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PubMed1989

Ventilatory strategy in catastrophic lung disease. Inversed ratio ventilation (IRV) and combined high frequency ventilation (CHFV).

In 105 patients with well-defined catastrophic lung disease, in whom conventional settings were unable to maintain life-sustaining gas exchange, the ventilatory strategy was changed from volume-controlled ventilation with an inspiratory-expiratory ratio (I:E) of 1:2 and PEEP of 15-20 cm H2O to pressure-controlled inverse ratio ventilation with an I:E of 2:1, 3:1 or 4:1 and a set PEEP of 4-8 cm H2O. All patients were ventilated on a Servo 900 B or C ventilator, the primary goal being to decrease the FIO2 below 0.6 and the peak pressure to below 50 cm H2O, while maintaining a PaO2 of 8.00 kPa and a PaCO2 within 10% of the upper limit of normal. In 67 patients the intervention was successful and peak pressure could be reduced to a median of 44 cm H2O (range 37-50). FIO2 could be reduced to a median of 0.50 (range 0.40-0.60). The auto-PEEP effect of IRV increased to a median of 12 cm H2O (range 7-22). No consistent pattern of change in cardiac output was observed. Sixty patients survived more than 3 weeks and 48 were discharged from hospital. The 38 IRV "failures" were changed to pressure-controlled ventilation with superimposed high frequency ventilation (CHFV). In 30 cases the FIO2 could be reduced to a median of 0.60 (range 0.50-0.60) and peak pressures to a median of 50 cm H2O (range 45-60). In 21 patients the PaCO2 increased. Auto-PEEP with CHFV had a median value of 15 cm H2O (range 10-25).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1990

Ventilation-perfusion relationships and atelectasis formation in the supine and lateral positions during conventional mechanical and differential ventilation.

Patients without respiratory symptoms were studied awake and during general anesthesia with mechanical ventilation prior to elective surgery. Ventilation-perfusion (VA/Q) relationships, gas exchange and atelectasis formation were studied during five different conditions: 1) supine, awake; 2) supine during anesthesia with conventional mechanical ventilation (CV); 3) in the left lateral position during CV; 4) as 3) but with 10 cm of positive end-expiratory pressure (PEEP) and 5) as 3) but using differential ventilation with selective PEEP (DV + SPEEP) to the dependent lung. Atelectatic areas and increases of shunt blood flow and blood flow to regions with low VA/Q ratios appeared after induction of anesthesia and CV. With the patients in the lateral position, further VA/Q mismatch with a fall in PaO2 and increased dead space ventilation was observed. Atelectatic lung areas were still present, although the total atelectatic area was slightly decreased. Some of the effects caused by the lateral position could be counteracted by adding PEEP. Perfusion of regions with low VA/Q ratios and venous admixture were then diminished, while PaO2 was slightly increased; shunt blood flow and dead space ventilation were essentially unchanged. During CV + PEEP, there was a decrease in cardiac output, compared to CV in the lateral position. DV + SPEEP was more effective than CV + PEEP in decreasing shunt flow and increasing PaO2 in the lateral position; in addition to this, cardiac output was not affected.

Adult↗
PubMedDate not supplied

Blood gas values during intermittent positive pressure ventilation and spontaneous ventilation in 160 anesthetized horses positioned in lateral or dorsal recumbency.

