Respiratory Care

The cost-effectiveness of pulmonary artery catheterization (PAC) has been questioned in many clinical situations. We sought to assess the cost-effectiveness of PAC in patients with an acute exacerbation of chronic obstructive pulmonary disease (COPD) requiring mechanical ventilation.

We constructed a decision analysis model and calculated the incremental cost/quality-adjusted life-year (QALY) saved for hypothetical patients, comparing a PAC strategy to one of no PAC. Sensitivity analyses were performed to test the stability of conclusions over wide ranges of values.

The incremental cost/QALY saved in the cost-effectiveness analysis using baseline data is $77,407 when catheterization-driven therapeutic changes result in a 5% improvement in survival. Cost-effectiveness is sensitive to variations in post-hospital life expectancy, quality of life, and the probability of favorable therapeutic changes resulting from the use of catheterization data.

Pulmonary artery catheterization in COPD exacerbation requiring mechanical ventilation is expensive compared to accepted medical interventions for other conditions, unless changes in therapy prompted by catheterization increase hospital survival to a level 8.7% above baseline. Randomized, controlled trials are needed to investigate the economic impact of PAC and its effect on morbidity and mortality of critically ill patients.

Hospital inpatients frequently leave their rooms for diagnostic procedures and for other reasons. For some, interruption of oxygen therapy during transport could lead to serious complications. In our institution, non-ICU patient transport is done mainly by nonclin-ical personnel from an independent transport service.

We re-viewed respiratory care department and transport service records for 5 arbitrarily selected days to determine the number of non-ICU patients receiving O2 therapy, the number of times these patients were transported, and the number of occasions on which O2 was used during the transport. We then interviewed the primary nurse for each patient transported without O2 and reviewed the charts of those patients to determine whether this practice was consistent with the therapy as it had been ordered. After our initial investigation showed a high rate of transport without prescribed O2, we sent memoranda to all nursing units describing proper procedures for transport of patients for whom O2 had been ordered. We then repeated the audit. Because the second audit showed the need, we conducted education sessions with all nursing personnel on the affected units and posted guidelines for O2 use during transport. A third audit was then conducted. In addition, we performed a telephone survey of respiratory care department man-agers to learn the patient-transport practices in all hospitals in our state with more than 200 beds, using a structured questionnaire.

During the initial 125 patient-days of O2 therapy, O2 accompanied patients on only 30 of 55 transports (55%). After distribution of memoranda, O2 use increased to 28 of 35 transports (80%) during 82 patient-days. The second educational effort resulted in O2 use with all 35 transports (100%) performed during 99 pa-tient-days. Survey results from 24 hospitals with 225-680 beds showed that 11 (46%) had sepa-rate transport services and that decisions on O2 use during patient transport were generally made by nursing staff. Although respiratory care departments supplied the O2 equipment, their personnel were involved in non-ICU transports in only 5/24 hospitals.

Patients receiving O2 therapy on acute-care wards are often transported to other areas of the hospital without O2. This potentially dangerous practice can be corrected by respiratory care practitioners through educational efforts targeted toward those responsible for administering O2 therapy in non-ICU hospital areas.

High-frequency oscillatory ventilation (HFOV) has been used to treat diffuse alveolar disease in neonates. The SensorMedics 3100 oscillator provides for varying inspiratory time (%IT), but little evidence exists for the clinical utility of this option. Because %IT has important effects on lung volume (LV), tidal volume (VT), and blood gas values during conventional mechanical ventilation, it is important to know whether such effects are present when HFOV is used.

We studied 12 New Zealand White rabbits after saline lung lavage to determine the effects of varying %IT on a/A02, PaCO2, cardiac output (C.O.), and VT and to discover whether these effects were dependent on LV. Animals were randomized to high LV (HLV) or low LV (LLV) and placed in a body plethysmograph. HLV and LLV were defined as baseline LV (BLV) ±33%. We collected data at 33, 50, and 70 %IT using both BLV and LLV and BLV and HLV. We tested our hypotheses using analysis of variance with repeated measures.

No effect of varying %IT was dependent on LV (p > 0.05). At HLV, oxygenation (a/A_O2) was significantly higher (p = 0.006), whereas C.O. was lower (p = 0.04), across all %ITs. The effect of %IT on VT and PaCO2 was highly significant (p < 0.0005) across all LVs.

In a saline-lavaged rabbit model, the cardiorespiratory effects of using 33, 50, and 70 %IT are independent of LV.

Constant-pressure inflation (CPI) and constant-flow inflation (CFI) are widely used forms of mechanical ventilation applied to critically ill patients. The relative advantages of these two approaches to ventilation are controversial. The purpose of this study was to determine the theoretical factors that affect the distribution of volume in a mathemati-cal model of the lung.

We postulated a lung model composed of two parallel lung units. Analysis of model response was performed for step inputs of pressure (ie, CPI) and flow (ie, CFI) using the Laplace transform.

For lung units with equal impedances, both CPI and CFI result in equal distribution of volume between the two lung units and distribu-tion is not a function of time. For lung units with different impedances but equal time con-stants (t), the distribution of volume will depend only on the ratio of compliances or resis-tances for both modes of ventilation. For different t but equal resistances, CFI gives more uni-form volumetric expansion and possibly lower risk of barotrauma than CPI. For different t but equal compliances, CPI gives more uniform volumetric expansion and possibly lower risk of barotrauma than CFI.

We conclude that in the absence of auto-PEEP lung time constants are the primary factors that determine the distribution of volume between lung units and that the relative superiority of one ventilatory mode over another depends on the underlying lung pathology that dictates the components of the time constant.