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CHAPTER 4: Advanced Principles

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Advanced Principles

During induction of general anesthesia, the pregnant patient quickly desaturates. Which factors most likely caused the desaturation?

(A) Increased functional residual capacity and increased oxygen consumption

(B) Decreased residual volume and increased expiratory reserve volume

(C) Decreased functional residual capacity and increased oxygen consumption

(D) Increased residual volume and decreased expiratory reserve volume

C. Rationale: Respiratory changes of pregnancy include decreased functional residual capacity (FRC), increased oxygen consumption, and decreased residual and expiratory reserve volumes. Decreased FRC and increased oxygen consumptions lead to rapid decrease in oxygen saturation.

Average maximum physiological changes associated with pregnancy.1
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Average maximum physiological changes associated with pregnancy.1
Parameter Change
Neurological
 MAC −40%
Respiratory
 Oxygen consumption +20-50%
 Airway resistance −35%
 FRC −20%
 Minute ventilation +50%
 Tidal volume +40%
 Respiratory rate +15%
 PaO2 +10%
 PaCO2 −15%
 HCO3 −15%
Cardiovascular
 Blood volume +35%
 Plasma volume +55%
 Cardiac output +40%
 Stroke volume +30%
 Heart rate +20%
 Systolic blood pressure −5%
 Diastolic blood pressure −15%
 Peripheral resistance −15%
 Pulmonary resistance −30%
Hematologic
 Hemoglobin −20%
 Platelets −10%
 Clotting factors2 +30-250%
Renal
 GFR +50%

1MAC, minimum alveolar concentration; FRC, functional residual capacity; GFR, glomerular filtration rate.

2Varies with each factor.

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Butterworth  J.F., Mackey  D.C., Wasnick  J.D. (2013). Ch 41 Morgan & Mikhail's Clinical Anesthesiology (5th ed.). New York, NY: McGraw-Hill.
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Longnecker  D.E., Brown  D.L., Newman  M.F., Zapol  W.M. (2012). Ch 22 Anesthesiology (2nd ed.). San Francisco, CA: McGraw-Hill.

Which cardiac variable leads to heart failure resulting from obesity?

(A) Decreased preload

(B) Left ventricular systolic dysfunction

(C) Decreased afterload

(D) Hypotension

B. Rationale: Volume overload and vascular stiffness result from obesity. Increased preload, increased afterload, and hypertension lead to left ventricular systolic dysfunction.

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Hines  R.L., Marschall  K.E. (2012). Ch 16 Stoelting's Anesthesia and Co-Exiting Disease (6th ed.). Philadelphia, PA: Saunders.

What is the average weight of a 6-year-old?

(A) 15 kg

(B) 18 kg

(C) 21 kg

(D) 24 kg

C. Rationale: A simple estimation of body weight by age is: 9 + (Age × 2).

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Butterworth  J.F., Mackey  D.C., Wasnick  J.D. (2013). ...

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