Basic Practice of Anesthesiology

Hany El-Zahaby, MD

Preoperative Evaluation

1. History-Current problem-Other known problems-Medical history (allergies, drug intolerance, present

therapy, tobacco and alcohol intake)-Previous anesthetics, surgeries, deliveries-Family history-Review of organ systems-Last oral intake

Preoperative Evaluation

2. Physical Examination

-Vital signs

-Airway (Thyromental distance, Malampati sign)

-Heart

-Lungs

-Extremities

-Neurological examination

Preoperative Evaluation

3. Routine Laboratory evaluation (healthy asymptomatic)

Hematocrite: All menstruating women, age >60 y, anticipated significant blood loss

S. glucose, creatinine: age >60 y

ECG: age >40 y

Chest radiograph: age >60 y

Pregnancy test: fertile women

American Society of Anesthesiology Risk Classification

ASA Class Description

1 Normal, healthy (0.06-0.08%)

2 Mild systemic disease (0.27-0.4%)

3 Severe systemic D, not incapacitating (1.8-4.3%)

4 Severe systemic D that is a constant threat to life (7.8-23%)

5 Moribund, not expected to live 24h (9.4-51%)

6 Care for organ donation

The Anesthetic Plan

Premedication Type of anesthesia

General (airway, induction, maintenance, relaxant)Regional (technique, agents)

Intraoperative managementMonitoring, positioning, fluids, MABL, special techniques

Postoperative managementPain control, ICU (ventilation, monitoring)

Preoperative Evaluation

Informed consent Gives the patient explanation of the options for

anesthesia and its realistic risks (general, regional, local, topical, intravenous sedation)

Regardless of the technique chosen, consent must always be taken for GA if other techniques prove inadequate e.g. LA

The Anesthetist-Patient relationship

Is The Patient Scared?

Surgery (cancer, physical disfigurement, pain, death)

Anesthesia (loss of control, not waking up, waking up during surgery, nausea, confusion, paralysis, headache)

Preoperative Evaluation

1-Unhurried, organized interview

2-Calm reassurance and expression of interest in the patient’s well being

3-Informing about:

NPO (no solids after m.n., clear fluids up to 2-3 h unless GER)

Time of surgery

Premedication and other daily medications

Tasks to occur on the day of surgery

Postoperative recovery or ICU

Premedication

Benzodiazepines:

Diazepam (5-10 mg PO 1-2 hours before surgery), never IM (pain, unpredictable)

Lorazepam (1-2 mg PO), intense prolonged amnesia and sedation

Midazolam (1-3 mg IV or IM) at the receiving area, 0.5 mg/kg PO for pediatrics

Premedication

Narcotics: painful fractures, planned extensive awake invasive monitoring devices

Morphine 5-10 mg IM 60-90 min before surgery

Anticholinergics (rare): Not Routine

Glycopyrrolate 0.2-0.4 mg IV to reduce oral secretions (fibreoptic intubation)

Premedication

Prophylaxis for pulmonary aspiration: Pregnant, hiatal hernia, GER, difficult airway, ileus,

obesity, CNS depression H2 blockers (ranitidine, 150-300 mg PO before

bedtime and early morning) Nonparticulate antacids (sodium citrate 30-60 ml) Metoclopramide (10 mg IV 1h before surgery to

enhance gastric emptying)

Premedication

Goals: Reduce anxiety, pain during vascular cannulation and regional blocks, facilitate smooth induction

Reduce the dose or withhold in elderly, debilitated, upper airway obstruction or trauma, central sleep apnea, neurologically obtunded, severe pulmonary or obstructive valvular disease

Monitoring

Standard monitoring for GA:

ECG, non-invasive BP, respiratory rate, oxygen saturation, end-tidal carbon dioxide, inspired oxygen concentration

Standard monitoring for regional anesthesia:

ECG, non-invasive BP, respiratory rate, oxygen saturation

IV access

IV access: (14-16 G if rapid fluid or blood transfusion or continuous drug infusions, better under local anesthetic infiltration)

Components of GA

Loss of consciousness

Loss of reflexes (Movement to pain)

Analgesia

Amnesia

Relaxation

Induction of Anesthesia

The environment in OR should be warm with minimal noise and all attention focused on the patient

Supine position with extremities in neutral position and head on firm pillow raised to ‘’sniff’’ position

