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PulmCrit – Awake Proning for COVID-19

May 5, 2020 by Josh Farkas

Recently, many on twitter have been engaged in a furious debate about how to ventilate patients with COVID-19.  Is it ARDS or not?  High PEEP or low PEEP?…  As an intensivist, these issues are near and dear to my heart.  However, the truth is that humble methods to keep patients off invasive ventilation altogether are probably more important.  One such technique is awake proning. 

Background – Evidentiary basis for Awake Proning of non-COVID patients

Scaravilli V et al  2015:  Prone positioning improves oxygenation in spontaneous breathing nonintubated patients with hypoxemic acute respiratory failure:  A retrospective study

This is a retrospective case series describing 15 non-intubated patients with hypoxemic respiratory failure who underwent proning.​1​  In general, most patients had pneumonia (13/15), were immunocompromised (8/15), never required intubation (13/15), and survived (12/15).  Proning was performed 43 times, a median of twice per patient.  Oxygen was most often provided with a facemask, BiPAP mask, or helmet CPAP.  Proning was performed for a median of 3 hours and a maximum of 8 hours.

During eighteen proning procedures, the patient was maintained on the same amount of respiratory support throughout the entire procedure.   Proning improved oxygenation, but this benefit was only transient (above figure).   Absence of a persistent benefit in oxygenation suggests that proning for a few hours with rotation back to a supine position may be insufficient to lead to stable recruitment of the lung tissue (analogous to the finding that among intubated patients, proning should be extended to ~16 hours for optimal effect). 

Proning had no effect on PaCO2, pH, respiratory rate, or hemodynamics.  Two prone procedures were interrupted due to patient intolerance, but otherwise no complications were noted.

The main limitation of this study is that it involved 15 patients over a time period spanning 2009-2015.  It’s likely that this patient cohort was highly selected, making it difficult to interpret the high success rate in clinical context. 

Evidentiary basis for awake proning of COVID patients

Sun et al.  Lower mortality of COVID-19 by early recognition and intervention: experience from Jiangsu Province

This may be the first article to recognize the value of awake proning in COVID-19 patients as a method to prevent alveolar collapse.​2​  These authors described a treatment strategy employed in their center which correlated with considerably lower intubation and mortality rates than observed in other locations.  Their strategy involved early intervention and awake proning with high-flow nasal cannula or non-invasive mechanical ventilation, to prevent alveolar collapse. 

Caputo et al:  Early self-proning in awake, non-intubated patients in the emergency department: A single ED’s experience during the COVID-19 pandemic

This is a case series describing 50 COVID-19 patients presenting to the Lincoln Hospital emergency department with oxygen saturation <90% while on either nasal cannula or non-rebreather facemask oxygen.​3​  The median oxygen saturation despite these traditional devices was 84%. 

In many medical centers, all of these patients would have been intubated.  Specifically, many centers have been using an early-intubation strategy which involves intubation of any patients who aren’t saturating well in response to low-flow nasal cannula (a misguided strategy which the IBCC has been cautioning against beginning with our first chapter in early march).​4​  

Instead, patients were instructed to awake-prone.  Within five minutes, the median oxygen saturation rose ten points to 94%.  Despite these improvements, 18 patients (36%) didnonetheless require intubation (13 within the first 24 hours, 3 within 24-48 hours, and 2 beyond 72 hours).  Most patients seem to have been managed with a strategy of ongoing positional rotation (e.g., 30-120 minutes in prone position, followed by left lateral decubitus position, right lateral decubitus position, and upright sitting position). 

This is a striking success story.  64% of patients improved and avoided intubation.  To provide a bit of context: 

  • BiPAP reduces the need for intubation in COPD exacerbation by the same amount (65%).​5​In the case of BiPAP for COPD, this 65% reduction in intubation rate correlates with a mortality reduction of 46%.  So, a reduction in intubation rates by 64% is a huge benefit which is likely correlates with improved mortality as well. 
  • Awake proning was being performed at New York City hospitals while under enormous strain.  This demonstrates that the technique is fairly simple to perform and achievable under extremely challenging circumstances. 
  • It doesn’t appear that high-flow nasal cannula was available during this study (due to the massive patient surge).  A strategy of awake proning plus high-flow nasal cannula might be able to achieve even higher success rates in the future, when more resources are available.​6​    

This study obviously isn’t an RCT, but it seems to represent a realistic description of applying an intervention during a pandemic.  Since patients initially met “early intubation” criteria for intubation, patients effectively served as their own controls.  

