Status asthmaticus.

Despite improved understanding of the pathophysiology and treatment of asthma, significant morbidity and mortality exist for both the pediatric and adult patient. The critical care practitioner must understand the chronic as well as the acute nature of the condition in order to provide effective intervention. This article reviews the epidemiology and pathophysiology of asthma, clinical assessment, management principles, therapeutic modalities, and future approaches to the management of asthma.

Prediction of outcome for critically ill patients with unexplained hypotension.

OBJECTIVES: To determine the clinical variables that affect the prognosis of critically ill patients with sustained unexplained hypotension. A further goal was to develop a prognostic scoring system based on clinical data available at the onset of hypotension. DESIGN: Prospective cohort study. SETTING: The intensive care units (ICUs) of an academic medical center. PATIENTS: One hundred one adult ICU patients with sustained (> 60 mins) unexplained hypotension. Using the initial 50 patients (derivation set), a prognostic score was developed that was then tested in the next 51 patients (validation set). INTERVENTIONS: None MEASUREMENTS AND MAIN RESULTS: The main outcome variable was death or hospital discharge. The overall hospital mortality in the combined sets was 58%. Using a multivariable model we identified three independent (p < .05) predictors of hospital mortality, including the Acute Physiology and Chronic Health Evaluation (APACHE) II score at the time of hypotension, the time from hospital admission to hypotensive episode, and hospital admission for surgery or treatment of malignancy. These variables were weighted and combined to create a Hypotension Score which separated patients in the combined sets into three prognostic groups: a) Hypotension Score of < 40, mortality 7%, (n = 27); b) Hypotension Score of 40 to 64, mortality 70%, (n = 50); and c) Hypotension Score of > or = 65, mortality 92%, (n = 24). The area under the receiver operating characteristic curve was .85 for the derivation set and .83 for the validation set vs. .76 for the APACHE II score alone. CONCLUSIONS: The prognosis of hypotension in the critical care setting is highly variable, but can be predicted from patient characteristics.

Indirect calorimetry in critically ill patients: role of the clinical dietitian in interpreting results.

Evaluation and interpretation of energy needs of critically ill patients require the expertise of clinical dietitians: Dietitians must be knowledgeable about the methods available to quantify energy needs and able to communicate effectively with physicians and nurses regarding nutritional requirements. Several prediction equations are available for calculating energy needs of critically ill patients. Indirect calorimetry is also used frequently to measure energy requirements in this patient population. This article defines when energy expenditure measured by indirect calorimetry may provide clinically useful information. Data obtained by indirect calorimetry must be interpreted carefully. Indirect calorimetry is based on the equations for oxidation of carbohydrate, protein, and fat. Errors in interpretation can be made when metabolic pathways other than oxidation dominate or when clinical conditions exist that affect carbon dioxide excretion from the lungs. Before incorporating data obtained from indirect calorimetry into a nutrition care plan, the clinical dietitian should carefully evaluate the following factors for a patient: clinical conditions when the measurement was made, desired weight loss or gain, tolerance to food or nutrition support, relationship between protein intake and energy need, and need for anabolism or growth. This article provides clinical examples illustrating how measured values compare with calculated values and recommendations for how to incorporate measured values into nutrition care plans.

Transesophageal echocardiography predicts mortality in critically ill patients with unexplained hypotension.

OBJECTIVES: This study sought to determine the prognostic yield and utility of transesophageal echocardiography in critically ill patients with unexplained hypotension. BACKGROUND: Transesophageal echocardiography is increasingly utilized in the intensive care setting and is particularly suited for the evaluation of hypotension; however, the prognostic yield of transesophageal echocardiography in these patients is unknown. METHODS: We prospectively studied 61 adult patients in the intensive care unit with sustained (> 60 min) unexplained hypotension. Both transthoracic and transesophageal echocardiography were performed, and results were immediately disclosed to the primary physician, who reported any resulting changes in management. Patients were classified on the basis of transesophageal echocardiographic findings into one of three prognostic groups: 1) nonventricular (valvular, pericardial) cardiac limitation to cardiac output; 2) ventricular failure; and 3) noncardiac systemic disease (hypovolemia or low systemic vascular resistance, or both). Primary end points were death or discharge from the intensive care unit. RESULTS: A transesophageal echocardiographic diagnosis of nonventricular limitation to cardiac output was associated with improved survival to discharge from the intensive care unit (81%) versus a diagnosis of ventricular disease (41%) or hypovolemia/low systemic vascular resistance (44%, p = 0.03). Twenty-nine (64%) of 45 transthoracic echocardiographic studies were inadequate compared with 2 (3%) of 61 transesophageal echocardiographic studies (p < 0.001). Transesophageal echocardiography contributed new clinically significant diagnoses (not seen with transthoracic echocardiography) in 17 patients (28%), leading to operation in 12 (20%). CONCLUSIONS: Transesophageal echocardiography makes a clinically important contribution to the diagnosis and management of unexplained hypotension and predicts prognosis in the critical care setting.

