Examkin

Question

Difficulty: MediumNormal Pregnancy and Prenatal Care

Match the following clinical presentations of healthy pregnant patients with the primary underlying physiologic mechanism responsible for their findings.

  • An arterial blood gas drawn from a healthy 2828-year-old primigravida at 3232 weeks gestation evaluated for mild dyspnea reveals a pH of 7.447.44 and PaCO 2_2 of 2828 mm Hg.Progesterone-mediated stimulation of central respiratory drive leading to increased tidal volume
  • Routine second-trimester laboratory evaluation in a 2424-year-old G2P1 at 2828 weeks gestation demonstrates a hemoglobin concentration of 10.510.5 g/dL with a normal mean corpuscular volume.Disproportionate expansion of plasma volume relative to the increase in total red blood cell mass
  • Physical examination of an asymptomatic 3131-year-old primigravida at 2424 weeks gestation reveals trace pedal edema, a bounding pulse, and a 2/62/6 systolic ejection murmur.Significant decrease in systemic vascular resistance resulting in an elevated cardiac output
  • Baseline metabolic panel results for a 2626-year-old G3P2 at 1616 weeks gestation reveal a blood urea nitrogen level of 88 mg/dL and a serum creatinine of 0.50.5 mg/dL.Increased renal plasma flow and subsequent elevation in glomerular filtration rate

Answer

The correct pairings match each physiologic finding to its normal adaptive mechanism during pregnancy: the respiratory alkalosis matches with progesterone's effect on tidal volume; the dilutional anemia matches with disproportionate plasma volume expansion; the hyperdynamic cardiovascular exam matches with decreased systemic vascular resistance; and the lowered BUN/creatinine matches with increased glomerular filtration rate.
Pregnancy induces profound maternal physiologic adaptations across multiple organ systems to support fetal growth and prepare for delivery. Progesterone centrally increases tidal volume, causing a mild, compensated respiratory alkalosis. Total blood volume expands significantly (with plasma increasing more than red blood cell mass), leading to physiologic, dilutional anemia. Systemic vascular resistance drops due to smooth muscle relaxation, prompting an increase in cardiac output that generates innocent flow murmurs. Finally, renal blood flow and glomerular filtration rate increase substantially, which lowers serum creatinine and BUN levels compared to the non-pregnant state.

Step-by-Step Solution

1
Analyze the arterial blood gas findings in the first patient vignette.
The findings show a primary, compensated respiratory alkalosis (pH 7.447.44, low PaCO 2_2).
Identifying the acid-base disturbance helps link it directly to progesterone's stimulatory effect on the central respiratory center, which increases tidal volume.
2
Evaluate the hematologic values in the second patient vignette.
The patient has a normocytic anemia with a hemoglobin of 10.510.5 g/dL.
This confirms physiologic anemia of pregnancy, a direct result of disproportionate plasma volume expansion relative to red blood cell mass production.
3
Assess the cardiovascular physical exam findings in the third patient vignette.
The systolic ejection murmur and bounding pulse indicate a hyperdynamic state.
Connecting these physical signs to the profound decrease in systemic vascular resistance and the necessary compensatory rise in cardiac output.
4
Interpret the basic metabolic panel in the fourth patient vignette.
BUN and serum creatinine are appropriately lower than non-pregnant baselines.
Recognizing that increased renal plasma flow and elevated glomerular filtration rate continuously enhance the clearance of these nitrogenous wastes.

Key Concept

Normal maternal physiologic adaptations to pregnancy
Rate this question

Topics

Normal Pregnancy and Prenatal Care

More questions from this topic