30 Steps to Administering General Anesthesia

A BRIEF GUIDE FOR STUDENTS

April 2004

D. John Doyle MD PhD

djdoyle@hotmail.com

DRUG DOSAGE NOTE

Doses and volumes discussed in this work apply to normal adult patients.

Adjustments for pediatric patients, frail patients, and patients with impaired renal,  hepatic, respiratory or cardiac status will be needed.

Drug interactions may also influence dosing needs.

Clinical drug dosing (and timing) is as much an art as a science.

1Identify Clinical Considerations

Review the history, physical examination and laboratory results to identify the principal clinical considerations for the patient  (e.g. hypertension, angina, asthma, anemia, etc.)

Sometimes just one or two sentences will do the job:

Mr. Desai is an otherwise healthy 81 kg 46 year old man with chronic anemia (hematocrit=0.29) and controlled hypertension (atenalol 50 mg BID) who is scheduled for a partial colectomy under general anesthesia. He has no allergies and functional enquiry is negative.

2Consultations

Ensure that all required consultations have been done (e.g. diabetic patients may need an endocrinology consult; patients with myasthenia gravis will need a neurology consult).

Here are some more random situations where formal or informal consultation may be appropriate:

•Recent myocardial infarction

•Severe metabolic derangements such as hyperkalemia or hyponatremia

•Uncontrolled severe hypertension

•Mitral or aortic stenosis

•Pheochromocytoma

•Patients with coagulopathies

•Patients with a suspected difficult airway

3Airway Assessment

Assess the patient's airway  using the Mallampati system and examining the patient’s oropharynx.

Consider also other criteria (degree of mouth opening,  head flexion /extension,  jaw size, “mandibular space”).

Take a good look for any loose, false or capped teeth. Warn patients with poor dentition that intubation carries a risk of chipped or loosened teeth.

Determine if special airway management techniques (such as awake intubation using a fiberoptic bronchoscope) are needed.

4Consent

Ensure that the consent for the surgery has been obtained and that it is correctly signed and dated.

Patients unable to give regular consent require special consideration: comatose patients, children, psychiatric patients etc.

Some centers require separate consents for anaesthesia and blood transfusions.

Central to proper consent is that the patient understands his or her options and their respective benefits and risks. It is not sufficient that the patient has merely and agreeably signed all papers placed before him.

5Blood Product Planning

Ensure that any needed blood products (packed red cells, platelets, stored plasma, fresh frozen plasma, cryo-precipitate - depending on clinical circumstances) are available.

Most smaller surgical cases have blood drawn for “group and screen” – determination of ABO / Rh blood grouping and screening for antibodies that might make crossmatching difficult.

Cross and Type: Larger surgical cases often have a number of blood units (usually packed cells) specifically tested for the patient and more or less immediately available (e.g., 4 units of packed cells for cardiac bypass patients in the OR fridge)

6Aspiration Prevention

Ensure that the patient has been NPO ("nil per os" - nothing by mouth) for an appropriate length of time, i.e. ensure that the patient has an empty stomach.

(Patients without an empty stomach may need a rapid sequence induction, awake intubation, or management with local or regional anaesthesia to reduce the chance of regurgitation and aspiration.)

Pharmacologic means to reduce gastric volume and/or acidity may be appropriate preoperatively, such as a particulate-free oral antacid (sodium citrate 0.3 molar 30 ml po prior to induction of anaesthesia) or agents such as cimetidine, ranitidine or Pepsid.

7Identify Routine Monitoring Needs

All patients undergoing surgery get the following routine monitors:

Noninvasive Blood Pressure (manual or automatic)

Airway Pressure Monitor / Disconnect Alarm

Electrocardiogram

Nerve Stimulator

Pulse Oximeter

Urometer

Airway Gas Monitor

Body Temperature

In addition, spirometry (tidal volume / minute volume) and agent analyzers

(% isoflurane etc) are desirable.

Body temperature may be measured in the axilla, the nasopharynx, the oral cavity or the rectum.

8Identify Special Monitoring Needs

CVP     =central venous pressure

PA=pulmonary artery

Determine whether special monitors (arterial line, CVP line, PA line etc.) are needed.  A CVP line is helpful to assess right-sided cardiac filling pressures. PA-lines are helpful when cardiac output must be measured or when right-sided cardiac pressure data would  not be expected to reflect what is happening on the left side.

Arterial lines allow beat-by-beat blood pressure monitoring, arterial blood gas monitoring and easy access to blood for tests.

