Comprehensive Notes on CPR in Special Situations and Environments

Potentially Reversible Causes of Cardiac Arrest: The Four Hs

In emergency medicine, particularly within the framework of initial healthcare in emergencies, certain cardiopulmonary arrests (PCR) are categorized by causes that can potentially be reversed if identified and treated promptly. These are traditionally grouped into the "Four Hs" and the "Four Ts." While the identification and advanced intervention of many of these causes require a Basic Life Support (SVA) unit, technical personnel in Basic Life Support (SVB) can detect and intervene in specific areas.

The first of the Four Hs is Hypoxia. Cardiac arrest caused by a lack of oxygen is usually the result of asphyxia, which is the primary non-cardiac cause of PCR. A common cause of this asphyxia is Foreign Body Airway Obstruction (OVACE). Rapid intervention by those present is vital. It is essential to recognize that traumatic asphyxia also exists, resulting from car accidents, trauma, or hangings. These cases present a more complex scenario, especially if there are injuries to the respiratory tract.

The second group involves Hypothermia and Hyperthermia. Normal body temperature (normothermia) ranges between $36.4\,^{\circ}\text{C}$ and $37.2\,^{\circ}\text{C}$. Hypothermia is defined as accidental exposure to low environmental temperatures. Vulnerable groups include children, the elderly, individuals who have consumed alcohol or drugs, and victims of mountain accidents or cold-water immersion. At approximately $30\,^{\circ}\text{C}$, cardiac cells become hyper-reactive as the body tries to compensate for heat loss. In a PCR situation, hypothermia provides some protection to the brain and vital organs, but recovering body temperature is essential. If the victim's temperature is below $30\,^{\circ}\text{C}$, the Automated External Defibrillator (DESA) should not be used for more than three shocks. Clinical signs of the cold include very slow, low-volume, and irregular pulse and respiration. Treatment involves progressive warming, removing wet clothes, moving to a warm environment, and providing warm drinks in small sips if the patient is conscious.

Hyperthermia occurs when the body temperature exceeds $41\,^{\circ}\text{C}$, absorbing heat faster than it can dissipate it. This is often due to high environmental temperatures combined with humidity or physical activity. It progresses from heat stress and heat exhaustion to heat stroke. Severe heat stroke can lead to cardiovascular dysfunction, multi-organ failure, and Disseminated Intravascular Coagulation (CID). Standard life support is applied along with cooling techniques such as ventilation, spraying with tepid water, or applying wet cloths to well-irrigated areas. Care must be taken with the DESA if the skin is wet from sweat or cooling efforts.

The third H is Hypovolemia. This can result from a decrease in intravascular volume, usually due to a hemorrhage. In cases of severe and continuous blood loss, CPR maneuvers will be ineffective until the bleeding is controlled. Hypovolemia can also result from intense vasodilation caused by anaphylaxis, a Type I hypersensitivity reaction. This acute hyper-reactivity to an antigen can cause arrest through hypoxemia (due to laryngeal edema) or hypovolemic shock (due to increased vascular permeability). Symptoms include skin reactions, hypotension, airway constriction, and a weak, rapid pulse. Intervention involves removing the causative agent, providing high-flow oxygen, and applying standard algorithms while awaiting SVA for pharmacological treatment like adrenaline.

The final H involves Hypokalemia, Hyperkalemia, and other electrolytic disorders. High or low concentrations of electrolytes like potassium ($K^+$), calcium ($Ca^{2+}$), and magnesium ($Mg^{2+}$) affect the heart's electrical system, causing life-threatening arrhythmias. Hyperkalemia is defined as a serum concentration above $5.5\,mmol/l$. It can be caused by renal pathologies or metabolic acidosis (such as diabetic ketoacidosis). Clinical manifestations include muscular weakness, flaccid paralysis, and cardiac toxicity leading to ventricular fibrillation or asystole.

Potentially Reversible Causes of Cardiac Arrest: The Four Ts

The "Four Ts" represent another group of potentially reversible causes, most of which require advanced medical intervention, though technical personnel must understand their implications.

