A consideration of neonatal resuscitation

There are currently two major areas of resuscitation of the newborn which have come into question: the use of intermittent positive pressure ventilation and the use of oxygen. There is evolving evidence that volutrauma associated with IPPV, especially in the premature infant, may induce changes in the lung which can lead to chronic lung disease. There is reason to believe that the use of continuous positive airway pressure in premature infants who are making respiratory efforts may be less harmful than the use of IPPV. With regard to the use of oxygen, it is clear that most infants can be successfully resuscitated with room air. Although we can identify markers for oxidative stress in newborns when resuscitated with 100% oxygen, the clinical importance of these markers remain an open issue. If the presence of these markers after resuscitation is shown to relate to clinical problems, then the use of oxygen may need to be considered.

[Intermittent mandatory ventilation]

Intermittent mandatory ventilation (IMV) is a mode of ventilation that allows the patient to make spontaneous breaths during the expiratory phase of mandatory ventilator breaths. There are two types of IMV according to whether respirator breaths are synchronized with the patient's respiratory efforts: Non-synchronized IMV and synchronized IMV (SIMV), and according to whether SIMV is volume- or pressure programmed. The main advantage of SIMV is that the respirator delivers the preset ventilator pressure and rate while allowing the patient to breath spontaneously, thus facilitating progressive weaning from mechanical ventilation. It diminishes the risk of barotrauma, produces less hemodynamic com-promise than control ventilation, reduces atrophy of respiratory muscles and the need for sedation and muscle relaxation and can be associated with pressure support ventilation.

[Long-term outcome of patients treated by home mechanical ventilation]

To investigate the long-term survival of 95 patients treated by home mechanical ventilation, we prospectively analyzed the outcomes of their cases (treatments: 34, tracheostomy; 61, non-invasive methods) using the database of the local registration system in Aichi Prefecture. The annual actuarial probability of continuing home mechanical ventilation for the tracheostomized patients was 97.0% in the first year, 79.0% in the second year, 79.0% in the third year, and 69.2% in the fourth year, and those for the patients treated by non-invasive ventilation were 85.6%, 67.9%, 56.8%, and 46.4%, respectively. In comparison with patients with neuromuscular disease, patients with respiratory disease (both tracheostomized and non-tracheostomized) tended to show a lower continuation ratio, but the difference was not statistically significant. These data were comparable to those of previous reports, suggesting that home respiratory care in Aichi Prefecture satisfied the normal standards of quality.

[Artificial respiration at home seen in a 5-year perspective. Established treatment, but remarkable differences among the counties]

The Swedish prevalence of home mechanical ventilation is 8.2 per 100.000 with 10% annual increase. There is a large span (20 vs 2 per 100.000) between "top level" and "low level" counties, in spite of Sweden's homogeneous publicly financed system for provision of health care. The largest prevalence difference was found in patients with obstructive sleep apnoea syndrome (Pickwickian type), but their blood gas and lung function data were identical in top-level vs low-level counties. These data refute the hypothesis of overprescription in top-level counties. We conclude that the most probable explanation is under-recognition of patients in low-level counties.

Treatment of type I spinal muscular atrophy with noninvasive ventilation and gastrostomy feeding

Type I spinal muscular atrophy (SMA) is a rapidly progressive, degenerative neuromuscular disease of infancy. In severe SMA, weakness, hypotonia, and bulbar involvement lead to progressive respiratory insufficiency and swallowing dysfunction, which are frequently complicated by aspirations. There are few studies reported in the literature that address the respiratory management of type I SMA. This article reports the results of treating four patients with infantile SMA with noninvasive positive pressure ventilation and gastrostomy feeding. All patients had gastroesophageal reflux disease, which was managed medically. Despite these therapies, survival was only 1 to 3.5 months after presenting with severe aspirations. The treatment strategy, which can be effective in less rapidly progressive neuromuscular diseases, did not alter the very poor prognosis of type I SMA. The treatment options are reviewed, and a strategy designed to optimize quality of life for infants with this fatal disease is presented.

