Flow rate: dependent


Indication: patient needs decreased WOB/muscle rest

High Frequency Ventilation:

What we set: RR, TV


How breath is delivered: low tidal volumes with high rate at low pressure


Initiated by: time (RR)


Limited by: volume


Indication: when gas exchange is needed at low airway pressures; shock lithotripsy, ENT surgery

Essential Requirements of Breathing System:

• Deliver the gases from the machine or device to the alveoli in the same concentration as set and in the shortest possible time
• Effectively eliminate carbon dioxide
• Have minimal apparatus dead space
• Have low resistance

Desirable (but not essential) Requirements of Breathing System:

• Economy of fresh gas
• Conservation of heat
• Adequate humidification of inspired gas
• Light weight
• Convenience during use
• Efficiency during spontaneous as well as controlled ventilation
• Adaptability for adults, children and mechanical ventilators
• Provision to reduce environmental pollution

Characteristics of an Open Breathing System:

• No gas reservoir bag
• No valves
• No rebreathing of exhaled gas
• Examples= insufflation/blow by and open drop

Advantages and Disadvantages of Insufflation:

Advantages→ simplicity, avoids direct patient contact, no rebreathing of CO2, no reservoir bag or valves
Disadvantages→ no ability to assist or control ventilation, may have CO2/O2 accumulation under drapes, no control of anesthetic depth/FiO2, environmental pollution

Advantages and Disadvantages of Open Drop System:

Advantages→ simplicity, low cost apparatus, portable
Disadvantages→ poor control of inspired concentration of anesthetics, accumulation of CO2 under mask, predisposes to hypoxia risk, spontaneous ventilation ONLY, OR pollution and health care provider risk

Characteristics of Semi-Open Breathing System

• Facemask
• Pop-off valve/APL valve
• Reservoir tubing
• Fresh gas inlet
• Reservoir bag
• Examples= Mapleson A-F, Bain, and Circle

Advantages and Disadvantages of Mapleson System:

Advantages→ simple components, lightweight, can provide positive pressure ventilation, low resistance, portable, more predictable anesthetic concentration
Disadvantages→ requires calculation of FGF which varies with type of circuit and mode of ventilation, control of anesthestic depth is variable, if FGF not maintained possibility of rebreathing CO2, minimal rebreathing of other gases, FGF costly, requires special assembly

Characteristics of Circle System:

• Fresh gas flow source
• Inspiratory and expiratory unidirectional valves
• Inspiratory and expiratory limbs/corrugted tubing
• Y-piece connector
• Adjustable pressure-limiting valve (APL)
• Reservoir bag
• CO2 absorber

Circle system arrangement MUST follow 3 rules:

1.) Unidirectional valves must be located between the patient and reservoir bag on both inspiratory and expiratory limbs
2.) Fresh gas flow cannot enter the system between the expiratory valve and the patient
3.) The APL valve cannot be located between the patient and the inspiratory valve

Three Types of Circle Systems:



(Plus basic characteristics)

1.) Semi-Open→ not used often, no rebreathing, requires very high fresh gas flows, APL is open all the way, no conservation of waste gases and heat
2.) Semi-closed→ most common, relatively low flow rates (1-3L/min), conserve some gas and heat, some rebreathing occurs, APL partially closed, CO2 absorber used
3.) Closed→ used in 3rd world countries, inflow gas matches exactly to metabolic needs (200ml/min), total rebreathing of all gases, total conservation of gases, APL valve close

Advantages of the Circle System:

• Relative stability of inspired gases
• Conservation of moisture and heat
• Prevention of OR pollution
• Can be used for closed system anesthesia
• Can be used with fairly low flows with no rebreathing of CO2
• Economy of anesthetics and gases
• Can scavenge waste gases

Disadvantages of Circle System:

• Complex design→ 7 components
• Has at least 10 connections→ sets the stage for potential leaks, obstruction or disconnection
• A third of malpractice claims resulted from unrecognized disconnects or misconnects of the circuit
• Potential of malfunctioning valves
• Increased resistance to breathing
• Less portable and convenient than the Mapleson systems due to its bulkiness

Circle System Leak and Flow Test:

• Set all gas flows to zero and occlude the Y piece
• Close the APL valve and pressurize the circuit to 30cm H2O pressure by using O2 flush valve
• Ensure pressure holds in reservoir bag for atleast 10 seconds and listen for sustained pressure alarm
• Open APL valve and ensure pressure decreases
• To check flow attach breathing bag to Y piece and turn on ventilator and assess integrity of unidirectional valves

