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标题: ANZCA EXAM Q 1999A01--obesity & anesthesia management [打印本页]

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作者: shenxiu2    时间: 2010-11-21 10:49
标题: ANZCA EXAM Q 1999A01--obesity & anesthesia management

1999A01: A 52 year old man, height 1.75m, weighing 130 kg presents for laparoscopic cholecystectomy under general anaesthesia. History and examination reveal no other abnormality. How does this patient's obesity influence your management of his anaesthetic up to the time of the first incision?

Obesity is a complex, multi-factorial disease, defined as a body weight 20% greater than ideal body weight. It can also be classified using the Body Mass Index (BMI) where: BMI = weight (kg) / height2 (m).

Obese: BMI > 30

Morbidly obese: BMI > 40

This patient has a BMI of 42, meeting criteria for morbid obesity.

Obesity is associated with increased peri-operative mortality and morbidity. This will influence the anaesthetic in the following ways:

Pre-operative assessment [presumably this has already been done?]

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Introduce self and obtain inform consent.

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Assess for comorbidities (see below)

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Assess for difficult airway – Mallampati score, thyromental distance, inter-incisor distance.

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Investigations

oRandom blood glucose: looking for unidentified diabetes.

oFBC: Hb, looking for polycythaemia associated with sleep apnoea.

oElectrolytes: looking for indication of renal disease, which may be associated with diabetes.

oECG: looking for signs of ischaemic heart disease and past AMIs.

oCXR: looking for heart size, as indicative of CCF.

Physiological changes of obesity

• Lung volumes – decreased FRC leads to lower oxygen stores and more rapid desaturation with apnoea, as may occur at induction.
• Lung compliance (decreased) and resistance (increased) requiring higher pressures for ventilation (IPPV).
• Gastric emptying decreased due to increased intraabdominal pressures, possibly increasing aspiration risk.
• Increased blood volume.

Pharmaceutical changes of obesity

• Increased volume of distribution.
• Decreased total body water.
• Decreased hepatic blood flow.
• Drug doses should be based upon lean body weight not actual weight.

Associated co-morbidities of obesity

• Obstructive sleep apnoea and ‘obesity hypoventilation syndrome’
  • 2-4% of the normal adult population and 5% of the obese.
  • Associated with: hypertension, hypoxaemia, hypercarbia and polycythaemia.
  • Increased sensitivity to CNS depressant drugs, increasing risk of post-operative respiratory failure.
• Diabetes mellitus---Associated with ischaemic heart disease, increased wound infection, poor wound healing.
• Hypertension – increasing blood pressure lability intra-operatively.
• Ischaemic heart disease – obesity is an independent risk factor.
• Congestive cardiac failure – LV hypertrophy worsens LV compliance, which combined with hypervolaemia leads to CCF.
• Pulmonary hypertension – due to combined chronic hypoxaemia and increased pulmonary blood volume. May lead to right heart failure.
• Thromboembolic disease – increased risk of DVT/PE due to polycythaemia, increased abdominal pressure, immobilisation.

Anaesthetic management

• Planning

·Pre-medication

oAcid prophylaxis – metoclopramide, ranitidine, sodium citrate.

oAnti-sialogogue (glycopyrrolate) if planning FOB intubation.

·Patient will require close monitoring post-operatively, as at high risk of peri-operative hypoxia in first 5 days. Suggest monitor in HDU if bed available for first 24 hours.

·If using CPAP device at home, own machine should be used in hospital. If not requiring CPAP, facility should be available post-operatively in case of respiratory decline.

·Not suitable for day surgery.

2.Technique

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Consider regional technique if appropriate (not suitable here for lap cholecystectomy).

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Mandatory intubation given further increased intra-abdominal pressure and possible increased risk of aspiration.

Extra monitoring

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5-lead ECG to detect cardiac ischaemia

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Invasive blood pressure monitoring may be required if either i) associated ischaemic heart disease, ii) NIBP cuff unsuitable due to patient size. If planned post-op HDU admission, also assists in HDU monitoring.

Induction

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If predicted difficult intubation, awake fibre optic intubation is indicated. Otherwise a rapid sequence induction is suitable.

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Set-up of theatre for possible difficult intubation is essential (ideal positioning with pillows to provide support; access to bougie, alternate laryngoscopes, etc.)

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Induction with propofol may offer a faster emergence than thiopentone.

Maintenance

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Use non-narcotic analgesia (paracetamol, NSAIDs, COX-2, local anaesthetic infiltration) and shorter-acting narcotics, such as fentanyl.

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Use short-acting neuromuscular blocking agents.

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For a short-medium length case such as this, choice of volatile agent (isoflurane, sevoflurane, desflurane) will have little impact on speed of recovery.

Emergence [ not for this answer ]

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Mandatory reversal of neuromuscular blockade.

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Extubate when fully awake.

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