Physiology of Pain

Pain is a subjective, unpleasant experience that can usually be localized. There is a strong affective component to pain in the form of a subjective emotional response which is determined by the current psychological state, anticipation and past experience of tissue damage. Pain has a protective function and may or may not be associated with tissue damage. The pain response to a noxious stimulus is not necessarily consistent. A situation can arise when the initial stimulus has disappeared but...

General Anaesthesia

Obstetric general anaesthesia is usually considered to be one of the higher risk specialities of anaesthesia because of the potential for urgency, uncontrolled bleeding and inhalation of gastric contents. In fact, as a cause of maternal mortality, anaesthesia ranks very low, on a par with amniotic fluid embolism and ruptured thoracic aneurysm. This low mortality is not a reason for complacency but a result of sustained work in eliminating the main causes of anaesthetic-related problems by...

Spontaneous Breathing

While oropharyngeal (Guedel) or nasopharyngeal airways are satisfactory (and sometimes essential) the laryngeal mask airway has virtually replaced them. One reason is the ease with which it is possible to maintain the airway with no hands, freeing the anaesthetist to deal with other tasks. The LMA also provides, in most patients, a better and more secure airway. Provided the depth of anaesthesia and muscular relaxation is appropriate for the surgery regurgitation of gastric contents and their...

General Surgery Laparotomy

The majority of patients requiring laparotomy will present an aspiration risk and, therefore, require rapid sequence induction and subsequent muscular relaxation with intermittent positive pressure ventilation (IPPV). In the case of a perforated viscus (duodenal ulcer, for example) electrolyte imbalance, dehydration and cardiovascular instability make for a high risk procedure. The presence of faecal soiling of the peritoneum is a particularly bad prognostic indicator. Anastomosis of the bowel...

Homozygous B Thalassaemia Thalassaemia Major Cooleys Anaemia

There is absent or greatly reduced P chain synthesis. This becomes apparent with the natural fall in foetal haemoglobin (a2 y2) levels due to the switch from y to P chain production. The infant presents with anaemia during the first 6 months of life. If transfusion therapy is not instituted then the infant may demonstrate the typical thalassaemic facies (frontal bossing, maxillary hyperplasia). With transfusion therapy there is normal development for the first decade, but iron overload then...

Synthetic Oxygen Carriers

Normally only 4 of the oxygen delivered is carried in solution (0.0225 ml 02 100 ml blood kPa), the rest is carried as oxyhaemoglobin. To rely entirely on dissolved oxygen (if this could all be extracted) would require either an increased cardiac output to 13 l min or an inspired oxygen pressure of 2-2.5 bar. The latter is the principle behind the treatment of carbon monoxide poisoning but requires hyperbaric equipment and risks oxygen toxicity. Therefore, an oxygen carrier is required that...

Renal Disease Applied Physiology

The kidneys excrete water, electrolytes, water-soluble drugs and water-soluble products of metabolism. Plasma electrolytes, urea and creatinine provide an indication of renal function. While the plasma urea also depends on liver function, the creatinine concentration also depends on the level of protein metabolism in the body. For the plasma creatinine to rise, renal function must be < 30 of normal. As renal function is reduced below this the creatinine and urea will rise, as will the plasma...

Exposure and Environmental Control

With a team approach, it is likely that the patient's clothes will have been removed by this stage. If not, the patient should be completely undressed and then protected from hypothermia with warm blankets. The detailed head to toe survey of the trauma patient should not begin until the resuscitation is well underway and the patient's vital signs are relatively stable. The patient must be continually re-evaluated so that ongoing bleeding is detected early. Patients with exsanguinating...

Transurethral Resection of Bladder Tumour TURBT

Bladder tumours are not usually large and rarely result in major blood loss. Occasionally patients will be anaemic at presentation from frank blood loss over a period of time. Anaemia should be corrected. Use of diathermy in the bladder can stimulate the obturator nerve, which is close by in the pelvis, lateral to the bladder. This causes mass movement of the patient's legs which can result in perforation of the bladder and vascular or bowel damage by the resectoscope. This situation can only...