PA catheters measure:

(1) CVP waveform 

(2) PA waveform

(3) PCWP (“wedge pressure”)

(4) Cardiac Output

(5) Right-sided resistance (PVR – pulmonary vascular resistance)

(6) Left-sided resistance (SVR – system vascular resistance)

(7) PA temperature

Evoked potential studies sometimes are useful to monitor the brain and spinal cord during neurosurgical and orthopedic procedures.

9Premedication

Order preoperative sedation, drying agents, antacids, H2 blockers, or other drugs as appropriate.

SAMPLE PREMEDICATION ORDERS

Preoperative sedation

Diazepam 10 mg po with sip water 90 min preop

Midazolam 1 mg IV in holding area if requested by patient

Morphine 10 mg / Trilaphon 2.5 mg IM one hr preop (heavier)

Drying agent (e.g., prior to awake intubation)

Glycopyrrolate 0.4 mg IM one hr preop

Reduce gastric acidity (e.g., patients at aspiration risk)

Ranitidine 150 mg po evening before surgery and again in am

Cardiac prophylaxis (e.g., mitral stenosis)

Antibiotics as per AHA protocol

10IV Access

Start an intravenous (IV) of appropriate size in the hand or forearm (first using local anesthesia.) 

A size 18 or 16 catheter hooked up to a bag of Normal Saline (0.9%) is usually used.

A large size 14 is often used in cardiac  cases and other large cases, or where the patient is feared to be hypovolemic.

Some cases (e.g., trauma cases) will require more than one IV or will require a fluid warmer to avoid hypothermia.

11Equipment Preparation

ANESTHESIA MACHINE CHECK

(HIGHLIGHTS ONLY – SEE FULL CHECKLIST)

Oxygen Line Pressure

Oxygen Flowmeter

Nitrous Line Pressure

Nitrous Flowmeter

Oxygen Tank Check

Check for Leaks

Vaporizer Check

Check Ventilator

AIRWAY EQUIPMENT   

Suction

Oxygen

Laryngoscope

Endotracheal Tube

Stylet (in ETT)

“SOLES” 

EMERGENCY STUFF

Resuscitator Bag

Defibrillator

Crash Cart

Emergency Drugs

Fire Extinguisher

12Drug Preparation

Prepare drugs in labelled syringes. Examples:

Drug            Conc’n         Use                    Syringe

Thiopental    25 mg/ml       Induction                       20 ml

Propofol       10 mg/ml       Induction                       20 ml

Fentanyl        50 mcg/ml    Analgesia                     5 ml

Midazolam   1 mg/ml        Amnesia / Hypnosis    5 ml

Succinylcholine   20 mg/ml       Intubation                     10 ml

Curare          3 mg/ml          Muscle Relaxation      5 ml

Vecuronium 1 mg/ml          Muscle Relaxation      5 ml

Pancuronium       2 mg/ml          Muscle Relaxation      5 ml

Not all these drugs will be drawn up at one in any one case (e.g. usually need only one induction agent). 

Most patients will not need the full amount of any of these syringes at any one time. 

 

13Emergency Drug Preparation

Prepare emergency drugs for the case.  Low risk cases may not need any of these drugs to be instantly ready. High risk cases may also require dopamine, epinephrine, norepinephrine  and other agents.

Sample Emergency Drugs

Atropine

1 ml syringe  0.6 mg /ml    Used to raise heart rate (HR)

Ephedrine

10 ml syringe5 mg /ml      Used to raise BP (and HR)

Phenylephrine

20 ml syringe50 mcg / ml Used to raise BP

Nitroglycerine

10 ml syringe0.2 mg / ml  Used to lower BP / treat heart ischemia

Esmolol

10 ml syringe10 mg /ml    Used to lower HR (and BP)

14Attach Monitors

Prior to induction of general anesthesia the electrocardiogram, blood pressure cuff and pulse oximeter should be attached and baseline vital signs taken.

The IV should also be rechecked before the induction drugs are given.

After induction / intubation the capnograph,  airway pressure monitor, neuromuscular blockade monitor and temperature probe should be attached. 

Special monitors (CVP, arterial line, evoked potentials. precordial Doppler) may also be needed.

15Give Preinduction Drugs

Curare 3 mg IV or rocuronium 3 to 5 mg IV may be given to prevent fasciculation (with resulting myalgesia) from succinylcholine (a rapid onset ultrashort acting intravenous depolarizing muscle relaxant used primarily for intubation).

