Clinical Update DOI-10.21304/2018.0504.00413 Kundan Mittal*, Amit Jain**, Teena Bansal***, Prashant Kumar****, Anupama Mittal***** *Senior Professor, Incharge PICU & Respiratory Clinic, ***Associate Professor, Anaesthesia and Critical Care ****Professor, Anaesthesia and Critical Care, Pt. B D Sharma, PGIMS Rohtak,*****Deputy Civil Surgeon, Rohtak,Haryana,India. **Associate Professor, Pharmacology Guru Gobind Singh Medical College Faridkot,Haryana, India Received:28-Jul-18/ Accepted:06-Aug-18/Published Online:30-Aug-18 ABSTRACT Oxygen is life and falls in the category of essential drug. It is vital for cellular function. Oxygen therapy is the administration of oxygen in acute or chronic conditions above higher concentration than atmospheric air to prevent hypoxemia. The delivery of oxygen depends on various factors. Oxygen is full of advantage but injudicious use or hyperxaemia (FiO2>0.5) may be harmful to human body. Care should be taken while prescribing the oxygen. Hypoxemia should be avoided as such to prevent mortality. Key words: Oxygen, devices, FiO2, flow Oxygen is colourless, odourless, and tasteless gasconstitutes approximately 20.94% of atmospheric air and transferred from environment to mitochondria from higher pressure of 21.2,19.9,13.4k Pa(concentration) to lower pressure of1.5kpa (concentration) of oxygen. The difference between PAO 2 of 104 mmhg and PVO 2 of 64 mmhg cause oxygen to diffuse in to pulmonary blood. Diffusion of oxygen into the cell is limited by the distance between the cell itself and the source of oxygen. A highly complex capillary network (microcirculation) exists to distribute the oxygen to cells and tissues. During exercise oxygen requirement increases 20 times from normal still no deficiency occurs because oxygen diffusion capacity increases four-fold. Also, blood remains three times as long as blood to cause full oxygenation, thus even during shortened time blood can be fully oxygenated. Normally 5mL of oxygen is transported to tissue by 100mL of blood and during exercise 15mL of oxygen is transported by 100mL of blood. Oxygen therapy is the administration of supplementary oxygen to achieve a higher inspiration of oxygen than is achieved when breathing room air. No oxygen no life. Oxygen should be used cautiously and judiciously. Hundred percent oxygen therapy is full of danger. Nitrogen in air stabilizes the alveoli. Oxygen should be prescribed safely like drug i.e. flow Correspondence: Dr. Kundan Mittal, Senior Professor Pediatrics, Pt B D Sharma, PGIMS, Rohtak Haryana, India, Phone-+919416514111, Email-kundanmittal@gmail.com L/min, device to be used, percentage of oxygen, high or low flow. Hypoxaemia is reduced oxygen concentration in arterial blood and hypoxia is oxygen deficiency in tissues. Any patient irrespective of age who is acutely illshould receive 100% oxygen. Various alternative methods to increase oxygen delivery are; protection of airway, maintain adequate cardiac output and tissue perfusion, correction of anemia, and avoiding respiratory depressants. 1-3 Clinical indicators of oxygen deficiency a. Anxious look b. Increased work of breathing c. Perspiration d. Hyperventilation e. Decreased oxygen saturation f. Tachycardia g. Arrhythmias h. Altered level of consciousness i. Peripheral vasodilatation j. Hypotonia (decrease muscle tone) k. Cyanosis l. Hypotension m. Polycythaemia n. Coma Etiology of Hypoxia a. Decrease in oxygen content (decrease 60
