Critical Care Nursing: Cardiac Dysrhythmias, Acid-Base, Ventilation, Trauma, and Adrenal Disorders

A comprehensive vocabulary review set covering high-yield definitions, parameters, and concepts across cardiac electrophysiology, dysrhythmias, acid-base imbalances, pacemakers, chest trauma and tubes, mechanical ventilation, ARF/ARDS, and adrenal disorders.

Automaticity

The ability of cardiac cells to initiate an electrical impulse spontaneously and repeatedly without external stimulation.

Conductivity

The ability of cardiac cells to transmit an electrical impulse along cell membranes in an organized pathway.

Contractility

The mechanical ability of cardiac muscle fibers to respond to an electrical impulse by shortening and squeezing.

Sinoatrial (SA) Node

The primary pacemaker of the heart, located in the upper right atrium, that generates impulses at an intrinsic rate of $60\text{--}100/\text{min}$.

Atrioventricular (AV) Node

The gatekeeper of the cardiac conduction system that delays the electrical impulse for approximately $0.1\,\text{second}$ to allow the atria to empty into the ventricles, with an intrinsic backup rate of $40\text{--}60/\text{min}$.

P Wave

The ECG waveform representing atrial depolarization as the impulse spreads from the SA node through the atria; normally upright and precedes every QRS complex.

PR Interval

The time required for an impulse to travel from the atria through the AV node, bundle of His, and bundle branches before the ventricles contract, measuring $0.12\text{--}0.20\,\text{seconds}$ ($3\text{--}5$ small boxes).

QRS Complex

The ECG waveform representing ventricular depolarization and contraction (systole), normally lasting less than $0.12\,\text{seconds}$ (under $3$ small boxes).

ST Segment

The ECG segment extending from the end of the S wave to the beginning of the T wave, representing the interval between ventricular depolarization and repolarization; normally flat on the isoelectric baseline.

T Wave

The ECG waveform representing ventricular repolarization (resting and filling phase); tall and peaked configurations are classic indicators of hyperkalemia.

QT Interval

The total duration of ventricular depolarization and repolarization measured from the start of the QRS complex to the end of the T wave ($0.34\text{--}0.43\,\text{seconds}$); prolongations past $0.43\,\text{seconds}$ create a risk for torsades de pointes.

Sinus Bradycardia

A regular cardiac rhythm originating from the SA node at a rate of less than $60/\text{min}$ with normal waveforms; treated when symptomatic using IV atropine, transcutaneous pacing, or dopamine/epinephrine infusions.

Sinus Tachycardia

A regular rhythm originating in the SA node firing at a rate of $101\text{--}180/\text{min}$ with normal P waves, PR intervals, and QRS complexes, typically triggered by stressors, fever, pain, or hypovolemia.

Supraventricular Tachycardia (SVT)

A regular, paroxysmal tachydysrhythmia originating from a reentrant circuit above the bundle of His with a rate of $151\text{--}220/\text{min}$, hidden P waves, and a narrow QRS complex; treated with vagal maneuvers, IV adenosine, or synchronized cardioversion.

Adenosine

A first-line drug for SVT with a half-life of about $10\,\text{seconds}$, administered as an ultra-rapid IV push over $1\text{--}2\,\text{seconds}$ followed by an immediate $20\,\text{mL}$ normal saline flush, producing brief expected asystole.

Synchronized Cardioversion

The delivery of a timed electrical countershock programmed to discharge directly on the R wave to treat unstable tachydysrhythmias with a pulse, preventing shock delivery during the vulnerable T wave period.

Atrial Flutter

An atrial tachydysrhythmia characterized by a reentrant loop in the right atrium producing regular sawtooth flutter (F) waves at an atrial rate of $200\text{--}350/\text{min}$.

Atrial Fibrillation

The total disorganization of atrial electrical activity from multiple ectopic foci resulting in an atrial rate of $350\text{--}600/\text{min}$, chaotic fibrillatory waves, an irregularly irregular ventricular response, and high stroke risk.

Premature Ventricular Contraction (PVC)

An early ventricular ectopic beat bypassing the normal conduction system, presenting as a wide ($>0.12\,\text{seconds}$) and bizarre QRS complex with no preceding P wave and a T wave deflected in the opposite direction.

