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 Table of Contents  
Year : 2021  |  Volume : 10  |  Issue : 3  |  Page : 178-180

Proning: Its anatomical basis and effect on oxygen saturation in COVID patients

1 Assistant Professor, Department of Anatomy, JSSMC, JSSAHER, Mysuru, Karnataka, India
2 Professor, Department of Anatomy, Azeezia Institute of Medical sciences, Kollam, Kerala, India
3 Professor (Additional), Department of Anatomy, All India Institute of Medical Sciences, Rishikesh, Uttarkhand, India
4 Professor and Head, Department of Pulmonology, Shri Sathya Sai Medical College and Research Institute, Chengalpattu, Tamil Nadu, India

Date of Submission19-Jun-2021
Date of Decision10-Jul-2021
Date of Acceptance23-Jul-2021
Date of Web Publication30-Jul-2021

Correspondence Address:
S Viveka
Professor, Department of Anatomy, Azeezia Institute of Medical Sciences, Kollam, Kerala- 691537
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/NJCA.NJCA_82_21

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Proning is the process of turning the patient from their supine (lying on their back) position to lying on their abdomen. It is a medically accepted position for improving oxygenation while breathing. Respiration in supine position, compresses the posterior surface of the lung preventing normal distension of the alveoli. This results in suboptimal oxygenation of the blood circulating in the lobes of the lung, particularly lower lobes. Lowered V/Q ratio from these regions of the lung contributes to the venous admixture. In the prone position, the heart with its pericardial chamber, occupies anterior dependent portion of the mediastinum, resulting in better expansion of the alveoli. This leads to improved V/Q ratio from these regions and lowers the physiological shunt effect on the oxygen saturation.

Keywords: Corona, COVID-19 pneumonia, partial pressure of oxygen, prone position

How to cite this article:
Pushpa N B, Viveka S, Ravi K S, Vallabhaneni V. Proning: Its anatomical basis and effect on oxygen saturation in COVID patients. Natl J Clin Anat 2021;10:178-80

How to cite this URL:
Pushpa N B, Viveka S, Ravi K S, Vallabhaneni V. Proning: Its anatomical basis and effect on oxygen saturation in COVID patients. Natl J Clin Anat [serial online] 2021 [cited 2022 Sep 25];10:178-80. Available from: http://www.njca.info/text.asp?2021/10/3/178/322811

  Introduction Top

With the alarming increase in the daily cases of COVID during the second wave of this terrible pandemic, the medical infrastructure is highly strained throughout the world. Subsequently, there is search for meaningful and effective home isolation methods. The state governments and other regulatory authorities are under tremendous pressure to meet the oxygen demand of the hospitalized patients. Simultaneously, there is thoughtful research for natural methods of improving oxygen levels by simple techniques.[1] Change in the diet, limited yet regular activity, slow and deep respiration as in meditation and yoga, proper hydration, and breathing clean air are expected to add value in improving patient's oxygen saturation (SpO2).[2] This shall lead to overall improvement in COVID-related health condition.

For all asymptomatic and mildly symptomatic COVID-positive patients, governments across the world are enforcing strict home isolation.[3] Home-isolated patients account for a major chunk of COVID-related suffering. These patients are to self-monitor their temperature and SpO2 using a digital thermometer and pulse oximeter, respectively. During their home isolation, the patients are advised to administer few medications including antiviral drugs, symptomatic management of cough, fever, cold, and vitamin supplements. The fulcrum of treatment plan for both hospitalised and home isolated patients revolves around level of oxygen saturation(SpO2). Saturation of >96% is considered normal. Patients with 93%–96% of SpO2 are encouraged to take a 6-min walk test (6MWT or 3MWT in case of age >60 years). If there is a drop of more than 4% of SpO2 after 6MWT, patients are advised to seek medical help. In order to improve the saturation, patients with SpO2 are advised to follow prone position. Proning is proven to increase the SpO2 not only in COVID patients[4] but also in severe acute respiratory distress syndrome (ARDS).[5],[6],[7]

