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Incidence of Hypocapnia, Hypercapnia, and Acidosis and the Associated Risk of Adverse Events in Preterm Neonates

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Incidence of Hypocapnia, Hypercapnia, and Acidosis and the Associated Risk of Adverse Events in Preterm Neonates Incidence of Hypocapnia, Hypercapnia, and Acidosis and the Associated Risk of Adverse Events in Preterm Neonates Melissa K Brown RRT RRT-NPS, Deborah M Poeltler PhD, Kasim O Hassen RRT RRT-NPS, Danielle V Lazarus RRT, Vanessa K Brown, Jeremiah J Stout, Wade D Rich RRT RRT-NPS, and Anup C Katheria MD BACKGROUND: Permissive hypercapnia is a lung-protection strategy. We sought to review our current clinical practice for the range of permissive hypercapnia and identify the relationship between P and pH and adverse outcomes. METHODS: A secondary analysis of a delayed aCO2 cord-clamping clinical trial was performed on all arterial blood gas tests in the first 72 h in infants < 32 weeks gestational age. All arterial blood gas values were categorized into a clinical range to determine the percent likelihood of occurring in the total sample. The univariate and multivariate relationships of severe adverse events and the time-weighted P , fluctuation of P , maximal aCO2 aCO2 and minimal P , base excess, and pH were assessed. RESULTS: 147 infants with birthweight of aCO2 g and gestational age of 28 ؎ 2 weeks were included. Of the 1,316 total samples, < 2% 395 ؎ 1,206 had hypocapnia (P <30 mm Hg), 47% were normocapnic (P 35–45 mm Hg), 26.5% had aCO2 aCO2 mild hypercapnia (P 45–55 mm Hg), 13% had moderate hypercapnia (P 55–65 mm Hg), aCO2 aCO2 and 6.5% had severe hypercapnia (P > 65 mm Hg). There were no adverse events associated aCO2 with hypocapnia. Subjects with death/severe intraventricular hemorrhage had a higher mean P aCO2 higher variability of P ,(006. ؍ of 52.3 versus 44.7 (odds ratio [OR] 1.16, 95% CI 1.04–1.29, P aCO2 and a lower ,(01. ؍ with a standard deviation of 12.6 versus 7.8 (OR 1.15, 95% CI 1.03–1.27, P There was no significant .(003. ؍ minimum pH of 7.03 versus 7.23 (OR 0, 95% CI 0–0.06, P difference in any variables in subjects who developed other adverse events. CONCLUSION: The routine targeting of higher than normal P goals may lead to a low incidence of hypocapnia and aCO2 associated adverse events. Hypercapnia is common, and moderate hypercapnia may increase the risk of neurologic injury and provide little pulmonary benefit. Key words: hypercapnia; hypocapnia; ventilator-induced lung injury; bronchopulmonary dysplasia; carbon dioxide; very low birthweight in- fant; intraventricular hemorrhage; premature; mortality; blood gas analysis. [Respir Care 2018;63(8):943–949. © 2018 Daedalus Enterprises] Introduction ever, the range of P that provides benefit with the least aCO2 risk is not yet known.1,2 Permissive hypercapnia may al- Permissive hypercapnia, or allowing the P levels to low the maintenance of an adequate minute ventilation aCO2 rise above normal, is a commonly utilized lung-protection with lower tidal volumes (VT), and it may help avoid the strategy in the management of premature neonates.1 How- lung injury that can occur from volutrauma and baro- trauma.3 The resultant reductions of mean airway pressure may also prevent lung injury as well as improve the car- All authors are affiliated with the Neonatal Research Institute at Sharp Mary Birch Hospital for Women and Newborns, San Diego, California. Ms Brown presented a version of this paper at the AARC International Correspondence: Melissa K Brown RRT RRT-NPS, Neonatal Research In- Congress, held October 15–18, 2016, in San Antonio, Texas. stitute at Sharp Mary Birch Hospital for Women and Newborns, 3003 Health Center Drive, San Diego, CA 92123. E-mail: [email protected]. Mr Rich discloses a relationship with Windtree Therapeutics. The other authors have disclosed no conflicts of interest. DOI: 10.4187/respcare.05801 RESPIRATORY CARE • AUGUST 2018 VOL 63 NO 8 943 HYPOCAPNIA,HYPERCARBIA AND ACIDOSIS IN PRETERM INFANTS diac output, which is frequently compromised in the crit- ically ill premature neonate.4 Enhanced delivery of oxygen QUICK LOOK to the brain and other vital tissues can also be facilitated by Current knowledge A strategy of mild hypercapnia (P ϭ 45-55 mm Hg) aCO2 SEE THE RELATED EDITORIAL ON PAGE 1070 can lead to a reduction in ventilator days and the need for ventilator assistance at 36 week corrected gesta- tional age when compared to a normocapnic group shifting the oxyhemoglobin dissociation curve to the right, (35-45 mm Hg) in extremely low birthweight infants, with- with respiratory acidosis and increases in P levels. aCO2 Previous randomized, controlled trials have demonstrated out an increase in neurodevelopmental adverse effects. a reduction in median ventilator days (2.5 vs 9.5) and the Bronchopulmonary dysplasia rates have not been signifi- need for ventilator assistance at 36 week corrected gesta- cantly reduced by a strategy of permissive hypercapnia. 