"Anesthetic Complications & Monitoring" — Practice

Question 1

The earliest sign of malignant hyperthermia is

Accepted Answer

A

Question 2

In carbon monoxide poisoning, pulse oximetry typically shows

Accepted Answer

A

Question 3

During laparoscopy the capnograph falls abruptly from 38 to 8 mmHg while the ventilator continues normally. What are the possibilities and how do you distinguish them?

Accepted Answer

An abrupt fall with unchanged ventilation means either that gas is no longer reaching the sampling line or that carbon dioxide is no longer reaching the lungs.

The first group is equipment: circuit disconnection, tube displacement or obstruction. These are excluded within seconds by inspecting the circuit, checking the tube and hand-ventilating to assess compliance.

The second group is circulatory, and in laparoscopy it specifically raises venous gas embolism, in which insufflated carbon dioxide enters an open vein and obstructs pulmonary outflow. Massive pulmonary embolism, sudden severe hypotension and cardiac arrest produce the same picture.

The response is to check the circuit and tube immediately, stop insufflation and release the pneumoperitoneum, give 100 per cent oxygen, position head-down with left lateral tilt if embolism is suspected, and support the circulation. Capnography announces this within a breath, whereas saturation would fall considerably later.

Question 4

A woman at 34 weeks becomes hypotensive shortly after being positioned supine. What is the mechanism and the first intervention?

Accepted Answer

Aortocaval compression. Beyond about 20 weeks of gestation the gravid uterus compresses the inferior vena cava against the vertebral column when the woman lies supine, obstructing venous return and reducing cardiac output.

The first intervention is mechanical rather than pharmacological: left lateral tilt of at least 15 degrees, or manual displacement of the uterus to the left, which relieves the obstruction directly.

Fluids and vasopressors are given alongside but do not address the cause, since the problem is obstructed venous return rather than absolute hypovolaemia or vasodilatation.

The same reasoning applies during resuscitation of a pregnant woman, where manual uterine displacement is maintained throughout chest compressions, because compressions cannot generate output if venous return is obstructed.

Question 5

Shortly after induction with a neuromuscular blocker and antibiotic, the patient becomes profoundly hypotensive with high airway pressures and no rash. What is happening?

Accepted Answer

Anaphylaxis until proved otherwise, and the absence of rash does not exclude it.

Under anaesthesia the presentation is cardiovascular rather than cutaneous. The patient cannot report itch, flushing or breathlessness, and the skin is largely covered by drapes, so severe hypotension, tachycardia, bronchospasm with rising airway pressures and a falling end-tidal carbon dioxide are what announce it.

Neuromuscular blocking agents are the commonest trigger in this setting, followed by antibiotics, chlorhexidine and latex, and both suspects are present here.

Management is to stop administration of all likely agents, call for help, give adrenaline intravenously in titrated doses since the patient is monitored and cannulated, give large-volume fluid resuscitation, and maintain the airway with 100 per cent oxygen. Serial tryptase samples and allergy referral follow.

Question 6

Thirty minutes into an operation the end-tidal carbon dioxide rises steadily, the patient is tachycardic and the temperature has risen by 1 degree. Diagnose and manage.

Accepted Answer

Malignant hyperthermia. The rising end-tidal carbon dioxide is the earliest and most sensitive sign, appearing before temperature rises, which is why the name is misleading.

The mechanism is uncontrolled calcium release through a defective ryanodine receptor, producing sustained muscle contraction with a massive increase in metabolic rate, which generates the carbon dioxide, the heat, the acidosis and eventually rhabdomyolysis.

The first action is to stop the trigger, meaning the volatile agent, and to call for help while switching to a clean circuit with high-flow 100 per cent oxygen and hyperventilating to clear the carbon dioxide load.

Dantrolene is given without waiting for confirmation, since it blocks calcium release at the ryanodine receptor and is the only specific treatment. Active cooling follows, alongside treatment of hyperkalaemia, acidosis and arrhythmia, with monitoring for myoglobinuria and renal failure. The family requires counselling and referral for testing, since inheritance is autosomal dominant.

Question 7

A patient extubated after surgery appears awake but has weak grip, cannot lift the head and desaturates in recovery. Diagnose and state how it should have been prevented.

Accepted Answer

Residual neuromuscular blockade.

Recovery of consciousness and recovery of neuromuscular function are separate processes, so a patient can appear awake while pharyngeal and respiratory muscles remain weak. Pharyngeal muscles are among the most sensitive to residual blockade, which is why airway obstruction and aspiration risk persist even when the patient can open their eyes and follow commands.

Clinical tests perform poorly. Head lift for five seconds and grip strength detect only substantial residual weakness and miss the degree that still impairs airway protection and the hypoxic ventilatory response.

Prevention is quantitative neuromuscular monitoring, using train-of-four ratio measured objectively rather than assessed visually, with reversal given until an adequate ratio is documented before extubation. Sugammadex reverses aminosteroid blockers rapidly and completely, and neostigmine with an antimuscarinic remains an option for partially recovered blockade.

Immediate management is oxygen, airway support and, if the patient is not protecting the airway, reintubation with further reversal.

Question 8

A 68-year-old with hypertension and stable angina is listed for hernia repair. A colleague requests echocardiography, stress testing and a full biochemical panel. Comment.

Accepted Answer

This is over-investigation, and it is likely to delay surgery without improving outcome.

The most informative assessment is functional capacity, obtained by asking what the patient can actually do. A patient who climbs two flights of stairs without stopping has a metabolic equivalent above four and generally tolerates non-cardiac surgery, and this single question outperforms most tests for that purpose.

Investigations should be directed by the history, examination and magnitude of surgery. Routine panels in patients without specific indications generate false positives that trigger further testing, cause anxiety and postpone operations, without changing management.

Cardiac stress testing is indicated where the result would alter management, which usually means where revascularisation is being contemplated, and a hernia repair in a patient with stable symptoms rarely meets that threshold.

What actually reduces his risk is different: continuing his beta blocker and statin, withholding angiotensin blockade on the morning of surgery because of induction hypotension, ensuring blood pressure control, correcting anaemia if present, and smoking cessation if relevant.

Question 9

A trauma patient anaesthetised for emergency laparotomy later describes hearing conversation during surgery. How did this happen and how is the risk reduced?

Accepted Answer

This is accidental awareness under general anaesthesia, and the trauma setting explains most of it.

Haemodynamic instability leads to deliberate reduction of anaesthetic dose, since volatile agents and propofol both cause vasodilatation and myocardial depression that a shocked patient tolerates poorly. The anaesthetist is therefore balancing the risk of awareness against the risk of cardiovascular collapse, and the balance sometimes tips.

Neuromuscular blockade compounds it. A paralysed patient who becomes aware cannot move, grimace or signal, so the usual clinical indicators of light anaesthesia are removed, and blood pressure and heart rate are unreliable in a patient who is already tachycardic and hypotensive from bleeding.

Risk is reduced by monitoring end-tidal anaesthetic agent concentration during inhalational anaesthesia, using processed electroencephalographic monitoring where a total intravenous technique removes that safeguard, giving amnesic agents such as midazolam or ketamine where dose must be limited, and avoiding unnecessary paralysis.

Afterwards, the episode is acknowledged rather than dismissed, since post-traumatic stress disorder follows a substantial proportion, and structured follow-up with psychological support is part of management.

Practice — "Anesthetic Complications & Monitoring"

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