· PC: pros and cons
· PK: pros and cons
· PD: pros and cons
Pros |
Cons |
· Liquid form -> efficient storage |
· Impurities from manufacturing: NH3, N2, NO, NO2 · e.g. NO2: airway damage, headache, heart failure |
· Sweet smell, non irritant -> good for gas induction |
· Set-up and maintenance costs: wall supply, cylinder manifolds etc. |
· Inert: no reaction with rubber, plastic, sodalime |
· Need to reduce filling ratio from 0.75 to 0.67 in hot climates |
· Low potency (MAC 105%): use as carrier gas |
· Entonox lamination: occurs if below pseudocritical temperature (-6°C) · Delivery of hyperoxic then hypoxic mixture |
|
· Supports combustion, although not itself flammable · Risk of fire, explosion in airway laser surgery · Destructive to ozone layer |
|
Pros |
Cons |
|
N2O 30x more soluble, blood-gas partition coefficient 0.47; equilibrates across membranes rapidly N2 30x less soluble, BGPC 0.014; equilibrates across membranes slowly |
|
A |
Rapid onset during gas induction:
1) Concentration effect: · Seen only with high volume carrier gases · Switch from N2/O2 to N2O/O2 · Rapid uptake N2O from alveolus, but very slow output of N2 · ↓ alveolar volume and pressure -> rapid inflow of N2O-rich fresh gas · Accelerated ↑ FA/FI N2O
2) Second gas effect: · Rapid uptake N2O, very slow output of N2 · Concentration of remaining alveolar gas · Accelerated ↑FA/FI volatile drug |
- |
D |
· Low muscle:blood PC (1.2) · Low fat:blood PC (2.3) · Minimal accumulation in long case |
Expansion of existing closed air spaces: · ↑size pneumothorax · ↑Bowel gas -> difficult laparoscopy · ↑Ocular gas (if surgery using SF6) · ↑Pneumocephalus (if brain surgery) |
M |
· Minimal (0.004%) |
- |
E |
|
Diffusion hypoxia: · Reverse of concentration effect · N2O/O2 off, N2/O2 on · N2O diffuses rapidly out of blood into alveolus · N2 slow to be taken up from alveolus · Dilution of alveolar O2 -> hypoxia |
|
Pros |
Cons |
CVS |
· Stability: ↑SNS offsets ↓inotropy |
· Direct negative inotropy may be unmasked if on exogenous intrope |
Resp |
· Mild ↑RR, ↓TV, minimal ↑PaCO2 |
· ↑RR, ↓TV · ↑SNS output -> ↑PVR -> ↑RV strain · Carrier gas -> ↓FiO2 |
CNS |
·
Additive with volatile anaesthetics · Analgesia (NMDA antagonist), may reduce risk of chronic pain |
· MAC 105%, MAC-awake 67%; inadequate alone for anaesthesia · Pro-emetic · ↑CBF · Minimal effect on EEG; BIS/entropy unhelpful · Euphoria, abuse potential |
Other |
· No vasodilation, MAC sparing -> ↓bleeding · Does not trigger MH |
Mutagenesis: · Oxidises cobalt atom in Vitamin B12, a cofactor for methionine synthetase · Impaired DNA synthesis · Megaloblastic anaemia · Subacute combined degeneration of the cord (chronic abuse) · Teratogenesis · ? ↑Risk abortion in PACU staff |
Feedback welcome at ketaminenightmares@gmail.com