Entonox: A Mixture of Nitrous Oxide and Oxygen

Entonox is a gas mixture of 50% nitrous oxide and 50% oxygen that is stored in cylinders. The cylinders have a French blue body with blue and white quarters at the top. It is important to note that if the gas mixture cools below its pseudocritical temperature of −6°C, the nitrous oxide and oxygen may separate out through a process called lamination. This can result in a potentially dangerous and hypoxic gas being administered.

Despite being a flammable mixture, Entonox is not considered explosive. It is effective in providing short-term analgesia and is safe for both infants and mothers. The onset of action occurs approximately 30 seconds after inhalation, and the duration of action after analgesia is approximately one minute.

It is important to distinguish nitrous oxide (N2O) from nitric oxide (NO) as they are not the same. Overall, Entonox is a useful gas mixture for providing short-term pain relief, but it must be stored and administered properly to avoid any potential risks.

Measuring Cardiac Output and Pressures with a Pulmonary Artery Catheter

A pulmonary artery catheter can provide direct and derived measurements for assessing cardiac function. Direct measurements include right atrial pressure, right ventricular pressure, pulmonary artery pressure, pulmonary artery wedge pressure, core temperature, and mixed venous saturation. The catheter can also be used to calculate cardiac output using the method of thermodilution. This involves a proximal port with a heater and a distal thermistor that senses changes in temperature.

Pulmonary artery wedge pressure is a direct measurement that can be obtained with the catheter, reflecting left atrial filling. However, it may not always accurately reflect the pressure in the left atrium due to various factors. Right ventricular pressure is another direct measurement that can be obtained.

Central venous saturation is a direct measure in some machines with a built-in saturation measurement probe, while in others, samples can be taken via the distal port and measured using a gas machine. Overall, a pulmonary artery catheter can provide valuable information for monitoring cardiac output and pressures in critically ill patients.

Importance of Adequate Hydration in Monitoring Organ Perfusion

Hourly urine output is a reliable indicator of organ perfusion, which is directly linked to hydration levels. However, if there is a urological obstruction, this measure may not be accurate. While a trend in central venous pressure (CVP) can be helpful, a single reading is not a reliable indicator of hydration status. Late signs of hypovolemia include dry mucous membranes and hypotension. Therefore, it is crucial to maintain adequate hydration levels to ensure proper organ perfusion and prevent hypovolemia.

Medications for Pain Relief in Various Conditions

Pinaverium is a medication that is commonly used to reduce the duration of pain in individuals with irritable bowel syndrome (IBS). On the other hand, carbamazepine is used to treat neuropathic pain that is associated with malignancy, diabetes, and other disorders. Clodronate is another medication that is used to treat malignant bone pain and hypercalcaemia by inhibiting osteoclastic bone resorption.

Corticosteroids are also used to treat pain caused by central nervous system tumours. These medications work by reducing inflammation and oedema, which in turn relieves the pain caused by neural compression. Nifedipine is another medication that is used to relieve painful oesophageal spasm and tenesmus that is associated with gastrointestinal tumours.

Lastly, oxybutynin is a medication that is used to relieve painful bladder spasm. Overall, these medications are used to treat pain in various conditions and can provide relief to individuals who are experiencing discomfort.

Understanding Heat Loss During Surgery: The Role of Radiation, Convection, Conduction, Evaporation, and Respiration

During surgery, the body can lose heat through various mechanisms. Radiation, which accounts for 40% of heat loss, depends on factors such as body temperature and the environment. To combat this, patients are covered with warming methods like the Bair Hugger™. Convection, or air movement, contributes to 30% of heat loss, while conduction (5%) occurs through contact with the operating table and surrounding air. Evaporation (15%) is higher if the abdomen is open, and humidity is kept at 50% in the theatre to reduce it. Finally, respiration accounts for 10% of heat loss. Understanding these mechanisms can help healthcare professionals better manage patient temperature during surgery.

The Use of Nasopharyngeal Airways in Seizure Management

Nasopharyngeal airways are a valuable tool in managing patients with seizures. During a seizure, jaw rigidity can make it difficult to position an oropharyngeal airway, making a nasopharyngeal airway a better option. These airways are used to secure an open airway in patients with a decreased Glasgow Coma Scale (GCS) score and those who cannot tolerate an oropharyngeal airway due to an intact gag reflex. The correct size of the airway is chosen by sizing the width of the patient’s nostril to the circumference of the tube, and insertion is facilitated by using a water-based lubricant. However, nasopharyngeal airways should not be used in patients with a patent airway or those with basal skull fractures and coagulopathy.