Ventricular Tachycardia (VT)

A life-threatening dysrhythmia characterized by a run of $3$ or more consecutive PVCs at a rate of $150\text{--}250/\text{min}$ with wide, bizarre QRS complexes; treated with antiarrhythmics if stable, cardioversion if unstable with a pulse, or CPR and defibrillation if pulseless.

Torsades de Pointes

A form of polymorphic ventricular tachycardia characterized by QRS complexes that twist around the baseline, associated with a prolonged QT interval and treated with IV magnesium.

Ventricular Fibrillation (VF)

A lethal, uncoordinated ventricular rhythm producing chaotic baseline undulations without discernible QRS complexes, pulse, or cardiac output; managed with immediate CPR and rapid unsynchronized defibrillation.

Pulseless Electrical Activity (PEA)

A state in which organized electrical activity is visible on the cardiac monitor, but the heart produces no mechanical contraction and no palpable pulse; non-shockable and treated with CPR, epinephrine, and resolving underlying Hs and Ts.

First-Degree AV Block

A conduction abnormality where every atrial impulse conducts to the ventricles but is delayed at the AV node, resulting in a constant, prolonged PR interval exceeding $0.20\,\text{seconds}$.

Second-Degree AV Block, Type I (Mobitz I / Wenckebach)

An AV nodal block characterized by progressive lengthening of the PR interval on successive beats until a P wave is completely blocked (dropped QRS complex), after which the cycle repeats.

Second-Degree AV Block, Type II (Mobitz II)

An infranodal block below the AV node featuring constant PR intervals on conducted beats followed by dropped QRS complexes without prior PR prolongation; carries high risk of progression to complete heart block.

Third-Degree AV Block (Complete Heart Block)

Complete absence of electrical conduction between atria and ventricles, causing independent pacing of atria and ventricles (AV dissociation); managed emergently with transcutaneous and transvenous pacing.

Demand Pacemaker

A pacemaker programmed to sense intrinsic cardiac electrical activity and discharge an impulse only when the patient's heart rate falls below a preset threshold.

Failure to Sense

A pacemaker malfunction in which the device fails to detect the heart's native electrical activity, causing it to discharge spikes at inappropriate intervals that risk landing on the vulnerable T wave.

Failure to Capture

A pacemaker malfunction where a delivered pacing spike fails to initiate myocardial depolarization and contraction, visible on an ECG as a pacing spike with no accompanying P wave or QRS complex.

Failure to Pace

A pacemaker malfunction occurring when the pulse generator fails to deliver an electrical output despite the patient's intrinsic heart rate falling below the programmed threshold.

Implantable Cardioverter-Defibrillator (ICD)

An implanted device that monitors cardiac rhythms and delivers an internal electrical countershock of $25\,\text{J}$ or less to terminate episodes of sustained ventricular tachycardia or ventricular fibrillation.

Respiratory Acidosis

An acid-base imbalance characterized by a blood pH $<7.35$ and a $\text{PaCO}_2 >45\,\text{mm\,Hg}$ caused by alveolar hypoventilation and carbonic acid excess, producing CNS depression, headache, and vasodilation.

Respiratory Alkalosis

An acid-base disturbance with a blood pH $>7.45$ and a $\text{PaCO}_2 <35\,\text{mm\,Hg}$ caused by alveolar hyperventilation blowing off excessive $\text{CO}_2$, resulting in decreased ionized calcium, numbness, tingling, and tetany.

Metabolic Acidosis

An acid-base deficit characterized by a blood pH $<7.35$ and serum $\text{HCO}_3^- <22\,\text{mEq/L}$ resulting from acid gain or bicarbonate loss; compensated by rapid, deep Kussmaul respirations.

Metabolic Alkalosis

An acid-base excess characterized by a blood pH $>7.45$ and serum $\text{HCO}_3^- >26\,\text{mEq/L}$ caused by gastric acid loss from vomiting or suction, or excess bicarbonate ingestion, accompanied by compensatory hypoventilation.

Tension Pneumothorax

A medical emergency in which air enters the pleural space during inspiration but cannot escape, causing elevated intrapleural pressure that collapses the lung, shifts the mediastinum to the contralateral side, and impairs cardiac output.

Flail Chest

An unstable chest wall segment resulting from the fracture of $3$ or more consecutive ribs in $2$ or more places, presenting with paradoxical chest motion (inward movement during inspiration and outward bulging during expiration).

Water-Seal Chamber

The compartment of a pleural drainage unit filled with $2\,\text{cm}$ of sterile water that acts as a one-way valve, permitting air to vent from the pleural cavity while preventing atmospheric air from re-entering.