One hundred sixty horses were anesthetized with xylazine, guaifenesin, thiamylal, and halothane for elective soft tissue and orthopedic procedures. Horses were randomly assigned to one of four groups. Group 1 (n = 40): Horses positioned in lateral (LRG1; n = 20) or dorsal (DRG1; n = 20) recumbency breathed spontaneously throughout anesthesia. Group 2 (n = 40): Intermittent positive pressure ventilation (IPPV) was instituted throughout anesthesia in horses positioned in lateral (LRG2; n = 20) or dorsal (DRG2; n = 20) recumbency. Group 3 (n = 40): Horses positioned in lateral (LRG3; n = 20) or dorsal (DRG3; n = 20) recumbency breathed spontaneously for the first half of anesthesia and intermittent positive pressure ventilation was instituted for the second half of anesthesia. Group 4 (n = 40): Intermittent positive pressure ventilation was instituted for the first half of anesthesia in horses positioned in lateral (LRG4; n = 20) or dorsal (DRG4; n = 20) recumbency. Spontaneous ventilation (SV) occured for the second half of anesthesia. The mean time of anesthesia was not significantly different within or between groups. The mean time of SV and IPPV was not significantly different in groups 3 and 4. Variables analyzed included pH, PaCO2, PaO2, and P(A-a)O2 (calculated). Spontaneous ventilation resulted in significantly higher PaCO2 and P(A-a)O2 values and significantly lower PaO2 values in LRG1 and DRG1 horses compared with LRG2 and DRG2 horses. Intermittent positive pressure ventilation resulted in normocarbia and significantly lower P(A-a)O2 values in LRG2 and DRG2 horses. In LRG2 the PaO2 values significantly increased from 20 minutes after induction to the end of anesthesia. The PaO2 and P(A-a)O2 values were not significantly different from the beginning of anesthesia after IPPV in DRG2 or DRG3. The PaO2 values significantly decreased and the P(A-a)O2 values significantly increased after return to SV in horses in LRG4 and DRG4. The PaO2 values were lowest and the P(A-a)O2 values were highest in all horses positioned in dorsal recumbency compared with lateral recumbency and in SV horses compared with IPPV horses. The pH changes paralleled the changes in PaCO2. Blood gas values during right versus left lateral recumbency in all groups were also evaluated. The PaO2 values were significantly lower and the P(A-a)O2 values were significantly higher during SV in horses positioned in left lateral (LRLG1) compared with right lateral (LRRG1) recumbency.(ABSTRACT TRUNCATED AT 400 WORDS)

Anesthesia, Intravenous↗
PubMed2005

Numerical and experimental study of velocity and temperature characteristics in a ventilated enclosure with underfloor ventilation systems.

UNLABELLED: Airflow and temperature distributions in an enclosure with heat sources ventilated by floor supply jets with floor or ceiling air exit vents were investigated using experimental and numerical approaches. These ventilation configurations represent the floor return or the top return underfloor ventilation systems found in real applications. Experiments and numerical simulations were performed on a full-sized environmental chamber. The results reveal that the temperature stratification in the enclosure highly depended on the thermal length scale of the floor supply jets. When the thermal length scale of the supply jet was >>1, temperature stratification was minor for all tested heat densities and air distribution methods. Significant vertical temperature gradients occurred when the jet thermal length scale was <<1. Changes in air distribution methods also became significant for temperature stratification at small supply jet thermal length scales. Temperature stratification also affected the terminal height of the momentum-dominant region of the vertical buoyant supply jets. The applicability of these results to underfloor ventilation design was also discussed. PRACTICAL IMPLICATIONS: In designing underfloor ventilation systems, supply jet conditions and heat load density have to be considered to avoid thermal discomfort because of excessive temperature stratifications. This study demonstrated, by both numerical simulations and experiments, that thermal length scale can be used as a design indicator to predict thermal stratifications under a floor return and a top return underfloor ventilation setting.

Air Pollution, Indoor↗
PubMed1980

The relationship between maximal ventilation, breathing pattern and mechanical limitation of ventilation.

