Respiratory Care

BACKGROUND: Because little is known of the effects of increased pressure on some mechanical ventilators, we studied the effects of a hyperbaric environment on the function of 19 mechanical ventilators, 13 of which had not previously been studied. METHODS & MATERIALS: Tests were performed on one of each of the following 19 ventilators: Bio-Med 1C-2A, Bio-Med ET-3, Bio-Med MVP-10, and Bio-Med P-7; Babybird, IMVbird, and Urgencybird; Oxylog; Autovent 2000; Oh-meda Logic 07; pneuPac Model 2 and pneuPac PNS 106; Omni-Vent HBC; Hy-draulic Emerson; Monaghan 225; Oxford (Penlon Ltd); Bird Mark 10 and Mark 14; and Bennett PR-2. Each ventilator was placed inside a hyperbaric chamber and adjusted to a rate of approximately 10 breaths/min, tidal volume of 1000 mL, and an inspiratory time of 1-2 s. Chamber pressure was then increased and output of the ventilator settings measured. The ventilators were grouped for evaluation into three functional groups: pneumatic time-cycled, pneumatic pressure-cycled, and volume-cycled (piston or bellows). RESULTS: Function of the ventilators was consistent within each group, with some minor exceptions; however, function var-ied between groups. Under the conditions of our study, the Oxford was the only currently available machine able to maintain rate, tidal volume, and inspiratory time under hyperbaric compression. CONCLUSIONS: The choice of a mechanical ventilator for use in a hyperbaric environment should be made carefully. Ven-tilator function may deviate from set levels during compression. A mechanical ventilator specifically developed for the hyperbaric environment is needed.

BACKGROUND: Numerous mechanical ventilators are presently available—some have never been evaluated for imposed work of breathing (WOBᵢ), and some have not been evaluated for WOBᵢ subsequent to being upgraded by the manufacturer. In this study, we evaluated the WOBᵢ of a free-standing CPAP system at 0 and 10 cm H₂O CPAP and of 9 mechanical ventilators at 0 cm H₂O PSV, 0 cm H₂O CPAP; 0 cm H₂O PSV, 10 cm H₂O CPAP; 10 cm H₂O PSV, 0 cm H₂O CPAP; and 10 cm H₂O PSV, 10 cm H₂O CPAP. METHODS: All evaluations were performed using a 2-chamber lung model powered by a Bear 5 ventilator set at Vᴛ 300 mL, V ˙ max 20 L/min; Vᴛ 400 mL, V ˙ max 40 L/min; and Vᴛ 500 mL, < L/min. RESULTS: Minimal WOBᵢ was measured at 0 cm H₂O PSV, 0 cm H₂O CPAP; 10 cm H₂O PSV, 0 cm H₂O CPAP; and 10 cm H₂O PSV, 10 cm H₂O CPAP. Markedly elevated WOBᵢ was measured (with most systems) at 0 cm H₂O PSV, 10 cm H₂O CPAP. All demand systems produced low levels of PSV (1.5-5 cm H₂O), even when the PSV lev-el was set at 0 cm H₂O. CONCLUSIONS: If properly maintained, most ventilator demand-valve systems impose minimal WOB that can be essentially eliminated by using 10 cm H₂O PSV. The addition of CPAP increases WOBᵢ, as does the use of a bubble-through humidifier. The free-standing CPAP system outperformed most ventilator demand-valve systems when a PEEP valve with minimal flow resistance was used and appropriate continuous flows were set.

BACKGROUND: The health occupations and management literature does not specifically address role stress among technical directors of respiratory care departments. We undertook an analysis of role conflict, role ambiguity, and job satisfaction among technical directors of respiratory care departments in Texas. METHODS & MATERIALS: We distributed a questionnaire designed to measure role conflict and ambiguity and a questionnaire to elicit demographic and organization data to 283 technical directors in all Texas hospitals with more than 75 beds. Organization characteristics and demographic factors were studied as moderators. RESULTS: Analysis of the 199 responses received revealed that both role conflict (mean [SD] 3.86 [0.97] on 7.0 scale) and role ambiguity (2.64 [0.93] on 7.0 scale) scores were low compared to the neutral point of measure. Role overload, a component of role conflict, was found to be above the neutral point (4.64 [1.85]). One-way analysis of variance revealed no significant differences between the role conflict or the role ambiguity measures based on age, race, gender, number of employees supervised, size of institution, and position to which the respondent reported. Role conflict and role overload were each found to have significant negative correlations with job satisfaction (p < 0.01). CONCLUSION: We are encouraged by the low role-conflict and ambiguity scores observed but concerned about the elevated role-overload scores. We believe that an in-depth study of role overload among respiratory care managers is warranted.

