Conventional Intermittent Mandatory Ventilation Research Articles

Episodes of hypoxemia during synchronized intermittent mandatory ventilation in ventilator‐dependent very low birth weight infants

Distinct patterns of asynchrony, and episodes of hypoxemia, may occur in a spontaneously breathing preterm infant during conventional intermittent mandatory ventilation (IMV) on traditional time-cycled, pressure-limited ventilators. Synchronized IMV (SIMV) and assist/control ventilation are frequent modes of patient-triggered ventilation used with infant ventilators. The objective of this study was to use computerized pulse oximetry to quantify the occurrence of episodes of hypoxemia (oxygen desaturation) during SIMV vs. IMV, in preterm infants < or = 1,250 g who required mechanical ventilation at > or = 14 days of age. We performed a randomized, crossover study with each infant being randomized to IMV or SIMV (Infant Star ventilator) for initial testing for a 1-hr period. Patients were subsequently tested on the alternate modality after a stabilization period of 10 min at the same ventilator and fractional inspired oxygen concentration (FiO2) settings. Pulse oximetry data were obtained with a Nellcor N-200 monitor, a microcomputer, and a software program (SatMaster). An investigator blinded to the randomized assignment evaluated all measurements. Eighteen very low birth weight (VLBW) infants with a birth weight of 777 +/- 39 g (mean +/- SEM) and gestational age 25.1 +/- 0.3 weeks were studied. The average pulse oximeter oxygen saturation (SaO2) was higher on SIMV than IMV (P < 0.01). During SIMV, these infants had significantly fewer episodes of hypoxemia (duration of episodes of oxygen desaturation as a percentage of scorable recording time) to 86-90% SaO2 (P < 0.01), 81-85% SaO2 (P < 0.01), and 76-80% SaO2 (P < 0.05) when compared to IMV. There was also a significant decrease in percentage of time of desaturation to SaO2 < 90% (P = 0.002), < 85% SaO2 (P = 0.003), and < 80% SaO2 (P = 0.02) during SIMV vs. IMV. Our preliminary findings indicate that the use of SIMV in a population of VLBW ventilator-dependent infants (> or = 14 days of age) results in better oxygenation and decreased episodes of hypoxemia as compared to IMV.

Impact of Improved Survival of Very Low-Birth-Weight Infants on Incidence and Severity of Bronchopulmonary Dysplasia

It has been suggested that improved survival of very low birth weight (VLBW) infants may have resulted in increased numbers of patients with bronchopulmonary dysplasia (BPD). To determine the impact of changes in mortality on the incidence and/or severity of BPD in three different time periods with distinct respiratory support strategies. Retrospective single center cohort study of VLBW infants: Cohort A (1986-1990): pre-surfactant era, use of conventional intermittent mandatory ventilation (IMV); cohort B (1993-1994): use of synthetic surfactant, nasopharyngeal continuous positive airway pressure (CPAP) and conventional IMV; cohort C (2000-2001): use of natural surfactant, early nasal prong CPAP, synchronized IMV with tidal volume monitoring and high frequency oscillatory ventilation (HFOV). BPD was classified as mild, moderate or severe according to Jobe and Bancalari. The median gestational ages and birth weights were 28 3/7 weeks and 1,120 g for cohort A (n = 97), 30 0/7 weeks and 1,340 g for cohort B (n = 100), and 29 1/7 weeks and 1,200 g for cohort C (n = 135). The use of partial or complete courses of antenatal corticosteroids (ANC) increased over time (58%, 72%, and 82%, p = 0.003). There was a 50% reduction of mortality between each time period with mortality rates of 30%, 14% and 7% in cohorts A, B and C, respectively (p < 0.001). The overall incidence of BPD was 26% in the pre-surfactant era, 11% during the mid-1990s and 19% in the most recent time period (r = -0.05, p = 0.36). Moderate and severe forms of BPD decreased over time and were seen in 11% in cohort A, 3% in cohort B and 2% in cohort C (p = 0.008). Changes in neonatal care of VLBW infants, including increased use of ANC and modified respiratory support strategies, have resulted in dramatically improved survival rates over the past 15 years without increasing moderate to severe pulmonary morbidity.

