Acute-on-chronic respiratory failure

Each year, over 400,000 patients in the United States receive mechanical ventilation as a result of acute or acute-on-chronic respiratory failure (1,2). About a quarter of acutely ventilated patients repeatedly fail attempts at weaning and may require prolonged mechanical ventilation (PMV) (Fig. 1) (3,4). The proportion of patients experiencing PMV ranges between 0% and 20% (5-13). Out of patients who survive PMV, 9-66% become dependent on long-term mechanical ventilation (LTMV) (4,9,14-21). Two factors account for these wide variations in the outcome. The first factor is differences in patient population. The second one is the nosology of what constitutes PMV and what constitutes LTMV is unsatisfactory. 

A three-month prospective cohort study of 26 Italian RICUs reported on 756 patients (14). Of all patients receiving invasive mechanical ventilation, 61% were tracheotomized and therefore considered ventilator dependent. According to the Acute Physiology and Chronic Health Evaluation II (APACHE II) score, the predicted mortality was 22%, while the actual mortality rate was 16%. The results indicate that units with a level of care below ICU can successfiilly manage patients with acute-on-chronic respiratory failure. 

Ambrosino N, Bmletti G, Scala V, et al. Cognitive and perceived health status in patient with chronic obstructive pulmonary disease surviving acute on chronic respiratory failure a controlled study. Intensive Care Med 2002 28 170-177. 

Obesity is defined as an excessive accumulation of fat, with a resulting increase of body mass index (BMI) > 30 kg/m. A BMI > 25 (overweight) represents a health-risk factor, and obesity is the most frequently found health risk in the United States, where more than one in three adults weigh 20% over the ideal value. The prevalence of obesity is 3.5 million in the United States (26% adults of 20-75 years), reaching 31% of the male and 35% of the female population. The prevalence of extreme obesity (BMI > 40 kg/m ) has quadrupled and that of BMI > 50 kg/m has increased fivefold (1). Obese patients frequently present with acute on chronic respiratory failure (CRF) in the emergency ward, or are discovered in a chronic status as they are investigated for suspicion of obstructive sleep apnea syndrome (OSAS), for assessment of CRF, or for preoperative evaluation. 

IV. Acute-on-Chronic Respiratory Failure and Obese Patients... 

As our population continues to grow, more and more patients are becoming dependent on longterm ventilatory support. Therefore, the need for quality options such as home mechanical ventilation is fast becoming a necessity. Ventilatory Support for Chronic Respiratory Failure (CRF) is the first resource to authoritatively address the needs of the acute or chronic respiratory patient through the transition from the hospital to the home-care setting. This reference covers best practices in the management of CRF patients who are ... 

Ethanol Multiple effects on neurotransmitter receptors, ion channels, and signaling pathways Antidote in methanol and ethylene glycol poisoning Zero-order metabolism duration depends on dose Toxicity Acutely, CNS depression and respiratory failure chronically, damage to many systems, including liver, pancreas, GI tract, and central and peripheral nervous systems Interactions Induces CYP2E1 Increased conversion of acetaminophen to toxic metabolite... 

The literature on the toxicity of benzene in humans is extensive. The acute effects of benzene exposure generally differ markedly from the chronic effects. Acute exposure to high doses of benzene in air (at concentrations in excess of 3000 ppm) causes symptoms typical of organic solvent intoxication. Symptoms may progress from excitation, euphoria, headache, and vertigo, in mild cases, to central nervous system depression, confusion, seizures, coma, and death from respiratory failure in severe cases. The rate of recovery depends on the initial exposure time and concentration, but, following severe intoxication, the symptoms may persist for weeks. 

