Approach to Anesthesia


Problem

Cause

Treatment

Difficulty/failure to ventilate

Circuit disconnection

Check circuit attachments

Obstruction—mucus plug, biting ETT

Suction of ETT, if biting ETT—insert oral airway, deepen anesthesia

Pneumothorax (no breath sounds)

Auscultate patient, inform surgeon

Bronchospasm (wheezing, high airway pressure)

Auscultate patient, 100 % O2, increase depth of anesthesia, beta-2 agonists, epinephrine

Right main stem intubation (low O2 saturation)

Auscultate patient, ETT at lip is usually 23 cm in males and 21 cm in females

Hypoventilation (anesthetic agents—opioids, inhalational agents, muscle relaxants)

Treat accordingly (opioid reversal—naloxone, check for adequate muscle strength recovery, controlled ventilation)

Pulmonary edema (fluid overload)

O2, diuretics

Hypotension

Anesthetic drugs, spinal/epidural anesthesia, blood loss

Vasopressors—phenylephrine (40–100 mcg IV), ephedrine (5–10 mg IV), norepinephrine, dopamine, fluids/blood

Hypertension

Pain

Opioids

Light anesthesia

Deepen anesthesia—propofol, inhalation agent

Increased sympathetic response (increased BP)

Labetalol, metoprolol, esmolol, hydralazine, nitroglycerine, nitroprusside

Tourniquet pain

Deflate tourniquet in consultation with surgeon

Arrhythmias

Anesthetic drugs, spinal anesthesia, venous air embolism, pulmonary embolus, myocardial ischemia

Treatment described in the chapter on cardiac arrhythmias

Anaphylaxis

Antibiotic, muscle relaxants

Epinephrine, O2, fluids

Hypothermia

Use of unwarmed IV fluids or unwarmed irrigation fluid for TURP, general/spinal anesthesia, convective, conductive, radiative, or evaporative fluid loss from the patient

Use of warmed fluids, fluid warmer, forced-air warming device, maintain OR temperature, radiant heat for pediatric patients, humidifier

Hyperthermia

Malignant hyperthermia

Stop the offending agent (inhalational/succinylcholine), dantrolene IV, fluids, supportive care

Sepsis

Antibiotics, vasopressors if needed

Blood transfusion reaction

Stop the transfusion, acetaminophen, diphenhydramine, steroids, fluids

Bradycardia

Increased vagal stimulation-surgical vagal stimulus (cranial, bladder surgery), anesthetic drugs (propofol, fentanyl), spinal anesthesia

Inform the surgeon to stop the surgery momentarily, glycopyrrolate IV

Hypoxia

Correct the ventilation, treat the cause

Myocardial infarction, heart block

See the chapter on cardiac arrhythmias



Steps involved in administration of general anesthesia include preoperative preparation, monitoring, induction of anesthesia, airway management, maintenance of anesthesia, reversal of anesthesia, and postoperative management.


Preoperative Preparation






  • Evaluating the patient—history and physical, airway evaluation, laboratory tests, NPO status—and formulating an anesthetic plan.


  • Preparing the patient for the OR—obtain consent, type and screen/crossmatch, preoperative medication, and line placement (IV, arterial/central line). Side of IV placement for breast surgery/AV fistula is usually opposite to the side of surgery.


  • Preparing anesthesia equipment—anesthesia machine, airway equipment, monitors, fluid warmer, and medications.

[Preoperative medication may include midazolam (sedative), metoclopramide and famotidine/ranitidine (acid prophylaxis), and opioid (if pain relief is required)].


Monitoring


After adequate preoperative preparation, the patient is transported to the operating room and monitors are applied.



  • Basic monitoring—pulse oximeter, noninvasive blood pressure monitoring, and electrocardiogram (rhythm, heart rate). Additional monitors include end-tidal CO2 monitoring, temperature monitoring (skin/esophageal/other), and urine output (if Foley catheter is inserted).


  • Specialized monitoring—nerve stimulator (facial/ulnar nerve, if muscle relaxants are used), inspired oxygen monitor, airway pressure monitor, and inhalational agent monitoring.


  • Arterial line—sites include radial/brachial/femoral/dorsalis pedis arteries. Indications include surgeries associated with significant blood loss and fluid shifts, patients with severe systemic disease, and drawing of repeated samples for blood gas/hematocrit.


  • Central venous pressure line and pulmonary artery catheter—sites include internal jugular/subclavian/femoral veins (the latter mainly for venous access). Indications include patients with significant systemic disease (cardiac/renal) undergoing major surgery, anticipated large fluid shifts and blood loss, and measurement of central venous pressure/cardiac output.


  • Transesophageal echocardiogram (TEE)—to evaluate cardiac function in patients undergoing cardiovascular surgery or in patients with reduced cardiac function undergoing major surgery. It can be also used to evaluate volume status in a patient and thus can be used together/instead of a pulmonary artery catheter.


