Non-Invasive Positive Pressure Ventilation (NIPPV) in the Pregnant Patient: A Case Series

Rationale: Acute respiratory failure is an uncommon complication of pregnancy. However, it is the most frequent organ dysfunction associated with obstetric admissions to an intensive care unit. The obstetric population is a different group due to its physiology and the presence of the fetus that lacks evidence in the literature within the subject of ventilatory support. Noninvasive positive pressure ventilation (NIPPV) is often avoided due to the lack of knowledge on the safety and efficacy of this modality. Currently, there are no guidelines for the management of respiratory failure in pregnancy. Objectives: To provide evidence in support of the use of NIPPV as a safe and reasonable modality for pregnant patients with respiratory failure. Methods: We retrospectively reviewed medical records of 29 pregnant patients of the Obstetric Critical Care Unit of a tertiary hospital in Panamá City who received NIPPV from 2013 to 2015. Failure to response was defined as the lack of increase in the paO2/FiO2 ratio or clinical deterioration 6 hours after initiating NIPPV. Demographics, indication for NIPPV, duration of treatment, as well as maternal and fetal outcomes were collected. Measurements and Main Results: Mean age was 28.4 ± 6 years, mean body mass index 27.4 ± 3.3, and mean gestational age at admission was 30 ± 5 weeks. Twenty-four patients (82.8%) met the criteria for acute lung injury (ALI) and an additional two (6.9%) for acute respiratory distress syndrome (ARDS). The mean duration of ventilation was 50.6 ± 17.27 hours. Statistically significant differences were noted between the paO2/FiO2 ratios in failure and successful patients within 2 hours of NIPPV therapy (P = 0.007) and paO2/FiO2 ratio within 6 hours of NIPPV therapy (P = 0.03). Success was defined when the patient was administered NIPPV, resulting in an improvement (increase in pa/FiO2 ratio) of her ventilatory parameters. Three patients (10.3%) failed to respond to How to cite this paper: Montufar-Rueda, C., Ditisheim, A., Gei, A.F., Pinilla, R., Dinh, E., Vélez, J., Castillo, B. and Farias, L. (2020) Non-Invasive Positive Pressure Ventilation (NIPPV) in the Pregnant Patient: A Case Series. Open Journal of Obstetrics and Gynecology, 10, 1563-1572. https://doi.org/10.4236/ojog.2020.10110140 Received: October 1, 2020 Accepted: November 13, 2020 Published: November 16, 2020 Copyright © 2020 by author(s) and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY 4.0). http://creativecommons.org/licenses/by/4.0/ Open Access C. Montufar-Rueda et al. DOI: 10.4236/ojog.2020.1011014


Introduction
Acute respiratory failure (ARF) is an uncommon but serious condition during pregnancy, complicating 0.1% to 0.2% of pregnancies, more commonly in the postpartum period [1]. It is one of the most frequent non-obstetric cause and the most common organ dysfunction associated with obstetric admissions to an intensive care unit (ICU) [2] [3] [4] [5].
Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are two important causes of acute respiratory distress. Unfortunately, there is no evidence to guide the management of these conditions during pregnancy and current literature on the subject consists mainly of case reports and case series based on a small number.
Originally developed for chronic respiratory failure, the use of non-invasive positive pressure ventilation (NIPPV) for acute respiratory failure has increased considerably over the past decades and became a first line therapy for some indications [6] [7] [8].
The main concern for using NIPPV in pregnancy is a theoretical increased risk of pulmonary aspiration of gastric contents [9] [10]. Endotracheal intubation carries a risk of failed intubation up to 8 times greater in the pregnant cohort due to airway changes including edema and hyperemia [11] [12] [13]. Recent studies have recognized NIPPV as an ideal modality for the management of obstetric respiratory complications avoiding the risks of endotracheal intubation and ICU length of stay [1] [9] [14].
We decided to report a case series of acute respiratory failure during pregnancy managed with NIPPV as the first line of therapy.

Methods
We retrospectively reviewed the medical records of pregnant patient of the Obstetric Critical Care Unit of a tertiary hospital in Panamá City, (Complejo Hospitalario de la Caja de Seguro Social, Panamá), who received non-invasive posi- Respiratory parameters were evaluated through arterial blood gases measurements performed before initiation of NIPPV. A paO 2 /FiO 2 ratio was calculated before initiation of NIPPV, and after 2 and 6 hours of therapy to evaluate the response to NIPPV. Failure to response was defined as the lack of increase in the paO 2 /FiO 2 ratio or clinical deterioration 6 hours after initiating NIPPV. The occurrence of aspiration and the need to convert to invasive ventilation were also documented, as well as the use of vasopressors. Neonatal outcome was evaluated by the Apgar score, NICU admission, duration of stay and neonatal death. This study was approved by the Ethic Committee of the institution and the need for the patient consent was waived for this retrospective study.
Data are expressed in mean (standard deviation) and in percentage (absolute number). Differences between groups of patients with failure and successful NIPPV therapy were evaluated with Chi square, Fisher exact test, Student's t test and Wilcoxon rank-sum as appropriate. A p value < 0.05 was considered statistically significant. All data analysis was performed with Stata software, version 12.1 (College Station; Texas).

