Biomedical subjects
Publications and source records attributed to R D Branson.
PaO2 can be increased by oxygen supplementation or by application of EEP and by manipulation of P(aw) during mechanical ventilation. Techniques and devices for accomplishing these maneuvers are many and varied. Clinicians should be aware of the appropriate application, complications, and limitations of each.
Mechanical ventilation with positive end-expiratory pressure (PEEP) limits hepatic blood flow (HBF) and oxygen delivery (HO2D). Early gut feeding may augment hepatic hemodynamics and avoid relative ischemia in this flow-limited environment. To examine these effects, canines were instrumented with arterial, pulmonary artery, portal, and hepatic vein catheters. Splenectomy and gastrostomy were performed and the hepatic artery and portal vein were encircled with flow probes. All animals underwent lung injury with oleic acid (0.08 ml/kg) followed by the addition of 10 cm H2O PEEP to correct shunt. One group (fed) was then given a bolus elemental feeding (1 kcal/ml, 10 ml/kg) and the Control group, sterile water. Cardiac index (CI), HBF, hepatic oxygen delivery (HO2D), and hepatic oxygen consumption (HO2C) were measured at baseline (T0), after PEEP (T1), and 1 (T2) and 2 hr (T3) after feeding. Data were tested for significant changes between time points in the same group by ANOVA and significant differences were subjected to t testing. PEEP significantly decreased CI, HBF, and HO2D compared to baseline. Subsequently, gut feeding increased HBF to baseline levels and improved HO2D. HO2C also increased but hepatic O2 extraction was unchanged. There was little change noted in the control group over this same period. We conclude that gut feeding augments HBF and HO2D in this flow-limited state and may preserve splanchnic integrity in critical illness.
Mechanical ventilation with high levels of positive end-expiratory pressure (PEEP) decreases hepatic blood flow (HBF) and hepatic oxygen delivery (HO2D). Noninvasive methods of detecting decreased HBF might prevent hepatic ischemia and dysfunction. Monoethylglycinexylidide (MEGX) is a hepatic metabolite of lidocaine, used clinically to determine graft function following hepatic transplantation. In order to test the hypothesis that MEGX production would be affected by changes in hepatic hemodynamics associated with lung injury, 12 dogs were instrumented with femoral and pulmonary artery catheters. Splenectomy was performed and the portal and hepatic veins cannulated. The hepatic artery and portal vein were encircled with flow probes. Lung injury was induced in six animals (INJURED group) with oleic acid (0.08 mL/kg) and 10 cm H2O PEEP was added to correct subsequent shunt. Levels of MEGX were measured 15 minutes after injection of intravenous lidocaine (1 mg/kg). Levels of HBF, HO2D, and MEGX were measured at BASELINE, after lung injury (INJURY time point), and after addition of PEEP (PEEP time point). CONTROL animals (n = 6) were studied at the same time points but without lung injury or PEEP. Hepatic blood flow and hepatic oxygen delivery were significantly decreased after lung injury and further decreased after PEEP. Levels of MEGX were unchanged in the CONTROL group but were significantly reduced by lung injury and PEEP in the INJURED group. Decreased MEGX production may be a useful clinical indicator of reduced hepatic flow and oxygen supply in critical illness.
We prospectively studied transport of a group of 100 surgery/trauma patients and a matched control group in the ICU. APACHE II scores for the two groups were 23 +/- 6 and 20 +/- 8. During transport both groups had ECG, heart rate, blood pressure, and oxygen saturation continuously monitored. We also determined the cost and results of transport for those patients requiring diagnostic testing. There were six diagnostic tests performed: CT scan of the abdomen (39%), CT scan of the head (31%), CT scan of the chest (8%), CT scan of the cervical spine (4%), angiography (14%), and tomography (4%). Average transport time was 74 +/- 16 minutes with a range of 20-225 minutes. Physiologic changes defined as a BP +/- 20 mm Hg, heart rate +/- 20 beats/min, respiratory rate +/- 5 breaths/min, or oxygen saturation +/- 5% for 5 minutes duration occurred in 66% of transported patients and 60% of ICU patients. There were no differences in arterial blood gas levels before and during transport. In 39% of transports, the results of diagnostic testing produced a change in patient management within 48 hours. Abdominal CT scanning and angiography were associated with the highest percentage of tests leading to a management change (51% and 57%). The average charge to the patient was $612.00 and the average cost to the hospital $452.00. Our results suggest that while physiologic changes are frequent during transport, they are also frequent in ICU patients as a consequence of the severity of illness.(ABSTRACT TRUNCATED AT 250 WORDS)
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These changes are proposed as a starting point for the more logical application of ventilator terminology and are for your consideration and debate. It is our contention that this system can be easily adopted once the basics of the classification system are understood.