5 Basic Components of Scavenging System:

• Gas collecting assembly
• Transfer means
• Scavenging interface
• Gas disposal tubing
• Gas disposal assembly

Open Scavenging Interface:

• No valves→ open to the atmosphere via holes in reservoir
• Require use of a central vacuum system and reservoir
• Gas enters system at top of canister and travels through narrow inner tube
• Vacuum control valve can be adjusted→ adjust to prevent OR pollution

Closed Scavenging Interface:

• Positive pressure relief only→ single positive pressure relief valve opens when a max pressure is reaches; passive disposal with no vacuum or reservoir bag
• Positive and negative pressure relief→ uses reservoir bag
• Used with an active disposal system→ vacuum control valve
• Gas is vented to atmosphere if system pressure exceeds +5cm H2O
• Room air is entrained if system pressure is less than – 0.5 cm H2O
• A backup negative pressure relief valve is open at -1.8cm H2O if the primary negative pressure valve becomes occluded

Passive Gas-Disposal Assembly:



(Characteristics, advantages, disadvantages)

• Waste gas is directed out of building via an open window, pipe passing through an outside wall or an extractor fan vented to outside air
• Advantages→ inexpensive to set up, simple to operate
• Disadvantages→ may be impractical in some buildings

Active Gas-Disposal Assembly:



(Characteristics, advantages, disadvantages)

• Most commonly used in hospitals


• Connect the exhaust of the breathing system to the hospital vacuum system via an interface controlled by a needle valve
• Advantages→ convenient in large hospitals where many machines in use in different locations
• Disadvantages→ vacuum system and pipework is a major expense, needle valve may need continual adjustment


Causes of Rising CO2 when Ventilation Unchanged:

• Malignant hyperthermia
• Release of tourniquet
• Release of aortic/major vessel clamp
• IV bicard administration
• Insufflation of CO2 into peritoneal cavity
• Equipment defects→ expiratory valve stuck, CO2 absorber exhausted

Causes of Decrease in EtCO2:

• Hyperventilation→ gradual decrease reflects increased minute ventilation
• PE, V/Q mismatch → rapid decrease
• Cardiac arrest
• Sampling error→ disconnects, high sampling rate with elevated gas flow

Soda Lime Characteristics:

• 80% calcium hydroxide and 4% sodium hydroxide
• Silica added for hardness to prevent dust
• Capable of absorbing 26L CO2/100g of absorbent granules
• Water is essential and present as thin film on granule surface
• Can regenerate with rest
• CO2 + H2O→ H2CO3
• H2CO3 + 2NaOH→ Na2CO3 + 2 H2O + HEAT
• Na2CO3 + Ca(OH)2→ CaCO3 + 2 NaOH (slower reaction)

Calcium Hydroxide Lime Characteristics:

• 80% calcium hydroxide and 4% calcium chloride
• Capable of absorbing 10L CO2/100g of absorbent granules
• CO2 + H20→ H2CO3
• H2CO3 + Ca(OH)2→ CaCO3 + 2H2O + HEAT

E Cylinder Capacity and Pressure:

• E size oxygen cylinders are considered full at 200-2200 psi with approximately 625-700L
• The pressure falls in proportion to the amount left in the tank
• Air cylinders are considered full at 1900-2000 psi with approximately 625L
• Like O2, the pressure falls in proportion to the amount left in the tank
• A full cylinder of N2O would read a pressure of 745 psi and have approximately 1590L and is stored as a liquid
• The pressure of N2O does not indicate the amount left in the tank→ does not drop its pressure until it is almost empty and weight is the only way to tell how full it is

DISS→ medical gas pipelines

• Diameter Index Safety System
• Provides non-interchangable connections for the medical gas lines
• Connection consists of a body, nipple, and nut combination
• Only properly mated parts will fit together and allow the threads to engage
• Required for every anesthesia machine

Safe Handling of Cylinders:

• Never stand a cylinder upright without support
• Never leave empty cylinders on the machine
• Never leave the plastic tape on the port while installing the cylinder
• Never rely only on the cylinders color for identification of its contents
• Never oil valves
• Before any fitting is applied to the cylinder valves, particles of dust, metal shavings, and other foreign matter should be cleared from the outlet by slowly and briefly “cracking” the valve away from yourself
• The valve should always be fully open when a cylinder is in use→ marginal opening may result in failure to deliver adequate ga

Vaporization:

• It is the conversion of liquid to a gas and is the basis for inhaled anesthestics
• It is dependent on vapor pressure, temperature, and amount of carrier gas used
• Vapor pressure is created by the gas molecules bombarding the surface of the liquid and the walls of the container


