Cardiac and Respiratory Medical Emergencies

SECTION 1

Historical Context & Motivation

Cardiac and respiratory emergencies have been the leading causes of prehospital mortality since the earliest days of organized emergency medical services. Understanding how the field evolved from rudimentary first aid to sophisticated, protocol-driven paramedicine reveals why modern paramedics must possess a deep working knowledge of cardiac and pulmonary pathophysiology. The development of cardiopulmonary resuscitation (CPR), defibrillation, and advanced airway management represents pivotal milestones that have directly shaped the scope of paramedic practice as tested on the NREMT examination. Each breakthrough emerged from clinical observation, landmark research, and the persistent realization that the time between symptom onset and definitive intervention determines survival.

1960

Modern CPR Established

Kouwenhoven, Jude, and Knickerbocker published the landmark study on closed-chest cardiac massage, establishing the foundation of modern CPR and making bystander resuscitation feasible for the first time.

1966

NAS White Paper on EMS

The National Academy of Sciences published "Accidental Death and Disability: The Neglected Disease of Modern Society," catalyzing the creation of organized EMS systems and training standards across the United States.

1973

EMS Systems Act

The U.S. Congress passed the Emergency Medical Services Systems Act, providing federal funding for regional EMS development, standardized paramedic curricula, and the systematic deployment of advanced cardiac life support (ACLS) in the field.

2000

AHA Guidelines Overhaul

The American Heart Association released evidence-based ACLS guidelines emphasizing early defibrillation, high-quality chest compressions, and the integration of 12-lead ECG interpretation into prehospital cardiac care.

2020

COVID-19 & Respiratory Crisis

The global pandemic underscored the critical importance of respiratory emergency management, ventilation strategies, and prehospital decision-making for acute respiratory distress syndrome (ARDS).

The central question that drives this lesson is: How does a paramedic rapidly differentiate, assess, and manage the most common life-threatening cardiac and respiratory emergencies in the field, where resources are limited and time is the most critical variable? Every protocol, pharmacological agent, and procedural intervention discussed in the following sections traces its origin to the milestones above and to the foundational principle that early recognition and aggressive treatment save lives.

SECTION 2

Core Principles & Definitions

Before examining specific pathologies, paramedics must internalize several foundational principles that govern the assessment and management of cardiac and respiratory emergencies. These principles form the conceptual scaffold upon which clinical decision-making rests, from the initial scene size-up through transport and handoff. The interplay between the cardiovascular and respiratory systems means that a primary failure in one almost invariably compromises the other, making a systematic approach essential for accurate differential diagnosis and effective treatment.

Oxygen Delivery Equation

Tissue oxygenation depends on cardiac output (CO) × arterial oxygen content (CaO₂). A failure in either pump function or gas exchange leads to cellular hypoxia and organ dysfunction.

Cardiac Output Determinants

CO is the product of heart rate (HR) and stroke volume (SV). Stroke volume is further governed by preload, afterload, and contractility—each of which can be independently compromised in emergencies.

Ventilation vs. Oxygenation

Ventilation refers to the mechanical movement of air in and out of the lungs, measured by minute ventilation (V_E). Oxygenation is the diffusion of O₂ across the alveolar-capillary membrane. These are distinct processes that require different interventions.

The Chain of Survival

For cardiac arrest, the Chain of Survival comprises early recognition, early CPR, early defibrillation, effective ACLS, and integrated post-cardiac-arrest care. Each weak link exponentially reduces survival probability.

Compensatory Mechanisms

The body initially compensates for cardiac or respiratory failure through the sympathetic nervous system (tachycardia, vasoconstriction) and increased respiratory effort. Recognizing the transition from compensated to decompensated states is a paramount paramedic skill.

✦ KEY TAKEAWAY

Think of the cardiovascular and respiratory systems as two halves of a single delivery service. The lungs are the loading dock where oxygen is picked up and CO₂ is dropped off, while the heart is the truck that delivers the cargo to every cell. If the loading dock shuts down (respiratory failure), the truck delivers empty packages. If the truck breaks down (cardiac failure), packages pile up at the dock and never reach their destination. A paramedic's job is to rapidly determine which half of the delivery system has failed—or whether both have—and intervene before the entire supply chain collapses.

SECTION 3

Visual Explanation — Cardiac & Respiratory Assessment Pathway

This flowchart illustrates the bifurcated assessment pathway a paramedic follows upon encountering a patient with cardiorespiratory distress. Beginning with the primary survey (ABCDEs), the clinician progresses toward a differential diagnosis that branches into the cardiac pathway (left) or the respiratory pathway (right), each with its own set of targeted assessments and likely diagnoses.