haemoglobin level, SaO2, PaO2) b. Abnormal affinity of oxygen to haemoglobin (abnormal haemoglobin) c. Decreased cardiac output d. Inability of lung to oxygenate (gas exchange) e. Hypoventilation f. Low pressure (high altitude) g. Ventilation-Perfusion mismatch h. Intrapulmonary or cardiac shunts i. Local tissue oedema or ischaemia Assessing inadequacy of oxygen delivery: Oxygen delivery: Cardiac output (Hb x 1.34 x SaO 2 ) + (PaO2 x 0.003) Various factors contribute in oxygen delivery to the tissues but we only measure PaO 2. Inspite of normal PaO 2 child may be having less oxygen delivery to tissues. Types of hypoxemia: Acute: Rapid onset (<6 hours) Subacute: 6 hours to 7 days Sustained: 7-90 days Chronic:>90 days Generational: Cross-generational Hyperoxia: PaO 2 120-150mmHg Assessment of oxygenation using various variables PaO 2 /FiO 2 SpO 2 /FiO 2 PAO 2 - PaO 2 PaO 2 / PAO 2 Oxygen Index = MAP x FiO 2 /PaO 2 Assessment of tissue oxygenation CaO2 (arterial) = (Hb x 1.34 x SaO2) + (PaO2 x 0.003) CvO2(venous) = (Hb x 1.34 x SvO2) + (PvO2 x 0.003) Oxygen consumption = CO x (CaO2 CvO2) x 10 Oxygen Extraction Ratio = Oxygen consumption/ Oxygen delivery Types of Oxygen Delivery Source Oxygen Concentrators: These are primarily used at home and in primary health care settings. These devices use room air for oxygen using molecular sieve. They can deliver oxygen from 0.5L to 10L/ min depending on type of concentrator. Increasing flow rate will decrease oxygen concentration. Most of them need electricity for their operation. Compressed gas cylinders: Portable compressed gas cylinders in different sizes are commonly used in hospitals and home. Usually available in two sizes i.e. 3.2kg and 2.1kg and last approximately 3.5 and 2.5hours at 2L/min. Duration can be increased if cylinder is made to deliver oxygen during inspiration only. There is increased risk of fire due to pasteurization. Devices are available which releases oxygen during inspiration only. Central gas supply:compressed or liquid gas is used in larger hospitals (at a pressure of 4bar, 400kPa) attached with flow meter, which is capable of delivering oxygen at 15L/min. Liquid oxygen (LOX: vacuum insulated evaporator): Oxygen can be stored in liquid form at a temperature of -183C and can be in gas form at a temperature of -118.6C and above. The refill unit last longer compared to compressed cylinder. If not used the cylinder will evaporate in 2days time. Hyperbaric oxygen (HBO): Oxygen constitute approximately 21% of air and air has atmospheric pressure of 760mmHg while oxygen (760 x 21/100) contributes 160mmHg. The concentration of gas in liquid is not only determined by pressure but also by solubility coefficient which is different for all gases and also varies for different fluids. Solubility coefficients of the important respiratory gases at body temperature are as follows: Oxygen: 0.024 ml O 2 /ml blood atm.po 2, CO 2 : 0.5 mlplasma/atm. PCO 2, and Nitrogen: 0.067 ml/ml plasma/atm.pn2. HBO involves oxygen under pressure greater than found on earth surface at sea level. 61
Calculation of life of cylinder in minutes PSI (Cylinder) - Safe residual (200PSI) = ------------------------------------------------ x Cylinder Factor Flow rate in litre/minute Type of cylinder Capacity (appox.) Bottle factor Life of cylinder at flow rate 8L/min D (steel) 350L 0.16 45 D (Alumunium) 414L 0.16 52 E 625L 0.28 78 G 5260L 2.41 660 M 3028L 1.56 378 H & K 6900L 3.14 864 Calculation of requirement of oxygen during transport Duration of journey in minutes x Flow in litre/minute No. Of = --------------------------------------------------------------- cylinders Cylinder capacity Note: Always keep double the requirement. Factors affecting amount of FiO 2 delivered Flow/min Device: High or low flow, fixed or variable flow Respiratory rate, depth of respiration, and pattern Example: TV 500mL, RR 20/min, I:E 1:2 (inspiratory time 1sec and expiratory time 2sec), Flow of oxygen 6L/min (100mL/sec) Dead Space 150mL (usually 1/3 rd of TV: 2mL/kg), nasopharyngeal space is 1/3 rd of dead space i.e. 50mL Usually no expiatory flow during last 1/4 th time of expiratory time The filling of reservoir occurs during initial 1/4 th of expiration time Example: 10kg child, breathing rate 40/min, flow of oxygen 2L/min Tidal Volume: 10x6 = 60mL Anatomical reservoir: 2/3 kg x 10 = 6.6mL Respiratory cycle= 60/40 (1.5sec) I : E ratio = 1:2 