Pain Control and Monitoring in Surgery

Pain Control

• Pain relief is crucial for proper recovery and minimizing complications.
• Preoperative visits can significantly benefit patients by addressing concerns and preparing them for surgery.
• Unrelieved pain can lead to numerous postoperative complications.
• Individual pain perception is influenced by factors like age, personality, premedication, surgical site, and anesthetic technique.
• Various administration routes are available, including IV, IM, oral, epidural, and rectal.
• Preemptive analgesia aims to prevent pain by reducing noxious stimuli and minimizing the need for higher doses of analgesics post-surgery.
• Patient-controlled analgesia (PCA) empowers patients to administer small doses of opioids for self-management of pain.
• PCA requires patients to be alert, and it involves setting specific bolus doses and lockout periods to avoid overuse.

Monitoring

• Monitoring is essential for patient safety and assessing physiological changes during surgery.
• While monitors with alarms enhance safety, they do not substitute for the anesthetist's vigilance.
• Physical examination combined with monitoring ensures optimal patient care.
• Basic monitoring includes blood pressure cuff, ECG, pulse oximeter, stethoscope, temperature probe, and capnometer (if intubated).
• Monitoring equipment and strategies vary based on surgery type, duration, location, and the patient's pre-existing conditions.

Pulse Oximeter

• Non-invasive device that measures oxygen saturation (SaO2) by detecting light absorption by hemoglobin.
• It provides valuable information about oxygenation status, especially during general anesthesia.
• It can display pulse waveforms for further analysis.
• Inaccurate readings can occur due to hypotension, vasoconstriction, dyes, nail polish, other hemoglobin types, limb compression, and movement.

Capnometer

• Measures exhaled carbon dioxide (CO2) to assess lung ventilation and cardiac output.
• It confirms endotracheal tube placement.

ECG

• Monitors heart rate, rhythm, and potential changes like ST segment elevation or depression, indicating cardiac abnormalities.

Other Commonly Used Devices

• Blood pressure cuff (manual or automatic)
• Stethoscope (precordial, esophageal)
• Thermometer (surface or core)
• Peripheral nerve stimulators (for monitoring neuromuscular blockade)
• Machine function monitors (volume, pressure, inspired oxygen alarms)
• Mass spectrometer/gas analyzer (identifies and measures inhaled/exhaled gases)

Less Frequently Used Monitors

• Urinary catheter and urometer
• Central venous line (for rapid fluid infusion, vasoactive drug delivery, and CVP measurement)
• Arterial line (for continuous blood pressure monitoring and frequent ABG sampling)
• Swan-Ganz catheter (measures CVP, PCWP, pulmonary artery pressures, cardiac output, mixed venous blood gases, and core temperature)
• Intracranial pressure (ICP) monitoring
• Electroencephalogram (EEG), brain and spinal cord evoked potentials
• Transcutaneous gas measurements
• Transesophageal echocardiography (TEE)

General Anesthetic Agents

• General anesthesia (GA) involves delivering anesthetic drugs (inhaled or infused) to achieve a desired state of central nervous system (CNS) depression.
• The "6 A's" of anesthesia encompass: anesthesia (loss of consciousness), analgesia (pain control), amnesia (loss of recall), areflexia (muscle relaxation), autonomic areflexia (decreased sympathetic nervous system function), and antiemetic (nausea and vomiting prevention).

Opioids

• Opioids are medications that bind to opioid receptors (also known as morphine receptors) in the brain and spinal cord, resulting in various effects.
• Opioid receptors play roles in pain perception, mood modulation, and respiratory depression.
• Commonly used for pre-, intra-, and postoperative analgesia, and as induction agents.
• They reduce the minimum alveolar concentration (MAC) required for volatile anesthetics.

Morphine

• Prototype opioid with numerous effects, primarily impacting the central nervous system (CNS) and various organ systems.
• CNS effects include analgesia, mood changes, sedation, respiratory depression, and decreased cough reflex.
• Other effects include vasodilatation, orthostatic hypotension, bronchial constriction, constipation, biliary colic, urinary retention, and histamine release.

Volatile Inhalational Agents

• Inhaled anesthetics are volatile liquids that vaporize at room temperature and enter the bloodstream through the lungs.
• They provide a rapid, reversible effect and are routinely used for inducing and maintaining anesthesia.
• Important considerations include their MAC values, which are essential for determining the required anesthetic depth.
• Commonly used agents include halothane, enflurane, isoflurane, sevoflurane, and nitrous oxide.

