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Ohm law is a relationship between three physical phenomena: current, voltage, and resistance. Current is defined as the flow of positive charge from a source to a negative charge source. The units for current are C/s for the amount of charge (C) that travels per unit time (s). The ampere (A) is the common unit of current equal to 1 C/s and the symbol for current is I. Current is an intrinsic property, as it depends on other aspects, such as the size of the system. To aptly compare the amount of current for different systems, the current is normalized per area or mass of the system. This is described as the following: J = I/A. J = I/m. Where J is the current density in I/(m·m) or I/g depending on how the systems are compared, I is the current (A), A is the cross-sectional area (m·m), and m is the mass (g). Note that often j is used for current instead of I to prevent confusion with imaginary numbers. Therefore, one should pay attention to the symbols’ definitions, as they can vary case-by-case. The voltage is another piece of Ohm law that states the amount of work needed to move a charge. The unit for voltage is J/C, which is equal to the ubiquitous unit the Volt (V). The voltage measures the electric potential an object possesses in reference to a charge. By applying a voltage, work is done on the charge which enables the movement of the charge. The amount of charge compared to an individual charge, known as a point charge, can be determined by the following: V = kq/(r·r). Where V is the electric potential (V), k is the constant 8.99 E 9 N·m·m/(C·C), q is the charge of the point (C), and r is the distance from the point charge (m). The resistance is the opposition to the movement of charge. The resistance is similar to friction effects in flowing water or a sliding object. The units for resistance are Ohms, which is denoted with the capital Greek letter Omega. To calculate the amount of resistance in an object, the following equation can be used: R = Rho·l/A. Where R is the resistance (Omega), Rho is the resistivity of the object (Omega·m), l is the length of the object (m), and A is the cross-sectional area of the object (m·m). The resistivity is different for every object and is based on the structure of the material. The calculation for resistivity is outside the scope of this article. The resistance can also be normalized to provide an apt, case-by-case comparison. The normalized resistance is given by: R’ = R·A. Where R is the normalized resistance (Omega·m·m). The resistance, which impedes the flow of charge, is inversely proportional to the current. As the current normalization is per units of area, the resistance normalization is multiplied by units of the cross-sectional area due to the inverse relationship. The inverse of resistance (1/R) is known as the conductance, which measures the ability of an object to conduct charge given in units of Siemens (S). Further discussion of conductance is outside the scope of this article; however, it is worth noting the inverse relationship conductance has with resistance. Given the current, voltage, and resistance, Ohm law is defined as: V = I·R. Dimensional analysis is needed to ensure consistent units., (Copyright © 2022, StatPearls Publishing LLC.)

Febrile seizures are seizures that are caused by a sudden spike in body temperature with fevers greater than 38C or 100.4F, with no other underlying seizure-provoking causes or diseases such as the central nervous system (CNS) infections, electrolyte abnormalities, drug withdrawal, trauma, genetic predisposition or known epilepsy. Febrile seizures categorize as either simple febrile seizures or complex febrile seizures. Differentiation between simple and complex febrile seizures is important as the approach and workup for each is different., (Copyright © 2022, StatPearls Publishing LLC.)

Arterial catheterization is a procedure that is common to the intensive care settings and the operating room. It involves placement of a catheter into the lumen of an artery to provide at least a continuous display blood pressure with access to frequent arterial blood sampling.  The discovery of the arterial waveform by insertion of a catheter into an artery dates to 1847 by the German Physiologist Carl Ludwig.  More recently, the widely known Seldinger technique has been adopted by guiding catheter into a vessel over a wire previously inserted into the lumen or the artery. With knowledge of anatomy, various sites of insertion are available. However, practitioners must be mindful of indications and contraindications, proper preparation of equipment and personnel as well as the technique of insertion. As all invasive procedures, the placement of arterial catheters may present complications, with an advised operator who must be ready to intervene promptly to prevent unnecessary harm to the patient., (Copyright © 2022, StatPearls Publishing LLC.)

Sturge-Weber syndrome (SWS) is a neurocutaneous syndrome characterized by angiomas involving the face, choroid, and leptomeninges. The facial capillary vascular malformation is also known as "port-wine stain" or "nevus flammeus" and usually is seen in the territory of the trigeminal nerve. Sturge-Weber syndrome is also called encephalotrigeminal angiomatosis. It is the third most common neurocutaneous syndrome after neurofibromatosis and tuberous sclerosis. The neurologic manifestations of SWS include atonic, tonic, or myoclonic seizures., (Copyright © 2022, StatPearls Publishing LLC.)