1. The extent to which the pattern of breathing at maximal ventilation in man is affected by the mechanical properties of the respiratory pump has been studied. 2. The maximal effort flow volume (MEFV) loop has been used to calculate the shortest possible inspiratory (TI) and expiratory (TE) durations associated with the highest ventilation for all tidal volumes (VT). These minimal TIS and TES hve been plotted on a VT-TI-TE diagram. 3. Such predicted minimal TIS and TES were compared with observed minimal values from five healthy subjects who tried to reach their maximal ventilations during three experimental conditions: maximal voluntary hyperventilation, rebreathing, and graded exercise. 4. We have found that exercise increases the maximal flows at all lung volumes and confirmed that rebreathing has no such effect. 5. During hyperventilation the mechanical limits were followed closely for all VTS. During exercise and rebreathing the VT-TI and the VT-TE relationships showed a definite maximum of VT at submaximal ventilation in half the cases. The calculated minimal TIS and TES were approached but not reached. This indicates that maximal ventilation is not entirely limited by the mechanical properties of the respiratory pump, but that mechanical factors influence the regulation of breathing pattern when ventilation approaches the maximal capacity of the respiratory pump.

Adult↗
PubMed1985

Effect of oral high frequency ventilation by jet or oscillator on minute ventilation in normal subjects.

Normal subjects were asked to breathe through an open ended tube while high frequency oscillations were superimposed on tidal breathing via a side arm, either an eight inch (20 cm) loudspeaker or a jet ventilator being used. Both systems were comfortable and well tolerated. Spontaneous minute ventilation fell by 19-46% at frequencies up to 33 Hz without a rise in transcutaneous PCO2. Maximum ventilatory savings occurred at 1.6 Hz with the jet ventilator (p less than 0.01) and at a frequency corresponding to respiratory system resonance with the loudspeaker. This suggests that during oral high frequency ventilation pulmonary gas exchange is improved and leads to more efficient carbon dioxide excretion for a given minute ventilation. This technique provides a practical and simple method of supplementing breathing in conscious subjects, and it may also have application in the management of patients with acute or chronic respiratory failure, where intubation and conventional ventilation might be avoided.

Adult↗
PubMed1996

Effects of assisted ventilation on the work of breathing: volume-controlled versus pressure-controlled ventilation.

During assisted ventilation, the same tidal volume can be delivered in different ways, with the possibility for the physician to vary the ventilatory target (pressure or volume) and the peak flow setting. We compared the effects on the respiratory work rate of assisted ventilation, delivered either with a square wave flow pattern (assist control ventilation [ACV]) or with a decelerating flow pattern and a constant pressure (assisted pressure-control ventilation [APCV]). In the first part of the study where seven patients were studied, inspiratory time and tidal volume were similar in the two modes of ventilation. High and moderate levels of tidal volume (VT) were studied (12 ml/kg and 8 ml/kg, respectively). To obtain moderate VT, inspiratory time was kept constant and, therefore, mean inspiratory flow was reduced. At high VT, no difference between ACV and APCV was noted for breathing pattern, respiratory drive indexes, respiratory muscle work, or arterial blood gases. All patients exhibited respiratory alkalosis. At moderate VT, normal pH was achieved. In this situation significantly lower levels were observed during APCV than during ACV for the power of breathing (10 +/- 2 versus 19 +/- 5 J/min, p<0.05), transdiaphragmatic pressure swing (7 +/- 1 versus 11 +/- 2 cm H2O, p<0.05), and pressure-time index (252 +/- 43 versus 484 +/- 114 cm H2O.s, p<0.05), even though breathing pattern and gas exchange were similar. In the second part of the study where six additional patients were studied, tidal volume was kept constant at a moderate level (8 ml/kg), and we studied the effect of shortening inspiratory time and increasing mean inspiratory flow. At moderate VT and high inspiratory flow, no significant differences could be found between ACV and APCV, and although pressure-time index tended to be lower during APCV, absolute levels of effort were of small magnitude (56 +/- 55 versus 76 +/- 55 cm H2O.s). We conclude that at moderate VT and low flow rates only, inspiratory assistance delivered at a constant pressure reduces the respiratory work rate more effectively than assist control ventilation.

Aged↗
PubMed2000

Compensation for increase in respiratory workload during mechanical ventilation. Pressure-support versus proportional-assist ventilation.