Drugs and Techniques

In choosing anaesthetic drugs and techniques, care should be taken to avoid those drugs that are excreted solely through the kidney. Fortunately, all of the induction agents undergo redistribution and biotransformation to inactive products before excretion. Renal impairment may delay the excretion of the opioids and prolong their action. Suxamethonium should be avoided as it causes the release of potassium from muscle cells and may precipitate cardiac arrhythmias in an already hyperkalaemic...

Renal Failure

Renal disease covers a wide spectrum of clinical pictures from decreased renal reserve, through varying degrees of renal impairment to end stage renal failure. Up to 80 of excretory function may be lost before a rise in serum urea or creatinine is seen. The creatinine value gives a useful indication of the degree of renal failure. The corresponding urea value is more readily affected by dietary protein, tissue breakdown and hydration and is, therefore, less useful. The cause of renal impairment...

Effect of Complications on Anaesthesia

Nephropathy causes hypertension and electrolyte disturbances, particularly of potassium and creatinine. These disturbances are a reflection of renal function and give some indication of the adequacy of fluid and electrolyte homeostasis and drug excretion. Neuropathy. Diabetic peripheral neuropathy is unpredictable in both distribution and effect. This may make the testing of peripheral nerve blocks more difficult. Autonomic neuropathy is not usually formally sought, the test being a formal...

Psychological Methods

There is no doubt that adequate psychological preparation for labour significantly reduces pain. Breathing and relaxation techniques are taught routinely in antenatal classes. Self hypnosis can also be successful in the suitably motivated patient. Transcutaneous electrical nerve stimulation (TENS) can work well if introduced early enough in labour. The technique depends on the gate theory of pain transmission (as described by Melzack and Wall 1965). Stimulation must be applied to the dorsal...

The Technique Of Femoral Nerve Block

Position the patient supine and identify the inguinal ligament and the femoral arterial pulse immediately distal to it. The point of injection should be 1 cm lateral to the pulsation and 1-2 cm distal to the inguinal ligament. Having raised a skin weal of lidocaine, insert a 22 G short bevel regional block needle at about 45 degrees, aiming cephalad. A distinct pop as the needle pierces the fascia lata may be felt followed by a secondary pop as it enters the nerve sheath. Parasthesiae in the...

Inadequate Mechanical Function of the Respiratory Muscles

Incomplete Reversal of Non Depolarizing Muscle Blockade This is distressing and potentially dangerous to the patient. It is an important cause of both hypoventilation and upper airway obstruction. There are many factors that contribute to incomplete reversal (see FACTORS ASSOCIATED WITH PROLONGED NEUROMUSCULAR BLOCKADE Hypokalaemia Hypocalcaemia Hyponatraemia Hypermagnesaemia Volatile agents Calcium channel blockers Aminoglycosides Diuretics Figure PO. 6). The use of short acting non...

Mechanism of Action of Anaesthetic Agents

In general, anaesthetic agents (IV and volatile) reduce excitatory activity and increase inhibitory activity, although there are some excitatory effects and reduction of some inhibitory effects. General anaesthesia reduces neuronal activity in the brain, especially in the ascending reticular system, reticular formation, cerebral cortex, olfactory cortex and the hippocampus. In the spinal cord, general anaesthesia suppresses both excitatory and inhibitory activity especially in lamina V of...

BNon depolarizing blockade

Benzylisoquinolinium esters Atracurium Doxacurium Mivacurium (acetylcholine) receptors of the skeletal muscle neuromuscular junction are generally used in clinical practice. These may be either depolarizing or non depolarizing. The features of an ideal neuromuscular blocking agent are shown in Figure NJ.2. FEATURES OF AN IDEAL NEUROMUSCULAR BLOCKING AGENT Pharmacologically inactive metabolites Unaffected by renal or hepatic failure Neuromuscular blockade may be assessed both by clinical...

Peripheral Mechanisms

The nociceptive pathway can be initiated by direct peripheral nerve damage or by the action of chemical mediators. Such chemical mediators include factors such as prostaglandins (PG) and kinins, which are released as a result of tissue damage. These substances not only initiate nociception, but also activate the inflammatory process by inducing the following changes Increases in local blood flow and vascular permeability Activation and migration of immune cells Release of growth and trophic...

