UNDERSTANDING ANESTHESIA

Objectives1. Identify the different types of anesthesia

management2. Identify common anesthetic agents & their

influence on patient subsystems3. Identify the stages of general anesthesia4. Discuss appropriate actions in the event of a

malignant hyperthermia crisis

AnesthesiaThe 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 1846The development of anesthesia has made today’s modern surgical techniques possible

ASA Physical Status Classification

ASA 1 – normal, healthy patientASA 2 – patient with mild, well-controlled systemic diseaseASA 3 – patient with severe systemic disease that limits activityASA 4 –patient with severe, life-threatening diseaseASA 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 AnesthesiaEffects 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

LaryngospasmNausea & VomitingDamage to teeth during intubationCorneal abrasionsAspirationMalignant hyperthermia

Regional AnesthesiaDefined 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

HypotensionInadvertent dural punctureInadvertent injection of anesthetic into the subarachnoid space

IV Regional Blocks

Also known as a Bier BlockUsed on surgery of the upper extremitiesPatient 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 anesthesiaAnesthesia 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 AnestheticsCause 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 AnesthesiaDuring 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 AnesthesiaCirculator 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 PatientPatients 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 AwakeLimit 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 oximeterBlood pressure monitorTemperature probeEsophageal or precordial stethoscopeEnd-tidal CO2 Monitor

Malignant Hyperthermia A rare, life-threatening complication of anesthesiaTriggered in susceptible patients by certain inhalation anesthetics (halothane, enflurane, isoflurane, sevoflurane, desflurane) and by the muscle relaxant succinycholine

MHSusceptibility 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 MHRapid rise in body temperature (temperature may exceed 110°F)-may be a late signMuscle rigidityHypercarbia (elevated CO2)Acidosis

Treatment of MHCall for help!Immediate discontinuation of all inhalation anestheticsHyperventilate with 100% oxygenEnd surgery if possibleMonitor core temperatureGive only “safe” anesthetics: IV narcotics, propofol (Diprivan), nitrous oxide

Treatment of MHGive 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 hoursContinue Dantrolene for at least 24 hours

Dantrolene Sodium (Dantrium)

Skeletal muscle relaxant

Dantrolene is stored in the OR in the Malignant Hyperthermia Boxbe sure that you know where this box is located!

Dantrolene ReconstitutionUse 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)

MHAUSFor 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 NursingMalignant 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