Inhalation of Helium-Oxygen Mixture in Two Cases of Maternal Respiratory Distress during Labor and Delivery

Introduction

Inhalation of helium/oxygen has been life-saving in patients afflicted respiratory distress secondary to a narrow airway [1]; it was first reported in the obstetric literature thirty years ago [2]. We could find no recent reports of helium/oxygen inhalation therapy in a parturient with upper airway obstruction. We report two parturients, each with severe tracheal stenos is (goiter), presenting with onset of significant respiratory distress. Inhaled helium/oxygen alleviated maternal distress. Maintenance of effective epidural analgesia during a passive second stage led to assisted vaginal delivery of a healthy neonate.

Discussion

Any further decrease in upper airway radius increases turbulence, impedance and work of breathing (i.e., to create negative intrathoracic pressure).The inhalation of helium (65-70%)/oxygen (30-35%) as a therapeutic gas improves respiratory mechanics, amelioratingdyspnea in patients with upper airway obstructive lesions [3]. Substituting helium in a mixture with oxygen decreases overall density of inhaled gas, decreasing the effort to create negative pressure. Our patients demonstrated severe airway compression. Though an established therapy in previously reported cases of partial upper airway obstruction, [1] inhalation of a mixture of helium/oxygen has rarely been reported in labor. In both cases presented, inhalation of a helium-oxygen (70%/30%, respectively) ameliorated respiratory distress presenting during second stage of labor. In second stage of labor, there are increased maternal oxygen requirements and hyperventilation due to: increased vaginal discomfort; voluntary/involuntary Valsalva-associated expulsive efforts; and, progressive metabolic academia [4]. Hyperventilation worsens turbulent flow of air and the sense of dyspnea [3]. Hypothesizing that Valsalva-associated expulsive effort in patients with extra-thoracic tracheal compression would make gas flow more turbulent, abeyance of expulsive efforts and initiation of inhaled of helium/oxygen mitigated maternal respiratory decompensation and improved maternal oxygenation. In hopes of mitigating any relationship between obstetric pain and increased work of breathing, neuraxial analgesia was induced “early” in labor. If this option had been rejected, then other forms of analgesia were considered. We believed that intravenous opioid analgesia (nurse-administered or even patient-controlled intravenous analgesia using fentanyl or remifentanil) might produce opioid-induced respiratory depression. Other forms of labor analgesia were considered. Over 60 years ago, Robert Hingson [5] described inhalation of helium/oxygen/cyclopropane to produce obstetric analgesia. Today, the use of inhaled nitrous oxide/oxygen (50%/50%) is accepted by some clinicians as an effective analgesic in labor [6]. The inhalant that we utilized contained 70% helium/ 30% oxygen. The respiratory therapists assigned to our Unit believed that initiating inhalation using a tank containing a fixed ratio of helium/oxygen was simpler than varying (blending) other ratios.If needed, higher concentrations of oxygen can be blended by respiratory therapists [7].

However, blending an inhalant with 50% nitrous oxide/30% helium would have precluded the use of increased inspired oxygen concentrations. In these two cases, the mixture was not varied. We did not analyze inspired and expired gas in these cases to verify the labeled mixture. The use of par cervical block and pudendal nerve block have been well reported to provide satisfactory analgesia for first and second stages of labor, respectively; their efficacy and side effects are well-reported [8]. Bilateral parasympathetic blocks have been reported to provide satisfactory analgesia [9]. Even intravenous infusion of dexmedetomidine was considered as a drug that would not further exacerbate any maternal respiratory decompensation [10]. The infusion of supplemental low- dose ketamine labor analgesia [11] was rejected due to the possibly increased airway secretions. If anesthesia for abdominal delivery was indicated (e.g., cephalopelvic disproportion or acute fetal decompensation),then we planned to inject the in situ neuraxialcatheter. Demonstrating satisfactory regional analgesia/anesthesia “early” in labor was therefore reassuring. If neuraxial anesthesia was deemed ineffective before surgery, we believed risk of airway management outweighed the benefit of a shorter decision-to-delivery time; CSE or single-injection spinal anesthesia would have been induced. If neuraxial anesthesia was deemed ineffective during surgery, then we first planned on infiltration with local anesthetic [12] supplemented by intravenous infusion of dexmedetomidine. Injection of intravenous ketamine was considered [13] but rejected due to the risk of increased airway secretions. If tracheal intubation was indicated (i.e., general anesthesia or part of maternal resuscitation), then the plan was to: preserve spontaneous ventilation; use awake fiber-optic assist; and, insert a small-sized (5.5mm ID) reinforced tracheal tube (Rusch R). Consultants experienced with rigid bronchoscopy were on standby; cricothyroidotomy or tracheotomies were not feasible. We planned any needed post-cesarean analgesia using PCEA with infusion of local anesthetic with/without low concentrations of lipid soluble epidural opioids and/or adjuvant intravenous dexmedetomidine [14]. After abdominal delivery, the patient would have been kept in an area of “intensive nursing” during the period of epidural infusion. Advanced planning was done to insure immediate availability of the proper resources, both materials (such as the helium/oxygen tanks and breathing apparatus) and personnel (availability of expert bronchoscopists) required to execute our plan of management. Discussion among the different physician and nursing groups involved in our patients’ care led us to our decision to manage these two patients on our Labor and Delivery Unit; and, not having them labor and deliver in an Intensive Care Unit or in a general-purpose operating room. Fetal safety of inhaled maternal helium has never been proven. However, helium is an inert gas. Fetal (neonatal) blood concentrations should decrease quickly after discontinuation of maternal inhalation (or delivery). In the gravid ewe model, short-term inhalation of 80% helium leads to a maternal blood helium concentration of about 7% with fetal blood helium concentration of about 1% [15]. In neither case presented was there decompensation of the electronic fetal heart rate recording associated with inhalation of helium. Each neonate was born vigorous.

Summary

Key in these two cases was early evaluation and careful multidisciplinary planning, including (but not limited to): “early” labor determination of a “working “neuraxial catheter; allowing a passive second stage; willingness to accept/perform operative vaginal delivery;“stand-by” assistance with rigid bronchoscopy; and, gathering of resources/equipment (e.g. canisters, blenders) to the labor suite. We believe that inhalation of helium-oxygen provided significant therapeutic benefit during labor. Given the ameliorating effects of inhaled helium/oxygen on maternal respiratory function, that helium is an inert gas, and it should be easily excreted across the placenta or lungs after birth, we would not hesitate to administer helium/oxygen to any future parturient suffering from respiratory distress secondary to a pathologic narrowing of the airway.

Author Contributions

1. Omar Alyamani MBBS: Planned and executed clinical care, planned and co-author of the manuscript

2. Shobana Bharadwaj MBBS: Planned and executed clinical care, planned and edited the manuscript

3. SrikarJonna MD: executed clinical care and contributed to the writing of the manuscript

4. Justin Li MD: executed clinical care and contributed to the writing of the manuscript

5. Andrew M Malinow MD: Planned, and authored manuscript Consent: obtained; approved by the Human Research Protection Office (UMB)