Peripheral Nerve Blocks Figure13.Landmarks for placement

of epidural/spinal anesthesia

• deposition of LA around the target nerve or plexus

• ultrasound guidance and peripheral nerve stimulation (needle will stimulate target nerve/plexus) may

be used to guide needle to target nerve while avoiding neural trauma or intraneural injection

• most major nerves or nerve plexuses can be targeted (e.g.brachial plexus block,femoral nerve block,

sciatic nerve block)

• performed with standard monitors

• approximately 2-4 per 10000 risk of late neurologic injury

• resuscitation equipment must be available

Contraindications to Peripheral Nerve Blockade

• absolute contraindications

• allergy to LA

patient refusal

• relative contraindications

certain types of pre-existing neurological dysfunction (e.g.ALS, MS,diabetic neuropathy)

local infection at block site

bleeding disorder

n

LJ

Local Anesthesia

+

Local Anesthetic Agents

• see Table 14, A23,forlist of LA agents

A23Anesthesia Toronto Notes 2023

Definition and Mode of Action

• LA are drugsthat block the generation and propagation of impulsesin excitable tissues:nerves,

skeletal muscle, cardiac muscle, brain

• LA bind to receptors on the cytosolic side of the Na T

channels, inhibiting Na +flux and thus blocking

impulse conduction

• different types of nerve fibres undergo blockade at different rates

Absorption, Distribution, and Metabolism

• LA readily crossesthe BBB once absorbed into the bloodstream

• ester-type LA (e.g. procaine, tetracaine) are broken down by plasma and hepatic esterases; metabolites

excreted via kidneys

• amide-type LA (e.g. lidocaine, bupivacaine) are broken down by hepatic mixed-function oxidases

(P450 system); metabolites excreted via kidneys

Selection of LA

• choice of LA depends on:

onset of action:influenced by pKa (the lower the pKa, the higher the concentration of the base

form of the LA, and the faster the onset of action)

duration of desired effects:influenced by protein binding (longer duration of action when protein

binding of LA isstrong)

potency:influenced by lipid solubility (agents with high lipid solubility penetrate the nerve

membrane more easily)

• unique needs (e.g.sensory blockade with relative preservation of motor function by bupivacaine

at low doses)

potential for toxicity

Table 14. Local Anesthetic Agents

Maximum Dose

(mg/kg)

Maximum Dose with Potency

Epinephrine (mg/kg)

Duration Onset

chloroprocaine 11

lidocaiiie

mep'

nracaine 5

bupivacaine 2.5

rophracaine 2.5

14 Lon 15-30 min Fast

5 7 Medium 1-2 h Fast

7 Medium 3-6 h Fast

3 High 3-8h Slow

3 High 2-8 h Medium

Systemic Toxicity

•see Table 14 for maximum doses, potency, and duration of action for common LA agents

•occurs by accidental intravascular injection, LA overdose, or unexpectedly rapid absorption

CNS Effects

•CNSeffects first appear to be excitatory due to initial block of inhibitory fibres,followed by subsequent

blockade of excitatory fibres

•effectsin order of appearance

numbness of tongue, perioral tingling, metallic taste

disorientation, drowsiness

• tinnitus

• visual disturbances

muscle twitching,tremors

unconsciousness

convulsions,seizures

generalized CNS depression, coma,respiratory arrest

CVS Effects

•vasodilation, hypotension

•decreased myocardial contractility

•dose-dependent delay in cardiac impulse transmission

• prolonged PR, QRS intervals

sinus bradycardia

•CVS collapse

y.: .< : .iv.r

r collapse

v

>^Comi

Convulsions

/

Unconsciousness

'

Muscle twitching

•

'

C - , aL I „• :

