Comparison of pulmonary vascular pressures based on blood volume and ventilator status

Pulmonary artery pressures (PAP), hemodynamic and oxygen transport variables, arterial blood gases (ABG), and blood volume (BV) were measured in 30 hypervolemic, normovolemic, and hypovolemic critically ill adults receiving physiologic levels of positive and expiratory pressure (PEEP). The measurements were taken while patients remained on the ventilator and during brief discontinuance of mechanical ventilation. The purposes of the study were to determine whether BV status could affect PAP and to quantify the effect of temporary discontinuance of ventilation on ABG. No differences were seen in PAP, mean arterial pressure, cardiac index, oxygen delivery, oxygen extraction, or oxygen consumption regardless of ventilator or BV status. Arterial oxygen tension dropped significantly, p less than .001, in less than 1 minute off ventilation and the decrease persisted for 1 hour after mechanical ventilation was resumed. These results suggest that recording PAP off the ventilator should be abandoned, as this technique contributes little to increased validity of PAP and may result in persistent hypoxemia.     

Traumatic respiratory insufficiency: comparison of conventional mechanical ventilation to high-frequency positive pressure with low-rate ventilation

Eleven patients suffering severe traumatic respiratory insufficiency were mechanically ventilated using a new system which combined high-frequency positive-pressure ventilation (HFPPV) with low-rate conventional mechanical ventilation (LRCMV). Ten similar patients were ventilated by conventional mechanical ventilation (CMV) with PEEP. HFPPV patients were fully conscious and cooperative during ventilation and did not need sedatives or muscle relaxants. Arterial oxygenation was significantly (p less than .005) better in HFPPV than CMV patients (89.91 +/- 10.24 vs. 78.43 +/- 11.13 torr, respectively), and pulmonary shunt was also better in the HFPPV group (13.1 +/- 4.7% vs. 20.4 +/- 6.4%, p less than .01). Moreover, inspired oxygen concentrations were lower (PaO2/FIO2 197.8 +/- 51.3 in the HFPPV group vs. 130 +/- 46.6 in the CMV group, p less than .005) and the time required for mechanical ventilation was shorter (4.2 +/- 0.91 vs. 6.1 +/- 0.8 days, p less than .1). All HFPPV patients immediately began breathing spontaneously when they were disconnected from the ventilator. We suggest this method as a better ventilatory mode for patients suffering traumatic respiratory insufficiency.     

The effect of positive end-expiratory pressure during partial liquid ventilation in acute lung injury in piglets.

OBJECTIVES: To investigate the effects of positive end-expiratory pressure (PEEP) application during partial liquid ventilation (PLV) on gas exchange, lung mechanics, and hemodynamics in acute lung injury. DESIGN: Prospective, randomized, experimental study. SETTING: University research laboratory. SUBJECTS: Six piglets weighing 7 to 12 kg. INTERVENTIONS: After induction of anesthesia, tracheostomy, and controlled mechanical ventilation, animals were instrumented with two central venous catheters, a pulmonary artery catheter and two arterial catheters, and an ultrasonic flow probe around the pulmonary artery. Acute lung injury was induced by the infusion of oleic acid (0.08 mL/kg) and repeated lung lavage procedures with 0.9% sodium chloride (20 mL/kg). The protocol consisted of four different PEEP levels (0, 5, 10, and 15 cm H2O) randomly applied during PLV. The oxygenated and warmed perfluorocarbon liquid (30 mL/kg) was instilled into the trachea over 5 mins without changing the ventilator settings. MEASUREMENTS AND MAIN RESULTS: Airway pressures, tidal volumes, dynamic and static pulmonary compliance, mean and expiratory airway resistances, and arterial blood gases were measured. In addition, dynamic pressure/volume loops were recorded. Hemodynamic monitoring included right atrial, mean pulmonary artery, pulmonary capillary wedge, and mean systemic arterial pressures and continuous flow recording at the pulmonary artery. The infusion of oleic acid combined with two to five lung lavage procedures induced a significant reduction in PaO2/FI(O2) from 485 +/- 28 torr (64 +/- 3.6 kPa) to 68 +/- 3.2 torr (9.0 +/- 0.4 kPa) (p < .01) and in static pulmonary compliance from 1.3 +/- 0.06 to 0.67 +/- 0.04 mL/cm H2O/kg (p < .01). During PLV, PaO2/FI(O2) increased significantly from 68 +/- 3.2 torr (8.9 +/- 0.4 kPa) to >200 torr (>26 kPa) (p < .01). The highest PaO2 values were observed during PLV with PEEP of 15 cm H2O. Deadspace ventilation was lower during PLV when PEEP levels of 10 to 15 cm H2O were applied. There were no differences in hemodynamic data during PLV with PEEP levels up to 10 cm H2O. However, PEEP levels of 15 cm H2O resulted in a significant decrease in cardiac output. Dynamic pressure/volume loops showed early inspiratory pressure spikes during PLV with PEEP levels of 0 and 5 cm H2O. CONCLUSIONS: Partial liquid ventilation is a useful technique to improve oxygenation in severe acute lung injury. The application of PEEP during PLV further improves oxygenation and lung mechanics. PEEP levels of 10 cm H2O seem to be optimal to improve oxygenation and lung mechanics.     