Prognostic Indicators for Hypoxic Brain Injury Patients

Hypoxic brain injury patients require ancillary tests to aid in determining their prognosis. Bilaterally absent somatosensory evoked responses (SSEPs) at 24–72 hours and complete generalised suppression of electroencephalographic (EEG) waves on day three are reliable indicators of poor prognosis. Absent pupillary or corneal reflexes at three days after cardiac arrest, along with the absence of motor response, is also a better prognostic marker. However, in the absence of either one of these factors, the prognosis should be evaluated using results from ancillary tests (SSEP/EEG). Extensor motor response on day three, despite the absence of motor response, is a reliable indicator for poor prognosis. Myoclonic status epilepticus (MSE) – bilateral and synchronous myoclonus of the face, limbs and axial skeleton – has been studied as a reliable marker for poor prognosis in these patients, even in the presence of brainstem and motor responses. However, it should not be considered in isolation as a prognostic indicator. It is important to note that the reliability of these indicators may be affected by factors such as noise interferences, hypothermia, and drugs given during resuscitation.

Calculating Fluid Requirements for a Patient with Fluid Overload

When determining a patient’s fluid requirements, it is important to consider their weight and any underlying medical conditions. For this particular patient, who weighs 48 kg, her maintenance fluid requirement is between 1200-1440 ml per day, calculated using 25-30 ml/kg/day.

However, this patient has developed fluid overload and pulmonary edema, likely due to receiving 2 liters of fluid per day. While this may have been necessary initially due to fluid loss from bowel obstruction, it is now important to step down to normal maintenance levels.

Giving the patient 1500-2000 ml of fluid per day would still be too much, as evidenced by examination findings of pitting sacral edema and widespread fine crackles. The maximum amount of fluid needed for maintenance therapy is 1440 ml per day.

It is crucial to monitor fluid intake and adjust as necessary to prevent further complications from fluid overload. Giving too much fluid, such as 2500-3500 ml per day, can be harmful for a patient with fluid overload and should be avoided.

Macintosh Laryngoscope: A Tool for Visualizing the Vocal Cords

The Macintosh laryngoscope is a medical instrument designed to aid in the visualization of the vocal cords. Its curved blade is specifically shaped to fit into the oral and oropharyngeal cavity. To use it, the blade is inserted through the right side of the mouth and gradually advanced, pushing the tongue to the left and out of view. The blade has a small bulbous tip that is intended to sit in the vallecula, a small depression between the base of the tongue and the epiglottis.

By lifting the laryngoscope up and forwards, the larynx is elevated, allowing for a clear view of the vocal cords. This tool is commonly used in medical settings, such as during intubation procedures or when examining the airway. Its design allows for a safe and effective way to visualize the vocal cords, aiding in the diagnosis and treatment of various medical conditions.

Hartmann’s Solution Composition and Metabolism

Hartmann’s solution, also known as lactated Ringer’s solution, is an intravenous fluid that is isotonic in nature. It contains various compounds, including sodium, chloride, potassium, calcium, and lactate. A litre of this solution contains 131 mmol of sodium, 111 mmol of chloride, 5 mmol of potassium, 2 mmol of calcium, and 29 mmol of lactate.

One of the unique features of Hartmann’s solution is the presence of lactate, which is metabolized by the liver to release bicarbonate. This process is important because bicarbonate would otherwise combine with calcium to form calcium carbonate, which can cause complications. Therefore, the metabolism of lactate helps to maintain the stability of the solution and prevent any adverse effects.

Central Venous Lines: Placement, Uses, and Complications

Central venous lines (CVLs) are commonly used in medical settings for various purposes, including the administration of inotropes such as adrenaline, parenteral nutrition, blood products, fluids, and measurement of central venous pressures. However, the use of CVLs is not without risks and complications, which include local site and systemic infection, arterial puncture, haematomas, catheter-related thrombosis, air embolus, dysrhythmias, atrial wall puncture, lost guidewire, anaphylaxis, and chylothorax.