/ ILc.iisMliSsturbjrcciti

SLigMheededness

\ --r . 1

=

’

r1

L J

I

Treatment of Systemic Toxicity

•earlv recognition ofsigns;get help

•100% Oz,manage ABCs

•diazepam or other anticonvulsant to prevent potential onset ofseizures

•manage arrhythmias

•Intralipid* 20% to bind local anesthetic in circulation

Ml M

Figure15.Local anesthetic systemic

toxicity +

A21Anesthesia Toronto Notes 2023

Local Infiltration and Hematoma Blocks

Local Infiltration

• injection of tissue with LA, producing a lack ofsensation in the infiltrated area due to LA acting on

nerves

• suitable forsmall incisions,suturing, and excising small lesions

• can use fairly large volumes of dilute LA to infiltrate a large area

• low concentrations of epinephrine (1:100000-1:200000) cause vasoconstriction, thus reducing

bleeding and prolonging the effects of LA by reducing systemic absorption

Fracture Hematoma Block

• special type oflocal infiltration for pain control during manipulation of certain fractures

• hematoma created by fracture is infiltrated with LA to anesthetize surrounding tissues

• sensory blockade may only be partial

• no muscle relaxation

Topical Anesthetics Local Anesthetics aid Regional Anaesthesia vs.

Conventional Analgesia for Preventing Persistent

Postoperative Pain in Adults and Children

Cochrane OBSyst Rev 2018:6:C0007105

Purpose:Compare L A and RA vs.convCBtional

anesthesia for the prevention of persistent

postoperative pain fPPP) beyond 3mo.

Methods:Searched CENTRAL MEDUNE. and

Embase to December 2016.RCTs comparing RAis.

conventional anesthesia were included.

Results:Total 63 RCTs included.Data on RA for the

prevention of PPP beyond 3mo aftersurgery from

39studies,enrolling a total of 3027 participantsin

inclusive analysis.Moderate quality evidence favoring

RA over conventional for thoracotomy.C-secbon (OR

0.52 and OR 0.46 respectively).Moderate quality

evidence showing the infusion of IV LA lor the

prevention of PPP3-6 mo after breast cancersurgery

with an OR of 0.24.Low quality evidence in RA for the

prevention of PPP3-12 mo after breast cancer surgery

with an OR of 0.43.

Conclusions:There is moderate-quality evidence

that RA may reduce the risk of developing PPP

after 3-t8 mo after thoracotomy and 3-T2 mo after

caesarean section.Further studiesiocludhig larger

populations are needed.

• various preparations of LAs available for topical use, which may be a mixture of agents (e.g. EMLA

cream is a combination of 2.5% lidocaine and prilocaine)

• must be able to penetrate the skin or mucous membrane

Postoperative Care

• pain managementshould be continuousfrom OR to PACU to hospital ward and home

Common Postoperative Anesthetic Complications

Uncontrolled/Poorly Controlled Pain

• See below

Nausea and Vomiting

• hypotension and bradycardia must be ruled out

• pain and surgical manipulation also cause nausea

• often treated with dimenhydrinate (Gravol*),ondansetron (Zofran*), granisetron (Kytril*),

dexamethasone (Decadron*), metoclopramide (Maxeran*; not with bowel obstruction),

prochlorperazine (Stemetil*)

Confusion and Agitation

• ABCs first- confusion or agitation can be caused by airway obstruction, hypercapnia, hypoxemia

• neurologic status(Glasgow Coma Scale, pupils), residual paralysisfro

• pain,distended bowel/bladder

• fear/anxiety/separation from caregivers, language barriers

• metabolic disturbance (e.g. hypoglycemia, hypercalcemia, hyponatremia - especially post-

'

l

'URP)

• intracranial cause (e.g.stroke, raised 1CP)

• drug effect (e.g. ketamine, anticholinergics,serotonin, benzodiazepines, opioids)

• elderly patients are more susceptible to postoperative delirium

Risk Factors for PONV

. Young age*

• Female*

. History of PONV

• Non-smoker*

• Type of surgery:ophtho,ENT,abdo/

pelvic,plastics

• Type of anesthetic:NvO,opioids,

volatile agents

These factors relef lo the Apiel tool lor PONV risk

itiaUliuhon and management

m anesthetic

Respiratory Complications

• susceptible to aspiration of gastric contents due to PONV and unreliable airway reflexes

