Question

A patient has the following Starling forces measured at the capillary level: capillary hydrostatic pressure = 18 mmHg, capillary oncotic pressure = 27 mmHg, interstitial oncotic pressure = 7 mmHg. If there is no net movement of fluid across the capillary wall, what is the value of the interstitial hydrostatic pressure?

• A. 0 mmHg
• B. +1 mmHg
• C. +2 mmHg
• D. $-2$ mmHg

Hint:

For no net capillary fluid movement: outward forces = inward forces.

Answer 1

The Correct Option is D

Concept: Starling forces determine fluid movement across capillary walls. For no net movement, outward forces must equal inward forces.

Step 1: Write the balance equation.
Outward forces: \[ P_c + \pi_i \] Inward forces: \[ P_i + \pi_c \] For no net movement: \[ P_c + \pi_i = P_i + \pi_c \]

Step 2: Substitute values.
\[ 18 + 7 = P_i + 27 \] \[ 25 = P_i + 27 \]

Step 3: Calculate interstitial hydrostatic pressure.
\[ P_i = 25 - 27 = -2 \text{ mmHg} \] Therefore, the correct answer is $-2$ mmHg.