Variation in respiratory impedance may occur in mechanically ventilated patients. During pressure-targeted ventilatory support, this may lead to patient-ventilator asynchrony. We assessed the hypothesis that during pressure-support ventilation (PSV), preservation of minute ventilation (V E) consequent to added mechanical loads would result in an increase in respiratory rate (RR) due to the large reduction in tidal volume (VT). WITH proportional-assist ventilation (PAV), preservation of V E would occur through the preservation of VT, with a smaller effect on RR. We anticipated that this compensatory strategy would result in greater patient comfort and a reduce work of breathing. An increase in respiratory impedance was obtained by chest and abdominal binding in 10 patients during weaning from mechanical ventilation. V E remained constant in both ventilatory modes after chest and abdominal compression. During PSV, this maintenance of VE was obtained through a 58 +/- 3% increase in RR that compensated for a 29 +/- 2% reduction in VT. The magnitudes of the reduction in VT (10 +/- 3%) and of the increase in RR (14 +/- 2%) were smaller (p < 0. 001) during PAV. During both PSV and PAV, chest and abdominal compression caused increases in both the pressure-time product (PTP) of the diaphragm per minute (142.9 +/- 26.9 cm H(2)O. s/min, PSV, and 117.6 +/- 16.4 cm H(2)O. s/min, PAV) and per liter (13.4 +/- 2.5 cm H(2)O. s/L, PSV, and 9.6 +/- 0.7 cm H(2)O. s/L, PAV). These increments were greater (p < 0.001) during PSV than during PAV. The capability of keeping VT and V E constant through increases in inspiratory effort after increases in mechanical loads is relatively preserved only during PAV. The ventilatory response to an added respiratory load during PSV required greater muscle effort than during PAV.

Adult↗
PubMed2001

Noninvasive proportional assist ventilation for acute respiratory insufficiency. Comparison with pressure support ventilation.

Noninvasive positive pressure ventilation (NPPV) is usually applied using pressure support ventilation (PSV). Proportional assist ventilation (PAV) is a newer mode that delivers assisted ventilation in proportion to patient effort. We hypothesized that PAV for NPPV would support gas exchange and avoid intubation as well as PSV and be more comfortable and tolerable for patients. Adult patients with acute respiratory insufficiency were randomized to receive NPPV with PAV delivered using the Respironics Vision ventilator or PSV using a Puritan-Bennett 7200ae critical care ventilator. Each mode was adjusted to relieve dyspnea and improve gas exchange until patients met weaning or intubation criteria, died, or refused to continue. Twenty-one and 23 patients were entered into the PAV and PSV groups, respectively, and had similar diagnoses and baseline characteristics, although pH was slightly lower in the PAV group (7.30 versus 7.35, p = 0.02). Mortality and intubation rates were similar, but refusal rate was lower, reduction in respiratory rate was more rapid, and there were fewer complications in the PAV group. We conclude that use of the PAV mode is feasible for noninvasive therapy of acute respiratory insufficiency. Compared with PSV delivered with the Puritan-Bennett 7200ae, PAV is associated with more rapid improvements in some physiologic variables and is better tolerated.

Acute Disease↗
PubMed1989

Ventilation-perfusion mismatching in chronic obstructive pulmonary disease during ventilator weaning.