• Sevoflurane= 160mmHg


• Enflurane= 172mmHg
• Isoflurane= 240mmHg
• Halothane= 244mmHg
• Desflurane= 669mmHg

Latent Heat of Vaporization

number of calories required to change 1 gram of liquid into vapor without a temperature change; energy comes from liquid itself

Specific Heat

the number of calories required to increase the temperature of 1 gram of substance 1 degree centigrade; substance can be in any state (liquid, gas, solid)

Thermal Conductivity

a measure of speed with which heat flows through a substance; the higher the conductivity the better the substance conducts heat

Altitude and Anesthesia

Increase altitude = decreased barometric pressure = increased concentration



Decrease altitude = increased barometric pressure = decreased concentration

Vaporizers

• All modern vaporizers are agent specific, temperature compensated and variable bypass
• Variable bypass→ a portion of gas flow will pass into the vaporizing chamber where it will become saturated with vapor and this vapor-laden air will then rejoin the gas flow for dilution to deliverable concentrations
• Desflurane needs a TEC 6 vaporizer that creates a false atmosphere of about 1500 atm by electronic heating so that the Desflurane remains liquid → need to deliver higher dialed concentration at higher altitude and lower concentrations at lower altitude

Potential Vaporizer Hazards

• Wrong agent in the vaporizer= high VP agent into low VP agent= higher concentration
• Contamination
• Tipping
• Overfilling
• Simultaneous administration of more than 1 vapor
• Leaks
• Pumping effect

Boyle’s Law

• The volume of an ideal gas is inversely proportional to the pressure= increased pressure causes a decease in volume
• Examples→ reservoir bag, a full E cylinder emptied into atmosphere, spontaneous breathing, bellows on ventilator

Charles’ Law

• The volume of a given gas is directly proportional to the Kelvin temperature provided the amount of gas and the pressure remains constant= increase in temperature causes an increase in volume
• Examples→ balloon burst on hot days

Gay Lussac’s Law

• At a constant volume, the pressure of a gas sample is directly proportional to the Kelvin temperature= increase in temperature causes an increase in pressure
• Examples→ full cylinder moved from indoors to the hot outdoors

Ideal Gas Law

• PV=nRT
• A cylinder of a compressed gas has a constant volume and the number of moles (n) of gas decreases as gas exits the cylinder, so the pressure decreases

Dalton’s Law

• The total pressure of a gas mixture was the sum of the partial pressure of each gas
• This can be used to calculate the partial pressure of gases in the gas mixture coming out at the common gas outlet→ O2 + N2O+ Anesthetic

Fick’s Law

• Rate of diffusion of a substance across a membrane is related to 5 things
• Directly→ concentration gradient, surface area of the membrane, and solubility
• Inversely→ thickness of membrane and molecular weight
• Examples→ 2nd gas effect, concentration effect, diffusion hypoxia, expansion of ETT cuff, placental transfer of drugs and oxygen

Graham’s Law

• A gas diffuses at a rate that is inversely proportional to the square root of its molecular weight = increase in molecular weight causes a decrease in the rate of diffusion

Henry’s Law

• The amount of gas dissolved in a liquid is directly proportional to the partial pressure of the gas in contact with the solution
• Examples→ allows calculation of O2 and CO2 dissolved in blood; can estimate PaO2 by multiplying FiO2 by 5

Critical Temperature

• The temperature above which a substance goes into gaseous form in spite of how much pressure is applied
• A gas cannot be liquefied if the ambient temperature is greater than the critical temperature→ example is O2
• A gas can be liquefied if sufficient pressure is applied at ambient temperature below the critical temperature→ N2O

Adiabatic Cooling

• A change in temperature of the matter without gain or loss of heat when matter changes phase
• Example→ N2O cylinder opened fully and frost can form on the outlet due to cooling

Joule-Thompson Effect

• Expansion of a gas causes cooling
• Example→ as gas leaves cylinder the expansion cools the surrounding air causing condensation of moisture on the cylinder

Poiseuille’s Law

• Describes the relationship between rate of flow and 4 factors
• Directly→ pressure gradient and radius to the 4th power of the tube
• Inversely→ length of tube and viscosity of the fluid
• Examples→ IV flow, airways, vascular flow, Thorpe tubes

Laminar vs Turbulent Flow

• Reynold’s number greater than 2000 is indicative of turbulent flow (velocity x density x diameter/ viscosity)→ low flows are governed by viscosity
• Higher flows are governed by density
• Factors that change flow from laminar to turbulent→ increased velocity, bend > 20 degrees, and irregularity in the tube