Secondary failure of nasal intermittent positive pressure ventilation using the Monnal D: effects of changing ventilator

BACKGROUND

Some patients started on nasal intermittent positive pressure ventilation (NIPPV) with the Monnal D ventilator deteriorate after a period. The effects of changing them to the Nippy ventilator were investigated.

METHODS

The records of such patients were examined retrospectively. Comparisons were made between blood gas tensions and overnight oximetry records before NIPPV, 12 weeks after the initiation of NIPPV with the Monnal D, at the time of deterioration, and 12 weeks after initiation of treatment with the Nippy ventilator.

RESULTS

Ten patients (seven women) were identified. Prior to starting NIPPV their mean (SD) age was 59.6 (8.39) years and their mean arterial oxygen and carbon dioxide tensions (PaO2 and PaCO2) while breathing air were 6.1 (1.79) and 9.6 (3.28) kPa, respectively. All were started on NIPPV with the Monnal D with improvements in symptoms, PaO2, PaCO2, and overnight oximetry after 12 weeks of treatment. After a mean interval of 118 (69.0) weeks all measures of ventilation had deteriorated and the patients were converted to the Nippy ventilator. Twelve weeks after initiation of treatment with the Nippy ventilator symptoms and overnight oximetry were improved again and the mean PaO2 and PaCO2 were 8.9 (1.27) and 6.9 (0.45) kPa, respectively. After a total mean period of 59 (26.9) weeks on the Nippy all but one of the patients have maintained this improvement.

CONCLUSIONS

Support with NIPPV using the Monnal D ventilator may fail after an interval and changing to the Nippy ventilator can reverse this deterioration, probably because of its superior responsiveness to leaks and patient effort. The regular follow up of patients on long term NIPPV is necessary if secondary treatment failure is to be identified and effectively treated.

Airway secretion clearance by mechanical exsufflation for post-poliomyelitis ventilator-assisted individuals

Pulmonary complications from impaired airway secretion clearance mechanisms are major causes of morbidity and mortality for post-poliomyelitis individuals. The purpose of this study was to review the long-term use of manually assisted coughing and mechanical insufflation-exsufflation (MI-E) by post-poliomyelitis ventilator-assisted individuals (PVAIs) and to compare the peak cough expiratory flows (PCEF) created during unassisted and assisted coughing. Twenty-four PVAIs who have used noninvasive methods of ventilatory support for an average of 27 years, relied on methods of manually assisted coughing and/or MI-E without complications during intercurrent respiratory tract infections (RTIs). Nine of the 24 individuals were studied for PCEF. They had a mean forced vital capacity (FVC) of 0.54 +/- 0.47L and a mean maximum insufflation capacity achieved by air stacking of ventilator insufflations and glossopharyngeal breathing of 1.7L. The PCEF were as follows: unassisted, 1.78 +/- 1.16L/sec; following a maximum assisted insufflation, 3.75 +/- 0.73L/sec; with manual assistance by abdominal compression following a maximum assisted insufflation, 4.64 +/- 1.42L/sec; and with MI-E, 6.97 +/- 0.89L/sec. We conclude that manually assisted coughing and MI-E are effective and safe methods of airway secretion clearance for PVAIs with impaired expiratory muscle function who would otherwise be managed by endotracheal suctioning. Severely decreased maximum insufflation capacity but not vital capacity indicate need for a tracheostomy.

An experimental randomized study of five different ventilatory modes in a piglet model of severe respiratory distress

OBJECTIVES

To characterize different modes of pressure- or volume-controlled mechanical ventilation with respect to their short-term effects on oxygen delivery (DO2). Furthermore to investigate whether such differences are caused by differences in pulmonary gas exchange or by airway-pressure-mediated effects on the central hemodynamics.

DESIGN

After inducing severe respiratory distress in piglets by removing surfactant, 5 ventilatory modes were randomly and sequentially applied to each animal.

SETTING

Experimental laboratory of a university department of Anesthesiology and Intensive Care.

ANIMALS

15 piglets after repeated bronchoalveolar lavage.