Complications of General Anesthesia

• Malignant hyperthermia (MH) is a rare but potentially fatal reaction to certain anesthetic agents, usually triggered by succinylcholine (SCh) or inhalational agents.
• MH presents with hyperthermia, muscle rigidity, tachycardia, tachypnea, and metabolic acidosis.
• Prevention involves careful patient history, avoiding triggering agents, and utilizing alternative medications.
• Management includes rapid discontinuation of triggering medications, hyperventilation with 100% oxygen, administration of dantrolene (muscle relaxant), and supportive care.

Myocardial Infarction (MI)

• Elective surgeries are generally postponed for 6 months after an MI to minimize the risk of reinfarction or death.
• Perioperative MI carries a high mortality rate.
• Invasive monitoring and intensive care unit (ICU) management can reduce this risk.

Respiratory Diseases

• Pulmonary disease can complicate ventilation and the delivery of volatile anesthetics, requiring careful pre-operative optimization and close intra- and postoperative monitoring.

Aspiration Syndrome

• The severity of gastric aspiration depends on the volume, acidity, and contamination of the aspirate, as well as the patient's health status.
• Avoiding reflex inhibition, reducing gastric volume and acidity, and employing rapid sequence induction can help prevent aspiration.

Airway Management

• Most acute airway problems in an unconscious patient can be managed with:
  • 100% O2 with the patient in the lateral position (contraindicated in known suspected C-spine fracture)
  • head tilt via extension at the atlanto-occipital joint (contraindicated in known/suspected C-spine fracture)
  • jaw thrust via subluxation of temporomandibular joint (TMJ)
  • suctioning (secretions, vomitus, foreign body)
  • positioning to prevent aspiration
  • inserting oro- or naso-pharyngeal airway
• Nasopharyngeal airway is indicated if an oropharyngeal airway is difficult (e.g. trismus, mouth trauma):
  • large adult 8-9 mm, medium adult 7-8 mm, small adult 6-7 mm internal diameter
  • complications include tube too long (esophagus), laryngospasm, vomiting, nasal mucosa injury and bleeding
• Oropharyngeal airway holds tongue away from the posterior wall of the pharynx:
  • large adult 100 mm, medium adult 90 mm, small adult 80 mm
  • facilitates suctioning of pharynx
  • prevents patient from biting and occluding endotracheal tube (ETT)
  • complications include tube too long (epiglottis vs. larynx obstruction), improper insertion (posterior tongue push)
• More advanced airway techniques include tracheal intubation (orally or nasally), cricothyroidotomy, tracheostomy.

Tracheal Intubation

• Definition: Insertion of a tube into the trachea either orally or nasally

Indications for Intubation - the 5 Ps

• Patency of airway required:
  • decreased level of consciousness (LOC)
  • facial injuries
  • epiglottitis
  • laryngeal edema (e.g. burns, anaphylaxis)
• Protect the lungs from aspiration:
  • absent protective reflexes (e.g. IV fluids)

IV Anesthetics (Excluding Opioids)

• IV administration provides rapid onset of effects:
  • given as a bolus or continuous infusion, titrated to effect
• Common agents used for induction:
  • Thiopental (Sodium Thiopental, Sodium Thiopentone, STP)
    • ultrashort-acting thiobarbiturate
    • most commonly used as an induction agent
    • prepared as a pale yellow 2.5% solution with pH 10.5 (alkaline)
    • rapid distribution to vessel rich organs (brain, liver, heart, kidney) leading to unconsciousness in 30 seconds
    • rapid redistribution from vessel rich tissues to muscle and fat causes short lived effect (5 minutes)
    • slow metabolism and elimination (T1/2 =5-12 hrs), resulting in residual sedation for hours
    • effects include unconsciousness, decreased cerebral metabolism and O2 requirements, reduction of cerebral blood flow, decrease in CO, BP, reflex tachycardia, respiratory depression (apnea with bolus dose).
    • no analgesic properties, may actually increase subjective feeling of pain (anti-analgesia)
    • no muscle relaxant properties
    • contraindications: lack of intubation and resuscitation equipment, potential difficult intubation, hypersensitivity, untreated hypovolemia, hypotension, shock-like states, cardiac failure, porphyria

