Introduction

Critical care medicine is a medical subspecialty focused on treating patients with life-threatening illnesses and injuries. These patients are treated in special critical care units of the hospital, commonly referred to as intensive care units or ICUs. They often require mechanical and pharmacologic support to maintain organ system functions and close hemodynamic monitoring of their vital signs. ICUs have a low staff to patient ratio, allowing for close monitoring, complicated therapies, and quick intervention when required. Patients are transferred to these ICUs after initial stabilization in the emergency department, following surgeries, or from the hospital wards if their condition worsens. ICUs include the medical intensive care unit or MICU, the coronary intensive care unit or CCU, the neuroscience critical care unit or NCCU, the pediatric intensive care unit or PICU, the neonatal intensive care unit or NICU, and the surgical intensive care unit or SICU. Post operative recovery units are also considered critical care units since patients here are emerging from anesthesia and are at risk for a variety of post operative complications. Emergency departments also routinely care for these critical patients. In the emergency department, care is supervised by emergency physicians often with the support and assistance of the critical care specialists who will take over care when the patient is transferred to the ICU.

Critical care specialists working in an ICU perform a variety of life-saving procedures including intubation and ventilator management, central venous catheterization, thoracostomy or chest-tube placement, and resuscitation during cardiopulmonary arrest. The most common pathway to becoming a critical care specialist is to complete a three-year internal medicine residency followed by a pulmonary and critical care medicine fellowship. Critical care fellowships may also be undertaken following a pediatric, surgical, emergency medicine, or anesthesiology residency. Some ICUs are staffed by anesthesiologists who have not completed an additional fellowship in critical care medicine.

The first recognized intensive care unit was developed in 1952 in response to a

massive polio outbreak in Denmark. Faced with hundreds of patients suffering from respiratory muscle paralysis, Danish anesthesiologist Dr. Bjorn Ibsen enlisted a small army of over fifteen hundred medical students working in shifts to manually ventilate patients who had tubes placed down their trachea to maintain their airways. His efforts reduced mortality for these patients from eighty seven percent to less than fifteen percent. He later established a specialized intensive therapy unit at the Municipal Hospital of Copenhagen and developed protocols to treat other diseases requiring intensive monitoring and therapy, including tetanus, in a critical care setting. Since then, the concept of intensive care units staffed by critical care specialists has grown to become its own specialty and key resource in caring for a hospital’s sickest patients. The specialty and practice has evolved alongside cutting edge monitoring technologies and the availability of new medications that can be utilized to stabilize and maintain organ system functions.

According to a study published by the Society of Critical Care Medicine, an estimated six million patients a year are cared for in intensive care units in the United States. Common conditions in adult ICU patients include cardiac, neurologic, respiratory, and infectious diseases. Respiratory diseases are the most common admission diagnosis in pediatric ICU’s. There are an estimated five thousand seven hundred adult ICU’s and more than four hundred pediatric ICU’s in the United States

Critical care units today are equipped with a variety of technologies including mechanical ventilators, cardiac telemetry monitors, and a variety of invasive monitoring approaches that often use catheters in veins and arteries to monitor blood pressure and other cardiac functions. The care approach is interdisciplinary with a low staff to patient ratio. In addition to the critical care physician at the helm, specially trained nurses, consulting physicians from other specialties, physician assistants, nurse practitioners, respiratory therapists, technicians, pharmacists, and nutritionists work together to care for and manage intensive care unit patients.

These health providers often have to deal with a variety of ethical dilemmas

related to patients in critical care settings. These ethical issues often pertain to end of life care, determination of brain death, withdrawal of medical support to sustain life, and advanced directives related to patients’ desire for cardiopulmonary resuscitation. These issues are complicated in the absence of formal advanced directives from the patient, especially in scenarios where family members disagree on the level of care to be provided. The approach of intensive care unit staff is often criticized as being too intensive, and may border on medical futility if patient life is prolonged without additional quality or hope of recovery, but at great financial and manpower expense.

This course provides an overview of the specialty of critical care medicine. It provides a general approach to evaluating and treating critically ill patients. It also reviews specific diseases associated with the various organ systems that are important to the practice of critical care medicine.

Chapter one provides an introduction to critical care and includes discussions on unstable patients, shock, and resuscitation in general. The general approaches to critically ill patients presented in this chapter are applicable both to the intensive care unit and to other care settings when treating patients.

Chapter two presents acid-base disorders relevant to critical care medicine including metabolic and respiratory acidosis and metabolic and respiratory alkalosis. Acid base disorders are common complications of a variety of illnesses affecting nearly every possible organ system, so it is important to consider these disorders when evaluating and treating all patients with critical illnesses.

Chapter three discusses pulmonary diseases including asthma, pneumonia, acute respiratory distress syndrome, and pulmonary embolisms. The chapter also outlines ventilator management guidelines and commonly used settings. Severe pulmonary disease is a common scenario treated in the intensive care unit.

Chapter four covers cardiovascular diseases managed in the intensive care unit. These include myocardial infarctions, commonly referred to as heart attacks, arrhythmias or irregular heartbeats, congested heart failure or CHF, and aortic dissections. Given the relative instability of cardiac patients, many severe cardiac

illnesses must be evaluated and treated in a critical care setting.

Chapter five discusses nephrology and the electrolyte disorders that are usually related to kidney dysfunction. Specific topics include acute renal failure, elevated or low potassium, and calcium and sodium abnormalities. The chapter also discusses rhabdomyolysis, which is a consequence of muscle breakdown. Muscle breakdown byproducts can subsequently cause damage to the kidneys. Indications for hemodialysis in critical care patients will also be discussed. Chapter six presents information on gastrointestinal disorders including diarrhea, gastrointestinal bleeding, and pancreatitis. The gastrointestinal system regulates digestion and several other bodily functions and is relevant to critical care patients both in terms of primary diagnoses and complications of critical care therapy. Chapter seven discusses neurology related to critical care patients. Relevant neurologic diseases include ischemic stroke, intra-cerebral hemorrhages, and status epilepticus, also known as uncontrolled seizures.

Endocrine disorders related to critical care patients are discussed in Chapter eight. Topics include diabetic ketoacidosis, other blood sugar disorders, adrenal crisis, pheochromocytoma, and thyroid diseases.

Chapter nine presents a discussion on infectious diseases in the ICU. Topics include sepsis and septic shock, meningitis, necrotizing fasciitis, nosocomial infections, and fever associated with neutropenia. Chapter ten provides information on toxicology and poisoned patients. Toxins discussed in this chapter include alcohol, acetaminophen, aspirin, Beta-blockers, calcium channel blockers, cocaine, and opiates. Chapter eleven presents the topic of traumatic injuries. Key injuries discussed in this chapter include head injuries, neck and spinal injuries, chest injuries, abdominal injuries, extremity injuries, drowning, and burns. Chapter twelve provides an overview of nutrition related to intensive care unit patients. This chapter discusses both enteral and parenteral nutrition approaches.

Finally, Chapter thirteen presents special topics in critical care medicine not covered in the previous chapters. These include therapeutic hypothermia and tumor lysis syndrome.