Biomedical subjects

C B DeHaven

Publications and source records attributed to C B DeHaven.

10 recordsLinked to original sources

PubMed1996

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.

Adult↗

PubMed1996

Breathing measurement reduces false-negative classification of tachypneic preextubation trial failures.

OBJECTIVES: There is increased awareness of imposed work of breathing contributing to apparent ventilatory dependency. This study evaluates the impact of tachypnea as an indicator of ventilatory failure during a room air-5 cm H2O continuous positive airway pressure, spontaneous breathing, preextubation trial when associated with increased imposed work of breathing. DESIGN: Prospective, descriptive, 1-yr data collection. SETTING: University hospital trauma intensive care unit (ICU). PATIENTS: Mechanically ventilated trauma ICU patients surviving to discharge. INTERVENTION: Patients were weaned to minimal mechanical ventilator support and underwent a 20-min room air-continuous positive airway pressure preextubation trial (FIO2 = 0.21, continuous positive airway pressure = 5 cm H2O [0.5 kPa]). When passed (PaO2 >/= 55 torr [>/= 7.3 kPa], PaCO2 </= 45 torr [</= 6.0 kPa] with prior eucapnea, arterial pH >/= 7.35, respiratory rate </= 30 breaths/min), extubation followed. If patients failed due to hypoxia, ventilatory support resumed. If tachypnea was the reason for failure, work of breathing was measured. If patient work of breathing was </= 1.1 joule/L, extubation proceeded despite tachypnea. If patient work of breathing was > 1.1 joule/L, imposed work of breathing was measured, and if residual "physiologic" work of breathing (patient work of breathing minus imposed work of breathing) was </= 0.8 joule/L, patients were extubated. MEASUREMENTS AND MAIN RESULTS: Of 589 extubations, 105 (18%) were classified as false negatives based on a preextubation rate of > 30 breaths/min. Of these, 97 were successfully extubated despite tachypnea ranging from 32 to 56 breaths/min, when combined with either a patient work of breathing </= 1.1 joule/L or physiologic work of breathing </= 0.8 joule/L. The rate of extubation failure within 72 hours was 7.8% (8/105) in the tachypneaic group, compared with 7.9% (38/484) for those patients with a respiratory rate of </= 30 breaths/min. Some of the stimulus for the tachypnea was possibly due to increased imposed work of breathing, as the increased respiratory rate usually abated within 18 hrs after extubation. The reliance on a respiratory rate of </= 30 breaths/min as an absolute preextubation criterion would have resulted in a sensitivity of 82%, a specificity of 17%, a positive predictive value of 92%, a negative predictive value of 8%, and an overall accuracy of 77%. The average duration of mechanical ventilation during the study period decreased by 2 days, from 8.6 to 6.3 days (p=.03). CONCLUSIONS: Tachypnea as a marker of respiratory distress is sensitive, but is not sufficiently specific to be used as a criterion in preextubation trials. Reliance on tachypnea as a preextubation trial failure criterion is likely to prolong intubation and ventilatory support for a large number of patients. Patient risks, determined by the extubation failures and reintubation rate, are the same.

Adolescent↗

PubMed1995

Elevated imposed work of breathing masquerading as ventilator weaning intolerance.

