|Year : 2018 | Volume
| Issue : 1 | Page : 7-9
Prone position ventilation in pregnancy: Concerns and evidence
Bikash R Ray, Anjan Trikha
Department of Anaesthesiology Pain Medicine and Critical Care, AIIMS, New Delhi, India
|Date of Web Publication||13-Apr-2018|
Dr. Anjan Trikha
Department of Anaesthesiology Pain Medicine and Critical Care, All India Institute of Medical Sciences, New Delhi
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Ray BR, Trikha A. Prone position ventilation in pregnancy: Concerns and evidence. J Obstet Anaesth Crit Care 2018;8:7-9
|How to cite this URL:|
Ray BR, Trikha A. Prone position ventilation in pregnancy: Concerns and evidence. J Obstet Anaesth Crit Care [serial online] 2018 [cited 2018 Jun 24];8:7-9. Available from: http://www.joacc.com/text.asp?2018/8/1/7/230058
Invasive mechanical ventilation with low tidal volume and optimum positive end-expiratory pressure (PEEP) is the standard treatment of severe acute respiratory distress syndrome (ARDS). When oxygenation goals are not met in a patient of ARDS with the lung protective ventilation in supine position, other ventilation techniques such as permissive hypercapnia, inverse ratio ventilation, prone position ventilation (PPV) and high-frequency ventilation are tried to improve oxygenation. Of all the ventilation techniques, PPV has been shown to be most effective in improving oxygenation and is now regularly used in such patients all over the world. Efficacy of prone ventilation in improving hypoxemia has been demonstrated in multiple studies.,, Although hypoxemia had been shown to improve after PPV, survival benefits were doubtful; however, recent studies have shown improvement in survival in patients with ARDS as well.,,
The estimated prevalence of ARDS in pregnancy has been reported to be 16–70 per 100,000, with high rates of foetal death and asphyxia. Preeclampsia, aspiration, infection and trauma are the leading causes of ARDS in pregnancy. The management of pregnant patients in intensive care units is challenging and requires consideration of the physiological and anatomical changes in pregnancy, placental blood flow and interactions of maternal–foetal circulation. There are certain management techniques that are very useful in non-pregnant critically ill patients but not as popular in sick parturients. These are non-invasive ventilation, PPV and extracorporeal membrane oxygenation. In pregnant patients, the initial management is driven by same principles with additional need for foetal monitoring. Usually PPV is tried in non-pregnant patients if hypoxemia remains uncorrected, but in parturients because of lack of evidence of this modality in this subgroup of ARDS patients it is not instituted. A literature search revealed only anecdotal case reports of use of PPV in pregnant patients.
In supine position, the dependent lung is partially collapsed by the heart and the diaphragm, which is aggravated by the pressure from the abdominal contents. During PPV, the heart lies on the sternum and it relives compression on the medial and the posterior portion of the lung parenchyma. In addition, the diaphragm is displaced caudally, which decreases the compressive effect it exerts on the inferior part of the lung. In pregnancy, the magnitude of diaphragmatic compression because of an increase in abdominal contents is more, which is relived in prone positioning. Another possible benefit of prone position in pregnancy is the release of compression of the major vessels by the gravid uterus leading to an increase in uterine blood flow. Nakai et al., in 23 healthy volunteers, studied uterine blood flow at 34 weeks of pregnancy in supine, right lateral, left lateral and prone position. Their study demonstrate that among all the positions, prone position provides optimal relief of umbilical artery compression as measured by the umbilical artery systolic–diastolic ratio. The percentage change in the systolic–diastolic ratio was maximum in prone position, indicating that complete relief of uterine compression on large vessels can only be achieved in prone position.
Other benefits of prone ventilation include improvement in ventilation perfusion mismatch, lung recruitment, homogeneous ventilation, better drainage of pulmonary secretions and better delivery of aerosol medications.,
When to initiate prone ventilation in pregnant patients
Indication of prone ventilation in a pregnant patient is the same as that of any other patient with ARDS. Patients with severe ARDS, who fail to improve oxygenation despite appropriate ventilator strategy, should be tried for prone ventilation. It is also used for patients waiting for extracorporeal membrane oxygenation (ECMO). Early initiation of prone ventilation is most effective as has been shown in many trials, hence a low threshold for initiating prone ventilation should benefit the patients.
