X

Figure PH.30 Good and bad electrical practice Figure PH.30 Good and bad electrical practice Electrocution can occur with very low voltages and currents when there is electrical contact directly with the heart, as with intracardiac electrodes, angiographic injection pumps or pacemakers. Currents of a fraction of a milliampere through the myocardium are then sufficient to cause ventricular fibrillation, a process known as micro-electrocution - as distinct from the gross electrocution where the...

Posterior Pituitary

Pituitary Posterior

The posterior pituitary secretes two peptides which are synthesized in the hypothalamus and then transported down axons within the pituitary stalk to be stored in vesicles ready for subsequent release into the bloodstream in response to appropriate stimuli (Figure EP.3). The anterior pituitary secretes six peptide hormones, ACTH, TSH, FSH, LH, prolactin and growth hormone. See below for details. Figure EP. 1 Portal system of the pituitary gland Figure EP. 1 Portal system of the pituitary gland...

Sickle Cell Disease

Sickle cell disease is due to a haemoglobinopathy which is inherited autosomally resulting in the formation of haemoglobin (Hb) S instead of haemoglobin A. The S variant consists of 2 normal alpha chains and 2 abnormal beta chains in which glutamic acid has been substituted by valine in the sixth amino acid from the N-terminal. Small decreases in oxygen tension cause HbS to polymerise and form pseudo-crystalline structures which distort the red blood cell membrane to produce the characteristic...

The Peritubular Capillaries

The end result of the transport processes described above is the passage of essentially isotonic fluid from the tubule lumen, into the lateral intercellular spaces (LIS). This occurs mainly through tubular cell reabsorption and secretion, but some paracellular movement also occurs into the LIS, but mainly in the late proximal tubule. From here, the NaCl-NaHCO3 solution can move in two possible directions either into the peritubular capillaries, or back into the tubular lumen. A proportion of...

Body Stores of Oxygen and CO2

Co2 Transport Blood

The oxygen stores of the body are relatively small in comparison to the consumption (around 250 ml min for an adult). Total body oxygen is about 1.5 litres, which is held as 20 in combination with myoglobin Not all stored oxygen is available for use since severe hypoxaemia occurs before even half of the oxygen stored in combination with Hb and myoglobin is released. These available stores will last only for 3-4 min of apnoea, assuming air breathing and normal oxygen consumption. Breathing 100...

Metabolism

This term is used to describe the complex mass of biochemical reactions which breakdown the absorbed products of digestion to extract chemical energy, synthesize substances for structural maintenance and growth, and synthesize or detoxify waste products. The organisation of metabolism can be visualized as being composed of three sets of interlinked pathways. These deal with the three main types of molecule fed into the system, and are often referred to separately, as carbohydrate metabolism,...

Henderson Hasselbach Equation

In any buffer system consisting of a dissociating weak acid HA, the pH of the buffer solution is dependent on the ratio of conjugate base concentration A- to undissociated acid concentration HA . Re-arranging the equation for K from above which is known as the Henderson-Hasselbach equation. Bicarbonate Buffer System In the body fluids, there are several buffer systems. These are summarized in Figure RE. 15. Haemoglobin (HHb Hb- and HHbO2 HbO2) Plasma proteins (H+-protein protein-) Phosphate...

Anti Convulsant Drugs

Epileptic events are the result of repetitive neuronal discharges in the CNS involving many neurones. Anti-convulsant drugs act by breaking these propagating and recycling currents either by increasing inhibitory neurotransmitter levels or by facilitating their action by modulating the y-amino butyric acid (GABA) receptor function. There is the potential for new drugs to be developed that would inhibit excitatory neurotransmitters and their receptors (the N-methyl-D-aspartate agonist-receptor...

Measurement of Humidity

Thermometer Hysteresis

Historically the measurement of humidity was an important contribution to the safe practice of anaesthesia. The combination of static electric sparks, and the use of flammable anaesthetic gases (e.g. ether) constituted a significant risk to both patient and anaesthetist. One of the measures used to reduce static electricity, and hence the incidence of fires and explosions was to maintain the relative humidity in the operating theatre > 50 . While this is no longer a major consideration in...

Function of Muscle Spindles

Stretch Spindle

The central portion of the muscle spindle detects the change in length of the muscle. When the muscle as a whole contracts, the muscle spindle relaxes and firing in its afferent axon stops. However, the opposite occurs when the muscle relaxes or is stretched passively. In other words, the muscle spindle acts as muscle length detector. This should not to be confused with the Golgi tendon apparatus, which are stretch receptors within tendons and respond to the tension, not length, within the...

Types of Gas Analyser

Gas and vapour analysers can be usefully divided into discrete analysers (extremely accurate), or continuous analysers (less accurate). Discrete analysers are rarely used in clinical anaesthesia. An example of discrete analysis is provided by gas liquid chromatography. In this method the unknown gas mixture is injected into a stream of carrier gas (e.g. nitrogen) flowing through a column of liquid coated particles, the 'stationary phase' (e.g. polyethylene glycol). As the gas mixture passes...

Electrolyte Disturbances

Disturbances of electroytes may be due to the underlying disease process, to drugs, particularly diuretics, or to iatrogenic causes. It is rare for a patient to exhibit overt clinical signs but electrolyte disturbances present several potential problems for the anaesthetist (Figure PR.3). It is particularly important to assess the volume status of the patient who has an electrolyte disturbance. Electrolyte disturbances are more likely to be acute and, hence, more serious in patients presenting...

Amide Linked Agents Bupivacaine

Bupivacaine is a long-acting local anaesthetic agent with a slow onset of action. Blockade of a large peripheral nerve such as the sciatic nerve may take 60 min depending on the approach but may last up to 48 H. Intrathecal injection in contrast produces an acceptable block within a few minutes. Bupivacaine is particularly prone to causing myocardial depression and, once compromised, reversal may be slow and difficult. In part this is due to the relatively high pKa but an affinity for cardiac...