INTERVENTIONS

Volume-controlled intermittent positive-pressure ventilation (IPPV) with either 8 or 15 cmH2O PEEP; pressure-controlled inverse ratio ventilation (IRV); pressure-controlled high-frequency positive-pressure ventilation (HFPPV) and pressure-controlled high frequency ventilation with inspiratory pulses superimposed (combined high frequency ventilation, CHFV). The prefix (L) indicates that lavage has been performed.

MEASUREMENTS AND RESULTS

Measurements of gas exchange, airway pressures, hemodynamics, functional residual capacity (using the SF6 method), intrathoracic fluid volumes (using a double-indicator dilution technique) and metabolism were performed during ventilatory and hemodynamic steady state. The peak inspiratory pressures (PIP) were significantly higher in the volume-controlled low frequency modes (43 cmH2O for L-IPPV-8 and L-IPPV-15) than in the pressure-controlled modes (39 cmH2O for L-IRV, 35 cmH2O for L-HFPPV and 33 cmH2O for L-CHFV, with PIP in the high-frequency modes being significantly lower than in inverse ratio ventilation). The mean airway pressure (MPAW) after lavage was highest with L-IRV (26 cmH2O). In the ventilatory modes with a PEEP > 8 cmH2O PaO2 did not differ significantly and beyond this "opening threshold" MPAW did not further improve PaO2. Central hemodynamics were depressed by increasing airway pressures. This is especially true for L-IRV in which we found the highest MPAW and at the same time the lowest stroke index (74% of IPPV).

CONCLUSIONS

In this model, as far as oxygenation is concerned, it does not matter in which specific way the airway pressures are produced. As far as oxygen transport is concerned, i.e. aiming at increasing DO2, we conclude that optimizing the circulatory status must take into account the circulatory influence of different modes of positive pressure ventilation.

Continuous positive airway pressure (CPAP) vs. intermittent mandatory pressure release ventilation (IMPRV) in patients with acute respiratory failure

Intermittent Mandatory Pressure Release Ventilation (IMPRV) is a positive pressure spontaneous breathing ventilatory mode in which airway pressure is released intermittently and synchronously with patient's spontaneous expiration in order to provide ventilatory assistance. Eight critically ill patients free of any factor known to alter chest wall mechanics (group 1) and 8 critically ill patients whose spontaneous respiratory activity was markedly altered by a flail chest, or by a C5 quadraplegia and/or by the administration of opioids (group 2) were studied prospectively. CPAP and IMPRV were administered to each patient in a random order during a 1 h period using a CESAR ventilator. Gas flow, tidal volume, tracheal pressure, esophageal pressure, end-expiratory lung volume and hemodynamic parameters were measured. In group 1 patients, the ventilatory assistance provided by IMPRV was associated with a significant decrease in spontaneous tidal volume whereas all other respiratory parameters remained unchanged. In group 2 patients, IMPRV increased minute ventilation from 8.0 +/- 2.61/min to 12.2 +/- 1.81/min (p less than 0.05), decreased PaCO2 from 46 +/- 7.3 mmHg to 38 +/- 6.8 mmHg (p less than 0.05) and reduced respiratory frequency from 21 +/- 10 bpm to 14 +/- 5.7 bpm (p less than 0.07). These results show that IMPRV provides significant ventilatory assistance to patients with mild acute respiratory failure either by decreasing patient's contribution to minute ventilation or by increasing alveolar ventilation in presence of respiratory depression of central or peripheral origin.

