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UNDERSTANDING ANESTHESIA
Objectives
1. Identify the different types of anesthesia management
2. Identify common anesthetic agents & their influence on patient subsystems
3. Identify the stages of general anesthesia4. Discuss appropriate actions in the event of a
malignant hyperthermia crisis
Anesthesia
The word is derived from the Greek words an, which means “without” and aithesia which means “feeling”
The use of medical anesthesia was first reported in 1846
The development of anesthesia has made today’s modern surgical techniques possible
ASA Physical Status Classification
ASA 1 – normal, healthy patient
ASA 2 – patient with mild, well-controlled systemic disease
ASA 3 – patient with severe systemic disease that limits activity
ASA 4 –patient with severe, life-threatening disease
ASA 5 – moribund patient not expected to survive for 24 hours with or without surgery
An “E” is added to the classification for emergent procedures
General Anesthesia
Effects of general anesthesia: Effects are produced by depression of the CNS &
blocking pain stimuli at the level of the cerebral cortex
1. Hypnosis (sleep)2. Analgesia3. Amnesia 4. Muscle relaxation
General Anesthesia
Anesthesia is generally induced by a combination of drugs: inhalation & intravenous anesthetics intravenous narcotics & sedatives muscle relaxants
Complications Associated with General Anesthesia
Laryngospasm
Nausea & Vomiting
Damage to teeth during intubation
Corneal abrasions
Aspiration
Malignant hyperthermia
Regional Anesthesia
Defined as “a reversible loss of sensation in a specific area of the body” Spinal anesthesia Epidural anesthesia IV Regional Blocks Peripheral Nerve Blocks
Spinal Anesthesia
A local anesthetic agent (lidocaine, tetracaine or bupivacaine) is injected into the subarachnoid space Spinal anesthesia is also known as a
subarachnoid block
Blocks sensory and motor nerves, producing loss of sensation and temporary paralysis
Possible Complications of Spinal
Anesthesia
Hypotension
Post-dural puncture headache (“Spinal headache”) caused by leakage of spinal fluid through the puncture hole in the dura-can be treated by blood patch
“High Spinal”- can cause temporary paralysis of respiratory muscles. Patient will need ventilator support until block wears off
Epidural Anesthesia
Local anesthetic agent is injected through an intervertebral space into the epidural space.
May be administered as a one-time dose, or as a continuous epidural, with a catheter inserted into the epidural space to administer anesthetic drug
Complications of Epidural Anesthesia
Hypotension
Inadvertent dural puncture
Inadvertent injection of anesthetic into the subarachnoid space
IV Regional Blocks
Also known as a Bier Block
Used on surgery of the upper extremities
Patient must have an IV inserted in the operative extremity
IV Regional Block
After a pneumatic tourniquet is applied to extremity, Lidocaine is injected through the IV
Anesthesia lasts until the tourniquet is deflated at the end of the case
IV Regional Blocks
IMPORTANT- to prevent an overdose of lidocaine it is important not to deflate the tourniquet quickly at the end of the procedure
The anesthesia provider will deflate/inflate tourniquet several times before complete deflation of tourniquet cuff
Peripheral Nerve Blocks
Injection of local anesthetic around a peripheral nerve
Can be used for anesthesia during surgery or for post-op pain relief
Examples: ankle block for foot surgery, supraclavicular block for post-op pain control after shoulder surgery
Monitored Anesthesia Care (MAC)
Generally used for short, minor procedures done under local anesthesia
Anesthesia provider monitors the patient and may provide supplemental IV sedation if indicated
Conscious Sedation
Used for short, minor procedures
Used in the OR and outlying areas (ER, Endo., etc)
Patient is monitored by a nurse and receives sedation sufficient to cause a depressed level of consciousness, but not enough to interfere with patient’s ability to maintain their airway
Inhalation Anesthetics
Nitrous Oxide- can cause expansion of other gases- use of N20 contraindicated in patients who have had medical gas instilled in their eye(s) during retinal detachment repair surgery
Inhalation Anesthetics
Cause cerebrovascular dilation and increased cerebral blood flow
Cause systemic vasodilation and decreased blood pressure
Post-op N&V
All inhalation anesthetics, except N20, can trigger malignant hyperthermia in susceptible patients
Intravenous Induction/Maintenance Agents
Propofol (Diprivan)- pain/burning on injection, can cause bizarre dreams
Pentothal (Sodium Thiopental)- can cause laryngospasm