Bernoulli’s Theorem

• The lateral wall pressure is least at the point of greatest constriction and the speed is the greatest
• Can be applied to the venturi tube and the measure of fluid flow
• Examples→ nebulizers, venturi oxygen masks, jet ventilation

Beer’s Law

• Absorption of radiation by a given thickness of a solution of a given concentration is the same as that of twice the thickness of a solution of half the concentration
• Each layer of equal thickness absorbs an equal fraction of the radiation that passes through it
• Examples→ Pulse Ox

Law of La Place

• Pressure gradient across the wall of a sphere or tube/cylinder is related directly to wall tension and inversely with radius
• Examples→ alveoli needing surfactant, aneurysm rupture, ventricular work of the heart

Ohm’s Law

• The resistance which will allow one ampere of current to flow under the influence of a potential of one volt
• Examples→ strain gauges in pressure transducers and thermistors
• Macroshock→ current distributed through the body; caused by faulty wiring, improper grounding, ranges from 1 millivolt to 6000 millivolt
• Microshock→ current applied in or near the heart; caused by pacing wires, fault equipment during cardiac cath; ranged from 50-100 microamps

Structures of the Upper Airway:

• Nasal passages→ septum, turbinates, adenoids
• Oral cavity→ teeth, tongue, hard palate, soft palate
• Pharynx→ nose to cricoid cartilage; nasopharynx and oropharynx
• Larynx→ thyroid, cricoid, arytenoids, epiglottis

Paired and Unpaired Cartilages: (3&3)

• Paired→ arytenoid, corniculate, cuneiform
• Unpaired→ thyroid, cricoid, epiglottis

Intrinsic Muscles of Larynx: (6)

Innervated by reccurent laryngeal, except cricothryoid



• Lateral cricoarytenoid→ adducts
• Arytenoids→ adducts
• Posterior cricoarytenoid→ aBducts
• Cricothryoid→ elongates vocal cords
• Vocalis→ shortens vocal cords
• Thyroarytenoid→ shortens and relaxes vocal cords

Extrinsic Muscles of Larynx: (4)

Move larynx as a whole



• Sternohyoid
• Thyrohyoid
• Omohyoid
• Sternothyroid


Sensory Innervation of Larynx: (3)

• Glossopharyngeal→ posterior 1/3rd of tongue and oropharynx to vallecula
• Interior superior laryngeal→ sensory to vocal cords and above
• Recurrent laryngeal→ supplies mucosa below vocal cords

Motor Innervation of Larynx: (2)

• External superior laryngeal→ supplies cricothryoid muscle
• Recurrent laryngeal→ supplies all intrinsic muscles

Airway Evaluation:

• Evaluation of the airway
• Evaluation of the surrounding tissue
• Patient physical characteristics
• Goal is to identify potential airway problems and identify a difficult airway→ includes Mallampati and Thyromental distance

Mallampati Classes:

• Class I→ faucil pillars, soft palate, uvula
• Class II→ uvula masked by tongue
• Class III→ soft palate, uvula base
• Class IV→ only hard palate seen

Components of Airway Setup: (7)

• Laryngoscope/blades 2 types (MAC and MILLER)
• Oral/nasal airways several sizes
• Tongue depressor
• ETT tubes 2 sizes (6.5/7.0 females, 7.5/8.0 males)
• Ambu-bag
• Stylet
• LMA

Complications of Tracheal Intubation: (7)

• Trauma to airway structures
• Esophageal intubation
• Endobronchial intubation
• Endotracheal tube ignition
• Sore throat
• Laryngospasm
• Croup

General Indications for Airway Blocks:

• To abolish or blunt reflexes
• To provide patient comfort and airway anesthesia during the performance of these procedures
• Complications→ systemic toxicity and hematoma formation
• Inclusion criteria→ head or neck deformities; angioedema; history of difficult intubation

Transtracheal Block:



(Indications, drugs, landmarks, procedure)

• Indications→ block recurrent laryngeal never for intubation; abolition of gag reflex or hemodynamic responses= results in anesthesia of trachea below vocal cords
• Drugs= 3-4ml of 2-4% Lidocaine
• Instruct patient to take deep breath
• Inject Lidocaine on inspiration
• Patient will cough and spread Lidocaine to above the vocal cords

Superior Laryngeal Block:



(Indications, drugs, landmarks, procedure)