Inspiratory time: 0.5sec Expiratory time: 1.0sec Flow: 2000/60 = 33.4mL/second Filling time: 1/4th of expiratory time = 0.25sec Inspiratory time x flow/sec: 0.5 x 33.4 = 16.7mL Anatomical reservoir: 0.25x33.4 = 8.4mL Actual is 6.6mL Room air volume: TV Anatomical reservoir = 60-16.7+6.6 = 36.7mL Oxygen concentration of room air volume: 36.7 x 0.21 = 16.7 + 6.6 + 7.7 = 31 FiO2: 31/60 = 52% Heliox is a mixture of helium and oxygen. Because helium is lessdense than oxygen, it is used to carry oxygen past airway oobstruction. Because heliox is less dense than pure oxygen hence it has a faster flow. Multiply flow reading by A factor of 1.8 (if ratio is 80:20) and 1.6 (if it is 70:30) to get actualflow Normal body humidity is expressed as 44 mg/l or 47 mmhg. This means that at 98.6 F (37 C) gas is saturated with 47 mmhg or 44 mg/l of water vapor. Flow depends on minute ventilation and I:E ratio Flow = MV x (I+E) Subtract 100 FiO 2-20 or 21 20 or 21 FiO 2 A Subtract 100-FiO 2 B Note: FiO2 is 0.40 use 20 and <40 use 21 (A and B: These 2 values will determine the Air: O2 ratio) Add the A and B numbers of the ratio X flow rate = Total flow Composition of Air: Gas % Atmosphere Partial Pressure Oxygen 20.95 159 Air 78.08 593 Carbon Dioxide 0.03 6.2 Argon 0.93 7 62
(Minute volume) : (Flow rate -Minute volume) I:E ratio = ------------------------------------------------------- (VT x f): (Flow rate - VT x f) Humidification of oxygen Oxygen if not humidified can lead to dryness of secretion. Oxygen can be humidified either by cold water or heated water. Heated water humidification is better but risk of injury is there. Oxygen more than 4L/ min or FiO2 >35% should be humidified. Humidified oxygen delivered through venturi can decrease FiO2 since it will block the holes. Water should be sterile and changed after 24hour. Bottle can be changed as per manufacture instruction. OXYGEN DELIVERY DEVICES Oxygen delivery devices can be classified in to two categories: 1. Low flow devices:variable performance (deliver variable fraction of oxygen concentration (FiO 2 ) e.g. nasal canula, mustache and pendant reservoir canula, pulse-demand oxygen system, simple face mask, rebreathing mask (partial and nonrebreathing), trans-tracheal catheter 2. High flow devices: Air entrainment mask, oxygen hood, incubator, oxygen tents, oxygen blenders, ventilator a. Fixed performance devices b. Variable performance devices Points to remember: a. High and low flow rate is defined in relation to patient inspiratory flow rate. b. Low flow does not mean delivery of low FiO 2. c. Dead space in children 1mL/Pound Low Flow devices: These devices deliver oxygen at flow rate less than the patient inspiratory flow rate/ demands. The FiO 2 depends upon patient s tidal volume, Inspiratory flow, minute volume, delivered oxygen flow, ventilatory pattern and size of oxygen reservoir. Low flow devices are useful in spontaneously breathing patients with fairly stable vitals. Low flow devices: 1. Nasal Cannula/Prong: a. Useful in patients who have good inspiratory effort and who require minimal oxygentherapy (30%). Nasal cannula delivers variable fraction of oxygen concentration. b. Available in variable designs and sizes for neonate, infant, child and adult. Size should not be more than 50% of nares diameter. c. Use humidified oxygen when flow rate is greater than 2L/minute. d. Flow > 6L/min can cause nasal irritation and dryness. Flow is kept <2L/min below 2years of age. e. Prong size should be approximately 50% of nares. f. Put the nasal cannula on the upper lip with prong pointed in the nostril and secure the cannula around head. g. Canula should be changed after 3days. h. Flow meter of different rate may be used (micro low-flow meter, low-flow meter, regular flow meter) Application of nasal cannula 2. Nasopharyngeal Catheters: a. Available in various sizes for bothchildren and adults (12-14F). b. Select size by comparing the external nostrils. c. Made of soft plastic having blind end with multiple holes on side near tip. d. Measure length from nostril to tragus of ear for nasal catheter. 63