Small doses of midazolam (e.g. 1 - 2 mg IV) and/or fentanyl (e.g. 50 - 100 mcg IV) may be given to "smooth out" induction. Larger doses may be appropriate where less  than usual doses of thiopental or propofol are planned (e.g. in cardiac patients).

Preinduction hemodynamic “tuning” using nitroglycerine or  esmolol may be needed in hypertensive patients or patients with coronary artery disease.

16Induce General Anesthesia

Tell the patient he / she will be going under.

Get baseline vital signs.

Using thiopental (e.g. 3-5 mg /kg), propofol (e.g. 2-3 mg/ kg) or other IV drugs, render the patient unconscious.

Consider using etomidate or  ketamine for hypovolemic patients.

Consider using fentanyl or sufentanil as the main induction agent for cardiac cases.

Use of an inhalation induction with a potent agent such as sevoflurane would also work, but is far less popular in adults.

17Provide Muscle Relaxation

After the patient is unconscious, as evidenced by loss of lid reflex, use a depolarizing muscle relaxant such as succinylcholine or a nondepolarizing agent such as vecuronium to paralyze the patient in order facilitate endotracheal intubation.

Succinylcholine is popular in this setting because of its rapid onset and offset (short duration of effect), but many clinicians never use succinylcholine routinely because of its occasionally lethal side effects.

(This step is not needed if a face mask or Laryngeal Mask Airway is used, or if the patient is intubated awake).

18Intubate the Patient (Secure the Airway)

Using your gloved left hand insert a laryngoscope to visualize the epiglottis and cords and then pass an endotracheal tube (ETT) through the abducted vocal cords with your right hand.Ordinarily the ETT should be positioned with lips at 21 cm for women, 23 cm for men.

Inflate the ETT cuff to 25 cm H2O pressure to establish a seal (about 5 ml air will usually suffice), then hook up ETT to patient breathing circuit.

Check for equal air entry with stethoscope and check for correct-appearing capnogram.

(If an LMA is used it is inserted without a laryngoscope).

19Ventilate the Patient

Although many cases can be done with the patient breathing on their own “breathing spontanously” , all cases using muscle relaxants need mechanical ventilation for a period.

USUAL VENTILATOR SETTINGS

Tidal volume 10-12 ml/kg.

Respiratory rate   8-12/min.

Oxygen concentration 30%

 

NOTE Aim for a PCO2  35 - 40 mm Hg in normal cases, and 28-32 mm Hg in patients with increased intracranial pressure. Ensure that all ventilation-related alarms (apnea, high airway pressure, etc.) are enabled and appropriately set.

20Look at Oxygenation

Room air is 21% oxygen. Under anesthesia patients are given a minimum 30 percent oxygen (Exception: cancer patients who have taken bleomycin get only 21% oxygen to reduce the chance of oxygen toxicity).

100 percent oxygen with aggressive PEEP (Positive End Expiratory Pressure) may be required in patients with severe respiratory failure (e.g., as in ARDS).

Aim for a pulse oximeter reading (arterial oxygen saturation) above 95%.

Drops in arterial oxygenation are often due to endotracheal tube displacement into the right broncus – check for equal air entry in all such cases.

21Dial in Inhaled Anesthetic

Provide maintenance anesthesia with nitrous oxide (N2O) 70%, oxygen 30% and a potent inhaled agent such as isoflurane (e.g. 1%).

Using blood pressure, heart rate and other indices of anesthetic depth, adjust the inhaled agent concentration as needed (or give increments of IV agents such as fentanyl or propofol).

Other volatile agents used in general anesthesia include sevoflurane, desflurane or halothane.  Ether is still used in some parts of the world.

22Add Intravenous Anesthetics

Add fentanyl, midazolam, propofol or other anesthetic agents as needed according to your clinical assessment of the anesthetic depth.

Increments of fentanyl (50 – 100 mcg) will help maintain analgesia.

Some clinicians  prefer an all IV technique - Total Intravenous Anaesthesia, or TIVA. This can be useful in patients with susceptibliity to Malignamt Hyperthermia (who cannot receive succinylcholine or potent inhaled agents such as halothane or isoflurane).

23Add Muscle Relaxants

Muscle relaxation is needed for abdominal surgery and many other clinical situations.

Using a neuromuscular blockade monitor add muscle relaxants as needed.