Tension Pneumothorax and Cardiac Tamponade are often the results of trauma. A tension pneumothorax occurs when air enters the pleural cavity, while cardiac tamponade is the pressure exerted on the heart when blood or fluid accumulates between the heart muscle and the pericardium. Both can lead to Traumatic Cardiac Arrest (PCT), which has very low survival rates. In these cases, thoracic compressions are not sufficiently effective because the primary cause must be treated. Until medical assistance arrives, SVB algorithms should be followed with urgent transport to a hospital.

Coronary Thrombosis and Pulmonary Embolism involve blood clots that block blood flow. Technical personnel cannot identify these causes and must apply the standard SVB protocol until an SVA unit can provide treatment and rapid evacuation to a prepared hospital.

Toxics refer to any chemical substance capable of causing death or harmful effects. Toxic-induced PCR is often identifiable and potentially reversible depending on the substance. Key intervention steps include decontamination (removing the toxic source) and identifying the agent to apply the correct treatment. Standard SVB algorithms are applied if the situation derives into PCR.

Life Support for Special Patients: Diseases

The ILCOR guidelines dedicate sections to special patients, including those with specific diseases or physiological conditions.

Asthma is a chronic, reversible inflammation of the lower airways. In cases of PCR, it is usually triggered by a crisis (infections, antigens) leading to secondary cardiac arrest. During SVB, ventilations might be difficult; the technician must check effectiveness, be wary of gastric insufflation (vaxing/vomiting), and may need to compress the thorax manually to help the patient exhale retained air.

Obesity affects approximately $18\%$ of the population and increases vascular risk factors and sudden death rates. The heart must increase cardiac output ($\text{Gasto cardiaco}$) to nourish the excess tissue, leading to dilated chambers and muscular hypertrophy ("obese cardiomyopathy"). This heart enlargement and subepicardial fat accumulation cause arrhythmias. During RCP, the patient must be in a supine position, and more force is required for chest compressions. Early tracheal intubation by SVA is recommended.

Diabetes affects glucose metabolism and doubles the risk of myocardial infarction. Continuous high glucose levels (> 180\,mg/dl postprandial) damage the heart, vessels (arteriosclerosis), and kidneys. Hypoglycemia causes hunger, agitation, loss of consciousness, and increased heart rate (FC), which can trigger PCR. If unconscious, SVB is applied and SVA is called to administer glucagon. Hyperglycemia leads to the mobilization of fats for energy, creating ketone bodies. This resulting diabetic ketoacidosis creates cellular toxicity and arrhythmias. Symptoms include dry mouth, polydipsia, abdominal pain, and fruity-smelling breath.

Life Support for Special Patients: Physiological Conditions

In Elderly patients (vejez), no modifications to standard protocols are required, but technicians should be aware of the high risk of sternum and rib fractures, with the incidence of injuries increasing alongside the duration of RCP maneuvers.

Pregnancy entails significant physiological changes, including increased blood volume, increased cardiac output, and increased ventilations per minute. A major risk after 20 weeks of gestation is the gravid uterus compressing the inferior vena cava (limiting venous return) or the aorta. This can cause hypotension, shock, and PCR. Other causes include life-threatening hemorrhage (ectopic pregnancy, placental abruption), and eclampsia (unexplained convulsions/coma following preeclampsia).

When performing SVB on a pregnant woman, the effectiveness of chest compressions is limited by the uterine obstruction of venous return. To improve this, the uterus should be manually displaced to the left (lateralization of $15\,^{\circ}$ to $30\,^{\circ}$). If trauma is suspected, manual displacement is preferred over tilting the whole body. Hand placement for compressions should be slightly higher on the chest due to the elevated diaphragm. There is no contraindication for DESA use. Emergency C-sections may be performed by SVA units: if the fetus is over 24 weeks, it can be saved if extracted within 5 minutes of PCR; between 20-23 weeks, it is done to help the mother survive, though the fetus will not. It is not performed before 20 weeks.

Support Vital in Special Environments: Trauma and Sports

Traumatic Cardiac Arrest requires distinguishing between non-traumatic and traumatic causes. If traumatic, the technician evaluates reversible causes like hypovolemia or tension pneumothorax. SVA is necessary for invasive treatments and airway management.

During Sporting Activities, sudden collapse is usually cardiac in origin. For young athletes, the most common cause is Hypertrophic Cardiomyopathy (undiagnosed thickening of the heart muscle), though Commotio Cordis (impact to the chest causing VF) is also possible. In older athletes, ischemic heart disease is more common. Attention should be provided in situ; if a defibrillator is available, up to three attempts should be made before moving the victim, as initial discharges have higher effectiveness.