Regional Anesthesia

• Definition: Local anesthetic applied around a peripheral nerve at any point for the purposes of reducing or preventing impulse transmission
• No CNS depression (unless overdose of local anesthetic); patient conscious
• Techniques include epidural and spinal anesthesia, peripheral nerve blockades, IV regional anesthesia

Preparation for Regional Anesthesia

• Patient Preparation:
  • thorough pre-op evaluation and assessment of patient
  • technique explained to patient
  • IV sedation may be indicated before block
  • monitoring should be as extensive as for general anesthesia
• Nerve Localization:
  • anatomical landmarks, local anatomy (e.g. iliac crests line crosses L3-L4 interspace, axillary artery guides brachial plexus)
  • paresthesias and peripheral nerve stimulation used as a guide to proper needle placement

Relative Indications for Regional Anesthesia

• Avoidance of dangers of general anesthesia (e.g. difficult intubation, severe respiratory failure)
• Patient specifically requests regional anesthesia
• For high quality post-op pain relief
• General anesthesia not available

Contraindications to Regional Anesthesia

• Allergy to local anesthetic
• Patient refusal, lack of cooperation
• Lack of resuscitation equipment
• Lack of IV access
• Coagulopathy
• Certain types of preexisting neurological dysfunction
• Local infection at block site

Complications of Regional Anesthesia

• Failure of technique
• Systemic drug toxicity due to overdose or intravascular injection
• Peripheral neuropathy due to intraneural injection
• Pain or hematoma at injection site
• Infection

Nerve Fibres

• Different types categorized as follows:
  • Sensory blockade with relative preservation of motor function (for pain management)
  • Motor blockade with relative preservation of sensory function (for surgery)
  • Complete blockade (both sensory and motor)
  • potential for toxicity

Maximum Doses for Local Anesthetics (LA)

• Always be aware of the maximum dose for the particular LA used
• Maximum dose usually expressed as (mg of LA) per (kg of lean body weight) and as a total maximal dose (adjusted for young/elderly/ill)
• Lidocaine maximum dose: 5 mg/kg (with epinephrine: 7mg/kg)
• Chlorprocaine maximum dose: 11 mg/kg (with epinephrine: 14 mg/kg)
• Bupivacaine maximum dose: 2.5 mg/kg (with epinephrine: 3 mg/kg)

Systemic Toxicity

• Occurs by accidental intravascular injection, LA overdose, or unexpectedly rapid absorption
• Systemic toxicity manifests mainly at CNS and CVS
• CNS effects first appear excitatory due to initial block of inhibitory fibres; subsequently, block of excitatory fibres
• CNS effects (in approximate order of appearance):
  • numbness of tongue, perioral tingling
  • disorientation, drowsiness
  • tinnitus
  • visual disturbances
  • muscle twitching, tremors
  • convulsions, seizures
  • generalized CNS depression, coma, respiratory arrest

Transfusion reactions

• Febrile - most common mild reaction (0.5% - 4%).
• Due to alloantibodies to WBC, platelet, or other donor plasma antigens
• Fever likely caused by pyrogens liberated from lysed cells
• More common if previous transfusion
• Mild fever < 38° with or without rigors, fever may be > 38° with restlessness and shivering
• Nausea, facial flushing, headache, myalgias; hypotension, chest and back pain (less common)
• Occurs near completion of transfusion or within 2 hours
• Up to 40% with mild reactions will not experience another reaction with future transfusions
• With severe/recurrent reactions, future transfusions may cause leukocyte depletion

Allergic

• Occurs in about 3% of transfusions
• Due to IgE alloantibodies vs. substances in donor plasma
• Mast cells activated with histamine release
• Usually occurs in pre-exposed e.g. multiple transfusions, multiparous
• Often have history of similar reactions
• Abrupt onset pruritic erythema/urticaria on arms and trunk, occasionally with fever
• Less common - involvement of face, larynx, and bronchioles

Pain Control

• Goal is to provide pain relief safely with minimal disturbance of homeostasis
• Unrelieved pain can be the cause of many postoperative complications
• Factors influencing the degree of pain include age, personality, premedication, surgical site, and anesthetic technique
• Routes - IV, IM, oral, epidural, rectal
• Preemptive analgesia
  • Prevent/reduce noxious stimuli which potentiate peripheral and central pain mechanisms
  • In postoperative period the dose of analgesic is decreased and the side effects are less frequent
  • Use - NSAID's, opioids, local anesthetics, combined agents
• PCA (patient controlled analgesia)
  • Self-administration of small doses of opiates via pump
  • Bolus dose is preset
  • Lockout period is set to limit frequency of self-administration
  • Requirements - oriented patient, IV, SC, or epidural access

