Guedel Stages & General Anesthesia
This stage is characterized by analgesia, sedation, and intact airway reflexes.
What is Stage 1 anesthesia?
Stage 1 consists of analgesia/sedation with intact protective reflexes and responsiveness.
This MAC multiple prevents movement in approximately 95% of patient
What is 1.3 MAC (MAC95)?
MAC95 is approximately 1.3 MAC.
This partition coefficient primarily determines speed of induction and emergence.
What is the blood:gas partition coefficient?
Blood:gas solubility determines anesthetic speed.
Increased lipid solubility produces increased potency (lower MAC) according to this rule
What is the Meyer-Overton rule.
Greater lipid solubility predicts greater potency.
What is higher during induction? ET anesthetic concentration or brain concentration?
ET concentration overestimates brain concentration during induction.
Brain anesthetic partial pressure rises more slowly than ET concentration during induction.
Modern IV induction agents rapidly pass through this stage, making it rarely observed.
What is Stage 2 (excitement/delirium)?
IV agents such as propofol rapidly traverse Stage 2, masking its classic findings.
This MAC fraction is associated with amnesia.
What is 0.25 MAC (MAC-amnesia)?
The anesthetic concentration that suppresses explicit memory formation (anterograde amnesia).
Lower blood:gas solubility produces this effect.
What is faster induction and emergence?
Less anesthetic dissolves in blood, allowing rapid equilibration.
DAILY DOUBLE:
This volatile anesthetic requires a heated, pressurized vaporizer.
What is this anesthestic's vapor pressure?
What is desflurane?
Desflurane's high vapor pressure necessitates a Tec 6 vaporizer.
Desflurane's vapor pressure is 669 mmHg?
This measurement more accurately reflects CNS anesthetic tension than vaporizer dial setting.
What is end-tidal anesthetic concentration?
ET concentration best approximates brain partial pressure.
This is the desired anesthetic stage for most surgical procedures.
What is Stage 3 (surgical anesthesia)?
Stage 3 provides adequate unconsciousness, immobility, and reflex suppression for surgery.
Blunting adrenergic responses to intense stimulation requires approximately this MAC range.
What is 1.7–2 MAC (MAC-BAR)?
MAC-BAR suppresses autonomic responses.
Among commonly used modern volatile agents, this anesthetic has the highest blood:gas coefficient.
What is isoflurane?
Isoflurane has the highest blood:gas coefficient and slowest emergence.
Most modern volatile anesthetics belong to this chemical class.
What are halogenated ethers?
Isoflurane, sevoflurane, and desflurane are ethers
This patient population is at particularly high risk for awareness because anesthetic doses may be intentionally reduced.
Who are trauma patients in shock?
Hemodynamic instability often limits anesthetic dosing.
Profound hypotension and apnea characterize this dangerous stage.
What is Stage 4 (medullary depression/anesthetic overdose)?
Stage 4 represents excessive anesthetic depth causing severe cardiorespiratory depression.
MAC reaches its highest value at approximately this age.
6 months
Highest MAC- infant at 6 months
The blood:gas coefficient of desflurane is approximately this value.
What is 0.42?
Desflurane's blood:gas coefficient is approximately 0.42.
This volatile anesthetic is preferred for pediatric mask induction.
What is sevoflurane?
Sevoflurane is non-pungent and minimally irritating.
A BIS value between these numbers is generally considered appropriate for general anesthesia.
What is 40 to 60?
BIS values between 40 and 60 are commonly targeted during general anesthesia to reduce awareness risk while avoiding excessive anesthetic depth.
Inadequate suppression at this CNS level can result in awareness despite paralysis.
What is the supraspinal (cortical) level?
Awareness occurs when cortical suppression is inadequate.
This EEG pattern typically appears at approximately 1.5 MAC.
What is burst suppression?
This partition coefficient predicts anesthetic potency.
What is the oil:gas partition coefficient?
Oil:gas solubility correlates strongly with potency.
Nitrous oxide may increase this hemodynamic parameter.
What is pulmonary artery pressure?
N₂O may increase pulmonary vascular resistance and PAP.
This period of anesthesia carries increased awareness risk because IV induction drugs are redistributing while volatile anesthetic concentrations are still rising.
What is the transition from IV induction to volatile maintenance anesthesia?
During this transition, there may be a temporary gap in hypnosis, increasing awareness risk.