INTRAVENOUS ANAESTHETICS - 1
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CNS | Agent | Thiopentone | Methohexitone | Propofol | Ketamine |
| EEG | 1. awake alpha 2. ↑amp ↓f δ τ 3. burst supression 4. flat EEG |
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| Dissociation thalamocortical and limbic systems | |
| CBF | ↓ (v/c) |
| ↓ (v/c) | ↑ > CMRO2 | |
| Autoregulation |
|
| Preserved | Preserved to pCO2 | |
| ICP | ↓ > ↓ MAP |
| ↓ 30%-50%if raised ICP | ↑ | |
| CPP | maintained |
| ↓ 10% |
| |
| CMRO2 | ↓ >> ↓ CBF (max 55%) |
| ↓ 36% | ↑ | |
| Protection | In regional ischaemia |
| yes |
| |
| Convulsant | anticonvulsant | Assoc with seizures | anticonvulsant | anticonvulsant | |
| IOP | ↓ 40% |
| ↓ 40% | ↑ | |
| SSEP | maintained |
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| Other |
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| ?seizures | Eyelash OK | |
| Mechanisms | ↓ Neuronal metab cerebral v/c |
|
| Catalepsy | |
|
CVS | CO | ↓ 20% if hypovol |
| ↓ | ↑ |
| BP | ↓ 10-20mmHg |
| ↓ 25% (v/d & ↓contr) | ↑ (central ↑Σ) | |
| SVR | No change |
| ↓ | ↑ | |
| Barorec reflex | Sl ↓ |
| Reset or inhibited | attenuated | |
| HR | Reflex ↑ | ↑ >thio | 0 | ↑ | |
| Contractility | ↓ ( |
| ↓ | ↑ (direct depression) | |
| Arrhythmias | no |
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| Mechanisms | ↓Σ → veno/d ↓ Ca transport (transmembrane, SR) & NO mech |
| (↓Σ & NO, direct effect on Ca mobilisation) | Central attenuation barorec reflex via NMDA rec in NTS Inhibit uptake 1 & 2 | |
|
Resp | Resp dep | + + |
| + + 50% ↓to CO2 | 0 |
| RR | ↓ then apnoea |
| 20%↑ then apnoea>30sec | Transient ↓ 2mins | |
| TV | ↑ |
| ↓40% |
| |
| Reflexes | Late depression |
| Obtund > thio | intact | |
| Bronchial m | ?b/c | No b/c | b/d | B/D | |
| Other | ↓ mucociliary clearance |
|
| ↑secn, | |
| Mechanisms |
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| Direct antagonism His & ↑Σ, anti-chol | |
| Hepatic | Blood flow | Small ↓ |
| ↓ |
|
| Enzymes | ↑ 20-40% in 2-7/7 |
| Inhibits cytP450 | Induction | |
| Renal | Blood flow | ↓RBF & GFR |
| Green urine |
|
| Obste- trics | Uterine tone | 0 |
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| Placental T/F | Low if <> |
|
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| |
| MH | Trigger |
| No | No |
|
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SEs | Pain on inject | 1-2% | Pain 80% | Pain 30-80% | Pain |
| Thrombophleb | Thrombophlebitis | Thrombosis 4% (>thio) |
|
| |
| Intra-art inject | Intra-art→gangrene | No problem |
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| |
| Other | Hangover Hyperalgesic Dose dep His | Excitatory 33% (hiccup, cough, twitch, hypertonus) | Anti-emetic/shiver Sexual disinhibit Allergy Bacterial growth | Psychic effects ↑cardiac O2 con PONV Potentiated NDMBs | |
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Special | CIs | Porphyria (AIP, variegate) ↑D-ALA synthetase tamponade, CCF hypovolaemia | Porphyria | Safe porphyria | IHD Raised ICP or IOP Psychiatric D
|
| Other | Tolerance sed > anticonv |
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| Analgesia (NMDA) |
Category: Pharmacology Notes
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