• Indications→ blocks the internal branch of SLN to block the supraglottic region; results in abolition of gag reflex or hemodynamic responses
• Drugs= 2-4ml of 1-2% Lidocaine
• Hyoid bone is palpated and displaces towards side to be injected
• Inferior border of the cornu palpated
• 1-2cc of LA injected above and below the thyrohyoid membrane aspirating→ if air too deep
• Repeat on opposite side

Glossopharyngeal Nerve Block:



(Indications, drugs, landmarks, procedure)

• Indications→ lingual branch of glossopharyngeal nerve blocked; abolition of gag reflex or hemodynamic response; when topical application is not effective
• Drugs= 2-4% Lidocaine solution, cetacaine spray, lidocaine spray or lidocaine gel 2-5%
• Use tongue blade to move patients tongue to the opposite side of mouth to form a gutter
• Insert a 25g spinal needle at the base of the palatoglossal arch 0.5cm deep and 0.5cm lateral to tongue base
• Aspirate before injecting 1-2cc of 2% lidocaine

Regional Anesthesia Advantages:

• If used as the primary anesthetic can avoid a general anesthetic
• Cardiac disease
• Pulmonary disease
• Avoid use of opiates
• Induced sympathectomy→ intraoperative reduction in blood loss, postoperative improvement in perfusion
• Reduced nausea/vomiting
• Preemptive analgesia→ reduces postoperative pain and analgesic requirements

Regional Anesthesia Contraindications:

• Patient refusal→ BIGGEST CONTRAINDICATION
• Patient cooperation
• Coagulopathy
• Neuro complications
• Infection near the site of injection
• Septicemia

Regional Anesthesia Preparation:

• Monitors
• Suction
• Ambu-bag, mask, oxygen
• Intubation equipment
• IV access
• Emergency medications

Brachial Plexus Structure:

• Roots→ C5-T1
• Trunks→ superior, middle and inferior
• Divisons→ 3 anterior, 3 posterior
• Cords→ lateral, posterior and inferior
• Branches→ musculocutaneous (C5,6,7), axillary (C5,6), radial (C6,7,8, T1), median (C7,8,T1), ulnar (C8,T1)

Terminal Branches of Brachial Plexus:

• Musculocutaneous Nerve→ exits sheath high and pierces coracobrachialis muscle; motor to biceps, brachilias and coracobrachialis to flex forearm; sensory to lateral mid-forearm up to wrist
• Axillary Nerve→ leaves plexus lower border of pectoralis muscle; motor to deltoid and teres minor; sensory of inferior shoulder and upper lateral arm
• Radial Nerve→ motor to triceps, supinator and extensors of forearm; sensory to posterior arm and forearm, lateral border of elbow, thumb and dorsal surface of hand
• Median Nerve→ motor to flexors and pronator muscles of forearm and flexion of wrist; sensory to palmar surface of hand, index and middle fingers
• Ulnar Nerve→ motor to flexor carpi ulnaris to abduct fingers; sensory to little fingers and medial ring finger

Interscalene Block:

• Ideal for surgery of the shoulder or upper arm→ provides anesthesia to upper branches of the brachial plexus and lower cervical plexus (ulnar nerve sparing)
• Patient supine with head turned toward opposite side
• Palpate posterior border of SCM muscle at the level of C6
• Roll fingers posterior palpate groove b/w anterior and middle scalene muscles
• Complications→ intravascular injection, subarachnoid/epidural injection, pneumothorax, recurrent laryngeal nerve block, Horner’s syndrome, phrenic nerve block
• Contraindications→ contralateral recurrent laryngeal never palsy, phrenic nerve palsy; relative= preexisting nerve injury, brachial plexus pathology, significant impaired pulmonary function

Superficial Cervical Plexus Blocks:

• Indications→ unilateral surgical procedures of neck,; may be combined with deep cervical plexus block; anesthesia for posterior shoulder
• Posterior border of SCM identified
• Needle inserted at the midpoint of the posterior border of SCM

Supraclavicular Block:

• Indications→ effective block for all portions of upper extremity (hand, forearm, and upper arm); carried out at “divisions” level; increased success of inferior trunk (radial and ulnar nerves)
• Lateral border of the clavicular head of SCM at the level of its insertion and the groove between the scalene muscles is identified
• Needle inserted 0.5-1cm cephalad to the midpoint of the clavicle
• Contraindications→ contralateral phrenic paralysis, recurrent nerve paralysis, contralateral pneumothorax
• Complications→ increased risk of pneumothorax, Horner’s syndrome, phrenic nerve block, recurrent laryngeal nerve paralysis, neuropathy

Infraclavicular Block:

• Indications→ for surgery on elbow, forearm, and hand
• Landmarks are the medial clavicular head and coracoid process
• Block is performed by inserting the needle at a 45 degree angle to the skin at the midpoint between the coracoid process and the medial clavicular head and needle advances in a parallel fashion
• Look for pectoralis twitch but ideally want medial, radial or ulnar twitch
• Good technique for continuous catheters

Axillary Block:

• Indications→ procedures below the elbow, safest approach to plexus, patient must be able to abduct arm and place at 90 degrees
• Contraindications→ lymphangitis, relative= preexisting nerve injury, brachial plexus pathology
• Nerve stimulator techniques→ insulated needle immediately superior or inferior to arterial artery, elicit twitch of hand, aspirate for heme and then inject 40 ccs LA
• Transarterial technique→ palpate axillary artery and aspirate blood and advance until no further blood is obtained, entire volume of LA injected behind artery
• Paresthesia technique→ elicit paresthesia in the terminal nerves, may take undue time and increase pt discomfort
• Evaluation→ push (radial), pull (musculocutaneous), close (median), and open (ulnar)
• Complications→ hematoma, intravascular injection, infection

Touch Up Nerve Blocks:

• Radial nerve→ needle inserted 1-2 cm lateral to biceps tendon and fanlike injection of 4-6mls of LA
• Median nerve→ needle introduced 1cm medial to brachial artery and inject 3-5mls LA
• Ulnar nerve→ needle introduced 1cm proximal to ulnar groove (b/w olecranon process and medial epicondyle) and inject 3-5mls of LA
• Musculocutaneous nerve→ inject deep in the body of the coracobrachialis muscle

Bier Block:

• A distal vein is cannulated and arm is exsanguinated while a proximal tourniquet is inflated
• 50mls of 0.5% lidocaine injected into the IV
• Onset of block within 5 minutes and ideal for forearm and hand cases that are 60-120 minutes
• Disadvantages→ local anesthesia toxicity

Local Anesthetic Toxicity:

• S/S→ tongue numbness, lightheadedness, dizziness, tinnitus, disorientation, visual disturbances, and seizure leading to CNS depression, respiratory depression and respiratory arrest
• Cardiac toxicity→ initial increase in BP and HR, may result in hypotension, arrhythmias, and cardiac arrest
• Treatment→
1. Stop administration of LA
2. Maintain airway, provide oxygen
3. Treat seizure with IV midazolam, propofol, or thiopental
4. Treat hypotension with ephendrine, epinephrine, and/or fluids
5. Consider lipids
6. May require CPR or CPB
• Prevention→ vigilant monitoring, limit dose accordingly, aspirate before each injection, inject small volumes, pharmacologic marker, preparation

Indications for Lumbar Plexus Approach:

• Surgery of lower extremity, knee, hip, femur
• Inguinal hernia repair (ilioinguinal, iliohypogastric nerves)
• Vasectomy (genitofemoral nerve)
• Sympathetic block required
• Postoperative pain management
• Prophylaxis against the development of RSD/CRPS

Femoral Nerve Block:

• Supplies the muscles of the anterior thigh, knee and hip joints→ produces anesthesia to the anterior portion of thigh, knee and small part of medial foot
• Results in inability to abduct leg or extend leg and works well with postop pain relief
• Lateral to the femoral artery and inferior to the inguinal ligament
• Complications→ intravascular injection, hematoma, direct nerve injury

Lateral Femoral Cutaneous Nerve Block:

• Purely sensory to lateral aspect of thigh and provides anesthesia to lateral aspect of thigh, lateral buttock, and distal to greater trochanter
• Inject 2cm medial and 2cm caudad to the anterior superior iliac spine

Sciatic Nerve Block:

• Provides anesthesia to foot and lower extremity distal to knee and posterior leg→ used in conjuction with psoas block or Winnie block
• Line drawn from greater trochanter to posterior superior iliac spine
• 2nd line drawn from greater trochanter to sacral hiatus
• Point where latter line intersects the perpendicular line marks the point of needle entry→ inject 20-30cc LA
• Complications→ block failure, hematoma

Ankle Block:

• Indicated for below the ankle procedures, essentially a field block, 5-7cc LA per nerve, do not use epinephrine***
• Posterior tibial nerve→ posterior tip of medial malleolus and is located posterior to tibial artery
• Deep peroneal nerve→ later to dorsalis pedis pulse b/w the extensor halluces longus and extensor digitorum longus
• Saphenous nerve→ 2cm lateral to deep peroneal nerve in subcutaneous tissue
• Superficial peroneal nerve→ blocked with a “ring” of subcutaneous LA to lateral aspect of ankle
• Sural nerve→ 1cm distal to tip of lateral malleolus in subcutaneous tissue

