Knowledge
The highest rated collections of articles, notes and knowledge from metajournal.
Airway
Analgesia
Anesthesia
Complications
Covid
Critical care
Decision making
Drugs
Epidural
Intrathecal
Intravenous anesthetics
Neuromuscular agents
Obstetric anesthesia
Opioid
Pain
Pediatric anesthesia
Perioperative medicine
Postoperative complications
Regional anesthesia
Sugammadex
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Sedative-hypnotic drug with anaesthetic and anticonvulsant effects.
A. Physiochemistry
- Thiobarbiturate
- Highly lipophilic
- Presented in glass ampoule containing 2.5% powdered form: a. 500 mg thiopentone (anhydrous yellow powder) b. 30 mg sodium carbonate (buffer) c. 0.8 atm of N2 (reduces oxidation)
- made up with H2O to 20 mL
- pH 10.8, pKa 7.6 (ie. ~ pH 11 pKa 7)
- Weak acid
- 60% non-ionised @ pH 7.4 (vs. methohexitone 75%)
- Racemic mixture (l potency > d)
- Demonstrates tautomerism, with water soluble enol form (double bond) in solution → lipid sol keto form at pH 7.4.
- First administered 1934
B. Pharmacokinetics
- Dose - 5 mg/kg (methohexitone 2-3x more potent)
- Absorption - IV, oral, rectal (at higher doses)
- Distribution - Vdcc 0.4 L/kg, Vdss 2.5 L/kg
- fat:blood coeff 11:1 (ie. thio will move into fat until [fat] 11x [blood])
- Protein binding - 75% (prop 98%, methohex 65%)
- Onset within 1 brain-arm circ time (< 60s), Offset 5-15 min
- Metabolism - alpha1 ½ 5 min, alpha2 ½ 1 h, ß ½ 8-11 h, CSHT-8h: 3 h; phase I p450 side-arm oxidation, desulfuration to pentobarbitone (t½ 40h) and ring cleavage to urea and 3-carbon fragments.
- some extrahepatic (renal) metab.
- NB: alpha1 ½ (fast-alpha) is equilibration with/from effect site - alpha2 ½ (slow-alpha) with slow compartments.
- Clearance - 4 mL/kg/min (methohexitone: 3x greater 12 mL/k/m)
C. Pharmacodynamics
- Mech - potentiates GABA inhibition, dec rate of GABA dissociation (like propofol) and at high doses directly activ GABA rec.
- CNS - anaesthetic, anticonvulsant, sedative, ant-analgesic.
- Dec CBF, CMRO2 (max 55%), ICP, IOP.
- EEG (alpha → theta → delta) ⇣ freq, ⇡ ampl → burst suppression → isoelectric.
- Some focal cerebral protection (requires 40 mg/kg !!)
- CVS - Negative inotrope (direct effect and indirect dec SNS outflow), dec CO 20%, vasodilation, dec venous return → ⇣ MAP 20-30%. Compensatory ⇡ HR.
- Histamine release & dysarrythmias rarely occur.
- Resp
- Respiratory depression (initial ⇡ TV, ⇣ RR)
- Bronchoconstriction & laryngospasm risk (due to ⇣ SNS outflow).
- Renal - ⇣ RBF & GFR 2° ⇣ BP.
- GIT - ⇣ GIT motility, ⇣ HBF, enzyme induction.
- SEs - inhibits neutrophil function; anaphylaxis 1:20,000; porphyria (stims d-ALA synth); inta-arterial injection; thrombophlebitis (> methohexitone 3-4%).
- Crosses placenta; foetal tß½ 11-44h.
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Although there remains much conflicting evidence, largely of a low-quality observational nature, the highest quality evidence to date refutes assertions that epidural fentanyl reduces breastfeeding rates.
Notably Lee et al.’s 2017 RCT of over 300 women showed no effect of epidural fentanyl up to 2 mcg/mL and successful maternal breastfeeding up to 6 weeks.
summary
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This growing collection of articles focuses on the evidence and expert guidance relating to the use of personal protective equipment (PPE) and the SARS-CoV-2 / COVID pandemic, with specific focus on PPE use by anaesthesiologists and anaesthetists.
More articles can found found via the PPE topic index.
What we know:
- Hospitals are frequent sources of outbreaks, among both staff, patients and the wider community.
- The quality of PPE evidence is low. Most evidence must be contextualised in consideration of expert opinion, and of the similarities between SARS-CoV-2 and SARS (SARS-CoV-1), MERS and influenza.
- Droplet-vs-airborne spread is a conceptual simplification and not a simple dichotomy. It is best understood as a spectrum of transmission risk.
- Time-exposed may be a more important consideration, especially in indoor, poorly ventilated spaces.
- PPE supply is globally limited, and so a pragmatic approach must be taken to its use, considering individual risk scenarios.
- Training, simulation and fit testing are critical for effective use of PPE.
- There are specific steps in the PPE donning & doffing workflow that are frequently associated with breaches exposing HCWs to infection. These require extra attention.
- Beyond cost, increasingly complex PPE (eg. PAPR, hoods, intubation boxes etc.) also increase the opportunity for PPE failure and exposure if users have not had adequate training in their use, and some PPE has been demonstrated to make intubation more difficult.
- The superiority of N95/P2 respirator masks over standard surgical masks for personal protection is unclear and unproven.
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Papers focusing on the history of anesthesia – both modern articles and the original historical, landmark articles themselves.
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