|Ahead of print publication
Oxygen Delivery Devices in Hypoxemic Respiratory Failure
Ranvijay Singh1, Sandeep Garg2, Sunita Aggarwal2, HS Hira3, Ranvir Singh4
1 Maulana Azad Medical College and Associated Lok Nayak Hospital, New Delhi, India
2 Department of Medicine, Maulana Azad Medical College and Associated Lok Nayak Hospital, India
3 Department of Medicine, Maulana Azad Medical College and Associated Lok Nayak Hospital, New Delhi, India
4 Lady Hardinge Medical College, New Delhi, India
|Date of Submission||15-Mar-2022|
|Date of Decision||27-Apr-2022|
|Date of Acceptance||23-May-2022|
|Date of Web Publication||03-Aug-2022|
Department of Medicine, MAMC and LNJP Hospital, New Delhi-110002
Source of Support: None, Conflict of Interest: None
Abstract Oxygen therapy by appropriate oxygen delivery device (ODD) at different stages is an essential part of hypoxemic respiratory failure management. The choice of ODDs depends on the degree of hypoxemia, precision of delivery, patient comfort, risk of transmission of infection to Health Care Worker (HCW), and the cost. Management of hypoxemic respiratory failure depends on underlying etiology and pathophysiology of the disease process. Study from the current global pandemic of novel coronavirus disease 2019 (COVID-19) showed that the severity of hypoxemia is independently associated with in-hospital mortality and can be an important predictor risk of admission to intensive care unit. In this review, we will discuss the different ODDs, their indication for use along with the advantages and disadvantages.
Keywords: Oxygen delivery devices, Non invasive ventilation, Respiratory distress, Positive pressure ventilation
| Introduction|| |
Joseph Priestley discovered oxygen in the late 18th century while attempting to melt mercury oxide using a magnifying glass and sun rays. Since then, oxygen therapy has been used for many clinical conditions. In hypoxemic respiratory failure, supplemental oxygen therapy is used as a first-line in the treatment. Oxygen delivery system is used to control, supplement, and deliver oxygen to increase arterial oxygenation in the patient. Factors that affect alveolar oxygen delivery include the fraction of inspired oxygen (FiO2) delivered in the supplemental flow, the device’s interface with the patient, supplemental oxygen flow rate, and inspiratory demand. We need to respond to the patient’s underlying pathophysiology as a basis for approach to choice of oxygen delivery device (ODD).
Gattinoni et al. proposed two phenotypes “L” and “H” for compliant lung and stiff lung in hypoxemic respiratory failure, respectively. Often, initially, patients present with L type which can progress to H type as the disease progresses. L type patients are proposed to have a low Ventilation and Perfusion Ratio (V/Q) but normal gas volume due to mild inflammation and capillary dilation. They are the so-called “happy hypoxics” as they may not be dyspneic and can respond well to the conventional oxygen therapy (COT) and high-flow nasal cannula (HFNC), which may reduce the need for invasive ventilation. In H type patients, lung volume available for gas exchange is significantly reduced due to alveolar interstitial edema and microthrombi formation, resulting in high V/Q ratio. These patients present with respiratory distress as they are not able to inhale the gas volume as expected. These subsets of patients are unlikely to improve unless positive end-expiratory pressure (PEEP) is provided. Early intubation strategy bypassing HFNC or Non Invasive Positive Pressure Ventilation (NIPPV) might be beneficial in this subset of patients. Hence, timely and adequate oxygen delivery through right choice of the delivery device can significantly alter the outcome of hypoxic diseases.
