Premedication Goals and Sedation Options

Premedication Goals

• Modern premedication aims to relieve anxiety using BZDs (-zolams).
• Goals include sedation, analgesia, prevention of nausea/vomiting, prevention of allergic reactions.
• Further goals are reduction of gastric fluid volume and acidity, and improvement of coagulation.
• The aim is to attenuate autonomic reflexes.

Premedication Cautions in Modern Surgery

• Patients might not be seen until the surgery day, possibly requiring completion of preoperative H&P.
• Patients may need to answer questions and sign documents before surgery.
• Patients may want to ask questions preoperatively.

Early Sedation Options

• Midazolam (BZD --> GABAa), given orally or rectally with Tylenol, has little impact on respiration and may cause prolonged sleepiness.
• Ketamine (CCB/NMDA antagonist), administered orally or IM, provides sedation and analgesia and may cause post-anesthesia delirium or prolong emergence in children.
• Dexmedetomidine (Alpha 2 agonist) is administered IV or intrabuccally (in peds), provides SA and decreases post-operative pain.

Ketamine for Pre-Op

• Oral or IM ketamine provides dose-dependent sedation and analgesia.
• Ketamine can cause postanesthesia delirium, particularly in children, and may lead to prolonged emergence.
• As a dissociative anesthetic, sedative, and analgesic, ketamine is administered IV/IM with rapid onset.
• Ketamine has antidepressant effects, which make it useful for pediatric and trauma/hypovolemic cases,
• It is used for postop pain control (infusion) and maintains airway reflexes.
• Compared to propofol, ketamine triggers less drop in blood pressure.
• It has a direct cardiac depressant effect
• Further, it acts synergistically with GABA agonists.

Contraindications for Depressant Pre-Meds

• Relative contraindications include newborns (<1 year).
• Relative contraindications include elderly, decreased level of consciousness, severe pulmonary disease, obstructive sleep apnea.
• Relative contraindications include hypovolemia.

Pre-Op Anticholinergics (Atropine)

• Anticholinergics reduces secretions (less important currently).
• These are used to prevent bradycardia, especially in newborns, infants, and asymptomatic adults, and act as an antiemetic.

Post-Op Nausea and Vomiting (PONV)

• Anesthetic factors such as opioids, especially postoperatively, nitrous oxide, and anticholinesterases for reversal of neuromuscular blockade, can cause nausea and vomiting

Consequences of Post-Op Nausea

• Post-operative nausea and vomiting (PONV) can cause adverse consequences.
• Adverse consequences put tension on abdominal and thoracic sutures.
• Aspiration, increased venous back pressure in the head and neck and increased intracranial and ocular pressure may further result.

Measures to Prevent Aspiration

• Aspiration prophylaxis involves using an H2 blocker to reduce gastric acid production.
• Aspiration prophylaxis can involve a gastropropulsive agent (metoclopramide) unless GI obstruction is present.
• It is important to use a non-particulate antacid.
• Rapid sequence induction with cricoid pressure can also be used in an emergency.

Nondepolarizing Muscle Relaxants

• There are two types of muscle relaxants, depolarizing and nondepolarizing.
• Nondepolarizing agents include Rocuronium, atracurium, cisatracurium, pancuronium, tubocurarine, mivacurium, and doxacurium.
• Nondepolarizing relaxants block the receptors; thus, acetylcholine can't work.

Clinical Use of Muscle Relaxants

• Muscle relaxants facilitate tracheal intubation through paralyzing pharyngeal muscles and preventing bucking and coughing.
• They provide muscle relaxation for surgery and reduce violent seizures with limb movement during electric shock therapy (ECT).
• Muscle relaxants prevent muscles from shivering in therapeutic hypothermia to minimize cerebral injury.
• These prevent patient-ventilator dyssynchrony, which stops a patient from fighting the ventilator.