Aside from the benefits, what are the risks and costs?  The cost of awake proning is minimal, as this may require at most a couple of extra pillows (compared to proning a paralyzed patient, proning an awake patient is extremely easy).  The main risk is that delayed deterioration could lead to a “crash intubation” scenario.  This doesn’t appear to be a major problem.  However, this does emphasize that awake proning should be done with adequate monitoring to detect early signs of deterioration.

Slessarev M et al:  Patient self-proning with high-flow nasal cannula improves oxygenation in COVID-19 pneumonia.

This is a case report of a patient with severe COVID pneumonia who was managed using a combination of high-flow nasal cannula and self-proning for 16-18 hours per day (including 8-10 hours at night).​7​  Proning corresponded with cyclical improvements in oxygenation.  During the day, he was able to eat, communicate with his family, and participate in self-directed physiotherapy. 

Ziehr et al:  Respiratory pathophysiology of mechanically ventilated patients with COVID-19: A cohort study.

This is a description of the respiratory physiology of a series of intubated COVID-19 patients in Boston which was already discussed on this blog.​4​  31 patients were proned.  Proning caused an improvement in oxygenation (P/F increased from median of 150 to 232) and a nonsignificant increase in compliance (median static compliance increased from 33 ml/cm to 36 ml/cm).   After the patients returned to a supine position, P/F ratio remained increased (median of 217) and the compliance remained a bit elevated (35 ml/cm). 

Obviously this isn’t a study on awake proned patients, but the physiology of prone positioning should be similar.  This study illustrates some important points regarding prone physiology in COVID-19:

  • Proning causes a substantial improvement in oxygenation (as reported by Caputo et al. and numerous other authors).
  • Improvements caused by proning appear to persist after the patient is returned to a supine position.  This is important, suggesting that pronation might actually have a disease-modifying effect (rather than merely causing a transient improvement in oxygenation while the patient is proned).

Physiology of proning – what is going on here? 

Improved oxygenation may relate roughly to either:

  1. Recruitment of previously collapsed alveoli in the posterior lungs.
  2. Improved secretion management (which may further serve to prevent atelectasis and improve recruitment of lung tissue).
  3. Shifting of perfusion towards healthier alveoli located in the anterior lungs (thereby improving the ventilation-perfusion matching).

Experimental evidence on prone positioning has previously indicated that the major mechanism of action is recruitment of lung tissue (#1-2), rather than improvements in ventilation-perfusion matching (#3).​8​  The above data in COVID-19 is entirely consistent with this concept that prone ventilation promotes lung recruitment.  If proning primarily caused an improvement in oxygenation due to ventilation/perfusion matching, this benefit should disappear immediatelyafter the patient is no longer prone – a pattern not observed clinically. 

So prone ventilation may be working largely to prevent progressive atelectasis of basilar lung tissue.  This issue of malignant atelectasis and lung recruitment has previously been discussed and summarized in the 1-minute video below:

Combination with other techniques

A major advantage of prone positioning is that it can be combined with a variety of additional techniques.  For example:​6​

  • Prone positioning + room air
  • Prone positioning + low-flow nasal cannula
  • Prone positioning + high-flow nasal cannula
  • Prone positioning + BiPAP/CPAP via a facial mask
  • Prone positioning + BiPAP/CPAP via a helmet interface

The main limitation here may be our own imagination and “comfort zone.”  European studies have long reported the use of prone positioning with BiPAP/CPAP.  The combining of prone positioning with CPAP is theoretically the most powerful duo to recruit lung bases and improve oxygenation.  I’ve used prone positioning only in combination with high-flow nasal cannula.  However, emerging evidence with COVID-19 is suggesting that some patients could benefit from more aggressive combinations of proning plus noninvasive ventilatory support. 

It’s worth noting that prone positioning could also be performed on room air or low-flow oxygen in resource-limited contexts.​9​ For example, this might be used as an oxygen-conservation strategy in a center with limited access to oxygen.  One advantage of awake proning is that it can be performed anywhere, with no special equipment.  It is arguably the single most versatile oxygenation strategy for COVID-19. 

Different approaches to positional adjustment in COVID-19

Arguably, the most evidence-based pronation strategy is complete pronation (with the patient lying on their abdomen, ideally for ~18 hours per day), as this draws its lineage directly from literature on proned intubated patients.​10​  However, this can be difficult in patients with obesity.  One strategy to overcome this is a pregnancy massage pillow, which is essentially an inflatable pillow with a cut-out to allow for a protuberant abdomen (figures below):

If you don’t have this pillow, it might be possible to simulate the same thing with a reverse mountain of towels (a huge pile of towels with a hollowed out area in the middle for the patient’s abdomen). 

