A ventilator requirement index

Detection of early nocturnal hypoventilation in neuromuscular disorders

Objective Nocturnal hypoventilation (NH) is a complication of respiratory involvement in neuromuscular disorders (NMD) that can evolve into symptomatic daytime hypercapnia if not treated proactively with non-invasive ventilation. This study aimed to assess whether NH can be detected in the absence of other signs of nocturnal altered gas exchange. Methods We performed nocturnal transcutaneous coupled (tc) pCO2/SpO2 monitoring in 46 consecutive cases of paediatric-onset NMD with a restrictive respiratory defect (forced vital capacity < 60%). Nocturnal hypoventilation was defined as tcPCO2 > 50 mmHg for > 25% of recorded time, and hypoxemia as tcSpO2 < 88% for > 5 minutes. Daytime symptoms and bicarbonate were recorded after overnight monitoring. Results Twenty-nine of 46 consecutive patients showed NH. Twenty-three patients did not have nocturnal hypoxemia and 18 were clinically asymptomatic. In 20 patients, PaCO2 in daytime blood samples was normal. Finally, 13/29 patients with NH had isolated nocturnal hypercapnia without nocturnal hypoxia, clinical NH symptoms, or daytime hypercapnia. Conclusions Paediatric patients with NMD can develop NH in the absence of clinical symptoms or significant nocturnal desaturation. Therefore, monitoring of NH should be included among nocturnal respiratory assessments of these patients as an additional tool to determine when to commence non-invasive ventilation.

Breathing intolerance index in healthy infants

BACKGROUND

The breathing intolerance index (BITI) is used to justify ventilator use in adult patients with pulmonary or chest wall disease. BITI in ventilated patients is mostly ≥0.15. The mean BITI of healthy adults in the upright sitting position and the supine position is 0.050 ± 0.009 and 0.057 ± 0.016, respectively. The aim of this study was to establish a normal BITI in infants.

METHODS

Thirty healthy infants were examined in the supine position. BITI was defined as BITI = (Ti/Ttot) × (TV/VC), where Ti is inspiratory time, Ttot is total breath cycle duration, TV is tidal volume, and VC is vital capacity. TV and Ti/Ttot were obtained from tidal breathing at rest and VC was obtained spirometrically. BITI was calculated using customized software.

RESULTS

The mean ± SD BITI of 30 healthy infants in the supine position was 0.120 ± 0.013. The BITI of infants was significantly higher than that of adults.

CONCLUSIONS

BITI was measured in healthy infants. Further evaluation is needed to determine the significance and usefulness of BITI.

Home-based overnight transcutaneous capnography/pulse oximetry for diagnosing nocturnal hypoventilation associated with neuromuscular disorders

OBJECTIVE

To determine the utility of home-based, unsupervised transcutaneous partial pressure of carbon dioxide (tc-Pco(2)) monitoring/oxygen saturation by pulse oximetry (Spo(2)) for detecting nocturnal hypoventilation (NH) in individuals with neuromuscular disorders.

DESIGN

Retrospective case series analyzed consecutively.

SETTING

Multidisciplinary neuromuscular respiratory failure (NMRF) clinic at an academic institution.

PARTICIPANTS

Subjects (N=35, 68.6% men; mean age, 46.9y) with spinal cord injury (45.7%) or other neuromuscular disorders underwent overnight tests with tc-Pco(2)/Spo(2) monitoring. Fifteen (42.9%) were using nocturnal ventilatory support, either bilevel positive airway pressure (BiPAP) or tracheostomy ventilation (TV).

INTERVENTIONS

A respiratory therapist brought a calibrated tc-Pco(2)/Spo(2) monitor to the patient's home and provided instructions for data collection during the subject's normal sleep period. Forced vital capacity (FVC), body mass index (BMI), and exhaled end-tidal Pco(2) (ET-Pco(2)) were recorded at a clinic visit before monitoring.

MAIN OUTCOME MEASURES

Detection of NH (tc-Pco(2) ≥50mmHg for ≥5% of monitoring time). Data were also analyzed to determine whether nocturnal oxygen desaturation (Spo(2) ≤88% for ≥5% of monitoring time), FVC, BMI, or daytime ET-Pco(2) could predict the presence of NH.

RESULTS

NH was detected in 18 subjects (51.4%), including 53.3% of those using BiPAP or TV. NH was detected in 43.8% of ventilator-independent subjects with normal daytime ET-Pco(2) (present for 49.4%±31.5% [mean ± SD] of the study period), and in 75% of subjects with an elevated daytime ET-Pco(2) (present for 92.3%±8.7% of the study period). Oxygen desaturation, BMI, and FVC were poor predictors of NH. Only 3 attempted monitoring studies failed to produce acceptable results.

CONCLUSIONS

Home-based, unsupervised monitoring with tc-Pco(2)/Spo(2) is a useful method for diagnosing NH in NMRF.