Support Vital in Special Environments: Drowning

Drowning is a frequent cause of accidental death where hypoxemia is the critical factor. Rescuing victims can be dangerous for untrained individuals. The SVB algorithm for drowning begins with 5 rescue ventilations before proceeding to the standard cycle. Even if more than 10 minutes have passed, RCP should be initiated, especially in cold water which prolongs the acceptable window for resuscitation.

Drowning victims are classified into several categories. Blue Drowning is the most common. Within this, "Dry" drowning involves an epiglottis spasm leading to asphyxia without water aspiration, while "Wet" drowning involves water entering the lungs. White Drowning involves a cardiac arrest without prior asphyxia, often due to a "Syncope by Hydrocution" (immersion syndrome). This is a thermal shock or "thermodifferential shock" caused by the temperature difference between the body and the water, leading to severe vasoconstriction and a vasovagal response.

The type of water matters significantly. In Fresh Water (agua dulce), the low salt content causes it to be absorbed rapidly into the bloodstream, increasing blood volume and causing red blood cells to burst. This releases high amounts of potassium ($K^+$) into the plasma, triggering PCR. In Salt Water (agua salada), the higher salt content prevents rapid absorption through diffusion, which generally results in a higher probability of survival.

Support Vital in Special Environments: Altitude, Avalanches, and Electricity

High Altitude Sickness (mal de altura) manifests above $2,500\,m$. As oxygen molecules dilute with decreasing pressure, the risk of PCR increases. Chest compressions are more exhausting for the rescuer. Acute Mountain Sickness involves anorexia and dizziness. High Altitude Pulmonary Edema (EAPE) resulting from rapid ascent presents with orthopnea and chest pain, requiring SVA. High Altitude Cerebral Edema (EACE) occurs between $4,000\,m$ and $5,200\,m$, causing hallucinations and confusion due to fluid accumulation.

Avalanche victims primarily die from asphyxia, trauma, and hypothermia. If a victim shows signs of total body freezing or injuries incompatible with life, RCP might not be started, though SVB technicians should start maneuvers if in doubt until medical arrival.

Electrical injuries involve three mechanisms: Electroporation (damage to cell membranes causing edema, arrhythmias, and tetany), Thermal injury (conversion of electricity to heat causing necrosis), and Mechanical injury (muscular contractions causing falls and trauma). In Electrocution (from equipment), the source must be cut before touching the victim. Ventricular fibrillation is the most common arrhythmia. Airway management is difficult due to facial burns. In Fulguration (lightning), the victim can be touched immediately. PCR is the main cause of death, but the prognosis for return of spontaneous circulation (RCE) is better than other causes, and resuscitation efforts should be vigorous and prolonged (> 30\,min).

Questions & Discussion

Question: What are the differences between a thrombus and an embolus? Response: A thrombus is a blood clot that forms in a vein or artery, whereas an embolus is anything (usually a piece of a thrombus) that travels through the blood vessels until it reaches a vessel too small to let it pass.

Question: In a traumatic tension pneumothorax with lung parenchyma rupture, how does lung collapse occur? Response: It occurs because air escapes the lung and enters the pleural space but cannot exit, increasing pressure that collapses the lung and shifts mediastinal structures.

Question: What is the Beck's Triad, and in what pathology does it appear? Response: Beck's Triad consists of low blood pressure, muffled heart sounds, and distended neck veins. it is indicative of cardiac tamponade.

Question: What is the difference between an antagonist and an antidote? Response: An antagonist is a substance that stops the action or effect of another substance (often at a receptor level), whereas an antidote is a substance that can counteract a specific form of poisoning.

Question: Why does cocaine intoxication cause arrest and what is the protocol? Response: Cocaine is a powerful stimulant that causes extreme vasoconstriction and tachycardia, leading to ischemia or arrhythmias. The protocol involves applying the standard SVB algorithm while monitoring for cardiovascular complications.

Question: Who has a better chance of survival: someone drowned in salt water or fresh water? Response: Salt water victims generally have a better chance of survival because salt water is not absorbed as rapidly as fresh water, avoiding the massive red blood cell destruction and potassium release associated with fresh water drowning.