Post Operative Nausea and Vomiting
Post operative nausea and vomiting PONV is one of the commonest complications in the post operative period despite the use of modern day anaesthetic techniques. It occurs in 20-40 of cases and results in patient discomfort and anxiety and can produce significant morbidity in some cases. In the immediate post operative period the patient is at increased risk of aspiration. Sudden increases in intra-ocular and intracranial pressure associated with vomiting may be detrimental in the ophthalmic and...
Complications Nil
The only significant complication of femoral nerve block is the accidental injection of local anaesthetic into the femoral vessels, which are immediately adjacent to the nerve. Attention to detail when performing the block and careful aspiration prior to injection will prevent this avoidable complication. The limb will be anaesthetic for many hours and it must, therefore, be protected from pressure sores and prolonged immobility. Figure RA.33 Inguinal Field Block Indications Inguinal field...
INTRAVENOUS INDUCTION OF ANAESTHESIA Advantages
Depression of pharyngeal reflexes allows early insertion of LMA Anti-emetic and anti-convulsive properties Disadvantages Venous access required Risk of hypotension Apnoea common Loss of airway control Anaphylaxis of consciousness. This is generally more acceptable to the patient than inhalational induction and has the advantage of minimising any excitement phase. The rapid intravenous administration of a drug sufficient to achieve a plasma concentration which results in central nervous system...
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...
Rheumatoid Arthritis
Rheumatoid arthritis is an auto-immune connective tissue disease. The dominant pathological feature is a chronic, destructive synovitis, which causes an inflammatory, typically symmetrical, deforming polyarthritis. Rheumatoid arthritis has many extra-articular features which greatly influence the morbidity and mortality of the disease Figure PR.15 . Approximately 70 of patients are positive for rheumatoid factor, which is a circulating IgM antibody to the patient's own IgG. The overall...
Osmotic Pressure
The osmotic activity of solute particles in an aqueous solution can be visualized as exerting an osmotic pressure', which would potentially draw water into the solution. This can be demonstrated as a hydrostatic pressure difference between two compartments separated by a semipermeable membrane, one containing solution and the other containing water alone. Osmotic pressure can thus be defined as the pressure required to prevent osmosis when the solution is separated from pure solvent by a...
Non LifeThreatening Transfusion Reactions
Febrile Non Haemolytic Transfusion Reactions FNHTR This is the most common type of transfusion reaction. It is due to recipient anti-leukocyte antibodies. These may be acquired following pregnancy or after transfusion of cellular blood components. The patient may experience a rigor, but the temperature may rise without one. There are no signs or symptoms to suggest a haemolytic reaction, however severe FNHTRs may be associated with moderate hypotension, nausea, vomiting, cyanosis and collapse....
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
1. 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
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
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
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
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...
Surfactant
Surfactant is a phospholipid based substance secreted by the alveolar type II cells, which lines the alveoli and acts by markedly reducing surface tension. This action has the following effects Reduction of surface tension, which helps to even out the distribution of compliance and hence ventilation, since if without surfactant, alveoli with low resting volumes are significantly more difficult to expand, than those with larger resting volumes. This effect is important in neonates, in whom...
Equivalent Weight
Chemical reactions between elements occur with fixed proportions of different elements by weight. A gram equivalent weight can be defined for each element. This is the weight of an element that reacts with 8.000 g O2. An electrical equivalent weight can also be defined for an ion, which is equal to the atomic weight divided by its valency. Thus, the electrical equivalent weight of Na atomic weight 23 is 23 1 23, while the electrical equivalent weight of Ca2 atomic weight 40 is 40 2 20. The...
Blood Supply
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...
Golgi Apparatus
This consists of flattened membranous sacs or cisterns that are stacked together to form a polarized structure with cis and trans ends, separated by a middle region. The Golgi apparatus prepares proteins for secretion via exocytosis by receiving the proteins from the ER at the cis side, coding them for destination and finally producing secretory granules or vesicles at the trans side Figure PG.6 . Figure PG.6 Golgi apparatus and protein processing
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...