THE SAFETY AND EFFICACY OF AUTOMATED-WEANING FROM MECHANICAL VENTILATION FOLLOWING CARDIAC SURGERY

Introduction: To determine the safety and efficacy of automatic weaning (AW), we compared adverse events associated with weaning by AW with conventional intermittent mandatory ventilation (IMV) in adult patients after cardiac surgery. Previously, in order to standardize weaning by eliminating clinician bias, we used an advanced algorithm for AW with volume-targeted variable pressure support and demonstrated significant reduction in time to extubation in patients undergoing coronary bypass. [1,2] Methods: Ninety eight patients undergoing elective surgical myocardial revascularization entered an IRB approved, randomized, prospective study comparing weaning from mechanical ventilation by an AW or by conventional IMV mode. Weaning for Group 1 was performed on a newly available mechanical ventilator, the Venturi (Cardiopulmonary Corporation, Milford, CT), employing an advanced algorithm for AW by volume-targeted variable pressure support. During apneic periods, the Venturi delivered the set tidal volume and rate by a volume control mode, whereas during spontaneous breathing, the ventilator automatically delivered 15 +/- 8 cm H2 O of pressure support to achieve a targeted tidal volume of 6-8cc/kg. Clinically stable patients with acceptable blood gases were eligible for extubation at pressure support levels < 7 cm H2 O. For Group 2, weaning was managed by the ICU team based on standard practice. Demographic and hemodynamic data, and ventilatory parameters were recorded. Adverse events were defined as serious (cardiopulmonary arrest and reintubation) and non-serious (PO2 < 60 mm Hg, PCO2 >55 mm Hg, and PH > 7.55). The incidence of non-serious events were derived from the total blood gas values obtained in each group. Continuous data are presented as mean +/- SD. Further analysis was performed using a Student's t-text and a p value <or=to0.05 was considered significant. Results: Consistent with our previous findings, the mean time to extubation was significantly reduced in the AW group (p<or=to0.05). The AW (N=48) and the IMV (N=50) groups had similar demographic and hemodynamic data and ventilatory parameters. There were no episodes of serious adverse events in either group. Non-serious adverse events are reported in Table 1 and were also clinically insignificant in both groups.Table 1Conclusion: Our results demonstrate that employing an automated weaning protocol is both safe and efficacious in patients following cardiac surgery.

Computer-controlled minute ventilation in preterm infants undergoing mechanical ventilation

Introduction: Computer-controlled minute ventilation (CCMV) continuously adjusts the ventilator rate to changes in spontaneous respiratory drive and pulmonary mechanics to maintain a preset total minute ventilation. Hypothesis: We hypothesized that CCMV would maintain ventilation and oxygenation with fewer mechanical breaths than conventional intermittent mandatory ventilation in very low birth weight infants. Methods: Very low birth weight infants in clinically stable condition who were undergoing mechanical ventilation were enrolled. The number of mechanical breaths, total and mechanical expiratory minute ventilation, mean airway pressure, oxygen hemoglobin saturation by pulse oximetry, and transcutaneous partial carbon dioxide and partial oxygen tensions were obtained during intermittent mandatory ventilation and CCMV (45 to 60 minutes) and compared by paired t test. Results: Fifteen infants were studied. Birth weight (median, range) was 700 gm (550 to 1205 gm), gestational age 26 weeks (23 to 34 weeks), age 21 days (3 to 50 days). When switched from intermittent mandatory ventilation to CCMV, the number of mechanical breaths was reduced (15 ± 2.8 to 8.6 ± 2.9 breaths per minute, p < 0.001), leading to lower airway pressure (3.97 ± 1.00 to 3.45 ± 1.00 cm H 2O, p < 0.001) and lower expiratory minute ventilation generated by the mechanical ventilator (116 ± 31 to 65 ± 28 ml/min per kilogram, p < 0.001), while total expiratory minute ventilation remained unchanged. Mean transcutaneous partial carbon dioxide and oxygen tensions, oxygen hemoglobin saturation, and the time spent within different oxygen hemoglobin saturation ranges did not differ between both ventilatory modes. Conclusion: CCMV maintained adequate ventilation and oxygenation with lower mechanical ventilatory support than IMV. CCMV may reduce barotrauma and chronic lung disease during long-term use.(J Pediatr 1997;131:910-3)