Monitoring

• Provides information that improves the safety of anesthesia and provides a means to assess physiological function
• Appropriate monitors with alarms are intended to enhance but not replace the vigilance of the anesthetist
• Physical examination, observation, assessment, and diagnosis remain the most important tools available to the anesthetist
• Routine monitors for all cases: BP cuff, ECG, O2 sat monitor, stethoscope, temperature probe, exposed part of patient visible, capnometer if intubated
• Organ systems monitored and other devices used to monitor will vary depending on the nature, length, location, and systems involved in the surgery, and patient’s pre-existing condition/diseases

Pulse Oximeter

• Measures SaO2 by red and infrared light absorption by Hb; oxygenated and deoxygenated Hb have different absorption characteristics
• Non-invasive
• Can show pulse waveforms on suitably equipped monitors
• If ventilation is accidentally terminated, the SaO2 may remain normal for several minutes in a well oxygenated patient due to the high partial pressure of O2 remaining in the lungs
• Inaccurate with hypotension, vasoconstriction, dyes
• Propofol (Diprivan)
  • Unique agent in its own class (an alkyl phenol)
  • Used for induction and/or maintenance of anesthesia
  • Thick white soybean-based solution
  • Pharmacological effects similar to that of thiopental; thus similar contraindications but is safe for porphyria patients
  • Metabolism and elimination much more rapid due to increased rate of liver metabolism compared to thiopental
  • Less residual sedative effect, patient recovers sooner (T1/2 = 0.9 hr), thus popular for out patient surgery since reduces post-anesthesia recovery time; decreased incidence of nausea and vomiting
  • More suited for continuous infusion than STP due to rapid elimination
  • More expensive

Benzodiazepines

• Also known as the minor tranquilizers
• Used as a premedication prior to induction or as an induction agent in combination with other drugs
• Oral and injectable formulations available
• Act on specific brain (GABA) receptors to produce selective anti-anxiety and sedative effects; in correct doses, causes only slight depression of CVS and respiratory systems
• Onset less than 5 minutes if given IV
• Duration of action long but variable/somewhat unpredictable
• Benzodiazepine antagonist flumazenil (Anexate)
  • Competitive inhibition
  • Does not affect benzodiazepine metabolism, therefore once effects of reversal wear off, sedation may return

Neuroleptics

• Also known as the major tranquilizers, rarely used in anesthesia
• Blockade of dopamine receptors at various locations in CNS
• Droperidol used in low dose as antiemetic

Narcotics/Opioids

• Opium: natural product derived from poppy plant extract
• Opiates: derived from opium

Regional Anesthesia

• Definition of regional anesthesia
• Preparation of regional anesthesia
• Nerve Fibres
• Epidural and Spinal Anesthesia
• IV Regional Anesthesia
• Peripheral Nerve Blocks
• Obstetrical Anesthesia

Local Infiltration, Hematoma Blocks

• Relatively safe – avoid intraneural injection and neurotoxic agents

Local Anesthetics

• Provides good operating conditions

Obstetrical Anesthesia

• All patients entering the delivery room potentially require anesthesia, whether planned or as an emergency
• Adequate anesthesia of obstetric patients requires a clear understanding of maternal and fetal physiology
• Options for pain relief during parturition (labour) are
  • Psychoprophylaxis – Lamaze method
    • Patterns of breathing and focused attention of fixed object
  • Systemic medication
    • Easy to administer but risk of maternal or neonatal depression
    • Common drugs: opioids, tranquilizers, ketamine
  • Regional anesthesia
    • Provides excellent analgesia with minimal depressant effects in mother and fetus
    • Hypotension as a consequence of sympathectomy is the most common complication
    • Maternal BP monitored q2-5 min for 15-20 min after initiation and regularly thereafter
    • Techniques used: epidural, combined spinal epidural, pudendal blocks, spinal, paracervical, lumbar sympathetic blocks
  • Inhalational analgesia
    • Easy to administer, makes uterine contractions more tolerable, but does not relieve pain completely
    • 50% nitrous oxide
• Anesthesia for cesarean section
  • Regional - spinal or epidural

Extrarenal Na+ Loss

• Gastrointestinal causes: vomiting, nasogastric suction, drainage, fistulae, diarrhea
• Skin/Respiratory causes: insensible losses (fever), sweating, burns
• Vascular causes: hemorrhage