e. Put the catheter from external nostril to just behind the uvula. f. Fix the catheter with tape. g. Nasal cavity acts as reservoir. h. Risk of blockade of catheter is high. i. Delivers variable FiO 2. j. Give humidified oxygen if flow rate is more than 2L/min and flow should not exceed >6L/ min. k. Useful in less severe cases. 3. Simple oxygen masks: a. Simple, transparent, light weight mask and covers both mouth and nose. b. Easily to apply and available for both pediatric and adult population. c. Minimum flow rate to be kept is 4-6L/min. d. Delivers variable FiO 2. e. Useful only in spontaneously breathing patients with respiratory distress. 6. Partial rebreathing and Nonrebreathing masks (NRM): a. These are simple, transparent, disposable oxygen masks with reservoir. Nonrebreathing mask have two types of one-way valve (one present between reservoir bag and mask and second at exhalation port) so that higher FiO 2 can be delivered. They are effective in spontaneously breathing patient for short period. b. Available in pediatric and adult size. c. Indicated in all types of seriously ill patients who are spontaneously breathing and require high concentration of oxygen. d. Keep the reservoir bag full i.e. flow of gas must be 6-8L/min to avoid rebreathing of carbon dioxide. Flow should be adequate to maintain the reservoir bag at least one-third to one-half full on inspiration. e. Application is similar to simple face mask. f. Partial rebreathing mask delivers FiO2 0.4-0.6 at flow of 6-8L/min depending on ventilatory pattern Simple face mask 4. Blow by oxygen: Children who can not tolerate device may be given oxygen by tubing or simple face mask (FiO 2 0.3-0.4 at 10L/min) for short term use. 5. Pocket mask or resuscitation mask Pocket mask is available in paediatric and adult size and used to deliver rescue or manual breath during resuscitation. 64
High flow oxygen delivery devices 1. Oxygen hood or head box: 1. Primarily used in children below one year of age or <10kg. 2. Flow of oxygen should be kept more than 6-8L/min. Flow of less than 6L/min can lead to CO2 rebreathing. 3. Delivers variable FiO2. Non-rebreathing masks Guidelines for estimating FiO 2 with low flow devices 100% O 2 Flow rate (L/ Predicted FiO 2 min) Nasal cannula or catheter 1 0.24 2 0.28 3 0.32 4 0.36 5 0.40 6 0.44 Oxygen mask 5-6 0.40 6-7 0.50 7-8 0.60 Oxygen mask with reservoir bag 6 0.60 7 0.70 8 0.80 9 0.80+ 10 0.80+ High flow nasal canula: HFNC (1 to 70L/min) is classified as a fixed-performance oxygen delivery system that is capable of delivering a specific oxygen concentration at flows that meet or exceed the inspiratory flow demand of the patient. Age Weight in Kg Starting flow L/min <30days 3-5 0.6 1mo -1year 5-<10 0.5 1-7years 10-<27 0.4 8-14years 20-<40 0.3 >14years 40 0.2 Oxygen hood 2. Self-inflating bag:these are primarily used during resuscitation or intubation. Reservoir bag is attached to the device to increase the oxygen concentration. Self-inflating or ambu bag can also work without oxygen source.in seriously ill or trauma victim open the airway and put the Guddel s airway (gag reflex absent) or LMA or Double lumen tube and attach to the self-inflating bag. 65