  Anatomical Basis Top

The heart is in the middle of the inferior mediastinum. It is situated in the anterior aspect of the thoracic cavity. Lungs occupy the posterior spaces in the thorax. Respiration in supine position, compresses the posterior surface of the lung. Such compression prevents normal distension of the alveoli [Figure 1]. Alveolar inflation follows gravity gradient. In supine position, inflation is more in non-dependent alveoli which are present towards the sternum. Inflation is less among dependent alveoli of posterior regions of the lung lobes.[8] The resultant ventilation-perfusion mismatch (V/Q ratio) in these parts of lung contribute to physiological lowering of the SPO2 of arterial blood.[9] The regions of lung with V/Q ratio less than one will act as shunt by returning less than 100% oxygenated blood to left side of the heart.[10],[11],[12],[13],[14] Trans-pulmonary pressure depends on difference between alveolar pressure and pleural pressure. More negative the alveolar pressure, greater is trans-pulmonary pressure. Alveolar pressure is again more in nondependent alveoli compared to dependent alveoli. Hence alveolar dimension is also more in nondependent alveoli.6 Prone position helps in more homogenous distribution of air within the lungs and increases lung recruitment.[15] Histological studies have also proved that prone position reduces extent and severity of lung damage.[16] In the prone position, the heart with its pericardial chamber, occupies anterior dependent portion of the mediastinum, resulting in better expansion of the alveoli. This leads to improved V/Q ratio from these regions and lowers the physiological shunt effect on the SPO2. .
Figure 1: (a and b) Schematic illustration of cross section of thorax at T6 vertebra, showing areas of lower ventilation perfusion ratio (*) in supine and prone position

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  Effect of Proning in COVID Pneumonia and Acute Respiratory Distress Syndrome Top

There are many attempts to evaluate the effect of proning among COVID patients and severe ARDS patients.[3],[5],[6],[7],[8],[9],[10] Jagan et al. retrospectively analyzed the effects of awake self-proning among 105 nonintubated COVID-positive patients in hospital setting and found that proning led to lesser intubation and lower mortality.[4] Weiss et al. advised prone breathing after observing 42 patients for 2 weeks.[17] However, they found no significant improvement in ratio of SpO2 to fraction of inspired oxygen level.[4] Guérin concludes from two meta-analyses[18],[19] and a trial that proning improves the outcomes in severe ARDS.[5] Rapid improvement of SpO2 from 94% to 98% was reported after observing proning among ten nonintubated COIVD19 patients by Damarla et al.[20]

Several mechanisms explain the benefits of proning among ARDS. Prone breathing may reduce nonphysiological stress and also strain of mechanical ventilation.[18] Thus, can reduce subsequent lung injury. This has resulted in a significant reduction of ICU mortality among severe ARDS patients.[19] Proning has been shown to improve saturation among 70%–80% of ARDS patients.[21],[22] After observing beneficial effects of proning among 170 severe ARDS patients, Lucchini et al. call for a dedicated protocol and involvement of five trained and skilled professionals to execute proning among intubated patients.[6] Proning Severe ARDS Patients clinical trial evaluating proning among ARDS patients concludes affirmatively with improved survival advantage.[23] ARDS Prone Position Network study ends with low complication rates and significant increase in oxygenation.[24]

However, in the prone position, due to compression of the abdominal content, there is a possibility of upward push of the diaphragm and subsequent compression of the lungs. This shall lead to increased shunting and much lower V/Q ratio. Therefore proning should be carefully practised immediately after food intake and in Obese patients. Nevertheless, proning is not a panacea for all respiratory-related ailments. A case report of increased intracranial pressure with a large pressure eschar over the sternum is reported after a week of proning in a middle-aged female patient with COVID-19.[25]

Patients with moderate-to-severe ARDS either with spontaneous breathing or assisted breathing tend to breathe with more effort. This itself may worsen already stressed out lung injury. With stronger respiratory efforts, leading to larger negative pleural pressure generates excessive lung stress and strain. Lung injury, especially in COVID patients, results in atelectasis in dependent regions of the lung.[26] To complicate the scenario, the pendelluft phenomenon, movement of air from nondependent to dependent regions without change in tidal volume, can increase the regional stress on the lung.[27] With prone position, flexible anterior chest wall being more dependent, there will be homogeneous distribution of ventilation and perfusion. Therefore, proning decreases the risk of strenuous breathing-induced lung injury and pendelluft.[28] However, the beneficial effects are short lived and readily get reversed with repositioning of the patient to supine.[29]

When the whole world is devastated with the deadly pandemic affecting millions of people, there is obvious shortage in the oxygen available to treat the needy and save life. In such crucial conditions even the minor maneuver, if it can cause some improvement in the SpO2, then it becomes very important saving lives of patients. If utilized properly, prone breathing can help in improving the patient condition during ongoing pandemic.