Repeated derecruitments accentuate lung injury during mechanical ventilation

OBJECTIVE: This study was performed to test the hypothesis that derecruitment itself might accentuate lung injury during mechanical ventilation. SETTING: Randomized, controlled trial. SETTING: Experimental laboratory. SUBJECTS: New Zealand White rabbits (2.8-3.5 kg). INTERVENTION: Twenty-four rabbits were ventilated in pressure-controlled mode with constant tidal volume (10 mL/kg). After lung injury was induced by repeated saline lavage (PaO2 <100 torr, 13.3 kPa), a pressure-volume curve was drawn to calculate the lower inflection point (Pflex), and randomization was done. The control group (n = 8) received ventilation with positive end-expiratory pressure (PEEP) fixed at Pflex for 3 hrs. The nonderecruitment group (n = 8) was ventilated at PEEP of 2 mm Hg (2.7 cm H2O) for the initial hour and then PEEP of Pflex for the remaining 2 hrs. The derecruitment group (n = 8) was ventilated for 3 hrs with six 30-min cycles consisting of 10 mins at PEEP of 2 mm Hg (2.7 cm H2O) and 20 mins at PEEP of Pflex to induce repeated derecruitments. MEASUREMENTS AND MAIN RESULTS: Variables of gas exchange, mechanics, and hemodynamics were measured, and histologic evaluation was done. In the control group, Pao2 remained >500 torr (66.7 kPa) for 3 hrs. In the nonderecruitment group, PaO2 was 40 +/- 16 (mean +/- SD) torr (5.3 +/- 2.1 kPa) at 1 hr but increased to >500 torr (66.7 kPa) for the remaining 2 hrs after increase in PEEP to Pflex. In the derecruitment group, there was progressive decline in Pao2 with each derecruitment to 220 +/- 130 torr (29.3 +/- 17.3 kPa) at 3 hrs (p <.05 compared with other groups). Histologically there was more hyaline membrane formation in the derecruitment group compared with control (p <.05) and significantly higher mean bronchiolar injury score in the derecruitment group (1.92 +/- 0.78) than both control (0.50 +/- 0.50) and nonderecruitment (0.78 +/- 0.42) groups (p <.05). CONCLUSION: Repeated derecruitments can accentuate lung injury during mechanical ventilation.     

Titrating positive end-expiratory pressure therapy in patients with early, moderate arterial hypoxemia

A prospective randomized study to compare two physiologic end-points for titrating positive end-expiratory pressure (PEEP) was performed in patients with early, moderate arterial hypoxemia after surgery or trauma. All patients initially received 5 cm H2O of PEEP. In group 1 patients, PEEP was increased only if PaO2 decreased below 65 torr on an inspired oxygen fraction (FIO2) of 0.45. PEEP was then added in 2- to 3-cm H2O increments until PaO2 again was above 65 torr. Group 2 patients were treated with incremental PEEP until the PaO2/FIO2 ratio was greater than 300 or physiologic shunt (Qsp/Qt) was less than 0.20. All therapy other than PEEP was similar in the two groups. There were no statistically significant differences in entry PaO2 (mean 85 +/- 11 [SD] and 87 +/- 11 torr in groups 1 and 2, respectively), and Qsp/Qt was 0.22 in each group. Five (28%) of 18 patients in group 1 and 19 (95%) of 20 patients in group 2 received more than 5 cm H2O of PEEP. Between groups 1 and 2 there were no statistically significant differences in days intubated (3.4 +/- 3 vs. 5.3 +/- 5, respectively), ICU days (5.3 +/- 3 vs. 6.6 +/- 5), hospitalization days (26 +/- 24 vs. 28 +/- 24), incidence of pulmonary barotrauma (0/18 vs. 1/20), ICU mortality (22% vs. 20%), or overall mortality (33% vs. 25%). The number of blood gas analyses and cardiac output measurements, and the total hospital charges were also similar in both groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

Selective tracheal gas insufflation during partial liquid ventilation improves lung function in an animal model of unilateral acute lung injury.

