K
Kallikreins. Serine protease enzymes in tissue and plasma, performing diverse physiological functions. Produce kinins from kininogens and may also catalyse formation of renin from prorenin. Plasma kallikrein is produced from prekallikrein by various activating substances, including part of activated coagulation factor XII. Plasmin, a fibrinolytic enzyme, catalyses the reaction, as does kallikrein itself. Inhibited by aprotinin. Prostate-specific antigen (PSA) is a kallikrein used as a biomarker for prostatic cancer.
Katharometer. Device used for gas analysis, following separation, e.g. by gas chromatography. A heated wire is placed in the gas flow; different gases have different thermal conductive properties and therefore produce different changes in electrical resistance of the wire. Particularly useful in detecting inorganic gases, e.g. helium, CO2, N2O and O2. Used to quantify the amount of a known gas, not to identify unknown ones.
Kawasaki disease (Musculocutaneous lymph node syndrome). Autoimmune systemic vasculitis of unknown aetiology, usually affecting children < 5 years old. Incidence is 3.4 per 100 000 in the UK; three and 30 times more common in the USA and Japan respectively. Important because arteritis can lead to formation of coronary artery aneurysms in 15% of cases if untreated, with mortality of up to 4%. May present with fever (typically for more than 5 days), conjunctivitis, reddened lips, mouth and tongue, desquamating rash, peripheral oedema and cervical lymphadenopathy. Diagnosis may be difficult because not all these features may be present at once, other non-specific symptoms may be present (e.g. cough, abdominal pain, vomiting, arthralgia) and there is no diagnostic test. Treatment is with iv immunoglobulin 2 g/kg over 10 h and aspirin 30 mg/kg/day in 3–4 divided doses.
[Tomisaku Kawasaki, Japanese paediatrician]
Harnden A, Takahashi M, Burgner D (2009). Br Med J 2009; 338: 1133–8
Kelvin. SI unit of temperature. One kelvin (K) = 1/273.16 of the thermodynamic scale temperature of the triple point of water (point at which solid, liquid and gaseous water are at equilibrium). nK = (n – 273.16)°C.
[William Thomson (1824–1907), Irish-born Scottish physicist; became Lord Kelvin in 1892]
Kerley’s lines. Opaque markings seen on the CXR:
Ketamine hydrochloride. Phencyclidine derivative (Fig. 94), first used as an iv anaesthetic agent in 1965. Increasingly used for postoperative analgesia and sedation on ICU. An antagonist at NMDA receptors; also interacts with opioid, monoamine and cholinergic receptors. Recently described anti-inflammatory effects may be via reduced expression of cytokines (e.g. interleukin-6) by activated macrophages.
induction of anaesthesia, traditionally in shocked patients. Produces a state of ‘dissociative anaesthesia’: intense analgesia with light sleep. Increased thalamic and limbic activity occurs, with dissociation from higher centres.
maintenance of anaesthesia as the sole agent, especially in burns and trauma, or short procedures (e.g. radiotherapy and radiological investigations). Widely used in battlefield and pre-hospital anaesthesia due to its relative preservation of upper airway reflexes. Its routine use at anaesthetic doses in adults is limited by psychomimetic emergence phenomena (see below).
perioperative analgesia: when given perioperatively, has a potent opioid-sparing effect, with reduced PONV and minimal side effects.
treatment of acute (e.g. postamputation) and chronic neuropathic pain.
adjunct in regional anaesthesia: has local anaesthetic properties, and has been used for spinal and epidural anaesthesia within clinical trials; concerns over direct neurotoxicity have restricted its use beyond the trial setting.
possible neuroprotective effects via its NMDA receptor antagonism.
abuse as a recreational drug (‘K’, ‘Special K’), leading to its classification as a Class C drug under the Misuse of Drugs Act in 2006.
Ketamine is commercially available as a racemic mixture of two isomers or as the pure S(+) enantiomer. The latter is 2–4 times as potent as the R(–) enantiomer and less psychoactive, with a higher clearance and thus more rapid recovery.
Presented in 10, 50 and 100 mg/ml solutions, containing benzethonium chloride (the 10 mg/ml solution since 1997). pH is 3.5–5.5; pKa 7.5. 12% bound to plasma albumin. Elimination half-life is about 3 h. Metabolised in the liver to weakly active metabolites, excreted in urine.
• Effects:
iv induction: smooth, but slower than thiopental (about 30 s).
– BP and heart rate usually increase; cardiac output is maintained. Changes are probably via direct myocardial and central sympathetic stimulation, and blockade of noradrenaline uptake by sympathetic nerve endings. Contraindicated in severe ischaemic heart disease and hypertension.
– respiratory depression after rapid iv injection, but less than with other agents.
– bronchodilatation via a direct action and sympathomimetic effects.
– analgesia at subanaesthetic doses.
– increased muscle tone, twitching, blinking and nystagmus.
– increased cerebral blood flow and ICP; contraindicated in pre-eclampsia and severe intracranial pathology.
– anterograde amnesia in some cases.
– at anaesthetic doses may cause vivid dreams and emergence phenomena, e.g. unpleasant hallucinations. Usually less distressing in patients < 15 or > 65 years. Hallucinations may be reduced by benzodiazepines, and delirium by butyrophenones. physostigmine has also been used. Preoperative counselling, opioid/hyoscine premedication and recovery in a quiet, darkened room may also reduce their incidence.
– may cause nausea and vomiting. Salivation is increased.
– increases intraocular pressure; contraindicated in open eye operations.
– does not cause histamine release.
• Dosage (for racemic ketamine; dosages for S-ketamine are approximately 50% lower):
iv induction: 1–2 mg/kg. Effects last for 5–10 min. Supplementary doses 0.5 mg/kg.
im induction; 10 mg/kg. Acts in 3–5 min, lasting 20–30 min.
sedation (e.g. whilst performing regional techniques or on ICU): 2 mg/kg im, 10 mg increments iv, or 1–2 mg/kg/h infusion.
to treat severe asthma: 0.5–2.5 mg/kg/h infusion.
Himmelseher S, Durieux ME (2005). Anesthesiology; 102: 211–20
Fig. 94 Structure of ketamine
Ketanserin. 5-HT antagonist, and weak α1–adrenergic receptor antagonist. Also has class III antiarrhythmic properties. Has been used to prevent vasoconstriction and bronchospasm in carcinoid syndrome, and also to provide vasodilatation and hypotension in cardiac surgery.
Ketoacidosis
