A physiologic approach to initiating, maintaining, and withdrawing mechanical ventilatory support during acute respiratory failure

The impact of long-term acute-care facilities on the outcome and cost of care for patients undergoing prolonged mechanical ventilation

OBJECTIVES

To compare the 6-month mortality rate of chronically ventilated patients treated either exclusively in a traditional acute-care hospital or transferred during hospitalization to a long-term acute-care facility. To analyze the hospital cost of care and estimate the amount of uncompensated care incurred by acute-care hospitals under the Medicare prospective payment diagnostic related groups system.

DESIGN

Retrospective chart review and questionnaire.

SETTING

Fifty-four acute-care referral hospitals and 26 longterm acute-care institutions.

PATIENTS

A total of 432 ventilated patients selected from 3,266 patients referred but not transferred to a study long-term acute-care facility and 1,702 ventilated patients from 4,174 patients referred and then subsequently transferred to the long-term acute-care facility. Six-month outcomes were determined for the subgroup of patients > or =65 yrs old (279 and 1,340 patients, respectively). Hospital charges were available for 192 of the 279 nontransferred patients who were > or =65 yrs old and 1,332 of the 1,340 transferred patients.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The 6-month mortality rate was 67.4% for the 279 nontransferred patients and 67.2% for the 1,340 transferred patients. On multiple regression analysis, variables associated with the 6-month mortality rate included initial admitting diagnosis, age, the acute physiology score, and presence of decubitus ulcer. After controlling for these variables, there was no significant difference in 6-month mortality rate, but admission to the long-term acute-care facility was associated with a longer mean survival time. Average total hospital costs for the 192 nontransferred patients was $78,474, and estimated Medicare reimbursement was $62,472, resulting in an average of $16,002 of uncompensated care per patient. Estimated costs for the long-term acute-care facility admissions were $56,825.

CONCLUSIONS

Patients undergoing prolonged ventilation have high hospital and 6-month mortality rates, and 6-month outcomes are not significantly different for those transferred to long-term acute-care facilities. These patients generate high costs, and acute-care hospitals are significantly underreimbursed by Medicare for these costs. Acute-care hospitals can reduce the amount of uncompensated care by earlier transfer of appropriate patients to a long-term acute-care facility.

Hypercapnic respiratory failure in COPD patients: response to therapy

INTRODUCTION

The clinical course of patients with acute exacerbations of underlying COPD presenting with hypercapnic respiratory failure was reviewed.

METHODS

This was a retrospective review of 138 episodes of hypercapnic respiratory failure (PaCO(2) > or = 50 mm Hg and pH < or = 7.35). Patients were admitted to the West Los Angeles VAMC Medical Intensive Care Unit between 1990 and 1994.

RESULTS

Of the 138 hypercapnic episodes, 74 (54%) required intubation. Comparison was made with the 64 cases in which patients responded to medical therapy. Patients requiring intubation had a greater severity of illness, with a higher APACHE II (Acute Physiology and Chronic Health Evaluation II) score (18 +/- 5 vs 16 +/- 4; p < 0.01), higher WBC, higher serum BUN, and greater acidosis (pH, 7.26 +/- 0.07 vs 7.28 +/- 0.06; p = 0.08). Those with the most severe acidosis (pH < 7.20) had the highest intubation rate (70%) and shortest time to intubation (2 +/- 2 h), and they required the longest period of time to respond to medical therapy (69 +/- 60 h). With an initial pH of < 7.25, there was a consistently higher intubation rate. Conversely, those with an initial pH of 7.31 to 7. 35 were less likely to be intubated (45%), had a longer time to intubation (13 +/- 18 h), and had a more rapid response to medical therapy (30 +/- 18 h). Of those patients requiring intubation, most (78%) were intubated within 8 h of presentation, and the vast majority (93%) by 24 h. Of those patients responding to medical therapy, half (52%) recovered within 24 h and the vast majority (92%) recovered within 72 h.

CONCLUSIONS

This study provides a better characterization of the response to therapy of COPD patients with hypercapnic respiratory failure. This should be useful in limiting or omitting medical therapy in high-risk patients, thereby avoiding delays in intubation as well as providing a framework for continued therapy in those more likely to improve.

Re-engineering ventilatory support to decrease days and improve resource utilization

OBJECTIVE

The objective of this study was to describe the development of a cost-effective ventilatory strategy using a portable microprocessor-controlled respiratory monitor (Bicore CP-100; Allied Healthcare Products, Riverside, CA.)

SUMMARY BACKGROUND DATA

Until recently, clinicians have had to accept the uncertainties of clinical judgment, which unfortunately, often biased the patient to a prolonged ventilatory course to avoid extubation failures, necessitating reintubation.

METHODS

Over a 4-year period, the authors attempted to re-engineer the process of ventilatory support based on measured work of breathing (WOB), including physiologic (WOBPhys), imposed (WOBImp) and total (WOBTot).