Using the multiple inert gas elimination technique, we studied ventilation-perfusion (VA/Q) relationships in eight patients with chronic obstructive pulmonary disease (COPD) during mechanical ventilation (MV) and again during weaning (spontaneous ventilation [SV] through an endotracheal tube) from MV needed for acute respiratory failure. The patients, seven men and one woman with a mean age of 63 +/- 2.8 (SEM) yr (FEV1 33 +/- 5.2% of predicted), required MV for 9.0 +/- 2.4 days prior to the study. The patients were studied at maintenance FIO2 (0.28 to 0.40) while breathing 100% O2, both during MV and SV. After 30 min of SV, PaCO2 increased from 48.9 +/- 3.4 to 58.3 +/- 3.1 mm Hg (p = 0.003) and pH decreased from 7.42 +/- 0.01 to 7.36 +/- 0.01 (p = 0.001) without significant changes in PaO2. Despite a decrease in tidal volume (VT) from 700.0 +/- 41.1 during MV to 313.0 +/- 39.6 ml during SV (p = 0.001), minute ventilation remained unchanged (from 8.2 +/- 0.7 during MV to 7.4 +/- 0.6 L/min during SV). Furthermore, cardiac output (QT), oxygen delivery (QO2), and mixed venous PO2 (PVO2) significantly rose during SV when compared with the MV (QT: from 4.7 +/- 0.4 to 6.7 +/- 0.7 L/min, p = 0.011; QO2: from 857.3 +/- 113.0 to 1078.5 +/- 158.9 ml/min, p = 0.0074; PVO2: from 36.7 +/- 1.1 to 42.3 +/- 2.2 mm Hg, p = 0.041). Overall VA/Q inequality worsened as blood flow was redistributed to low VA/Q areas (from 9.4 +/- 4.4 to 19.6 +/- 5.3% of QT, p = 0.05). The dispersion of the ventilation distribution (log SDV) significantly worsened during SV (from 1.0 +/- 0.08 during MV to 1.2 +/- 0.08 during SV, p = 0.044). No changes were observed in either series dead space or ventilation of high VA/Q ratio units.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1991

Distribution of ventilation and perfusion with different modes of mechanical ventilation.

We compared pulmonary gas exchange during synchronized intermittent mandatory ventilation (SIMV), pressure support ventilation (PSV), and airway pressure release ventilation (APRV). Nine subjects aged 56 to 75 yr were studied from 4 to 19 h after cardiac operations. When subjects were ready to be weaned from mechanical ventilation their ventilation-perfusion distribution was estimated using the multiple inert gas elimination technique during SIMV. The subjects then received PSV and APRV during alternating periods on a randomized basis, and the gas-exchange measurements were repeated. Vasoactive infusions and inspired oxygen fraction were held constant throughout the investigation. The results indicated that the major characteristics of the main mode of the VA/Q distributions (mean, standard deviation, and skew) were similar during all three modes. Dead space was lower during APRV (30.1 +/- 1.7% [SEM]) than during SIMV (36.2 +/- 1.5%) and PSV (37.1 +/- 2.7%) (p less than 0.05). Right-to-left shunt was significantly greater during APRV (19.9 +/- 2.3%) than during SIMV (15.4 +/- 1.7%) (p less than 0.05). Peak airway pressure (Paw) was higher during SIMV (32.8 +/- 1.3 cm H2O) than both PSV (19.4 +/- 2.1 cm H2O) and APRV (14.3 +/- 1.0 cm H2O) (p less than 0.05). Minute ventilation was lower during APRV (7.5 +/- 0.07 L/min) than during SIMV (9.4 +/- 0.6 L/min) and PSV (9.0 +/- 0.5 L/min) (p less than 0.05). Hemodynamic variables were similar during all three modes. We conclude that all three modes provide acceptable oxygenation and ventilatory support.

Aged↗
PubMed2005

The theoretical basis for using apnoeic oxygenation via the non-ventilated lung during one-lung ventilation to delay the onset of arterial hypoxaemia.

At the time one-lung ventilation is initiated, nitrogen from the atmosphere may enter the non-ventilated lung via a double-lumen tube connector that has been left open to air, even momentarily. Ongoing oxygen uptake from the non-ventilated lung raises the partial pressure of nitrogen. This should lead to activation of hypoxic pulmonary vasoconstriction and a reduction in intra-pulmonary shunting. However, in spite of this, some patients still become hypoxaemic. In such cases, it may be advantageous to have excluded nitrogen from the non-ventilated lung by connecting it to an oxygen source at ambient pressure. Ongoing apnoeic oxygenation, while the airways are patent, and as the lung collapses, should delay the onset of arterial desaturation. In this paper we review the theoretical basis for apnoeic oxygenation during one-lung ventilation, and in particular on oxygen uptake by the non-ventilated lung prior to and during its subsequent collapse.