Control of Gastric Motility and Emptying

The rate at which chyme is released from the stomach into the duodenum is carefully controlled so that the small bowel is presented with partially digested material at the optimum rate to allow further digestive and absorption processes to occur. Several factors affect the tone of the proximal stomach. The activity of the distal stomach and the tone of the pylorus are particularly important in controlling the mixing of gastric contents, and the rate of gastric emptying. The overall integration...

Measurement of Gas Flow

Benedict Roth Spirometer

The measurement of gas flow and volumes is applied in clinical practice for the following uses To test pulmonary function in patients To monitor gas flows in anaesthetic machines To monitor respiratory flows and tidal volumes in patient breathing circuits Devices used in pulmonary function testing are outlined below. Figure CM.20 Benedict-Roth Spirometer Figure CM.20 Benedict-Roth Spirometer Consists of a light bell that traps a closed volume of air over water. The subject breathes in and out...

Absorbance Curves for HbO2 and Hb

Absorbance can be plotted against wavelength to give curves for HbO2 and Hb (Figure CM.37). It can be seen that the absorbance of both compounds is high for shorter wavelengths (< 600 nm) of light since they are both basically red in colour. However, at longer wavelengths in the red region of the electromagnetic spectrum, the absorbance of HbO2 is less than that of Hb. This gives HbO2 a brighter red appearance than Hb. At these longer wavelengths, the curves display secondary peaks in...

Clinical Pictures Seen After Hiv Infection

PGL (persistent generalised lymphadenopathy) PGL is characterised by the presence of extra-inguinal lymph nodes for more than 3 months, and may be painful. Histology generally shows reactive change. One third progress to AIDS within 5 years. ARC has the following features chronic fatigue, weight loss, night sweats, recurrent fever, chronic skin infections, intermittent diarrhoea and myalgia. Inevitable progression to AIDS is seen. AIDS encephalopathy is a psychomotor and psychoneurological...

Airway and Cervical Spine

The priority during the resuscitation of any severely injured patient is to ensure a clear airway and maintain adequate oxygenation. A pulse oximeter probe should be applied to the patient as soon as possible remembering that peripheral vasoconstriction may make it impossible to obtain a reliable reading. If the airway is obstructed, immediate basic manoeuvres such as suction, chin lift, and jaw thrust may temporarily clear it. A soft nasopharyngeal airway (size 7.0-7.5 mm) may be particularly...

Anti Depressant Agents

There are several different classes of anti-depressant agents. The classic groups of tricyclic agents and TYPES OF EPILEPSY AND DRUG CHOICE Status epilepticus Phenytoin or Phenobarbitone or Chlormethiazole or Paraldehyde Carbamazepine or Phenytoin or Valproate or Phenobarbitone Valproate or Clonazepam or Ethosuximide (Usually childhood especially if any cerebral damage) Clonazepam or Ethosuximide or Lamotrigine or Phenobarbitone or Phenytoin or Valproate inhibitors of monoamine oxidase have...

Sequelae of Anaesthesia

Complications occurring after surgery result from a combination of patient, surgical, and anaesthetic factors. Morbidity directly attributable to anaesthetic practice is often relatively minor, e.g. post operative sore throat, but can result in permanent disability, e.g. hypoxic brain damage. An increasing number of medico-legal claims are made against anaesthetists each year which highlight the virtues of diligence, attention to detail and continued observation throughout the administration of...

ENT and Dental Surgery

The core of both ENT and dental anaesthesia is the problem of the shared airway. In both types of surgery the anaesthetist and the surgeon need good access to a clear airway kept free of debris and blood. This has resulted in the development of special equipment and techniques for this situation. In the main, dental surgery in children is restricted to simple exodontia. Historically the main indication was caries but with improvements in dental hygiene and fluoridation of water the reason has...

Digestion and Absorption

Digestion is the chemical breakdown of ingested food by GI enzymes into substances that can then be absorbed from the intestines into the systemic circulation. The organ principally responsible for these functions is the small intestine, although some digestion and absorption may occur in the mouth and stomach. The small bowel can only absorb the carbohydrates glucose, fructose and galactose. Therefore, all dietary carbohydrate must be broken down to one of these monosaccharides. Cellulose is a...

Smoking

Figure PR.4 ECG changes associated with hypo- and hyperkalaemia Figure PR.4 ECG changes associated with hypo- and hyperkalaemia A heavy smoker is anyone who smokes 20 or more cigarettes per day. Smoking causes several perioperative problems increased airway reactivity increased sputum production and retention bronchospasm coughing and atelectasis associated with an increased risk of post operative chest infection. Associated diseases include ischaemic heart disease and chronic obstructive...

Section 213 Physiology of Pregnancy

Cardiovascular system Haematology Respiratory system Gastro-intestinal system Central nervous system Endocrine system Renal function Musculoskeletal system Weight gain Embryology and anatomy Functions of the placenta Placental transport Hormone secretion Placental transfer of drugs Normal pregnancy involves major physiological and anatomical adaptations by maternal organs. It is important that anaesthetists involved in the care of the pregnant woman understand these changes to provide...

Automaticity of Pacemaker Cells

Automaticity is the ability of pacemaker cells to maintain a spontaneous rhythm and depends mainly on the leakage of sodium into the cell in phase 4 of the AP. This occurs via specific sodium channels that are activated when the membrane potential has become hyperpolarized i.e. reached about 50 mV during repolarization. These channels then allow an inward hyperpolarization current (if), which commences the spontaneous depolarization of phase 4. The sodium current (if) is aided to a small extent...