Patient-triggered ventilation using cutaneous sensors

Patient-triggered ventilation (PTV) prevents asynchrony between spontaneous and ventilator breaths which can be problematic on conventional intermittent mandatory ventilation (IMV). Cutaneous sensors sensitively detect spontaneous breathing in very low birthweight infants despite very small spontaneous airway flow or pressure changes, and lack interference due to air leaks, secretions or surfactant in the airway. The Star Sync module and the Graseby capsule taped to the abdomen enable the InfantStar ventilator to provide the synchronized intermittent mandatory ventilation (SIMV) and assist-control (A/C) modes of PTV. Short-term studies in very low birthweight infants have shown better oxygenation, increased and more consistent tidal volumes and reduced cerebral blood flow velocity variability on SIMV than on IMV. A large, multicentre randomized trial showed an overall reduction in mean airway pressure, and in specific birthweight groups there was improved oxygenation, decreased need for sedation, shorter duration of ventilation, less need for long-term supplemental oxygen and earlier weight gain on SIMV than on IMV. The Sechrist IV-200 synchronized assisted ventilation of infants (SAVI) system uses modified transthoracic impedance to produce PTV and it decreased the duration of ventilation in very low birthweight infants in one study. Appropriate cutaneous placement of the sensors of both of these systems is necessary in order to optimize the clinical response time and reliability of PTV. Since their cutaneous sensors are not affected by airway leak, both systems may be used to reliably provide PTV via nasal prongs.

Randomized multicenter trial comparing synchronized and conventional intermittent mandatory ventilation in neonates

OBJECTIVE: To compare synchronized intermittent mandatory ventilation (SIMV) and conventional intermittent mandatory ventilation (IMV) in neonates. STUDY DESIGN: Prospective, multicenter, randomized clinical trial. SETTING: Level III neonatal intensive care units at six university or children's hospitals. PATIENTS: Three hundred twenty-seven infants receiving conventional IMV for respiratory distress syndrome, pneumonia, or meconium aspiration pneumonitis were randomly assigned at 7.5 ± 6 hours of age to either continue with IMV or change to SIMV. Infants assigned to each mode of ventilation had similar birth weight (BW), gestational age, and Apgar scores at birth, and similar oxygenation indexes at randomization. They received similar surfactant therapy and had similar incidence of sepsis, seizures, secondary pneumonia, and necrotizing enterocolitis. In the infants with BW less than 1000 gm, more infants receiving IMV had surgical ligation of their patent ductus arteriosus than did those receiving SIMV (27 vs 7%; p = 0.02). ANALYSIS: Data was analyzed overall for all infants and also separately within three BW groups: less than 1000 gm, 1000 to 2000 gm, and more than 2000 gm. The 1000 to 2000 gm BW group was further analyzed in subgroups weighing 1000 to 1499 gm and 1500 to 2000 gm. RESULTS: In all infants, at 1 hour after randomization, the infants receiving SIMV had a lower mean airway pressure than those receiving IMV (8.08 ± 2.15 vs 8.63 ± 2.59; p <0.05), with similar fractions of inspired oxygen and oxygenation indexes. Infants whose BW was 1000 to 2000 gm at 0.5 hour required a lower fraction of inspired oxygen with SIMV than with IMV (0.52 ± 0.20 vs 0.62 ± 0.27; p <0.05) and had better oxygenation at 1 hour, as shown by lower oxygenation indexes with SIMV than with IMV (6.14 ± 4.17 vs 9.42 ± 8.41; p = 0.01). Infants whose BW was 1000 to 2000 gm received a lower number of unit doses of sedative/analgesic drugs per infant during the first 4 days of SIMV than did infants receiving IMV (3.8 ± 3.4 vs 6.3 ± 5.5 unit doses; p = 0.02). Infants whose BW was more than 2000 gm had a shorter duration of mechanical ventilation with SIMV than with IMV (median, 72 vs 93 hours; p = 0.02). Three of the forty-six infants receiving IMV but none of the 47 infants receiving SIMV required extracorporeal membrane oxygenation. In the infants with BW less than 1000 gm, fewer infants treated with SIMV required supplemental oxygen at 36 weeks of postconceptional age than did those treated with IMV (47 vs 72%; p <0.05). In 83 infants whose lungs were mechanically ventilated for 14 days or longer, all with BW less than 2000 gm, those treated with SIMV regained their BW earlier than those treated with IMV (median, 21.5 vs 29 days; p <0.01). There were no differences in the rates of death, intraventricular hemorrhage (grades III and IV), air leak, need for pharmacologic paralysis, or need for supplemental oxygen at 28 days. CONCLUSIONS: We found that SIMV was at least as efficacious as conventional IMV, and may have improved certain outcomes in BW-specific groups. (J P EDIATR 1996;128:453-63)

Patient-triggered ventilation decreases the work of breathing in neonates.

