Comparison of intratracheal pulmonary ventilation and hybrid intratracheal pulmonary ventilation with conventional mechanical ventilation in a rabbit model of acute respiratory distress syndrome by saline lavage

OBJECTIVES

To study changes in PaCO2 and PaO2 during intratracheal pulmonary ventilation (ITPV) and hybrid intratracheal pulmonary ventilation (h-ITPV) compared with conventional mechanical ventilation (CMV) in a rabbit model of respiratory failure, and to define the technique of h-ITPV that combines conventional mechanical ventilation and ITPV.

DESIGN

Prospective, interventional study.

SUBJECTS

Twelve adult New Zealand White rabbits.

INTERVENTIONS

Surfactant deficiency was induced by saline lavage, and rabbits were randomized to either ITPV or h-ITPV. The study consisted of four phases: phase 0, CMV after saline lavage, ventilator rate 30 breaths/min; phase I, ITPV or h-ITPV initiated at the same pressure and rate as in phase 0; phase II, ITPV or 1.0 L/min h-ITPV bias flow, with peak inspiratory pressure (PIP) decreased and ventilator rate increased to achieve the lowest tidal volume while maintaining adequate gas exchange; and phase III, animals returned to CMV.

MEASUREMENTS AND MAIN RESULTS

In phase I, no difference in PaCO2 was observed between ITPV, h-ITPV, or CMV. There was a decrease in PaO2 when switching from CMV to ITPV but not to h-ITPV. In phase II, it was possible to decrease PIP (average of 37% for ITPV and 36% for h-ITPV) and tidal volume (average of 64% for ITPV and 53% for h-ITPV) without compromising gas exchange (p < .05). Oxygenation tended to improve from phase 0 to the end of phase II. In phase III, PaCO2 increased (average of 71% for ITPV and 79% for h-ITPV) and pH decreased (p < .05). Normocapnia was achieved using significantly higher PIP and tidal volume, compared with phase 0 (p < .05).

CONCLUSIONS

ITPV and h-ITPV can effectively ventilate and oxygenate rabbits with surfactant-deficient lungs at tidal volumes and therefore pressures lower than required with CMV. Maximum benefit appears to occur at high ventilator rates. These findings suggest that both modes of ventilation may represent powerful new tools in the management of patients with acute respiratory failure. (Crit Care Med 2000; 28:774-781)

Definitive external irradiation in stages A (T1) and B (T2) carcinoma of the prostate

This is a retrospective review of records of 38 patients with clinical stage A (T1a,b), 131 with stage B1 (T2a), and 113 with B2 (T2b) histologically proven adenocarcinoma of the prostate treated with definitive irradiation. All patients have been followed for a minimum of 3 years (median follow-up: 6.5 years; maximum: 23 years). Patients were treated with high-energy photons (18-22 MV) with either 4,500 cGy to pelvic fields and a boost of about 2,000 cGy to the prostate or 6,600 cGy to the prostate and periprostatic tissues. Five patients with stage A1 (T1a) tumors had no failures. The local recurrence rate was 11% in stage T1b, 14% in T2a, and 17% in T2b tumors. Distant metastasis rates were 16% in patients with stage T1b, 20% in T2a, and 21% in T2b. The disease-free survival rate was approximately 70% at 5 years and 55% at 10 years in patients with stages T1b or T2, without significant differences among the various groups. The cause-specific survival was 90% at 5 years and 70% at 10 years in the various groups. The results are comparable to those reported in several surgical or radiation therapy series at various institutions. A significantly lower disease-free survival was observed in patients with poorly differentiated tumors (40% at 5 years) in comparison with those with well- and moderately differentiated tumors (80% DFS at 5 years) (p < .001). Likewise, the cause-specific survival was lower in patients with poorly differentiated tumors (75% at 5 years) than in the other patients (91%) (p = .0003). No difference in the local recurrence rates with various degrees of differentiation was noted. However, patients with poorly differentiated tumors had a greater incidence of distant metastasis (30%-40%) than patients with well or moderately differentiated lesions (10%-20%). Performance of transurethral resection also was associated with a higher incidence of distant metastasis (40%) in patients with stage B2 (T2b) tumors than in those diagnosed by needle biopsy (20%) (p = .12) but not in the other groups. Age, race, volume irradiated, or doses of irradiation lower or higher than 6500 cGy did not significantly affect outcome. Radiation therapy is an effective treatment for patients with stage A (T1) or B (T2) carcinoma of the prostate. Careful selection and refinement of treatment techniques, including three-dimensional treatment planning and conformal delivery irradiation or brachytherapy, may improve the management of these patients.

