Principles of Critical Care Medicine

Approach to the Critically Ill Patient

Initial care often involves resuscitation of patients at the extremes of physiologic deterioration using invasive techniques (mechanical ventilation, renal replacement therapy) to support organs on the verge of failure.Successful outcomes often depend on an aggressive approach to treatment, with a sense of urgency  about intervention.Resource management and quality-of-care assessments can be facilitated by the use of illness-severity scales.APACHE II is the most common such scale in use in North America.The score is derived from determination of the type of ICU admission (elective postoperative care, nonsurgical, emergent surgical), a chronic health score, and the worst values recorded for 12 physiologic variables in the first 24 h of intensive care.APACHE should not be used to drive clinical decision-making for individual patients. 

Shock (See Chap.14)

Defined not by blood pressure measurement but by the presence of multisystem end-organ hypoperfusion.The approach to the patient in shock is outlined in Fig.14-1. 

MechanicalVentil atory Support

Principles of advanced cardiac life support should be adhered to during initial resuscitative efforts.Any compromise of respiration should prompt consideration of endotracheal intubation and mechanical ventilatory support.Mechanical ventilation may decrease respiratory work, improve arterial oxygenation with improved tissue oxygen delivery, and reduce acidosis.Reduction in arterial pressure after institution of mechanical ventilation is common due to reduced venous return from positive thoracic pressure, reduced endogenous catecholamine output, and concurrent administration of sedative agents.This hypotension often responds in part to volume administration. 

Respiratory Failure

Four common types of respiratory failure are observed, reflecting different pathophysiologic derangements. 

Type I or Acute Hypoxemic Respiratory Failure

Occurs due to alveolar flooding with edema (cardiac or noncardiac), pneumonia, or hemorrhage.Acute respiratory distress syndrome (ARDS) (see Chap.12) describes diffuse lung injury with airspace edema, severe hypoxemia (ratio of arterial PO to inspired 2 oxygen concentration—PaO /FIO _ 200).Causes include sepsis, pancreatitis, 2 2 gastric aspiration, multiple transfusions.Current ventilator strategy requires the use of low tidal volumes (4–6 mL/kg ideal body weight) to avoid ventilatorinduced lung injury. 

Type II Respiratory Failure

This pattern reflects alveolar hypoventilation and inability to eliminate CO2 due to: • Impaired central respiratory drive (e.g., drug ingestion, brainstem injury, hypothyroidism)

• Impaired respiratory muscle strength (e.g., myasthenia gravis, Guillain-Barre´ syndrome, myopathy)

• Increased load on the respiratory system (e.g., resistive loads such as bronchospasm or upper airway obstruction, reduced chest wall compliance due to pneumothorax or pleural effusion, or increased ventilation requirements with increased dead space due to pulmonary embolism or acidosis). Treat the underlying cause and provide mechanical support with mask or endotracheal ventilation. 

Type III Respiratory Failure

Occurs as a result of atelectasis—commonly occurs postoperatively.Treatment requires deep breathing and sometimes mask ventilation.  

Type IV Respiratory Failure

Seen as a consequence of hypoperfusion of respiratory muscles in shock or with cardiogenic pulmonary edema.Mechanical ventilatory support is required. 

TREATMENT Care of the Mechanically Ventilated Patient

Many patients receiving mechanical ventilation will require pain relief and anxiolytics.Less commonly, neuromuscular blocking agents are required to facilitate ventilation when there is extreme dyssynchrony that cannot be corrected with manipulation of the ventilator settings. 

Weaning from Mechanical Ventilation

Daily screening of patients who are stable while receiving mechanical support facilitates recognition of patients ready to be liberated from the ventilator.The rapid shallow breathing index (RSBI, or f/VT—respiratory rate in breaths/min divided by tidal volume in liters during a brief period of spontaneous breathing)—may predict weanability. A f/VT _ 105 should prompt a spontaneous breathing trial of up to 2 h with no or minimal [5 cmH2O positive end-expiratory pressure (PEEP)] support.If there is no tachypnea, tachycardia, hypotension, or hypoxia, a trial of extubation is commonly performed. 

Multiorgan System Failure

Defined as dysfunction or failure of two or more organs in patients with critical illness. A common consequence of systemic inflammatory response (e.g., sepsis, pancreatitis).May cause hepatic, renal, pulmonary, or hematologic abnormalities. 

Monitoring in the ICU

With critical illness, close and often continuous monitoring of vital functions is required.In addition to pulse oximetry, frequent arterial blood-gas analysis can reveal evolving acid-base disturbances.Modern ventilators have sophisticated alarms that reveal excessive pressure requirements, insufficient ventilation, or overbreathing.Intraarterial pressure monitoring and, at times, pulmonary artery pressure measurement can reveal changes in cardiac output or oxygen delivery. 

Prevention of Complications

Critically ill patients are prone to a number of complications, including the following:

• Anemia—usually due to inflammation and often iatrogenic blood loss

• Venous thrombosis—may occur despite standard prophylaxis with heparin and may occur at the site of central venous catheters

• Gastrointestinal bleeding—most often in patients with bleeding diatheses or respiratory failure, necessitating acid neutralization in such patients

• Renal failure—a tendency exacerbated by nephrotoxic medications and dye studies. Evidence suggests that strict glucose control [glucose _ 6.1 mmol/L (_110 mg/dL)] improves mortality in critically ill patients. 

Limitation or Withdrawalof Care

Technological advances have created a situation in which many patients can be maintained in the ICU with little or no chance of recovery.Increasingly, patients, families, and caregivers have acknowledged the ethical validity of withdrawal of  care when the patient or surrogate decision maker determines that the patient’s goals for care are no longer achievable with the clinical situation, as determined by the caregivers.