General Anesthesia
During induction the room should be as quiet as possible
The circulator should be available to assist anesthesia provider during induction & emergence
Never move/reposition an intubated patient without coordinating the move with anesthesia first
General Anesthesia
Laryngospasm may happen in a patient having a procedure with general anesthesia
When laryngospasm occurs, it is usually during intubation or emergency
Assist anesthesia provider as needed- call for anesthesia back-up if necessary
Difficult Airway Cart
Anesthesia maintains a “Difficult Airway Cart” containing equipment & supplies for difficult intubations
This cart is stored in one of the anesthesia supply rooms
Page anesthesia tech if the cart is needed for your room
Cricoid Pressure or Sellick Maneuver
Used for patients at risk for aspiration during induction, due to a full stomach or other factors such as a history of reflux
Pressure on the cricoid cartilage compresses the esophagus against the cervical vertebrae and prevents reflux
Sellick Maneuver
Cricoid pressure is maintained, as directed by anesthesia provider, until the ETT cuff is inflated:
Regional Anesthesia
Circulator may need to assist anesthesia provider with positioning for spinal or epidural anesthesia
Patient usually is positioned laterally for placement of regional anesthesia, but may be positioned sitting upright
The Awake Patient
Patients undergoing surgery with regional or local anesthesia, even if sedated, may be aware of conversation and activity in room
Post sign on door to OR, “Patient is Awake” so that staff entering room will be aware that patient is conscious
When Patient is Awake
Limit any discussion of patient’s medical condition and prognosis
Avoid discussion of other patients & limit unnecessary conversation-- a sedated patient can easily misinterpret conversation they overhear
Anesthesia Monitoring Devices:
Electrocardiograph (EKG or ECG)
Pulse oximeter
Blood pressure monitor
Temperature probe
Esophageal or precordial stethoscope
End-tidal CO2 Monitor
Malignant Hyperthermia A rare, life-threatening complication of anesthesia
Triggered in susceptible patients by certain inhalation anesthetics (halothane, enflurane, isoflurane, sevoflurane, desflurane) and by the muscle relaxant succinycholine
MH
Susceptibility to MH is inherited (autosomal dominant- 50% of children of parents with MH will inherit the gene)
MH can be diagnosed by muscle biopsy-this biopsy is indicated for people who have a family history of MH
MH
The mortality rate from MH has been reduced from 80% to around 10% due to improvements in early recognition and treatment
Signs of MH
Rapid rise in body temperature (temperature may exceed 110°F)-may be a late sign
Muscle rigidity
Hypercarbia (elevated CO2)
Acidosis
Treatment of MH
Call for help!
Immediate discontinuation of all inhalation anesthetics
Hyperventilate with 100% oxygen
End surgery if possible
Monitor core temperature
Give only “safe” anesthetics: IV narcotics, propofol (Diprivan), nitrous oxide
Treatment of MH
Give Dantrolene until signs of MH are controlled
If patient is hyperthermic (core temp > 39° C or 102.2 ° F), immediately start aggressively cooling the patient: pack patient in ice, infuse chilled IV fluids, irrigate NG tube & foley catheter with ice water
MH Post Acute Phase
Observe patient in ICU for at least 24 hours
Continue Dantrolene for at least 24 hours
Dantrolene Sodium (Dantrium)
Skeletal muscle relaxant
Dantrolene is stored in the OR in the Malignant Hyperthermia Box
be sure that you know where this box is located!
Dantrolene Reconstitution
Use only preservative-free sterile water
Add 60cc sterile water to each 20mg vial of dantrolene-shake vial until solution is clear. Dantrolene is very difficult to mix up
Initial dosage 2.5 mg/kg IV push - administer drug until symptoms of MH subside or until maximum dosage of 10mg/kg is reached
(in some cases more than 10mg/kg is needed to reverse MH)
For More Information…
The Malignant Hyperthermia Association of the United States (MHAUS) has a 24-hr hotline to assist medical professionals in dealing with a malignant hyperthermia crisis:
1-800-MH-HYPER
(1-800-644-9737)
MHAUS
For non-urgent needs, information about MH can be obtained through the MHAUS organization’s web site:
http://www.mhaus.org/
References
Gutierrez, K. (1999) Pharmacotherapeutics: Clinical Decision Making in Nursing
Malignant Hyperthermia Association of the United States (2005). Emergency therapy for malignant hyperthermia.
Web site: http://www.mhaus.org/
(MHAUS hotline: 1-800-MH-HYPER)
Rothrock, J. (2002) Alexander’s Care of the Patient in Surgery