Thu18November0317AM 3

A super morbidly obese patient presents for a bariatric surgical procedure (BMI 56).

The patient has non-insulin dependent diabetes and longstanding hypertension. You are considering what physiological changes might occur when the patient is laid flat for induction of anaesthesia.

Which one of the following physiological changes of the respiratory system is the most important?

(Please select 1 option)

Peak expiratory flow rate will decrease

Functional residual capacity will decrease Correct

Respiratory rate will increase

Chest compliance will increase

Inspiratory reserve volume will increase

Explanation

The most important changes in pulmonary function are a reduction of functional residual capacity (FRC) and expiratory reserve volume (ERV). In morbid obesity, even in the upright position, the fall in FRC can be so marked that it approaches residual volume (RV).

The patient is at risk of premature airway closure and significant ventilation perfusion mismatch resulting in hypoxia. The FRC decreases by 40% when supine as the diaphragm is pushed upward into the thorax by the abdominal contents. Further falls in FRC occur following induction of anaesthesia.

Total respiratory compliance is reduced by up to two-thirds of normal:

Chest wall; due to fat deposition around diaphragm, ribs and abdomen, and

Lung; due to increased pulmonary blood.

This can further deteriorate in the recumbent position volume as the chest wall become less compliant and increase in respiratory resistance.

Whilst morbid obesity results in an increase in inspiratory reserve volume and reduced FEV1, PEFR and ERV, the reduction of FRC (an oxygen reservoir) is very important.

Answer Statistics

1

2%

2

97%

3

1%

4

1%

5

2%

Times answered: 245