When it comes to the placement of CVLs, the site of choice is the subclavian vein, although the complication risk is higher. Femoral lines are more susceptible to infection due to the flora within the groin area. Consideration of the age of all lines should be made on daily review within the Intensive Care Unit/High Dependency Unit environment, as routine replacement of a CVL every fortnight is uncommon.

Lastly, a check radiograph for placement is recommended on insertion of both subclavian and internal jugular lines to confirm correct placement within the superior vena cava and to exclude a procedural pneumothorax. However, this does not need to be repeated on removal, as there are no needles or incisions involved in the removal of the line.

Anesthesia Grading Score for Patient Risk

The American Society of Anesthesiologists developed a grading score in 1963 to assess patient risk during surgery. The score ranges from one to five and uses Roman numerals to indicate the severity of a patient’s systemic disease. Patients without systemic disease are classified as grade I, while those with mild to moderate systemic disease that does not limit their activities are classified as grade II. Patients with severe systemic disease that causes functional limitations are classified as grade III, and those with severe systemic disease that poses a constant threat to life are classified as grade IV. Additionally, the letter E is added to indicate emergency surgery. Finally, patients who are moribund and unlikely to survive more than 24 hours with or without surgery are classified as grade V. This grading system helps anesthesiologists determine the appropriate level of care and monitoring needed during surgery.

Management of Anaphylaxis: Medications and Dosages

Anaphylaxis is a severe and potentially life-threatening allergic reaction that requires immediate treatment. The first-line management for anaphylaxis is the administration of adrenaline, also known as epinephrine. The dosage of adrenaline varies depending on the age of the patient. For adults, 0.5 ml of 1 : 1000 adrenaline should be given intramuscularly (im), and the dose can be repeated after 5 minutes if there is no response. In children, the dosage ranges from 150 to 500 micrograms depending on age.

Intravenous (iv) administration of adrenaline is not recommended at a concentration of 1 : 1000. However, iv adrenaline can be administered at a concentration of 1 : 10 000 by an anaesthetist, titrated according to effect. An adrenaline infusion may be necessary for cardiovascular support of the patient.

Chlorpheniramine and hydrocortisone are also part of the treatment for anaphylaxis, but adrenaline takes priority. The dosages of these drugs vary depending on the age of the patient and can be given either im or through a slow iv injection.

It is important to note that anaphylaxis is a medical emergency, and prompt treatment with the appropriate medications is crucial for a positive outcome.

Multi-Wavelength Oximetry Analysis for Diagnosis of CO Poisoning

Carbon monoxide (CO) poisoning can be diagnosed through a thorough history and physical examination, but measuring the presence of dissolved CO in blood is necessary. Multi-wavelength oximeters can detect carboxyhaemoglobin and methaemoglobin in addition to oxyhaemoglobin and deoxyhaemoglobin. Normal CO levels are 1-3%, and any higher levels confirm CO poisoning. Arterial p(O2) levels remain unchanged in CO poisoning, so they cannot be used for diagnosis. CT scans can rule out other causes of neurological complications, and ECGs and cardiac enzyme measurements are necessary for patients with higher exposures or pre-existing cardiac conditions. Standard pulse oximetry cannot distinguish between carboxyhaemoglobin and oxyhaemoglobin and is not useful for diagnosing CO poisoning.

Importance of Correct Patient Identification in Transfusions

Transfusions are a crucial aspect of medical treatment, but incorrect patient identification of samples and blood products can lead to fatal consequences. In fact, it is the most common cause of death following transfusion. Therefore, it is essential to ensure that patient identification is accurate and consistent throughout the process.

If there are any inconsistencies or doubts about the patient’s identity, it is crucial to stop the transfusion immediately and inform the laboratory. This step can prevent serious harm or even death. It is better to err on the side of caution and take the necessary steps to ensure that the patient receives the correct blood product.

In emergency situations where blood is needed immediately, and there is uncertainty about the patient’s identity, group O negative blood may be used. However, this should only be a temporary solution until the patient’s identity is confirmed, and the appropriate blood product can be administered.

In conclusion, patient identification is a critical aspect of transfusions, and any errors or inconsistencies should be addressed immediately to prevent harm to the patient. It is better to take the necessary precautions and ensure that the patient receives the correct blood product, even if it means delaying the transfusion.

