INTRODUCTION:

Basic need concept is the main physical requirement for human survival. Efforts to achieve higher needs may be interrupted temporarily by a deficit of primal needs. If not achieved, leads to an increase in displeasure and incentive within an individual to fulfill a necessity. If a person does not feel safe in an environment, they will seek safety before attempting to meet any higher level of survival. Hypoxia is a condition in which the body or a region of the body is deprived of adequate oxygen supply at the tissue level. It will disturb the adaptation at both the systemic and cellular level. Treatment also depends on the cause of Hypoxia and Correct the underlying conditions.

Definition:

It is an abnormally low amount of oxygen in the arterial blood. It is also named as type 1 respiratory failure.

Parameters for evaluation of hypoxia:

· Partial pressure of Oxygen

· Oxygen binding capacity

· Blood oxygen content

· Oxygen saturation

· Difference between arterio-venous oxygen⁵^,⁷

Causes of hypoxaemia:

· Pneumonia

· Pulmonary emboli

· Pulmonary fibrosis

· Pulmonary edema

· Chronic respiratory conditions such as COPD

· Distended abdomen such as pancreatitis, ascites⁵^,¹⁰

Causes of hypoxia in covid-19:

· Intra pulmonary shunting

· Loss of lung perfusion regulation

· Intravascular micro thrombi

· Impaired diffusion capacity⁵

Factors Influencing Hypoxia:

· Altitude

· Rate of ascent

· Duration of exposure to altitude

· Individual tolerance

· Physical fitness

· Psychological stresses

· Temperature

· Medication

· Hypoglycemia

· Physical activity²^,¹¹

Factors affecting po2:

· Fraction of inspired oxygen

· Pulmonary function

· Venous-to-arterial shunt

· Oxygen binding capacity of hemoglobin when fully oxygenated

· Quantity and quality of hemoglobin²^,¹¹

Classification of hypoxaemia:

· Hypoxic hypoxemia – Inability to transfer oxygen across the pulmonary membrane. Eg. COPD, pulmonary fibrosis, asthma, CF, pneumonia, pul.edema

· Ischaemic hypoxaemia – Inadequate blood flow through the lung. Eg.Pulmonary emboli, pulmonary trauma, COPD

· Anaemic hypoxaemia – Reduction in the oxygen carrying capacity of the blood. Eg.Shock, anemia, sickle cell crisis

· Toxic hypoxaemia – Difficulty in the utilization of oxygen. Eg. Carbon monoxide poisoning, cyanide poisoning¹^,⁴

Stages of Hypoxaemia:

It based on altitude and physiological symptoms.

· Indifferent stage: (0-1500m, 0-5000ft) – No physiological responses due to hypoxia, typically observed between these altitudes for a person in good health

· Complete compensatory stage: (1500-3500m, 5000-11400 ft) – Performance of tasks may be decreased due to memory issues, nervous system is able to maintain its primary functions, visual sensitivity is depleted by 10% at 5000ft, 30% at 10000ft,

· Partially compensatory stage: (3500-6000m, 11400-20000 ft ) – A drastic increase in breathing is needed to maintain proper cardiovascular function, nervous system begins to degrade in these altitudes. Cognitive disturbances are characterized by difficulty in thinking and loss of self-monitoring

· Critical stage: (above 5500m, 18000ft) – All senses fail , and a pilot will become unconscious within a very short period of time.³^,⁷

Pathophysiology of Oxygen Delivery:

Oxygen depends on three parameters such as alveolar ventilation, ventilation-perfusion distribution and VO2

· Oxygen reserves–Changes in oxygen reserve over time is linear in both blood and tissue compartments

· Oxygen consumption–Time can be doubled with the correct applied pre oxygenation

· Ventilation/ perfusion incompatibility–Pre oxygenation leads to an increase in shunt and micro atelectasis after induction of anesthesia^2,11

Altitude	Time of useful consciousness
22000	10 minutes
25000	5 minutes
28000	2.5-3 minutes
30000	1.5 minutes
35000	0.5-1 minute
40000	15 seconds
65000	9 seconds

Physiological consequences of hypoxaemia:

· Depressed airway reflexes

· Increased ventilatory drive because of activation of carotid chemoreceptors

· Changes in respiratory oxygen

· Increases afterload

· Dilated regional systemic arteriolar beds

· Sympathetic-driven hypertension and tachycardia

· Increases cerebral blood flow

· Respiratory alkalosis and metabolic acidosis

· Decreased in diuresis

· Decreased hepatic oxygen consumption

· Increased renal release of erythropoietin

· Release of pro-inflammatory cytokines

· Decreased alveolar oxygen, perfusion of gas exchange surfaces

· Decreased mixed venous oxygen content^4,8

Effects of hypoxia:

· Airway reflexes: increased depth of poor oxygenation , asphyxia,cough depression

· Respiratory effects : decreasing PaO2 causes an increase in minute ventilation

· Effects on gas exchange : difference in partial pressures between the capillary blood and the alveolar content, alveolar hypoxia, influencing the function of pulmonary vessels