Comparison of intratracheal pulmonary ventilation with hybrid intratracheal pulmonary ventilation in a rabbit model of acute respiratory distress syndrome by saline lavage

We compared different hybrid mode ITPV (h-ITPV) flow rates, and h-ITPV with intratracheal pulmonary ventilation (ITPV) with respect to CO2 clearance and oxygenation. Surfactant deficiency was induced in six adult rabbits with saline lavage. The study consisted of three phases. Phase 0: Stabilization on conventional mechanical ventilation (CMV). Phase I: Bias flow initiated at same pressure and respiratory rate as Phase 0. Flow rates of 25%, 50%, 75% h-ITPV, and ITPV were initiated. Animals were transitioned from CMV to 25% h-ITPV proceeding sequentially to ITPV or vice versa. Phase II: Animals were returned to CMV. Statistical analysis included the two-way analysis of variance (ANOVA) and repeated measures ANOVA with Tuckey's test. No difference in PaCO2 was observed among all h-ITPV flow rates or between h-ITPV and ITPV. After bias flow was introduced (transition from Phase 0 to Phase I), PaCO2 decreased by 37%. PaCO2 increased by 119% during Phase II. Oxygenation improved in all animals, particularly in those transitioned to 25% h-ITPV and proceeding to ITPV. No difference in CO2 clearance between ITPV and h-ITPV was observed. Even at low bias flows, excellent CO2 clearance was achieved. Oxygenation was superior when animals were transitioned from CMV to h-ITPV. Hybrid-ITPV offers some advantages over ITPV and may represent a powerful tool in the management of acute respiratory distress syndrome (ARDS).

Local hyperthermia and irradiation in cancer therapy

The preliminary experience at the Mallinckrodt Institute of Radiology with hyperthermia and irradiation is reported and current issues in clinical application of heat are reviewed. Twenty-nine lesions were treated with 400 rad fractions given every 72 hr (twice weekly) for a total dose of 2400 to 4000 rad followed by hyperthermia (1450-MHz or 915-MHz microwaves, 42.0 degrees -43 degrees, 90 min, every 72 h). Eight of 12 recurrent epidermoid carcinomas of the head and neck showed complete regression (67%) and one more than 50% response. Of 5 metastatic melanoma nodules treated with irradiation an hyperthermia, 4 (80%) showed complete regression of the tumors an 1 almost complete response. Of 9 recurrent adenocarcinoma of breast nodules in the chest wall treated with 3200 to 4000 rad 5 lesions exhibited complete regression and 2 others about 80%. Of 6 lesions treated with 1500 rad and hyperthermia (RTOG protocol), 2 metastatic melanomas showed complete regression (CR) and 3 tumors exhibited partial regression. Of the 35 sites treated, 4 (11%) developed blisters, 7 (20%) erythema only, 3 (8%) moist desquamation and 27 (77%) dry desquamation. Additional clinical trials are in progress to assess the potential value of hyperthermia alone or combined with irradiation in the treatment of selected cancer patients.