RESULTS

The authors made 90 determinations of WOB in 31 patients. The coefficient of determination (i2) of WOBTot, with the breathing frequency was 0.35, with tidal volume was 0.10, and with the rapid shallow breathing index (f/V(tau)) was 0.23; therefore, the authors discarded them as reliable inferences. Of 27 patients ventilated for > 2 days with satisfactory blood gases, but with breathing frequency > 30 breaths/minute, 6 had WOBTot < 0.8 J/L and were extubated successfully. In 21 patients, WOBTot was elevated to 1.6 +/- 0.83 J/L, WOBImp was 1.1 +/- 0.64 J/L, approximately twice the WOBPhys (0.5 +/- 0.26 J/L), a normal value. Extubation was successful in 20 of those 21 patients. This approach was extended to the spontaneous breathing pre-extubation trial. In addition, the ventilator was adjusted so that the patient sustained a WOBTot of 0.6 to 1 J/L during the ventilatory support. This evolution was tracked for 18 months in a series of 838 trauma intensive care unit patients. Average duration of ventilation decreased from 8.2 to 4.2 days (49%; p < 0.01). This translated into approximately 2400 decreased ventilator days per year.

CONCLUSION

Objective measurement to guide the adequacy of ventilatory support and interpret apparent clinical weaning failures decreased total ventilatory time by 50%, permitting extubation in nearly 20% of patients previously considered failures.

Acute respiratory distress syndrome

The acute respiratory distress syndrome (ARDS) is a serious and complex clinical problem that often threatens the lives of patients. Emerging clinical data suggest that the survival of patients with this disorder may have improved during the last two decades, presumably because of advances in supportive medical care. Among the supportive therapies used to treat patients with ARDS, none is more complex than mechanical ventilation. New strategies for administering mechanical ventilation to patients with ARDS may reduce the occurrence of iatrogenic volotrauma and oxygen toxicity, accounting in part for the recently observed improvements in patient survival. Prevention and cure of ARDS have remained elusive goals because of the lack of specific therapies directed against the known pathogenic factors. Ongoing investigations are aimed at identifying specific therapies to interrupt the mechanisms of inflammation and lung injury responsible for this syndrome. Until such therapies become available, clinicians caring for patients with ARDS should attempt to minimize additional morbidity and mortality resulting from nosocomial infections and iatrogenic injuries.

Initiation of mechanical ventilation in the emergency department

Mechanical ventilation is frequently initiated by emergency physicians. Further, the physician on duty in the emergency department is frequently responsible for evaluating ventilated patients who decompensate in the intensive care unit when other physicians are not present in the hospital. A bewildering array of features on new mechanical ventilators has made their appropriate and effective use increasingly complex. Knowledge of the pathophysiology of acute respiratory failure and changes in lung physiology during positive pressure ventilation will aid the emergency physician in choosing an appropriate ventilator modality and initial settings to maximally benefit patients with respiratory insufficiency due to various causes. An appreciation of the adverse effects of mechanical ventilation and problems commonly encountered in patients on ventilators will prepare the emergency physician to rapidly assess and effectively manage the patient who deteriorates in this setting.

Noninvasive pressure support ventilation in patients with acute respiratory failure. A randomized comparison with conventional therapy

The benefit of noninvasive pressure support ventilation (NIPSV) in avoiding the need for endotracheal intubation and reducing morbidity and mortality associated with endotracheal intubation was evaluated in 41 patients who presented with acute respiratory failure not related to chronic obstructive pulmonary disease (COPD). Patients were randomly assigned to receive conventional therapy (n = 20) or conventional therapy plus NIPSV (n = 21). NIPSV was delivered to the patient by a face mask connected to a ventilator (Puritan-Bennett 7200a) set in inspiratory pressure support (IPS) mode. The mean levels of IPS, positive end-expiratory pressure (PEEP), and fraction of inspired oxygen (FIO2) were respectively 15 +/- 3 cm H2O, 4 +/- 2 cm H2O, and 57 +/- 22%. The rate of endotracheal intubation (62 vs 70%, p = 0.88), the length of ICU stay (17 +/- 19 days vs 25 +/- 23 days, p = 0.16), and the mortality rate (33 vs 50%, p = 0.46) were not different between patients treated with NIPSV and those treated conventionally. Post hoc analysis suggested that in patients with PaCO2 > 45 mm Hg (n = 17), NIPSV was associated with a reduction in the rate of endotracheal intubation (36 vs 100%, p = 0.02), in the length of ICU stay (13 +/- 15 days vs 32 +/- 30 days, p = 0.04), and in the mortality rate (9 vs 66%, p = 0.06). We conclude that NIPSV is of no benefit when used systematically in all forms of acute respiratory failure not related to COPD. A subgroup of patients, characterized by acute ventilatory failure and hypercapnia, may potentially benefit from this therapy and further studies are needed to focus on this aspect.

