Respiratory Care

Patients with severe adult respiratory distress syndrome, burns, or multisystem failure may have such high minute ventilation requirements and such low respiratory system compliance (C) that older ventilators such as the MA-1 are incapable of ventilating them. Materials and Methods: Using an MA-1 for comparison and employing a test lung with variable C, we determined the maximum ventilatory capabilities of four currently manufactured, state-of-the-art ventilators: the Bear 5, the Puritan-Bennett 7200a, the Siemens Servo 900C, and the Hamilton Veolar. We incrementally increased dialed minute volume (V) by manipulating ventilator rate, and we measured actual V output with a pneumotachometer at three different tidal volumes and three settings of C and positive end-expiratory pressure. Inspiratory (I) and expiratory times (E) were determined from strip-chart recordings, and each ventilator's maximum ventilatory capability was considered to be its greatest V output before the I:E ratio exceeded 1.0. Results: The capabilities of the 7200a, 900C, and Veolar varied somewhat under individual test settings but were similar, with none of the three clearly outperforming the others; the Bear 5 had maximum ventilatory capabilities much greater than those of the MA-1 but somewhat lower than those of the other test machines. Conclusions: Current ventilators are far superior to their ancestors in ventilatory capabilities, and the clinical importance of the differences among them is uncertain. (Respir Care 1986;31:1054-1058.)

Although not necessary for most day-to-day clinical management, precise quantitation of the volume of gas leaked through a bronchopleural fistula during mechanical ventilation is important in research on the natural history or therapy of such leaks. We could find no previous studies evaluating the accuracy of the various devices available for such quantitation in the clinical setting and so constructed an experimental system in which three such devices measured a controlled air leak simultaneously. Using a Tissot 120-liter water-sealed spirometer as a reference standard, we tested a heated pneumotachometer, a Bourns LS-75 ventilation monitor, and a Wright Respirometer, using leaks of 1.07 to 8.66 liters per minute. The pneumotachometer agreed with the Tissot spirometer within 5% except at the lowest flow tested, while the other two devices indicated leak volumes that differed from the standard by at least 10% on 8 of 18 measurements. The Bourns LS-75 indicated only 60.0 and 8.4% of the two lowest leak volumes, respectively. Accuracy of the device used for quantitating air leak should be taken into consideration in studies of bronchopleural fistula during mechanical ventilation, especially when the leaked volumes are small. (Respir Care 1986;31:1065-1068.)

Auto-PEEP is unintentional positive end-expiratory pressure (PEEP) that occurs at the alveolar level in mechanically ventilated patients when there is incomplete exhalation; this complication is not evident unless looked for. Auto-PEEP is a recognized hazard in patients with chronic obstructive pulmonary disease (COPD), but its prevalence in a broad spectrum of mechanically ventilated patients with high minute volume ( V ⋅ E ) requirements (> 10 L) has not previously been studied. We designed this study of the incidence, severity, and detection of auto-PEEP in a major medical center to aid the clinician in predicting when this complication might occur and to describe simple maneuvers to measure it in a reproducible manner. Method: We looked for auto-PEEP in patients on controlled ventilation only (not assisting or breathing spontaneously). We checked for auto-PEEP through three ventilators-the Siemens Servo 900B and 900C and the Bennett MA-1- in patients requiring VE above 10 L. Results: Of 164 mechanically ventilated patients admitted to our ICUs during the study period, 62 were on controlled ventilation, required V ⋅ E > 10 L, and entered the study. We recorded measurable auto-PEEP- ranging from 1 to 16 cm H2O upon initial measurement-in 24 (39%) of the patients. In subsequent measurements, auto-PEEP increased from as little as 1 to as much as 25 cm H₂O in 7 (29%) of the 24 patients despite efforts to minimize it. Only 5 (21%) of the 24 had a known history of COPD. The incidence of auto-PEEP in subjects with a V ⋅ E above 20 L was 100%. The incidence of auto-PEEP increased with patient age: of those less than 40 years of age, 16% had auto-PEEP; 33% of those between 40 and 60 years old had it; and 60% of those above 60 years of age had this complication. The VE requirement to experience auto-PEEP decreased with age. When patients were classified by diagnosis, we found that most had primarily respiratory or cardiopulmonary disorders. Conclusions: We conclude that regardless of COPD, auto-PEEP is common in patients on controlled ventilation with a V ⋅ E above 10 L and that clinicians should regularly screen for it. Those at high risk are over 60 years of age, have respiratory or cardiopulmonary disorders, and/or require V ⋅ E over 20 L. (Respir Care 1986;31:1069-1074.)