Steps for effective proning

Ministry of health and family welfare, Government of India has given recommended following steps for effective proning [Figure 2].[30] The concept of dependent drainage in perfusion of lungs holds the key. Anatomical basis of proning adds lots of untouched concepts and strong points in improving saturation. The effect of proning on cardiac output and shunting is important in outcomes of lung diseases. In addition, the post proning nursing care is crucial to prevent complications such as aspirations and poor cardiac output among obese individuals. However, the effects of proning are temporary and cause of fall in SpO2 needs to be treated for permanent results.
Figure 2: Flowchart of prone breathing to be followed by patients with lower oxygen saturation during home isolation[30]

Click here to view

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Conflicts of interest

There are no conflicts of interest.

  References Top

Lupon E, Lellouch AG, Zal F, Cetrulo CL Jr., Lantieri LA. Combating hypoxemia in COVID-19 patients with a natural oxygen carrier, HEMO2Life® (M101). Med Hypotheses 2021;146:110421.  Back to cited text no. 1
Russo MA, Santarelli DM, O'Rourke D. The physiological effects of slow breathing in the healthy human. Breathe (Sheff) 2017;13:298-309.  Back to cited text no. 2
Ministry of Health & Family Welfare. Revised Guidelines for Home Isolation of Mild/Asymptomatic COVID-19 Cases. Government of India, Ministry of Health & Family Welfare; 2021. Available from: https://www.mohfw.gov.in/pdf/RevisedguidelinesforHomeIsolationofmilda symptomaticCOVID19 cases.pdf. [Last accessed on 2021 Jun 10].  Back to cited text no. 3
Jagan N, Morrow LE, Walters RW, Klein LP, Wallen TJ, Chung J, et al. The POSITIONED study: Prone positioning in nonventilated coronavirus disease 2019 patients – A retrospective analysis. Crit Care Explor 2020;2:e0229.  Back to cited text no. 4
Guérin C. Prone position. Curr Opin Crit Care 2014;20:92-7.  Back to cited text no. 5
Lucchini A, Bambi S, Mattiussi E, Elli S, Villa L, Bondi H, et al. Prone position in acute respiratory distress syndrome patients: A retrospective analysis of complications. Dimens Crit Care Nurs 2020;39:39-46.  Back to cited text no. 6
Marion BS. CE Credit: A turn for the better: Prone positioning” of patients with ARDS. Am J Nurs.2001;101:26-35.  Back to cited text no. 7
Bigeleisen PE. Models of venous admixture. Adv Physiol Educ 2001;25:159-66.  Back to cited text no. 8
Guérin C, Albert RK, Beitler J, Gattinoni L, Jaber S, Marini JJ, et al. Prone position in ARDS patients: Why, when, how and for whom. Intensive Care Med 2020;46:2385-96.  Back to cited text no. 9
Petersson J, Glenny RW. Gas exchange and ventilation-perfusion relationships in the lung. Eur Respir J 2014;44:1023-41.  Back to cited text no. 10
Ansari A. Anatomy and clinical significance of ventricular Thebesian veins. Clin Anat 2001;14:102-10.  Back to cited text no. 11
Ravin MB, Epstein RM, Malm JR. Contribution of thebesian veins to the physiologic shunt in anesthetized man. J Appl Physiol 1965;20:1148-52.  Back to cited text no. 12
Aviado DM, Daly MD, Lee CY, Schmidt CF. The contribution of the bronchial circulation to the venous admixture in pulmonary venous blood. J Physiol 1961;155:602-22.  Back to cited text no. 13
Cooper CB, Celli B. Venous admixture in COPD: Pathophysiology and therapeutic approaches. COPD 2008;5:376-81.  Back to cited text no. 14