Section 41 Basic Physics

Universal constants Scalars and vectors BASIC MATHEMATICAL CONCEPTS Functions Basic calculus Mass, force and acceleration Work and energy Power and efficiency Boiling point and pressure Cooling by evaporation Mechanisms of energy transformation Pressure volume and temperature Henry's Law and Graham's Law Hydrodynamics Electrical charge Electrical current Electrical resistance Electrical energy Capacitance and inductance Transformers Electrical components ELECTRICAL SAFETY Physiological aspects...

Coronary Blood Flow

Total coronary blood flow at rest is about 250 ml min. The myocardium normally extracts about 70 of the oxygen content of coronary blood at rest thus, increasing coronary perfusion is the only way to increase oxygen delivery. At rest the oxygen requirement of the myocardium is 10 ml min 100 g at rest giving a total basal oxygen requirement of 30 ml min for an adult. Cardiac muscle is versatile in its use of substrate, normally using 60 fatty acid and 40 carbohydrate as fuel. It may adapt to use...

Assessment

A pre-operative visit from the anaesthetist is appreciated by patients and has been shown to be a more effective anxiolytic than premedication. The aim of the pre-operative assessment is to ensure that the patient's health is optimal and that any potential difficulties during anaesthesia are anticipated. The operation details, including laterality, should be confirmed. A history should be taken of previous anaesthetic experiences and of any family history of problems connected with anaesthesia....

Retinal Surgery

Retinal detachments present sporadically but are not usually so urgent that they have to be done immediately on presentation. The patients are often hypertensive, though whether this is cause or effect is debatable. The surgery may be prolonged and is often carried out in semi-darkness. In this situation too soft an eye may be a disadvantage in that the low intra-ocular pressure may cause further tearing of the retina. Controlled ventilation is advantageous due to the duration of the surgery. A...

Special Senses Vision

Before reaching the photoreceptors on the retina, light must pass through the optical apparatus that is made up of the cornea, aqueous humour, lens and vitreous humour. The globe is protected by the sclera, which becomes transparent in the anterior part of the eye known as the cornea (Figure NE.9). Aqueous humour is produced by the ciliary processes and catalysed by the action of carbonic anhydrase it passes from the posterior chamber through the pupil into the anterior chamber of the eye. It...

The Electrocardiogram

In an electrophysiological sense the heart consists of two chambers. The two atria function as a single electrophysiological unit and are separated from the bi-ventricular unit by the fibrous AV ring. Electrical communication between these two units is only possible through the specialized conduction system. The main electrical events of the cardiac cycle are the mass de- and repolarization of the atria and ventricles. These can be thought of as waves of depolarization (or repolarization) that...

Placental Transport of Substances

The placenta acts as a barrier between maternal and foetal tissues. However, it is an imperfect barrier and most substances will cross the placenta as detailed below. Oxygen crosses the placenta by simple diffusion that depends mainly on the difference between the oxygen tension of the maternal blood in the intervillous space and the foetal blood in the umbilical artery. The PO2 of blood in the intervillous space varies greatly but will be dependent on maternal arterial PO2 (Figure PN.14)....

Transfusion Medicine

Transfusion medicine involves the procurement, processing, testing and administration of blood and its components. It is also concerned with the prevention, investigation and treatment of transfusion-related complications. To many disciplines this translates into the provision of safe red cells for transfusion as soon as possible. While emphasis is rightly placed on virological safety, the important objective of serological compatibility is the responsibility of the laboratory and clinicians,...

Expiration

In contrast with inspiration, the diaphragm relaxes during exhalation and the elastic recoil of the lungs, chest wall and abdominal structures compresses the lungs. Forced expiration for a cough or when airway resistance is increased requires the abdominal muscles and the internal intercostals. Paralysis of abdominal muscles produced by regional anaesthesia does not usually influence alveolar ventilation. Compliance of the Chest Wall and Lungs Mechanically the respiratory system consists of two...

Oxygen Therapy Devices

Oxygen enriched air can be provided to a tracheal tube connector or to disposable face mask in either an uncontrolled manner or from a delivery system that provides a known FIO2. Uncontrolled oxygen therapy from a face mask is usually adequate for the majority of patients whereas controlled oxygen is required for those dependent on the hypoxic drive to stimulate respiration. The simplest method is to deliver a low flow of pure oxygen to a lightweight plastic disposable mask. This flow is...

Morphology and Cellular Organisation of the Kidney

Each human kidney has 1-1.5 million functional units called nephrons. The nephron is a blind ended tube, the blind end forming a capsule (Bowman's capsule) around a knot of blood capillaries (the glomerulus). The other parts of the nephron are the proximal tubule, loop of Henle, distal tubule and collecting duct, although in transport terms the nephron has been divided into additional segments (Figure RE.1). The glomeruli, proximal tubules and distal tubules are in the outer part of the kidney,...

Non Adaptive Evolution

Non adaptive evolution suggests that the ageing process has evolved as an optimum balance between the limited energy sources available to the organism and the demands of normal function and repair. Several cellular mechanisms are associated with ageing. It is unclear at present whether any of these predominate in determining the rate and extent of the process. The more important processes are Accumulation of cells with random DNA mutations Increased cross-linking of collagens and proteins by...

Decreased Ventilatory Drive

The commonest cause of central respiratory depression is the residual effect of inhalational anaesthetic agents or peri-operative opioid administration. The effect of volatile anaesthetic agents is compounded as they are predominantly excreted via the lungs. An unconscious patient with low respiratory rate and pinpoint pupils is typical of opioid overdosage. Supportive treatment includes the administration of oxygen, maintenance of the airway and manual ventilation by mask or tracheal tube if...

Angiotensin II

A primary action of angiotensin II is its action on the zona glomerulosa of the adrenal cortex to promote the release of aldosterone. Very little aldosterone is stored but stimulation of its release promotes further aldosterone biosynthesis. Figure RE.12 Renin-angiotensin system Angiotensin II is an extremely potent vasoconstrictor. Normally this action plays a minor part in the maintenance of systemic blood pressure, but intrarenally this can alter the distribution of glomerular filtration A...

