Free TCRN Basics Practice Questions with Answers

First, calculate Mean Arterial Pressure (MAP): MAP = [SBP + (2 x DBP)] / 3. MAP = [108 + (2 x 62)] / 3 = 232 / 3 = 77.3 mmHg. Next, calculate CPP: CPP = MAP - ICP. CPP = 77.3 - 24 = 53.3 mmHg. Target CPP: According to Brain Trauma Foundation guidelines (current through 2026), the target CPP for TBI patients is 60-70 mmHg. Clinical Pearl: A CPP < 60 mmHg is associated with ischemia and poor outcomes, while a CPP > 70 mmHg may increase the risk of ARDS due to aggressive fluid/vasopressor use. BCEN frequently tests the ability to perform this two-step calculation (MAP then CPP) under pressure.

This waveform pattern indicates reduced intracranial compliance. In a normal ICP waveform: - P1 (Percussion): Arterial pulsation, usually the highest peak. - P2 (Tidal): Represents intracranial compliance. - P3 (Dicrotic): Venous pulsation. When P2 > P1, the brain's ability to compensate for additional volume (compliance) is exhausted. The patient is on the steep part of the pressure-volume curve, meaning even small increases in volume (edema, blood) will cause rapid, dangerous spikes in ICP. Exam Strategy: BCEN emphasizes recognizing non-compliant waveforms before the ICP numerical value becomes critically high.

High PEEP (>10-15 cmH2O) can increase ICP and decrease CPP. Mechanism: Elevated intrathoracic pressure is transmitted to the venous system, impeding venous return from the cerebral circulation via the jugular veins. This increases cerebral venous volume and ICP. Furthermore, high PEEP can decrease cardiac output (via reduced preload), which lowers MAP and subsequently lowers CPP (CPP = MAP - ICP). Exam Tip: If a question asks how to optimize ICP in a ventilated patient, ensure the head is midline and the HOB is elevated 30 degrees to facilitate venous drainage, especially if high PEEP is required for oxygenation.

The Monro-Kellie Doctrine states that the cranial vault is a fixed, rigid box containing three components: Brain tissue (80%), Blood (10%), and CSF (10%). If one component increases in volume (e.g., an epidural hematoma), the others must decrease to maintain a constant pressure. Compensation occurs first by displacing CSF into the spinal subarachnoid space and shunting venous blood out of the cranium. Clinical Application: Once these compensatory mechanisms are exhausted, ICP rises exponentially. Management focuses on removing the extra volume (evacuating the hematoma) or reducing the other components (e.g., using mannitol to shrink brain tissue or an EVD to drain CSF).

Cerebral autoregulation is the brain's ability to maintain constant CBF despite fluctuations in MAP. The normal autoregulatory range is a MAP of 50 to 150 mmHg. In this scenario (MAP 45): The patient is below the lower limit of autoregulation. At this point, cerebral vessels are maximally dilated and can no longer compensate. CBF becomes pressure-dependent, meaning any further drop in MAP leads to a linear drop in CBF, causing profound global ischemia. Exam Strategy: BCEN often tests the MAP range of 50-150. Remember that in chronic hypertension or TBI, this curve may shift to the right, requiring higher MAPs to maintain perfusion.