Orthopaedic Surgery

The most frequently performed operations in this category are hip and knee arthroplasty. Total hip replacement may be carried out under epidural, spinal or general anaesthesia. Peripheral nerve blockade may be useful for post operative analgesia (e.g. paravascular 3 in 1' and iliac crest block) but the hip joint is not easy to denervate in this manner due to its multiple nerve supply. Hip replacement may be carried out in the supine or lateral positions with the specific problems of these (see...

Figure PO13 Treatment of Pain Systemic Opioids

The dose of opioid required in the post operative period shows marked interpatient variability. This is due to both pharmacokinetic and pharmacodynamic factors with up to a 5 fold difference in plasma concentrations after identical doses of IM opioid. There are also differences in opioid receptor sensitivity between patients that may explain the poor results attained with the conventional regime of on-demand IM opioid. Subcutaneous opioid administration via indwelling cannulae is associated...

Pulmonary Stretch Receptors

These are believed to lie in the smooth muscle of the airways. These inhibit inspiration in response to lung distension, and slow ventilatory rate by increasing expiratory time. This reflex was first reported by Hering and Breuer in 1868, who noted that lightly anaesthetised, spontaneously breathing animals would cease or decrease ventilatory effort during sustained lung distension. This response is abolished by bilateral vagotomy. The Hering-Breuer reflex is only weakly present in man, who can...

Actions of Aldosterone

The principal function of aldosterone is to control extracellular fluid volume and to maintain a normal plasma concentration of potassium. It achieves these objectives by promoting retention of sodium and loss of potassium in the following manner Re-absorption of sodium - aldosterone causes active re-absorption of sodium from the distal renal tubules and collecting ducts. Water follows sodium leading to an expansion of the extracellular fluid volume and plasma volumes. By this mechanism...

Blood Brain Barrier

The blood brain barrier exists between the circulation and the interstitial fluid in the brain. It consists of the ultrafiltration barrier in the choroid plexuses and the barrier around cerebral capillaries. The latter consists of capillary endothelium, basement membrane and a fenestrated layer of astrocyte endfeet. Tight junctions, impermeable to solutes, join capillary endothelial cells and form a basic component of the blood brain barrier. Water, carbon dioxide and oxygen diffuse freely...

Biochemical

Metabolic acidosis with compensatory respiratory alkalosis Pancreatic disease, e.g. pancreatitis, pancreatectomy, neoplastic disease, cystic fibrosis Non insulin-dependent diabetes mellitus Excess production of insulin antagonists, e.g. growth hormone (acromegaly), glucocorticoids (Cushing's syndrome), thyroid hormones, catecholamines (phaeochromocytoma) Drugs, e.g. corticosteroids, thiazides Liver disease Glycosuria that has been detected on routine urine testing performed pre-operatively may...

Consequences of Autonomic Stimulation

In life-threatening situations, the sympathetic nervous system discharges almost as a complete unit, a phenomenon known as mass discharge. This may occur when the hypothalamus is activated by fear, noxious stimulus or severe pain. There is stimulation of different systems and organs simultaneously to prepare the individual for survival. The resulting sympathetic 'stress' response is summarized in Figure NE.24. The parasympathetic nervous system, on the contrary, is more organ-specific. For...

Non Steroidal Anti Inflammatory Drugs

These agents have both analgesic and anti-inflammatory properties. They are effective for treatment of mild-to-moderate post operative pain and, after the first 24 to 36 hours, may be used as the sole analgesic in major surgical patients. NSAID also have an opioid sparing effect with a reduction of opioid requirement after major surgery of greater than 20 when given regularly. NSAID have several advantages over opioid analgesics. Their use is not associated with respiratory depression or...

Ischaemic Heart Disease IHD

In the UK 12-20 of patients undergoing surgery have pre-operative evidence of myocardial disease. This is almost always due to atheroma although rarely other disease processes may be responsible. With increasing age atheromatous plaques form in the intima of arteries. These plaques grow and evolve with time, decreasing blood flow through a vessel and possibly occluding it. The rate of progression of individual plaques within any patient is variable and explains why although peripheral vascular...