Cornejo RA, Díaz JC, Tobar EA, Bruhn AR, Ramos CA, González RA, et al. Effects of prone positioning on lung protection in patients with acute respiratory distress syndrome. Am J Respir Crit Care Med 2013;188:440-8.  Back to cited text no. 15
Nakos G, Batistatou A, Galiatsou E, Konstanti E, Koulouras V, Kanavaros P, et al. Lung and 'end organ' injury due to mechanical ventilation in animals: Comparison between the prone and supine positions. Crit Care 2006;10:R38.  Back to cited text no. 16
Weiss TT, Cerda F, Scott JB, Kaur R, Sungurlu S, Mirza SH, et al. Prone positioning for patients intubated for severe acute respiratory distress syndrome (ARDS) secondary to COVID-19: A retrospective observational cohort study. Br J Anaesth 2021;126:48-55.  Back to cited text no. 17
Gattinoni L, Carlesso E, Taccone P, Polli F, Guérin C, Mancebo J. Prone positioning improves survival in severe ARDS: A pathophysiologic review and individual patient meta-analysis. Minerva Anestesiol 2010;76:448-54.  Back to cited text no. 18
Abroug F, Ouanes-Besbes L, Dachraoui F, Ouanes I, Brochard L. An updated study-level meta-analysis of randomised controlled trials on proning in ARDS and acute lung injury. Crit Care 2011;15:R6.  Back to cited text no. 19
Damarla M, Zaeh S, Niedermeyer S, Merck S, Niranjan-Azadi A, Broderick B, et al. Prone positioning of nonintubated patients with COVID-19. Am J Respir Crit Care Med 2020;202:604-6.  Back to cited text no. 20
Dirkes S, Dickinson S, Havey R, O'brien D. Prone positioning: Is it safe and effective? Crit Care Nurs Q 2012;35:64-75.  Back to cited text no. 21
Pelosi P, Caironi P, Taccone P, Brazzi L. Pathophysiology of prone positioning in the healthy lung and in ALI/ARDS. Minerva Anestesiol 2001;67:238-47.  Back to cited text no. 22
Guérin C, Reignier J, Richard JC, Beuret P, Gacouin A, Boulain T, et al. Prone positioning in severe acute respiratory distress syndrome. N Engl J Med 2013;368:2159-68.  Back to cited text no. 23
Guérin C, Beuret P, Constantin JM, Bellani G, Garcia-Olivares P, Roca O, et al. A prospective international observational prevalence study on prone positioning of ARDS patients: The APRONET (ARDS Prone Position Network) study. Intensive Care Med 2018;44:22-37.  Back to cited text no. 24
Le MQ, Rosales R, Shapiro LT, Huang LY. The down side of prone positioning: The case of a coronavirus 2019 survivor. Am J Phys Med Rehabil 2020;99:870-2.  Back to cited text no. 25
Brochard L, Slutsky A, Pesenti A. Mechanical ventilation to minimize progression of lung injury in acute respiratory failure. Am J Respir Crit Care Med 2017;195:438-42.  Back to cited text no. 26
Yoshida T, Torsani V, Gomes S, De Santis RR, Beraldo MA, Costa EL, et al. Spontaneous effort causes occult pendelluft during mechanical ventilation. Am J Respir Crit Care Med 2013;188:1420-7.  Back to cited text no. 27
Riad Z, Mezidi M, Subtil F, Louis B, Guérin C. Short-term effects of the prone positioning maneuver on lung and chest wall mechanics in patients with acute respiratory distress syndrome. Am J Respir Crit Care Med 2018;197:1355-8.  Back to cited text no. 28
Chatte G, Sab JM, Dubois JM, Sirodot M, Gaussorgues P, Robert D. Prone position in mechanically ventilated patients with severe acute respiratory failure. Am J Respir Crit Care Med 1997;155:473-8.  Back to cited text no. 29
Ministry of Health & Family Welfare, Government of India. COVID-19 Proning for Self Care; 2021. Available from: https://www.mohfw.gov.in/pdf/COVID19ProningforSelfcare3.pdf. [Last accessed on 2021 Jul 07].  Back to cited text no. 30


  [Figure 1], [Figure 2]


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