High frequency jet ventilation in experimental pulmonary emphysema

The effects of high frequency jet ventilation (HFJV, f = 2 Hz and 8 Hz, I:E = 0.43, FiO2 = 0.4) were studied and compared with intermittent positive pressure ventilation (IPPV, f = 10-14 breaths/min, VT = 15 ml/kg, I:E = 0.5, FiO2 = 0.4) in 8 dogs before and after induction of panlobular emphysema (PLE). PLE increased alveolar-arterial PO2 difference (PA-aO2) during all modes of ventilation, whereas PaCO2 did not change significantly. In both periods of the study, HFJV8 Hz was less effective in terms of CO2-elimination and oxygenation. In the control-period, functional residual capacity (FRC) was 937 +/- 212 ml. The increase during HFJV (HFJV2 Hz: 1156 +/- 508 ml, HFJV8 Hz: 1153 +/- 433 ml) did not reach significance (P = 0.09). Closing volume (CV) increased from 1.5 +/- 4.3% of vital capacity (%VC) (IPPV) to 6.3 +/- 7.1%VC (HFJV2 Hz) and 10.8 +/- 9.8% VC (HFJV8 Hz), respectively. In the PLE-period, FRC and CV increased significantly to 1107 +/- 207 ml and 14.1 +/- 7.0% VC respectively during IPPV (P less than 0.05). Application of HFJV neither increased FRC (HFJV2 Hz: 1153 +/- 433 ml, HFJV8 Hz: 1005 +/- 344 nor CV 14.8 +/- 6.0% VC and 13.9 +/- 8.1% VC, respectively). It is concluded that HFJV induces no alveolar overdistension in dogs with emphysematous lungs.

An experimental randomized study of six different ventilatory modes in a piglet model with normal lungs

A randomized study of 6 ventilatory modes was made in 7 piglets with normal lungs. Using a Servo HFV 970 (prototype system) and a Servo ventilator 900 C the ventilatory modes examined were as follows: SV-20V, i.e. volume-controlled intermittent positive-pressure ventilation (IPPV); SV-20VIosc, i.e. volume-controlled ventilation (IPPV) with superimposed inspiratory oscillations; and SV-20VEf, i.e. volume-controlled ventilation (IPPV) with expiratory flush of fresh gas; HFV-60 denotes low-compressive high-frequency positive-pressure ventilation (HFPPV) and HVF-20 denotes low-compressive volume-controlled intermittent positive-pressure ventilation; and SV-20P denotes pressure-controlled intermittent positive-pressure ventilation. With all modes of ventilation a PEEP of 7.5 cm H2O was used. In the abbreviations used, the number denotes the ventilatory frequency in breaths per minute (bpm). HFV indicates that all gas was delivered via the HFV 970 unit. The ventilatory modes described above were applied randomly for at least 30 min, aiming for a normoventilatory steady state. The HFV-60 and the HFV-20 modes gave lower peak airway pressures, 12-13 cm H2O compared to approximately 17 cm H2O for the other ventilatory modes. Also the mean airway pressures were lower with the HFV modes 8-9 cm H2O compared to 11-14 cm H2O for the other modes. The gas distribution was evaluated by N2 wash-out and a modified lung clearance index. All modes showed N2 wash-out according to a two-compartment model. The SV-20P mode had the fastest wash-out, but the HFV-60 and HFV-20 ventilatory modes also showed a faster N2 wash-out than the others.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of SIMV plus inspiratory pressure support on VA/Q distributions during postoperative weaning

Since the introduction of synchronized intermittent mandatory ventilation (SIMV) several advantages have been attributed to this ventilatory mode, one of them being a more homogeneous distribution of ventilation and perfusion than during controlled mechanical ventilation (CMV). Up to now no data are available to confirm whether this is true when SIMV is used in combination with inspiratory pressure support (IPS). Therefore, we compared the influence of CMV and SIMV + IPS on the distributions of ventilation and perfusion in 9 patients undergoing weaning from postoperative mechanical ventilation. Continuous distributions of ventilation and perfusion were assessed using the multiple inert gas elimination technique (MIGET). SIMV + IPS did not induce any change in the hemodynamic or oxygenation parameters, in particular CI and PaO2 remained constant. Physiological dead space (VD/VT) increased, but PaCO2 remained unchanged due to increased minute ventilation (from 9.5 +/- 0.9 l.min-1 to 11.3 #/- 1.2 l.min-1). The perfusion distributions remained unaltered; there was no change in QS/QT nor in the perfusion of the low VA/Q lung regions. This result was underscored by the unchanged dispersion of the perfusion distribution (log SDQ). The increased VD/VT was caused by increased inert gas dead space (from 22.0 +/- 9.6 to 26.8 +/- 8.7%) which was accompanied by increased ventilation of lung regions with high VA/Q ratios (10 less than VA/Q less than 100) in 3 patients. These results show that in our group of patients partial removal of CMV together with pressure support assistance of spontaneous ventilation did not induce a clinically significant loss of the efficiency of the breathing pattern.(ABSTRACT TRUNCATED AT 250 WORDS)