• airway obstruction (secondary to reduced muscle tone from residual anesthetic,soft tissue trauma

and edema, or pooled secretions) may lead to inadequate ventilation, hypoxemia, and hypercapnia

• airway obstruction can often be relieved with head tilt, jaw elevation, and anterior displacement of the

mandible.If the obstruction is not reversible, a nasal or oral airway may be used

Hypotension

• must be identified and treated quickly to prevent inadequate perfusion and ischemic damage

• reduced cardiac output (the most common cause is hypovolemia) and/or peripheral vasodilation (e.g.

residua) anesthetic agent)

• first step in treatment is usually the administration of fluids ± inotropic agents

Hypertension

• pain,hypercapnia, hypoxemia, increased intravascular fluid volume, and sympathomimetic drugs

can cause hypertension

• IV nitroglycerin, hydralazine, calcium channel blockers, or p-blocking drugs(e.g. esmolol and

metoprolol) can be used to treat hypertension

Set Landmark Anesthesiology Trials table for more

information on results from the IMPACT trial which

comparesthe efficacy of six weltestaWished

prophylactic antienetic interventions in patients

sclredjled to undergo elective surgery during general

anesthesia at high risk for postoperative nausea

and vomiting.

r T

See landmark Anesthesiology Trials table lor more

information on resultsfrom the DREAMS trial,which

details the effect of preoperative deiainethasone

administration in patients with postoperative

vomiting.

+

A25 Anesthesia Toronto Notes 2023

Pain Management

Definitions

• pain: an unpleasant sensory and emotional experience associated with, or resembling that associated

with, actual or potential tissue damage (International Association for the Study of Pain (IASP);

definition updated in 2020)

• nociception: detection, transduction, and transmission of noxiousstimuli

See Landmark Anestlresnlngi1 Trials table for

more information on study by HJ Shin et al. 2019.

which highlights differences inpostoperative

analgesic effectol intreopeiitnre sedation with

deimedetomidine (OEXfrs. propofol.

Pain Classifications

• temporal: acute vs. chronic

• mechanism: nociceptive vs. neuropathic

Acute Pain

• pain of short duration (<6 wk) usually associated with surgery, trauma, or acute illness; often

associated with inflammation

• usually limited to the area of damage/trauma and resolves with healing

Opioid for moderate to severe pam

(e g morphine)

i Non-opioid,iAdjuvant

.=cd

Ventral posterior Sensorv cortex \!

lateralnucleus of

thalamus

Opioid for mild to moderate pain ©

(eg.codeine)

3rdorder i Non-opioid,iAdjuvant

afferent neuron

Tissue

damage by:

•thermal

•chemical

•mechanical forces

'

/

jyA Non-opioid

leg.NSAID)

vJ Modulatory z. Non-opioid,i. Adjuvant

i neurons release:

'

j

*

) •endorphins

, i •enkephalins

'

IT'

'

v / •norepinepluine

•serotonin

•GABA

’

y

A

Figure 17. WHO analgesia ladder r

Nociceptors

detect pain

stimulus

X/

u

LX

STT

1storder

afferent neuron

Inhibitrelease ot

substance P or make

post-synaptic

membrane more

difticultto polaiize

:

i

Dorsal horn

olspinal cord I

a.

2nd order

afferent neuron STT:spinothalamic tract Qj

Figure 16. Acute pain mechanism

Pharmacological Management of Acute Pain

• ask the patient to rate the pain out of 10 or use visual analog scale to determine severity

• pharmacological treatment guided by WHO analgesia ladder ( Figure 17)