During conventional intermittent mandatory ventilation (IMV) in neonates, asynchrony between mechanical and spontaneous breaths is frequent. We tested the hypothesis that patient-triggered ventilation (PTV) reduces the work of breathing (WOB) by providing synchronized assistance for each breath. Accordingly, six intubated preterm infants were studied at the median postnatal age of 34 days while they were being weaned from mechanical ventilation (MV). Patients were ventilated using the Draeger Babylog 8000 (software #3) and studied in four successive modes of MV with a constant level of positive end-expiratory pressure. They were randomly assigned to IMV, PTV with peak inspiratory pressure of either 10 cm H2O (PTV10) or 15 cm H2O (PTV15), and spontaneous ventilation with continuous positive airway pressure. PTV was achieved in the assist/control mode. During PTV, infants adapted their pattern of breathing in response to an increase in tidal volume (median 7.5 ml/kg in IMV versus 8.2 in PTV10 and 8.5 in PTV15, p<0.05) by decreasing their respiratory rate, thus maintaining minute ventilation (439 ml/min/kg in IMV versus 422 in PTV10 and 455 in PTV15, NS) and transcutaneous CO2. WOB fell significantly during PTV compared with its level during IMV (0.81 J/L in IMV versus 0.48 and 0.47 during PTV10 and PTV15, respectively, p<0.05). Power of breathing decreased in the same proportions. These results demonstrate that PTV mode allows reduction of the workload imposed on the respiratory muscles.

Prospective Randomized Comparison of High-Frequency Oscillatory and Conventional Ventilation in Respiratory Distress Syndrome

A prospective randomized trial with a crossover design was conducted to compare the efficacy and safety of two distinct strategies of high-frequency oscillatory ventilation (HFOV) to conventional intermittent mandatory ventilation (CV) in the management of respiratory distress syndrome. Only premature neonates with a birth weight less than 1.751 kg were eligible for enrollment into the study. Of 83 patients studied, 26 patients were assigned to CV-only, 27 to HFOV for 72 hours followed by CV (HFOV/CV), and 30 to HFOV-only until extubation. There was no difference among the three groups with respect to the incidence of pulmonary airleak, intraventricular hemorrhage, or death. The highest incidence of chronic lung disease was in the CV-only group. Although both HFOV groups had a lower incidence of chronic lung disease assessed at 30 days and 36 weeks postconception age, the difference was statistically significant only between the CV-only and HFOV-only groups (65% vs 30% at 30 days; P = .008; 38% vs 10% at 36 weeks postconception age, P = .013). These results suggest that use of HFOV as the predominant mode of ventilation in the management of respiratory distress syndrome is as safe as CV and can contribute to a decreased incidence of chronic lung disease. Furthermore, a short (72-hour) period of HFOV support does not provide the same advantage as continuous HFOV.

High-Frequency Oscillatory Ventilation Versus Intermittent Mandatory Ventilation: Early Hemodynamic Effects in the Premature Baboon with Hyaline Membrane Disease

We studied the hemodynamic consequences during the first 24 h of life in premature baboons (140 d) with hyaline membrane disease that were treated with high-frequency oscillatory ventilation (HFOV) or conventional intermittent mandatory ventilation (IMV). Cardiac output and organ blood flow were measured at three time-points using the radiolabeled microsphere technique. Seven of seven HFOV and six of eight IMV animals survived the 24-h period. By design, initial mean airway pressure (Paw) was higher in the HFOV group (p less than 0.01). HFOV Paw was progressively reduced during the study period because of improving oxygenation as measured by the arterial to alveolar oxygen ratio. In contrast, it was necessary to increase Paw in the IMV animals to maintain the arterial to alveolar oxygen ratio. By 23 h, the IMV group required higher Paw than the HFOV group (p less than 0.05) and had a lower arterial to alveolar oxygen ratio (p less than 0.05). We found no significant differences in left ventricular output, effective systemic flow, organ blood flow, or central venous pressure between the two groups at 3, 8, or 23 h. The HFOV strategy used in our study resulted in significant improvement in oxygenation during the initial 24 h of treatment without adverse effect on left ventricular output, cerebral blood flow, or central venous pressure. We conclude that when appropriate changes in Paw are made during HFOV in response to improvement in arterial oxygenation and changes in lung inflation as assessed by chest radiographs HFOV can be achieved without depressing cardiovascular dynamics more than during conventional therapy with IMV.