5 tional age (16% vs 1%) with a strategy of mild hyper- What this paper contributes to our knowledge 4 capnia (PaCO 45–55 mm Hg) when compared to a nor- 2 Moderate to high levels of permissive hypercapnia mocapnic group (PaCO 35–45 mm Hg) in extremely low 2 Ͼ birthweight infants, without an increase in neurodevelop- ( 55 mm Hg) in the first 72 h of life has found its way mental adverse effects. However, bronchopulmonary dys- into neonatal clinical practice, which may increase neu- plasia (BPD) rates have not been significantly reduced by rologic risk and provide little pulmonary benefit. Tar- 4-7 geting higher than normal P levels may help avoid a strategy of permissive hypercapnia. aCO2 Hypercapnia can increase cerebral vasodilation and ce- the adverse events associated with hypocapnia. rebral blood flow; conversely, hypocapnia can lead to va- soconstriction and significantly decreased cerebral blood flow.8-10 Progressive increases in the P level can also projected sample size. A P target of 55–65 mm Hg aCO2 aCO2 impair the autoregulation of cerebral blood flow and may was associated with trends toward higher mortality and lead to ischemic damage of the neonatal brain.2,8,9 Hyper- higher incidence of neurodevelopmental impairment, and capnia, hypocapnia, fluctuations in P , and acidosis have a significant increase in the combined outcome of mental aCO2 all been positively associated with intraventricular hemor- impairment or death (P Ͻ .05). Higher ventilator rates to rhage (IVH), periventricular leukomalacia, and poor neu- achieve gas exchange with low VT may have diminished 10-13 rodevelopmental outcomes in preterm neonates. the advantage of minimal ventilation. VT was kept similar Previous studies have questioned the safe ranges of per- in both groups (high-rate strategy pH Ͼ 7.25 with sodium missive hypercapnia and the role that pH plays in the bicarbonate administration). A strategy of reducing VT by relationship. The acceptable limits for acidosis are poorly increasing the P target was not in effect in this cohort aCO2 defined and difficult to isolate from the effects of hyper- (as utilized in ARDSnet15), possibly negating any pulmo- capnia. Moderate hypercapnia (P Ͼ 55 mm Hg) has nary impact between groups. The trial had difficulty achiev- aCO2 not yet been demonstrated to be either beneficial or safe, ing the high P target in non-paralyzed infants, and aCO2 although it has been reported to be a common clinical although the P difference was statistically significant aCO2 practice. Randomized controlled trials investigating the (6 mm Hg, P Ͻ .001), it did not meet the study goal of safety and effectiveness of moderate hypercapnia have been 55–65 mm Hg. difficult to complete due to infant subjects’ ability to reg- The Permissive Hypercapnia in Extremely Low Birth- ulate their own ventilation and override the study P weight Infants (PHELBI) trial enrolled 362 infants at 16 aCO2 targets. Two randomized clinical trials attempted to deter- centers in Germany before being stopped early after an mine whether targeting moderate levels of hypercapnia is interim analysis.7 The authors hypothesized that a higher safe or beneficial. Both had negative results, and the au- target P 55–65 mm Hg (day 1–3) as compared to aCO2 thors did not recommend that they be attempted again in 40–50 mm Hg and then escalating gradually over 14 d the future.7,14 would reduce the rate of BPD or death. The trial was Although most of the early positive trial results that lead terminated when no benefit in the treatment group and a to the adoption of permissive hypercapnia of neonates com- trend toward benefit in the control group was found. The pared mild levels of hypercapnia to normal values, Thome high-target group had a significantly higher rate of necro- at al randomized mechanical ventilated infants Ͻ 28 weeks tizing enterocolitis and did not have a shorter duration of within6hofbirth to a higher P target of 55–65 mm Hg ventilation. Although the high-target group did have lower aCO2 or 35–45 mm Hg for the first 7 postnatal days.14 The ventilator pressures, it did not translate into better out- primary outcome measure was BPD or death and neuro- comes. The infants with severe disease in the high target developmental outcome at 18–22 months corrected age. group (P 55–65 mm Hg) had a higher incidence of aCO2 The trial was stopped early after enrolling 31% of the BPD, necrotizing enterocolitis, and death. The PHELBI 944 RESPIRATORY CARE • AUGUST 2018 VOL 63 NO 8 HYPOCAPNIA,HYPERCARBIA AND ACIDOSIS IN PRETERM INFANTS investigators were unable to reach the desired targets with Table 1. Demographics and Neonatal Outcome Data the high PaCO group. The mean PaCO difference was only 2 2 All Subjects Ͻ 28 Weeks 6.2 mm Hg between days 2 and 11. The authors suggest Characteristics Subjects Gestational Age that the high targets may be impossible to achieve in a randomized, controlled trial and probably should not be Gestational age (wk), mean Ϯ SD 28.4 Ϯ 2.3 25.4 Ϯ 1.3 Ϯ Ϯ Ϯ attempted either clinically or in future studies.7 Birth weight (g), mean SD 1,206 395 840 203 Our goal was to review our current clinical practice for 1 min Apgar (IQR) 7 (5, 7) 4.5 (2, 7) 5 min Apgar (IQR) 8 (7, 8) 7 (6, 8) the range of permissive hypercapnia in premature neonates Ͻ Male, n (%) 75 (51) 28 (58) 32 weeks gestational age, and to identify a relationship Cesarean section, n (%) 121 (82.3) 39 (81.3) between P and pH during the first 72 h and adverse aCO2 Premature rupture of 25 (17) 10 (20.8) neonatal outcomes.
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