(The degree of neuromuscular blockade is estimated by examining the finger movement patterns when the ulnar nerve is stimulated electrically with a series of four high-voltage shocks spaced 500 milliseconds apart.)

Remember that not all cases require muscle relaxation and that all patients getting muscle relaxants must be ventilated mechanically.

24Fluid Management

Ensure adequate hematocrit, coagulation, intravascular volume and urine output by giving adequate IV fluids and blood products.

For most cases run an IV of Normal Saline or Ringer’s solution at 250 ml/hr to start, then adjust to meet the following goals:

[1] In first two hours of case, replace any preoperative fluid deficit (e.g. NPO for 8 hours x 125 ml maintenance fluid needed per hour kept NPO = 1000 ml to give in first 2 hrs)

[2] Meanwhile, for entirety of case replace “third space” surgical losses at   2 - 10 ml/kg/hr (e.g., 2 for carpal tunnel repair, 5 for lap chole, 10 for bowel surgery.)

[3] Maintain urine output over 50 ml / hr or 0.5 to 1.0 ml/kg/hr

[4] Maintain hematocrit in safe range (above 0.24 in everyone; at or above 0.3 in selected patients at risk).

25Monitor Depth of Anesthesia

Unintended intraoperative awareness during surgery, while rare, is a monumental tragedy to the patient and can trigger post-traumatic stress disorder. It may happen when a vaporizer inadvertently empties or other problem (e.g. infusion pump failure).occurs. Remember that awake surgical patients cannot signal their distress if they are paralyzed with muscle relaxants.

Using clinical assessment, ensure that the patient is unconscious. This is more of an art than a science, but takes into account autonomic findings such as BP and HR and the amounts of drugs given to date. Use of a potent inhaled agent like isoflurane is especially likely to ensure unconsciousness.

A BIS monitor (Bispectral Index Monitor) is frequently advocated as a monitor of anesthetic depth.

26Prevent Hypothermia

Perioperative hypothermia can be a serious problem for some patients. For example, patients who shiver in the recovery room after surgery use excessive oxygen and may “put a strain on the heart” (induce myocardial ischemia in patients with coronary artery disease)

Keep core temperature above 35 Celsius using fluid warmers, forced air heaters or just keeping the room warm.

Measure axillary, rectal or oropharyngeal temperature to ascertain the degree of hypothermia.

Temperature monitoring also helps detect the occurance of an episode of Malignant Hyperthermia (a hypermetabolic syndrome).

27Emergence

When the surgery is nearing completion, discontinue the anesthetic agents and reverse any neuromuscular blockade (e.g. neostigmine 2.5 - 5 mg IV with atropine 1.2 mg or glycopyrrolate 0.4 mg IV).  Neostigmine is never given alone (or your patient will get severe bradycardia or cardiac arrest).

Use a neuromuscular blockade monitor (nerve stimulator) to ensure that any muscle relaxation has been well-reversed.

Allow spontaneous ventilation to resume. Check respiratory pattern visually and via capnograph.

Wait for consciousness to return.

28Extubation

Once the patient is awake and obeying commands, suction out the oropharynx with a large-bore mouth sucker,  remove air from the ETT cuff with a 10 ml syringe, and pull out the ETT.

Apply 100% oxygen by face mask after extubation.

Supply jaw-thrust, oral airway, nasal airway or other airway interventions as needed to maintain good spontaneous breathing.

Keep a close eye on the patient’s breathing and on the pulse oximeter (keep above 95%).

29Transport to PACU (Recovery Room)

When the case is over and the paperwork done, bring the stretcher into the OR and put the patient on it without pulling out lines and disconnecting monitors.

Don't forget the oxygen tank and oxygen mask.

Monitor patients breathing visually.  Keep a finger on a pulse while moving the patient (in appropriate cases), but use a transport monitor for sick patients or for big surgical cases (eg, cardiac surgery).

Give report to RNs in PACU as well as to the anesthetist running the PACU (complex cases).

PACU = Post Anesthetics Care Unit

30Arrange Postoperative Care

Before leaving, take care of any remaining paperwork.

This includes analgesic orders (e.g. morphine 2 - 4mg IV prn), oxygen orders (e.g. nasal prongs 4 liters/min or face mask 35% oxygen), antibiotics, feeding orders, fluid orders and post-operative tests such as electrolytes and hematocrit.

Be sure to identify any special concerns you have about the patient.

Where appropriate, discuss current clinical situation with patient’s family.