Respiratory Care

Aerosolized albuterol is commonly used in the treatment of neonatal respiratory illnesses. Clinical and in vitro studies have identified numerous factors that affect aerosol drug delivery during neonatal mechanical ventilation, including the choice of metered-dose inhaler (MDI) or nebulizer, the use of a holding chamber, time between actuations, the volume of nebulized solution, and the position and placement of the nebulizer or MDI. Because there is no consensus on the optimal method of administration, there is probably substantial variability among institutions in how aerosolized albuterol is administered to mechanically ventilated infants in the neonatal intensive care unit (NICU). OBJECTIVE: Survey academic medical centers in the United States regarding their practices of administering aerosolized albuterol to intubated newborns in the NICU. METHODS: A survey instrument was developed that queried 18 aspects of albuterol administration in mechanically ventilated infants, including the frequency of MDI and nebulizer use, the average and maximum dose, the time between MDI actuations and following the final actuation, the use of a holding chamber, and the placement location of the holding chamber or nebulizer. Respiratory therapists and respiratory therapy managers having direct knowledge of neonatal clinical practices in their neonatal fellowship program NICUs were surveyed via telephone. Those who did not respond via telephone were surveyed via fax. RESULTS: Eighty institutions were surveyed and there were 68 respondents (85% response rate). Responders averaged 35 ± 13 NICU beds and 11 ± 5 ventilators/d. Nineteen percent of the respondents reported administering albuterol via MDI 100% of the time; 22% use MDIs 75-99% of the time; 9% use MDIs 50-74% of the time; 4% use MDIs 25-49% of the time; and 43% never use MDIs to deliver albuterol. The average dose via MDI was: 1 puff: 30%; 2 puffs: 65%; and 4 puffs: 5%. The maximum dose via MDI was: 2 puffs: 30%; 3 puffs: 14%; 4 puffs: 36%; 6 puffs: 11%; and 8 puffs: 6%. Thirty-one percent of the respondents place the holding chamber in-line with the ventilator circuit, 56% administer the aerosol via manual ventilation, and 13% use both methods. Fifty-six percent place the in-line holding chamber between the endotracheal tube and ventilator circuit, and the other 44% place the in-line holding chamber in the inspiratory limb. The time between MDI actuations depended on whether the holding chamber was placed in-line or the aerosol was administered via manual ventilation (MV): ≤ 0.5 min: 18% in-line and 28% MV; 1 min: 47% in-line and 43% MV; 2 min: 6% in-line and 4% MV; 3 min: 6% in-line and 0% MV. Eighty-three percent of respondents indicated that dead space introduced by a holding chamber/spacer was not a concern. Forty-three percent use nebulizers exclusively to administer albuterol to mechanically ventilated patients. Seventy-four percent of centers that nebulize albuterol use a dose of 1.25-2.5 mg. Eighty-eight percent of the surveyed institutions place nebulizers in-line with the ventilator circuit, and the other 12% use manual ventilation to administer the nebulized aerosol. Of those that use in-line nebulization, 95% place the nebulizer in the inspiratory limb of the circuit, and the other 5% place the nebulizer between the endotracheal tube and circuit Y-piece. Among centers that place the nebulizer in the inspiratory limb, 52% place it adjacent to the circuit Y-piece, 36% place it midway upstream in the inspiratory limb, and 12% place it near the humidifier. CONCLUSION: There is substantial variability among NICUs in albuterol administration to mechanically ventilated infants, with the majority of institutions now administering albuterol via MDI.

BACKGROUND: Partial liquid ventilation improves lung mechanics and gas exchange in paralyzed mechanically ventilated animals. OBJECTIVE: Examine the work of breathing (WOB) in a spontaneously breathing animal model during partial liquid ventilation with and without the use of pressure-support ventilation (PSV). METHODS: This was a prospective study including 6 lambs (mean weight 10.9 ± 1.3 kg). Baseline measurements, including total work of breathing (WOBT), elastic work of breathing (WOBE), and resistive work of breathing (WOBR), were obtained using pressure-controlled synchronized intermittent mandatory ventilation with positive end-expiratory pressure of 5 cm H2O at PSV levels of 0, 5, and 10 cm H2O. The animals' lungs were filled with perflubron through an endotracheal tube, in 10-20 mL aliquots, until filled, approximately 30 mL/kg or functional residual capacity. Repeat measurements were obtained at 10 mL/kg, 20 mL/kg, and full. Perflubron was then allowed to evaporate from the lungs and repeat measurements were obtained 3 additional times, with at least a 1 hour separation between phases, for up to 7 hours after the lungs were filled. RESULTS: No differences were detected in WOBT, WOBR, or WOBE between the gas-filled lung and the lung filled to functional residual capacity with perflubron. However, compared to the gas-filled lung, WOBT and WOBR were higher during the filling (p < 0.05) and evaporative phases (p < 0.05). The PSV level affected WOB. Work of breathing was least at PSV 10 cm H2O. CONCLUSION: In this pilot study of healthy animals breathing spontaneously with perflubron-filled lungs, there was an acceptable amount of WOB, which decreased with the addition of PSV. However, WOB increased when the perflubron level was not maintained at functional residual capacity.