OBJECTIVE: During unilateral lung injury, we hypothesized that we can improve global lung function by applying selective tracheal gas insufflation (TGI) and partial liquid ventilation (PLV) to the injured lung. DESIGN: Prospective, interventional animal study. SETTING: Animal laboratory in a university hospital. SUBJECTS: Adult mixed-breed dogs. INTERVENTIONS: In six anesthetized dogs, left saline lung lavage was performed until PaO(2)/FiO(2) fell below 100 torr (13.3 kPa). The dogs were then reintubated with a Univent single-lumen endotracheal tube, which incorporates an internal catheter to provide TGI. In a consecutive manner, we studied 1) the application of 10 cm H(2)O of positive end-expiratory pressure (PEEP); 2) instillation of 10 mL/kg of perflubron (Liquivent) to the left lung at a PEEP level of 10 cm H(2)O (PLV+PEEP 10 initial); 3) application of selective TGI (PLV+TGI) while maintaining end-expiratory lung volume (EELV) constant; 4) PLV+TGI at reduced tidal volume (VT); and 5) PLV+PEEP 10 final. MEASUREMENTS AND MAIN RESULTS: Application of PLV+PEEP 10 initial did not change gas exchange, lung mechanics, or hemodynamics. PLV+TGI improved PaO(2)/FiO(2) from 189 +/- 13 torr (25.2 +/- 1.7 kPa) to 383 +/- 44 torr (51.1 +/- 5.9 kPa) (p <.01) and decreased PaCO(2) from 55 +/- 5 torr (7.3 +/- 0.7 kPa) to 30 +/- 2 torr (4.0 +/- 0.3 kPa) (p <.01). During ventilation with PLV+TGI, reducing VT from 15 mL/kg to 3.5 mL/kg while keeping EELV constant decreased PaO(2)/FiO(2) to 288 +/- 49 torr (38.4 +/- 6.5 kPa) (not significant) and normalized PaCO(2). At this stage, end-inspiratory plateau pressure decreased from 19.2 +/- 0.7 cm H(2)O to 13.6 +/- 0.7 cm H(2)O (p <.01). At PLV+PEEP 10 final, measurements returned to those observed at previous baseline stage (PLV+PEEP 10 initial). CONCLUSIONS: During unilateral lung injury, PLV with a moderate PEEP did not improve oxygenation, TGI superimposed on PLV improved gas exchange, and combination of TGI and PLV allowed a 77% reduction in VT without any adverse effect on PaCO(2).     

Gas exchange during conventional and high-frequency pulse ventilation in the surfactant-deficient lung: influence of positive end-expiratory pressure

High-frequency pulse ventilation (HFPV) was compared to conventional ventilation (CV) in a model of severe respiratory failure induced by serial lung lavages with warm saline in 8 mongrel dogs. Before the lavage, during HFPV at 4 Hz with a pulse volume (PV) of 125 ml, mean PaO2 was 107 torr and mean PaCO2 was 34 torr. After the last lavage, during CV at an inspired oxygen fraction FIO2 of 1.0 and a tidal volume (VT) of 535 ml, the PaO2 averaged 60 torr and PaCO2 was 45 torr. At an FIO2 of 0.21, 20 cm H2O of positive end-expiratory pressure (PEEP) was applied to prevent hypoxemia. The resulting PaO2 was 87 torr; PaCO2 was 40 torr. Peak airway pressure (Ppa) rose from 21 to 51 cm H2O. When ventilation was switched to HFPV on room air, a PV similar to the control levels was associated with severe hypoxemia (PaO2 less than 45 torr, PaCO2 greater than 50 torr). As PV was increased PaO2 improved, reaching 113 torr at a PV of about 470 ml. The corresponding mean airway pressure (Paw) was about 20 cm H2O. Thus, application of PEEP during HFPV at low PV did not improve PaO2 even when measured Paw approximated 20 cm H2O. This suggests that HFPV with high PV is more effective than either CV with PEEP, or HFPV with low PV and PEEP.     