Table 15. Commonly Used Analgesics

Acetaminophen NSAIDs Opioids

Tylenol 5 Oral:codeine,oxycodone,morphine,hydromorphone

Parenteral:morphine,hydromorphone.fenlanyl

Oral:moderate acute pain

Parenteral:moderate- severe acute pain

Dampens nociceptive transmission between Island 2nd order

neurons in the dorsal horn

Activates ascending modulatory pathways resulting inrelease

of inhibitory neurotransmitters

Inhibits peripheral inflammatory response and hyperalgesia

Allccts mood and anxiety - alleviates the affective

component of perceivedpain

Limited by analgesic No analgesic ceiling(except lor codeine)

ceiling beyond which there Can be administered intrathecally (e.g.spinal block) or by

is no additional analgesia continuous infusion

Opioid-sparing

Significant inter-individual anti emetics.laxatives

variation in efficacy

Aspirinr.ibuprofen,

naproxen,ketorolac (IV)

Mild-moderate pain

Examples

Indications First-line lor mildacute pain

Mechanism of Unclear,hypothesized

cyclooxygenase-2(C0X-2)

inhibition

Unclear,hypothesized

modulation olendogenous

cannabinoid system

Nonsclective C0X-1 and

-2inhibition reducing

proinflammalory

prostaglandin synthesis

Action

r T

Cautionary Use of NSAIDs in Patients

with:

• Asthma

• Coagulopathy

• G! ulcers

• Renal insufficiency

• Pregnancy,3rd trimester

L J

Dosing/ limited by analgesicceiling

Administration beyond which there is no

additional analgesia

Opioid-sparing

Max dose ot 4 g/24 h

Consider breakthrough dose and/or co-administration with

+

A26 Anesthesia Toronto Notes 2023

Table 15. Commonly Used Analgesics

Acetaminophen NSAIDs Opioids

Gastric ulceration/blcedinq Respiratory depression

Decreased renalperfusion Constipation and abdominal pain

Urinary retention

Sedation

Side Effects/

Toxicity

Considered relatively safe

liver toxicity in elevated doses

Photosensitivity

Premature closure ol

the ductus arteriosus in N/V

Pruritus

Confusion (particularly in the elderly)

Dependence

pregnancy

Table 16. Opioids

Relative Dose

to 10 mg

Morphine IV

Agent Moderate Onset Duration Special Considerations

Dose Opioid Conversion

Parenteral Equivalent

(IV) Oral Dose

10 mg 30 mg

4 mg

200 mg

20 mg

Codeine 100 mg IV

200 mgP0

15-30 mg PO Late Moderate

(4-6 h)

Primarily postoperative use,not for IV use

Not ideal,as analgesic effect depends on

highly variable CYP2D6 metabolism

Anticholinergic,hallucinations,less pupillary

constriction than morphine,metabolite build

up may cause seizures

Decreased use lor pain management due to

potential toxicity compared to other opioids.

Typically reserved to treat postoperative

shivering.Absolute contraindication in

patients taking MAO-inhibitors

Histamine release leading lo decrease in BP

(30-60 min) Morphine

Hydromorphone 2 mg

Codeine 120 mg Meperidine 2 3 mg/kgIV

(Demerol )

75 mg IV Moderate

(10 min)

Moderate

(2-4 h)

Oxycodone

Fentanyl

N' A

100 pg N/A

10 mg IV

30 mg P0

0.2-0.3 mg/kg IV Moderate

0.40.6 mg/ (5 -10 min)

Morphine Moderate

(4 5h)

kg P0

Morphine Extended

Release (e.g

MEslon . MS

Contin - )

Oxycodone Controlled

Release (Oxyneo:

)

Oxycodone Regular

Tablet (OxylR *

)

Hydromorphone

(Dilaudid1)

Hydromorphone

Extended Release

(e.g.Hydromorph

Contin)

Fentanyl

20 mg PO 5- 20 mgP0 Late long Do not split,crush,or chew lablel

20 mg P0 10-20 mgP0 Late (30- 45 min) Long (8-12 h) Do not split crush,or chew tablet (but can be

difficult to swallow)

Percocel '

- oxycodone 5 mg

*

acetaminophen 325 mg

less pruritus.N/V.and sedation compared

to morphine

Do not split,crush or chew tablet

(no IV)

20 mg P0|no IV) 5-15 mg P0 Moderate

(15 min)

Moderate

(15 min)