Another approach to awake proning is to rotate positions, including lying on either side and sitting bolt upright (as used by Caputo et al.).​3​  The Intensive Care Society recommends the following protocol for this: 

A strategy of rotating positions could be easier for many patients to tolerate (as opposed to ongoing periods of complete proning).  If the mechanism of action of proning is prevention of atelectasis, then this strategy of shifting multiple positions ought to work well.  Currently there is no definitive evidence regarding whether a strategy of rotating positions or complete pronation is superior – either strategy may be beneficial if tolerated by the patient.  Caputo et al. suggested empiricism over rigidity, recommending “do not maintain a position that does not improve the patient’s breathing and comfort” – so adjusting treatment based on what works for any individual patient may be best.​3​   

  • Awake proning has been demonstrated in numerous studies to improve oxygenation.  In COVID-19 patients, pronation may interrupt the process of progressive basilar atelectasis which may drive rapid deterioration. 
  • Caputo et al. recently published a consecutive series of 50 patients in New York City with refractory hypoxemia, despite nasal cannula or non-rebreather facemask.​3​  An awake proning strategy was successful in avoiding intubation among 64% of patients – an impressive and clinically meaningful endpoint. 
  • Awake proning can be combined with a variety of other oxygenation strategies (e.g. high-flow nasal cannula, CPAP, or BiPAP).​6​  Alternatively, awake proning may be performed on room air in emergent situations, or in resource-limited contexts with a tenuous oxygen supply. 
  • Proning for a few hours with a return to supine position may lead only to transientimprovements in oxygenation.  More durable benefit might result from longer periods of pronation, or regimens involving ongoing rotation between several different positions.  Regardless of which strategy is employed, the key principle might be to avoid spending much time in a flat, supine position (“coffin position”).
  • Awake pronation appears to be a safe, inexpensive, and versatile strategy which can be leveraged across a variety of different healthcare systems. 

references

  1. 1. Scaravilli V, Grasselli G, Castagna L, et al. Prone positioning improves oxygenation in spontaneously breathing nonintubated patients with hypoxemic acute respiratory failure: A retrospective study. J Crit Care. 2015;30(6):1390-1394. doi:10.1016/j.jcrc.2015.07.008
  2. 2. Sun Q, Qiu H, Huang M, Yang Y. Lower mortality of COVID-19 by early recognition and intervention: experience from Jiangsu Province. Ann Intensive Care. 2020;10(1):33. doi:10.1186/s13613-020-00650-2
  3. 3. Caputo N, Strayer R, Levitan R. Early Self-Proning in Awake, Non-intubated Patients in the Emergency Department: A Single ED’s Experience during the COVID-19 Pandemic. Acad Emerg Med. April 2020. doi:10.1111/acem.13994
  4. 4. Ziehr DR, Alladina J, Petri CR, et al. Respiratory Pathophysiology of Mechanically Ventilated Patients with COVID-19: A Cohort Study. Am J Respir Crit Care Med. April 2020. doi:10.1164/rccm.202004-1163le
  5. 5. Osadnik CR, Tee VS, Carson-Chahhoud KV, Picot J, Wedzicha JA, Smith BJ. Non-invasive ventilation for the management of acute hypercapnic respiratory failure due to exacerbation of chronic obstructive pulmonary disease. Cochrane Database of Systematic Reviews. July 2017. doi:10.1002/14651858.cd004104.pub4
  6. 6. Ding L, Wang L, Ma W, He H. Efficacy and safety of early prone positioning combined with HFNC or NIV in moderate to severe ARDS: a multi-center prospective cohort study. Crit Care. 2020;24(1):28. doi:10.1186/s13054-020-2738-5
  7. 7. Slessarev M, Cheng J, Ondrejicka M, Arntfield R, Critical Care Western Research Group. Patient self-proning with high-flow nasal cannula improves oxygenation in COVID-19 pneumonia. Can J Anaesth. April 2020. doi:10.1007/s12630-020-01661-0
  8. 8. Gattinoni L, Busana M, Giosa L, Macrì M, Quintel M. Prone Positioning in Acute Respiratory Distress Syndrome. Semin Respir Crit Care Med. 2019;40(1):94-100. doi:10.1055/s-0039-1685180
  9. 9. Dondorp A, Hayat M, Aryal D, Beane A, Schultz M. Respiratory Support in Novel Coronavirus Disease (COVID-19) Patients, with a Focus on Resource-Limited Settings. Am J Trop Med Hyg. April 2020. doi:10.4269/ajtmh.20-0283
  10. 10. Guérin C, Reignier J, Richard J, et al. Prone positioning in severe acute respiratory distress syndrome. N Engl J Med. 2013;368(23):2159-2168. doi:10.1056/NEJMoa1214103

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