Anesthesia, Inhalation↗
PubMed2004

Lung recruitment improves the efficiency of ventilation and gas exchange during one-lung ventilation anesthesia.

UNLABELLED: Atelectasis in the dependent lung during one-lung ventilation (OLV) impairs arterial oxygenation and increases dead space. We studied the effect of an alveolar recruitment strategy (ARS) on gas exchange and lung efficiency during OLV by using the single-breath test of CO(2) (SBT-CO(2)). Twelve patients undergoing thoracic surgery were studied at three points in time: (a) during two-lung ventilation and (b) during OLV before and (c) after an ARS. The ARS was applied selectively to the dependent lung and consisted of an increase in peak inspiratory pressure up to 40 cm H(2)O combined with a peak end-expiratory pressure level of 20 cm H(2)O for 10 consecutive breaths. The ARS took approximately 3 min. Arterial blood gases, SBT-CO(2), and metabolic and hemodynamic variables were recorded at the end of each study period. Arterial oxygenation and dead space were better during two-lung ventilation compared with OLV. PaO(2) increased during OLV after lung recruitment (244 +/- 89 mm Hg) when compared with OLV without recruitment (144 +/- 73 mm Hg; P < 0.001). The SBT-CO(2) analysis showed a significant decrease in dead-space variables and an increase in the variables related to the efficiency of ventilation during OLV after an ARS when compared with OLV alone. In conclusion, ARS improves gas exchange and ventilation efficiency during OLV. IMPLICATIONS: In this article, we showed how a pulmonary ventilatory maneuver performed in the dependent lung during one-lung ventilation anesthesia improved arterial oxygenation and dead space.

Adult↗
PubMed1999

Percutaneous transtracheal jet ventilation: a safe, quick, and temporary way to provide oxygenation and ventilation when conventional methods are unsuccessful.

INTRODUCTION: Percutaneous transtracheal jet ventilation (PTJV) with a large-bore angiocath that is inserted through the cricothyroid membrane can provide immediate oxygenation from a high-pressure (50 lb per square inch) oxygen wall outlet, as well as ventilation by means of manual triggering. The objective of this retrospective study is to highlight the potential benefit of PTJV as a temporary lifesaving procedure during difficult situations when oral endotracheal intubation is unsuccessful and bag-valve-mask ventilation is ineffective for oxygenation during acute respiratory failure. METHODS: The medical records of 29 consecutive patients who required emergent PTJV within the past 4 years were reviewed. PTJV was required because the pulse O(2) saturation could not be maintained at > 90% with bag-mask-valve ventilation and because the airway could not be secured quickly with direct laryngoscopy. RESULTS: The cricothyroid membrane was cannulated successfully in 23 patients. In these patients, pulse O(2) saturation was raised to > 90% and was maintained with PTJV until the airway was secured. All but 3 of the 23 patients were subsequently intubated orally. In one patient, PTJV maintained adequate gas exchange until an emergent tracheostomy was performed. In two patients, airway exchange catheters were inserted into the trachea due to a small glottic aperture. The endotracheal tube was slid over the catheter. In 6 of the 29 patients, there was difficulty inserting a catheter through the cricothyroid membrane or there was inability to insufflate the oxygen with a jet ventilator. There were no immediate fatalities from the use of PTJV. CONCLUSION: Based on the subsequent insertion of an endotracheal tube into the trachea, there were two important benefits in the patients who underwent PTJV successfully. First, PTJV provided effective oxygenation, while allowing adequate time for upper airway visualization and possible suctioning of oropharyngeal secretions. Second, tracheal intubation was subsequently easier, possibly because the high tracheal pressure from the gas insufflation opened the collapsed glottis, making visualization of the glottic aperture better. PTJV is safe and quick in providing immediate oxygenation, and therefore should be considered as an alternative to insistent, multiple intubation attempts, when neither bag-mask-valve ventilation nor endotracheal intubation is feasible in providing adequate gas exchange.