Moderate

(3 6 h)

Moderate

(4 5 h)

Lale (30- 45 min) long

1.5-2.0 mgIV

6 8 mgP0

4.0-6.0 mg P0

40 60 pg/kgIV

2-4 mgP0

3-12 mg P0

tOOpgIV 2-3 pg/kgIV Rapid Short Transient muscle rigidity in very high doses

(<5 min) (0.5-1h)

Rapid (1-3 min) Ultra short Only use during induction and maintenance

(«10 min) ol anesthesia

Rapid (8 min) 15-90 h (24 h Can only be prescribed byfederally/

average) provincially licensed physicians andnurse

practitioners

Acts through both NMDA and p-opioid

receptors

Challenging due tovariable equianalgesic

dose and half-life

Alter titration,accumulates In tissue for

once/twice daily dosing

Metabolized by CYP3A4

Caution with high doses,may cause 01

prolongation,baselineECG required

For moderate to severe chronic pain and

opioid addiction

Ceiling effect for respiratory depression but

not analgesia

High affinity lo p- oproid receptors,very

resistant to reversal with opioid antagonists

Remilentanil TOOpgIV 0.54.5 pg/kgIV

Methadone (opioid

agonist)

Morphine to

methadone

conversion is

variable based

on patient's

morphine dose.

Ranges (rom1/4

to1/20

15-40 mgrd in

divided doses

PCA Parameters

• Loading dose

• Bolus dose

• Lockout interval

• Continuous infusion (optional)

• Maximum 4h dose (limit)

Buprenorphine

(opioid agonist

antagonist)

Film:2 mg up to

max of 24 mg

Varies depending Moderate (30 6-8 h

on route of

administration

(pill/film,

transdcrmal)

min)

In general,parenteral route is2-3x more potent than oral

r t

Patient Controlled Analgesia

• patient controlled analgesia (PCA) involves the use of computerized pumps that can deliver a constant

infusion and bolus breakthrough doses of parenterally-administered opioid analgesics

• limited by lockout intervals

• most commonly used agents: morphine and hydromorphone

• see Table 17 for suggested infusion rate, PCA dose, and lockout intervals

L J

Advantages of PCA

• Improved patient satisfaction

• Fewer side effects

• Accommodates patient variability

• Accommodates changes in opioid

requirements +

A27 Anesthesia Toronto Notes 2023

Table 17. Opioid PCA Doses

Agent PCA Dose PCA Lockout Interval PCA 4 h Maximum

Patient Controlled Opioid Analgesia vs.

Non-Patient Controlled Opioid Analgesia for

fcstoperative Pain

Cochrane D8 Sys!Rev 2015:CD003348

Purpose:To evaluate the efficacy of patient

controlled analgesia (PCA|vs. non patient controlled

opiod analgeua of as-needed opioid analgesia for

postoperative pain icliel.

Methods: Meta-analyses of RCIs comparing PCA

ss.conventional administration ol opioid analgesia.

Assessmentemployeda visual analog scale|YAS|

for pan intensity along with overall analgesic

consumption, patientsatisfaction, length of stay, and

adverse side effects.

Results:49 studieswith a total of 1725 patients

receiving PCAand 1687 patients assigned to a control

group.PCA had a lower VAS pain intensity score vs.

non-patient controlled analgesia over most lime

itervalsin the first 48 h.PCA was associated with

higher patient satisfaction and consumed higher

amounts of opiods than controls. PCA was also

associated with higher incidence ol pruritus hut not

Othei adverse events.

Conclusions: Moderate lo low quality evidence

that PCA a an efficacious alternative to non-patient

controlled systemic analgesia for postoperative

pain control.