Portable volume ventilators

We evaluated 5 portable volume ventilators from 4 manufacturers. Ventilation requirements in general patient care areas in the hospital differ from those for home care; therefore, we considered use of the units for these applications separately. None of the units are ideal for either application because of the limitations and risks of each ventilator. All units are rated Conditionally Acceptable, but are ranked for hospital use only. The primary conditions for acceptable hospital use are that exhaled-volume monitoring be performed for all patients and that O2 monitoring be performed both when setting FIO2 and continuously when FIO2 levels are critical. For home care, users should carefully weigh the advantages and disadvantages of each unit and base their choice of a unit primarily on individual patient needs, ease of use, and safety factors.

Demand and continuous flow intermittent mandatory ventilation systems

A mechanical lung was used to evaluate the pressure and flow characteristics of four demand and two continuous flow intermittent mandatory ventilation (IMV) systems. The amount of negative pressure required to initiate inspiratory flow and peak expiratory resistance were measured. The inspiratory pressure required to initiate flow in the demand mode was also compared to pressures generated in the assist mode. In addition, the peak expiratory resistance was measured with four commercially available exhalation valves. Results showed that the ventilator manometer measuring internal machine pressures significantly underestimated the amount of negative pressure required to open the demand valve (p less than 0.01). There are major differences in the flow and pressure characteristics among demand and continuous flow IMV systems. Systems that impose high inspiratory elastic threshold loads and expiratory flow resistive loads may have a deleterious effect on the mechanics of breathing, and thereby limit weaning success and eventually impair the recovery of certain patients in respiratory failure. The basic methodology, especially the simple technique of inserting an aneroid manometer in line next to a patient's ET tube, for measuring proximal negative inspiratory force (NIF test) can be easily applied to any and all ventilators at any practitioner's individual institution.

[Adjustment of synchronized intermittent ventilation with the Drager Company's SIMV Pulmolog]

When choosing an IMV frequency in a respirator, the aim should be to guarantee a minimum of ventilation. With most respirators the "time-window" for the synchronisation of the mandatory stroke volume is within the ventilatory cycle. Thus, the IMV frequency corresponds to the adjusted minimum mechanical ventilation frequency and can be increased only by the patient's spontaneous breathing activity. With the Dräger "Pulmolog", however, the spontaneous breathing phase--not the ventilatory cycle--is already determined by choosing the IMV frequency. This difference is most important for daily clinical practice, as the minimum IMV frequency may be below the adjusted one. The manufacturer has reacted by changing the data on the manufacturer's label.

Extubation criteria after weaning from intermittent mandatory ventilation and continuous positive airway pressure

The "traditional" weaning criteria, arterial blood gases, and a number of other physiologic variables were measured in 47 patients to evaluate to what extent reduced ventilatory reserves or extrapulmonary organ dysfunction affect successful extubation. All patients had been weaned from continuous positive airway pressure (CPAP) and from mechanical ventilation according to the intermittent mandatory ventilation (IMV) method; at the time of study, all patients had compromised arterial oxygenation relieved by supplemental inspired oxygen. No significant difference between patients successfully extubated and those who required reintubation was found using the traditional weaning criteria or blood gases. On the other hand, patients who required reintubation had significantly lower urine volume (p less than 0.01), lower respiratory quotient values (p less than 0.05), and a higher incidence of positive blood culture (p less than 0.05). These 3 variables also correlated best to the patients' outcome after extubation.

Efficiency of manual ventilation using the original EMO system

The efficiency of the Oxford Inflating Bellows for intermittent positive pressure ventilation using a partially closed Heidbrink expiratory valve has been assessed by measuring the arterial carbon dioxide tension (PaCO2) after various intervals of IPPV on eight patients. It was found that satisfactory alveolar ventilation was achieved if a degree of hyperventilation was employed.