Non Steroidal Anti Inflammatory Drugs NSAIDS

The NSAIDs are a heterogeneous class of drugs grouped together by their common anti-inflammatory, analgesic and anti-pyretic properties. They are used for the treatment of mild-to-moderate pain, the treatment of chronic inflammatory conditions and in the management of post operative pain where they have an opioid sparing effect. The NSAIDs primarily mediate their effects by inhibition of the enzyme cyclo-oxygenase, which reduces prostaglandin synthesis. Prostaglandins are part of a large family...

Blood Gases

PaCO2 decreases to 3.7-4.2 kPa by the end of the first trimester and remains at this level until term (Figure PN.7). This is due to alveolar hyperventilation and gives rise to various compensatory mechanisms in an attempt to maintain normal pH. Metabolic compensation for the respiratory alkalosis reduces the serum bicarbonate concentration to about 18-21 mmol l, the base excess (BE) by 2-3 mmol l and the total buffer base by about 5 mmol l. Metabolic compensation is not complete, which explains...

Complications Of Epidural Analgesia

Intrathecal injection Intravascular injection Neurological Backache Pressure areas Dural tap occurs in about 0.5 of obstetric epidurals. Once recognised, the management is straightforward. There should be no bearing down in the second stage of labour and there should be an elective forceps delivery. After delivery an epidural infusion should be set up with 0.9 saline or Hartmann's solution, and 1 litre infused over 24 hours. The patient should be reviewed daily by a senior member of staff. If...

Hyperglycaemia

Decreased end organ sensitivity to insulin Excess administration of glucose solutions Treatment of hypoglycaemia is directed towards administration of glucose and removal of the root cause. Treatment of hyperglycaemia includes removal of the cause, administration of insulin in the acute phase and at a later stage augmentation of both the secretion and effect of endogenous insulin. Ideally, glucose should be administered by mouth. Its rapid absorption ensures rapid correction of limited...

Special Circumstances The Full Stomach

A patient with a full stomach requires a rapid sequence induction (RSI) to minimise the time from loss of consciousness to intubation with a cuffed endotracheal tube. Before beginning the induction it is necessary to minimise the pH and volume of gastric contents. This can be achieved by pharmacological methods if time allows and physical methods such as the aspiration via a nasogastric tube (see above). The term Rapid sequence induction' is preferable to crash induction', which implies an...

Adrenal Gland

The adrenal gland, on the upper pole of each kidney, consists of an outer adrenal cortex and inner medulla. The cortex forms about 70 of the gland, while the remainder is medullary tissue. The cortex and medulla form two distinct endocrine glands. Anatomically the adrenal cortex is divided into three zones (Figure EP.8). The outermost zona glomerulosa secretes mineralocorticoids (mainly aldosterone), the zona fasiculata secretes glucocorticoids (cortisol and corticostorone), while the innermost...

Ionic Basis of Membrane Potential

Like other excitable tissues in the body, the electrical potential of a neurone in the resting state is more negative on the inside of the cell compared with the outside. This polarity is maintained by the active transport of Na+ ions out of the cell, together with the active transport of K+ ions into the cell. However, there is a tendency for both ions to diffuse passively down their concentration gradient through leaky ion channels. During its resting state, the membrane is more permeable to...

The Pregnant Patient

Obstetric anaesthesia requires detailed knowledge of the physiological changes associated with pregnancy. Whilst these are covered thoroughly in Section 2, Chapter 13, the salient points are outlined below to aid the reader. As pregnancy progresses, the maternal blood volume increases and, although total haemoglobin increases, the haemoglobin concentration falls by dilution. The concentration of clotting factors increases causing a tendency to deep vein thrombosis exacerbated by pressure on the...

Anti Parkinsonian Drugs

Parkinson's disease is caused by a dysfunction within the basal ganglia. The predominant change is a deficit of dopamine with an increase in dopamine D2 receptors but other neurotransmitters are also implicated in the pathology of the disease. Drugs that affect Parkinson's disease may act in any of the following ways Increased dopamine synthesis (levodopa) Decreased peripheral conversion of L-DOPA (carbidopa) Decreased dopamine breakdown (selegiline) Dopamine receptor antagonists...

Measurement of Depth of Anaesthesia

Geudal Classification

In 1845, Snow made the first documented attempt to assess anaesthetic depth, describing five levels of ether anaesthesia. This was refined by Guedel during the First World War, who developed the chart classification of ether anaesthesia based on lacrimation, pupil size and position, respiratory pattern, and peripheral movements. Advances in anaesthesia (in particular the introduction of curare soon after the Second World War) made previous classifications obsolete. As a consequence a new system...

Coagulation

Pregnancy is associated with enhanced platelet turnover, clotting and fibrinolysis (Figure PN.5). Thrombocytopenia (platelets < 100 x 109 l) occurs in 0.8-0.9 of normal pregnant women, while increases in platelet factor and P thromboglobulin suggest elevated platelet activation and consumption. Since there is no change in platelet count in the majority of women during pregnancy, there is probably an increase in platelet production to compensate for the increased consumption. The...

List Of Abbreviations Used In Fundamentals Of Anaesthesia

Antibody dependent cell mediated cytotoxicity ADH American National Standards Institute AP action potential (in cardiac physiology) AP activated partial thromboplastin time AQP adult respiratory distress syndrome ASA American Society of Anaesthesiology ASIS ambient temperature and pressure saturated AUC basal metabolic rate of oxygen consumption BNP body temperature and pressure saturated c continuous ambulatory peritoneal dialysis CB cerebral function analysing monitor CGRP cerebral metabolic...