Changes in acetylcholine receptor number in muscle from critically ill patients receiving muscle relaxants: an investigation of the molecular mechanism of prolonged paralysis.

OBJECTIVE: Previous reports have described prolonged paralysis after the administration of muscle relaxants in critically ill patients. The purpose of this study was to examine possible pathophysiologic causes for this paralysis by measuring muscle-type, nicotinic acetylcholine receptor number in necropsy muscle specimens from patients who had received muscle relaxants to facilitate mechanical ventilation before death. DESIGN: Prospective laboratory study of human muscle collected at autopsy. SETTING: Medical and surgical intensive care units (ICUs) at a university hospital and a research laboratory. PATIENTS: Fourteen critically ill patients, with a variety of diagnoses, all of whom required mechanical ventilatory support before their deaths in the ICU and who underwent post mortem examination. Patients were arbitrarily divided into three groups, according to their total vecuronium dose and number of days mechanically ventilated before death. Three patients were in the control group (defined as dying within 72 hrs of initiation of ventilatory support and receiving a total dose of < 5 mg of vecuronium). Six patients were in the low-dose group (defined as requiring ventilatory support for > 3 days before death and receiving a total vecuronium dose of < or = 200 mg). Five patients were in the high-dose group (defined as requiring ventilatory support for > 3 days before death and receiving a total vecuronium dose of > 200 mg). INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Nicotinic acetylcholine receptor numbers as measured by specific 125I-alpha-bungarotoxin binding to human rectus abdominis muscle obtained at autopsy were determined. In general, receptor number reflected the clinical requirements for the muscle relaxants of each patient. Patients who had increasing requirements for muscle relaxants before death had increases in receptor number, as compared with control values. CONCLUSIONS: The increase in nicotinic acetylcholine receptor number in muscle from patients with an increasing requirement for muscle relaxants before death suggests that nicotinic acetylcholine receptor up-regulation may underlie the increased requirements for muscle relaxants seen in some patients. Furthermore, these findings suggest that muscle relaxant-induced, denervation-like changes may at least be partially responsible for prolonged muscle paralysis after the long-term administration of muscle relaxants. This study may provide the first information into the molecular mechanisms underlying prolonged paralysis.

Death and other complications of emergency airway management in critically ill adults. A prospective investigation of 297 tracheal intubations.

BACKGROUND: Hospitalized patients outside of the operating room frequently require emergency airway management. This study investigates complications of emergency airway management in critically ill adults, including: (1) the incidence of difficult and failed intubation; (2) the frequency of esophageal intubation; (3) the incidence of pneumothorax and pulmonary aspiration; (4) the hemodynamic consequences of emergent intubation, including death, during and immediately following intubation; and (5) the relationship, if any, between the occurrence of complications and supervision of the intubation by an attending physician. METHODS: Data were collected on consecutive tracheal intubations carried out by the intensive care unit team over a 10-month period. Non-anesthesia residents were supervised by anesthesia residents, critical care attending physicians, or anesthesia attending physicians. RESULTS: Two hundred ninety-seven consecutive intubations were carried out in 238 adult patients. Translaryngeal tracheal intubation was accomplished in all patients. Intubation was difficult in 8% of cases (requiring more than two attempts at laryngoscopy by a physician skilled in airway management). Esophageal intubation occurred in 25 (8%) of the attempts but all were recognized before any adverse sequelae resulted. New infiltrates suggestive of pulmonary aspiration were present on chest radiography after 4% of intubations. Seven patients (3%) died during or within 30 min of the procedure. Five of the seven patients had systemic hypotension (systolic blood pressure < or = 90 mmHg), and four of the five were receiving vasopressors to support systolic blood pressure. Patients with systolic hypotension were more likely to die after intubation than were normotensive patients (P < 0.001). There was no relationship between supervision by an attending physician and the occurrence of complications. CONCLUSIONS: In critically ill patients, emergency tracheal intubation is associated with a significant frequency of major complications. In this study, complications were not increased when intubations were accomplished without the supervision of an attending physician as long as the intubation was carried out or supervised by an individual skilled in airway management. Mortality associated with emergent tracheal intubation is highest in patients who are hemodynamically unstable and receiving vasopressor therapy before intubation.