As depicted in the diagram, the assessment process is neither purely linear nor exclusively cardiac or respiratory. Many patients present with overlapping pathologies—for instance, a patient in acute decompensated heart failure will exhibit both cardiac compromise (reduced ejection fraction, S₃ gallop) and respiratory distress (pulmonary edema, crackles on auscultation, hypoxia). The paramedic must continuously reassess and be prepared to shift treatment priorities based on evolving clinical findings. Critical diagnostic tools include the 12-lead electrocardiogram for cardiac etiologies and capnography (EtCO₂) for respiratory etiologies, though both tools inform the other pathway's differential.

SECTION 4

Pathophysiology & Mechanisms of Cardiac Emergencies

Acute Coronary Syndromes (ACS)

Acute coronary syndromes encompass a spectrum of myocardial ischemia ranging from unstable angina (UA) through non-ST-elevation myocardial infarction (NSTEMI) to ST-elevation myocardial infarction (STEMI). The underlying mechanism in most cases involves rupture or erosion of a vulnerable atherosclerotic plaque within a coronary artery, which triggers platelet aggregation and thrombus formation. In UA, the thrombus is non-occlusive and transient; in NSTEMI, partial occlusion causes subendocardial ischemia with biomarker elevation; in STEMI, complete occlusion produces transmural ischemia, ST-segment elevation on the 12-lead ECG, and progressive myocardial necrosis unless reperfusion is achieved. The paramedic's goal is to recognize the presentation—classically substernal chest pressure radiating to the left arm or jaw, associated with diaphoresis and dyspnea—obtain a diagnostic 12-lead ECG, administer aspirin, nitroglycerin, and analgesia per protocol, and expedite transport to a percutaneous coronary intervention (PCI)-capable facility.

CARDIAC OUTPUT

CO = HR × SV

Where CO = cardiac output (L/min), HR = heart rate (beats/min), and SV = stroke volume (mL/beat). In acute MI, SV drops due to impaired contractility, triggering compensatory tachycardia to maintain CO.

Cardiac Dysrhythmias

Dysrhythmias arise from disturbances in impulse formation, impulse conduction, or both. Ventricular fibrillation (VF) and pulseless ventricular tachycardia (pVT) are shockable rhythms representing chaotic or rapid ventricular electrical activity that produces no effective cardiac output. Asystole and pulseless electrical activity (PEA) are non-shockable arrest rhythms. For PEA, the paramedic must search for reversible causes using the H's and T's mnemonic: Hypovolemia, Hypoxia, Hydrogen ion (acidosis), Hypo/Hyperkalemia, Hypothermia, Tension pneumothorax, Tamponade (cardiac), Toxins, Thrombosis (pulmonary or coronary). Symptomatic bradycardias are managed with atropine initially, followed by transcutaneous pacing if pharmacotherapy fails. Unstable tachycardias receive synchronized cardioversion.

MEAN ARTERIAL PRESSURE

MAP = DBP + ⅓(SBP − DBP)

Where MAP = mean arterial pressure (mmHg), DBP = diastolic blood pressure, SBP = systolic blood pressure. A MAP < 65 mmHg indicates inadequate organ perfusion and warrants aggressive intervention.

Congestive Heart Failure & Acute Pulmonary Edema

In congestive heart failure (CHF), the heart fails to pump blood efficiently enough to meet metabolic demands. Left-sided failure leads to pulmonary congestion as blood backs up behind a weakened left ventricle, producing acute pulmonary edema with bilateral crackles, frothy sputum, and severe dyspnea. Right-sided failure results in systemic venous congestion manifested by jugular venous distension (JVD), hepatomegaly, and peripheral edema. Prehospital management of acute pulmonary edema centers on continuous positive airway pressure (CPAP) at 5–10 cm H₂O, nitroglycerin for preload and afterload reduction, and judicious use of diuretics such as furosemide when permitted by local protocol.

SECTION 5

Classification of Respiratory Emergencies

Respiratory emergencies can be broadly classified by the anatomical level of pathology and the mechanism of gas exchange failure. A structured classification helps the paramedic rapidly narrow the differential and select the most appropriate intervention. The following diagram organizes the major respiratory emergencies encountered in the prehospital setting according to whether the primary problem involves the upper airway, lower airway, lung parenchyma, pleural space, or central respiratory drive.