Medullary Centres
The medulla contains two pools of ventilatory control neurones, an inspiratory pool and an expiratory pool. These inspiratory and expiratory neurones function by a system of reciprocal innervation. As activity increases in one centre, a rising level of inhibitory activity is relayed from the opposite centre, resulting in a reversal of the ventilatory phase. The inspiratory pool is located in the dorsal medullary reticular formation and is the source of basic ventilatory rhythm i.e. it is the...
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 PreJunctional
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
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
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
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...
Diffusion Hypoxia
At the end of anaesthesia nitrous oxide leaves the blood and enters the alveoli diluting the gases already present. If the patient is breathing air, nitrogen will be absorbed into the blood at a slower rate than nitrous oxide enters the alveoli resulting in a decrease in alveolar oxygen concentration and a potentially hypoxic gas mixture. In practice, the effect of diffusional hypoxia is transient and is simply overcome by administering supplemental oxygen for approximately 10 minutes in the...
Red Blood Cells
Red blood cells erythrocytes provide the system for oxygen delivery from the lungs to the tissues and evolution has produced one of the most specialized cells for this purpose. The erythrocyte lacks organelles and a nucleus and instead is no more than a membrane enclosing a solution of protein and electrolytes. Over 95 of the protein is the oxygen transport protein haemoglobin, the remainder being enzymes required to maintain haemoglobin in a functional, reduced state and enzymes for...
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
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
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...
Bainbridge Reflex
This reflex was described by the English physiologist Bainbridge in 1915, who noted an increase in heart rate in response to rapid intravascular infusion of fluid into anaesthetized animals. The receptors are the atrial A and B receptors described above. The afferent limb of the reflex is the vagus nerves, while the efferent limb consists of sympathetic nerves to the sinus node. Heart rate is, thus, influenced by the two opposing actions of the arterial baroreceptor reflex and the Bainbridge...
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...
FrankStarling 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
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...
When to Stop Resuscitation
A lay person is taught to continue BLS until help arrives or exhaustion supervenes. In the hospital setting, decisions have to be made whether to continue or to abandon resuscitation. If the arrest has been caused by severe hypothermia, near drowning or drug overdose, particularly in children, then all possible measures should be continued, if necessary, for several hours. The decision to abandon resuscitation should not be solely influenced by the time spent resuscitating. However,...
Vasomotor Centres in the CNS
The vasomotor centres are areas of the reticular formation in the medulla oblongata and bulbar parts of the pons. The pressor region is located rostrally in the ventrolateral medulla, and provides a tonic output that maintains a background level of vascular smooth muscle tone. When the pressor centre is stimulated it causes increased vasoconstriction, increased heart rate and increased myocardial contractility. The depressor region is caudal and ventromedial to the pressor area. When stimulated...
Rapid Depolarization
An AP is produced when an electrical stimulus increases RMP causes it to become less negative to a threshold potential TP . At this value, fast sodium channels open for a very short period and potassium channels close. Sodium rapidly enters the cell under the influence of its concentration gradient and the electrostatic attraction of the intracellular anions, to make the inside positive in comparison with the outside by 20 mV. At the end of this stage, the sodium channels close. This phase...
Unipolar Limb Leads aVR aVL aVF
Unipolar leads record the difference between an active limb electrode and an indifferent zero potential electrode at the centre of Einthoven's triangle Figure HE.11 . These signals are of lower amplitude than other leads and require increased amplification hence referred to as augmented leads aVR the augmented unipolar right arm lead faces the heart from the right side and is usually orientated to the cavity of the heart. Therefore, all the deflections P, QRS and T are normally negative in this...
MultiUnit Smooth Muscles
Multi-unit smooth muscles rarely contain gap junctions, compared with single unit smooth muscles, but are densely innervated by autonomic nerve fibres. Each muscle fibre responds independently of its adjacent fibre and therefore behaves as independent multiple units. Contractility of the whole muscle depends on the number of muscle fibres activated and on the frequency of nerve stimulation. Spontaneous action potentials do not usually occur in multi-unit smooth muscles. Stretching does not...