Auto-positive end-expiratory pressure during tracheal gas insufflation: testing a hypothetical model

OBJECTIVE: The major benefit of tracheal gas insufflation (TGI) is an increase in CO2 elimination efficiency by removal of CO2 from the anatomical deadspace. In conjunction with mechanical ventilation, TGI may also alter variables that affect CO2 elimination, such as minute ventilation and peak airway pressure (peak Paw) and cause the development of auto-positive end-expiratory pressure (auto-PEEP). We tested the hypothesis that TGI-induced auto-PEEP alters ventilatory variables. We predicted that TGI-induced auto-PEEP offsets the beneficial effects of TGI on CO2 elimination and that keeping total PEEP (ventilator PEEP + auto-PEEP) constant enhances the CO2 elimination efficiency afforded by TGI. DESIGN: Prospective study of two series of patients with acute respiratory distress syndrome receiving mechanical ventilation. SETTING: Intensive care units at a university medical center. PATIENTS: Each series consisted of eight sequential hypercapnic patients. INTERVENTIONS: In series 1, we examined the effect of continuous TGI at 0 and 10 L/min on PaCO2, without compensating for the development of auto-PEEP. In series 2, we examined this same effect of continuous TGI while reducing ventilator PEEP to keep total PEEP constant. TGI-induced auto-PEEP was calculated based on dynamic compliance measurements during zero TGI flow conditions (deltaV/deltaP) after averaging the two baseline values for peak Paw and tidal volume and assuming compliance did not change between the zero TGI and TGI flow conditions (deltaVTGI/deltaPTGI). MEASUREMENTS AND MAIN RESULTS: In series 1, total PEEP increased from 13.2 +/- 3.2 cm H2O to 17.8 +/- 3.5 cm H2O without compensation for auto-PEEP (p = .01). PaCO2 decreased (p = .03) from 56.2 +/- 10.6 mm Hg (zero TGI) to 52.9 +/- 9.3 mm Hg (TGI at 10 L/min), a 6% decrement. In series 2, total PEEP was unchanged (p = NS). PaCO2 decreased (p = .03) from 59.5 +/- 10.4 mm Hg (zero TGI) to 52.2 +/- 8.3 mm Hg (TGI at 10 L/min), a 12% decrement. There was no significant change in PaO2; there were no untoward hemodynamic effects in either series. CONCLUSIONS: These data are consistent with the hypothesis that mechanical ventilation + TGI causes an increase in auto-PEEP that can blunt CO2 elimination. In addition to the ventilator modifications necessary to keep ventilatory variables constant when TGI is used, it is also necessary to reduce ventilator PEEP to keep total PEEP constant and further enhance CO2 elimination efficiency.     

Alterations in regional blood flow during positive end-expiratory pressure ventilation

PEEP improves the gas-exchange abnormalities that accompany adult respiratory distress syndrome (ARDS). However, since PEEP decreases cardiac output, it may also alter regional blood flow and therefore, substrate delivery to specific organs. To test this hypothesis, radiolabeled 15-mu microspheres were used to directly quantify the effects of mechanical ventilation with PEEP on regional blood flow to individual organs in animals. Mechanical ventilation alone produced a -21.2 +/- 3.6% and a -28.1 +/- 5.2% decrease in cardiac output at 30 and 60 min, respectively. The addition of 14 cm H2O PEEP resulted in little further reduction in cardiac output at 30 and 60 min (-28 +/- 2.3% and -36.4 +/- 4.9%, respectively). However, 25 cm H2O PEEP reduced markedly (p less than .01) cardiac output (-59.2 +/- 6.1% at 30 min and -55.1 +/- 4.0% at 60 min). Although blood flows to the kidney and brain were maintained, decreases in cardiac output were invariably accompanied by proportional decreases in blood flow to the heart. Intravascular volume expansion with saline (20 ml/kg) during 14 cm H2O PEEP significantly improved cardiac output (3.23 +/- 0.34 to 4.22 +/- 0.13 L/min; p less than .01) and proportionately increased blood flow to several regional vascular beds, including the heart. These data suggest that PEEP decreases cardiac output to produce reversible alterations in blood flow to a number of regional vascular beds. These PEEP-induced alterations in regional blood flow may have important implications for the development of multiple-organ failure in ARDS patients.     

Laboratory and clinical evaluation of the MAX transport ventilator

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.     