The acute respiratory distress syndrome

ARDS is a complex response of the lung to direct (inhalational) and indirect (hematogenous) insults. It is easy to be pessimistic about the benefit of the approaches we have described, but there is evidence that overall survival has improved in recent years. To maintain this progress, new therapies for ARDS must be rigorously evaluated, and their routine use should be recommended only after careful scrutiny of the evidence. Such a course will eliminate the unnecessary risks and costs often associated with unproved therapies.

Additive effect on gas exchange of inhaled nitric oxide and intravenous almitrine bismesylate in the adult respiratory distress syndrome

OBJECTIVE

To assess the additive effect of inhaled nitric oxide (NO) and intravenous almitrine bismesylate (ALM) on gas exchange.

DESIGN

Prospective self-controlled study.

SETTING

3 medico-surgical intensive care units.

PATIENTS

17 patients with severe hypoxemia (PaO2/FIO2 ratio: 88 +/- 30 mmHg, venous admixture: 47 +/- 7%) and elevated mean pulmonary artery pressure (MPAP: 30 +/- 5 mmHg) due to adult respiratory distress syndrome (ARDS).

INTERVENTIONS

5 conditions were studied: 1) baseline, 2) 5 to 10 ppm of NO during 30 min, 3) discontinuation of NO during 30 min, 4) ALM infusion (0.5 mg/kg) during 30 min, 5) ALM infusion (0.5 mg/kg) during 30 min in combination with 5 to 10 ppm of NO.

MEASUREMENT AND RESULTS

The PaO2/FIO2 ratio rose from 88 +/- 30 to 98 +/- 37 mmHg (NS) with NO alone, and from 92 +/- 25 to 130 +/- 56 mmHg (p < 0.01) with NO + ALM (p < 0.05 vs NO alone). Seven patients were considered as "NO-responders" (rise in PaO2/FIO2 ratio of 10 mmHg or more with NO); in this subgroup the PaO2/FIO2 ratio rose from 87 +/- 30 to 128 +/- 39 mmHg (p < 0.05) with NO alone, and from 93 +/- 20 to 169 +/- 51 mmHg (p < 0.01) with NO + ALM (p < 0.05 versus NO alone). MPAP decreased from 30 +/- 5 to 26 +/- 5 mmHg (p < 0.01) with NO alone, increased slightly from 28 +/- 5 to 31 +/- 5 mmHg (NS) with ALM alone and decreased to 27 +/- 5 mmHg (p < 0.05) with NO + ALM.

CONCLUSIONS

NO + ALM had additive effects on gas exchange while decreasing MPAP in patients with ARDS. The effects of NO alone were small and non significant, except in a subgroup of 7 patients in whom the combination of both therapies had the more pronounced results.

Noninvasive pressure support ventilation in patients with acute respiratory failure

To further delineate indications for noninvasive pressure support ventilation (NIPSV), we proposed this noninvasive technique as an alternative to endotracheal intubation in 17 consecutive patients with acute respiratory failure from various causes. Eight patients (47 percent) were successfully ventilated with NIPSV, while in 9 (53 percent), NIPSV failed. Gas exchange values before initiating NIPSV were different between the 2 groups: patients successfully ventilated with NIPSV had a higher PaCO2 (57 +/- 15 mm Hg vs 37 +/- 17 mm Hg; p = 0.01), a lower pH (7.33 +/- 0.03 vs 7.45 +/- 0.08; p = 0.02), and a lower alveolo-arterial oxygen pressure difference (P[A-a]O2) (144 +/- 46 mm Hg vs 265 +/- 18 mm Hg; p = 0.01), suggesting that CO2 retention without major hypoxemia is a better indication for NIPSV than severe hypoxemia alone. Acute respiratory failure occurring after extubation seemed to be a good indication for NIPSV, with an 83 percent rate of success. In both groups of patients, gas exchange improved after 1 h on NIPSV, but such values were not improved on the first day in patients who failed with NIPSV.

Facilitation of mechanical ventilation in status asthmaticus with continuous intravenous thiopental

Mechanical ventilation in status asthmaticus is associated with a significant mortality and morbidity. To facilitate intermittent positive pressure ventilation (IPPV), we have used continuous IV thiopental (thiopentone) together with traditional ventilatory techniques. With this policy, we were able to achieve rapid correction of arterial blood gas tensions in a group of 20 severe asthmatics requiring IPPV. By 1 hour, peak airway pressure (PAP) had fallen from 58.6 +/- 15.7 to 30.2 +/- 10.9 cm H2O (p less than 0.001). During the same period, PaCO2 fell from 51.3 +/- 15.3 to 40.17 +/- 8.2 mm Hg (p less than 0.05) and pH rose from 7.25 +/- 0.1 to 7.33 +/- 0.1 (p less than 0.001). Morbidity was low and in particular, no episode of barotrauma was noted. All patients survived the acute attack and were successfully liberated from the ventilator. We conclude that these results are largely attributable to our use of early and continuous IV anesthesia induced by thiopental.