The upper half classifies respiratory emergencies by anatomical level: upper airway (stridor, inspiratory obstruction), lower airway (wheezing, expiratory obstruction), parenchymal (crackles, diffuse hypoxia), pleural (unilateral diminished sounds), and CNS drive failure (decreased rate and tidal volume). The lower half maps key prehospital interventions across airway management, pharmacotherapy, and procedural categories.

Rapid-Reference: Common Respiratory Emergencies & Prehospital Management

Condition	Key Finding	First-Line Prehospital Tx	Critical Action
Asthma (severe)	Expiratory wheezing, prolonged expiratory phase, accessory muscle use	Nebulized albuterol 2.5 mg + ipratropium 0.5 mg	If silent chest → prepare for intubation
COPD Exacerbation	Barrel chest, pursed-lip breathing, ↓ SpO₂, ↑ EtCO₂	Low-flow O₂ (titrate to 88–92% SpO₂), bronchodilators, CPAP	Avoid over-oxygenation; monitor for CO₂ narcosis
Tension Pneumothorax	Unilateral absent breath sounds, tracheal deviation, JVD, hypotension	Needle decompression: 2nd ICS, midclavicular line (14G)	Do NOT delay for imaging; this is a clinical diagnosis
Pulmonary Embolism	Sudden dyspnea, pleuritic chest pain, tachycardia, clear lungs, ↓ EtCO₂	High-flow O₂, IV fluid bolus, rapid transport	If arrest → consider thrombolytics per protocol
Anaphylaxis	Stridor, urticaria, angioedema, bronchospasm, hypotension	Epinephrine 0.3–0.5 mg IM (1:1,000), repeat q 5 min	Secure airway early; prepare for surgical airway if edema progresses

SECTION 6

Worked Example — Field Management of STEMI with Cardiogenic Shock

The following scenario walks through a realistic prehospital encounter requiring integrated cardiac and respiratory decision-making. Each step mirrors the thought process expected on the NREMT examination and in clinical practice.

Scenario: 62-Year-Old Male with Chest Pain and Respiratory Distress

Step 1 — Scene Size-Up & Primary SurveyYou arrive to find a 62-year-old male sitting upright in a recliner, diaphoretic, with labored breathing. He is clutching his chest and states, "It feels like an elephant is sitting on me." Scene is safe, no immediate hazards. Primary survey: Airway is patent, breathing is labored at 28/min with bilateral crackles heard to the mid-lung fields, circulation shows weak radial pulse, skin is cool, pale, and diaphoretic. GCS is 15.

Impression: Acute cardiac event with pulmonary edema. Priority 1 patient.

Step 2 — Obtain 12-Lead ECG & Vital SignsApply the cardiac monitor and obtain a 12-lead ECG. Findings: ST elevation >2 mm in leads II, III, and aVF with reciprocal ST depression in I and aVL, suggesting an inferior STEMI. Vital signs: HR 110, BP 82/54, SpO₂ 88% on room air, RR 28, EtCO₂ 30 mmHg. Calculate MAP: MAP = 54 + ⅓(82 − 54) = 54 + 9.3 ≈ 63 mmHg.

MAP ≈ 63 mmHg — below perfusion threshold of 65 mmHg. STEMI + hypotension = cardiogenic shock.

Step 3 — Initiate Pharmacological InterventionsAdminister aspirin 324 mg PO (chewed). Because the patient is hypotensive (SBP < 90 mmHg), nitroglycerin is contraindicated. Additionally, with an inferior STEMI, obtain a right-sided V₄R lead to rule out right ventricular involvement, as nitrates could precipitate further hemodynamic collapse. Establish IV access with a large-bore catheter and administer a cautious 250 mL normal saline bolus, reassessing lung sounds and BP after each bolus.

ASA given. NTG withheld. Fluid challenge initiated. V₄R obtained.

Step 4 — Manage Respiratory CompromiseApply high-flow oxygen via non-rebreather mask at 15 LPM. Given bilateral crackles and SpO₂ of 88%, the patient has concurrent pulmonary edema. If SpO₂ does not improve above 94% or work of breathing increases, apply CPAP at 5 cm H₂O, but use caution in the setting of hypotension as positive pressure ventilation can further reduce preload. Continuously monitor EtCO₂ waveform for changes suggesting worsening ventilation.

SpO₂ improves to 93% on 15 LPM NRB. CPAP on standby. EtCO₂ stable at 30 mmHg.

