CBET cheat sheet

Cardiac output = heart rate × stroke volume; normal adult resting cardiac output is about 4–8 L/min.

Intrinsic pacemaker rates: SA node 60–100 bpm, AV junction 40–60 bpm, ventricular Purkinje fibers 20–40 bpm.

ECG correlates: P wave = atrial depolarization, QRS complex = ventricular depolarization, T wave = ventricular repolarization.

Normal ECG intervals: PR 0.12–0.20 s, QRS < 0.12 s, QT rate-dependent; QTc = QT ÷ √(RR interval).

MAP ≈ diastolic pressure + 1/3 (systolic − diastolic); a MAP below about 60 mmHg compromises organ perfusion.

Blood pressure = cardiac output × systemic vascular resistance.

Adult vital-sign ranges: heart rate 60–100/min, respiratory rate 12–20/min, SpO2 95–100%, temperature 36.5–37.5 °C.

Kidneys filter roughly 125 mL/min (GFR) and regulate fluid volume, electrolytes, and acid–base balance through the nephron.

Autonomic division: sympathetic produces fight-or-flight effects (↑ heart rate, bronchodilation); parasympathetic, largely vagal, slows heart rate and increases GI activity.

Ohm's law: V = I × R. Power: P = V × I = I²R = V²/R.

Series: R_total = R1 + R2 + … with common current. Parallel: 1/R_total = 1/R1 + 1/R2 + …, common voltage, and R_total is smaller than the smallest branch.

Reactance: X_L = 2πfL rises with frequency; X_C = 1/(2πfC) falls with frequency; impedance Z = √(R² + (X_L − X_C)²).

Kirchhoff's laws: currents entering a node sum to zero (KCL); voltages around a closed loop sum to zero (KVL).

Sine wave: V_rms = V_peak ÷ √2 ≈ 0.707 × V_peak; 60 Hz mains has a period of about 16.7 ms.

Capacitor: i = C dv/dt, energy = ½CV², blocks DC and passes high frequencies; inductor: v = L di/dt, energy = ½LI², passes DC and blocks high frequencies.

Silicon diode forward drop is approximately 0.7 V; transformer turns ratio V_secondary/V_primary = N_secondary/N_primary provides step-up or step-down and isolation.

IEC 60601 leakage limits: patient leakage current 100 µA normal condition / 500 µA single fault; earth leakage current 5 mA normal / 10 mA single fault.

Battery capacity (Ah) = current (A) × time (h); series cells add voltage, parallel cells add capacity.

HL7 v2 messages are pipe-delimited segments terminated by carriage returns; ADT carries admit/discharge/transfer data, ORM carries orders, ORU carries observation results.

DICOM defines medical image file format and network services (C-STORE, C-FIND, C-MOVE) used between modalities, workstations, and PACS.

HIPAA: the Privacy Rule governs use and disclosure of PHI; the Security Rule requires administrative, physical, and technical safeguards for ePHI.

IEEE 802.3 = wired Ethernet, 802.11 = Wi-Fi, 802.1X = port-based network access control; VLANs segment medical and enterprise traffic.

TCP is connection-oriented and retransmits lost packets; UDP is connectionless and is used where low latency matters more than guaranteed delivery.

DHCP assigns IP addresses and network settings; DNS resolves host names to IP addresses; IPv4 addresses are 32-bit, IPv6 128-bit, MAC addresses 48-bit.

Backup rule 3-2-1: three copies of data, on two different media, with one copy off-site; restores must be tested, not just backups taken.

Encryption: AES-256 for data at rest and TLS for data in transit; audit trails must record who accessed which record and when.

Standard ECG display settings are 25 mm/s paper speed and 10 mm/mV gain; lead II is the usual continuous monitoring lead.

Pulse oximetry compares light absorption at about 660 nm (red) and 940 nm (infrared); the ratio R of absorbances is mapped to SpO2 by a calibration curve.

Capnography: normal end-tidal CO2 is 35–45 mmHg; an abrupt loss of waveform suggests disconnection, obstruction, or esophageal intubation.

Lung-protective ventilation uses tidal volume 6–8 mL/kg predicted body weight; modes include volume control, pressure control, SIMV, CPAP, and pressure support.

Defibrillation energy: biphasic 120–200 J, monophasic up to 360 J; synchronized cardioversion times the discharge to the QRS complex.

Monopolar electrosurgery requires a large-area return electrode; return electrode monitoring (REM) circuitry detects pad detachment to prevent burns.

CT Hounsfield units: water = 0, air ≈ −1000, dense bone ≈ +1000; window width and level set displayed tissue contrast.

MRI uses superconducting magnets at 1.5 T or 3 T; a quench releases cryogen and requires evacuation and oxygen-level monitoring.

Infusion flow rate (mL/h) = volume (mL) ÷ time (h); drop rate (drops/min) = (volume × drop factor) ÷ time in minutes.

Troubleshooting sequence: verify and reproduce the complaint → isolate the fault (half-split, substitute known-good) → confirm root cause → repair → verify performance → document.

Inspect power source, cord, fuses, batteries, connectors, and transducers before board-level diagnosis; these account for a large share of equipment failures.

Half-split method: test the midpoint of the signal chain first, then the midpoint of the faulty half, halving the search area at each step.

Protective earth resistance from the plug ground pin to exposed metal should be ≤ 0.2 Ω (many programs apply a stricter 0.15 Ω limit).

Electrical safety test order: visual inspection → ground resistance → chassis leakage → lead-to-ground leakage → performance verification.

Lockout/tagout and a verified zero-energy state are required before opening equipment supplied by hazardous energy.

Calibrate with standards traceable to a national metrology institute and record as-found and as-left values on the CMMS work order.

Root-cause tools include 5 Whys and the fishbone (Ishikawa) diagram; document the corrective action, not only the repair performed.

Clean and disinfect equipment before servicing and follow the facility exposure control plan and PPE requirements for bloodborne pathogens.

Fire classes: A ordinary combustibles, B flammable liquids, C energized electrical, D combustible metals, K cooking oils; use CO2 or dry chemical on electrical fires, never water.

RACE = Rescue, Alarm, Confine (close doors), Extinguish/Evacuate; PASS = Pull the pin, Aim at the base, Squeeze the handle, Sweep side to side.

NFPA 99 governs healthcare electrical, medical gas, vacuum, and environmental systems; NFPA 70 (NEC) and NFPA 101 (Life Safety Code) also apply.

US medical gas cylinder colors: oxygen green, nitrous oxide blue, nitrogen black, carbon dioxide gray, medical air yellow.

Oxygen-enriched areas require no smoking, no open flame, and no oil or grease on fittings; cylinders are stored upright and secured against falling.

ALARA radiation protection uses time, distance, and shielding; dose rate from a point source falls with the square of the distance.

OSHA 1910.147 covers lockout/tagout; OSHA 1910.1030 covers bloodborne pathogens and requires an exposure control plan and hepatitis B vaccination offer.

Chemical spills: consult the safety data sheet, use the appropriate spill kit, and report; mercury spills need special cleanup and must never be vacuumed.

Patient handling: use mechanical lifts and gait belts, lock stretchers and wheelchairs during transfers, and post signage for wet floors.