INTRODUCTION: Motion artifact and low perfusion often lead to faulty or absent pulse oximetry readings in clinical practice. OBJECTIVE: Determine the impact of motion artifact and low perfusion on newly introduced pulse oximetry technologies during hypoxemic episodes in healthy volunteers. METHODS: Five different pulse oximeters from 4 manufacturers (the Datex Ohmeda 3900P; the Agilent; the Nellcor N-3000; the Nellcor N-395; and the Schiller OX-1, which is the European version of the Ivy SatGuard 2000 with Masimo SET) were compared with respect to their ability (separated or in combination) to provide accurate readings in the presence of motion artifact and low perfusion. Four of these oximeters represent the latest available oximetry technology, and one (the N-3000) represents a previous generation of oximeters. Oxygen saturation values (Spo₂) and pulse rate from the oximeters were recorded during episodes of induced hypoxemia in 10 healthy volunteers. Standardized and repeatable motion artifacts were generated by a motion machine and by having the test subject perform tapping and scratching motions. Perfusion to the finger was reduced by an inflatable balloon impinging on the brachial artery. The pulse oximetry readings from the test oximeters were compared to readings from control pulse oximeters on the unperturbed reference hand. The pulse rates from the test oximeters were compared to the electrocardio-graphically-measured heart rate. RESULTS: The frequency of faulty readings was increased by increasing motion interference and decreasing perfusion. The Spo, deviation was within ± 3% of the reference reading > 95% of the time for all instruments during the control desaturation period in the absence of motion and with normal perfusion. With the combination of motion and low perfusion, the Spo, error was within ± 3% less than 62% of the time for all oximeters tested. A significant difference in the frequency of large Spo, errors was observed only in the direct comparison of the N-395 and N-3000. The N-395 exhibited less frequent Spo, error exceeding 6% of Spo₂ in the combination of the most challenging situations (motion and motion with reduced perfusion). In the same situation the Datex-Ohmeda 3900P and Nellcor N-3000 showed significantly higher pulse rate errors than the other devices (Datex-Ohmeda 3900P 53% of the time and N-3000 37% of the time). CONCLUSIONS: The established model of creating motion artifact and low perfusion is capable of simulating a hierarchy of severe clinical situations. With solely motion or solely reduced perfusion the percentage of errors exceeding ± 3% of Spo, increased by 20% and 10%, respectively, compared to the control period. Simultaneous presence of motion and reduced perfusion leads to a relative incidence of > 35% of errors > 3% of Spo, for the various oximeters. In this situation the N-3000 and the Datex-Ohmeda 3900P exhibited differences between estimated pulse rate and electrocardiographically-measured heart rate > 25 beats/min > 37% of the time.

The unique electromagnetic environment of the magnetic resonance imaging (MRI) scanner presents particular problems for critically ill patients requiring mechanical ventilation during MRI. Most currently available MRI-compatible ventilators are limited in scope and function and thus may not be suitable for patients requiring high peak inspiratory pressure or flow. METHODS: To determine whether a standard critical care ventilator could be used under MRI conditions, we modified a Siemens Servo 900C by replacing the standard oxygen blender with an MRI-compatible blender. We then calibrated the ventilator and tested it on a mechanical lung during active MRI scanning at magnetic fields up to 1.5 tesla. After verifying adequate function, we used the ventilator to support 21 critically ill patients requiring mechanical ventilation during MRI. RESULTS: In all cases we found no alterations in ventilator performance resulting from the electromagnetic interference typical of an MRI scan. We also found no abnormalities in the alarm systems for fraction of inspired oxygen, high inspiratory pressure, or minute volume. Finally, we found no degradation of MRI image quality resulting from ventilator operation during test scanning. CONCLUSIONS: We conclude that with minor modifications the Siemens 900C ventilator can safely ventilate critically ill patients during MRI.

A 7-year-old girl presented to the pediatric intensive care unit following a craniotomy that left her with dysphagia, poor cough, and problems with retained secretions. Pulmonary function and blood oxygen saturation worsened for 3 days after surgery. Noninvasive positive-pressure ventilation and increased fraction of inspired oxygen improved oxygenation. Glycopyrrolate was administered to decrease secretions but had little effect. The first chest radiograph showed left lung hyperinflation. The right lung showed loss of volume and elevation of the right hemidiaphragm. There was no mediastinal shift. Another chest radiograph 3 hours later showed substantial improvement. We discuss the causes of acute lung volume asymmetry and possible interpretations of the radiographs.