Exam 3 Flashcards
What 3 things does diffusion depend on?
- Partial pressure gradient of the gas.
- Solubility of the gas.
- Membrane thickness
What is a good indicator of anesthesia depth & recover from anesthesia?
Alveolar pressure
What are the 3 partial pressure gradients?
- Anesthetic machine to alveoli (Boyle).
- Alveoli to Blood.
- Arterial blood to brain
What affects VA uptake from alveoli to blood?
- Blood: gas partition coefficient.
- Cardiac Output.
- A-v partial pressure difference
What affects VA uptake from blood to brain?
- Brain: blood partition coefficient.
- Cerebral blood flow.
- a-v partial pressure difference.
What affects VA input from machine to alveoli?
- Inspired partial pressure.
- Alveolar ventilation (RR & volume).
- FRC.
- Anesthetic breathing system (re-breathing)
What is the main concept of Pt’s going to sleep?
Concentration effect
What is over pressurization?
Used in emergencies to get someone to sleep fast. Crank up VA for a few breaths until asleep then dial back down.
What is the second gas effect?
- The use of N2O with another volatile gas.
- N2O helps create a higher concentration gradient & increases uptake of 2nd volatile gases in the alveoli leading to faster equilibrium.
When should nitrous not be used & why?
- In bowel, ear, eye Sx or Pt’s with a pneumothorax.
- N2O diffuses very fast into air-filled cavities then expands creating pressure build-up.
- Very bad in non-compliant areas like eyes & ears.
What does inhaled gases solubility look at?
A distribution ratio of VA between 2 compartments at equilibrium.
How does temperature affect solubility of VA?
Increased blood temp decreases solubility
If blood solubility is high, then induction is?
Prolonged as large amounts of the VA must be dissolved.
List the VA in order from high to low solubility.
Halothane,
Isoflurane,
Sevoflurane,
Desflurane,
N2O
What is the Blood: Gas Partition coefficient for Halothane?
2.54
What is the Blood: Gas Partition coefficient for Enflurane?
1.90
What is the Blood: Gas Partition coefficient for Isoflurane?
1.46
What is the Blood: Gas Partition coefficient for Sevoflurane?
0.69
What is the Blood: Gas Partition coefficient for Desflurane?
0.42
What is the Blood: Gas Partition coefficient for Nitrous oxide?
0.46
What 3 VA has the highest Fat: Blood coefficient?
Halothane
Sevoflurane
Isoflurane
What VA has the lowest Fat: Blood coefficient?
Nitrous oxide
What is 1.3 MAC?
The percentage of gas when 99% of Pt’s do not move.
What is MAC awake?
- 0.3-0.5 MAC, the point a Pt may open their eyes.
- Only VA is used.
What happens in MAC bar?
No SNS response when intubating only using a VA
MAC is based on what 3 things?
- Age 30-55y/o
- Temp of 37 degrees C.
- Pressure of 1atm
What is the MAC of N2O?
104%
MAC changes how much per decade?
6%
MAC peaks at?
1 year old
What 4 things increase MAC?
- Hyperthermia.
- Excess pheomelanin.
- Drug-induced increases in catecholamines.
- Hypernatremia
What decreases MAC?
- Anything that decreases metabolism
- Alpha-2 agonists
- Acute EtOH
- Pregnancy
- Lidocaine
- MAP <40 mmHg
- Hyponatremia
- Cardiopulmonary bypass
- PaO2 <38
- Post-partum <72hrs
How do VA affect spinal mobility?
- Depress AMPA & NMDA (glutamate receptors).
- Enhance glycine.
- Act on Na+ channels (block presynaptic glutamate release)
How do VA act on the brain?
- Inhibit GABA transmission (Especially in RAS).
- Potentiate glycine activity in brainstem.
- Do not affect AMPA, NMDA or kainite
What is vapor pressure?
The pressure at which vapor and liquid are at equilibrium
What does Henry’s law state?
The amount of dissolved gas in a liquid is proportional to its partial pressure above the liquid.
What is the vapor pressure for desflurane?
669 torr
What is the vapor pressure for sevoflurane?
157 torr
What is the vapor pressure for halothane?
243 torr
What is the vapor pressure for enflurane?
175 torr
What is the vapor pressure for isoflurane?