High-frequency oscillation in the rescue of infants with persistent pulmonary hypertension

High-frequency oscillatory ventilation (HFOV) was used to treat 41 infants with persistent pulmonary hypertension of the newborn (PPHN). Of the 37 patients who showed early improvement on HFOV, three died. The remaining 34 patients demonstrated, within one hour of the switchover to HFOV, a rise in mean arterial/alveolar oxygen tension ratio (PaO2/PaO2) from 0.093 +/- 0.041 (SD) to 0.132 +/- 0.051 (p less than .001), and a fall in mean PaCO2 from 42 +/- 10 to 34 +/- torr 9 (p less than .01). Mean airway pressure (Paw) fell significantly (p less than .01) within 12 h. The mean duration of conventional mechanical ventilation before starting HFOV was longer in 13 patients who developed bronchopulmonary dysplasia (BPD) than in 21 non-BPD patients (44.7 +/- 32.3 vs. 19.1 +/- 15.6 h, p less than .002), as was the duration of exposure to Paw greater than 15 cm H2O during that treatment mode (31.8 +/- 21.3 vs. 9.5 +/- 6.0 h, p less than .001). HFOV is often effective in the treatment of patients with PPHN, and early initiation of this type of mechanical ventilation may be associated with a reduced incidence of BPD.     

Is 50% oxygen harmful?

Pulmonary gas exchange after tracheal extubation was evaluated in 25 patients to determine the effect of 50% oxygen administered during mechanical ventilation following aortocoronary bypass grafting. Twenty-five patients received postoperative mechanical ventilation for 16 to 24 h, 13 with an inspired oxygen fraction (FIO2) of no more than 0.30 and 12 with an FIO2 of 0.50. After tracheal extubation, all patients spontaneously breathed room air (FIO2 0.21). Postextubation the calculated venous admixture of patients who had received 50% oxygen (0.20 +/- 0.03 [SD]) was significantly (p less than .01) greater than that calculated for patients who received lower oxygen concentrations (0.13 +/- 0.04). Consequently, the PaO2 of patients who had received 50% oxygen (60 +/- 5 torr) was significantly (p less than .03) lower than the PaO2 of patients who had received no more than 30% oxygen (66 +/- 7 torr). Thus, administration of 50% oxygen, supposedly nontoxic, to mechanically ventilated patients may cause impairment of pulmonary gas exchange after tracheal extubation. Although high concentrations of supplemental oxygen are sometimes required, unnecessary elevation of FIO2 is not likely to significantly increase oxygen delivery and may contribute to postextubation pulmonary dysfunction.     

Mechanical ventilation with permissive hypercapnia increases intrapulmonary shunt in septic and nonseptic patients with acute respiratory distress syndrome

OBJECTIVE: To compare the effects of conventional mechanical ventilation with low-volume, pressure-limited ventilation (LVPLV) and permissive hypercapnia on ventilation-perfusion (V/Q) distributions in patients with acute respiratory distress syndrome. We hypothesized that the advantageous cardiopulmonary effects of LVPLV would be greater in patients with sepsis than in those without sepsis. PATIENTS AND INTERVENTIONS: Twenty-two patients with acute respiratory distress syndrome were studied (group 1: 12 patients with hyperdynamic sepsis; group 2: 10 nonseptic patients). Intrapulmonary shunt (Qsp/Qt) (percentage of cardiac output), perfusion of "low" V/Q areas (percentage of cardiac output), ventilation of "high" V/Q areas (percentage of total ventilation [VE]), and deadspace ventilation (percentage of VE) were calculated from the retention/excretion data of six inert gases. Data were obtained during conventional mechanical ventilation and during LVPLV. MEASUREMENTS AND MAIN RESULTS: In group 1, LVPLV increased PaCO(0)rom 38 +/- 6 torr (5.1 +/- 0.8 kPa) to 61 +/- 12 torr (8.1 +/- 1.6 kPa). Qsp/Qt increased from 28 +/- 16% to 36 +/- 17%, whereas Pao2 (84 +/- 15 torr [11.1 +/- 2.0 kPa] vs. 86 +/- 21 torr [11.5 +/- 2.8 kPa]) and Qt (10.6 +/- 2.3 vs. 11.5 +/- 2.5 L x -1) remained unchanged and PVO(2) (40 +/- 4 [5.3 +/- 0.5 kPa] vs. 49 +/- 6 torr [6.5 +/- 0.3]) increased. In group 2, LVPLV increased PaCO(2) from 38 +/- 6 torr (5.1 +/- 0.8 kPa) to 63 +/- 11 torr (8.4 +/- 1.5 kPa). For Qsp/Qt (24 +/- 9% to 34 +/- 16%), the increase was not significant, whereas Qt (7.4 +/- 1.8 vs. 10.2 +/- 2.2 L x -1), PVO(2)(38 +/- 4 torr [5.1 +/- 0.5 kPa] vs. 50 +/- 6 mm Hg [6.7 +/- 0.8 kPa]), and PaO(2) (89 +/- 16 torr [11.9 +/- 2.1 kPa] vs. 98 +/- 19 torr [13.1 +/- 2.5 kPa]) increased. In both groups, the scatter of perfusion distribution (log SDQ) was greater than expected for normal subjects but was not different between the groups or altered by the treatments. CONCLUSIONS: In patients with acute respiratory distress syndrome, LVPLV with permissive hypercapnia, tended to increase Qsp/Qt, without a concomitant decrease of PaO(2). This occurs because, although atelectasis and increased shunt result from the low ventilatory volume, the effects on PaO(2) are offset by increased PVO(2) resulting from the hypercapnic stimulation of cardiac output. This result was independent of the presence or absence of sepsis.     