Renal Na+ and H2O Loss

• Diuretics
• Osmotic diuresis
• Hypoaldosteronism
• Salt-wasting nephropathies

Renal H2O Loss

• Diabetes insipidus (central or nephrogenic)

Hypovolemia with Normal or Expanded ECF Volume

• Decreased cardiac output (CO)
• Redistribution: hypoalbuminemia (cirrhosis, nephrotic syndrome), capillary leaking (acute pancreatitis, rhabdomyolysis, ischemic bowel)

Management of Dehydration

• Replace water and electrolytes based on patient needs
• With chronic hyponatremia, correction should be over >48 hours to avoid CNS central pontine myelinolysis

Signs and Symptoms of Dehydration

• Mild (5% loss): decreased skin turgor, sunken eyes, dry mucous membranes, dry tongue, reduced sweating
• Moderate (10% loss): oliguria, orthostatic hypotension, tachycardia, low volume pulse, cool peripheries, reduced filling of peripheral veins and central venous pressure (CVP), hemoconcentration, apathy
• Severe (15% loss): profound oliguria and compromised CNS function with or without altered sensorium

Febrile Reaction to Transfusion

• Most common mild reaction, 0.5%-4% of transfusions
• Due to alloantibodies to WBC, platelet, or other donor plasma antigens
• Fever likely caused by pyrogens liberated from lysed cells
• More common if previous transfusion
• Mild fever < 38° with or without rigors, fever may be > 38° with restlessness and shivering
• Nausea, facial flushing, headache, myalgias; hypotension, chest and back pain (less common)
• Near completion of transfusion or within 2 hours
• Up to 40% with mild reactions will not experience another reaction with future transfusions
• With severe/recurrent reactions, future transfusions may cause leukocyte depletion

Management of Febrile Reaction to Transfusion

• Rule out fever due to hemolytic reaction or bacterial contamination
• Mild < 38°: decrease infusion rate and antipyretics
• Severe: stop transfusion, antipyretics, antihistamines, symptomatic treatment

Allergic Reaction to Transfusion

• Mild allergic reaction occurs in about 3% of transfusions
• Due to IgE alloantibodies vs substances in donor plasma
• Mast cells activated with histamine release
• Usually occurs in pre-exposed individuals (e.g., multiple transfusions, multiparous)
• Often have history of similar reactions
• Abrupt onset pruritic erythema/urticaria on arms and trunk, occasionally with fever
• Less common: involvement of face, larynx, and bronchioles

Management of Allergic Reaction to Transfusion

• Mild: slow transfusion rate, IV antihistamines
• Moderate to severe: stop transfusion, IV antihistamines, subcutaneous epinephrine, hydrocortisone, IV fluids, bronchodilators
• Prophylactic: antihistamines 15-60 minutes prior to transfusion, washed or deglycerolized frozen RBC

Preoperative Optimization

• Diuretics, oral hypoglycemics, anticoagulants, steroids, monamine oxidase inhibitors (MAOI), and drugs with CNS side effects
• Optimization of medical treatment preoperatively will reduce peri- and postoperative complications
  • Diabetes mellitus (DM): optimize glycemic control
  • Nutritional status: correct malnourished states
  • Smoking: encourage cessation
  • Obesity: encourage weight loss
  • Chronic obstructive pulmonary disease (COPD): optimize respiratory status, teach postoperative exercises (e.g., incentive spirometry)

Anesthesia History

• Previous anesthetic experience and complications, previous intubations, medications drug allergies, and allergies to topical preparations
• Focused review of systems
  • CNS: seizures, transient ischemic attack (TIA), cerebrovascular accident (CVA), raised intracranial pressure (ICP), spinal disease, arteriovenous malformation (AVM)/aneurysm, neuromuscular disease
  • Resp: smoker, asthma, COPD, upper respiratory tract infection (URTI), dyspnea, stridor
  • CVS: angina/coronary artery disease (CAD), MI, HTN, congestive heart failure (CHF), valvular disease, conditions requiring endocarditis prophylaxis, arrhythmia, peripheral vascular disease
  • GI: liver disease, gastroesophogeal reflux disease (GERD), vomiting, diarrhea, last meal
  • Renal: insufficiency, dialysis
  • Hematologic: anemia, coagulation disorders, sickle cell
  • Musculoskeletal (MSK) (arthritis - risk of C-spine subluxation during intubation)
  • Endocrine: diabetes, thyroid, adrenal
  • Other: morbid obesity, pregnancy, ethanol and drug use
• Family history of malignant hyperthermia, atypical cholinesterase (pseudocholinesterase), or other abnormal drug reactions