Nn0 Nn0

Figure V.4 Chemical structure of volatile agents Two iorms c -e*ist as o r n n1 hybrid Cerebral blood flow H, E > D, I ICP H, E > D, I Respiratory System A dose-dependent depression of respiration occurs. This is manifest as reduced tidal volume with increased rate (except sevoflurane, which lowers rate), causing an overall reduction in alveolar minute volume. This is most marked with enflurane. Arterial CO2 levels rise. The responses to hypercarbia and hypoxia are reduced. Halothane, in...

Ophthalmic Surgery Cataract Surgery

Cataracts may be congenital, traumatic, steroid- or radiation-induced, or degenerative. In degenerative cataracts there will also be other medical conditions of the ageing population. While diabetics have no more cataracts than the general population, they tend to present earlier and so there seems to be a preponderance of diabetic patients presenting for cataract surgery. Steroid induced cataracts present in patients taking long term steroids for other conditions, particularly eczema or asthma...

Chronic Obstructive Pulmonary Disease

Chronic bronchitis and emphysema are different pathologically but frequently co-exist as chronic obstructive pulmonary disease. A patient's condition may fall anywhere in a spectrum from solely chronic bronchitis to solely emphysema, with the majority of patients possessing symptoms and signs of both. The main feature of both diseases is generalised airflow obstruction. Chronic bronchitis is defined as daily cough with sputum production for at least three consecutive months a year for at least...

Section 210 Gastro Intestinal Physiology

MOTILITY CHARACTERISTICS OF THE SPECIALIZED REGIONS OF THE GI TRACT SECRETORY FUNCTIONS OF GASTROINTESTINAL TRACT Salivary glands Gastric secretion Pancreatic secretion Biliary secretion Post operative nausea and vomiting (PONV) The primary functions of the gastro-intestinal (GI) tract are the digestion of ingested food, the absorption of water, nutrients, electrolytes and vitamins, and the excretion of indigestible and waste products. The GI tract should not be thought of as a single organ,...

Calcium Antagonists

Calcium is involved not only in muscle contraction but also in neurotransmitter release, hormone secretion, platelet aggregation and enzyme function. There are numerous calcium channels across cell and other membranes. These may be active or passive, triggered by chemical mediators or voltage changes, and may be coupled with other ionic exchange. The term calcium antagonist is generally used to describe those agents with a role in cardiovascular manipulation. These act primarily on the voltage...

Pathophysiology of Trauma and Hypovolaemia

Several mechanisms are involved in the development of cellular injury after severe trauma. The commonest is haemorrhage resulting in circulatory failure with poor tissue perfusion and generalised hypoxia (hypovolaemic shock). Myocardial trauma may result in cardiogenic shock while spinal cord trauma may cause neurogenic shock. Severe trauma is a potent cause of the systemic inflammatory response syndrome (SIRS) and this may progress to the multiple organ dysfunction syndrome (MODS)....

Asthma

Asthma is common, affecting 10-20 of the population. In many patients the condition is mild and requires only occasional treatment, but in others there may be frequent and severe attacks requiring hospital admission and, in a few patients, ventilation on the Intensive Care Unit. There are two main groups although there is some overlap early onset asthma (atopic or extrinsic) and late onset asthma (non atopic or intrinsic). The symptoms of asthma are wheeze, cough, chest tightness and dyspnoea....

Pharmacology of Haemostasis

Calcium chelating drugs FIBRINOLYTIC AGENTS Plasminogen activators Fibrinolytic inhibitors ANTI-PLATELET DRUGS Aspirin Prostacyclin OTHER HAEMOSTATIC MODIFIERS Viscosity The ways that haemostatic processes may be altered pharmacologically are classified in Figure CP. 1. MODE OF ACTION OFPHARMACOLOGICAL ALTERATION OFHAEMOSTASIS Aspirin Oriol or Mcoo ulorils LM'W Heporin Aspirin Oriol or Mcoo ulorils LM'W Heporin Figure CP.2 Effect of drugs on the coagulation pathway Figure CP.2 shows the effects...

Ear Nose and Throat Surgery Tonsillectomy

Anaesthesia for tonsillectomy with or without adenoidectomy requires defence of the shared airway from blood and debris. This necessarily involves endotracheal intubation after induction, which may be gaseous or IV. If an uncuffed tube is used in the child patient, a suitable pack (ribbon gauze, for example) should be placed around the laryngeal additus to protect the larynx from contamination of blood and saliva. Use of a Boyle-Davis gag (Figure SI.3) will prevent compression of the tube...

Arterial PCO2

A relatively linear response exists between PaCO2 values of 2.6 and 10.7 kPa. At the lower end of this range CBF will be half normal and correspondingly double at the higher end. Reduced PaCO2 decreases both cerebral blood flow and intracranial pressure ICP , mediated by CSF pH. After a step change in PaCO2, the CSF bicarbonate concentration returns to normal over the next 24 H and the ICP and CBF return to normal even if the change in PaCO2 is maintained. Hyperventilation can, therefore, only...

The Role of the Vasa Recta

In most tissues, the selective permeability of capillaries ensures that the composition of interstitial fluid remains uniform. If medullary capillaries served this purpose, the osmotic gradient built up by the loop of Henle would be dissipated. However, this does not occur, because the hairpin arrangement of the vasa recta enables them to function as countercurrent exchangers distinguished from countercurrent multipliers by the fact that no energy is necessary . This enables the vasa recta to...