Advantages of Neuroaxial Anesthesia:

• Decreased metabolic stress response to surgery and anesthesia compared with general anesthesia
• Avoids airway instrumentation
• Decreased incidence of post-op nausea
• Less intraoperative sedation
• Post-op pain relief
• Allows patient to remain awake during c-section

Disadvantages of Neuroaxial Anesthesia:

• Hypotension
• Slower case start if challenging placement
• Failure rate depends on experience
• Urban legends

Spinal Meninges:

• Dura mater→ thickest meningeal tissue, begins at foramen magnum and ends caudally at S2, abuts the arachnoid mater (subdural space)
• Arachnoid mater→ principal physiological barrier for drugs moving b/w epidural space and spinal cord, abuts pia mater giving rise to subarachnoid space
• Subarachnoid space→ contains CSF, continuous with cranial CSF and provides vehicle for drugs in spinal CSF to reach brain, houses spinal nerve roots and rootlets
• Pia mater→ adheres to the spinal cord

Tissues Layers Transversed Epidural/SAB:

• Skin
• Subcutaneous tissue
• Supraspinous ligament
• Intraspinous ligament
• Ligamentum flavum
• Epidural space*
• Dura mater (subdural space)
• Arachnoid mater
• Subarachnoid space**
• Pia mater
• Spinal cord

Procedure for SAB:

• Anatomic landmarks for the blocks are identified→ L2-3, L3-4, L4-5
• Superior iliac crests palpated and L4 identified, palpate transverse process of upper vertebrae to ensure midline
• The dose is slowly injected, aspirating after instillation
• All needles are removed intact and the patient is positioned

Contraindications for SAB:

• Patient refusal
• Infection at injection site
• Increased ICP
• Clotting defects/anticoagulant therapy
• Severe hemorrhage or hypovolemia
• CNS disease or meningitis
• Hysteria/inability to remain still for block placement
• Bacteremia
• Septicemia

Physiological Changes and Effects of Neuroaxial Blocks:

• Cardiovascular→ venous dilation, decreased SVR, CO decreased, HR decreased if T1-4, MAP decrease
• Pulmonary→ low level blocks have minimal effects, with profound hypotension may see ischemia of central respiratory centers causes respiratory arrest
• GI/ Renal→ N/V, hyperperistalsis, hepatic BF dependent on BP, renal BF autoregulated, urinary retention
• Metabolic/endocrine→ blocks stress response, catecholamine release may be blocked, cortisol secretion is delayed, shivering

Factors Affecting Spread of LA in SAB:

• Baracity of the local anesthetic solution
• Position of the patient
• Concentration and volume injected
• Level of injection
• Barbotage /rate of injection
• Direction of needle and bevel

Limitations/Advantages of SAB:

• Single shot= duration is limited
• Anesthesia→ lower extremities, GU, GYN, lower abdominal procedures
• Analgesia

Preprocedure SAB/epidural:

• Appropriate monitors
• Fluid bolus (500-1000ml)
• Equipment for airway management and resuscitation are available
• Emergency drugs drawn and available
• Consider sedation prior to procedure

Lumbar Epidural Placement:

• Need needle placement into ligamentum flavum
• Perpendicular angle of insertion
• Ligamentum flavum depth from the skin is 4cm (80% of patient between 3.5-6cm)
• 5-6mm thick at midline in lumbar region
• LOR technique→ steady pressure on plunger compress air bubble while advancing the needle- when epidural space entered resistance is gone and fluid is easily injected
• Hanging drop method→ drop of solution is placed in hub of needle- subatmospheric pressure sucks drop in when epidural space is entered
• Before advancing the catheter advance the needle 1-2mm more
• Advance catheter 2-3cm into the epidural space (4-6 laboring patients)

Indications for SAB/Epidural Block:

• Anesthesia→ sole anesthetic, combined SAB/CLE, combined GA/Regional (major abdominal procedures or lower extremity vascular cases)
• Analgesia→ postoperative, labor and delivery

Caudal Anesthesia:

• Involves the delivery of local anesthetic to the epidural space via injection through the sacral hiatus
• Identify the sacral hiatus and posterior superior iliac spine
• Uses→ pediatric post-op pain = hypospadias, inguinal hernia repair, procedures of the perineal and sacral areas
• Limitations→ variable anatomy in adults, high risk of injection into a venous plexus, difficulty maintaining sterility should a catheter be used

Complications and Management of Spinal/Epidural/Caudal:

• Hypotension
• Bradycardia
• Sudden cardiac arrest
• N/V
• Unintentional intravascular injections
• Unintentional intrathecal injection
• Catheter shearing
• Postdural puncture headache*
• High blockage
• Inadequate blockage
• Neurologic complications*
• Backache
• Infections→ septic meningitis
• Urinary retention
• Epidural hematoma*

Post Dural Puncture Headache:

• Increased incidence in→ younger patients, female patients, Caucasian, larger needle size, pregnancy, dehydration, cutting tipped needles, and multiple puncture attempts
• Due to decreased intracranial pressure with compensatory cerebral vasodilation
• Treatment→ bedrest, hydration, oral analgesics, abdominal binder, epidural saline injection, caffeine, epidural blood patch
• Epidural blood patch→ forms a clot over the meningeal hole preventing further leak of CSF; aspectic autologous blood draw of 10-20cc with aseptic epidural injection into epidural level at same level or more caudad; relief is almost 90% effective

Epidural Hematoma:

• Presents with numbness or lower extremity weakness
• Consult neurosurgery immediately if a hematoma is suspected 6-8 hours before permanent injury
• Greater than 8 hours makes the odds of decompression less successful
• Primary cause is coagulation defect
• Hold LMWH 10-12 hours pre-placement of epidural and 10-12 hours post surgical procedure
• Do not remove epidural catheter until it has been 10-12 hours after the last dose—wait 2 hours before giving LMWH again

Phenylephrine:

• Synthetic non-catecholamine
• Primarily alpha1 adrenergic receptor stimulant→ vasoconstrict arteries/veins
• Venocontriction greater than arterial constriction
• Less potent than norepinephrine but longer lasting
• Dose→ 50-200micrograms IV, can be used as continuous infusion (20-50 micrograms/min)
• Treat hypotension in OR→ increased MAP, SBP, SVR, CO and decreased HR
• Not used in OB anesthesia
• Double dilute in 100 ml
• Used with decrease blood pressure and decreased heart rate

Ephedrine:

• Synthetic non-catecholamine
• Indirect acting→ stimulates beta and alpha adrenergic receptors by working on vesicles containing norepi
• Dosage→ 5-25 mg IV/IM dilute once
• Treat hypotension in OR due to various reasons, can be used in OB anesthesia
• CV effects similar to epinephrine but 10x longer lasting
• Effects mostly contractility→ increased MAP, SBP, DBP, HR, Coronary BF, decreased renal/splanchnic BF
• Tachyphylaxis is common with this agent due to indirect effect and occupying of receptors
• Used with decreased blood pressure but normal heart rate

Atropine:

• Anticholinergic→ anatagonizes effect of Ach at cholinergic post ganglionic muscarinic receptors (present in heart, salivary glands, smooth muscle of GU/GI tract)
• Alkaloid of belladonna plant and resembles cocaine in structure
• Combines reversibly with muscarinic receptors and prevents Ach from binding to these sites, competitive inhibitors
• Drug of choice from treating intra op bradycardia
• Dose→ 15-75 micrograms/kg IV
• Other effects→ antisialagogue, bronchodilation, mydriasis, decreased GI motility and acid production, bronchodilation, sedation

Glycopyrrolate (Robinul):

• Similar to atropine but is a much more potent antisialoagogue
• Does not easily cross the BBB so no sedative effects
• Dosage→ 0.2-0.4 mg IV
• Combine with anticholinestrases for reversal, 0.5-0.7 mg/kg

Succinylcholine:

• Depolarzing muscle relaxant→ SCh attatches to each of alpha subunits of the nicotininc cholinergic receptor and mimics the action of Ach, depolarizing the post-junctional membrane
• Hydrolysis of SCh is slower than Ach resulting in sustained depolarization of the receptor ion channels
• Dosage→ 0.5-1mg/kg and duration of action is 3-5 minutes
• Used for emergency airway situations, rapid sequence induction and laryngospasm (20-40 mg)
• Can cause→ dysrhythmias, hyperkalemia, myalgias, increased GI pressure, ICP, and IOP

Labetalol:

• Nonselective beta blocker as well as alpha blockade (more beta 7:1)
• Usual IV dose is 0.25mg/kg and can repeat every 10 minutes
• Bolus of 10mg typically and can last 2-18 hours
• Make sure patient has adequate HR and do not give to asthmatics

Esmolol:

• Beta 1 selective agent at small doses
• Dosage→ bolus dose of 500 micrograms/kg IV and onset in 2 minutes
• Half life is 9 minutes, in OR use 10-15 mg and then dose accordingly