Women are at greater risk than men for malpositioning of the endotracheal tube after emergent intubation.

OBJECTIVES: To investigate the occurrence of endotracheal tube malpositioning after emergent intubation in critically ill adults and to determine the need for a routine postintubation chest radiography to assess endotracheal tube position. DESIGN: Prospective study. SETTING: All adult critical care and acute care units of a 560-bed university teaching hospital. PATIENTS: Study of 297 consecutive intubations (185 intubations in males and 112 intubations in females) in 238 adult patients. METHODS: Emergent endotracheal intubations were performed by resident physicians with supervision from an intensive care unit (ICU) or anesthesia attending physician or an anesthesia resident. After intubation, proper positioning of the endotracheal tube was verified by the intubating physician using clinical criteria, including auscultation of bilateral breath sounds, symmetric chest expansion, and palpation of the endotracheal tube cuff in the suprasternal notch. The endotracheal tube position relative to the lower anterior incisors or alveolar ridge was recorded using the centimeter markings printed on the endotracheal tube. A chest radiograph was obtained after intubation to verify endotracheal tube position. Appropriate endotracheal tube position on chest radiograph was defined as between > 2 and < or = 6 cm above the carina. MEASUREMENTS AND MAIN RESULTS: Of the 297 intubations, 26 were excluded from analysis because a chest radiograph was not obtained or the patient was not of normal stature. For the remaining 271 intubations, 42 (15.5%) endotracheal tubes were inappropriately placed, according to the radiographic assessment. The percentage of malpositioned endotracheal tubes was significantly higher in women than in men (61.9% vs. 38.1%, respectively; chi-square: p < .001). Thirty-three (78.6%) of 42 malpositioned endotracheal tubes were placed < 2 cm from the carina, with the highest occurrence (24/33) of proximal malposition occurring in women. Positioning of endotracheal tubes using the centimeter markings printed on the tube referenced to the lower incisors did not accurately identify malposition as documented by chest radiograph. CONCLUSIONS: Emergent endotracheal intubations result in a significant occurrence of malpositioned endotracheal tubes that are undetected by clinical evaluation. Malpositioning is not detected by routine clinical assessment, but only by chest radiograph. Women are at greater risk than men for endotracheal tube malpositioning after emergent intubation; in women, the endotracheal tube is more likely to be positioned too close to the carina. A chest radiograph for confirmation of endotracheal tube position after emergent intubation should remain the standard of practice.

Use of capnography in critically ill adults.

A major responsibility of the critical care practitioner is to assure adequate ventilation of the critically ill patient. The traditionally used methods for evaluating ventilation, such as physical examination and measurement of vital signs, are indirect. The most commonly used direct method, measurement of arterial carbon dioxide tension, is invasive and intermittent. Capnography provides the critical care practitioner with a continuous, noninvasive, and accurate assessment of ventilation. To interpret capnographic data, the practitioner must have a clear understanding of normal and abnormal patterns of carbon dioxide elimination in the lung. We review relevant respiratory physiology as a basis for understanding the value of capnography. The technology on which capnography is based is described with emphasis on methods of gas sampling, limitations of capnography, and features available on currently marketed instruments. Representative capnograms are presented and the data interpreted to enable the practitioner to determine when capnography is an appropriate monitor for the critically ill adult.

Pulse oximetry. Uses and abuses.

Pulse oximetry has made a significant contribution to noninvasive monitoring in a wide variety of clinical situations. It allows for continuous reliable measurements of oxygen saturation while avoiding the discomfort and risks of arterial puncture. As the extent of hypoxic episodes during various procedures and clinical settings is better appreciated, the role of continuous noninvasive monitoring will undoubtedly expand. An understanding of the principles and technology of pulse oximetry will allow physicians to obtain maximal clinical benefit from its use.

Comparison of transesophageal echocardiographic and scintigraphic estimates of left ventricular end-diastolic volume index and ejection fraction in patients following coronary artery bypass grafting.