Left Shift of the ODC

This represents an increase in the affinity of Hb for oxygen in the pulmonary capillaries but requires lower tissue capillary PO2 to achieve adequate oxygen delivery. P50 is reduced by factors causing a left shift, which include Decreased concentration of 2,3-DPG Presence of HbF rather than adult forms of Hb Figure RR.16 Oxyhaemoglobin dissociation curve Figure RR.16 Oxyhaemoglobin dissociation curve

Anaesthesia for Patients with Severe Trauma Induction of Anaesthesia

Trauma patients can present the anaesthetist with a number of problems in the peri-operative period. The induction of anaesthesia during the resuscitation phase is been described above. Induction of anaesthesia at any stage during management of the acute trauma patient will require all appropriate precautions for the full stomach' case. The need for a rapid sequence induction in a patient who may be hypovolaemic is a particularly difficult scenario to manage. Continuous monitoring of central...

Shunt Equation

Physiological shunt can be calculated as a fraction of total pulmonary blood flow cardiac output . Figure RR.21 shows the flows and oxygen contents of systemic, pulmonary capillary and shunt circulations. Cci5, pulmonary capillary Oj content The total O2 content of blood leaving the lungs is cardiac output X arterial Oa content But the total oxygen content is also sl tllll fluw X miii'd vellum O , CLHHdll pulmonary capillary flow x pulmonary C T x aca Qs x CvO, Qr-Cjs x This can be rearranged...

Tolerance and Dependence

Tolerance can be defined as a state of decreased responsiveness to the pharmacological effects of a drug resulting from previous exposure. Tolerance to most effects of opioids is seen, excluding constipation and miosis. The tolerance shows selectivity so that tolerance to one opioid is not necessarily accompanied by tolerance to others and the mechanism is ill-defined. Mechanisms such as down regulation or decoupling of receptors have been suggested but the underlying mechanism is probably...

Body Temperature and Thermoregulation

Body temperature is tightly regulated. Many enzyme and transport systems cannot tolerate excessive temperature changes. Normal body temperature is 37 C and thermoregulatory mechanisms maintain this temperature with a standard deviation of about 0.2 C. There are normal variations within this range, such as a circadian variation of up to 0.7 C. A variation during the menstrual cycle produces a rise in temperature at ovulation. Body temperature may be altered by various factors including exercise,...

Benzocaine

Benzocaine is an unusual ester local anaesthetic agent in that the side chain is an ethyl group with no amine component and, therefore, remains unionized. Benzocaine has a low potency but it may cause methaemoglobinaemia. It is a component of some throat lozenges, and may be applied directly to painful skin ulcers. Cocaine is a naturally occurring ester derived from benzoic acid, and extracted from the leaves of Erythroxylum coca. It is available in solution and pastes in concentrations ranging...

Chest Wall Compliance

Lung Chest Wall Compliance

If a pressure-volume curve is plotted for the isolated thoracic cage Figure RR.8 the chest wall compliance can be obtained from the gradient, and is also about 200 ml cmH2O at FRC. The chest wall compliance can be reduced by disease as in ankylosing spondylitis in which the chest wall can become virtually rigid giving an extremely low compliance value. Figure RR.8. Lung and chest wall compliance Figure RR.8. Lung and chest wall compliance In the respiratory system the lungs and chest wall move...

Management

Initial measures are directed at preventing the tongue from falling backwards and obstructing the airway. The unconscious patient should be recovered in the lateral position with the jaw supported. Blood and secretions should be cleared by suction and supplemental oxygen given via a face mask. If upper airway obstruction develops the head should be tilted backwards and the jaw pushed forward by applying pressure behind the angle of the jaw. If this measure does not rapidly clear the airway then...

Diabetes Mellitus

Diabetes mellitus is characterised by a persisting state of hyperglycaemia due to lack or diminished effectiveness of endogenous insulin. It presents problems to the anaesthetist both in respect of the need to ensure adequate peri-operative control of blood glucose and in respect of the known long term complications of the condition. Diabetes mellitus may be classified as primary or secondary Figure PR.18 . There are two types of primary diabetes mellitus insulin-dependent diabetes mellitus...

Recommendations For Standards Of Monitoring During Anaesthesia And Recovery

The anaesthetist should be present throughout the conduct of the whole anaesthetic and should ensure that an adequate record of the procedure is made. 2. Monitoring should be commenced before induction of anaesthesia and continued until the patient has recovered from the anaesthetic. 3. Monitoring of anaesthetic machine function should include an oxygen analyser with alarms and devices which enable leaks, disconnections, rebreathing or overpressure of the breathing system to be detected. 4....

Haematological Disease Anaemia

A patient is considered anaemic if the haemoglobin is below the normal range and polycythaemic if above the normal range. For adult females this is 12-16 g dl and for adult males 13-17 g dl. In children the range varies and a child is considered to be anaemic if the haemoglobin value is less than 18 g dl at birth, less than 9 g dl at 3 months, less than 11 g dl from 6 months to 6 years and less than 12 g dl from 6 to 12 years. Iron deficiency hypochromic Thalassaemia hypochromic Chronic disease...

Indications for IPPV

The decision to use IPPV, with or without a muscle relaxant, is often a personal one and depends upon the site, nature, extent and to a degree the likely duration of the operation. Posture and access to a secure airway are also important. Advice must be coloured by the introduction in the last decade of minimally invasive surgery' and by the increasing use of the laryngeal mask. Operations may be divided into surface' and non surface'. Surface procedures should not need muscle relaxation and...

Ventricular Interdependence

Ventricular Interdependence

Right and left ventricles are situated inside the same non compliant pericardium. This means that they are both exposed to the same intrathoracic and intraalveolar pressures. Changes in volume and pressure of one ventricle will directly affect the other. Normally LV pressure is greater than RV pressure and the interventricular septum bows into the RV. However, the thin free wall of the RV makes it more sensitive to increases in afterload than the LV, and any increase in afterload e.g. pulmonary...