Aspiration is common, even in healthy patients. Aspiration can have significant morbidity and mortality in certain circumstances. It is categorized based on the predominant material in the aspirate. If oropharyngeal secretions, orally ingested material, or partially digested gastric contents are aspirated, one would expect infectious pneumonia to develop. However, if pure gastric secretions are aspirated, then chemical pneumonitis is the result. If partially digested gastric contents are aspirated along with some gastric acid, a mixture of chemical pneumonitis and inoculation of the lungs with potentially pathogenic organisms can occur. In practice, it is prudent to treat chemical pneumonitis with prophylactic antibiotics because a superimposed infection occurs in over 25% of cases. It is difficult to determine the quality of the aspirate in most cases, and a combination of bacterial and chemical injury is common., (Copyright © 2022, StatPearls Publishing LLC.)

Serotonin syndrome is a potentially life-threatening condition precipitated by the use of serotonergic drugs. It may be a consequence of therapeutic medication use, accidental interactions between medications or recreational drugs, or intentional overdose. Symptoms can range from mild to fatal and classically include altered mental status, autonomic dysfunction, and neuromuscular excitation. Several criteria exist for making this clinical diagnosis, but the Hunter criteria are generally accepted as the most accurate. The diagnosis can be made in patients with a history of exposure to a serotonergic drug plus one or more of the following: spontaneous clonus, inducible clonus with agitation and diaphoresis, ocular clonus with agitation and diaphoresis, tremor and hyperreflexia, hypertonia, temperature over 38 C with ocular or inducible clonus. Management consists of immediate discontinuation of serotonergic agents, hydration, and supportive care to manage blood pressure, hyperpyrexia, and respiratory and cardiac complications. Sedation is best facilitated with benzodiazepines. Refractory cases may respond to the antidote, cyproheptadine, which must be given orally or via gastric tube. The effectiveness of cyproheptadine is unproven, but multiple case reports support its use in patients who do not respond to sedation and supportive care., (Copyright © 2022, StatPearls Publishing LLC.)

Blood gas analysis is a commonly used diagnostic tool to evaluate the partial pressures of gas in blood and acid-base content. Understanding and use of blood gas analysis enable providers to interpret respiratory, circulatory, and metabolic disorders. [1]  A "blood gas analysis" can be performed on blood obtained from anywhere in the circulatory system (artery, vein, or capillary).  An arterial blood gas (ABG) tests explicitly blood taken from an artery. ABG analysis assesses a patient's partial pressure of oxygen (PaO2) and carbon dioxide (PaCO2). PaO2 provides information on the oxygenation status, and PaCO2 offers information on the ventilation status (chronic or acute respiratory failure). PaCO2 is affected by hyperventilation (rapid or deep breathing), hypoventilation (slow or shallow breathing), and acid-base status. Although oxygenation and ventilation can be assessed non-invasively via pulse oximetry and end-tidal carbon dioxide monitoring, respectively, ABG analysis is the standard.  When assessing the acid-base balance, most ABG analyzers measure the pH and PaCO2 directly. A derivative of the Hasselbach equation calculates the serum bicarbonate (HCO3) and base deficit or excess. This calculation frequently results in a discrepancy from the measured due to the blood CO2 unaccounted for by the equation. The measured HCO3 uses a strong alkali that liberates all CO2 in serum, including dissolved CO2, carbamino compounds, and carbonic acid. The calculation only accounts for dissolved CO2; this measurement using a standard chemistry analysis will likely be called a "total CO2". For that reason, the difference will amount to around 1.2 mmol/L. However, a larger difference may be seen on the ABG, compared to the measured value, especially in critically ill patients. [2]  The calculation has been disputed as both accurate and inaccurate based on the study, machine, or calibration used and must be interpreted appropriately based on your institutional standards.[3] Arterial blood gases are frequently ordered by emergency medicine,  intensivist, anesthesiology, and pulmonology clinicians but may also be needed in other clinical settings. Many diseases are evaluated using an ABG, including acute respiratory distress syndrome (ARDS), severe sepsis, septic shock, hypovolemic shock, diabetic ketoacidosis, renal tubular acidosis, acute respiratory failure, heart failure, cardiac arrest, asthma, and inborn errors of metabolism., (Copyright © 2022, StatPearls Publishing LLC.)

Aspiration is common, even in healthy patients. Aspiration can have a significant morbidity and mortality in certain circumstances. It is categorized based on the predominant material in the aspirate. If oropharyngeal secretions, orally ingested material, or partially digested gastric contents are aspirated, one would expect infectious pneumonia to develop. However, if pure gastric secretions are aspirated, then a chemical pneumonitis is the result. If partially digested gastric contents are aspirated along with some gastric acid, a mixture of chemical pneumonitis and inoculation of the lungs with potentially pathogenic organisms can occur. In practice, it is prudent to treat a chemical pneumonitis with prophylactic antibiotics because a superimposed infection occurs in over 25% of cases. It is difficult to determine the quality of the aspirate in most cases, and a combination of bacterial and chemical injury is common.[1][2], (Copyright © 2022, StatPearls Publishing LLC.)