· Cardio vascular effects: coronary arterial vasodilation

· Central nervous system effects : arterial hypoxaemia

· Acid base changes : Respiratory alkalosis (mild), metabolic acidosis (severe)

· Renal function and electrolytes : increases in natriuresis

· Hepatic function : drop in its oxygenation

· Hematological response: increasing rate of erythropoietin

· Immune response: increased pro-inflammatory cytokine production, interleukin-8, TNF production and chemotaxis.⁷^,⁸

Laboratory testing:

· Arterial blood gas values

· Chest X-ray

· CT scan

· Ultrasound

· Ventilation-perfusion scan

· Respiratory mechanics-FVC, FEVI, PEF, MIP and MVV

· Hemoglobin, hematocrit

· Electrolytes, BUN, Creatinine

· EKG, ECG

· EMG

· Nerve conduction study⁶^,⁹

Medical Treatment of Hypoxaemia:

· Controlled oxygen therapy- Continuous positive airway pressure, non-invasive ventilation or mechanical ventilation

· Heated humidification

· Treat the underlying causes

· Physiotherapy

· Positioning

· Active cycle of breathing exercises

· Autogenic drainage

· Through percussion or vibrations

· Bubble PEP

· Cough assist or IPPB

· Home oxygen therapy⁶^,⁹

Potential covid-19 hypoxaemia work flow:

· Spo2 >88% -reposition to prone position 1hr

· Spo2 <88% - placein prone position with samesetting

· If unable to achieve spo2 and Fio2 – switch to NIV

· Spo2 <88% on NIV for > 10 min – place in prone position with the same setting of NIV

· If none of the above – consider for intubation⁹

Preventing hypoxaemia:

· Increasing barometric pressure

· Cabin pressurization- Keeps the cabin barometric pressure at a value higher than the barometric pressure

· Supplemental oxygenation

· Technique for pressure breathing – Establish mental discipline, conscious tension of the respiratory muscles, pause to lung inflation and positively increase muscle tension

· PRICE check before lowering canopy

P=Pressure

R=Regulator

I=Indicator

C=Connections

E=Emergency oxygen system

· Periodic check of following systems such as regulator, cabin pressurization system and pressure suits

· Supportive therapy – nutritional support, rehabilitation¹⁰

Devices for delivering oxygen via inhalation include:

· Nasal cannula

· Simple oxygen facemask

· Non-rebreather mask

· Bag valve mask

· Transport ventilator^9,10

Complications with hypoxaemia:

· Respiratory acidosis

· Cardiac arrhythmia

· Cerebral hypoxemia

· Altered mental state including coma

· Cardio respiratory arrest⁸

CONCLUSION:

Your blood carries oxygen to the organs and tissues of your body. Hypoxemia can be caused by a variety of conditions. Shortness of breath is an uncomfortable condition that makes it difficult to fully get air into your lungs. It is a serious medical situation and requires prompt medical attention. Even people who need ongoing therapy due to chronic conditions can live normal lives. Oxygen therapy can increase life expectancy.

REFERENCES:

1. Pollak, Charles P.; Thorpy, Michael J.;Yager,Jan (2010).The encyclopedia of sleep and sleep disorders, 3^rd ed, New York, NY.P.104

2. Eckman, Margaret (2010). Professional guide to pathophysiology, 3^rd ed, Philadelphia: Wolterw Kluwer/Lippincott Williams and Wilkins.p.208

3. Signs and symptoms of hypoxaemia, https://www.youtube.com/ watch?v=Qj3xxNfWsH8

4. Simon M, Braune S, Frings D, Wiontzek AK, Klose H (2014), Acute hypoxaemic ventilation, Critical care, Dec 1; 18(6): 712

5. Harden B, Cross J, Broad MA(2009), Respiratory physiotherapy: An on-call survival guide. Elsevier Health Sciences

6. Hardinge M, Annandale J, Bourne S, Cooper B (2015), Society guidelines for home oxygen use in adults: accredited by NICE. Thorax, Jun 1; 70(suppl 1): i1-43

7. Krzywinska, Ewelina and Christian Stockmann. (2018), Hypoxia, metabolism and immune cell function, Biomedicines 6.2: 56

8. Eckert, Danny J., et al.(2008), Effects of hypoxia and sleep in healthy men, Journal of Applied Phsiology 104.5: 1426-1435

9. Marini JJ,Gattinoni L, Management of COVID-19 respiratory distress, JAMA-J Am Med AssocAmerican Medical Association. 2020. Epub ahead of print.

10. Sheffield, Heimbach (1985). “Respiratory physiology-In: Fundmentals of Aerospace Medicine, DeHart ed, Lea and Febiger, Philadelphia, pp.91-102

11. Ilknur Hatice Akbudak and Asli Mete (2018), “Pathophysiology of Apnea, Hypoxia, and Preoxygenation”, Open access peer-reviewed chapter, doi:10.5772/intechopen.76851

Received on 06.03.2021 Modified on 18.03.2021

Int. J. Nur. Edu. and Research. 2021; 9(3):361-363.

DOI: 10.52711/2454-2660.2021.00083