Induction of Anesthesia

Techniques:1- IV induction preceded by oxygen via face mask until

loss of consciousness using thiopentone or propofol2- Inhalational anesthetics either by low concentration

with incremental increase every 3-4 breaths or by a single vital capacity breath technique using sevoflurane or halothane

Intravenous InductionThiopentone Propofol

3-5 mg/kg 2-2.5 mg/kg

--- IVI 6-10 mg/kg/h

--- Painful injection

Slower onset, slower recovery Rapid induction, rapid clear-headed recovery

Hypotension ++ Hypotension +++

Depress respiration Depress respiration

Contraindicated in porphyria Less N,V

Airway Management

Face-mask with:

Oro-pharyngeal airway

Naso-pharyngeal airway LMA ETT with a muscle relaxant (depolarizing as succinyl

choline or non-depolarizing as tracrium, cistracrium, rocuronium)

Muscle Relaxants

Depolarizing MR (succinylcholine) mimics the action of acetylcholine i.e. causes depolarization of the motor end plate and muscle membrane but for longer time than Ach. Used for rapid-sequence induction in patients with full stomach

Non-depolarizing MR produce reversible competition with Ach at the motor end plate that produce relaxation for longer duration

Succinylcholine

Dose:1mg/kg produce relaxation in 1 min Side effects:

Muscle pains, ganglionic stimulation, increase S. K+ level by 0.5-1 mEq/L, increase intraoccular pressure, increased intragastric pressure, increase intracranial pressure, prolonged block due to decrease or inhibition or atypical plasma cholinesterase, malignant hyperthermia

Non-Depolarizing MR

Atracurium: 0.5 mg/kg, Hofmann elimination

Cisatracurium (Nimbex): 0.15 mg/kg, Hofmann elemination, less histamine release

Vecuronium: 0.1 mg/kg, hepatic metabolism

Rocuronium (Esmeron): 0.5 mg/kg, hepatic metabolism (short duration)

TOF

Twitch Height After Succinyl Choline

Twitch Height After Non-Depolarizing

Clinical Assessment of the Blockade

Evoked response Clinical correlate

95% -- single twitch Good intubating condition

TOF response =1 Surgical relaxation without inhalation anesth.

TOF response =3 Surgical relaxation with inhalation anesth.

TOF ratio > 0.75 Possible extubation

TOF ratio = 1 Normal VC

Laryngoscopy and Intubation

Profound sympathetic responses (hypertension, tachycardia) can be attenuated by hypnotics, inhalation anesthetics, opioids, lidocaine, or beta blockers

ETT Size

Premature: 2.5-3

Full term: 3

6 M -1 y:3.5

2 Y: 4.5

Over 2y: 4+(age/4)► 4 +(6/4) ►5.5

Length (at mouth cm): 10+(age/4) ► 10 +(6/4) ►11.5cm

Positioning

Movement of supine anesthetized patient into another position may cause hypotension due to lack of intact compensatory hemodynamic reflexes. Patient’s head and limbs should be protected and padded. Hyperextension or over-rotation of the neck and limbs must be avoided.

Maintenance

Depth of anesthesia (surgical anesthesia)

+Muscle relaxation

Signs of inadequate depth of anesthesia:

Somatic responses (movement, coughing, changes of respiratory pattern)

Autonomic responses (tachycardia, hypertension, mydriasis, sweating, tearing)

Stages of General Anesthesia

Stage I

Amnesia

From induction to loss of consciousness, pain perception is

maintained

Stage II

Delirium

Exaggerated responses to noxious stimulus, dilated pupils, divergent

gaze, irregular breathing

Stage III

Surgical anesthesia

Central gaze, constricted pupils, regular respiration, no somatic or

autonomic responses

Stage IV

Overdosage

Depressed respiration, dilated fixed pupils, marked hypotension

Maintenance

If spontaneous breathing is needed, minimal opioids with nitrous oxide and inhalation anesthetic

If muscle relaxation is needed, nitrous oxide-opioid-relaxant with minimal inhalation anesthetic and controlled ventilation (Balanced anesthesia)

TIVA: Continuous infusion of propofol-opioid + muscle relaxant (nothing through inhalation)

Inhalation Anesthetics

Blood-gas partition coefficient is inversely related to the rate of induction

MAC: minimal alveolar concentration that prevent movement in response to a skin incision in 50% of patients

