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PubMedDate not supplied

High-frequency ventilation: is there a clinical role?

Mechanical ventilation of the lungs is an integral component of modern medical practice, being utilized predominantly in the operating room and intensive care unit. The first mechanical ventilators were of the negative-pressure type. Currently, positive-pressure mechanical ventilation with frequency rates of up to 60 breaths per minute is referred to as conventional mechanical ventilation. In the 1960s, Sjöstrand developed the concept of high-frequency positive-pressure ventilation. This development was a logical continuation of physiology studies that built on earlier observations, which were then directly applied to clinical use. This paper is a synopsis of the current rationale for the clinical use of high-frequency ventilation.

Carbon Dioxide↗
PubMed1988

Home mechanical ventilation.

Recently, interest in the use of mechanical ventilation outside the hospital setting has been increasing. Patients with various types of chronic respiratory failure may benefit from this approach. Evaluation for long-term mechanical ventilation necessitates assessment of the underlying disease process, the goals of the medical team, and the needs of the patient and family. Externally applied negative-pressure devices can provide adequate ventilation for many patients, particularly those with neuromuscular diseases. Positive-pressure ventilation by means of a tracheostomy provides greater control of the airway, allows adjustment of tidal volume and minute ventilation, and may be delivered by portable equipment. Ongoing care and support services in the home must be provided. A variety of mechanical devices and new techniques of ventilator support have made home mechanical ventilation a realistic option for long-term care.

Adult↗
PubMed1998

Evaluating the control of tuberculosis among healthcare workers: adherence to CDC guidelines of three urban hospitals in California.

OBJECTIVE: To evaluate adherence to components of the Centers for Disease Control and Prevention (CDC) guidelines for preventing the transmission of Mycobacterium tuberculosis in healthcare facilities. DESIGN: Multihospital study using direct observation and a standardized questionnaire. SETTING: Three urban hospitals (two county hospitals and one private community hospital) in counties in California with a high number and incidence rate of tuberculosis (TB) cases. MEASUREMENTS: The ventilation performance of treatment and TB-patient isolation rooms was assessed. Questionnaire data regarding TB control policy and procedures were obtained through interviews with the person(s) responsible for each program component; review of written TB control plans, training, and educational materials; and attendance at hospital TB control meetings and trainings. RESULTS: Twenty-eight percent of isolation rooms tested (7/25) were under positive pressure; 83% of rooms tested (20/24) had six or more nominal air changes per hour (ACH), but supply air did not mix rapidly with room air. Therefore, the nominal ACH likely overestimated the effective ACH and the subsequent protection provided. In virtually all rooms tested (26/27), air potentially containing M tuberculosis aerosol moved toward, rather than away from, likely worker locations. None of the hospitals regularly checked the performance of engineering controls. Only one hospital adhered to the CDC minimum requirements for respiratory protection. Training of healthcare workers generally was underutilized as a TB prevention measure. Hospitals did not provide comprehensive counseling regarding the need for healthcare workers to know their immune status and the risks associated with M tuberculosis infection in an immunocompromised individual. Employee representatives did not have a voice in TB-related decision making. CONCLUSIONS: Important aspects of day-to-day TB control practice did not conform to the written TB control policy. Subsequent to the identification of TB patients, healthcare workers at all three hospitals were potentially exposed to M tuberculosis aerosol due to breaches in negative-pressure isolation, the limitations of dilution ventilation, and the failure to maintain engineering controls and to implement respiratory protection controls fully. These findings lend support to the Occupational Safety and Health Administration's policy presumption that, absent clear evidence to the contrary, newly acquired healthcare-worker M tuberculosis infections are work-related.

California↗
PubMed1993

Phrenic nerve pacing--an alternative to positive pressure ventilation: the required nursing care.

Phrenic nerve pacing as a method of ventilation was first recognized in 1783. For years, this technique was not used because of the lack of practical technology. Interest in phrenic nerve pacing was renewed in the 1960s with the development of a radio frequency transmission system. Applicable to a limited patient population, phrenic nerve pacing has several benefits over positive-pressure ventilation. Benefits include greater patient mobility, verbal articulation, less mechanical noise, and breathing by natural negative-pressure. This article provides information for nurses who care for patients ventilated by phrenic nerve pacing.

Diaphragm↗
PubMed1992

Historical perspectives on the development and use of mechanical ventilation.

