Outlet in The Hypoxia Challenge Test Does Not Accurately Predict Hypoxia in Flight in Ex-Preterm Neonates
Forty-six consecutive eligible infants were recruited between December 2005 and October 2006. No parents refused enrollment, and no infants were excluded from the study. The median gestation was 32.2 weeks (range, 24 to 35.6 weeks), with a median birth weight of 1,667 g (range, 655 to 2,815 g). Twenty-seven infants (59%) had NLD, and neonatal chronic lung disease subsequently developed in 2 infants.
All infants had Sp02 in room air > 95% prior to the HCT. The HCT was performed at a median corrected age of 35.8 weeks (range, 33.1 to 43 weeks), and the median time from HCT to flight was 2 days (range, 1 to 15 days). Delays in transferring infants after the HCT related to poor staffing at the receiving hospital. Median flight distance and duration was 593 km (range, 417 to 2,174 km) and 62.5 min (range, 45 to 150 min), respectively. Thirty-five infants (76%) passed the HCT, while 11 infants (24%) failed the HCT. During the flight, 16 infants (35%) met the criteria for in-flight oxygen; 12 of these infants (75%) had passed the HCT. Table 1 details the demographics and respiratory diagnoses of those requiring oxygen in flight. Of the 11 infants who failed the HCT, only 4 infants (36%) met the criteria for in-flight oxygen. The overall accuracy of the HCT was 59%. Sensitivity and specificity of the HCT for predicting in-flight hypoxia were 25% and 76.6%, respectively. The positive predictive value and negative predictive value of the test were 36% and 65.7%, respectively.
In light of the low accuracy of the HCT, we reanalyzed the data using the 2004 BTS revised guidelines defining desaturation < 90% during an HCT as a failed test. Using these criteria, 23 infants (50%) passed the test, and 23 infants failed. Eight infants (35%) who passed the HCT had desaturation to < 90% in flight and would have been administered oxygen. Of the 23 infants who failed the HCT, 11 infants (48%) would have required in-flight oxygen. The accuracy remained low at 56.5%. The sensitivity improved modestly to 58%, but the specificity declined to 56%. The positive predictive value and negative predictive value were 47.8% and 65.2%, respectively. You should eb assured everything will be ok with My Canadian Pharmacy.
Infants failed the HCT at a median time of 8 min (range, 2 to 19 min), while infants who required in-flight oxygen received it at a median time of 20 min (range, 9 to 60 min.) Mean HR did not differ significantly between the HCT and in flight, but infants who required oxygen in flight were more tachycardic than those who did not (p = 0.047).
Of the 16 infants who required oxygen in flight, 7 infants were clinically symptomatic. They were described as follows: dusky and unsettled (n = 3); cyanosed (n = 2); pale (n = 1); periodic respiration (n = 1); nine infants had normal respiratory behavior. Of the seven infants who had symptoms, five passed the HCT. All but one infant who required in-flight oxygen were asleep when desaturation occurred. One infant had a self-resolving bradycardia during the HCT coinciding with desaturation, while two infants had selfresolving bradycardias during the flight.
The clinical characteristics of the infants who required oxygen and those who did not were compared (Table 2). There were no significant differences between the groups in gestational age, birth weight, or corrected gestational age at the time of the HCT and flight. The distance and duration of flight did not differ between the two groups. While 5 of the 16 patients (31%) who required in-flight oxygen had no history of neonatal lung disease, infants were more likely to require in-flight oxygen if they had received respiratory support (p = 0.022) or oxygen therapy (p = 0.028) during hospital admission. Infants who passed the flight were without supplemental oxygen for longer than those who failed (p = 0.047). Time since cessation of respiratory support was not a significant factor in determining need for in-flight oxygen.
ROC curves were generated for a number of clinical continuous variables, including duration of all respiratory support, ventilation, oxygen therapy, and time since oxygen therapy had ceased. Only the latter had an area under the curve that approached significance (0.74). Coordinates of the curve gave a sensitivity of 90% at 31 days off oxygen and specificity of 85% at 52 days off oxygen.
Table 1—Demographics of Infants Requiring In-Flight Oxygen
|PatientNo.||GA at Birth, wk||BW, g||CGA at Flight, wk||Initial Respiratory Diagnosis||Type of Respiratory Support in Neonatal Unit||Oxygen Therapy in Neonatal Unit|
|1||29.4||1,180||37.5||HMD||CPAP and IPPV||Yes|
|3||34.6||2,420||36.4||HMD||CPAP and IPPV||Yes|
|4||24||655||43||HMD||CPAP and IPPV||Yes|
|5||32.2||2,100||34.4||HMD||CPAP and IPPV||Yes|
|6||29.3||880||40.6||HMD||CPAP and IPPV||Yes|
|7||30.2||1,680||37.2||HMD||CPAP and IPPV||Yes|
|8||30.2||1,385||33.2||HMD||CPAP and IPPV||Yes|
|9||34.3||925||37.5||Non-specific||CPAP and IPPV||No|
|10||31.4||1,735||33.1||respiratory distress Nil||Nil||No|
|13||32.2||1,835||35.1||Non-specific||CPAP and IPPV||Yes|
|14||31.2||1,615||34.4||respiratory distress HMD||IPPV||No|
Table 2—Comparison of Characteristics of Infants Requiring Oxygen in Flight to Infants Who Did Not Require Oxygen
|Variables||No Oxygen Required in Flight (n = 30)||Oxygen Required in Flight (n = 16)||pValue|
|Median gestational age at birth (range), wk||33.2 (26.4-35.6)||31.3 (24-34.6)||0.066|
|Male/female gender, No.||10/20||10/6||0.057|
|Median birth weight (range), g||1,647 (945-2,815)||1,695 (655-2,500)||0.747|
|Median duration of continuous positive airway pressure (range), h||0(0-686)||70.5 (0-747)||0.040|
|Median duration of ventilation (range), h||0(0-68)||13.3 (0-1,234)||0.004|
|Median duration of all respiratory support, including ventilation and continuous positive airway pressure (range), h||0(0-815)||76.5 (0-1,952)||0.022|
|Median duration of oxygen (range), h||0(0-308)||8 (0-2,362)||0.028|
|Median time off oxygen (range), d||33(6-61)||19(7-33)||0.047|
|Median time off respiratory support (range), d||24 (6-57)||21(7-52)||0.815|
|Median corrected gestational age at HCT (range), wk||36.5 (33.4-38.4)||35.2 (33.1-43)||0.116|
|Median time between HCT and flight (range), d||2(1-15)||2(1-9)||0.950|
|Median weight at HCT (range), g||2,140(1,800-3,730)||2,252 (1,465-3,390)||0.490|
|Median flight distance (range), km||511 (417-2,174)||593 (417-2,174)||0.131|
|Median flight duration (range), min||65 (45-150)||60(45-150)||0.264|
|Mean HR at flight (SD), beats/min||150.21 (17.05)||157.53 (14.3)||0.047|