OBJECTIVE: To test the hypothesis that, if apparent ventilatory insufficiency observed during a weaning or preextubation trial is due to a significant contribution of imposed work of the endotracheal tube and breathing apparatus (WOBImp), and the patient's actual physiologic work of breathing (WOBPhys) is not excessive, it should be possible to extubate these patients safely. DESIGN: Prospective descriptive study. SETTING: University hospital trauma intensive care unit. PATIENTS: A total of 28 (17% of all ventilated patients) adults intubated for 48 h or longer, who developed tachypnea (40 +/- 9 breaths/min) but whose blood gas exchange met predefined extubation criteria, were evaluated over a 3-month period. INTERVENTIONS: Using a microprocessor-based monitor (Bicore Monitoring Systems Inc, Irvine, Calif) total patient work of breathing (WOBTOT) was determined by integrating the change in intraesophageal pressure with tidal volume measured with a miniature pneumotachograph positioned at the airway opening. If the patient's WOBTOT was equal to or greater than 0.8 J/L, WOBImp was determined by integrating the changes in carinal pressures with tidal volume. If neither the patient's WOBTOT or WOBPhys was excessively greater than that of spontaneous breathing at rest (ie, < 0.8 J/L: normal range, 0.5 to 0.6 J/L), the patient was extubated. MEASUREMENTS AND RESULTS: Breathing frequency, peak inspiratory flow rate (PIFR), auto-Peep (PEEPa), dynamic compliance (CDXN) WOBTOT, WOBImp, resistance to expiratory airway flow (RAWE) were measured, and WOBPhys calculated (WOBTOT) minus WOBImp). The means and SDs were calculated, and data were analyzed by unpaired t test and linear regression. Six patients (5%) were found to have WOBTOT of < 0.8 J/L and were successfully extubated without determination of WOBImp. Twenty-one patients were found to have an elevated WOBTOT (1.6 +/- 0.83 J/L), and had WOBImp measured. In these 21 patients, WOBImp (1.1 +/- 0.64 J/L) was twice WOBPhys (0.5 +/- 0.26 J/L). Extubation was successful in 20 of 21 patients in which WOBPhys was determined not to be excessive (ie, < 0.8 J/L). The last patient had an elevated WOBPhys (1.4 J/L) and was not extubated until his disease improved later. Overall, reintubation rate was 4%. CONCLUSIONS: Increased WOBTOT may be misinterpreted as a patient failure (ie, tachypnea) and weaning halted or extubation not done, prolonging intubation. The ability to measure the contribution of WOBImp to WOBTOT can identify those patients who may be safely extubated when WOBphys (WOBTOT minus WOBImp) is acceptable and the apparent ventilatory insuffiency is related to significant WOBImp.

Adult↗

PubMed1995

Breathing frequency and pattern are poor predictors of work of breathing in patients receiving pressure support ventilation.

OBJECTIVE: To evaluate the relationships between directly measured work of breathing (WOB) and variables of the breathing pattern commonly used at the bedside to infer WOB for intubated, spontaneously breathing patients treated with pressure support ventilation (PSV). DESIGN: In vivo measurements of the WOB were obtained on a consecutive series of adults. Breathing frequency (f), tidal volume (VT), the index of rapid, shallow breathing (f/V T), the duration of respiratory muscle contraction expressed as the ratio of inspiratory time over total respiratory cycle time (TI/TTOT), and a breathing pattern score (applied to approximately 50% of the patients) which ranks f, VT, sternocleidomastoid muscle activity, substernal retraction, and abdominal paradox on a scale were variables of the breathing pattern were also measured. The greater the breathing pattern score, the lower the WOB and vice versa. SETTING: Surgical ICUs in two university teaching hospitals. PATIENTS: Sixty-seven adults (42 men and 25 women, aged 20 to 78 years) who had acute respiratory failure from various etiologies were studied. All patients were breathing spontaneously receiving continuous positive airway pressure and PSV. INTERVENTIONS: Intraesophageal pressure (indirect measurement of intrapleural pressure) was measured with an esophageal balloon integrated into a nasogastric tube. VT was obtained by positioning a flow sensor between the "Y" piece of breathing circuit and the endotracheal tube. Data from these measurements were directed to a bedside respiratory monitor (Bicore; Allied Healthcare Products; Riverside, Calif) that calculates WOB using the Campbell diagram. Patients received PSV at levels deemed reasonable to unload the respiratory muscles. All measurements were obtained after 15 to 20 min at each level of PSV, averaged over 1 min, and then variables of the breathing pattern were regressed with directly measured values for WOB. RESULTS: All breathing pattern variables poorly predicted WOB as evidenced by the low values for the coefficients of determination (r2). Breathing frequency correlated positively with WOB (r = 0.47, p < 0.001) and predicted or explained only 22% (r2 = .22) of the variance in WOB. VT correlated negatively and f/VT and TI/TTOT each correlated positively with WOB. However, these variables predicted only 20 to 27% of the variance in WOB. The breathing pattern score correlated negatively with WOB and predicted only 43% of the variance in WOB. A prediction model taking all variables into consideration using multiple regression analysis predicted only 50% of the variance in WOB; thus, it too was a poor to moderate predictor of WOB. CONCLUSION: Our data reveal that WOB should be measured directly because variables of the breathing pattern commonly used at the bedside appear to be inaccurate and misleading inferences of the WOB. The clinical implication of these findings involves the traditional and empirical practice of titrating PSV based on the breathing pattern. We do not imply that the patient's breathing pattern should be ignored, nor undermine its importance, for it provides useful diagnostic information. It appears, however, that relying primarily on the breathing pattern alone does not provide enough information to accurately assess the respiratory muscle workload. Using the breathing pattern as the primary guideline for selecting a level of PSV may result in inappropriate respiratory muscle workloads. A more comprehensive strategy is to employ WOB measurements and the breathing pattern in a complementary manner when titrating PSV in critically ill patients.