Squint Surgery

The majority of patients for squint surgery are children, though occasional adults may present for cosmetic corrections. This operation is difficult to carry out with local anaesthesia because of the age of the patient and the manipulations necessary in the orbit. General anaesthesia should be carried out with the airway maintained by either a laryngeal mask or tracheal tube. There is little to choose between spontaneous or controlled ventilation. All patients having squint surgery should...

Pre Existing Lung Disease

Patients with chronic obstructive airways disease (COAD) are at increased risk of hypoventilation in the post operative period. They may not be able to further increase their work of breathing to maintain an adequate PaCO2, particularly if bronchospasm or excessive airway secretions are present. Bronchospasm may occur in asthma, COAD, smokers and in patients with acute respiratory infection. It is commonly precipitated by upper airway irritation either during airway manipulation or if...

The Paediatric Patient

For the purposes of this volume only those children of 20 kg in weight or greater will be considered. In practice, this will usually equate with an age of about five years. Pre-operative assessment in children should be as rigorous as in adults and questions should be addressed to the child even though the parents may answer for them. Most children are healthy but chronic conditions such as asthma, multiple allergies, congenital heart disease and systemic conditions (such as muscular dystrophy)...

Actions of Glucocorticoids

The numerous effects of the glucocorticoids include catabolic, cardiovascular and anti-inflammatory effects. Catabolic Effects The main catabolic effects seen are the promotion of the following Cortisol increases the supply of glucose to the body tissues through its metabolic effects and prevents hypoglycaemia. Glucocorticoids are essential for the normal cardiovascular responses to stress. The increased sympathetic activity, which results in vascular smooth muscle constriction, becomes...

False positive results

Tube in oesophagus after exhaled gases have been forced into stomach Tube in oesophagus after drinking carbonated beverages Distal end of endotracheal tube in pharynx stomach with gas containing carbon dioxide. The CO2 waveform in this situation may initially appear normal but rapidly diminishes to zero after a few breaths. Carbon dioxide in expired gas can also be detected chemically. pH-sensitive chemical indicator devices that reversibly change colour on exposure to CO2 are available. These...

Parathyroid Gland and Calcium Homeostasis

The maintenance of a normal plasma calcium is essential for the normal function of excitable cells and other vital processes such as excitation-contraction coupling in muscle as well as blood clotting. The excitability of nerve and muscle is increased by a fall in plasma calcium leading to spontaneous or prolonged muscle contraction (tetany) and cardiac arrhythmias. Regulation of plasma calcium depends principally upon the actions of parathyroid hormone (also known as parathormone) vitamin D...

Cardiovascular System

Most local anaesthetic agents (except cocaine) relax vascular smooth muscle causing vasodilatation. In addition, centrally administered drugs cause asodilatation by sympathetic blockade. Direct cardiovascular toxicity occurs due to the membrane stabilizing activity of the drugs on myocardial muscle, by blocking voltage-gated fast sodium channels. This reduces the maximum rate of rise of the cardiac action potential and reduces the duration of the action potential. Conduction of the action...

Concurrent Surgical Disease Intestinal Obstruction

Patients with intestinal obstruction often have electrolyte disturbances due to vomiting or, if incomplete obstruction, diarrhoea. They may have been ill at home for several days and not been able to take their usual medication for any concurrent medical condition. These patients may be dehydrated and possibly hypovolaemic due to gastro-intestinal losses or to third space losses into their gut. Inappropriate intravenous fluid therapy on a surgical ward may have exacerbated the problems....

Anaphylactoid Reactions

Anaphylactoid reactions are very rare with amide local anaesthetics, and some of those reported have been due to preservatives (such as metabisulphite and methylparaben). Effects range from local erythema and swelling to systemic hypotension and bronchospasm. More commonly, the reactions are due to co-administration of adrenaline, intravascular injection or psychological effects (vaso-vagal episodes). Reactions are relatively common with esters and cross sensitivity may occur. The metabolism of...

Blood Sugar Control

The physiological control of blood glucose is complex. While the major role belongs to insulin, a multitude of other hormonal influences apply. It should also be remembered that insulin has other actions beyond the regulation of blood glucose. Pharmacological control of blood glucose becomes necessary in situations of elevation and depression of blood glucose beyond the homeostatic limits, in other words due to hyperglycaemia or hypoglycaemia. The causes of failure in regulation of blood...