An Overview of Common Anaesthetic Induction Agents and Their Advantages and Adverse Effects

Propofol, ketamine, fentanyl, methohexital, and thiopental are commonly used anaesthetic induction agents. Propofol is the preferred choice for most people due to its rapid onset and offset of action, antiemetic and anticonvulsive effects, bronchodilation, and decreased cerebral metabolic oxygen demand and cerebral blood pressure. Ketamine is ideal for hypotensive patients due to its rapid onset, analgesic effects, bronchodilation, and maintenance of airway reflexes and respiratory drive. Fentanyl is an opiate analgesic used for pain relief, while methohexital is used for electroconvulsive therapy. Thiopental is a barbiturate used in general and regional anaesthesia. However, each agent has its own set of advantages and adverse effects that must be considered before use. For example, ketamine can increase intracranial pressure, cardiac output, and blood pressure, while thiopental can cause bronchoconstriction and is contraindicated in asthmatics and patients with a history of porphyria. It is important to carefully evaluate each patient’s medical history and condition before selecting an appropriate anaesthetic induction agent.

Managing a ‘Can’t Intubate’ Scenario in a Patient with Neck of Femur Fracture

In a ‘can’t intubate’ scenario with a patient who has a neck of femur fracture, the priority is delivering oxygen. If attempts at intubation have been difficult and the patient is desaturating, the Difficult Airway Society recommends attempting ventilation with a laryngeal mask airway (LMA) as a temporary measure. If this fails and the patient continues to desaturate, an emergency cricothyrotomy is advised for urgent oxygen delivery. Using a videolaryngoscope to secure a definitive airway is not recommended if oxygenation is a priority. Similarly, attempting a fibreoptic intubation or using a long blade for further attempts at intubation can cause damage and swelling in the airway, leading to laryngospasm. Waking the patient up is also not advisable in this emergency situation, as neck of femur fractures have a high mortality rate if left untreated.

Calculating Oxygen Remaining in a Cylinder

When using an oxygen cylinder, it’s important to know how much oxygen is left to avoid running out. To calculate the remaining oxygen, you need to know the cylinder size and the flow rate. For example, if a cylinder has 340 litres of oxygen and is flowing at 10 litres per minute, how much oxygen is left after 6 minutes?

In 12 minutes, 120 litres of oxygen would have already been used (12 min × 10 l/min = 120 l). To find out how much oxygen is left, subtract the amount used from the total amount: 340 – 120 = 220 litres. Then, divide the remaining gas by the flow rate (10 l/min) to get the remaining time: 220/10 = 22 minutes.

It’s important to note that if the flow rate is higher or the cylinder size is smaller, the remaining time will be shorter. Therefore, it’s crucial to monitor the oxygen levels and have a backup cylinder on hand in case of emergency.

Resuscitation Council (UK) Recommendations for Choking Emergencies

When faced with a choking emergency, the Resuscitation Council (UK) recommends a specific course of action. If the patient is able to cough effectively, encourage them to do so. If not, but they are conscious, try five back blows followed by five abdominal thrusts (Heimlich manoeuvre) and repeat if necessary. However, if the patient becomes unconscious, begin CPR immediately. It is important to note that a finger sweep is no longer recommended as it can push the obstruction further into the airway. Additionally, high flow oxygen is necessary for breathing, but nasopharyngeal airways will not help in this situation. Removal with forceps is also not recommended as it can be hazardous. If the Heimlich manoeuvre fails, a cricothyroidotomy should be considered. While this procedure is recommended in the US and UK, it is not encouraged in some countries like Australia due to the risk of internal injury from over-vigorous use.

Coagulase-Negative Staphylococci: Commonly Isolated Bacteria in Clinical Microbiology Laboratories

Coagulase-negative Staphylococci are frequently encountered in clinical microbiology laboratories. These bacteria, including Staphylococcus epidermidis, are susceptible to novobiocin and have become a significant cause of infection, especially in patients who are hospitalized and have foreign bodies implanted or those who have weakened immune systems.

The prevalence of coagulase-negative Staphylococci in clinical settings highlights the importance of identifying and treating these bacteria promptly. With the rise of antibiotic resistance, it is crucial to monitor the susceptibility patterns of these organisms to ensure effective treatment. By the characteristics and potential risks associated with coagulase-negative Staphylococci, healthcare providers can take appropriate measures to prevent and manage infections caused by these bacteria.