Step 5 — Transport Decision & Ongoing CareActivate the cardiac catheterization lab via early notification to the receiving PCI-capable hospital. Total on-scene time goal: < 10 minutes. During transport, reassess vitals every 5 minutes, transmit the 12-lead ECG to the receiving facility, and prepare for potential deterioration into VF/VT arrest (defibrillator pads already applied). If the patient progresses to cardiac arrest, begin high-quality CPR at 100–120 compressions/min with a depth of 5–6 cm, ventilate at 10 breaths/min via advanced airway, and administer epinephrine 1 mg IV/IO every 3–5 minutes.

Cath lab activated. ECG transmitted. Transport initiated. Door-to-balloon clock starts.

SECTION 7

Cardiac vs. Respiratory Failure — Differentiating Features

One of the most challenging tasks for the field paramedic is distinguishing primary cardiac failure from primary respiratory failure when both systems are in distress simultaneously. The following comparison table highlights the key differentiating features that guide clinical decision-making. While overlap is common—indeed, most patients in extremis will show signs of both—the ability to identify the primary etiology directs the most appropriate initial intervention and transport destination.

Differentiating Primary Cardiac vs. Respiratory Failure in the Prehospital Setting

Feature	Primary Cardiac Failure	Primary Respiratory Failure
Chief Complaint	Chest pain/pressure, palpitations, syncope	Dyspnea, cough, inability to speak in full sentences
Lung Sounds	Bilateral crackles (pulmonary edema) or clear	Wheezing, rhonchi, diminished, or absent unilaterally
ECG Findings	ST changes, dysrhythmias, axis deviations	Usually sinus tachycardia; may show right heart strain in PE
EtCO₂	Low-normal (unless cardiogenic shock → metabolic acidosis)	Elevated in COPD/hypoventilation; low in hyperventilation/PE
JVD	Present in right heart failure, tamponade	Present in tension pneumothorax; absent in most other conditions
Response to O₂/CPAP	CPAP dramatically improves CHF pulmonary edema	Bronchodilators improve asthma/COPD; O₂ alone may not help PE
Key Diagnostic Tool	12-lead ECG, serial troponins (in-hospital)	Waveform capnography, pulse oximetry, peak flow

✦ KEY TAKEAWAY

Consider the analogy of a flooded basement. If the water main broke (respiratory failure), you fix the pipe first, then pump out the water. If the sump pump failed (cardiac failure), the pipe is fine but water accumulates anyway—you need to restore pump function. In many real scenarios, however, both the pipe and the pump are compromised, and the paramedic must determine which repair is most urgent. The 12-lead ECG and capnography are your two most powerful diagnostic flashlights in that dark basement.

SECTION 8

Connection to Advanced Practice & Hospital Continuum

The prehospital management of cardiac and respiratory emergencies is only the opening chapter of the patient's care continuum. Understanding how field interventions connect to in-hospital advanced therapies helps paramedics make more informed decisions about transport destination, intervention timing, and patient communication. This section bridges the gap between what you do in the field and what happens after your patient crosses the ED threshold.

Prehospital-to-Hospital Continuum of Care

Prehospital Intervention	Hospital-Based Advanced Therapy	Clinical Rationale for Linkage
12-lead ECG with STEMI identification	Percutaneous coronary intervention (PCI) / cardiac catheterization	Early field identification and cath lab activation reduces door-to-balloon time, directly improving myocardial salvage
CPAP for pulmonary edema	BiPAP, invasive mechanical ventilation, afterload reduction with IV vasodilators	Prehospital CPAP reduces intubation rates by up to 50%, bridging to definitive CHF management
Needle decompression for tension pneumothorax	Chest tube thoracostomy, video-assisted thoracoscopic surgery (VATS)	Needle decompression is temporizing; definitive tube thoracostomy is required in the ED
Epinephrine and amiodarone in cardiac arrest	Targeted temperature management (TTM), ECMO-assisted resuscitation, coronary angiography	Quality CPR and early ROSC enable access to advanced post-arrest care pathways that significantly improve neurological outcomes
Waveform capnography monitoring	Arterial blood gas (ABG) analysis, CT pulmonary angiography	EtCO₂ trends documented in the field guide ED clinicians in interpreting acid-base status and ventilation adequacy

As prehospital medicine continues to evolve, paramedics increasingly serve as the first link in a seamlessly integrated care team. Emerging technologies such as point-of-care ultrasound (POCUS) in the field, mechanical CPR devices, and telemedicine-guided assessment are expanding the paramedic's diagnostic and therapeutic toolkit. For the NREMT examination, the critical takeaway is that every prehospital decision—from the choice to apply CPAP versus intubate, to the decision to bypass a closer hospital for a PCI center—has downstream consequences that directly impact patient outcomes. The best paramedics think not only about what they are doing right now, but about what the next provider in the chain needs to accomplish.