Low abdominal contribution to breathing as daytime predictor of nocturnal desaturation in adolescents and young adults with Duchenne Muscular Dystrophy

In the respiratory management of DMD patients it is still under debate what parameter should indicate the correct timing for institution of nocturnal non-invasive ventilation (NIV), in addition to forced vital capacity, which is generally considered as a prognostic marker of disease progression. The aim of this study was to determine if volume variations of rib cage and abdominal compartments measured by Opto-Electronic Plethysmography can be helpful to distinguish between those patients who are in the early stages of nocturnal oxygen desaturation development and those who do not yet. Pulmonary function, abdominal contribution to tidal volume and to inspiratory capacity (%Abd IC) and a set of breathing pattern indexes were assessed in 40 DMD patients older than 14 years and not yet under nocturnal NIV. ROC analysis revealed that among all the considered parameters, %Abd IC in supine position was the best discriminator between DeSat (at least 10% of the night time with SpO(2) < 95%) and NonDeSat patients, providing an area under the curve with 95%CI equal to 0.752. In conclusion, in adolescents and adults DMD patients who present either no sign or only mild nocturnal oxygen desaturation, a reduced abdominal contribution to inspiratory capacity is a marker of the onset of diaphragm weakness and should be considered to identify the correct timing for the institution of nocturnal NIV.

Indicators for ventilator use in Duchenne muscular dystrophy

BACKGROUND

Noninvasive mechanical ventilation is being used up to continuously by patients with Duchenne muscular dystrophy (DMD). Invasive and noninvasive tests are used to assess ventilatory function but there are few reports relating them to extent of ventilator dependence for which simple and cost effective parameters are needed.

OBJECTIVE

To investigate the relative efficacy of noninvasive lung function parameters for determining extent of need for ventilator use.

MATERIALS AND METHODS

83 DMD patients were divided into three groups: no ventilator use (asymptomatic) (n = 26) [Group 1], nocturnal ventilator use (symptomatic) (n = 20) [Group 2], and full-time ventilator dependence (n = 37) [Group 3]. Tidal volume (TV), vital capacity (VC), respiratory rate (RR), inspiratory time (Ti), respiratory cycle time (Ttot), rapid shallow breathing index (RSBI [RR/TV]), breathing intolerance index (BITI), ventilator requirement index (VRI) and a new parameter RR/VC were monitored and compared. Data were analyzed with receiver-operating-characteristic curves (ROC) and the area under the curve (AUC) was calculated.

RESULTS

In group 2 and 3, patients used NIV for 3.3 ± 2.1 and 11.2 ± 4.7 years, respectively. By ROC comparison, RR/VC (RR/VC ≥ 0.024 [AUC, 0.921] and ≥0.071 [AUC, 0.935]), RR/TV (RR/TV ≥ 0.024 [AUC, 0.905] and ≥0.153 [AUC, 0.905]), and VC (VC ≤ 770 ml [AUC, 0.896] and ≤370 ml [AUC, 0.898]) represented to introduce nocturnal and continuous ventilator use, respectively. TV/VC, BITI, and VRI were either less sensitive or less specific.

CONCLUSIONS

Lung function parameters including RR/VC, RR/TV, and VC are useful and inexpensive in predicting the extent of need for ventilator use. Overall, RR/VC is the most appropriate predictor for determining extent of need for ventilator use.

Noninvasive determination of the tension-time index in Duchenne muscular dystrophy

OBJECTIVE

Noninvasive determination of the tension-time index of the inspiratory muscles (TT MUS) can identify predisposition to respiratory muscle fatigue in neuromuscular disease. We correlated TT MUS with age and extent of need of ventilator use for patients with Duchenne muscular dystrophy.

DESIGN

Maximal inspiratory pressure, inspiratory pressure 0.1 sec after the onset of inspiration (P 0.1), and the breathing pattern during spontaneous breathing were measured in 46 subjects with Duchenne muscular dystrophy and in 46 healthy males of the same age. TT MUS (TT MUS = T I/T TOT x P I/MIP) was determined by calculating P I from P 0.1 (P I = 5 x P 0.1 x T I). The data were compared with normal values and related to age and ventilator use.

RESULTS

TT MUS was significantly higher in the entire Duchenne muscular dystrophy group than in controls (0.21 +/- 0.11 vs. 0.06 +/- 0.02, P < 0.001) and increased with age in the patients (P < 0.001). TT MUS was significantly higher in subjects ventilated 8-20 hrs per day than in nocturnal-only users and in patients ventilated >20 hrs per day than in those ventilated 8-20 hrs per day (P < 0.001). TT MUS surpassed 0.23 in 95% of subjects ventilated 8-20 hrs. TT MUS exceeded 0.37 in 95% of individuals ventilated >20 hrs per day, whereas it was less than this value in 95% of patients ventilated 8-20 hrs.

CONCLUSIONS

TT MUS increases significantly with disease progression and is a sensitive indicator of risk of inspiratory muscle fatigue and ventilator use. Longitudinal determination of TT MUS in patients with Duchenne muscular dystrophy may help to justify the extent of need for mechanical ventilation.