Different Flow Rates of Cannulas for Infusions

Cannulas are small tubes inserted into a vein to administer medication or fluids. Different sizes and colors of cannulas are available, each with varying flow rates. The grey 16G cannula has the highest flow rate of 180 ml/min, while the blue 22G cannula has the lowest flow rate of 33 ml/min. The pink 20G cannula is the most commonly used in adults for standard infusions, with a flow rate of 54 ml/min. The green 18G cannula has a flow rate of 80 ml/min, and the orange 14G cannula has the largest size and highest flow rate of 270 ml/min. It is important to choose the appropriate cannula size and flow rate for each patient’s needs.

Managing Malignant Hyperpyrexia: An Anaesthetic Emergency

Malignant hyperpyrexia is a life-threatening anaesthetic emergency triggered by inhalational anaesthetics and muscle relaxants in genetically susceptible individuals. It causes a hypermetabolic state, leading to increased CO2 production, oxygen consumption, heat production, metabolic and respiratory acidosis, hyperkalaemia, activation of the sympathetic nervous system, and disseminated intravascular coagulation.

Early signs include a rise in end-tidal CO2, rigid muscles, tachycardia, and tachypnoea. Treatment involves discontinuation of the triggering agent, rapid administration of dantrolene, active cooling, and treatment of hyperkalaemia. Dantrolene inhibits calcium release from the sarcoplasmic reticulum and reverses the hypermetabolic state.

It is important to inform the surgeon and stop the operation. Once the initial reaction is controlled, the patient will require transfer to the ICU and monitoring for 24-48 hours.

In contrast, giving more muscle relaxant or antibiotics is not recommended. Active management and stabilisation of the patient should precede discussion with the ICU. Malignant hyperpyrexia requires prompt recognition and management to prevent serious complications and death.

Suxamethonium: A Depolarising Muscle Relaxant

Suxamethonium is a type of muscle relaxant that causes muscular fasciculations after being injected intravenously. It quickly induces neuromuscular paralysis, but recovery is spontaneous once it is metabolized by the enzyme pseudo or plasma cholinesterase, which is produced in the liver. However, certain pesticides and drugs, such as ecothiopate iodide, can inhibit cholinesterase activity and prolong the effects of suxamethonium. Additionally, reduced levels of plasma cholinesterase can be caused by liver disease, malnutrition, and pregnancy, while genetically determined abnormal enzymes can also lead to a prolonged action of suxamethonium. It’s important to note that neostigmine and other anticholinesterase drugs do not serve as reversal agents and can actually potentiate the neuromuscular block caused by suxamethonium.

When administering suxamethonium, it’s important to be aware that bradycardia (a slow heart rate) may occur in children after the first dose and in adults after repeated doses. Premedication with atropine should be considered to prevent this. It’s also crucial to note that suxamethonium is a potent trigger of both anaphylaxis and malignant hyperpyrexia, with the incidence of anaphylaxis being highest with rocuronium, atracurium, and suxamethonium.

Halothane Hepatitis and Precautions

Halothane hepatitis is a condition that can range from minor liver function issues to severe liver failure. It occurs when liver damage appears within 28 days of exposure to halothane, after excluding other known causes of liver disease. About 75% of patients with halothane hepatitis have antibodies that react to halothane-altered antigens. Therefore, it is important to take precautions when using halothane.

Halothane should be avoided if there has been a previous exposure within three months, if there is a known adverse reaction to halothane, if there is a family history of adverse reactions, or if there is pre-existing liver disease. These precautions can help prevent the occurrence of halothane hepatitis and ensure the safety of patients. It is important to carefully consider the use of halothane and take necessary measures to avoid any potential harm.

Common Inducing Anaesthetic Agents and Their Uses

Propofol, etomidate, ketamine, midazolam, and thiopental are all commonly used inducing anaesthetic agents with varying properties and uses.

Propofol is the drug of choice for RSII procedures in normotensive individuals without obvious cardiovascular pathology. It has amnesic, anxiolytic, anticonvulsant, and muscle relaxant properties, but no analgesic effects.

Etomidate provides haemodynamic stability without histamine activity and minimal analgesic effects. It is used in RSI procedures in patients with raised intracranial pressure and cardiovascular conditions, often in combination with fentanyl.