⚡ NREMT Exam Tip

The NREMT frequently tests the concept of transport decision-making. Know when to bypass a closer facility: STEMI patients go to PCI centers, stroke patients to stroke centers, and trauma patients to trauma centers. The correct answer often involves matching the patient's primary pathology to the appropriate specialty resource, even if the transport time is longer.

SECTION 9

Practice Problems

PROBLEM 1 — CONCEPTUAL

A patient in acute decompensated heart failure presents with bilateral crackles to the apices, an SpO₂ of 82%, and a blood pressure of 168/98 mmHg. Explain why CPAP is the preferred initial respiratory intervention over endotracheal intubation for this patient, and describe the physiological mechanism by which CPAP improves both oxygenation and cardiac function.

PROBLEM 2 — BASIC CALCULATION

A patient has a blood pressure of 96/62 mmHg and a heart rate of 118 bpm. Calculate the mean arterial pressure (MAP) and determine whether this value indicates adequate organ perfusion. Then calculate the estimated cardiac output if the stroke volume is 45 mL/beat.

PROBLEM 3 — INTERMEDIATE

You are treating a 55-year-old female with acute-onset dyspnea, pleuritic right-sided chest pain, tachycardia (HR 130), clear bilateral lung sounds, SpO₂ of 89%, and an EtCO₂ of 22 mmHg. Her ECG shows sinus tachycardia with a right axis deviation and an S₁Q₃T₃ pattern. What is your most likely field diagnosis, what is the pathophysiology explaining the low EtCO₂ with clear lungs, and what is your prehospital treatment plan?

PROBLEM 4 — APPLIED

You respond to a 70-year-old male with a history of COPD who is in severe respiratory distress. His SpO₂ is 78%, respiratory rate is 8 breaths/min, EtCO₂ is 68 mmHg, and he is becoming increasingly obtunded (GCS 9). You are 25 minutes from the nearest hospital. Describe your complete airway management strategy, including the specific risks of oxygen administration in COPD patients, your ventilation goals post-intubation, and how you will use capnography to guide management during transport.

PROBLEM 5 — CRITICAL THINKING

You are managing a 48-year-old male in cardiac arrest. The initial rhythm is ventricular fibrillation. After two rounds of CPR and defibrillation, you achieve ROSC. The post-ROSC 12-lead ECG shows ST elevation in V₁–V₄. The patient's blood pressure is 78/50, heart rate is 52, and he remains unresponsive. You have two hospital options: Hospital A is a community hospital 8 minutes away with an ED and ICU but no catheterization lab; Hospital B is a PCI-capable cardiac center 28 minutes away. Critically analyze the factors that should influence your transport decision, and justify your choice with reference to current evidence-based guidelines.

SUMMARY

Comprehensive Summary

Cardiac and respiratory emergencies represent the most time-sensitive conditions a paramedic will encounter, and their management forms the backbone of NREMT testing at the paramedic level. The primary survey (ABCDEs) initiates a systematic assessment that branches into cardiac and respiratory pathways based on clinical findings. Acute coronary syndromes—including UA, NSTEMI, and STEMI—require early 12-lead ECG acquisition, aspirin administration, and rapid transport to PCI-capable facilities. Cardiac dysrhythmias are classified as shockable (VF/pVT) or non-shockable (asystole/PEA), with the H's and T's guiding the search for reversible causes. Congestive heart failure with acute pulmonary edema responds dramatically to CPAP, which reduces preload, decreases afterload, and improves oxygenation simultaneously.

Respiratory emergencies are classified by anatomical level: upper airway obstruction (stridor, anaphylaxis), lower airway disease (asthma, COPD with wheezing), parenchymal pathology (pneumonia, pulmonary edema with crackles), pleural emergencies (tension pneumothorax requiring needle decompression), and CNS drive failure (opioid overdose reversed by naloxone). The two indispensable diagnostic tools are the 12-lead ECG for cardiac etiologies and waveform capnography for respiratory etiologies. Throughout, the paramedic must think beyond the immediate intervention to the hospital continuum—selecting the right transport destination and communicating findings that enable seamless, time-critical handoffs to receiving teams.