Insulin controlled

Admit the day before surgery. Half usual dose of short acting insulin the evening before surgery. Fast from midnight for a morning list. No insulin in the morning. Blood glucose result one hour pre-operatively. The evening after surgery give one third dose of short acting insulin with supper. Check blood glucose three hours after supper. Return to usual treatment the day after surgery. Fast from 08-00 for an afternoon list. Half dose of short acting insulin...

Regulation of Insulin Secretion

There are several agents regulating the secretion of insulin (Figure EP.14) but the major factors are CONTROLLING FACTORS IN INSULIN SECRETION has effects on carbohydrate and lipid metabolism as detailed below. Carbohydrate Metabolism Glucagon promotes the hepatic output of glucose by Glucose sparing through preferential P oxidation of fatty acids for energy. This leads to the formation of ketone bodies. Glucagon activates lipase resulting in an increased plasma level of fatty acids and...

Association of Anaesthetists of Great Britain and Ireland 1995

THE FIRST OBSERVED CLINICAL FEATURES OF ANAPHYLAXIS Others (ECG changes, swelling, urticaria) Association of Anaesthetists of Great Britain and Ireland 1995 Irrespective of the mode of triggering, all the clinical manifestations of an allergic reaction occur as a result of the liberation of vasoactive substances. The typical clinical features of anaphylaxis are hypotension, bronchospasm, oedema and the development of a rash (Figure I.4). Cardiovascular collapse is one of the most common early...

Critical Incidents During Anaesthesia

Central cyanosis can usually be detected at an arterial oxygen saturation of about 80-85 , depending on whether the patient is anaemic. Note that Absence of cyanosis does not necessarily mean normal arterial oxygen levels' (Nunn, 1993). Even at an oxyhaemoglobin saturation of 93 the patient is very close to the steep part of the saturation curve. At 89 saturation the PaO2 is only 7.5 kPa so that by the time central cyanosis is detectable the patient can be severely compromised. Cyanosis may be...

Transfer of the Head Injured Patient

Head injured patients and those with suspected intracranial haemorrhage may require transfer between hospitals for either CT scanning or definitive management of their injuries. This can be a difficult and dangerous enterprise and should be carried out with the greatest of care. Facilities in ambulances, helicopters and scanning rooms are limited, as is space, but nevertheless the management of the airway and ICP must take precedence over speed or convenience. The patient must be stabilised...

Concurrent Medication

Individual drugs have been covered in each section on concurrent medical disease however, two important groups deserve additional mention. Tricyclic antidepressants competitively block noradrenaline re-uptake by postganglionic sympathetic nerve endings. Patients taking these drugs are, hence, more sensitive to catecholamines so sympathomimetics may cause hypertension and arrhythmias. Under the influence of anaesthesia arrhythmias and hypotension may be seen. Monoamine oxidase inhibitors (MAOI)...

Features of Plasma Proteins

The main plasma proteins involved in drug transport are albumin and globulin. Other molecules such as alpha1 acid glycoprotein, which binds basic drugs, and specific carriers for cortisol and thyroxine contribute to the transport system. These molecules are large (albumin has a molecular weight of 69 000 Daltons) and have multiple, relatively non specific binding sites. As with all binding sites, the shape and charge of the site are important. The bonds are a combination of any of the...

Drug Usage in Peri Arrest Arrhythmias

The administration of drugs and their adverse side effects are summarised in Figure RS.11. Complications of CPR Iatrogenic complications of CPR are relatively common and may pose post resuscitation problems. Rib and sternal fractures occur frequently. Other complications of chest compressions may include visceral trauma (usually liver) and cardiac trauma. Complications related to poor airway and ventilatory management are inhalation of gastric contents, inadvertent oesophageal intubation and...

Management of Head Injury

Head injury should be considered significant if there has been certain loss of consciousness (however brief). Blood or CSF in the ear canal or nose imply skull fracture with the accompanying risk of meningitis due to the ingress of pathogens. In closed head injury, even of a relatively minor nature, there is a variable amount of oedema and cerebral contusion which increases the volume of the intracranial contents, displacing both CSF and blood volume and reducing compliance. Extra- and subdural...

