General principles of anaesthesiology

Introduction
Preoperative History and Physical
IV’s and Premedication
Commonly Used Medications
Room Setup and Monitors
Induction and Intubation
Maintenance
Emergence
PACU Concerns
Lecture plan

Definitions
Anesthesia - From the Greek meaning lack of sensation; particularly during surgical intervention.

On October 16, 1846, in Boston, William T.G. Morton - the first publicized demonstration of general anesthesia using ether.
The pre-existing word anesthesia was suggested by Oliver Wendell Holmes, Sr. in 1846 as a word to use to describe this state.

History of anaesthesia

History of anaesthesia

General anesthesia–
a condition characterized by temporary shutting down
consciousness
pain sensitivity
reflexes
relaxation of skeletal muscles
due to exposure to the anesthetics on the Central nervous system

Reversible, drug-induced condition
Amnesia & unconsciousness
Analgesia
Muscle relaxation
Attenuation of autonomic responses to noxious stimulation
Homeostasis of Vital
Functions

Anaesthesiology is the science of managing the life functions of the patients organism in time of surgery or aggressive diagnostic procedure.

General Anesthesia
Preoperative evaluation
Intraoperative management
Postoperative management

Physical Examination
Physical exams of all systems.
Airway assessment to determine the likelihood of difficult intubation

Unlike the standard internal medicine H&P, ours is much more focused, with specific attention being paid to the airway and to organ systems at potential risk for anesthetic complications. The type of operation, and the type of anesthetic will also help to focus the evaluation.
Preoperative History and Physical

• Elective: operation at a time to suit both patient and surgeon; for example hip replacement, varicose veins.
• Scheduled: an early operation but not immediately life saving; operation usually within 3 weeks; for example surgery for malignancy.
.
Classification of operation

• Urgent: operation as soon as possible after resuscitation and within 24 h; for example intestinal obstruction, major fractures.
• Emergency: immediate life-saving operation, resuscitation simultaneous with surgical treatment; operation usually within 1h; for example major trauma with uncontrolled haemorrhage, extradural haematoma
Classification of operation

Of particular interest in the history portion of the evaluation are:
Coronary Artery Disease
Hypertension
Asthma
Kidney or Liver disease
Reflux Disease
Smoking
Alcohol Consumption or Drug Abuse?
Diabetes
Medications
Allergies
Family History
Anesthesia history
Last Meal
Preoperative History and Physical

Coronary Artery Disease
What is the patient’s exercise tolerance? How well will his or her heart sustain the stress of the operation and anesthetic.
Asking a patient how he feels (ie. SOB, CP) after climbing two or three flights of stairs can be very useful as a “poor man’s stress test”.
Preoperative History and Physical

Coronary Artery Disease
What is the patient’s exercise tolerance? How well will his or her heart sustain the stress of the operation and anesthetic.
Asking a patient how he feels (ie. SOB, CP) after climbing two or three flights of stairs can be very useful as a “poor man’s stress test”.

Hypertension
How well controlled is it? Intraoperative blood pressure management is affected by preoperative blood pressure control

Asthma
How well controlled is it? What triggers it? Many of the stressors of surgery as well as intubation and ventilation can stimulate bronchospasm.
Is there any history of being hospitalized, intubated, or prescribed steroids for asthma? This can help assess the severity of disease
Preoperative History and Physical

Kidney or Liver disease
Different anesthetic drugs have different modes of clearance and organ function can affect our choice of drugs.

Reflux Disease
Present or not? Anesthetized and relaxed patients are prone to regurgitation and aspiration, particularly if a history of reflux is present
Preoperative History and Physical

Smoking
Currently smoking? Airway and secretion management can become more difficult in smokers.
Preoperative History and Physical

Alcohol Consumption or Drug Abuse?
Drinkers have an increased tolerance to many sedative drugs (conversely they have a decreased requirement if drunk), and are at an increased risk of hepatic disease, which can impact the choice of anesthetic agents.
Preoperative History and Physical

Diabetes
Well controlled? The stress response to surgery and anesthesia can markedly increase blood glucose concentrations, especially in diabetics
Preoperative History and Physical