The clinical manifestations of serum phosphate depletion depend on the length and degree of the deficiency. Moderate hypophosphatemia of 1.5 to 2,4 mg/dL (0.48 to 0.77 mmol/L) is usually not associated with clinical signs and symptoms (unless chronic, when osteomalacia or rickets develops). Plasma concentrations less than 1.5 mg/dL (0.48 mmol/L) may produce clinical manifestations. Because phosphate is necessary for the formation of ATP, glycolysis and cellular function are impaired by low intracellular phosphate concentrations. Muscle wealmess, acute respiratory failure, and decreased cardiac output may occur in phosphate depletion. At very low serum phosphate (<1 mg/dL or <0.32 mmol/L), rhabdomyolysis may occur. Phosphate depletion in erythrocytes decreases erythrocyte 2,3-diphosphoglycerate, which causes tissue hypoxia because of increased affinity of hemoglobin for oxygen. Severe hypophosphatemia (serum phosphate concentration <0.5 mg/dL [<0.16 mmol/L]) may result in hemolysis of the red blood cells. Mental confusion and frank coma also may be secondary to the low ATP and tissue hypoxia. If hypophosphatemia is chronic, impaired mineralization of bone produces rickets in children and osteomalacia in adults. 

HUMAN HEALTH RISKS Acute Risks eczematous dermatitis convulsions CNS depression rise in blood pressure peripheral vasoconstriction respiratory failure Chronic Risks skin sensitization effects on liver, kidneys, CNS, cardiovascular system and red blood cells. 

HUMAN HEALTH RISKS Acute Risks irritation of mucous membranes, upper respiratory tract, eyes and skin may cause allergic reaction bums colored urine muscle twitch CNS excitement suffocation delirium increased pulse rate without fall in blood pressure respiratory failure Chronic Risks dermatitis anemia skin depigmentation effects on kidney and eyes corneal and conjunctival discoloration cancer. 

HUMAN HEALTH RISKS Skin man TDLo 20 mg/kg for 6 weeks EPA Group B2/C probable human carcinogen Acute Risks irritation of eyes, skin, nose and throat itchiness headache seizures respiratory failure nausea vomiting diarrhea tremors weakness anemia convulsions cyanosis Chronic Risks local sensitivity effects on liver, blood, cardiovascular and immune systems. 

The most sensitive indicators of acute chlordane toxicity in humans are central nervous system effects including headache, confusion, behavioral aberrations, and tremors (EPA 1980a Harrington et al. 1978). At high levels of exposure, central nervous system effects include convulsions, coma, respiratory failure, and eventually death. Effects on the liver appear to be the only manifestations in humans of chronic exposure to chlordane (EPA 1980a Ogata and Izushi 1991). 

Respiratory Sensation, edited by L. Adams and A. Guz Pulmonary Rehabilitation, edited by A. P. Fishman Acute Respiratory Failure in Chronic Obstructive Pulmonary Disease, edited by J.-P. Derenne, W. A. Whiteiaw, and T. Simiiowski Environmental Impact on the Airways From Injury to Repair, edited by J. Chretien and D. Dusser... 

Hypercapnic respiratory failure is due to failure of the ventilatory pump caused by acute (drug overdose, acute neuromuscular diseases) or chronic (chest wall abnormalities, chronic neuromuscular diseases) disorders. It is characterized by alveolar hypoventilation, which leads to hypercapnia with coexistent, usually mild, hypoxemia. The central drive may be globally reduced with the fall in Pa02 resulting from the increase in alveolar CO2. More commonly, the drive remains high, but the mechanical load on the respiratory systan is too great or the capacity of the muscles too low to ensure efficient CO2 elimination (Fig. 1). 

A 53-year-old woman with severe chronic obstructive pulmonary disease, on home oxygen, had been admitted to the ICU on three occasions in 2003, for acute respiratory failure consequent upon an acute exacerbation, always unresponsive with a Glasgow Coma Scale 8/15 (Table 9). She received noninvasive positive pressure ventilation (NIPPV) by mask on each admission and after 24 hours had greatly improved. On each occasion, her LOS was 17 days before discharge home, representing acute care cost of 8880 (seven days ICU = 6300 plus 10 days ward = 2580, for a total of 8880 per admission). 

Meanwhile, years of productive research have demonstrated that patients with chronic respiratory insufficiency can also benefit from mechanical ventilation. As the Preface of this volume mentions their survival as well as their health status may be dependent on long-term ventilatory support. The ever increasing incidence and prevalence of chronic respiratory disease suggests that the use of ventilatory support will markedly increase. However, the techniques and strategies to use it, and when and where (non-intensive care unit, or home), are very different from treating the respiratory failure resulting from acute conditions and in patients with structurally near normal lungs. 

---