Ketamine is a non-competitive glutamate N-methyl-D-aspartate (NMDA) receptor blocker that produces dissociative anaesthesia. It can be used for induction of anaesthesia in patients with hypotension, status asthmaticus, and shock, but is avoided in hypertensive patients due to relative contraindications.

Midazolam is a benzodiazepine with anticonvulsive, muscle relaxant, and anaesthetic actions. At higher doses or in combination with other opioids, it induces significant cardiovascular and respiratory depression.

Thiopental is administered intravenously as an inducing anaesthetic agent or as a short-acting anaesthetic. It is also used as an anticonvulsant agent and to decrease intracranial pressure in neurosurgical procedures.

Respiratory Alkalosis: Causes and Effects

Respiratory alkalosis is a condition that occurs when a person hyperventilates, leading to a decrease in the partial pressure of carbon dioxide (PaCO2) in the alveoli. This decrease in PaCO2 causes an increase in the ratio of bicarbonate concentration (HCO3) to PaCO2, which in turn increases the pH of the blood. As a result, the patient may appear to have an alkalosis with a high pH of 7.5, low pCO2, and normal PO2. However, the body tries to compensate for this by lowering the bicarbonate concentration. This condition can be caused by a variety of factors, including anxiety, fever, hypoxia, and pulmonary disease. It can also be a side effect of certain medications or a result of high altitude. Treatment for respiratory alkalosis depends on the underlying cause and may include addressing the underlying condition, breathing techniques, or medication.

Treatment for Mild Hypokalaemia

Mild hypokalaemia can be treated with oral supplementation. If a patient is able to eat, intravenous fluids are unnecessary. It is best to advise the patient to take oral supplements for a few days. Foods such as tomatoes and bananas contain high levels of potassium and could be offered as well. However, it is important to note that the maximum concentration of potassium that can be given via a peripheral line is 40 mmol/L. It is also important to avoid loop diuretics as they can make the patient’s potassium levels even lower. As long as the patient is asymptomatic and able to eat, mild hypokalaemia can be easily treated with oral supplementation.

Comparison of Different Anesthetic Agents

Propofol is a short-acting anesthetic agent with an elimination half-life of four hours. It is commonly used for day case procedures and sedation in intensive care units. On the other hand, etomidate is no longer preferred due to its side effects such as postoperative nausea and vomiting, venous thrombosis, and interference with glucocorticoid production. Ketamine, a phencyclidine derivative, can cause hallucinations and nightmares. Methohexitone may lead to involuntary muscular movement and epileptiform activity on an EEG. Lastly, thiopentone has the longest elimination half-life of 12 hours, which can cause a prolonged hangover effect.

In summary, different anesthetic agents have their own advantages and disadvantages. It is important to choose the appropriate agent based on the patient’s condition and the type of procedure being performed.

Medical Interventions for a Post-Operative Patient with Reduced Consciousness

When dealing with a post-operative patient with reduced consciousness, it is important to rule out any reversible causes before administering any medical interventions. In the case of opiate toxicity, administering naloxone, an opiate antidote, can reverse the effects of the opiates. However, if the patient’s reduced Glasgow Coma Scale score and lack of respiratory effort are not caused by hypoglycemia, giving intravenous glucose is not necessary. It is also important to consider the patient’s age and wait a little longer to rule out any reversible causes. Administering a second dose of muscle relaxant reversal is unlikely to help if the patient has adequate contraction on train of four testing. Lastly, before re-sedating the patient for a CT head, it is necessary to rule out any reversible causes such as opiate toxicity.

Post-Operative Foot Drop Caused by Prolonged Pressure on Common Peroneal Nerve

Prolonged pressure on the common peroneal nerve during anaesthesia is a well-known cause of post-operative foot drop. It is important to ensure that patients are adequately padded on the fibula head when positioning them under general or regional anaesthesia for extended periods of time. While a central neurological cause is unlikely to cause such well-defined peripheral nerve lesions, it is essential to take precautions to prevent nerve damage during surgery.

Treatment for post-operative foot drop is typically conservative, and the transient neuropraxia can often pass. However, in some cases, this may result in permanent injury. It is crucial to monitor patients closely after surgery and provide appropriate care to prevent further complications. By taking preventative measures and providing proper post-operative care, healthcare professionals can help reduce the risk of post-operative foot drop and other nerve injuries.