Medications
Many medications interact with anesthetic agents, and some should be taken on the morning of surgery (blood pressure medications) while others should probably not (diuretics, diabetes medications).
Preoperative History and Physical

Allergies
We routinely give narcotics and antibiotics perioperatively, and it is important to know the types of reactions that a patient has had to medications in the past.
Preoperative History and Physical

Family History
There is a rare, but serious disorder known as malignant hyperthermia that affects susceptible patients under anesthesia, and is heritable
Preoperative History and Physical

Anesthesia history
Has the patient ever had anesthesia and surgery before? Did anything go wrong?
Preoperative History and Physical

Last Meal
Whether the patient has an empty stomach or not impacts the choice of induction technique
Preoperative History and Physical

All patients must have an assessment made of their airway, the aim being to try and predict those patients who may be difficult to intubate.
Preoperative History and Physical

Finding any of these suggests that intubation may be more difficult.
• limitation of mouth opening;
• a receding mandible;
• position, number and health of teeth;
• size of the tongue;
• soft tissue swelling at the front of the neck;
• deviation of the larynx or trachea;
• limitations in flexion and extension of the cervical spine.
Preoperative History and Physical

Also, any loose or missing teeth should be noted, as should cervical range of motion, mouth opening, and thyromental distance, all of which will impact the actual intubation prior to surgery.
During the physical examination, particular attention is paid to the airway by asking the patient to “open your mouth as wide as you can and stick out your tongue” The classification scale of Mallampati is commonly used.
Preoperative History and Physical

Mallampati Classification
Class I: Entire uvula and tonsillar pillars visible
Class II: Tip of uvula and pillars hidden by tongue
Class III: Only soft palate visible
Class IV: Only hard palate visible
Preoperative History and Physical

Mallampati Classification

Finally, a physical status classification is assigned, based on the criteria of the American Society of Anesthesiologists (ASA1-5), with ASA-1 being assigned to a healthy person without medical problems other than the current surgical concern, and ASA-5 being a moribund patient, not expected to survive for more then twenty-four hours without surgical intervention. An “E” is added if the case is emergent. The full details of the classification scale can be found below.
Preoperative History and Physical

ASA Physical Status Classification
ASA-I: Healthy patient with no systemic disease
ASA-II: Mild systemic disease , no functional limitations
ASA-III: Moderate to severe systemic disease, some functional limitations
ASA-IV: Severe systemic disease, incapacitating, and a constant threat to life
ASA-V: Moribund patient, not expected to survive > 24 hours without surgery
ASA-VI: Brain-dead patient undergoing organ harvest
E: Added when the case is emergent
Preoperative History and Physical

general anesthesia
Simple (one-component) anaesthesia
Inhalation
mask
endotracheal
Noninhalation
intravenous
Combined (multi-component anaesthesia
Inhalation + Inhalation
Noninhalation + Noninhalation
Noninhalation + Inhalation
Combined with miorelaxanthams
Classification of anaesthesia

local anesthesia
Terminal anesthesia
Infiltration anesthesia
Nerve block anesthesia
trunk
plexus
regional anesthesia
Spinal anesthesia
Epidural anesthesia
Clasification of anaesthesia

Every patient (with the exception of some children that can have their IV’s inserted following inhalation induction) will require IV access prior to being brought to the operating room.
Normal saline, Lactated Ringer’s solution, or other balanced electrolyte solutions (Plasmalyte, Isolyte) are all commonly used solutions intraoperatively.
IV’s and Premedication

Premedication refers to the administration of any drugs in the period before induction of anaesthesia.
a wide variety of drugs are used with a variety of aims
The 6 As of premedication
• Anxiolysis
• Amnesia
• Antiemetic
• Antacid
• Antiautonomic
• Analgesia

Many patients are understandably nervous preoperatively, and we often premedicate them, usually with a rapid acting benzodiazepine such as intravenous midazolam (which is also fabulously effective in children orally or rectally).
Metoclopramide and an H2 blocker are also often used if there is a concern that the patient has a full stomach,
and anticholinergics such as glycopyrrolate or atropin can be used to decrease secretions.
IV’s and Premedication