Reversal of Muscle Relaxation

• Reversal of NMB requires giving reversal agents in combination with a muscarinic antagonist.
• This is because the dramatic increase in acetylcholine would cause an overdose at the muscarinic receptors.

Signs of Termination

• Head lift or leg lift for 15 seconds, grip strength test, and a nerve stimulator are signs of termination
• Nerve stimulator is the most objective test.
• Train of four involves stimulating the nerve 4 times to test muscle response/twitch using an electrode at the thumb.
• Even if 4/4 responses (twitches) are present, 70-75% of receptors could still be blocked.
• 8% of patients in the recovery room have residual blockade.

Muscle Relaxants and Tachydysrhythmias

• Depolarizing and nondepolarizing agents are the two types of muscle relaxants.

Depolarizing Muscle Relaxants

• Succinylcholine (sux) is the only example in clinical use.
• The adverse effects are myalgias from fasciculation, transient serum K+ increase, malignant hyperthermia trigger, tachydysrhythmias, and bradycardia (especially in children).

Non-depolarizing Muscle Relaxants and Hyperkalemia Risk Factors

• Hyperkalemia can stop the heart / cause dysrhythmias.
• It can be caused by muscle injury, which is K+ release from the muscle or denervation of muscles.
• Muscle injury from burns, bodily crush, massive trauma, bedbound patients w/ atrophy, myopathies, and rhabdomyolysis.
• Denervation of Muscles due to UMN injury (stroke), demyelinating lesion, denervation injury, head trauma, polyneuropathies, encephalopathy, and SC injury

Pre-Op Evaluation Protocols

• Elements of evaluation include: medical history, physical exams, and patient history, labs, and testing.

Elements of Evaluation

• A medical history of allergies, cardiac history, pulmonary history, hematologic Hx, renal Hx, prior anesthesia/surgery, meds, and supplements
• Physical exams should include vitals, heart, lungs, airway, OSA eval, fluid status.
• Patient history should take into account planned procedure, family history, NPO, and any acute changes.

Labs and Testing

• Tests that won't change management should be avoided
• False positives can result, leading to unnecessary further testing and procedures.

Tests Driven by H&P: Indications

• Coagulation studies should be conducted if there is a history of excessive bleeding or a known coagulation disorder, liver disease, malnutrition / vit K deficiency, or anticoagulant use.
• CXR: COPD, Lung Operation or symptomatic smoker should be checked but otherwise age does not matter.
• EKG for asymptomatic heart disease should be carried out if the patient displays arrhythmias or symptoms, risk factors for CAD, high-risk surgery, long procedures, and neurosurgery or spinal surgery patients but otherwise age does not matter.
• Electrolytes should be checked for patients with diabetes, kidney disease, lithium use, contrast use, or use of medications that affect kidney function
• A CBC is indicated with a history of anemia/bleeding, immune deficit, chemo/radiation history, chronic renal failure, or bleeding/bruising.
• Check blood type.
• Get Pregnancy test (bHCG) for women, but avoid when patient refuses.

Minimally Invasive Procedures and Tests

• Minimally invasive surgery (cataracts, knee arthroscopy, etc.) usually requires no pre-op testing without specific indications.
• Testing indicated are short cases w/ no fluid shifts or abnormal tests in the absence of abnormal history/symptoms.

ASA Physical Status

• ASA physical status (PS) classification compares groups of patients, classifies physical status, and is designed as a simple description of the patient's condition.
• It is useful for comparing groups of patients in studies, only deals with physical status, and does not take the procedure into account.
• ASA 2= pts w/ asthma but under control, ASA 3= not under control, ASA 4 = constant threat to life, ASA 5= my patient is dying.
• If it's a heart failure, move 3 → 4.

Surgeon and Anesthesiologist Responsibility for Pre-Op Clearance

• The surgeon is responsible for surgical clearance
• An anesthesiologist is responsible for anesthesia clearance.