| Recognition and Assessment|| |
Clinical manifestations are highly variable and nonspecific in hypoxemic respiratory failure. Hence, clinical and laboratory parameters are used to determine the severity of tissue hypoxia. Patients can present with profound hypoxemia without respiratory distress called “happy hypoxia/silent hypoxia.” When PaO2 falls below 60 mm Hg, it stimulates the arterial chemoreceptors in carotid and aortic bodies resulting in increased ventilatory drive, ultimately leading to dyspnea and tachypnea; still, cyanosis occurs very late in severe hypoxemia. Arterial hypoxemia causes autoregulatory systemic vasodilation, but lungs will have hypoxic pulmonary vasoconstriction. Cerebral hypoxia causes headache, confusion, agitation, seizure, and coma. Neuronal death begins within minutes of acute profound hypoxia (PaO2 < 30 mm Hg). In cardiovascular system, sympathetic activation causes initial tachycardia and later, severe hypoxia results in angina and ischemic hypotension.
|Figure 3 Flowchart showing algorithmic approach to choice of ODD in respiratory failure.|
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Laboratory assessment of hypoxemia is done by measuring PaO2 (normal: 80–100 mm Hg), arterial hemoglobin oxygen saturation (normal: 95%–100%), and serum lactate levels (normal: <2.0 mmol/L). PaO2 and SaO2 are excellent guides to appropriate oxygen therapy in isolated arterial hypoxemia. Measuring only SaO2 may be sufficient to assess arterial hypoxemia and is done noninvasively by pulse oximetry. Various early warning scores including National Early Warning Score (NEWS) 2 and Pediatric Early Warning Score (PEWS) 6-minute walk test can be used to assess degree and severity of tissue hypoxemia.
| Saturation target in hypoxemic respiratory failure|| |
Liberal or conservative oxygen therapy in Acute Respiratory Distress Syndrome (ARDS) has been debated for a long time. Recent LOCO2 (Liberal or Conservative Oxygen) randomized trial divided ARDS patients to a conservative oxygen arm (target SpO2 88%–92%) or a liberal oxygen arm (target SpO2 ≥ 96%). Though the trial was stopped early due to futility and possible harm, trial observed that at 28-day and 90-day conservative had high risk of death. Risk difference (RD) at 28 day and 90 days was 7.8% (95%CI: 4.8–20.6) and 14.0% (95%CI: 0.7–27.2), respectively. Five cases of mesenteric ischemia were also noted in the conservative group. Considering the associated patient harm at the extremes of SpO2 targets and increased cost of liberal oxygen use, as well as the potential reduction in equity if oxygen resources are depleted, there needs to be a vigilant monitoring of the recommended oxygen target. Recommended oxygen saturation target by the various institution is between 92% and 96%.,
| Oxygen Delivery Devices|| |
ODDs used in hypoxemic respiratory failure can be low-flow and high-flow devices, each with their own advantage and disadvantage. The choice of ODD depends on: degree of hypoxemia, requirement for precision of delivery, patient comfort, cost, aerosol generation, and exposure to health care workers. Whereas, FiO2 delivered by various devices depends on: equipment factor (oxygen flow rate, mask volume, areas of holes in mask, and quality of mask fit), patient factors [respiratory rate, tidal volume, and peak inspiratory flow (PIF) rate], and additional factors (presence of other gases and vapors).
Low-flow devices depend on inspiration of room air to meet inspiratory flow and volume demand of the patient while they do not meet the demand of severe hypoxemic patients. This results in inspiration of more room air and eventually oxygen dilution.
High-flow system uses reservoirs or very high flow rate to meet the large PIF demands and exaggerated minute volumes found in the severe hypoxemic patient. This is important, as patients in acute respiratory failure can become extremely tachypneic, and their PIFs, which may normally be 30 L/minute to 60 L/minute at rest, can reach upwards of 120 L/minute in acute respiratory failure. If these patients with respiratory failure with PIF rates of up to 60 L/minute to 120 L/minute and high minute volumes (>20 L/minute in some adults) are placed on a 15 L/minute Non Rebreather (NRB) mask, then this may not provide adequate support resulting in oxygen dilution. One of the main mechanisms to improve a patient’s work of breathing is to attempt to match their PIF demands with the use of these high-flow devices.