Evaluation of 45 degrees C hyperthermia and irradiation. I. Studies in a murine rhabdomyosarcoma model

This report describes biologic experiments using transplanted RIF-1 tumors (diameter 0.5 or 1 cm) in C3H/He inbred mice (12 to 20 per treatment group) to compare the results with heat alone (43 degrees C for 60 minutes or 45 degrees C for 15 minutes, twice weekly via radiofrequency electrodes), irradiation alone (400 cGy twice weekly for a total of 4,000 cGy with 140 kVp x-rays), or a combination of both therapies. Animals receiving combined treatment had significantly greater complete regression than those treated with either therapy alone. Tumor regrowth curves were equivalent for 43 degrees C or 45 degrees C following irradiation. In tumors 0.5 cm in diameter the overall tumor cure rates were 17% for 43 degrees C for 60 minutes and 25% for 45 degrees C for 15 minutes with heat alone and 8% with irradiation alone; the combination of irradiation and heat at both temperatures yielded comparable complete cure rates (75 and 67%). With 1-cm tumors the corresponding cure rates were 0% with heat alone (either temperature), 5% for irradiation alone, 33% for irradiation and 43 degrees C heat, and 64% for irradiation and 45 degrees C heat (p = .3). Approximately 20% of the animals in the various groups developed moist or dry desquamation in the area treated, whereas 40 to 66% exhibited moist desquamation. There was a slight increase in this sequela (73%) for mice that received irradiation and 45 degrees C compared with 50% in mice treated with 43 degrees C, but the difference was not statistically different (p = .54). Experimental studies demonstrated equivalent efficacy of 10 hyperthermia sessions at 43 degrees C or 45 degrees C combined with irradiation. Caution must be exercised in the clinical application of thermal iso-effect heat dose concepts until further clinical trials have been performed and there is a better understanding of the time-temperature relationship.

Biological, physical factors in clinical assessment of outcome of cancer therapy

Complex molecular and cellular biological phenomena influence the response of tumor and normal cell to cytotoxic agents, including irradiation. Innovative 3-D treatment planning and IGRT techniques allow more quantitative optmization of irradiation dose distribution in target volumes and OAR. More detailed reporting on radiation doses is required with incorporation of biological parameters in treatment planning and dose specification. TCP and NTCP models should be validate with actual clinical data. Quality assurance in radiation oncology is mandatory. Because of increasing concerns with health care costs, technology assessment and cost benefit studies should be an integral component of clinical outcome reporting.

Functional imaging in treatment planning in radiation therapy: a review

The remarkable technical developments obtained in radiation oncology have resulted in an increasing use of image-based treatment planning in radiation therapy for three-dimensional and intensity modulated radiation therapy, stereotactic irradiation and image-guided brachytherapy. There has been increased use of computer-based record and verify systems as well as electronic portal imaging to enhance treatment delivery. From the data presented it is evident that PET scanning and other functional imaging techniques play a major role in the definition of tumor extent and staging of patients with cancer. The recent introduction of a combined CT and PET scanner will substantially simplify image acquisition and treatment planning.

Uncertainties in radiation therapy: target volume definition in prostate cancer

Accurate definition of target volumes and pelvic organs at risk is critical to improve the outcome in patients treated with irradiation for localized carcinoma of the prostate. Precise delineation of these structures will assist in more rational therapeutic decisions and optimized radiation therapy treatment planning and delivery. Increased conformity in radiation dose distribution allows delivery of higher doses of irradiation and dose escalation studies and results in improved tumor control, lower incidence of distant metastasis, improved survival and better quality of life. Multiple imaging methods are available and significant advances have been made in image fusion to enhance target volume definition. An exhaustive review of the literature is presented.

Dose fractionation and biological optimization in carcinoma of the prostate

Three-dimensional conformal radiation therapy (3-D CRT) or intensity-modulated radiation therapy (IMRT) have been increasingly used as an alternative to radical prostatectomy in patients with localized carcinoma of the prostate and in patients at high risk, in combination with hormonal therapy. To better understand the implications of dose-time and fractionation in prostate cancer, it is important to be familiar with some laboratory investigations dealing with the cell kinetics characteristics of this tumor. Biological and clinical considerations of dose fractionation, total dose of irradiation and local tumor control, elapsed overall treatment time and sequelae of irradiation are illustrated, based on an exhaustive review of the literature.