Tidaling

The normal respiratory fluctuation of the fluid column within the water-seal chamber of a chest tube drainage unit, rising during inspiration and falling during expiration in a spontaneously breathing patient.

Rapid Sequence Induction (RSI)

The simultaneous, rapid administration of a sedative-hypnotic agent and a neuromuscular blocking agent to induce immediate unconsciousness and flaccid paralysis for emergency endotracheal intubation.

Positive End-Expiratory Pressure (PEEP)

A mechanical ventilator parameter that maintains positive pressure in the airways at the end of exhalation (physiologic baseline $5\,\text{cm\,H}_2\text{O}$, up to $10\text{--}20\,\text{cm\,H}_2\text{O}$ in ARDS) to splint alveoli open and increase functional residual capacity.

Assist-Control (AC) Ventilation

A full-support mechanical ventilation mode delivering a preset tidal volume at a scheduled rate, where any spontaneous patient effort triggers the ventilator to deliver the full preset tidal volume.

High-Pressure Ventilator Alarm

An alarm triggered by increased resistance within the breathing circuit or reduced lung compliance, commonly caused by secretions, tubing kinks, patient coughing or biting the tube, bronchospasm, or pneumothorax.

Low-Pressure Ventilator Alarm

An alarm triggered by an unexpected decrease in circuit pressure, typically caused by a loose connection, circuit disconnection, or endotracheal tube cuff leak.

Ventilator-Associated Pneumonia (VAP)

A healthcare-acquired lower respiratory infection developing $48\,\text{hours}$ or more following endotracheal intubation, prevented via bundle practices including head-of-bed elevation of $30\text{--}45^\circ$, daily spontaneous breathing trials, and chlorhexidine oral care.

Hypoxemic Respiratory Failure

A form of acute respiratory failure defined by a $\text{PaO}_2 <60\,\text{mm\,Hg}$ despite supplemental oxygen, caused by ventilation-perfusion mismatch, intrapulmonary shunting, or diffusion impairment.

Hypercapnic Respiratory Failure

Ventilatory failure characterized by a $\text{PaCO}_2 >50\,\text{mm\,Hg}$ with an arterial blood $\text{pH} <7.35$, reflecting an inability of the respiratory system to eliminate carbon dioxide.

Intrapulmonary Shunt

An extreme ventilation-perfusion mismatch occurring when deoxygenated blood bypasses non-ventilated, fluid-filled, or collapsed alveoli, resulting in refractory hypoxemia that cannot be corrected by oxygen administration alone.

Acute Respiratory Distress Syndrome (ARDS)

A sudden, progressive form of acute respiratory failure characterized by diffuse inflammatory damage to the alveolar-capillary membrane, noncardiogenic pulmonary edema, surfactant inactivation, and refractory hypoxemia.

P/F Ratio

The clinical index of arterial oxygen tension to fractional inspired oxygen ($\text{PaO}_2 \div \text{FiO}_2$ as a decimal); normal is $>400$, mild ARDS is $<300$, moderate ARDS is $<200$, and severe ARDS is $<100$.

Prone Positioning

A therapeutic strategy for severe ARDS where the patient is positioned on their stomach for at least $12\,\text{hours}$ (up to $16\,\text{hours}$) daily to recruit collapsed dorsal alveoli, redistribute pulmonary blood flow, and relieve cardiac compression.

Addison Disease

Primary adrenocortical insufficiency characterized by the autoimmune destruction of all three zones of the adrenal cortex, causing deficiencies in cortisol, aldosterone, and androgens with elevated ACTH levels causing bronze skin hyperpigmentation.

Addisonian Crisis

A life-threatening acute adrenal insufficiency triggered by stress, infection, trauma, or abrupt steroid cessation, presenting with refractory hypotension, dehydration, hyponatremia, hyperkalemia, and hypoglycemia.

Cushing Syndrome

A clinical condition resulting from chronic exposure to excess corticosteroids (most commonly exogenous prednisone), manifesting as central obesity, moon face, buffalo hump, purple striae, muscle wasting, hyperglycemia, and hypertension.

Cushing Disease

A specific endogenous etiology of Cushing syndrome caused by an ACTH-secreting pituitary adenoma, accounting for approximately $85\%$ of non-iatrogenic cases and treated surgically via transsphenoidal hypophysectomy.