| Common low-flow devices|| |
- Nasal cannula
- Face mask
- Partial rebreathing mask (PRM)
- Nonrebreathing mask (NRM)
| Nasal cannula|| |
Consists of two soft prongs attached to O2 supply tubing. Available in different sizes and different prong shapes, frequently used in patients with mild and moderate hypoxia because of simplicity and better compliance. To be effective, nasal passage must be patent but patient need not breathe through the nose. In mouth breather, this airflow produces a venturi effect in the posterior pharynx entraining oxygen from the nose. High flow rates and poorly humidified gases damage the nasal mucosa resulting in epistaxis, ear tenderness, and laryngitis. To prevent the nasal mucosa from drying oxygen must be humidified if flow exceeds 4 L/minute. Flow rate ranges from 0.25 to 6 L/minute, hence cannot provide high flow and FiO2 oxygen as there is no increase in FiO2 if flow is more than 6 L/minute.
FiO2 delivered by nasal cannula follow the 1:4 rule. Each 1 L/minute oxygen administered via nasal cannula will deliver 4% FiO2 above room air (21%).
This device is recommended in mild and moderate hypoxemia without distress.
| Simple face mask|| |
Simple face mask consists of a mask with two side ports. The side port allows mixing of room air with oxygen supplied. Mask enlarges the reservoir of oxygen by an additional 100 to 200 mL. It delivers FiO2 of 40% to 60% predictably when patient exhibits normal respiratory pattern. Flow rate ranges from 5 to 15 L/minute but gas flow of >8 L/minute does not increase the FiO2 above 60% as oxygen reservoir gets filled up. The flow rate should always be >5 L/minute to prevent CO2 accumulation and rebreathing. It requires tight seal otherwise escape air will cause ocular drying and irritation. Oxygen delivered by simple mask depends on the ventilatory pattern of the patients. The flow rate of 4 L/minute delivers FiO2 of about 35% to 40%, providing there is a normal respiratory pattern.,
It is recommended in mild to moderate hypoxemia without distress but requires FiO2 and flow higher than nasal cannula.
| Partial rebreathing mask|| |
It consists of mask with reservoir bag of capacity 600 mL to 1000 mL. It has a side port that allows entry of room air and exit of exhaled gases. With properly applied mask, inspired gas does not mix with room air. However, patient can breathe room air through exhalation ports if oxygen supply gets interrupted. PRM delivers flow range from 8 to 15 L/minute and FiO2 of 60% to 80% in a properly applied mask with normally ventilating patient. Reservoir bag is filled by first one-third of exhaled air derived from anatomic dead space containing little CO2. During inspiration, gases from reservoir and the fresh gases are inhaled therefore called partial rebreathing. A minimum flow of 8 L/minute should enter the mask to remove exhaled CO2 and to refill oxygen reservoir. Flow rate must be sufficient to keep bag one-third to one-half inflated at all times. It is recommended in moderate to severe hypoxemic cases requiring high FiO2.,,
| Nonrebreathing mask|| |
NRM is similar to a PRM but with three unidirectional valves. Two valves on side of the mask that prevent the entry of room air but allow exit of exhaled gases. The third valve is between the reservoir bag and mask which prevents entry of exhaled gases into the bag. Malfunction of valve can result in CO2 buildup and suffocation. For this reason, mask is provided with a spring-loaded tension valve called safety valve or one of the side valves is removed. Best results will be achieved by adequate flow rate such that the reservoir bag empties by no more than a third during inspiration and by best seal possible between the mask and the face. It provides highest possible FiO2 without intubation. FiO2 in range of 80% to 95% can be achieved with an oxygen flow rate of 10 to 15 L/minute., It is recommended in moderate to severe hypoxemic cases requiring high FiO2.