The term "auto-PEEP" has been applied to PEEP that occurs during mechanical ventilation when there has been incomplete exhalation of a delivered breath at the onset of the next inspiration. We hypothesized that shortening inspiratory time by increasing flowrate and/or using a circuit with low compressible volume (LCV) would decrease auto-PEEP. Methods: We first constructed a laboratory model to test our hypothesis under controlled conditions. Using a Manley test lung connected to an MA-1 ventilator, we created auto-PEEP by applying a screw clamp to the endotracheal tube and quantitated auto-PEEP by use of calibrated transducers on either side of the obstruction. To confirm the bench studies clinically, we randomly varied inspiratory flow and circuitry-keeping corrected tidal volume (V_T) and frequency (f) constant- in five adult patients with auto-PEEP. Results: In the bench studies, when auto-PEEP was 20 cm H₂O with standard ventilator circuitry (corrected VT = 550 ml and f = 24/min), increasing inspiratory flow from 60 to 100 L/min reduced auto-PEEP to 7.5 cm H₂O. Switching to LCV circuitry at the same V_T and f produced auto-PEEP of 10 cm H₂O at 60 L/min flow and 5 cm H₂O at 100 L/min. In the clinical studies of adult patients, at flowrates of 60 and 100 L/min, mean auto-PEEP values were 15.8 and 9.0 cm H₂O, respectively, with standard tubing; with LCV tubing the respective auto-PEEP values were 12.6 and 5.8 cm H₂O. (P < 0.05 in both clinical studies.) We conclude that higher inspiratory flowrates and a low compressible volume circuit are effective in reducing auto-PEEP in mechanically ventilated adults. (Respir Care 1986;31:1075-1079.)

During mechanical ventilation, inadvertent positive end-expiratory pressure (auto-PEEP) results when there is insufficient time for the lung to return to functional residual capacity prior to initiation of the next breath. Auto-PEEP has generally been seen in patients with obstructive lung disease. We investigated whether auto-PEEP might also result when high minute ventilation is provided via a small endotracheal tube. Method: We ventilated a test lung 40 times per minute with a tidal volume of 1.1 liters and assessed auto-PEEP and air trapping under 12 different conditions: lung compliance was set at 40, 80, and 120 ml/cm H2O, and tubes of 6-, 7-, 8-, and 9-mm diameter were tested at each compliance. Results: Auto-PEEP was present under all 12 conditions but increased markedly with the smaller tubes, reaching more than 30 cm H2O with the 6-mm tubes. Air trapping correlated directly with tube resistance and compliance. Conclusion: At high minute ventilation, the use of small endotracheal tubes may result in auto-PEEP and unintended lung distention. (Respir Care 1986;31:1080-1082.)

In patients with permanent tracheostomies, the clinician can encounter difficulty in creating a satisfactory seal between the patient and pulmonary function testing (PFT) equipment. We have developed a simple apparatus and procedure for effecting a tight seal during testing. Materials and Methods: The seal around the tracheostomy is made with a newborn-size resuscitation mask, the hole of which is larger than the tracheal stoma. A sealing lubricant is applied to the soft rim of the mask and around the tracheostomy site, and adapters enable connection of the resuscitation mask and the large-bore PFT-equipment tubing. After affixing the adapters to the mask, we check that the seal is tight; if airleak is evident, more lubricant or a mask of different size or style may be necessary. Once a tight seal is achieved without airway compromise, the mask is attached to the PFT equipment and testing can begin. During testing, the patient should wear nose clips to prevent volume loss through the upper airway. Comments: This equipment is simple, inexpensive, and readily available. Further, it permits pulmonary function testing whether or not a tracheostomy tube is in place, an advantage if variable extrathoracic upper airway obstruction is a consideration. If the patient has a cuffed tracheostomy tube in place, the PFT equipment can be connected directly to the tube. We have found that this apparatus and technique are well tolerated and that test results are reproducible. (Respir Care 1986;31:1083-1085.)

Multiple-use (M-U) closed-system endotracheal suction catheters are effective in preventing arterial oxygen desaturation in patients on positive end-expiratory pressure (PEEP) and may lessen the frequency of bradycardia and hypotension in unstable patients who are prone to these complications of suctioning. However, because M-U catheters remain attached to the ventilator circuit and are reintroduced repeatedly into the patient's airway over 24 hours or longer, they could become heavily contaminated with pathogens. We hypothesized a risk of autocontamination to the patient by re-inoculation of the respiratory tract with organisms that flourished on the M-U catheter while it was isolated from the patient's immune defenses or antibiotic therapy. Methods: We tested this hypothesis in 30 mechanically ventilated adult patients with positive sputum cultures. We measured and compared the amount of bacteria present on an M-U catheter at the end of a 24-hour use period, the amount of bacteria present in the patient's sputum at that time, and the amount of bacteria present on a single-use (S-U) catheter at that time, after it had made one pass into the patient's airway. Organisms recovered and colony counts were also compared to results of a sputum culture obtained before the study began. Results: Fourteen different pathogens or potential pathogens were recovered, in numbers of 2 × 10¹ to 2 × 10⁷ colony-forming units. The greatest number of colonies was most often recovered from the sputum specimen, and statistical analysis showed no differences in rate or magnitude of contamination between M-U and S-U catheters. We found no clear indication of either increased or decreased risk to the patient from use of an M-U catheter for 24 hours in this study. Further evaluation of the impact of an M-U catheter on the rate and magnitude of colonization of the lung would be useful, considering the potential advantages of this device. (Respir Care 1986;31:1086-1092.)