Mechanical ventilation with positive end-expiratory pressure (PEEP) diminishes gut and hepatic blood flow and redistributes cardiac output away from the splanchnic circulation. This flow-limited environment can aggravate underlying hypoperfusion and ischemia in the postinjury setting. To examine the effects of low dose dopamine on a lung injury PEEP model of gut hypoperfusion, six anesthetized, splenectomized canines were instrumented with arterial, pulmonary artery, portal vein, and hepatic vein catheters. Electromagnetic flow probes were placed around the hepatic artery and portal vein for continuous flow measurements. Gut and hepatic blood flow, oxygen delivery, oxygen consumption, and extraction ratio were calculated at four time points: baseline, 1 hr after lung injury with oleic acid, 1 hr after ventilation with 10 cm H2O PEEP, and 1 hr after the continuous infusion of dopamine. Portal flow and gut oxygen delivery fell significantly with the infusion of PEEP. These values returned to near baseline levels with the addition of dopamine. Gut oxygen extraction increased from 16 +/- 2% to 35 +/- 3% with PEEP but returned to near baseline with dopamine (20 +/- 4%, P less than 0.01 compared to PEEP). We conclude that dopamine improves blood flow and oxygen delivery to the gut in this flow-limited model. This may preserve splanchnic physiology during PEEP ventilation for acute lung injury.
The current-generation mechanical ventilators are certainly enhanced in performance, style, and cost. Many of these enhancements appear to benefit both the patient (eg, reduced work of breathing, wider range of operation) and the hospital (eg, reduced maintenance costs). Although vast areas for refinements remain, my plea is that efforts be made to learn about and take advantage of the current technology, before embarking upon new technology. As we have learned, you have to have the right tool for the right job. Unfortunately, it's not the right tool, if you don't know how to use it.
We designed a model to evaluate the effectiveness of various noninvasive methods of ventilation. The upper airway was simulated with the head of a Resusci-Annie which was attached to a test lung. The esophagus and stomach were simulated with a Penrose drain connected to a rolling seal spirometer via a PEEP valve. Fifteen paramedic volunteers ventilated the model utilizing mouth-to-mouth, mouth-to-mask, bag-valve-mask, or portable field ventilator (Impact or HARV). Recording of tidal volume, gastric volume, and proximal and distal airway pressure was completed at three different levels of compliance. At normal compliance, all methods except the HARV met or exceeded American Heart Association standards. As compliance decreased, tidal volume fell and gastric insufflation increased. At a compliance of 0.02 L/cm H2O all methods failed to meet AHA standards and gastric insufflation volume equalled delivered tidal volumes for mouth-to-mouth and mouth-to-mask techniques. Mouth-to-mouth and mouth-to-mask techniques generated the largest tidal volumes but also created the largest volume of gastric insufflation. The Impact ventilator provided an acceptable tidal volume with minimal gastric insufflation. Our results suggest that mouth-to-mask ventilation with supplemental oxygen enrichment is the most efficient technique for non-invasive airway management.
Acute respiratory failure (ARF) following trauma or sepsis has a mortality rate of 50% to 85%. The mainstays of treatment are mechanical ventilation and positive end-expiratory pressure (PEEP). In the past decade, many reports have claimed superiority of high frequency ventilation (HFV) in the treatment of ARF. We structured a prospective randomized trial of HFV versus conventional mechanical ventilation (CMV) in the treatment of acute respiratory failure. All patients admitted to the Surgical Intensive Care Unit (SICU) were eligible for the study. On admission patients identified for being at risk of developing acute respiratory failure were randomized to receive either HFV or CMV. Patients were treated to the same therapeutic endpoint (pH greater than 7.35, PaCO2 35 to 45 torr, PaO2/FIO2 greater than 225). Daily ventilatory support, fluid and drug requirements, and cardiopulmonary variables were recorded. One hundred thirteen patients were entered into the study. Of these, 100 completed the study (HFV n = 52, CMV n = 48) and 60 developed acute respiratory failure (HFV n = 32, CMV n = 28). Patients on HFV reached the therapeutic endpoint at a lower level of continuous positive airway pressure and mean airway pressure; however there were no differences in mortality, SICU days, hospital days, incidence of barotrauma, number of blood gases, or cardiovascular interventions. This report suggests that HFV offers no concrete advantages over CMV when applied in a prospective fashion for the treatment of acute respiratory failure.