Contemporary advancements in cardiothoracic and abdominal surgical procedures have been historically dependent on the development and adoption of controlled airway management, specifically endotracheal intubation, controlled positive-pressure ventilation, and the use of automatic positive-pressure mechanical ventilators. More than 400 years elapsed before the 16th Century theories of Paracelsus and the demonstrations of Vesalius were routinely adopted to solve the "pneumothorax problem" that prevented complicated or prolonged surgical procedures within the pleural cavity. Acceptance and implementation of controlled positive-pressure ventilation was impeded for decades by the inability to maintain and protect the airway. Consequently, emphasis on the development of mechanical ventilation was directed toward machinery that provided safer negative-pressure respiratory support. The introduction of curare into European anesthesia practice and the adoption of protective airway practices during the poliomyelitis epidemics led to routine use of controlled positive-pressure ventilation and construction of dependable machinery. Laboratory investigations, exploring complications from cardiothoracic surgery, brought about American acceptance and established controlled positive-pressure mechanical ventilation as an indispensable part of conventional intraoperative management.

Europe↗
PubMed1997

A comparison of two different bronchial cuff designs and four different bronchial cuff inflation methods.

OBJECTIVE: To compare directly measured pressures at the cuff/trachea interface that are associated with two different bronchial cuff designs and four different methods of bronchial cuff inflation suggested for use with one-lung ventilation. DESIGN: In vitro study. SETTING: Experimental laboratory in a university-affiliated hospital. INTERVENTIONS: The bronchial cuffs of two different endotracheal tubes were inflated using one of four different methods of determining the cuff volume and pressure necessary to "just seal" the bronchus and obtain lung separation; positive-pressure test, negative-pressure test, CO2 analysis, and a new test using an anesthesia ventilator. When each method predicted the "just-seal" state, the pressure at the cuff/bronchus interface as well as cuff inflation pressure and volume were recorded. MEASUREMENTS AND MAIN RESULTS: Although the new test was incompatible with the bronchial blocker, the other three tests all accurately predicted lung separation with the Univent, with no significant differences in pressures exerted on the trachea. However, when used with the double-lumen tube, the new test produced significantly lower measured parameters than the other inflation methods. CO2 analysis did not reliably predict bronchial seal with the double-lumen tube. CONCLUSIONS: To achieve lung separation with the lowest pressure on the trachea, the new test is the most appropriate method for use with the double-lumen tube; however, the negative-pressure test appeared to be the easiest and fastest method for use with the bronchial blocker. Although the bronchial blocker was associated with lower pressures transmitted from the cuff to the trachea, the in vitro model cannot predict which bronchial cuff design would be superior in vivo.

Adult↗
PubMed1998

Laryngeal-receptor responses to phasic CO2 in anesthetized cats.

We compared the effects of CO2 applied continuously and during expiration on laryngeal-receptor activity in paralyzed, artificially ventilated and nonparalyzed, spontaneously breathing cats by using an isolated larynx, artificially ventilated to approximate a normal respiratory cycle. The majority of quiescent negative-pressure and all cold receptors were excited by 5 and 9% CO2 applied both continuously and during expiration. In general, quiescent positive-pressure, tonic negative-pressure, and tonic positive-pressure receptors were inhibited by 5 and 9% CO2 applied continuously and during expiration. There were no significant differences between responses to 5 and 9% CO2 or to continuous and expired CO2 or between paralyzed and nonparalyzed preparations. In conclusion, laryngeal receptors respond to changes in CO2 concentration occurring during a normal respiratory cycle. Because laryngeal-receptor stimulation exerts reflex effects on ventilation and upper airway muscle activity, these results suggest that airway CO2 plays a role in reflex regulation of breathing and upper airway patency.

Anesthesia↗
PubMed1997

Negative-pressure pulmonary edema in the otolaryngology patient.

It is estimated that 11% of all patients requiring active intervention for acute upper airway obstruction develop negative-pressure pulmonary edema. This pathologic process typically has a benign and rapidly resolving clinical course with the prompt use of mechanical ventilation and positive end expiratory pressure. A review of the literature, however, has revealed a morbidity and mortality rate of 11% to 40% in reported series. During the years 1991 through 1993, six patients were identified in whom negative-pressure pulmonary edema developed after various otolaryngologic procedures. Five (84%) of the six patients had complete resolution of the pulmonary edema within 24 hours, and the sixth patient progressed to prolonged mechanical ventilation and eventual death. In an effort to further understand the pathophysiology of this disease, a cardiac evaluation was performed by use of echocardiography on all six patients. In three of the six patients, studies revealed an underlying cardiac anomaly not previously identified by history or physical examination. Findings included one case of hypertrophic cardiomyopathy and two cases of pulmonary and tricuspid valvular insufficiency. This 50% incidence of cardiac anomalies is striking, in contrast to the less than 1% incidence of these anomalies in the general adult population. To our knowledge, this is the first study to implicate an underlying cardiac cause for the generation of negative-pressure pulmonary edema. On the basis of this study, we recommend that echocardiography be a part of the routine evaluation of all patients who manifest negative-pressure pulmonary edema.

Acute Disease↗
PubMed1988

Ventilatory responses to increased blood flow and decreased lung volume in awake dogs.