High-frequency oscillatory ventilation combined with intermittent mandatory ventilation in critically ill neonates: 3 years of experience.

A heterogeneous group of 45 neonates with severe pulmonary disease and inadequate gas exchange on conventional intermittent mandatory ventilation (IMV) was treated with a high-frequency oscillator combined with an IMV (HFO-IMV) system (Emerson Airway Vibrator connected to a BABYBird 1 ventilator). The mean gestational age was 33 weeks (25.5-43) and mean birth weight 2.02 kg (0.66-4.24). Primary diagnoses included respiratory distress syndrome (RDS; 23), pneumonia (12), persistent fetal circulation (PFC; 6), diaphragmatic hernia/hypoplastic lungs (4). The IMV rate was reduced from 78 to 29 BPM (P less than or equal to 0.0005), while maintaining lower partial pressure of carbon dioxide (PaCO2) (P less than 0.005) and higher partial pressure of oxygen (PaO2) (P less than or equal to 0.0025). Active air leaks were present in 20 infants and these infants responded most favourably to HFO-IMV. HFO-IMV failed to improve ventilation in neonates with diaphragmatic hernia/hypoplastic lungs. Complications during HFO-IMV were increased pulmonary secretions (11), worsening or recurrence of pre-existing air leaks (11), or occurrence of new air leaks (10). In 4 patients death was related to major air leak complications. Twenty-four infants died, 18 of them of a respiratory cause. Twenty-one infants finally survived. We assembled a well-tolerated system to provide HFO-IMV and to successfully ventilate neonates with severe respiratory disease, who failed to respond to conventional IMV. Initiation of HFO-IMV earlier in the course of the disease in this type of infant may improve survival.

Diagnosis and therapy of necrotizing tracheobronchitis in ventilated neonates.

From January 1983 to September 1984 our neonatal ICU (NICU) treated eight endotracheally intubated infants who had suspected airway obstruction characterized by hypercarbia dissonant with severity of lung disease and difficulty in ventilation with lack of chest movement, both on conventional intermittent mandatory ventilation and high-frequency oscillation. Bronchoscopic removal of necrotic tissue was possible in six infants, two of whom survived. Bronchoscopy showed desquamation of epithelial surfaces, leaving encrusted exudations considered to be characteristic of necrotizing tracheobronchitis (NTB). The four nonsurvivors of bronchoscopy and one of the infants not submitted to bronchoscopy had NTB confirmed at autopsy. NTB was not associated with any specific lung disease, humidifier, or ventilator. The autopsy frequency of NTB during this period was 5 per 160 NICU admissions. A separate chart review of unselected autopsied cases in 1981 and 1982 showed that 12 of 284 neonates admitted to the NICU had NTB. NTB appears to be a rediscovered condition related to endotracheal intubation and mechanical ventilation using high mean airway pressures.

Combined high-frequency oscillatory ventilation and intermittent mandatory ventilation in critically ill neonates

Combined high-frequency oscillatory ventilation (HFOV) and intermittent mandatory ventilation (IMV) was used in 12 neonates with inadequate gas exchange with conventional IMV. Diagnoses included diaphragmatic hernia with hypoplastic lungs, pneumonia, persistent fetal circulation, and severe respiratory distress syndrome. In most patients there was severe air leak. Within 10 hours of beginning HFOV-IMV the mean arterial PCO2 fell from 60 +/- 5 (means +/- SEM) to 38 +/- 2 mm Hg (P less than 0.01) and the mean IMV rate was reduced from 96 +/- 8 to 17 +/- 4 breaths per minute (P less than 0.001). The mean arterial-alveolar oxygen tension ratio rose from 0.05 +/- 0.01 to 0.09 +/- 0.01 (P less than 0.005). Mean airway pressure in the trachea was reduced from 16 +/- 2 to 10 +/- 3 cm H2O (P less than 0.05). Four patients died, three of whom had diaphragmatic hernias with hypoplastic lungs. Five of the eight survivors had mild bronchopulmonary dysplasia requiring supplemental oxygen. These studies demonstrate that in some neonates with respiratory failure who fail to respond to conventional IMV, combined HFOV-IMV can be successful.