Physiological Shunt Venous Admixture Shunt Fraction

Venous Admixture

Arterial blood may be less well oxygenated than blood leaving the alveoli for several reasons, for example Venous blood may bypass the lungs entirely e.g. intracardiac shunts, thebesian veins, bronchial circulation Blood may pass through parts of the lung which are not ventilated adequately, in which case lt 1 e.g. pneumonia CcQ, pulmonary capillary o rgin content Qt-Qs - pulmciMjrf rtipillnry blood flow Figure RR.21 Diagram of shunt in the lung Blood may pass through areas of the lung which...

Golgi Tendon Organ Reflex

Golgi Tendon Organ

Another reflex that modulates contraction and relaxation of skeletal muscles is mediated by the Golgi tendon organs. These are situated in the muscle tendon just adjacent to the muscle fibres. The Golgi tendon organs also respond to muscle stretch but supply a feed back signal via Ib afferents to inhibitory neurones in the spinal cord. These neurones synapse with the a motor neurones, inhibiting them and reducing skeletal muscle tone during contraction. The Golgi tendon feedback signal also...

Differences in Timing Between Left and Right Sides of the Heart

Cvp Waveform And Pressure Volume Loop

Although the sequence of events on each side of the heart is similar, events occur asynchronously. This disparity in timing reflects differences in anatomy and working pressures between left and right sides of the heart. RA systole precedes LA systole however, RV contraction starts after LV contraction. In spite of contracting later, the RV starts to eject blood before the LV because pulmonary artery pressure is lower than aortic pressure. Differences of timing also occur in the closure of the...

Blood Supply

Crico Thyroid Muscle

The pharynx receives arterial supply from the ascending pharyngeal, superior thyroid, lingual, facial and maxillary vessels. Venous drainage is provided by the internal jugular vein via the pharyngeal plexus. This is mainly from the pharyngeal plexus, which lies on the surface of the middle constrictor muscle. The plexus is formed by three main components 1 Sensory fibres in the pharyngeal branches of the glossopharyngeal CN IX and vagus CN X nerves. 2 Motor fibres from the nucleus ambiguous...

Summary Definition Of Contractility

Physiological definition Systolic myocardial work done with given pre- and afterload Physiological index Ventricular stroke work index maximum slope dp dt of ventricular isovolumetric contraction curve Practical concept Ejection fraction for given CVP and MAP Practical index Ejection fraction Contractility can be increased by various factors including Increased serum calcium levels Contractility can be decreased by various factors including Decreased serum calcium levels Parasympathetic...

Fundamentals of Anaesthesia

Edited by Colin Pinnock Ted Lin Tim Smith Greenwich Medical Media Ltd. 137 Euston Road London NW1 2AA While the advice and information in this book is believed to be true and accurate, neither the authors nor the publisher can accept any legal responsibility or liability for any loss or damage arising from actions or decisions based in this book. The ultimate responsibility for the treatment of patients and the interpretation lies with the medical practitioner. The opinions expressed are those...

Anaphylaxis

Modern anaesthesia requires the use of several drugs to provide hypnosis, analgesia and muscular relaxation and thus, in view of the large number of patients receiving anaesthesia annually it is not surprising that untoward reactions occasionally occur. An adverse reaction to drugs administered by the intravenous route, rather than by inhalation, is likely to be more severe because the absorption of drugs across mucous membranes is relatively slow and may offer a degree of immunological...

Starling Forces and Filtration

The balance of hydrostatic and colloid osmotic oncotic pressures between capillary plasma and interstitial fluid, causes fluid to be filtered out of a capillary at the arteriolar end and re-absorbed at the venous end. These forces acting to move fluid in and out of a capillary are sometimes referred to as Starling forces. In a capillary hydrostatic pressure PC falls from 33 mmHg at the arterial end to 15 mmHg at the venous end. Interstitial hydrostatic pressure PIF can vary from 9 to -9 mmHg,...

Lung Function at High Altitude

The most important environmental change at high altitude is the decrease in barometric pressure, because this gives a proportional reduction in inspired oxygen tension PIO2 . Barometric pressure at an altitude of 5500m, is reduced to about half the value at sea level, i.e. about 50 kPa. Inspired Oxygen Tension PiO2 at High Altitude PIO2 at an altitude of 5500 can be calculated by Extracellular metabolism by endothelium Intracellular metabolism by endothelium Noradrenaline, serotonin...

Acetylcholine Synthesis and Storage Pre Junctional

Acetylcholine Synthesis Storage Release

Synthesis of acetylcholine involves the reaction of acetyl-coenzyme A acetyl-CoA and choline, catalysed by the enzyme choline acetyltransferase. Acetyl-CoA is synthesized in the mitochondria of the axon terminals from pyruvate. About 50 of the choline is derived from the breakdown of Ach the remaining is extracted from the extracellular fluid by a Na -dependent active transport process in the cell membrane which is the rate-limiting step in Ach synthesis. Choline acetyltransferase is originally...

Vertebral Column

Thoracic Duct Traverses Sibson Fascia

There are 7 cervical vertebrae, the atlas, axis and the similar C3-6. There are 12 thoracic vertebrae and five lumbar vertebrae. Five fused sacral segments form the sacrum and the coccyx has four fused segments. Structures of typical vertebrae are shown below in Figures CA.24-CA.27. Figure CA.24 Cervical vertebra, superior and lateral views Figure CA.25 Thoracic vertebra, superior and lateral views Figure CA.26 Lumbar vertebra, superior and lateral views The thoracic inlet slopes downwards and...

Acetylcholine Receptors

Ach receptors in the post junctional membrane of the motor endplate are of the nicotinic type. A normal neuromuscular endplate on average contains about 50 million Ach receptors. They are situated at the crests of the junctional folds. The nicotinic Ach receptor is a protein with a molecular weight of about 250 000 Daltons and is made up of five polypeptide subunits two identical a subunits, one P, one y replaced by s in adult mammals and one 5 subunit. Each subunit is encoded by a different...