| High-flow devices|| |
- Venturi mask/air entrainment mask
| Venturi mask/air entrainment mask|| |
It is a high-flow ODD because it provides predictable and reliable FiO2 ranging from 24% to 60%, which is independent of the patient’s respiratory pattern. It delivers total flow (oxygen supplied and room air) ranging from 15 to 50 L/minute. Venturi mask entrains the room air by venturi modification of the Bernoulli principle. In this phenomenon, rapid velocity of gas (oxygen) moving through a restricted orifice produces a viscous shearing force that creates a decreased pressure gradient downstream relative to surrounding gases. This pressure gradient causes room air to be entrained until pressure is equalized. The size of the constriction determines the final concentration of oxygen for a given gas flow. The smaller the orifice, greater the negative pressure generated; hence, the more ambient air entrained. Therefore, here high flow will result in lower FiO2 delivery. Because of the high fresh gas flow rate, the exhaled gases are rapidly flushed from the mask via its holes, so there is no rebreathing and no increase in dead space. Aerosol devices should not be used with venturi mask as water droplet can occlude the injector. Vapor-type humidity adapter collar can be used when humidity is needed.
Venturi masks are of two types:
Fixed FiO2 model – these devices have color-coded and labelled jets that deliver fixed FiO2 with a given flow.
Variable FiO2 model – have labelled graded adjustment port for entry of room air that can be adjusted to allow variation in delivered FiO2.
Venturi masks are used when patients require high flow with predictable FiO2 to decide whether the oxygen requirement is increasing or decreasing. It is recommended in moderate to severe hypoxemic cases.
| Heat and humidified HFNC|| |
The use of HFNC has become increasingly popular in the treatment of hypoxemic respiratory failure. HFNC circuit consists of a flow meter, oxygen–air blender connected to a humidifier which delivers high-flow oxygen to patients via a nasal interface. It delivers heated (32°C–37°C) and humidified (up to 100% relative humidity) oxygen with FiO2 of 21% to 100% at high flow rate (up to 60 L/minute). FiO2 and flow can be titrated independently based on the patient’s requirement. FiO2 delivered by HFNC follow the 1:4 rule, that is, each 1 L/minute oxygen administered will deliver 4% FiO2 above room air (21%). HFNC system has two important components in addition to providing oxygen.
- It warms delivered air, as cold air will irritate the airways and significant heat loss can occur from the patient’s body.
- It also humidifies the air, as dry air is an irritant to airways and dries up the secretions and mucous membranes.
High oxygen flow will minimize oxygen dilution and washout dead space air and thereby gives continuous flow of fresh gases. It also provides PEEP estimated 1 cm H2O for every 10 L/minute flow delivered by closed mouth breathing and therefore reduces the work of breathing. Mauri et al. demonstrated this effect in their study of hypoxemic patients with an arterial partial pressure of oxygen PaO2/FiO2 <300. They noted that HFNC set at 40 L/minute significantly reduced work of breathing and respiratory metabolic demand compared with oxygen delivered by face mask at 12 L/minute. High flow rate of HFNC meets elevated flow demand of respiratory failure patients. WHO clinical guidelines on COVID-19 (March 13, 2020) recommend use of HFNC in selected patients who are not maintaining oxygen saturation with supplemental oxygen therapy.
Recommended flow rate and FiO2 are:
Pediatric – 2 L/kg/minute; FiO2 < 60%.
Adult – up to 60 L/minute; FiO2 < 60%.
| Predictors of HFNC failure|| |
Early prediction/recognition of progressive respiratory failure despite HFNC therapy is critical. Delaying intubation beyond 48 hours when on HFNC, results in prolonged mechanical ventilation and also increases mortality. Persistently elevated respiratory rates, worsening hypoxemia, thoracoabdominal asynchrony in the presence of no progressive pulmonary organ failure may also indicate failure of HFNC therapy.