Morphine

Hydromorphone

Fentanyl

1-2 mg

0.2-0.4 mg

25-50 pg

5 min

5 min

30 mg

10 mg

5 min 400 pg

Opioid Antagonists (naloxone, naltrexone)

• indication: opioid overdose (manifests primarily at CNS, e.g. respiratory depression )

• mechanism of action: competitively inhibit opioid receptors, predominantly p-opioid receptors

• naloxone is short-acting (tl/2 = I h); effects of narcotic may return when naloxone wears off;

therefore, the patient must be observed closely following its administration

naltrexone is longer acting (tl/2 = 10 h); less likely to see return of opioid effects

• side effects: relative overdose of naloxone may cause nausea, agitation,sweating, tachycardia, H'

l

'N,

re-emergence of pain, pulmonary edema,seizures (essentially opioid withdrawal)

Neuropathic Pain

• see Neurology. N43

Chronic Pain

•chronic pain: pain greater than 3 mo,or recurrent pain that occurs at least 3 times throughout 3 mo

period

pain of duration or intensity that persists beyond normal tissue healing and adversely affects

functioning

•in the perioperative period, consider continuing regular long-acting analgesics and augmenting with

regional techniques, adjuvants, additional opioid analgesia, and non-pharmacological techniques (e.g.

mindfulness, physiotherapy, acupuncture)

Nociceptive Pathways in Labour and

Delivery

Labour

• Cervical dilation and cffacemcnt

stimulates visceral nerve fibres

entering the spinal cord at T10- L1

Delivery

• Distention of lower vagina and

perineum causessomatic nociceptive

impulses via the pudendal nerve

entering the spinal cord atS2-S4

Central Sensitization

•central sensitization: hyperalgesia ( i.e. increased sensitivity to pain) as a result of CNS mechanisms

•may have nociceptive and neuropathic components;dysregulation of analgesic pathways implicated

•plays a role in fibromyalgia

Chronic Post-Surgical Pain

•chronic post-surgical pain (CPSP):pain that develops aftersurgery and persistsfor at least 2 mo

•primary predictor of CPSP is history of chronic pain; other risk factors include female gender, surgical

procedure/approach, poor social supports, catastrophizing behaviour

ipidntil vs. Non Epidural or Ho Analgesia lor Pain

Management in labour

Cocfra - e DB Syst Rev 201SCD00033I

Purpose:to assess effectiveness and safety of an

types of epidural analgesia when compared with

non-epidural or no pain relief during labour.

Methods:Systematic renew of BCIs comparing

epdural with any form of pain relief not involving

regonal blockade,or no pan relief in labour.

Results:52 studiesinvolving over 11000 women

were included:34 studies compared epidural

analgesia with opioids. Epidural analgesia was

associated with lower pain intensity, higher

satisfaction, and decreased need for additional pam

relief vs.opiods While it was also associated w t:

creased risk pi assisted vaginal birth ( AR 1.44. 95%

(11.29-1.60). post- hoc analysisofstudies conducted

after 2005 elimi natesthis risk (RR 1.19. 95% 00.97-

1.46).Women with epidural analgesia expenenced

more hypotension,motor blockage,(ever,and urinary

retention with less risk ol respiratory depresson and

nauseafromiting.Iherewas no differencem neonatal

outcomes,admission to NIC U. caesarean section

rates,or maternal long-term backache.

Conclusions: Ep dural analgesia may be more

efiective in reducing pain during labour and

creasing maiernalsatisfaction than non - epidural

methods and. when considering modern approaches,

is not associated with increased instrumentation.

Epidural analgesia had no impact on the risk ol

caesarean section or long-term backache,and did

not a ppear to have an enmediate effect on neonatal

status as determined by Apgar scores or m admissions

to MCI).

Obstetrical Anesthesia

Anesthesia Considerations in Pregnancy

• Airway

possible difficult airway as tissues becomes edematous and friable, especially in labour

• RespiratorySystem

decreased TRC and increased 02 consumption cause more rapid desaturation during apnea

• Cardiovascular System

increased blood volume > increased RBC mass results in mild anemia

• decreased SVU proportionately greater than increased CO results in decreased BP

• prone to decreased BP due to aortocaval compression (supine hypotensive syndrome)