Analgesic use of nitrous oxide (N₂O) in nontraditional settings requires safe and effective scavenging systems to rid the work area of hazardous waste gas. Significant health risks to health care workers are associated with repetitive exposure to excessive levels of N₂O. Regulations limit the exposure level to 25 parts per million and also require the use of effective scavenging systems. We tested the existing room ventilation and a suction-powered scavenging system in our burn unit's hydrotherapy room and found them to be inadequate in maintaining safe room air levels. We therefore developed a fan-powered scavenging system using a ceiling-mounted hood, under which N₂O is administered, and found it to maintain safe levels while requiring little patient cooperation and allowing complete access to the patient. (Respir Care 1986;31:1092-1095.)

An accurate knowledge of the ratio of physiologic dead space to tidal volume (VD/VT) is useful in managing mechanically ventilated patients. When collecting the sample of exhaled gases, one must separate the gas compressed in the ventilator circuit during inspiration from the gas exhaled by the patient. This is best accomplished by placing a separate gas-collection valve at the patient Y-piece, which will allow the patient's exhaled volumes to be collected separately. We designed a gas-collection valve for use with Siemens-Elema Servo 900B and 900C ventilators that performs this function over a wide range of ventilatory conditions. Our system has several distinct advantages over the option provided by the manufacturer: Its economical cost represents significant savings, and it is more versatile than the Siemens gas analyzer. A larger variety of gas analyzers can be used for the measurement, and more accurate CO2 production values can be provided, along with directly determined VD/VT values. (Respir Care 1986;36:1096-1098.)

A 63-year-old man required emergency endotracheal intubation and mechanical ventilation for complications of acute myocardial infarction. After the patient was extubated, a tooth, which had apparently been dislodged during intubation and had remained in the posterior pharynx, was aspirated into the right lower-lobe bronchus. Vigorous chest percussion and postural drainage administered every 2 hours enabled the patient to cough up the tooth 17 hours after its discovery. He subsequently recovered uneventfully from both the myocardial infarction and the foreign-body aspiration. Although bronchoscopy, with either a rigid or a flexible instrument, is currently the treatment of choice for an adult patient with a foreign object in the lower airway, chest physiotherapy could represent a less invasive, less expensive initial therapy for patients who can cough and who can be moved into the appropriate drainage position. (Respir Care 1986;31:1099-1101.)

A 77-year-old man developed progressive difficulty in swallowing, garbled speech, and diplopia in the presence of a chronically ulcerated scar on his face. Toxigenic Corynebacterium diphtheriae (biotype intermedius) was cultured from the lesion, and he was treated with diphtheria antitoxin and antibiotics. Over several days he developed progressive respiratory muscle weakness, as evidenced by decreasing serial measurements of vital capacity (VC) and maximum inspiratory force (MIF), and required mechanical ventilation. Progressive peripheral muscle weakness followed, and VC and MIF further declined, eventually to as low as 150 ml and 5 cm H2O, respectively. Nerve conduction studies were consistent with the demyelinating neuropathy seen following diphtheria. Beginning at about Day 60, these abnormalities began to resolve, and despite recurrent atelectasis, nosocomial pneumonia, depression, and tracheal stenosis, the patient survived. He required mechanical ventilation for 72 days and was hospitalized 142 days, eventually regaining normal neuromusclar function. Occurring during an epidemic of diphtheria in Seattle, this case has features typical of cutaneous diphtheria and severe postdiphtheritic neuropathy. Clinicians should be aware of this possible etiology for unexplained acute respiratory muscle weakness. (Respir Care 1986;31:1102-1106.)

The following 50 publications are reflective of the areas of research at our institution during the last decade and have been chosen for their usefulness to clinicians working in respiratory and critical care. The contributions have come not only from the Department of Respiratory Care and the Division of Respiratory and Critical Care Medicine, but also from Anesthesiology, Cardiology, Neurological Surgery, Neurology, Nursing, Otolaryngology, Psychiatry, Social Work, and Surgery at Harborview Medical Center.