Before bringing the patient to the room, the anesthesia machine, ventilator, monitors, and cart must be checked and set up.
The anesthesia machine must be tested to ensure that the gauges and monitors are functioning properly, that there are no leaks in the gas delivery system, and that the backup systems and fail-safes are functioning properly.
Room Setup and Monitors

The monitors that we use on most patients include the pulse oximeter, blood pressure monitor, and electrocardiogram, all of which are ASA requirements for patient safety.
Each are checked and prepared to allow for easy placement when the patient enters the room.
You may see some more complicated cases that require more invasive monitoring such as arterial or central lines
Room Setup and Monitors

The anesthesia cart is set up to allow easy access to intubation equipment including endotracheal tubes, laryngoscopes, stylets, oral/nasal airways and the myriad of drugs that we use daily.
A properly functioning suction system is also vital during any type of anesthetic
Room Setup and Monitors

Other preparations that can be done before the case focus on patient positioning and comfort, since anesthesiologists ultimately are responsible for intraoperative positioning and resultant neurologic or skin injuries. Heel and ulnar protectors should be available, as should axillary rolls and other pads depending on the position of the patient.
Room Setup and Monitors

Four Phases
Induction
Maintenance
Emergence
Recovery
General Anesthesia

Four Phases
Induction
Maintenance
Emergence
Recovery

You now have your sedated patient in the room with his IV and he’s comfortably lying on the operating table with all of the aforementioned monitors in place and functioning. It is now time to start induction of anesthesia.
Induction is the process that produces a state of surgical anaesthesia in a patient.
Induction and Intubation

Stage I – Amnesia
Stage II – Excitement
Stage III – Surgical Intervention (4 planes)
Stage IV – Overdose
Guedel’s stages of anaesthesia

Stage I (stage of analgesia or disorientation): from beginning of induction of general anesthesia to loss of consciousness.
Stage II (stage of excitement or delirium): from loss of consciousness to onset of automatic breathing. Eyelash reflex disappear but other reflexes remain intact and coughing, vomiting and struggling may occur; respiration can be irregular with breath-holding.
Guedel’s stages of anaesthesia

Stage III (stage of surgical anesthesia): from onset of automatic respiration to respiratory paralysis.
It is divided into four planes:
Plane I - from onset of automatic respiration to cessation of eyeball movements. Eyelid reflex is lost, swallowing reflex disappears, marked eyeball movement may occur but conjunctival reflex is lost at the bottom of the plane
Guedel’s stages of anaesthesia

Plane II - from cessation of eyeball movements to beginning of paralysis of intercostal muscles. Laryngeal reflex is lost although inflammation of the upper respiratory tract increases reflex irritability, corneal reflex disappears, secretion of tears increases (a useful sign of light anesthesia), respiration is automatic and regular, movement and deep breathing as a response to skin stimulation disappears.
Guedel’s stages of anaesthesia

Plane III - from beginning to completion of intercostal muscle paralysis. Diaphragmatic respiration persists but there is progressive intercostal paralysis, pupils dilated and light reflex is abolished. The laryngeal reflex lost in plane II can still be initiated by painful stimuli arising from the dilatation of anus or cervix. This was the desired plane for surgery when muscle relaxants were not used.
Guedel’s stages of anaesthesia

Plane IV - from complete intercostal paral
ysis to diaphragmatic paralysis (apnea).
Stage IV: from stoppage of respiration till death. Anesthetic overdose cause medullary paralysis with respiratory arrest and vasomotor collapse.
Guedel’s stages of anaesthesia

The first part of induction of anesthesia should be preoxygenation with 100% oxygen delivered via a facemask.
Again, using the example of a normal smooth induction in a healthy patient with an empty stomach, the next step is to administer an IV anesthetic until the patient is unconscious. A useful guide to anesthetic induction is the loss of the lash reflex, which can be elicited by gently brushing the eyelashes and looking for eyelid motion.
Induction and Intubation

Patients frequently become apneic after induction and you may have to assist ventilation.
The most common choices used for IV induction are Propofol, Thiopental, and Ketamine.
Induction and Intubation