Adult↗

PubMed1987

The role of high-frequency ventilation in post-traumatic respiratory insufficiency.

Post-traumatic pulmonary insufficiency or the adult respiratory distress syndrome is not infrequently associated with multiple organ-system injury. Mortality presently approaches 50%. Mechanical ventilation (CMV) with continuous positive airway pressure (CPAP) remains the mainstay of therapy. High peak inspiration (PIP) and mean airway (PAW) pressure in association with the delivery of large, conventional mechanical breaths are major determinants of complications. The efficacy of HFV was evaluated in this patient population (45 patients, mean age, 32.7 +/- 14.4 years; range, 11-75). CMV was provided with a time-cycled ventilator delivering 12-15 cc/kg tidal volume and a mechanical rate adjusted to provide a PaCO2 38-42 torr for patients previously eucapneic. CPAP was titrated to achieve a preselected endpoint of an intrapulmonary shunt of less than equal to 15%. FIO2 was maintained at or below 0.45 whenever possible. The Trauma Index Score for the group was 8.8 +/- 2.4. CMV yielded a mechanical rate of 6.3 +/- 3.2 and a CPAP of 13.9 +/- 8.5 cm H2O. High-frequency ventilation was provided by either a solenoid-based jet ventilator (HFJV) or a pneumatic cartridge high-frequency pulse generator (HFPG). Measured and calculated hemodynamic and pulmonary variables were obtained prior to and 20 minutes after transition to HFV. Thirty-three patients received HFJV; 12 patients received HFPG. Data were evaluated with a paired t-test. All patients on HFJV demonstrated improved CO2 elimination with the same hemodynamic profiles. Those on HFPG demonstrated comparable gas exchange and hemodynamic profiles with lower CPAP/PIP. Where measured, PAW was significantly lower with HFPG when compared with CMV.

Adolescent↗

PubMed1986

Evaluation of two different extubation criteria: attributes contributing to success.

We evaluated extubation criteria in 48 postoperative general surgical and trauma patients receiving ventilatory support with intermittent mandatory ventilation (IMV) and continuous positive airway pressure (CPAP). Extubation criteria based on conventional respiratory mechanics demonstrated at 48% false-negative prediction of outcome, while those based on gas exchange values correctly predicted outcome in 94% of patients. Thus, conventional respiratory-mechanics extubation criteria may prolong mechanical airway and ventilatory support when used with IMV/CPAP in these patients.

Adolescent↗

PubMed1985

Comparison of conventional mechanical ventilation and synchronous independent lung ventilation (SILV) in the treatment of unilateral lung injury.

Eight patients presenting with severe unilateral pulmonary injury responded poorly to conventional mechanical ventilation. Synchronous independent lung ventilation (SILV) was employed to provide support of ventilation and oxygenation without creating the ventilation/perfusion (V/Q) mismatch observed during conventional ventilation. All patients demonstrated improved oxygenation (mean increase, 80 torr) during SILV with the FIO2 unchanged from previous therapy. Invasive hemodynamic monitoring in five of eight patients showed no difference in the commonly measured cardiopulmonary parameters with the two forms of mechanical ventilation. Peak inspiratory pressure (PIP), continuous positive airway pressure (CPAP), and pressure change secondary to tidal volume delivery to the uninvolved lung were significantly less during SILV. SILV is an effective method of improving oxygenation in patients with severe unilateral pulmonary injury.