Management of Steroid Use and Elective Procedures

• Patients using steroids recently may have impaired adrenal function, usually requiring 100mg IV hydrocortisone pre-anesthesia and 100mg every 8 hours.
• There is risk of acute Addisonian crisis w/ refractory hypotension
• Check to see if Steroid use longer than 2 weeks previously.

Management of Pre-Op Meds: Problematic Meds

• Diabetic medications can be problematic: insulin, oral hypoglycemic agents (metformin), and GLP-1 drugs
• Take ½ dose of insulin.
• Hold oral hypoglycemic agents (metformin) and GLP-1 drugs b/c usually hyperglycemic the day of surgery (stress increased).
• Hold SLGT-2 drugs 3 to 4 days prior to the procedure.
• ACEIs (-pril) and ARBs (-sartan); antihypertensives other than these are okay before operation.
• Naltrexone medications for opioid use disorder should be stopped 3 days prior to surgery.
• MAO inhibitors (also tramadol and St John’s Wort).
• Anticoagulants and antiplatelet medications can pose a big issue.

Supplemental Oxygen and Sedated Patients

• Sedation and anesthesia can reduce ventilation.
• These reduce ventilation by diminished response to hypoxia and hypercarbia. Reduced muscle tone can be attributed.
• Reduction in tidal volume and/or possible obstruction are possible.
• Pre and post supplemental O2 is given.
• Nasal Cannula, HFNC (High-Flow Nasal Cannula), and Masks are all options.

Supplemental Oxygen Types

• All these devices can be used in a conscious/responsive patient and are simple to use with no special expertise required,
• None increase tidal volume significantly.
• None actively remove CO2, or treat obstruction.

Management of Upper Airway Obstruction

• You must relieve the obstruction.
• Chin lift pulls the tongue forward away from the throat.
• Head tilt lines up the oral, pharyngeal, and laryngeal axes, which allows for a straight path for airflow
• Jaw thrust is used if suspect cervical injury.

Successful Endotracheal Intubation: Placement of ETT

• Checking for placement of ETT (endotracheal tube) through bilateral breath sounds, absence of sounds in the stomach, chest wall movement, and vapor in ETT is imperative.
• Expired CO2 is the winning value.

Evaluating Signs of Upper Airway Obstruction

• Look for the following signs: Rocking boat movement, accessory muscles start to work harder.
• The clavicle becomes prominent w/ inspiration, rocking chest motion (chest falls + abd rises → opposite of normal) appears.
• Diaphragm descends maximally → push abd contents up (abd rises), negative pressure w/o air coming into the chest cavity (chest falls), and a nasal flaring appear.
• Faint/absent breath sounds and Cyanosis (late and unreliable sign) → indicates O2 saturation < 85%.

Ambu Bag Use

• Proper mask seal is imperative, don't press too hard on the patient's face, and don’t fight the patient’s ventilation.
• Used once airway is established from #21

Signs of Difficult Airway

• Indicators: short mento-hyoid / mento-thyroid distance, prominent maxilla, immobility of TMJs, and inability to fully open mouth.
• Indicators range from long overriding incisors, limitations of neck extension/flexion to thick neck.
• FONA – Front of Neck Airway as 1. Cricothyrotomy or 2. Tracheostomy / Tracheotomy are performed.
• Mallampati score describes and predicts intubation difficulty during pre-op (III or IV will be difficult intubation).

Cormak Lehane Grades

• During direct laryngoscopy, Grades are the view of the glottis.
• Grades III or IV will be difficult intubation
• 1: see everything; 2: see vocal cord; 3: see the hood of epiglottis; 4: cannot see epiglottis

Rapid Sequence Induction

• Rapid sequence induction is used if intubation is unsuccessful.
• Preoxygenation and Hypnosis/sedation are critical.
• Intubation involves higher failure rate.