• Propofol
Typical adult induction
dose 1.5–2.5 mg/kg
Popular and widely used drug associated with rapid and ‘clear-headed' recovery. Rapid metabolism and lack
Pro: Prevents nausea/vomiting, Quick recovery if used as solo anesthetic agent
Con: Pain on injection, Expensive, Supports bacterial growth, Myocardial depression), Vasodilation
IV Anesthetics

• Thiopental Sodium
Typical adult induction dose 3–5 mg/kg (2.5% solution)
The ‘gold-standard’ against which all other drugs are judged. Smooth induction in one arm–brain circulation time
Pro: Excellent brain protection, Stops convulsion , Cheap
Con: Myocardial depression, Vasodilation, Histamine release.
IV Anesthetics

Ketamine
Typical adult induction dose 0.5–2 mg/kg
Useful for sedation with profound analgesia. Increases pulse rate and blood pressure and useful for the induction of patients suffering from acute trauma
Pro: Works IV, PO, PR, IM – good choice in uncooperative patient without IV, Stimulation of SNS, often preserves airway reflexes
Con: Dissociative anesthesia with postop. dysphoria and hallucinations, bad for patients with compromised cardiac function, increases airway secretions
IV Anesthetics

Ketamine

Assuming that you are now able to mask ventilate the patient, the next step is usually to administer a neuromuscular blocking agent such as succinylcholine (a depolarizing relaxer).
Once the patient is adequately anesthetized and relaxed, it’s time to intubate, assuming you have all necessary supplies at the ready.
Induction and Intubation

. Hold the laryngoscope in your left hand (whether you’re right or left handed) then open the patient’s mouth with your right hand, either with a head tilt, using your fingers in a scissors motion, or both. Insert the laryngoscope carefully and advance it until you can see the epiglottis, sweeping the tongue to the left. Advance the laryngoscope further into the vallecula (assuming you’re using a curved Macintosh blade), then using your upper arm and NOT your wrist, lift the laryngoscope toward the juncture of the opposite wall and ceiling. There should be no rotational movement with your wrist, as this can cause dental damage. When properly done, the blade should never contact the upper teeth. Once you see the vocal cords, insert the endotracheal tube until the balloon is no longer visible, then remove the laryngoscope, hold the tube tightly, remove the stylet, inflate the cuff balloon, attach the tube to your circuit and listen for bilateral breath. If you have chest rise with ventilation, misting of the endotracheal tube, bilateral breath sounds and end tidal CO2, you’re in the right place and all is well! Tape the tube securely in place, place the patient on the ventilator, and set your gas flows appropriately.
Induction and Intubation

Intubation

Careful and continues vigilance of vital sings and depth of anesthesia is the integral part of the maintenance phase.
Pulse oximetry, End-tidal carbon dioxide tension, patient's temperature, ECG and blood pressure are continuously monitored during the maintenance phase. End-tidal concentration of nitrous oxide and inhalation agents (isoflurane, halothane etc) is continuously monitored for the proper depth of anesthesia (analgesia, amnesia, sedation and muscle relaxation).
Maintenance

It is important to keep track of the blood loss during the case and should be replaced hourly with crystalloid. Fluid therapy should be guided by monitoring hourly urine output (0.5 cc/Kg/Hr).
Maintenance

It is also vital to pay attention to the case itself, since blood loss can occur very rapidly, and certain parts of the procedure can threaten the patient’s airway, especially during oral surgery or ENT cases. It is also important to keep track of the progress of the case.
Vigilance is key to a good anesthesia.
Maintenance

One can also prepare for potential post-operative problems during the case, by treating the patient intraoperatively with long-acting anti-emetics and pain medications.
Maintenance

Volatile Anesthetics
Halothane
Pro: Cheap, Nonirritating so can be used for inhalation induction
Con: Long time to onset/offset, Significant Myocardial Depression, Sensitizes myocardium to catecholamines, Association with Hepatitis
Commonly Used Medications

Volatile Anesthetics
Sevoflurane
Pro: Nonirritating so can be used for inhalation induction, Extremely rapid onset/offset
Con: Expensive, Due to risk of “Compound A” exposure must be used at flows >2 liters/minute, Theoretical potential for renal toxicity from inorganic fluoride metabolites
Commonly Used Medications