Early Rapid Repolarization

This phase describes a brief fall in membrane potential towards zero following the rapid rise in phase 0. This occurs due to the start of potassium flow out of the cell under the positive intracellular electrical gradient and chemical gradients. At the same time slow, L type, Ca2 channels open, providing a prolonged influx of calcium ions which maintains the positive intracellular charge There is also movement intracellularly of chloride following sodium into the cell along the electrical...

Asystole

Bls Algorithm Rcuk

Asystole is characterised by ventricular standstill on the ECG but a mistaken diagnosis must be avoided since fibrillation can be more successfully treated. An ECG example of asystole is shown in Figure RS.12. The ALS algorithm for the management of cardiac arrest in adults RCUK 97 Ref. Kloeck W, Cummins R, Chamberlain D, Bossaert L, Callanan V, Carli Pt et al. The Universal ALS Algorithm. An Advisory Statement by the Advanced Working Group of the International Liaison Committee on...

Gravity and the Venous System

The pressure in the venous system is largely determined by gravity since the system can be visualized as a simple manometer Figure CR.19 . In the erect position, a hydrostatic gradient is produced from head to toe. The hydrostatic pressure difference between any two points in the venous system can be calculated by taking the product of the difference in height between the points h , the density of blood p 1.050 g cm3 , and the acceleration due to gravity g 980 cm s . These figures give a...

Measurement of Airway Resistance

Airway resistance can be measured during spontaneous breathing by simultaneous recording of air flow, and the pressure gradient between mouth and alveoli. In practice the alveolar pressure is difficult to obtain since it must be derived using a body plethysmograph. Intrapleural pressure can be used instead, but will include the pressure gradient required to overcome lung tissue resistance and inertial properties. Thus, this technique measures the resistance to air flow, the viscous resistance...

Management of Burns

Lund And Browder Chart For Burns

The standard ABC' principles apply to managing patients with severe burns. Patients with severe burns should be stabilised and transferred to the nearest burns centre. The patient with a thermal injury to the respiratory tract may rapidly develop airway obstruction from the oedema. All patients suspected of having thermal or smoke injury to the respiratory tract should be given humidified high concentration oxygen. Arterial blood gas sampling and estimation of carboxyhaemoglobin level is...

Post Operative Fluid Therapy

The aims of post operative fluid therapy are to maintain adequate hydration, blood volume, renal function and electrolyte balance. It is indicated in patients with pre-operative fluid abnormalities or ongoing fluid losses, and also in any patient undergoing a major surgical procedure. Total body water TBW accounts for 50-70 of body weight dependent on age, sex, body habitus and fat content. TBW is distributed between three fluid compartments the intravascular space 8 TBW , the interstitial...

Central Venous Pressure and Blood Volume

Vascular Function Curve

The venous system contains about two-thirds of the blood volume and can be visualized as a 'venous reservoir' supplying blood flow to the heart. Central venous pressure CVP is therefore a balance between blood volume, venomotor tone and the demands of the cardiac pump. At a given blood volume, as cardiac output increases, the rate at which blood is removed from the venous reservoir increases and central venous pressure falls. Similarly when cardiac output decreases a rise in CVP is produced....

Technique

Tuffier Line Line

Successful spinal anaesthesia depends on a reliable lumbar puncture technique. First establish venous access with a wide bore cannula and then position the patient either in the lateral position with the spine flexed maximally to open up the gaps between the vertebral spines or in the sitting position with the feet placed on a low stool at the side of the bed and the elbows resting on the thighs Figure RA.7 . Each position has drawbacks and advantages and the choice is usually made on personal...

Cerebral Blood Flow

Mean cerebral blood flow is about 55 ml 100 g min and is maintained within a relatively narrow range compared with other organs. It varies between the anatomical structures of the brain with grey matter in general receiving more than twice 70 ml 100 g min the blood flow of white matter 30 ml 100 g min . The brain consumes about 3.5 ml 100 g min oxygen leaving the jugular venous blood 65 saturated. Structures such as the colliculi and basal ganglia receive much greater blood flows than the brain...

Cardiac Output Measurement

In animal models CO can be measured directly by cannulating the aorta, pulmonary artery or any of the great veins and then using an electromagnetic or ultrasonic flowmeter. However, this is not appropriate in a clinical situation and CO is usually measured by indirect methods. Thermodilution is at present the most commonly used method to measure CO at the bedside. A pulmonary artery catheter PAC is inserted, cold saline injected into the RA, and the change in blood temperature is measured by...

Frank Starling Curve

Ventricular Function Curve

The function of the heart as a pump is based on cardiac muscle. The contractile properties of cardiac muscle not only provide the engine to drive the cardiac pump but also give the heart an intrinsic ability to adapt its performance to a continually varying venous return. The mechanism underlying this adaptive ability is the Frank-Starling relationship. Frank demonstrated in isolated muscle fibre preparations that the tension developed on contraction, was dependent on the initial length of the...

Muscle Spindles and the y Efferent System

Good control of muscle tone and stretch is essential for the maintenance of posture and for accuracy of movements. This control is mediated by stretch receptors in the skeletal muscles, called 'muscle spindles'. These fusiform structures are scattered throughout the fibres of a skeletal muscle. They are small specialized structures composed of 4-20 intrafusal within spindle fibres and are supplied by both sensory Ia and IIa afferents and motor y efferent nerves. In the control of muscle tone...

The Technique Of Caudal Anaesthesia

Caudal Anaesthesia

Place the patient in the lateral position as for a spinal or lumbar epidural. Note that the posterior superior iliac spines and the sacral hiatus form an equilateral triangle Figure RA.21 . Use the index finger of the non dominant hand to palpate the sacral cornuae either side of the hiatus which normally feels like a small depression between the bony landmarks. With the hiatus located, sterilise and prepare the area and insert the needle at an angle of about 60 degrees to the skin through the...