Anesthesia Physical Examination

• Oropharynx + airway assessment to determine the likelihood of difficult intubation
  • No single test is specific or sensitive - all aid in determination of ease of intubation
  • Degree of mouth opening + TMJ subluxation
  • Jaw size (micro/retrognathia), "thyromental distance"
  • Tongue size
  • Posterior pharynx, tonsillar pillars, uvula easily visible
  • Dentition, dental appliances/prosthetics/caps - inform of possibility of damage
  • C-spine stability, neck flexion/extension
  • Tracheal deviation
  • Nasal passage patency (if planning nasotracheal intubation)
• Mallampati classification of airways
  • Class 1: able to visualize soft palate, fauces, uvula, ant and post tonsillar pillars
  • Class 2: able to visualize all of the above, except anterior andposterior tonsillar pillars are hidden by the tongue
  • Class 3: only the soft palate and base of the uvula are visible
  • Class 4: only the soft palate can be seen (uvula not visualized)
• For emergency operations, add the letter E after classification

Anesthesia Patient Optimization

• From the history, physical exam, and labs/investigations, the anesthetist can determine whether or not the patient is in OPTIMAL condition for the proposed surgical procedure
• Goal is to optimize the non-surgical disease states prior to surgery
• In emergency cases, it is not always possible to optimize coexistent or chronic disease states; goal is then to accomplish what is possible in the time available

Postoperative Management

• Usually begins in O.R. with discontinuation of anesthetic drugs and extubation (exception - if going to intensive care unit (ICU))
• Patient can be transported to post-anesthesia care unit (PACU) when ABC's stable
• Patient can be released from the unit when the PACU discharge criteria for ventilation, circulation, consciousness, motor function, and colour have been met
• Potential complications:
  • CNS: agitation, delirium, somnolence
  • Respiratory: aspiration, upper airway obstruction, hypoxemia, alveolar hypoventilation, upper airway trauma (intubation/extubation)
  • CVS: hypothermia (rewarm patient), shivering (due to hypothermia or postanesthetic effect), hypotension, hypertension, dysrhythmias
  • GI: nausea and vomiting

Regional Anesthesia Definition

• Local anesthetic applied around a peripheral nerve at any point along the length of the nerve (from spinal cord up to, but not including, the nerve endings) for the purposes of reducing or preventing impulse transmission
• No CNS depression (unless overdose (OD) of local anesthetic); patient conscious
• Regional anesthetic techniques categorized as follows:
  • Epidural and spinal anesthesia
  • Peripheral nerve blockades
  • IV regional anesthesia

Regional Anesthesia Preparation

• Patient Preparation:
  • Thorough pre-op evaluation and assessment of patient
  • Technique explained to patient
  • IV sedation may be indicated before block
  • Monitoring should be as extensive as for general anesthesia
• Nerve Localization:
  • Anatomical landmarks, local anatomy (e.g. line joining iliac crests crosses L3-L4 interspace; axillary artery as guide to brachial plexus)
  • Paresthesias and peripheral nerve stimulation used as a guide to proper needle placement

Relative Indications for Regional Anesthesia

• Avoidance of some of the dangers of general anesthesia (e.g., known difficult intubation, severe respiratory failure, etc.)
• Patient specifically requests regional anesthesia
• For high quality post-op pain relief
• General anesthesia not available

Contraindications to Regional Anesthesia

• Allergy to local anesthetic
• Patient refusal, lack of cooperation
• Lack of resuscitation equipment
• Lack of IV access
• Coagulopathy
• Certain types of preexisting neurological dysfunction
• Local infection at block site

Complications of Regional Anesthesia

• Failure of technique
• Systemic drug toxicity due to overdose or intravascular injection
• Peripheral neuropathy due to intraneural injection
• Pain or hematoma at injection site
• Infection

Nerve Fibres

• Different types categorized as follows:
  • ...