  • Bispectral index (BIS) monitor—to monitor depth of anesthesia so as to decrease incidence of patient awareness under anesthesia. It processes electroencephalogram (EEG) to give a number (up to 100). The higher the number, the more awake the patient. A number below 60 is aimed for adequate depth of anesthesia.


Induction of Anesthesia


Once the monitors are applied to the patient, the preinduction vital signs are measured (BP, HR, O2 saturation). The next step is to preoxygenate the patient with 100 % O2 via the anesthesia circuit. In emergency, trauma, or cesarean section patients, additional preinduction considerations may include full stomach precautions, possibility of alcohol and drug intoxication, and cervical spine and hemodynamic instability.



  • Techniques of induction—intravenous (used commonly) or inhalational (children, adults without IV access)


  • Drugs used for IV induction—propofol (1–2 mg/kg), thiopental (5–7 mg/kg), etomidate (0.3 mg/kg), ketamine (1 mg/kg), or midazolam (0.1 mg/kg)


  • Drugs used for inhalational induction—O2, N2O with sevoflurane (nonpungent)


Airway Management


Once the patient is asleep, the next step is to control the airway. Airway control can be achieved via the following:



  • Insertion of laryngeal mask airway (LMA)—different sizes are available by weight/age. It is important to establish an IV access before inserting an LMA, if induction is done via inhalational agents.


  • Insertion of endotracheal tube (ETT)—once the patient is asleep the patient is ventilated via a face mask. Muscle relaxants are used to facilitate intubation, either succinylcholine (1–2 mg/kg) or a nondepolarizing muscle relaxant—rocuronium (0.6–0.9 mg/kg)/vecuronium (0.1 mg/kg). The next step is to intubate the patient via an appropriate size of ETT using a laryngoscope (Macintosh/Miller blade).


  • Rapid sequence intubation—patients on full stomach precautions (trauma, bowel obstruction) and acid reflux disease can be intubated via this technique (to prevent pulmonary aspiration). The premedication is omitted (no midazolam/fentanyl), the patient is preoxygenated with 100 % O2, and the anesthesia is induced with an IV induction agent followed immediately with the administration of succinylcholine. The patient is not given any positive pressure breaths via the face mask, a cricoid pressure is applied gently, and the patient is intubated to secure the airway.


  • Difficult airway patients—patients with known and anticipated difficult airway may be intubated with the help of specialized intubating equipment (instead of direct laryngoscopy), such as fiber-optic intubation and use of a Glidescope or Airtraq.


Positioning


Proper patient positioning and padding are required while the patient is asleep under general anesthesia, to avoid pressure on the peripheral nerves and soft tissues (eyes, breasts, AV fistula). Besides the supine position, surgery may be carried out in the prone, lateral, lithotomy, or jack-knife positions. The ulnar nerve is the most common nerve to be injured under anesthesia. It is important to remember that a sudden change from the supine position may lead to hemodynamic effects.


Maintenance






  • Gases—oxygen, nitrous oxide or air, and an inhalational agent (isoflurane, sevoflurane, or desflurane). Nitrous oxide is contraindicated in patients with bowel obstruction, pneumothorax, and tympanoplasty as it leads to dilation of closed air spaces.


  • Analgesics—narcotics such as fentanyl, morphine, or hydromorphone.


  • Muscle relaxants—required to provide muscle relaxation for bowel surgery and used in patients who should not move during surgery (cardiac or neurosurgery). Nondepolarizing muscle relaxants, such as rocuronium, vecuronium, or cisatracurium, are used. Cisatracurium is beneficial for patients with renal failure as it is eliminated by Hoffman degradation (not dependent on liver/renal routes for metabolism).


  • Adjuncts—epidural anesthesia/nerve blocks are commonly used in addition to general anesthesia for intraoperative/postoperative pain management.


  • Monitor patient’s vital signs and ventilation, assess blood loss, and communicate with the surgeon.


  • Fluid management—4 ml/kg/h for the first 10 kg of weight, 2 ml/kg/h after first 10 kg up to 20 kg of weight, and 1 ml/kg/h thereafter. When calculating fluid requirements under anesthesia, one needs to consider fluid deficit from NPO status, maintenance fluid requirements, additional fluid requirements secondary to blood loss, and losses through the gastrointestinal and respiratory systems. Replacement of blood loss by crystalloid is done by a ratio of 1:3 and for colloid by a ratio of 1:1. This means that every milliliter of blood loss should be replaced with 3 ml of crystalloid or 1 ml of colloid.


  • Blood components—blood (packed RBCs), platelets, and fresh frozen plasma. Blood transfusion is required when excessive blood loss leads to hemodynamic instability or a hemoglobin of less than 7 g/dl (note: with rapid blood loss, the measured hematocrit may not be accurate).

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Sep 18, 2016 | Posted by in ANESTHESIA | Comments Off on Approach to Anesthesia

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