Top Tweets for #differentialblockade

8 months ago

🧠 C Fibres in Regional Anesthesia: Blockade, Vulnerability, and Misconceptions #RegionalAnaesthesia #Cfibres #DifferentialBlockade #LocalAnaesthetics #Neurotoxicity #PainPhysiology #AnesthesiaEducation #EDRA #FRCA #RAPM #LASusceptibility #UltrasoundGuidedBlocks #AnatomyMeetsAnaesthesia #KnowBeforeYouBlock #TipOfTheDay #MyRATips Tip of the Day: 🧬 Structural Reality 🔸 C fibres are unmyelinated and therefore do not possess internodal distances 🔸 Their response to local anaesthetics (LAs) cannot be explained using mechanisms applicable to myelinated fibres ⚡ Why C Fibres Appear to Block Early 🔸 C fibres are often described as relatively resistant to LA-induced conduction block 🔸 Yet, they may appear blocked earlier during differential blockade 🔸 This is not due to higher intrinsic LA sensitivity, but because of: 🔸 small axonal diameter 🔸 continuous (non-saltatory) conduction 🔸 high tonic firing rates 🔸 use-dependent sodium channel blockade 🔸 These factors allow conduction failure with fewer blocked channels 🔄 Sequence of Differential Blockade 🔸 Differential blockade depends on fiber diameter, firing frequency, and sodium channel kinetics, not myelination alone 🔸 The classical order of susceptibility is: B → A-δ → C → A-γ → A-β → A-α 🔸 B fibres (preganglionic autonomic) block first 🔸 Followed by A-δ and C fibres (pain and temperature) 🔸 Then A-γ and A-β fibres (muscle tone and touch) 🔸 A-α fibres (motor) are blocked last ⚠️ Blockade Susceptibility ≠ Damage Susceptibility 🔸 Susceptibility to LA-induced conduction blockade and susceptibility to LA-induced neural damage are two fundamentally different concepts 🔸 Fibres that block early are not necessarily more sensitive to LA toxicity 🔸 Conversely, fibres relatively resistant to blockade (e.g., C fibres) may be more vulnerable to cytotoxic injury ☠️ Why C Fibres Are More Vulnerable to LA Damage 🔸 unmyelinated structure 🔸 high surface-area–to–volume ratio 🔸 lack of myelin insulation 🔸 prolonged or high-concentration LA exposure 🎯 Clinical Take-Home 🔸 Early analgesia from C-fiber block ≠ higher anesthetic sensitivity 🔸 Block characteristics must not be equated with neurotoxic susceptibility 🧠 Mnemonic to Lock It In "High Pressure Load on BACK" 🔸 🫁 Hypoxia → B fibres 🔸 🧱 Pressure → A fibres 🔸 💉 Local anaesthetic toxicity → C fibres 👉 Hypoxia–B | Pressure–A | LA–C

KartikBSonawane's tweet photo. 🧠 C Fibres in Regional Anesthesia: Blockade, Vulnerability, and Misconceptions

#RegionalAnaesthesia #Cfibres #DifferentialBlockade #LocalAnaesthetics #Neurotoxicity #PainPhysiology #AnesthesiaEducation #EDRA #FRCA #RAPM #LASusceptibility #UltrasoundGuidedBlocks #AnatomyMeetsAnaesthesia #KnowBeforeYouBlock
#TipOfTheDay #MyRATips

Tip of the Day:

🧬 Structural Reality

🔸 C fibres are unmyelinated and therefore do not possess internodal distances
🔸 Their response to local anaesthetics (LAs) cannot be explained using mechanisms applicable to myelinated fibres

⚡ Why C Fibres Appear to Block Early

🔸 C fibres are often described as relatively resistant to LA-induced conduction block
🔸 Yet, they may appear blocked earlier during differential blockade
🔸 This is not due to higher intrinsic LA sensitivity, but because of:
🔸 small axonal diameter
🔸 continuous (non-saltatory) conduction
🔸 high tonic firing rates
🔸 use-dependent sodium channel blockade
🔸 These factors allow conduction failure with fewer blocked channels

🔄 Sequence of Differential Blockade

🔸 Differential blockade depends on fiber diameter, firing frequency, and sodium channel kinetics, not myelination alone
🔸 The classical order of susceptibility is:
B → A-δ → C → A-γ → A-β → A-α

🔸 B fibres (preganglionic autonomic) block first
🔸 Followed by A-δ and C fibres (pain and temperature)
🔸 Then A-γ and A-β fibres (muscle tone and touch)
🔸 A-α fibres (motor) are blocked last

⚠️ Blockade Susceptibility ≠ Damage Susceptibility

🔸 Susceptibility to LA-induced conduction blockade and susceptibility to LA-induced neural damage are two fundamentally different concepts
🔸 Fibres that block early are not necessarily more sensitive to LA toxicity
🔸 Conversely, fibres relatively resistant to blockade (e.g., C fibres) may be more vulnerable to cytotoxic injury

☠️ Why C Fibres Are More Vulnerable to LA Damage

🔸 unmyelinated structure
🔸 high surface-area–to–volume ratio
🔸 lack of myelin insulation
🔸 prolonged or high-concentration LA exposure

🎯 Clinical Take-Home

🔸 Early analgesia from C-fiber block ≠ higher anesthetic sensitivity
🔸 Block characteristics must not be equated with neurotoxic susceptibility

🧠 Mnemonic to Lock It In

"High Pressure Load on BACK"
🔸 🫁 Hypoxia → B fibres
🔸 🧱 Pressure → A fibres
🔸 💉 Local anaesthetic toxicity → C fibres

👉 Hypoxia–B | Pressure–A | LA–C

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