Aged↗
PubMed2000

Protocol weaning of mechanical ventilation in medical and surgical patients by respiratory care practitioners and nurses: effect on weaning time and incidence of ventilator-associated pneumonia.

STUDY OBJECTIVES: (1) To determine the effect of a single ventilator management protocol (VMP) used in medical and surgical ICUs on the duration of mechanical ventilation. (2) To determine the effect of a VMP on the incidence of ventilator-associated pneumonia (VAP). DESIGN: Prospective, randomized, controlled study. SETTING: : University medical center. PATIENTS: Three hundred eighty-five patients receiving mechanical ventilation between June 1997 and May 1998. INTERVENTIONS: A respiratory care practitioner- and registered nurse-driven VMP. RESULTS: Intervention and control groups were comparable with respect to age, sex, severity of illness and injury, and duration of respiratory failure at the time of randomization. The duration of mechanical ventilation for patients was decreased from a median of 124 h for the control group to 68 h in the VMP group (p = 0.0001). Thirty-one total instances of VAP were noted. Twelve patients in the surgical control group had VAP, compared with 5 in the surgical VMP group (p = 0.061). The impact of the VMP on VAP frequency was less for medical patients. Mortality and ventilator discontinuation failure rates were similar between control and VMP groups. CONCLUSIONS: A VMP designed for multidisciplinary use was effective in reducing duration of mechanical ventilatory support without any adverse effects on patient outcome. The VMP was also associated with a decrease in incidence of VAP in trauma patients. These results, in conjunction with prior studies, suggest that VMPs are highly effective means of improving care, even in university ICUs.

Adult↗
PubMed2001

Is it safe for patients with chronic hypercapnic respiratory failure undergoing home noninvasive ventilation to discontinue ventilation briefly?

STUDY OBJECTIVES: A brief discontinuation (< 1 week) of long-term ventilation may be necessary in patients who are not totally ventilator-dependent in cases of technical problems, intolerable nasal irritation, upper airway congestion, or travel. We examined the incidence, timing, and causes of possible clinical deterioration after a brief withdrawal of ventilation in patients with chronic respiratory failure (CRF) who were well-established on long-term noninvasive mechanical ventilation (NIMV). STUDY DESIGN: Prospective clinical study. PATIENTS: Eleven inpatients in clinically stable condition (COPD, 6 patients; and restrictive thoracic disease [RTD], 5 patients) who had severe CRF (PaCO(2), > 50 mm Hg) and had been receiving NIMV for (mean +/- SD) 19.3 +/- 5.3 months were enrolled. INTERVENTIONS AND MEASUREMENTS: Arterial blood gas (ABG) levels, maximal inspiratory pressure (PImax), breathing pattern, dyspnea rating, and life symptoms (measured by a questionnaire) were recorded daily after NIMV withdrawal for 6 days or until the patients showed clinical and/or ABG level deterioration. Pulmonary function tests were performed and neuromuscular drive was measured at the beginning and the end of the study. RESULTS: Five of the 11 patients (45.4%) [COPD, 3 patients; and RTD, 2 patients] were reconnected to a ventilator before the scheduled time because of ABG level deterioration. Despite these changes, none of the patients reported severe worsening of symptoms or other medical complications. The patients whose ABG levels worsened had statistically significant decreases in tidal volume and PImax, suggesting that the development of alveolar hypoventilation was related to respiratory muscle weakness. CONCLUSIONS: A brief discontinuation of NIMV in patients who were affected by chronic hypercapnic respiratory failure and were well-established on NIMV is associated with a relatively high incidence of ABG level worsening due to the development of alveolar hypoventilation. If NIMV must be briefly interrupted for clinical reasons, the patient should be monitored closely for abrupt worsening, and prompt technical intervention should be provided if a ventilator fails.

Adult↗
PubMed2006

Prolonged invasive ventilation following acute ventilatory failure in COPD: weaning results, survival, and the role of noninvasive ventilation.