Physiologic effects of early administered mask proportional assist ventilation in patients with chronic obstructive pulmonary disease and acute respiratory failure

OBJECTIVE: To evaluate the physiologic short-term effects of noninvasive proportional assist ventilation (PAV) in patients with acute exacerbation of chronic obstructive pulmonary disease (COPD). DESIGN: Prospective, physiologic study. SETTING: Respiratory intermediate intensive care unit. PATIENTS: Seven patients with acute respiratory failure requiring noninvasive mechanical ventilation because of exacerbation of COPD. INTERVENTIONS: PAV was administered by nasal mask as first ventilatory intervention. The setting of PAV involved a procedure to adjust volume assist and flow assist to levels corresponding to patient comfort. Volume assist was also set by means of the "run-away" procedure. Continuous positive airway pressure (CPAP) amounting to 2 cm H2O was always set by the ventilator. This setting of assistance (PAV) was applied for 45 mins. Thereafter, CPAP was increased to 5 cm H2O (PAV + CPAP-5) without any change in the PAV setting and was administered for 20 mins. Oxygen was delivered through a port of the mask in the attempt to maintain a target SaO2 >90%. MEASUREMENTS AND MAIN RESULTS: Arterial blood gases, breathing pattern, and inspiratory effort were measured during unsupported breathing and at the end of PAV, and breathing pattern and inspiratory effort were measured after 20 mins of PAV + CPAP-5. PAV determined a significant increase in tidal volume and minute ventilation (+64% and +25% on average, respectively) with unchanged breathing frequency and a significant improvement in arterial blood gases (PaO2 with the same oxygen supply, from 65 +/- 15 torr to 97 +/- 36 torr; PaCO2, from 80 +/- 11 torr to 76 +/- 13 torr; pH, from 7.30 +/- 0.02 to 7.32 +/- 0.03). The pressure-time product calculated over a period of 1 min (from 318 +/- 87 to 205 +/- 145 cm H2O x sec x min(-1)) was significantly reduced. PAV + CPAP-5 resulted in a further although not significant decrease in the pressure-time product calculated over a period of 1 min (to 183 +/- 110 cm H2O x sec x min(-1)), without additional changes in the breathing pattern. CONCLUSIONS: Noninvasive PAV is able to improve arterial blood gases while unloading inspiratory muscles in patients with acute exacerbation of COPD.     

Clinical results with the "open lung concept"

Elements of the "open lung concept" are being increasingly included in clinical ventilatory strategies. Despite encouraging experimental investigations to date, relatively few studies exist that examine the clinical application of the complete concept. The aim of this study was to prove that with effective recruitment maneuvers and titrated PEEP levels this concept is applicable in clinical settings. We sought to determine if it was possible to achieve a significant improvement in oxygenation and also to examine what side-effects resulted. Twenty consecutive patients who had had an acute lung injury (ALI) for less than 72 hours, with an oxygenation index (P/F-Ratio = quotient from arterial partial pressure of oxygen [PaO2] and the inspiratory fraction of oxygen [FiO2]) of less than 200 torr, and with a PEEP > or = 10 cmH2O were treated using a recruitment manoeuvre (RM). A PEEP was titrated to keep the lung open, and the patients were kept under pressure-controlled ventilation. The P/F-Ratio increased while using a recruitment pressure of 66 +/- 13 cmH2O from 137 +/- 41 to 381 +/- 150 torr (p < 0.001). The titrated PEEP which kept the lung open after recruitment was 17 +/- 3 cmH2O. One patient developed a pneumothorax. The dose of norepinephrine was increased in ten patients from 0.24 +/- 0.12 to 0.31 +/- 0.1 microgram/kg/min. Due to elevated liver enzymes within the first 48 hours, titrated PEEP had to be decreased in three patients. The clinical application of the "open lung concept" demonstrated a quick and effective improvement in oxygenation in many patients. Side-effects in some patients limited the use of high PEEP levels.     