Adolescent↗

PubMed1985

Use of CPAP mask as the sole mode of ventilatory support in trauma patients with mild to moderate respiratory insufficiency.

Thirty-three trauma patients presenting with hypoxemia and normo- or hypocarbia were treated with continuous positive airway pressure (CPAP) via a snug-fitting face mask. All patients had demonstrated continued hypoxemia despite supplemental oxygen administration before institution of CPAP therapy as the primary mode of ventilatory support. Therapeutic end-point of PaO2/FIO2 greater than 300 was achieved in 32 of 33 patients. Duration of CPAP treatment was 28 +/- 19 hours. Two patients (6%) required intubation, but neither for elevation in PaCO2. CPAP mask appears an effective means of support for mild to moderate post-traumatic respiratory insufficiency.

Adolescent↗

PubMed1984

Use of high frequency jet ventilation during mechanical hyperventilation to reduce intracranial pressure in patients with multiple organ system injury.

Eleven patients with multiple organ system injury, including significant closed head injury, all required positive end-expiratory pressure (PEEP) for treatment of their pulmonary pathological condition. Additionally, the need for intracranial pressure (ICP) monitoring had previously been established on clinical evaluation by the Neurosurgery Service. Seven of the 11 patients met the criteria for invasive hemodynamic monitoring. Hemodynamic monitoring data are supplied for these 7 patients. All patients, after the initial institution of conventional means of hyperventilation, were transitioned to high frequency jet ventilation (HFJV) to evaluate the effects of HFJV during mechanical hyperventilation. There was a statistically significant decrease in ICP (mean decrease of 7.2 mm Hg). There was also a statistically significant fall in PaO2 from 131 to 101 torr. This was not associated with an appreciable decrease in oxygen delivery. There was no change in cardiac output or intrapulmonary shunt fraction. It is concluded that successful control of ICP was possible in all cases without impairment of cardiac output, oxygen delivery, or cerebral perfusion pressure, even when the pulmonary abnormality required the use of PEEP.

Adolescent↗

PubMed1984

Adult respiratory distress syndrome: improved oxygenation during high-frequency jet ventilation/continuous positive airway pressure.

The role of high-frequency jet ventilation (HFJV)/continuous positive airway pressure (CPAP) and HFJV/intermittent mandatory ventilation (IMV) in the treatment of surgical patients with the adult respiratory distress syndrome were evaluated. To compare the efficacy of HFJV to IMV at a constant FiO2 and positive end-expiratory pressure, patients in surgical intensive care were randomized to receive IMV/CPAP therapy or one of three modes of HFJV: (1) HFJV/CPAP alone, (2) HFJV/CPAP + IMV (1), or (3) HFJV/CPAP + IMV (2). Each patient served as his own control. During comparison of HFJV/CPAP + IMV (1) to HFJV/CPAP + IMV (2) (n = 9) and HFJV/CPAP to HFJV/CPAP + IMV (1) (n = 7), cardiac output, PaCO2, PaO2, PvO2, and variables consisting of intrapulmonary shunt fraction (Qsp/Qt), PaO2/FiO2 ratio, and A-a gradient were calculated. The subgroup placed on HFJV/CPAP demonstrated a fall in PaO2 of 13 torr (p = NS; n = 5). HFJV/CPAP + IMV (1) compared with HFJV/CPAP significantly (p less than 0.005) increased PaO2 by 52 +/- 24 torr and decreased Qsp/Qt by 8.9 +/- 1.0 (p less than 0.025). Cardiac output remained unchanged. Comparison of HFJV/CPAP + IMV (2) to HFJV/CPAP + IMV (1) demonstrated a significant improvement in oxygenation (p less than 0.025), but of lesser magnitude (8.4 +/- 11 torr). PaO2/FiO2 ratio and A-a gradient improved in both IMV (1) and IMV (2) subgroups. Oxygenation and ventilation/perfusion (V/Q) matching significantly improved with HFJV/CPAP + IMV (1), to a greater magnitude than with HFJV/CPAP + IMV (2) or HFJV/CPAP alone, and was the preferred method of ventilatory support.

Humans↗