Volatile Anesthetics
Isoflurane
Pro: Cheap, Excellent renal, hepatic, coronary, and cerebral blood flow preservation
Con: Long time to onset/offset, Irritating so cannot be used for inhalation induction
Commonly Used Medications

Volatile Anesthetics
Desflurane
Pro: Extremely rapid onset/offset
Con: Expensive, Stimulates catecholamine release, Possibly increases postoperative nausea and vomiting, Requires special active-temperature controlled vaporizer due to high vapor pressure, Irritating so cannot be used for inhalation induction
Commonly Used Medications

Nitrous Oxide
Pro: Decreases volatile anesthetic requirement, Dirt cheap, Less myocardial depression than volatile agents
Con: Diffuses freely into gas filled spaces (bowel, pneumothorax, middle ear, gas bubbles used during retinal surgery), Decreases FiO2, Increases pulmonary vascular resistance
Commonly Used Medications

Muscle Relaxants
Depolarizing
Succinylcholine inhibits the postjunctional receptor and passively diffuses off the membrane, while circulating drug is metabolized by plasma esterases. Associated with increased ICP/IOP, muscle fasciculations and postop muscle aches, triggers MH, increases serum potassium especially in patients with burns, crush injury, spinal cord injury, muscular dystrophy or disuse syndromes.
Rapid and short acting.
Commonly Used Medications

Nondepolarizing
Many different kinds, all ending in “onium” or “urium”. Each has different site of metabolism, onset, and duration making choice depend on specific patient and case. Some examples: Pancuronium - Slow onset, long duration, tachycardia due to vagolytic effect. Cisatracurium - Slow onset, intermediate duration, Hoffman (nonenzymatic) elimination so attractive choice in liver/renal disease. Rocuronium - Fastest onset of nondepolarizers making it useful for rapid sequence induction, intermediate duration.

EMERGENCE FROM GENERAL ANESTHESIA
1. Reversal of muscle relaxation.
2. Turning off the inhalation agents and nitrous oxide
3. Meeting the extubation criteria
4. Extubation of trachea
5. Transfer of the patient to post anesthesia care unit.
Emergence

First, the patient’s neuromuscular blockade must be re-assessed, and if necessary reversed and then rechecked with a twitch monitor.
Next, the patient has to be able to breathe on his own, and ideally follow commands, demonstrating purposeful movement and the ability to protect his airway following extubation. Suction must always be close at hand, since many patients can become nauseous after extubation, or simply have copious oropharyngeal secretions
Emergence

. Once the patient is reversed, awake, suctioned, and extubated, care must be taken in transferring him to the gurney and oxygen must be readily available for transportation to the recovery room/Post-Anesthesia Care Unit (PACU). Finally, remember that whenever extubating a patient, you must be fully prepared to reintubate if necessary, which means having drugs and equipment handy.
Emergence

The anesthesiologist’s job isn’t over once the patient leaves the operating room. Concerns that are directly the responsibility of the anesthesiologist in the immediate postoperative period include nausea/vomiting, hemodynamic stability, and pain.
PACU Concerns

Other concerns include continuing awareness of the patient’s airway and level of consciousness, as well as follow-up of intraoperative procedures such as central line placement and postoperative X-rays to rule out pneumothorax. A resident and staff member are usually assigned to the PACU specifically to follow up on these concerns, since we frequently have to return to the OR for subsequent cases, and may not be available if problems should arise.
PACU Concerns

Opioids
Morphine – long acting, histamine release, renally excreted active metabolite with opiate properties therefore beware in renal failure
Dilaudid – long acting, no active metabolites or histamine release, same onset/duration as morphine
Demerol − euphoria, stimulates catecholamine release, so beware in patients using MAOI’s, renally excreted active metabolite associated with seizure activity, renally excreted metabolite with seizure potential therefore beware in renal failure
Fentanyl/Alfentanil/Sufentanil – low doses produce brief effect, but larger doses are long acting, increased incidence of chest wall rigidity vs. other opiates, no active metabolites
Remifentanil – almost instantaneous onset/offset of action due to metabolism by plasma esterases, must be given as continuous infusion, significant incidence of chest wall rigidity and nausea/vomiting
Commonly Used Medications