High-frequency positive-pressure ventilation in neonates

Twenty-five newborn infants with severe respiratory failure responding poorly to conventional mechanical ventilation were switched to high-frequency positive-pressure ventilation (HFPPV) at 90 to 180 cycle/min (mean 158), an estimated tidal volume less than or equal to 3 ml/kg body weight, an inspiratory time of 0.1 sec, and a PEEP of 3 to 17 cm H2O. In all infants, HFPPV increased PaO2 (mean 66 torr) and decreased PaCO2 (mean 14 torr) within 1 h. Fourteen hours after onset of treatment, the FIO2 requirement had decreased from 1.0 to 0.6 in all infants. Mean airway pressure (Paw) with HFPPV was usually less than or equal to Paw during conventional ventilation. In spite of the often high level of PEEP used, pneumothorax occurred in only 2 infants and bronchopulmonary dysplasia in 1. Eighteen (72%) infants survived and none died of respiratory failure. The use of HFPPV might be beneficial in neonates with severe respiratory failure that responds poorly to conventional therapy.     

Translaryngeal tracheostomy in acute respiratory distress syndrome patients

OBJECTIVE: To prevent gas exchange deterioration during translaryngeal tracheostomy (TLT) in patients with acute respiratory distress syndrome (ARDS) ventilation is maintained through a small diameter endotracheal tube (ETT; 4.0 mm i.d.) advanced beyond the tracheostoma. We report on the feasibility of uninterrupted ventilation delivered through a high-resistance ETT in ARDS patients, and relevant ventilatory adjustments and monitoring. DESIGN AND SETTING: Prospective, observational clinical study in an eight-bed intensive care unit of a university hospital. Patients: Eight consecutive ARDS patients scheduled for tracheostomy. INTERVENTIONS: During TLT volume control ventilation was maintained through the 4.0-mm i.d. ETT. Tidal volume, respiratory rate, and inspiratory to expiratory ratio were kept constant. Fractional inspiratory oxygen was 1. Positive end expiratory pressure (PEEP) set on the ventilator (PEEP(vent)) was reduced to maintain total PEEP (PEEP(tot)) at baseline level according to the measured intrinsic PEEP (auto-PEEP). MEASUREMENTS AND MAIN RESULTS: Data were collected before tracheostomy and while on mechanical ventilation with the 4.0-mm i.d. ETT. Neither PaCO(2) nor PaO(2) changed significantly (54.5+/-10.0 vs. 56.4+/-7.0 and 137+/-69 vs. 140+/-59 mmHg, respectively). Auto-PEEP increased from 0.6+/-1.1 to 9.8+/-6.5 cmH(2)O during ventilation with the 4.0-mm i.d. ETT. By decreasing PEEP(vent) we obtained a stable PEEP(tot) (11.4+/-4.3 vs. 11.8+/-4.3 cmH(2)O), and end-inspiratory occlusion pressure (26.7+/-7.4 vs. 28.0+/-6.6 cmH(2)O). Peak inspiratory pressure rose from 33.8+/-8.1 to 77.8+/-12.7 cmH(2)O. CONCLUSIONS: The high-resistance ETT allows ventilatory assistance during the whole TLT procedure. Assessment of stability in plateau pressure and PEEP(tot) by end-inspiratory and end-expiratory occlusions prevent hyperinflation and possibly barotrauma.     