The effect of decreased lung volume on ventilatory responses to arteriovenous fistula-induced increased cardiac output was studied in four chronic awake dogs. Lung volume decreases were imposed by application of continuous negative-pressure breathing of -10 cmH2O to the trachea. The animals were surgically prepared with chronic tracheostomy, indwelling carotid artery catheter, and bilateral arteriovenous femoral shunts. Control arteriovenous blood flow was 0.5 l/min, and test flow level was 2.0 l/min. Arterial blood CO2 tension (PaCO2) was continuously monitored using an indwelling Teflon membrane mass spectrometer catheter, and inhaled CO2 was given to maintain isocapnia throughout. Increased fistula flow alone led to a mean 52% increase in cardiac output (CO), whereas mean systemic arterial blood pressure (Psa) fell 4% (P less than 0.01). Negative-pressure breathing alone raised Psa by 3% (P less than 0.005) without a significant change in CO. Expired minute ventilation (VE) increased by 27% (P less than 0.005) from control in both of these conditions separately. Combined increased flow and negative pressure led to a 50% increase in CO and 56% increase in VE (P less than 0.0025) without any significant change in Psa. Effects of decreased lung volume and increased CO appeared to be additive with respect to ventilation and to occur under conditions of constant PaCO2 and Psa. Because both decreased lung volume and increased CO occur during normal exercise, these results suggest that mechanisms other than chemical regulation may play an important role in the control of breathing and contribute new insights into the isocapnic exercise hyperpnea phenomenon.

Animals↗
PubMedDate not supplied

Historical perspective, current applications: the chest cuirass.

The chest cuirass, a negative-pressure breathing device, is composed of a domed plastic shell that covers the patient's chest and upper abdomen and a motor that is connected to the shell by means of a wire-reinforced hose. Although the cuirass was most widely used in the rehabilitation of polio patients, it is still indicated in the treatment of certain restrictive diseases and neurological disorders.

History, 20th Century↗
PubMed1993

Pulmonary edema following post-operative laryngospasm: a case report and review of the literature.

The pathophysiology of acute, negative-pressure pulmonary edema following post-anesthetic laryngospasm (PLPE) is unclear. We present a patient and review the literature to propose etiology and management. Nineteen reported patients (3 female, 16 male, aged 3 months to 60 years) with PLPE had undergone 10 otolaryngologic, three orthopedic, four skin/soft tissue, one intraabdominal, and one ophthalmologic procedures. Twelve patients (63%) had significant medical history. Initial intubation was performed without difficulty in 17 patients, there were no predisposing trends in anesthetic management, and post-anesthetic extubation was performed without difficulty in 18 patients. Thirteen patients developed laryngospasm in less than 2 minutes. Eight were ventilated with bag/mask, 15 required reintubation, and nine required paralysis. Onset of PLPE was less than 3 minutes in 12 patients; chest roentgenograms showed edema in 17 patients. Mechanical ventilation was required for less than 24 hours in all patients. PLPE cleared in less than 24 hours in most patients. Furosemide was administered in nine patients, digoxin in one, theophylline in two, and steroids in four patients. The precise pathophysiologic mechanism of PLPE is unclear despite numerous proposed mechanisms. PLPE resolves rapidly with short-term ventilatory support. Use of diuretics/airway dilators is variable, and their contribution to management is unclear.

Adolescent↗
PubMed1970

Negative pressure artificial respiration: use in treatment of respiratory failure of the newborn.

Ninety-one infants with respiratory failure secondary to primary pulmonary disease and with a birth weight of 1000 g. or over have been managed in a negative-pressure respirator (Air-Shields) over a three-year period. Of these the failure in 87 was due to respiratory distress syndrome (RDS) and in four it resulted from massive meconium aspiration. Respiratory failure was indicated initially by arterial blood gas tensions (while breathing 100% O(2)) of Po(2) <40 mm. Hg, pH <7.10 and Pco(2) >75 mm. Hg in the initial 47 cases; these levels were subsequently raised to Po(2) < 50 mm. Hg, pH <7.20 and Pco(2) >70 mm. Hg for the remainder. Fifty-four (59.3%) of the infants survived the use of the respirator and 47 of these (51.6%) were subsequently discharged alive and well. Mean time in hours to normalization of blood gas values while on the respirator were as follows: for Po(2), 10.5; for pH, 11.6; and for Pco(2), 22.6. These values indicate that the respirator is more efficient in promoting oxygenation (raising Po(2)) than ventilation (lowering Pco(2)). They also suggest that the observed acidosis is in large part secondary to the hypoxia rather than the result of co(2) retention. For the survivors the average time of total respirator dependency before commencement of weaning was 53.7 hours. All the infants were managed without the use of endotracheal tubes although the use of the respirator and/or administration of 100% oxygen were either continuous or intermittent for periods of up to two weeks. There have been no instances of so-called respirator lung disease in the survivors or in those who died, which suggests that the use of high oxygen concentration by itself is not the major factor in the pathogenesis of this complication.

Age Factors↗