238 torr
List the VA from lowest to highest vapor pressure?
- Sevoflurane,
- Enflurane,
- Isoflurane,
- Halothane,
- Desflurane
(SEIH)
An increased splitting ratio means?
More carrier gas is going through the vaporizer, picking up VA.
What is the MAC & MAC 1.3 of Halothane?
- 0.75%
- 0.975%
What is the MAC & MAC 1.3 of Enflurane?
- 1.63%
- 2.12%
What is the MAC & MAC 1.3 of Isoflurane?
- 1.17%
- 1.52%
What is the MAC & MAC 1.3 of desflurane?
- 6.6%
- 8.58%
What is the MAC & MAC 1.3 of sevoflurane?
- 1.8%
- 2.34%
When is a priming dose given?
When intubating with Scc
NDMB are antagonized by?
Anticholinesterase drugs
Why is there fade with NDMB?
Some fibers are more susceptible to NDMB
What cardiac receptors are agonized by NDMBs?
- Cardiac muscarinic
- nACh-r at automatic ganglia
Which NDMB’s ED95 is the same as the TD?
Pancuronium
Who is at risk for critical illness myopathy?
Pt’s with MODS, who were ventilated > 6days
What class of NDMB was given to someone that developed critical illness myopathy?
Aminosteroid blocker
Altered response with VA happens due to?
Dose dependent inhibition of nACh-r –> prolonged response @ nACh-r
What blocker is dosed on actual body weight?
Succinylcholine
How do diuretics, corticosteroids, reglan & LA affect NDMB?
- Prolong blockade.
- Increase ACh release.
- Depress cholinesterase activity.
- Depress nerve conduction
How does magnesium affect NDMB?
- Enhance blockade.
- Decrease presynaptic ACh release.
- Decrease postsynaptic membrane sensitivity
Which NDMB are very sensitive to hypothermia?
Vecuronium & Pancuronium –> doubles the duration
How does acute hypo & hyperkalemia affect NMB?
Hypokalemia:
- leads to resistance to Scc.
- Increased sensitivity to NDMB.
Hyperkalemia:
- Increased effect of Scc.
- Resistance to NDMB.
What is the timeframe of resistance to NDMB in burn Pt’s?
10 after burn up to 60 days.
How can the resistance to NMB in burn Pt’s be overcome?
Give 1.2 mg/kg of Rocuronium
Which NDMB is least & most likely to cause an allergic reaction?
- Least: Cisatracurium
- Most: Scc
What is the dose, onset, duration & class for Pavulon?
- Dose: 0.1 mg/kg
- Onset: 3-5mins
- Duration: 60-90mins.
- Aminosteroid
Which NDMB should not be given for renal transplant Sx?
Vecuronium(Norcuron)
How do acidosis & NDMB relate?
- If acidotic prior to NDMB then blockade will remain the same.
- If NDMB is given and then Pt becomes acidotic then blockade is prolonged.
Which NDMB’s degradation is affected by pH & temp?
Nimbex (Cisatracurium) & Atracurium
When is a larger dose of Pancuronium dose needed?
In liver failure
What are the pros of N2O?
- Does not cause muscle relaxation
- Does not blunt HPV
- Does not cause cardiac depression / minimal arrhytmia
- Slight increase in CO
- No N/V with <0.5 MAC
- Useful for mom’s post-delivery d/t analgesic effects without opioids
What are the cons of N2O?
- Do not give to pregnant ppl w/ B12 deficiency
- Causes bone marrow suppression
- Increase in myocardial events w. atherosclerosis
- Increases PVR
- Do not use in ear, eye, abdominal & pneumothorax cases
Who should not receive N2O?
- pregnant w/ low B12
- atherosclerosis
- osteoporosis
- anemic Pt’s
- immune suppressed
- pulmonary HTN Pt’s
- eye, ear or abd Sx
What are the pros (2) of Halothane?
- Bronchodilation
- Low risk for N/V
What are the cons (6) of Halothane?
- Increases ICP & CBF
- Decreases portal vein flow
- Arrhythmias
- Hepatic necrosis
- Pediatric bradycardia
- Decomposes into HCL acid
Who should not receive Halothane?
- Pt’s wtih ESRD
- hepatic failure
- neuro Pts
- Pt’s w/ arrhythmias