Evidence for prone ventilation in pregnancy
Prone positioning to improve oxygenation in ARDS patients has been used since 1976; however, its use in clinical practice was not significant till the Proning Severe ARDS Patients (PROSEVA) trial demonstrated a survival benefit. Before this trial, prone ventilation was used as a rescue strategy in severe ARDS to improve oxygenation. Thus, prone positioning was not tried in pregnant patient with ARDS because of concern of foetal well-being. However, there were many reports of prone positioning during pregnancy for successful conduct of anaesthesia and surgery., It was during influenza pandemic during 2009 that many patients including pregnant patients received prone ventilation as a rescue therapy. In a report from an Australian cohort, two pregnant patients prone ventilation for pregnant patients has increased after these reports and the PROSEVA trial, till now there are only few case reports describing its successful use in severe ARDS.,
Kenn et al. reported management of a case of ARDS following blunt chest trauma, in a pregnant patient at 34 weeks of gestation, with use of prone ventilation. In this case, prone ventilation for 8 h resulted in significant improvement in oxygenation, which allowed extubation the following day, without any feto-maternal complication. During prone positioning, meticulous care was taken to avoid pressure on the abdomen, while foetal well-being was monitored closely by continuous cardiotocography (CTG). Samanta et al. reported a similar case of successful management of H1N1-induced ARDS, in a pregnant patient at 31 weeks of pregnancy, with prone ventilation. The patient was ventilated in prone position after the authors failed to obtained adequate oxygenation despite 100% oxygen and inverse ratio ventilation. Dramatic improvement in oxygenation and lung compliance was noticed only after 6 h of ventilation. Proning for 16 h on the following 3 days helped in wean the patient off ventilation. The authors used large rollers underneath the chest and iliac crest to prevent any abdominal compression. Foetal well-being was ensured with CTG, throughout the proning session. Umbilical artery Doppler was also performed before and after each proning session.
Ventilation in prone position does always results in improved oxygenation in all the patients. It has been found that approximately 60% of patients show improvement in oxygenation after prone ventilation. Hence, cases of minimal benefit from proning in pregnancy have been reported, which was latter managed with ECMO.
How to do prone positioning?
Currently, there is little literature available to guide prone positioning during pregnancy. Because of the lack of evidence specific to pregnancy, management decisions must be drawn from studies done in the general population.
Proning can be done manually or by commercially available beds. These beds avoid the risk during turning; however, no studies are available to justify their use. In addition, these beds are not designed to address the problems specific to pregnancy. Manual proning is a labour-intensive procedure and requires four to five persons. Every person should be well accustomed with the procedure and it is important to assign specific duties to each person during positioning. Adequate provision should be made to quickly turn the patient back to supine position, if required. Ensuring proper position and fixation of tubes and catheters before prone positioning decreases the chances of dislodgment. Proper size support for head and body should be arranged. While placing pregnant patients in prone a special care should be given for preventing pressure on abdomen. Large size boulders or pillows may be used to make the abdomen free of compression, as used by Samanta et al. Support to pressure points and eye is vital to prevent injuries.
Ventilatory strategy in prone position remains the same as that in supine position. Lung protective strategy with optimal PEEP should be used. Neuromuscular blocking agents may be required in severe ARDS for maintaining oxygenation.
Monitoring of pregnant patient in prone position does not change from that of supine position. Special importance should be given for foetal monitoring. Continuous CTG monitoring has been advocated in previous reported cases., Umbilical artery flow should be monitored before and after each proning season. Arterial blood gas (ABG) should be checked intermittently. On the basis of ABG, the patients are classified as responders (PaO2:FiO2 ratio increase by 20% or by >20 mm Hg) or non-responders. The response is normally visible in first few hours or may take 1216 h. If prone ventilation fails (no change or worsening of gas exchange, lung mechanic, or cardiovascular status), the patient should be put back to supine position and alternate rescue strategies should be planned.
The duration of prone ventilation varied from 6 o 8 h/day to 16–20 h/day, in different studies. PROSEVA trial showed mortality benefit using a mean duration of 17 h/day of prone position with an average of total of four sessions. So based on this current evidence, it can be advised to maintain prone ventilation for long periods (16–20 h/day), even in pregnant patients. This is supported by the case reported by Samanta et al.
Complications during proning
The centres that are adequately equipped and have experience in prone positioning show better results and less complications. The most common complications seen after prone positioning are related to pressure point-related side effects. Pregnant patients may be more prone to pressure-related complications such as facial edema and skin breakdown, because of their thin and fragile skin. However, pregnancy-specific complications have not been reported. Other common complications during proning are as follows: dislodging of endotracheal tube, vascular catheters and drainage tubes, worsening of arterial saturation and lung compliance, nerve injury, transient arrhythmias, haemodynamic instability, retinal damage, pneumothorax, intolerance to enteral nutrition and difficulty in procedures and instituting cardiopulmonary resuscitation (CPR). PROSEVA trial did not show any difference in rate of expected complications (e.g. unplanned extubation, tube obstruction, desaturation, bradycardia and severe hypotension) between the groups.
| Conclusion|| |
In summary, there is very limited evidence to guide the management of a pregnant patient with severe ARDS who requires prone ventilation. From all the literature that we have looked at, it appears that prone ventilation in late pregnancy for ARDS is feasible with potential good maternal and foetal outcome and should not be avoided. However, prone positioning should be considered only in severe oxygenation impairment, as the fetus is also affected. Meticulous planning and knowledge of feto-maternal interaction helps increase success and decrease complications of proning during pregnancy. Avoiding abdominal compression and regular assessment of maternal and foetal well-being are essential for optimal outcome. Close multidisciplinary assessment is pivotal to correctly establish the timing for treatment and to help determine clinical outcome.
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