Effects of different continuous positive airway pressure devices and periodic hyperinflations on respiratory function

OBJECTIVE: To compare the effect on respiratory function of different continuous positive airway pressure systems and periodic hyperinflations in patients with respiratory failure. DESIGN: Prospective SETTING: Hospital intensive care unit. PATIENTS: Sixteen intubated patients (eight men and eight women, age 54 +/- 18 yrs, PaO2/FiO2 277 +/- 58 torr, positive end-expiratory pressure 6.2 +/- 2.0 cm H2O). INTERVENTIONS: We evaluated continuous flow positive airway pressure systems with high or low flow plus a reservoir bag equipped with spring-loaded mechanical or underwater seal positive end-expiratory pressure valve and a continuous positive airway pressure by a Servo 300 C ventilator with or without periodic hyperinflations (three assisted breaths per minute with constant inspiratory pressure of 30 cm H2O over positive end-expiratory pressure). MEASUREMENTS AND MAIN RESULTS: We measured the respiratory pattern, work of breathing, dyspnea sensation, end-expiratory lung volume, and gas exchange. We found the following: a) Work of breathing and gas exchange were comparable between continuous flow systems; b) the ventilator continuous positive airway pressure was not different compared with continuous flow systems; and c) continuous positive airway pressure with periodic hyperinflations reduced work of breathing (10.7 +/- 9.5 vs. 6.3 +/- 5.7 J/min, p <.05) and dyspnea sensation (1.6 +/- 1.2 vs. 1.1 +/- 0.8 cm, p <.05) increased end-expiratory lung volume (1.6 +/- 0.8 vs. 2.0 +/- 0.9 L, p <.05) and PaO2 (100 +/- 21 vs. 120 +/- 25 torr, p <.05) compared with ventilator continuous positive airway pressure. CONCLUSIONS: The continuous flow positive airway pressure systems tested are equally efficient; a ventilator can provide satisfactory continuous positive airway pressure; and the use of periodic hyperinflations during continuous positive airway pressure can improve respiratory function and reduce the work of breathing.     

适当呼气末正压及不同通气模式对肝移植患者血流动力学和氧代谢动力学的影响

目的 寻找适宜的呼气末正压(PEEP),研究不同机械通气方式对肝移植术后患者血流动力学及氧代谢动力学的影响.方法 采用随机、单盲、交叉试验方法.选取11例背驮式肝移植术后呼吸机辅助通气患者为观察对象,经漂浮导管、桡动脉导管进行持续心排血量(CO)、平均肺动脉压(MPAP)、平均动脉血压(MABP)、中心静脉压(CVP)和气道压力监测.压力调节容量控制通气(PRVCV)的PEEP定为0、5、10和15 cm H2O(1 cm H2O=0.098 kPa),不同水平PEEP各用30 min;交替使用PRVCV和压力控制同步间歇指令通气加压力支持通气(PC-SIMV+PSV)各60 min;观察4种PEEP水平和两种通气模式下血流动力学和氧代谢动力学指标的变化.结果 不同水平PEEP时肝移植术后患者气道峰压、平均气道压、CVP及MPAP差异均有显著性,其中在PEEP为10 cm H2O和15 cm H2O时显著高于PEEP为0和5 cm H2O时;不同水平PEEP对pH、动脉血二氧化碳分压(PaCO2)、动脉血氧分压(PaO2)、动脉血氧饱和度(SaO2)、氧供给(DO2)、氧消耗(VO2)、氧摄取率(O2ER)均无明显影响.PRVCV模式时平均气道压明显低于PC-SIMV+PSV模式[(8.78±1.53)cm H2O比(11.64±3.30)cm H2O,P＜0.05];PRVCV模式时VO2虽低于PC-SIMV+PSV模式,但差异无显著性.两种通气模式对患者的其他血流动力学指标以及氧代谢动力学指标并无显著影响.结论 为减少对患者体循环及移植肝脏血液回流的影响,肝移植术后患者通气支持时宜选用5 cm H2O的低水平PEEP.PRVCV模式可作为肝移植术后患者呼吸支持和脱机过渡较为理想的通气模式.     

探讨无创机械通气治疗COPD合并Ⅱ型呼吸衰竭的观察与护理

目的：探讨无创机械通气治疗慢性阻塞性肺部疾病（COPD）合并Ⅱ型呼吸衰竭的观察与护理。方法：收集2007年5月-2008年5月收治的COPD合并Ⅱ型呼吸衰竭80例患者的临床资料,观察无创机械通气治疗前后动脉血气分析的变化。结果：治疗后动脉血氧分压（PaO2）较治疗前显著升高（P〈0．01）,动脉血二氧化碳分压（PaC02）较治疗前明显下降（P〈0．01）。结论：无创机械通气是救治COPD合并早期Ⅱ型呼吸衰竭的有效方法,细致周密护理是治疗成功的关键。