Inspired Oxygen Dilution

• Inspired oxygen (O2) can be diluted by room air
• Facial masks with an O2 reservoir deliver O2 concentrations greater than 60%
• An O2 flow rate of 6L/min provides 60% O2, and each increase of 1L/min O2 concentration by 10%

High Flow Oxygen Systems

• Venturi masks provide consistent and predictable inspired O2 concentrations (FIO2)
• Venturi masks allow for the control of gas humidity

Total Body Water (TBW)

• In a 70kg adult, TBW accounts for 60% of total body weight
• TBW is divided into intracellular fluid (ICF, 2/3) and extracellular fluid (ECF, 1/3)
• ECF further comprises interstitial fluid (3/4) and intravascular fluid (1/4)
• Starling's forces maintain the balance of intravascular fluid

Fluid Balance and ECF Volume

• ECF excess leads to pulmonary edema, dependent edema, S3 heart sound, and increased jugular venous pressure (JVP)
• ECF deficit causes decreased JVP, hypotension, tachycardia, dry mucous membranes, decreased skin turgor, lethargy, weight loss, sunken eyes, decreased urine output, and depressed fontanelle in infants
• Hematocrit decreases with ECF expansion and increases with ECF deficit
• Fluid intake and output determine total body fluid balance, which is influenced by renal function, syndrome of inappropriate ADH secretion (SIADH), diabetes insipidus (DI), osmoles, and drugs (diuretics)

IV Fluid Therapy

• Total fluid requirement is calculated by adding maintenance, deficit, and ongoing losses, and subtracting oral intake, total parenteral nutrition (TPN), and medication solutions
• Dehydration is classified into mild (less than 5% TBW loss), moderate (5-10% TBW loss), and severe (greater than 10% TBW loss)
• Total sodium content controls ECF volume, while sodium concentration determines ICF volume

Anaphylactic Shock

• A rare but potentially lethal reaction in IgA deficient patients with anti-IgA antibodies
• Immune complexes activate mast cells, basophils, eosinophils, and the complement system, causing symptoms after transfusion of blood products containing IgA
• Symptoms include apprehension, urticarial eruptions, dyspnea, hypotension, laryngeal and airway edema, wheezing, chest pain, shock, and sudden death
• Management involves circulatory support with fluids, catecholamines, bronchodilators, and respiratory assistance as indicated

Transfusion-Related Acute Lung Injury (TRALI)

• A form of noncardiogenic pulmonary edema occurring 2-4 hours after transfusion
• An immunologic cause, unrelated to fluid overload or cardiac failure
• Respiratory distress ranging from mild dyspnea to severe hypoxia
• Chest x-ray shows acute pulmonary edema, but pulmonary artery and wedge pressures are not elevated
• Usually resolves within 48 hours with O2, mechanical ventilation, and supportive treatment

Immunosuppression

• Studies associate perioperative transfusion with postoperative infection, earlier cancer recurrence, and poorer outcome

Immune-Hemolytic Transfusion Reactions

• The most serious and life-threatening transfusion reaction
• Caused by donor incompatibility with recipient blood

Non-Immune Transfusion Reactions

• Infectious risks include HIV, hepatitis, Epstein-Barr virus (EBV), cytomegalovirus (CMV), brucellosis, malaria, salmonellosis, measles, and syphilis
• Hypervolemia and electrolyte changes, particularly increased potassium in stored blood
• Coagulopathy, hypothermia, citrate toxicity, and hypocalcemia

Shock

• Remember that hypotension is not synonymous with shock
• Shock refers to inadequate organ perfusion
• General approach involves:
  • ABCs first
  • Identification of the cause
• General management includes O2, fluids, inotropes, and monitoring urine output, vital signs, central venous pressure (CVP), and potentially pulmonary capillary wedge pressure (PCWP)
• Beware of complications, such as hypovolemic shock leading to cardiac ischemia and cardiogenic shock

Types of Shock

• S: Septic/Spinal
• H: Hemorrhage/Hypovolemia
• O: Obstructive
• C: Cardiogenic
• K: Anaphylactic

Septic Shock

• Caused by bacterial (often Gram-negative), viral, or fungal infections
• Endotoxins and mediators cause blood pooling in veins and capillaries
• Associated with contamination of open wounds, intestinal injury, or penetrating trauma, and can occur with minimal history.
• Clinical features include warm skin (fever), decreased JVP, wide pulse pressure, increased cardiac output (CO), decreased systemic vascular resistance, and increased heart rate (HR)
• Initial treatment includes antibiotics and volume expansion

Spinal/Neurogenic Shock

• Decreased sympathetic tone
• Hypotension without tachycardia or peripheral vasoconstriction, resulting in warm skin