We evaluated the use of end-tidal PCO₂ (Petco₂) as an indication of changes in Paco, in 24 adult patients being weaned from mechanical ventilation following cardiac surgery. METHODS: Patients were weaned by synchronous intermittent mandatory ventilation (SIMV) and T-piece trials. After each change in the weaning process (SIMV rate, T-piece trial), arterial blood gases were obtained from an indwelling catheter, and the Petco, and respiratory rate were recorded. All patients were hemodynamically stable, and all pulse oximeter saturations were ≥ 90% throughout the weaning period. A total of 113 data sets were collected. RESULTS: The correlation between Paco, and Petco, was r = 0.82, although the Paco, overestimated the Petco, by 4.0 ± 3.7 torr. There was no significant difference between changes in Paco, and changes in Petco, (p = 0.63). However, in 43% of cases the change in Petco, incorrectly indicated the direction of change in Paco, When Pco, changes of ≥ 5 torr occurred, Petco, incorrectly indicated the direction of change in 30% of the cases. The respiratory rates displayed by the capnograph (15 ± 5/min) were similar to the patients' actual respiratory rates (16 ± 5/ min). CONCLUSIONS: Although changes in Petco, were not statistically different from changes in Paco, Petco, did not precisely indicate changes in Paco, during weaning from mechanical ventilation following cardiac surgery. Based on these results, we do not recommend the routine use of Petco, as a noninvasive indicator of Paco, during weaning from mechanical ventilation following cardiac surgery.

We conducted this study to compare the quantity of secretions removed with a closed-circuit suction catheter (Ballard Trach-Care) to that removed with a conventional suction catheter. METHODS: Adult patients receiving chest physiotherapy at 4- or 6-hour intervals were studied. For two consecutive treatments, they were suctioned with a Ballard catheter during one treatment and with a conventional catheter during the other treatment. The order was randomly assigned, and both catheters were used on the same shift. A suction pressure of 120 torr and size 14-Fr catheters were used. All sputum obtained during each treatment was collected in a Luken's trap, and the mass of the secretions was determined with an O-Haus Cent-O-Gram balance. Twenty-eight comparisons of results with the two catheters were made in 25 patients (16 men, 9 women, median age 59 yr, median 8 days of intubation). The median PEEP was 3 cm H2O (range 0-10); the median Fio, was 0.45 (range 0.30-0.80). RESULTS: There was no significant difference between the quantities of secretions removed with the Ballard closed-circuit catheter (median 1.7 g) and with the conventional catheter (1.9 g) (p = 0.88). CONCLUSIONS: The results of this short-term study suggest that the Ballard catheter removes secretions as effectively as does a conventional catheter. Further work is needed to evaluate the Ballard's effectiveness during prolonged use and the cost of using the Ballard versus a conventional suction catheter.

BACKGROUND: Lectures and demonstrations have been the teaching and testing strategies most often employed by the American Heart Association in Advanced Cardiac Life Support (ACLS) training. I compared the abilities of interactive videodisc (IVD) courseware and ACLS instructors to evaluate airway management skills. METHODS & MATERIALS: Twenty-two subjects were simultaneously tested during 30 attempts at endotracheal (ET) intubation and 34 attempts at esophageal obturator airway or esophageal gastric tube airway (EOA/EGTA) insertion. The instructors were blind to the visual and auditory messages produced. RESULTS: The IVD program and the ACLS instructors showed high agreement in their evaluation of student performance for time of intubation (95.5% ET; 100% EOA/EGTA), proper tube placement (91% ET; 93% EOA/EGTA), appropriate tube assessment (95.5% ET; 100% EOA/EGTA), and correct EOA/EGTA cuff inflation (100%). Lower levels of agreement were noted with ET and EOA/EGTA appropriate head positioning, and the evaluation of tooth pressure with ET intubation (60.5%, 76.5%, and 66.0%, respectively). The IVD system was unable to detect certain procedural errors associated with appropriate intubation procedure-syringe attachment, syringe removal after cuff inflation, and control of tube after intubation. The low agreement for tooth pressure suggests that the sensor-equipped manikin may better evaluate tooth pressure than does the observer. CONCLUSIONS: Although the IVD system shows promise as an adjunct method for instruction and testing, it cannot be considered suitable for 'stand-alone' instruction. Further research is needed to explore costs, skills retention, and possible impact of the medium for training hospital and prehospital-care personnel.