Self-inflating bag 3. Flow inflating bags: They are used in patients who are not breathing spontaneously and intubated with ET tube or LMA. This device gives 100% FiO2. Oxygen source is essential. They are primarily used operation theatres. Venturi Flow JR Circuit 4. Venturi Mask: Venturi mask is low flow fixed oxygen concentration (24-50%) device based on Bernoulli s principle and useful in patient having risk of acute carbon dioxide retention. 1. Mixes a specific volume of air and oxygen. 2. Useful for accurately delivering the low concentrations of oxygen. 3. Valves are colour coded and flow rate required to deliver a fixed concentration is shown on each valve 4. Deliver oxygen concentrations between 24-60% Venturi FiO % 2 O flow L/min 2 Total flow L/min Blue 24 4 105 Yellow 28 6 68 White 31 8 63 Green 35 10 56 Pink 40 12 50 Orange 50 12 33 FiO2 = (air flow x 0.21) + (oxygen flow x 1.0)/Total flow Oxygen: Air ratio Oxygen FiO 2 21 ----------- = -------------- Air 100 - FiO 2 FiO 2 = (0.21x 1st flow) + (FiO 2 x 2nd flow) /Total flow Desired FiO 2 = PAO 2 [(PaO 2 /(a/a ratio)]+ 50/713 Air to Oxygen Entrainment Ratio Room air to O 2 Concentration Ratio 25:1 24% 10:1 28% 8:1 30% 5:1 35% 3:1 40% 1.7:1 50% 1:1 60% 0:1 100% 66
5. Closed incubators: Oxygen is attached to the incubators at higher flow rate during neonatal transport. 6. Ventilators: Ventilator can give fixed FiO2 up to 100% Monitoring a child with oxygen therapy Pulse rate Respiratory rate: rate/min, shallow or deep breathing Respiratory effort: Strong or poor Oxygen flow rate: Litre/min Oxygen saturations: Usually after 5minutes of start of therapy. Limitations are poor perfusion, anemia, CO poisoning, skin pigmentation, nail varnish. Type of device Connections: To check leaks Capillary refill time: >3sec is always abnormal Blood pressure ABG (SOS) Lactate level SOS Monitoring response to oxygen therapy during transport 1. Oxygen saturation (SpO2) and FiO2 (if requirement of FiO2 increases, this signifies worsening of the patient s condition). 2. Colour (cyanosis or blue discoloration indicates increase in demand, worsening patient condition, malfunction of equipment s or empty container). 3. Respiratory rate (increase in rate indicates increase demand, or decrease supply or malfunctioning of equipment or disconnection from ventilator). 4. Respiratory efforts (worsening respiratory effort indicates increase demand, equipment failure, loss of supply or empty cylinder). 5. Decrease in mental status may also be due to decrease oxygen supply. Points to remember FiO2 remains constant at all altitude Flow rate does not increase FiO2, it is oxygen saturation which is important Inspiratory flow rate: 30 x 21 = 630% 630 30 = 21% If flow 10L/min of 100% oxygen and 20L/min 21% - (10 x 100) + (20 x 21) = 1420% - 1420 30 = 47% If flow rate is 50L/min - (10 x 100) + (40 x 21) = 1840% - 1840 50 = 37% If flow rate is 20L/min (10 x 100) + (10 x 21) = 1210% 1210 20 = 60% Body does not store oxygen No need to humidify oxygen <4L/min FiO2 depends on breathing rate, depth of respiration Oxygen is a drug and proper prescription should be written Target should be defined Monitoring device should be available Delivery system and flow rate should be defined After 10-15min of change saturation should be recorded Documentation of oxygen treatment Critical oxygen delivery is 4mL/kg/min Prolonged exposure of FiO2>0.5 is dangerous Hyperoxaemia leads to decrease in heart rate, cardiac output, coronary blood flow, brachial artery blood flow, and increase in vascular resistance Conservative oxygen therapy includes target SaO2>90% (88-92%) Every 50mmHg difference in P(A-a)O2 shunt increases 2% P(A-a) O 2 increases by 4 every 10years of age Conflict of Interest : Nil Source of Funding : Nil 67
References 1. Price AM, Smith SA, Challiner A. Ward-based Critical Care: A Guide for Health Professional. 2 nd ed. M K publishing; UK:2016 2. Webb A, Angus D, Finer S, Gattinoni L, Singer M. Oxford textbook of critical care. 2 nd edition. Oxford University Press; UK: 2016. 3. Haque A, Rizvi M, Arif F. Pediatric : A Clinical Update. J Ayub Med Coll Abbottabad 2016;28(3):630-634 How to cite this article: Mittal K, Jain A, Bansal T, Kumar P, Mittal A.Clinical Update :. J Pediatr Crit Care 2018;5(4):60-68. How to cite this URL: Mittal K, Jain A, Bansal T, Kumar P, Mittal A. Clinical Update :. J Pediatr Crit Care 2018;5(4):60-68. Available from: http://jpcc.in/userfiles/2018/0504-jpcc-jul-aug-2018/jpcc0504010.html 68