BACKGROUND: Invasive ventilation for COPD has significant mortality, and weaning can be difficult. At Papworth Hospital, we provide a specialist weaning service using noninvasive ventilation (NIV) for patients requiring prolonged invasive ventilation after recovery from acute illness. We analyzed our results for patients with COPD to identify factors associated with weaning outcome and survival. METHODS: A retrospective analysis was conducted of COPD patients admitted for weaning from invasive ventilation, from 1992 to 2003. Weaning success and survival were assessed. Associations were sought between these outcomes and age, sex, spirometry, arterial blood gas levels, APACHE (acute physiology and chronic health evaluation) II score, length of stay (LOS), and the use of NIV and long-term oxygen therapy. RESULTS: Sixty-seven patients were identified, all of whom were receiving tracheostomy ventilation on transfer to the Respiratory Support and Sleep Centre (RSSC). Sixty-four patients (95.5%) were weaned, and 62 patients survived to hospital discharge. NIV was used in weaning 40 patients and in the long term in 25 patients. Median survival was 2.5 years (interquartile range, 0.7 to 4.6 years). One-year, 2-year, and 5-year survival rates were 68%, 54%, and 25%, respectively. Long-term survival was inversely associated with age and LOS in the ICU and the RSSC. The provision of maintenance NIV after weaning was associated with better long-term survival, independent of age and LOS (hazard rate, 0.48; p = 0.03). CONCLUSIONS: These results demonstrate that a specialist multidisciplinary approach, including the use of NIV, can be successful in weaning most COPD patients from prolonged invasive ventilation. The data also suggest that long-term NIV may improve survival in selected patients.

Aged↗
PubMed2006

Therapeutic hypercapnia and ventilation-perfusion matching in acute lung injury: low minute ventilation vs inspired CO2.

STUDY OBJECTIVES: Hypercapnic acidosis has antiinflammatory effects in animal models of acute lung injury (ALI) and improves ventilation-perfusion (V/Q) matching in normal lungs. The effect of hypercapnia on V/Q matching in ALI is conflicting. Hypercapnic acidosis produced by reduced tidal volumes (Vts) was associated with an increased shunt fraction (QS/QT) in patients with ALI compared with control subjects. Vt differences between groups make the assessment of hypercapnic acidosis on V/Q matching difficult. Adding CO2 to the inhaled gas allows the comparison of gas exchange under identical Vt conditions. We hypothesized the presence of hypercapnic acidosis from inspired carbon dioxide (ICD) would improve gas exchange in ALI and would be superior to that of low minute ventilation (LVe) produced by reduced respiratory rate, rather than Vt. DESIGN: University laboratory study of anesthetized New Zealand White rabbits. INTERVENTIONS: Assessment of V/Q relationships using the multiple inert gas elimination technique was performed in 10 saline solution-lavaged animals, which were ventilated with 6 mL/kg Vts and a positive end-expiratory pressure of 8 cm H2O. Each rabbit was studied while it was in eucapnia, followed by hypercapnia (Pa(CO2), 95 to 100 mm Hg) induced by LVe from decreased respiratory rate and by 10% ICD, in random order. MEASUREMENTS AND RESULTS: The Pa(O2) was greater in ICD and LVe compared to eucapnia, but no significant differences in alveolar-arterial oxygen pressure difference or Pa(O2)/fraction of inspired oxygen ratio occurred. LVe statistically reduced the mean V/Q distributions compared with ICD and eucapnia. Log SDs of ventilation and combined retention and excretion curves of the dispersion index were both increased during LVe, indicating the presence of unfavorable changes in ventilation distribution. Neither LVe nor ICD altered the QS/QT. CONCLUSIONS: LVe slightly impairs overall gas exchange and ventilation distribution, but does not increase QS/QT compared with eucapnia and ICD. While ICD does not significantly improve gas exchange, it may be superior to LVe in achieving the antiinflammatory effects of "therapeutic" hypercapnia, since it does not adversely alter gas exchange and has the potential to make the lung more uniformly acidotic.

Animals↗