Preoperative Optimization

• Diuretics, oral hypoglycemics, anticoagulants, steroids, monamine oxidase inhibitors (MAOI), and drugs with central nervous system (CNS) side effects can influence anesthetic procedures
• Optimize medical treatment preoperatively to reduce peri- and postoperative complications:
  • Diabetes mellitus (DM): optimize glycemic control
  • Nutritional status: correct malnourished states
  • Smoking: encourage cessation
  • Obesity: encourage weight loss
  • Chronic obstructive pulmonary disease (COPD): optimize respiratory status, teach postoperative exercises (e.g., incentive spirometry)

History

• Gather information regarding:
  • Previous anesthetic experience and complications
  • Previous intubations
  • Medications
  • Drug allergies
  • Allergies to topical preparations
• Conduct a focused review of systems:
  • CNS: seizures, transient ischemic attack (TIA), cerebrovascular accident (CVA), raised intracranial pressure (ICP), spinal disease, arteriovenous malformation (AVM)/aneurysm, neuromuscular disease
  • Resp: smoker, asthma, COPD, upper respiratory tract infection (URTI), dyspnea, stridor.
  • Cardiovascular (CVS): angina/coronary artery disease (CAD), MI, HTN, congestive heart failure (CHF), valvular disease, conditions requiring endocarditis prophylaxis, arrhythmia, peripheral vascular disease
  • GI: liver disease, gastroesophageal reflux disease (GERD), vomiting, diarrhea, last meal
  • Renal: insufficiency, dialysis
  • Hematologic: anemia, coagulation disorders, sickle cell
  • Musculoskeletal (MSK): arthritis (risk of C-spine subluxation during intubation)
  • Endocrine: diabetes, thyroid, adrenal
  • Other: morbid obesity, pregnancy, ethanol, and drug use

Family History

• Inquire about family history of malignant hyperthermia, atypical cholinesterase (pseudocholinesterase), or other abnormal drug reactions

Oropharynx and Airway Assessment

• Assess oropharynx and airway to determine the likelihood of difficult intubation
• Multiple factors can affect intubation difficulty:
  • Degree of mouth opening and temporomandibular joint (TMJ) subluxation
  • Jaw size (micro/retrognathia)
  • "Thyromental distance"
  • Tongue size
  • Visibility of posterior pharynx, tonsillar pillars, and uvula
  • Dentition, dental appliances/prosthetics/caps
  • C-spine stability, neck flexion/extension
  • Tracheal deviation
  • Nasal passage patency (if planning nasotracheal intubation)

Mallampati Classification of Airways

• A classification system used to assess airway visibility:
  • Class 1: Visible soft palate, fauces, uvula, anterior and posterior tonsillar pillars
  • Class 2: Visible soft palate, fauces, uvula, but anterior and posterior tonsillar pillars are hidden by the tongue
  • Class 3: Only the soft palate and base of the uvula are visible
  • Class 4: Only the soft palate is visible (uvula not visualized)

Local Anesthetics (LA)

• LA provide sensory blockade while relatively preserving motor function
• Used for both pain management and surgical procedures
• Potential for toxicity

Maximum Doses for Local Anesthetics

• Always be aware of the maximum dose for the LA being used
• Maximum dose is usually expressed as mg of LA per kg of lean body weight and as a total maximum dose
• Maximum doses vary based on the specific LA:
  • Lidocaine: maximum dose 5 mg/kg (with epinephrine: 7 mg/kg)
  • Chlorprocaine: maximum dose 11 mg/kg (with epinephrine: 14 mg/kg)
  • Bupivacaine: maximum dose 2.5 mg/kg (with epinephrine: 3 mg/kg)

Systemic Toxicity

• Occurs due to accidental intravascular injection, LA overdose, or rapid absorption
• Manifests primarily in the central nervous system (CNS) and cardiovascular system (CVS)
• Initial CNS effects are excitatory due to blockade of inhibitory fibers, followed by blockade of excitatory fibers
• CNS effects in approximate order of appearance:
  • Numbness of tongue, perioral tingling
  • Disorientation, drowsiness
  • Tinnitus
  • Visual disturbances
  • Muscle twitching, tremors
  • Convulsions, seizures
  • Generalized CNS depression, coma, respiratory arrest

This quiz explores the importance of pain control and monitoring during surgical procedures. It discusses various pain management techniques, including preemptive analgesia and patient-controlled analgesia, alongside the significance of monitoring for patient safety. Test your knowledge on these critical aspects of surgical care.