Transesophageal echocardiography (TEE) has become a commonly used monitor of left ventricular (LV) function and filling during cardiac surgery. Its use is based on the assumption that changes in LV short-axis ID reflect changes in LV volume. To study the ability of TEE to estimate LV volume and ejection immediately following CABG, 10 patients were studied using blood pool scintigraphy, TEE, and thermodilution cardiac output (CO). A single TEE short-axis cross-sectional image of the LV at the midpapillary muscle level was used for area analysis. Between 1 and 5 h postoperatively, simultaneous data sets (scintigraphy, TEE, and CO) were obtained three to five times in each patient. End-diastolic (EDa) and end-systolic (ESa) areas were measured by light pen. Ejection fraction area (EFa) was calculated (EFa = (EDa - ESa)/EDa). When EFa was compared with EF by scintigraphy, correlation was good (r = 0.82 SEE = 0.07). EDa was taken as an indicator of LV volume and compared with LVEDVI which was derived from EF by scintigraphy and CO. Correlation between EDa and LVEDVI was fair (r = 0.74 SEE = 3.75). The authors conclude that immediately following CABG, a single cross-sectional TEE image provides a reasonable estimate of EF but not LVEDVI.

Withholding and withdrawal of life support from the critically ill.

We investigated decisions to withhold or withdraw life support from patients in the medical-surgical intensive care units at the Moffitt-Long Hospital of the University of California and San Francisco General Hospital, from July 1987 through June 1988. Among 1719 patients admitted to the two intensive care units, life support was withheld from 22 (1 percent) and withdrawn from 93 (5 percent). The reason for limiting care was poor prognosis. Of these 115 patients (18 of whom were considered brain-dead), 89 died in the intensive care unit (accounting for 45 percent of all deaths there), and all but 1 of the remaining patients died after transfer from the intensive care unit. Thirteen (11 percent) had earlier expressed the wish that their terminal care be limited, but this affected care in only four cases. Only 5 of the 115 patients made the actual decision to limit care; the others were incompetent at the time. Of the latter, 102 had families who participated in the decision; family members of the other 8 incompetent patients could not be found, and the decisions were made by physicians. Only 10 families initially disagreed with the recommendations to limit care, and they later agreed. The median duration of intensive care among the patients from whom life support was withheld or withdrawn was eight days at Moffitt-Long Hospital and four days at San Francisco General, as compared with medians of three and one days, respectively, for other patients who died in the intensive care units. We conclude that although life-sustaining care is withheld or withdrawn relatively infrequently from patients in the intensive care unit, such decisions precipitate about half of all deaths in the intensive care units of the hospitals we studied. In most of these cases the patients are incompetent, but physicians and families usually agree to limit care.

Assessment of routine chest roentgenograms and the physical examination to confirm endotracheal tube position.

We consecutively and prospectively studied 219 critically ill patients to evaluate the accuracy of the physical examination in assessing ETT position and the appropriateness of taking routine chest x-ray films after intubation in the ICU. As a result of x-ray findings, 14 percent of the patients required ETT repositioning, and 5 percent had main-stem intubations. Endobronchial intubation was more common in females than in males, and frequently occurred after emergency intubations. Sixty percent of the main-stem intubations occurred despite the presence of equal breath sounds on examination. Techniques to minimize the risk of tube malposition, such as cuff ballottement in the suprasternal notch and referencing the ETT centimeter markings, were not completely reliable. This study confirms the unreliability of the physical examination to assess ETT position. Chest x-ray films after intubation are indicated to verify tube position, particularly after emergency intubations. Other techniques such as use of a lighted stylet require evaluation to determine whether they are more cost-effective in verifying ETT placement in patients who have no other indication for postintubation x-ray films.

Washin and washout of isoflurane administered via bubble oxygenators during hypothermic cardiopulmonary bypass.

Washin and washout of a volatile anesthetic given through the oxygenator during hypothermic (23.4 +/- 2.1 degrees C) cardiopulmonary bypass were studied in nine patients. The authors administered isoflurane and measured its partial pressure in arterial (Pa) and venous (Pv) blood and the gas exhausted from the oxygenator (PE) at 1, 2, 4, 8, 16, 32, and 48 min during washin. These measurements were repeated during washout, which coincided with rewarming. During washin, PE, Pa, and Pv progressively rose toward inlet gas partial pressure (PI). Equilibration of Pa with PI was 41% after 16 min, 51% after 32 min, and 57% after 48 min of washin. During washout, Pa declined to 24% of its peak after 16 min and to 13% after 32 min. Washin and washout were considerably slower in mixed venous blood. Washin of isoflurane appeared to occur more slowly during cardiopulmonary bypass than during administration via the lungs in normothermic patients, presumably because hypothermia increases tissue capacity, compensating for the effect of hemodilution that otherwise would decrease the blood/gas partition coefficient. During rewarming, washout appeared to occur as rapidly as from the lungs of normothermic patients. This may have resulted from the declining blood/gas partition coefficient (due to rewarming) and relatively limited tissue stores of isoflurane. The relationship between exhaust and arterial partial pressures was reasonably consistent; for clinical purposes, measurement of PE can be used to estimate Pa.