Indications for Rapid Sequence Induction

• In cases of those at high risk of aspiration: Pregnant, obese, recently eaten fatty meal, Trauma pt, Delayed gastric emptying, Pt who swallowed gastrograffin (constant), and Pt w/ bleeding in mouth, oropharynx, or upper GI.

Aspiration Injury (Prevention)

• Aspiration the main risk of between induction + securing the airway.
• Aspiration has worse outcomes with rapid intubation.

Aspiration Pneumonia

• Particulate aspiration is more dangerous, and non-particulate antacids should be used to decrease risk.
• Fecal aspiration has the highest mortality.
• Alveolar Capillary Breakdown: Interstitial edema, Intra-alveolar hemorrhage, Atelectasis, Increase airway resistance, and Hypoxia are issues.

Prevention of Aspiration

• H2 blocker decreases the production of gastric acid.
• A Gastropropulsive agent (metoclopramide) unless a GI obstruction in present.
• A non-particulate antacid should be used. Rapid sequence induction w/ cricoid pressure if used.

Cardiovascular Complications of General Anesthesia, Atelectasis

• Pulmonary complications: Post-op hypoventilation and or Post-op ciliary dysfunction.
• Post-op ciliary dysfunction means is there is Poor clearance of pulmonary secretions!

Atelectasis

Atelectasis is due to the following:

• Worsened V/Q mismatch & shunt post-op, or can be prevented/treated by mobilizing the patient quickly and using an incentive spirometer

Cardiac/Cardiovascular

• Cardiac/cardiovascular issues: Hypotension, Hypertension, Arrhythmias, worsening of conduction defects,Perioperative myocardial infarction, Myocardial depression (pump failure), Significant fluid shifts, and or Thrombo-embolic phenomena.

Patients at Risk for Aspiration, Brochospasm Anesthesia

• Pregnant women (from the start of the second trimester).
• Obese patients and Patients who have recently eaten (esp. Meals high in fat).

At Risk due to Aspiration

• Patients who have recently swallowed gastrograffin.
• Pts w/ delayed gastric emptying (bowel obstruction, acute abdomen, ileus, narcotic use, etc.).

Bronchspasm Risk

• Bronchospasm – patients at risk: History of asthma or COPD, History of smoking, or Current or recent respiratory tract infection. You’ll see an inflamed, hyperreactive airway.

Hypotension during General Anesthesia

• Hypotension during GA is usually due to decreased cardiac output (CO), reduced systemic vascular resistance (SVR), or hypovolemia.

Causes of Low BP

• Chronic hypotension can cause labile BP during case
• Cardiac MI → low BP, or a Rapid fluid shift → low BP

Post Op Hypoventilation

• Post-op hypoventilation due to Related to meds: opiates, NMB (decrease ventilation).
• Related to pain: “splinting”(decrease breathing – hypoventilate).

Closing Capacity

• Closing capacity increase in children ( 6) and elderly (> 60) compared to FRC (functional residual capacity).

Children and Elderly

• They have increased atelectasis → increased V/Q mismatch → increased problems w/ ventilation Worsen post-op atelectasis or Prolong recovery time.

Small Children Respiration

• Dec resp muscles
• Dec strength
• Inc wall compliance
• Less recoil.

Small Children Diaphragm

• Cardiac/cardiovascular system – child
• Heart muscle is weaker and less stiff or Limited stroke volume

Limited Stroke Volume

• Not responsive to increased venous return (preload)
• Cardiac output (CO) = stroke volume (SV) x heart rate (HR)
• Cant increase SV response to demand; Very dependent on HR Bradycardia = low CO
• Neonate w/ HR , give red cells, plasma, and platelets in a ratio of 1:1:1 to increase oxygen support and better lung function.
• This is especially needed with hypoxia
• High blood volume per kga

Treatment for Reaction

• Packed Red Blood Cells (PRBCs).
• Plasma (FFP)orCryoprecipitate
• Platelets Hematocrit levels in small children Neonates have Hct 60% compared to adults 40-45%