UNLABELLED: Transport of critically ill, mechanically ventilated patients from intensive care units for diagnostic and therapeutic procedures has become common in the last decade. Maintenance of adequate oxygenation and ventilation during transport is mandatory. We evaluated the Hamilton MAX transport ventilator in the laboratory and in the clinical arena to determine its usefulness during in-hospital transport. METHODS: In the laboratory, we determined the MAX's ability to assure tidal volume (VT) delivery in the face of decreasing compliance of a test lung, and we tested the alarm system. Using a two-compartment lung model modified to simulate spontaneous breathing, we also evaluated the responsiveness of the demand valve. The clinical evaluation was accomplished by comparing arterial blood gases and ventilator settings in the intensive care unit to those during transport. RESULTS: As lung compliance was reduced from 0.1 to 0.02 L/cm H2O [1.0 to 0.20 L/kPa], delivered VT fell significantly at each set VT. The alarm systems performed according to manufacturer's specifications. The demand valve triggered appropriately without positive end-expiratory pressure (PEEP), but as PEEP was increased, triggering became more difficult. The demand valve is referenced to ambient pressure and cannot compensate for elevated end-expiratory pressures. During patient transport, arterial blood gases were comparable to those achieved in the ICU. Because an inspired oxygen concentration of 1.0 was used during transport, arterial oxygenation (PaO2) was significantly greater (123 +/- 75 vs 402 +/- 85 torr [16.4 +/- 10 vs 53.6 +/- 11 kPa]). A higher ventilator rate was required during transport to prevent tachypnea (7 +/- 3 vs 12 +/- 6 breaths/min), and peak inspiratory pressure (PIP) was higher during transport (40 +/- 8 vs 52 +/- 11 cm H2O [3.9 +/- 0.8 vs 5.1 +/- 1.1 kPa]). CONCLUSIONS: The MAX is a reliable transport ventilator, capable of maintaining adequate ventilation and oxygenation in a majority of mechanically ventilated patients. Care should be taken to assure adequate VT delivery at high PIP, and ventilator rate may require adjustment to prevent tachypnea associated with triggering the non-PEEP-compensated demand valve when PEEP greater than 8 cm H2O [0.8 kPa] is used.
Pressure support ventilation (PSV) is a newer mode of ventilatory support that augments the patient's spontaneous inspirations to a preselected peak inspiratory pressure. We studied the effects of adding low levels of PSV (5 to 10 cm H2O) in conjunction with intermittent mandatory ventilation (IMV) on 15 patients who required mechanical ventilation for flail chest and pulmonary contusion. Patients were selected for the study if, during weaning from IMV, the following criteria were met: (1) a PaCO2 level greater than 45 mm Hg, (2) a spontaneous respiratory rate (RR) greater than 30 breaths per minute, (3) a minute ventilation (VE) greater than 9.0 L/min, and (4) spontaneous tidal volumes (VT) of less than 2 mL/kg. The PSV was added to the IMV at a level that augmented spontaneous VT to greater than 4 mL/kg. An average of 9 +/- 3 cm H2O of pressure support resulted in a fall in the level of PaCO2 (50 +/- 4 to 43 +/- 5 mm Hg), spontaneous RR (36 +/- 5 to 16 +/- 3 breaths per minute), VE (12 +/- 2 to 8.4 +/- 1.5 L/min), and dead space-tidal volume ratio from (0.68 +/- 0.1 to 0.47 +/- 0.05). Mean airway pressure and PaO2 both increased, but these changes were not statistically significant. Oxygen consumption was also unchanged. These results suggest that in patients who are difficult to wean due to respiratory muscle fatigue (characterized by increasing RR and decreasing VT), PSV normalizes lung volumes, improves ventilation, and may expedite the weaning process.
Transportation of critically ill patients requiring ventilatory support represents a common, yet difficult, problem faced by clinicians. We examined 28 patients requiring transport in a prospective, randomized fashion, comparing manual ventilation with ventilation provided by a transport ventilator. Patients were ventilated to their destination with one method and returned with the alternate method. After manual ventilation, all patients showed a marked respiratory alkalosis (pH increased from 7.39 to 7.51 and PaCO2 decreased from 39 to 30 torr). After ventilation with the transport ventilator, no appreciable changes in pH or PaCO2 were seen. Oxygenation remained stable with both methods. No patient suffered hemodynamic instability, although two patients in the manual ventilation group developed cardiac arrhythmias. We conclude that when ventilatory support is required during transport, a transport ventilator produces reliable control of ventilation.
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We evaluated 38 patients with combined head injury and respiratory failure requiring manipulation of mean airway pressure in order to achieve satisfactory oxygenation. All patients were initially maintained on conventional ventilatory support. When entry criteria were met, patients were transitioned to high-frequency percussive ventilation (HFPV) and cardiorespiratory variables were measured. HFPV resulted in a statistically significant decrease in intracranial pressures in patients when ICP remained greater than 15 mm Hg in spite of optimum medical management. Satisfactory oxygenation was obtained at approximately half the level of CPAP and peak inspiratory pressure as that on conventional ventilation. Thus HFPV provides an acceptable alternative method of ventilatory support in patients with combined head injury and respiratory failure.
These guidelines were developed by the American Association for Respiratory Care in response to a request by the Health Care Financing Administration for professional assistance in defining criteria for establishment of demonstration units for management of chronic ventilator-dependent patients in hospitals. Although the exact method by which these demonstration units (3 to 5 in number) will be selected has not been announced, these guidelines will have an important role in assuring that appropriate sites are chosen and that patient selection and data collection are adequate to document the possible benefits of such units.
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.
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.