Pulmonary Critical Care

Acute coronary syndrome (ACS) encompasses conditions that include confirmed or suspected myocardial ischemia or myocardial infarction (MI). ACS, which includes non-ST-elevation MI (NSTEMI), ST-elevation MI (STEMI), and unstable angina, usually results from thrombus formation on a ruptured atherosclerotic plaque in the epicardial arteries. Patients most commonly present with chest pain but also may have atypical symptoms. Diagnosis is by clinical history, ECG changes, elevated cardiac enzymes (preferably, high-sensitivity cardiac troponin), and/or evidence of wall motion abnormalities on imaging. Both STEMI and NSTEMI have loss of myocardial tissue, but STEMI is due to transmural ischemia (indicating complete major coronary artery obstruction). NSTEMI occurs because of subendocardial ischemia (indicating partial major coronary artery obstruction). Unstable angina occurs when ischemia does not result in infarction (no troponin elevation and typically with non-ST-elevation changes on ECG). Management of STEMI depends on the timing of the presentation and local resources with regard to thrombolytic therapy versus percutaneous intervention. Both unstable angina and NSTEMI are managed the same way, with both conservative (medical) and invasive strategies available. Additionally, routine medical therapy includes dual antiplatelet therapy, nitrates, oxygen, pain control, and beta-blockers.

Volume status is a balance between water and solutes, the majority of which is Na. Volume depletion (also known as hypovolemia) refers to a loss of both water and Na, whereas dehydration refers only to a loss of water. Dehydration is primarily caused by decreased water intake and presents with increased thirst and can progress to altered mental status and low blood pressure if severe. Volume depletion can be caused by GI losses, renal losses, bleeding, poor oral Na intake, or third spacing of fluids. The clinical presentation has relatively nonspecific symptoms but will ultimately cause low blood pressure if severe. The diagnosis of these imbalances is based on lab findings in addition to clinical symptoms and signs, which can be subtle and unreliable. Management requires differentiation between these 2 conditions. The treatment is to administer fluids with tonicity similar to those lost; isotonic fluids are used for volume depletion, and hypotonic fluids are used for dehydration.

MI is ischemia and death of an area of myocardial tissue due to insufficient blood flow and oxygenation, usually from thrombus formation on a ruptured atherosclerotic plaque in the epicardial arteries. Clinical presentation is most commonly with chest pain, but women and patients with diabetes may have atypical symptoms. Diagnosis is by clinical history, ECG changes, an increase in cardiac enzymes, and evidence of wall motion abnormalities on imaging. Management depends on the timing of the presentation and local resources with regard to thrombolytic therapy versus percutaneous intervention. All patients receive nitrates, pain control, aspirin, anticoagulation, and beta-blockers (unless contraindicated).

A toxidrome is a group of clinical signs and symptoms associated with a toxic ingestion or exposure. There are 5 traditional toxidromes: anticholinergic, cholinergic, opioid, sympathomimetic, and sedative-hypnotic. Toxidromes often arise from ingestion of overdose amounts, accumulation of medications with resultant elevated serum levels, adverse drug reactions, or interactions between 2 or more medications. Rapid recognition of a toxidrome can help determine the specific poison or class of toxin that was ingested. On presentation of a suspected toxidrome, appropriate airway, breathing, and circulation assessment is initiated. Decontamination is performed, and the patient is stabilized. Diagnosis is accomplished with clinical findings based on medication and exposure history, vital signs, mental status, and physical examination. Testing generally includes toxicology and drug levels, electrolytes, and ECG. Management consists of supportive care and antidote administration if indicated.

An antidote is a substance that counteracts poisoning or toxicity. Substances that can cause poisoning include heavy metals (from occupation, treatments, or diet), alcohols, environmental toxins, and medications. An increase in the concentration of these substances to toxic levels can occur accidentally or intentionally, resulting in both acute and chronic presentations. Some substances can be detected using specific laboratory tests, whereas the detection of others relies on nonspecific findings. Thus, it is important to recognize substance poisoning by history, individual risk factors, and physical examination. Antidotes along with supportive care and monitoring are part of the management.

Shock is a life-threatening condition associated with impaired circulation that results in tissue hypoxia. The different types of shock are based on the underlying cause: distributive (↑ cardiac output (CO), ↓ systemic vascular resistance (SVR)), cardiogenic (↓ CO, ↑ SVR), hypovolemic (↓ CO, ↑ SVR), obstructive (↓ CO), and mixed. The most common symptoms include tachycardia, tachypnea, hypotension, altered mentation, and oliguria. Treatment measures vary depending on the suspected cause of shock and may include mechanical ventilation, IV crystalloids, vasopressors, and blood transfusion.