Inhalation Anesthetics

Blood/gas PC MAC

Nitrous oxide 0.47 104

Halothane 2.3 0.74

Isoflurane 1.4 1.15

Sevoflurane 0.69 2.05

Desflurane 0.42 6.0

Ventilation

Spontaneous/assisted:

All inhalation anesthetics depress respiration and moderately increase PaCO2

Can be affected by positioning, peritoneal insufflation, open chest, surgical packing and opioids

Ventilation

Controlled Ventilation:Initial setting with TV=10-15 ml/kg, RR=10-12/min, notice the PIP, If>30, decrease TV and increase RRA sudden drop in PIP → circuit leakA sudden increase in PIP → kink, endo-bronchial intubation, peritoneal insufflation

IV Fluids

Maintenance: first 10kg→ 4ml/kg/h

Second 10 kg → 2ml/kg/h

After 20 kg → 1 ml/kg/h Third-space loss: Tissue edema and evaporation,

varies from 5-10 ml/kg/h Blood loss: Replaced in 1:3 with isotonic crystalloid,

or 1:1 with blood

IV Fluids (60 kg fit adult fasting for 6h)

1st h 2nd h 3rd h

Fasting 300 150 150

Maintenance (100ml/h)

100 100 100

3rd space 5x60=300 5x60=300 5x60=300

Blood loss -- -- --

Total 700 550 550

Estimated Allowable Blood Loss

70 kg, Hct 35 EABL = EBV X (Hctstart-Hctallowable)

Hctstart

EABL = 4900 X (35 – 27)= 980ml

35

Estimating Volume of Blood to be Transfused

70 kg, with present Hct of 23 Volume=EBV X (Hctdesired - Hctpresent)

Hct transfused blood

Volume=4900 X (30-23) =490ml

70

Emergence from GA

Goals: awake, responsive with full muscle strength so he can maintain patent airway, cannot aspirate and can be assessed neurologically

Technique: withdraw anesthetics near the end of surgery, reverse muscle relaxation with neostigmine (0.03-0.06 mg/kg) and atropine (0.2-0.4 mg/kg)

Emergence from GA

Environment: Warm and calm Positioning: Supine, tonsillectomy if full stomach Mask ventilation: 100% oxygen, avoid stimulation of

the airway during stage II

Emergence from GA

Extubation:

1-Awake (desirable) with fully recovered protective reflexes, follow simple verbal commands, breathe spontaneously with good oxygenation and ventilation (lidocaine 1mg/kg IV)

2- Deep extubation (during stage III) reduce risk of laryngospasm and bronchospasm (in asthmatic) avoid coughing ( eye surgery, hernia repair)

Emergence from GA

Agitation: due to hypoxia, hypercarbia, airway obstruction, full bladder, pain or sevoflurane and desflurane anesthesia. Treated by treating the cause, fentanyl 25μg IV or morphine 2mg IV increments

Delayed awakening: Continue ventilatory support and airway protection and reverse the etiology

Transport

Stable patient can be transferred without oxygen or monitor to PACU

Unstable patient should be transferred with oxygen, monitors, tools for re-intubation to PACU or ICU

Anesthetist should give concise but thorough summary to PACU or ICU staff

Acute postoperative pain management

Optimal pain control is an integral component of accelerated recovery

Although opioids are the most effective, acute postoperative pain management is now based on multimodal analgesia and opioid sparing

Acute postoperative pain management

Psychological Preparation Assessing Pain (0-10 Verbal Analogue Scale is now

the fifth vital sign to be recorded in the record) Preemptive Analgesia (peripheral injury ►central

sensitization ►increase pain sensitivity

Acute postoperative pain management

Treatment Options:

1- NSADs:

Oral alone ► mild to moderate pain, begin preop., gastric irritation, coagulopathy, mask fever

Oral with opioids ►reduce opioid intake

Parentral ►keorolac 30 mg then 15-30 mg/6h, expensive, can replace opioids

Paracetamol (Perfalgan), 1 gm/6h

Acute postoperative pain management

2- Opioids:

PO (chronic pain)

IM ( morphine 0.1mg/kg, pethidine 1mg/kg) painful, unreliable

IV-bolus (morphine 2mg every 5 min, max 10-15mg)

IVI ( morphine 10- 20 μg/kg/h)

Monitor the respiratory rate

Acute postoperative pain management

3- PCA:

Provide analgesic doses immediately based on patient needs using microcomputer-controlled infusion pumps which avoids extreme swings in plasma levels. Special order sheet is needed with detailed pump setting (demand dose, start dose, delay time, basal rate) and monitoring (pain level, sedation level, verbal response)

Acute postoperative pain management

4- Epidural Analgesia

Abdominal , vascular & L.L. surgery

Contraindications: patient refusal, coagulopathy, LMWH, bacteremia, local infection

0.1% Bupivacaine + 1-2 µg/ml Fentanyl ►5-10 ml/h

▼Bupivacaine if hypotension or motor block

▼Fentanyl if pruritis

Complications: Inadequate analgesia, PDPH, epidural hematoma or abcess

Acute postoperative pain management

5- Neuraxial Morphine (preservative-free)

Epidural: 1-4 mg

Intrathecal: 0.1-0.4 mg (Respiratory depression)

6- Intraoperative Neural Blockade (esp. children)

Local Anesthetics

Ester/ Amide

AmineAromatic Ring

Local Anesthetics

Esters: procaine, chloroprocaine, tetracaine (metabolised by plasma esterase, allergen)

Amides: lidocaine, bupivacaine, ropivacaine (liver metabolism)

Local Anesthetics

Potency ►lipophilicity

Duration ► protein binding

Onset ► pKa (pH at which 50% are uncharged ions ► diffuse to nerve membrane)

Local Anesthetics

Sequence of block:Sympathetic ►pain & temp. ►proprioception ►touch &

pressure ►motor Additives:

Epinephrine 1:200,000►prolong duration, ▼systemic toxicity, ▲intensity of block, ▼surgical bleedingSodium bicarbonate: 1 meq:10ml lidocaine, 0.1meq:10 ml bupivacaine (avoid ppt)►fasten onset

LA: Systemic Toxicity

CNS Light-headedness, tinnitus, metallic taste, visual disturbance, cicumoral numbness, muscle twitching, seizures, loss of consciousness

Treatment: stop injection, oxygen, midazolam 1-2 mg, thiopentone 50-200 mg

CVS ▼contract., ▼ conduct., VD ►collapse (esp. Bupivacaine)

Treatment: oxygen, volume, vasopressors ►ACLS

Local Anesthetics: Spinal Anesthesia

Spinal Needle: 25G pencil point with 19G introducer

Position: Sitting or lateral

Level: L3-4, L4-5

Approach: Midline or paramedian

Drugs: Bupivacaine (Heavy) 0.5% 2-3 mls

Local Anesthetics: Spinal Anesthesia

Complications:

Hypotension►0.5-1L of LR before the block, ephedrine 5-10 mg boluses

Bloody tap► if does not clear rapidly, withdraw & reinsert

Nausea & vomiting ►treat hypotension

Apnea (total spinal) ►support ventilation

PDPH: bed rest, IV fluids, analgesics, caffeine 30mg, epidural blood patch

Local Anesthetics: Epidural Anesthesia

Epidural Needle: 17G Tuohy needle

Position: Sitting or lateral

Level: L3-4, L4-5

Approach: Midline or paramedian

Drugs: Bupivacaine 0.125- 0.25% 15-20 ml

Techniques: Loss of resistance

Hanging drop method

Test dose: 3 ml lidocaine 1% with epinephrine 1:200,000

Local Anesthetics: Epidural Anesthesia

Drugs: 1.5 ml/segment

Decrease dose 50% in old age

Decrease dose 30% in pregnancy

Epinephrine increase duration

Opioids (fentanyl 50-100 µ) improve the quality

Sodium bicarbonate speeds the onset

Local Anesthetics: Epidural Anesthesia

Complications:

Dural puncture 1% ► Convert to spinal

► Reinsert one space above

Inability to thread the epidural catheter (too lateral, partial bevel insertion)

Insertion into a vein (withdraw)

Catheter break off (inform patient & leave it)

Local Anesthetics: Combined Spinal-Epidural Anesthesia

Combine advantages and avoid disadvantages of both techniques

Rapid onset, solid sacral block, less volume

Longer time, more control on level

Local Anesthetics: Caudal Epidural

Through the sacrococcygeal membrane

Can reach high level in children: 1 ml/kg Bupivacaine 0.2-0.25% with 1;200,000 Epinephrine reach T6-8 level

THANK YOU