Results
Data from 29 patients admitted to the Obstetric Critical Care Unit between 2013 and 2015 was collected. Characteristics of the cohort are shown in Table 1 and Table 2. The maternal mean age was 28.4 ± 6.0 years with mean body mass index of 27.4 ± 3.3 kg/m 2 . The mean gestational age at admission was 30.7 ± 5.7 weeks. Eight women (27.5%) delivered while on ventilatory support; four (13.7%) of which were spontaneous labor and the other four (13.7%) were induced for preeclampsia with severe features. All other women delivered after being discharged from the ICU. Mean gestational age at delivery was 33.1 ± 4.9 weeks. There were no maternal deaths.
Respiratory and ventilatory characteristics of the cohort are summarized in Table 3. The two main conditions leading to acute respiratory failure were pneumonia and extrapulmonary sepsis. Twenty-four patients (82.8%) met the criteria for ALI and two additional patients (6.9%) met criteria for ARDS. All patients received ventilation in the bilevel positive airway pressure mode (Bi-PAP), with a full-face mask. Inspiratory positive airway pressure (IPAP) settings ranged from 14 -16 cmH 2 O, expiratory positive airway pressure (EPAP) ranges from 8 -10 cmH 2 O and the fraction of O 2 percentage from 40% -100%, according to the clinical response to NIPPV. The mean duration of ventilation was 50.6 ± 17.2 hours at the term. Three patients (10.3%) failed to respond to NIPPV and needed to be converted to invasive mechanical ventilation ( Figure 1). Open Journal of Obstetrics and Gynecology    Statistically significant differences were noted between patients with successful and failed NIPPV therapy over time, in paO 2 /FiO 2 ratio within 2 hours of NIPPV therapy (P = 0.007) and paO 2 /FiO 2 ratio within 6 hours of NIPPV therapy (P = 0.03).
Correlation between paO 2 /FiO 2 ratios in patients with successful and failed NIPPV therapy before initiation of NIPPV did not reach statistical significance.
Patients who required intubation had a longer duration of ICU stay (P = 0.006) and overall hospital stay (P = 0.03). None of the patients presented aspiration during NIPPV therapy.
Neonatal outcomes are shown in Table 4. The mean birthweight was 2002.5 ±

Comment
The pregnant state is a predisposition for the development of ARDS, with reported incidence rates higher than those found in the general population [9] [15] [16] [17].
In non-pregnant adults, the use of NIPPV has shown to be associated with a reduced rate of endotracheal intubation, lower rates for associated complications and overall ICU length of stay [18] [19]. Pregnancy has so far been considered a relative contraindication due to theoretical risk of aspiration. Aspiration in pregnancy can be associated with an increased intraabdominal pressure, reduced gastroesophageal sphincter tone and decreased gastric emptying due to the mechanical effects of the uterus and increased levels of progesterone [9] [10]. On the other hand, endotracheal intubation during pregnancy is associated with higher failure rates due to changes in the airway including edema and congestion [11] [12] [13]. Pregnant women are also more susceptible to desaturation due to the increased metabolic rate and the oxygen demands of the fetus [20].  [26]. These characteristics make pregnant women an attractive subset of patient to avoid the most common predictors of failure for NIPPV, which we speculate is the reason behind the high rates of success of this modality Open Journal of Obstetrics and Gynecology of ventilation in other reported series [27].
Of interest, in this study, the pregnant women (n = 3; 10.3%) who required invasive mechanical ventilation developed ventilator-associated pneumonia (VAP). The immunity of pregnancy is known to affect the response to infectious agents and avoiding an invasion of their airway may be a strategic goal of initial ventilator support.
Failure of NIPPV could be detected within 2 hours based on clinical response and paO 2 /FiO 2 ratios. This finding can potentially assist clinicians to make preparations for invasive mechanical ventilation well in advance to respiratory claudication.
The strengths of this study include its number and the variety of pathologies treated. The favorable response rate cannot be attributed to a "healthy population bias" since over 90% of them met accepted criteria for ALI or ARDS [28].
One limitation of this study is the missing pregnancy and neonatal outcomes of patients who were treated with NIPPV and were able to continue their pregnancies. Most of these women deliver in their communities of origin. This fact limits the conclusions that can be made regarding the fetal/neonatal safety and complications of this modality of ventilation. Based on the oxygenation response we speculate that NIPPV attenuated the potentially hypoxemic effects of the background condition and allowed for pregnancy continuation that would otherwise be impossible.

Conclusions
In conclusion, this case series adds to the existing evidence in favor of the successful application of NIPPV for the management of respiratory failure in carefully selected and closely monitored pregnant patients. In this cases report, we show that in case of deciding to install ventilatory support, it is possible to do it with the non-invasive mechanical ventilation modality (CPAP or BiPAP) without the dreaded risk of bronchoaspiration; in addition, it is possible to avoid endotracheal intubation with its infectious consequences (ventilator-associated pneumonia), or a poor outcome due to airway management in some patients. We believe that further trials will determine guidelines for the appropriate use of NIPPV in pregnant women, optimal patient selection and safety profile particularly regarding maternal and fetal/neonatal outcomes.