Post Operative Analgesia

The provision of effective pain relief during the post operative period is dependent on anaesthetic technique, type and extent of surgery and the patient's perception of pain. In practice, a combination of opioid, non steroidal anti-inflammatory drugs (NSAID) and local anaesthetic techniques is often used. Good pain control not only alleviates patient distress but also prevents or modifies many adverse effects (Figure PO.13). The increase in sympathetic activity associated with pain results in...

Liver Disease Applied Physiology

The liver is the largest organ in the body receiving 30 of cardiac output. The majority of nutritional, haematological and detoxification metabolism occurs in the liver, including the breakdown or excretion of many anaesthetic drugs. Other physiological roles of the liver include the manufacture of proteins, lipoproteins and carbohydrates which includes the clotting factors and the proteins to which most anaesthetic drugs are bound. Globulins are not produced in the liver. The liver also acts...

Renal Effects of Anti Diuretic Hormone

The main determinant of whether the urine will be copious and dilute, or low in volume and concentrated, is the level of circulating anti-diuretic hormone (ADH). Re-absorption of water in the nephron occurs at several sites. GFR 180 1 day. About 70 of this is re-absorbed in the proximal tubule. A further 15 of the glomerular filtrate is re-absorbed by the loop of Henle. This leaves about 23 litres to enter the distal tubules and collecting tubules. It is these 23 litres that are mainly either...

Transurethral Syndrome

Endoscopic surgery requires continuous irrigation with a solution of glycine (1.5 in water). This solution is deliberately non electrolytic so that the diathermy current is applied to the tissue rather than being dissipated in the fluid. If significant volumes of this solution get into either the general circulation or the tissues, from where it is absorbed then there may be serious fluid and electrolyte disturbances. The most obvious are water excess and hyponatraemia. Cerebral oedema develops...

Figure SC12 Complications

The complications of diabetes are listed in Figure SC. 12. Patients with diabetes may present for incidental surgery or for surgery related to their diabetes, particularly abscesses, wound debridement, amputation of toes, feet or limbs, and cataract surgery, although diabetic patients do not have a higher incidence of cataracts, simply an earlier presentation of the condition. Whether the surgery is incidental or not, and whether the diabetes is insulin or non insulin dependent, there is an...

Regulation of Glucocorticoid Activity

The most important stimulus for the secretion of cortisol is the release of ACTH from the anterior pituitary. ACTH release is promoted by hypothalamic release of corticotrophin releasing hormone (CRH) into the hypophyseal portal blood. Cortisol exerts a direct negative feedback control with inhibition of both CRH and ACTH release. Glucocorticoid secretion is also modulated by a normal circadian pattern whereby cortisol levels peak in the early morning and reach a trough in the middle of the...

Changes in Foetal Circulation at Birth

At birth, pulmonary vascular resistance falls markedly as the lungs expand and become aerated. This reduces pulmonary arterial pressures and increases blood flow to the left atrium. Umbilical vessels constrict strongly when exposed to trauma, tension, catecholamines, angiotensin and PaO2. These stimuli occur at birth and placental circulation ceases resulting in a rise in systemic vascular resistance and arterial pressure. These changes make left atrial pressure higher than right atrial...

Deficient Secretion

Hypoadrenalism (Addison's disease) can be either primary or secondary. Primary hypoadrenalism is caused by a failure of the adrenal cortex as a consequence of auto-immune disease, infection or surgery. As a consequence, ACTH levels are high because of a low circulating cortisol level. Melanocytestimulating hormone (MSH) is secreted in conjunction with ACTH leading to the characteristic pigmentation of the skin and buccal mucosa. Secondary hypoadrenalism results from reduced levels of ACTH...

Cardiovascular Coupling

In clinical practice assessment of cardiac function often relies on the available measurements of filling pressures (CVP and PCWP), arterial pressures (pulmonary and aortic) and CO. These measurements are dependent on two sets of characteristics that reflect Contractile performance of the heart Elastance (PV relationship) of the vascular system Assessing the relative effects of cardiac contractility and vascular system elastance on pressure measurements is important clinically, since it can...

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

Ecg Output Types

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...

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

Where Angiotensin Stored

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...