- a

pregnant patient is positioned in left uterine displacement (approximately 15°- angle) using a

wedge under her right Hank when supine

• Central Nervous System

decreased MAC due to hormonal effects

increased block height due to engorged epidural veins

• Gastrointestinal System

delayed gastric emptying

increased volume and acidity of gastric fluid

• decreased LtS tone

increased abdominal pressure

• combined, these lead to an increased risk of aspiration; therefore, for surgery, a pregnant patient

is given sodium citrate 30 cc PC) immediately before surgery to neutralize gastric acidity

Options for Analgesia during Labour

• psychoprophylaxis- Lamaze method

• patterns of breathing and focused attention on fixed object

+

A28 Anesthesia Toronto Notes 2023

•systemic medication

• easy to administer, but risk of maternal or neonatal respiratory depression

opioids most commonly used if delivery is not expected within 4 h;fentanyl can be considered

•inhalational analgesia

easy to administer, makes uterine contractions more tolerable, but does not relieve pain

completely

• 50% nitrous oxide is insufficient alone but good safety profile for mother and child

•neuraxial anesthesia

provides excellent analgesia with minimal depressant effects

• hypotension is the most common complication

maternal BP monitored q2-5 min for 15-20 min after initiation and regularly thereafter

• epidural usually given as it preferentially blockssensation, leaving motor function intact

Techaiques lor Preventing Hypotension During

Spinal Anaesthesia for Caesarean Section

Cochrane DflSyst Rev 2011:8:00002251

Purpose:In assessthe effects of prophylactic

interventions for maternal hypotension following

spinal anesthesia for caesarean section.

Methods:Searched Cochrane Pregnancy and

Childbirth'strials Register and reference lists,

lododed RCIs comparing interventions to prevent

hypotension with placebooc alternative treatment.

Results:126 studies were included involving 9565

participants. Identified 3 intervention groups

which were IV fluids(corod vs.crystalloid vs. no

fluid), pharmacological interventions(ephedrine

vs.phenylephrine,orondansetron vs.control),and

physical interventions(lower bmb compression,or

lying vs.walking),til groupsshowed better control

ol hypotension with no differences between colloid

vs. crystalloid, ephedrinevs. phenylephrine,or lying

vs. walking,til evidence was very-low quality to

low-quality.

Conclnsions:Wlale interventionssuch as

crystalloids, colloids,ephedrine, phenylephrine,

ondansetron,or lower leg compression can redoce

the incidenceol hypotension,none have been shown

to be superior to t lit other.

Options for Caesarean Section

•neuraxial:spinal or epidural

•general: used if contraindications or time precludes regional blockade (see Regional Anesthesia,

Epidural and Spinal Anesthesia, A21)

Paediatric Anesthesia

Respiratory System

• in comparison to adults, anatomical differencesin infants include:

• large head,short trachea/neck, large tongue, larynx positioned more superior and anterior,

adenoids, and tonsils

• narrow nasal passages (obligate nasal breathers until 5 mo)

narrowest part of airway at the level of the cricoid vs.glottis in adults

epiglottis islonger, U-shaped and angled at 45°; carina is wider and is at the level of T2 ( 14 in

adults)

• physiologic differences include:

faster respiratory rate, immature respiratory centres that are depressed by hypoxia/hypercapnia

(airway closure occursin the neonate at the end of expiration)

less 02 reserve during apnea - decreased total lung volume, vital capacity, and FRC together with

higher metabolic needs

• to increase alveolar minute ventilation in neonates, increase respiratory rate, not tidal volume

• neonate:30-40 breaths/min

age 1-13:(24 -[age/2]) breaths/min

greater V/Q mismatch -lower lung compliance due to immature alveoli (mature at 8 yr)

greater work of breathing -greater chest wall compliance,weaker intercostals/diaphragm, and

higher resistance to airflow

Cardiovascular System

• blood volume at birth is approximately 80 mL/kg;transfusion should be started if >10% of blood

volume islost

. children have a high HR and low BP

• CO is dependent on HR, not SV because of low heart wall compliance) therefore, bradycardia severely

compromises CO

Adult Upper Airway

pharynx

((

^