Roca et al. proposed the respiratory rate oxygenation (ROX) index. This index is used as a predictor of intubation in patients with hypoxemic respiratory failure on HFNC. ROX index ≥ 4.88 at 2, 6, and 12 hours after HFNC initiation is associated with lower risk for intubation. Whereas, ROX < 2.85 at 2 hours, <3.47 at 6 hours, and <3.85 at 12 hours suggest the failure of HFNC
| Noninvasive Ventilation|| |
Noninvasive ventilation (NIV)-positive-pressure ventilation (PPV) delivered through a noninvasive interface (nasal mask, facemask, helmet, or nasal plugs), traditionally by Bilevel Positive Airway Pressure (BPAP) and CPAP. PPV delivered by NIV distends the collapse alveoli and increases the gas exchange and ventilation of patients.
Various studies have found HFNC to be better than NIV or COT in acute hypoxemic respiratory failure, with more ventilator-free days, reduced rate of intubation, and lower mortality.- One such trial is FLORALI (Clinical Effect of the Association of Non-invasive Ventilation and High-Flow Nasal Oxygen Therapy in Resuscitation of Patients with Acute Lung Injury) trial which addressed these outcomes by comparing HFNC with conventional low-flow oxygen and NIV. FLORALI trial randomized adults without preexisting lung disease presenting with a respiratory rate >25 breaths/minute, a PaO2/FiO2 ≤300 on >10 L/ minute of oxygen and a PaCO2 <45 mm Hg. This study found no difference between the three modalities as it pertains to its primary outcome of rates of intubation. However, there was a significant difference in ventilator-free days at day 28 and mortality at 90 days in the HFNC arm. A post hoc analysis of the FLORALI trial did show a significant reduction in rates of intubation in the HFNC therapy arm, in the subgroup with a PaO2/FiO2 ≤ 200. A study by Hernández et al. on high-risk patients with postextubation respiratory failure found that similar intubation rates (22.8% in HFNC versus 19.1% in NIV) over 72 hours; less respiratory failure overall in HFNC (26.9% versus 39.8%); and more adverse events in NIV. A meta-analysis of over 3000 patients found that HFNC reduced the need for endotracheal intubation compared to COT and NIV (odds ratio: 0.60; 95% confidence interval: 0.41–0.86).
Recommended preferences for NIV are:
First choice: Continuous Positive Airway Pressure (CPAP) without humidification and with hood/helmet, having PEEP between 10 and 12 cm H2O, which can be increased up to 15 to 20 cm H2O considering the patient’s needs, tolerance, and any side effects.
Second choice: CPAP with mask.
Third choice: NIV with face mask (total full face mask/oronasal face mask with filter between mask respiratory port).
Current evidence suggests that NIV used in COVID-19 can be associated with delayed intubation, high failure rate, and increased risk of aerosolization and exposure to HCW., NIV can be effective in COVID-19 patients presented with hypercapnic respiratory failure, such as those with concomitant respiratory condition like Chronic Obstructive Pulmonary Disease (COPD). WHO in the guidelines statement recommends use of HFNC prior to intubation in the overall plan of management. Similarly, the surviving sepsis guidelines of Society Of Critical Care Medicine (SCCM) recommends use of HFNC when COT fails and preferentially over NIV.
HFNC should be considered first-line therapy for patients in acute hypoxemic respiratory failure. Trial of NIPPV can be given where HFNC facility is not available by experienced personnel capable of performing intubation in case patient acutely deteriorates or does not improve after a short trial of about 1 hour (pH < 7.25 on optimal NIV, Respiratory Rate (RR) persisting >25, new on confusion or respiratory distress). Deteriorating patients should be considered for early intubation.
| Positioning of patient|| |
Prone positioning is a simple cost-effective intervention that improves pulmonary function. It can be done in both conscious and mechanically ventilated patient. Supine positioning affects the pulmonary function as it overinflates the ventral alveoli and causes atelectasis of dorsal alveoli, resulting in V/Q mismatch. It also compresses the alveoli by direct pressure from heart and diaphragm. Whereas, prone positioning will recruit the posterior lung segments resulting in reversal of atelectasis and improvement in V/Q mismatch. It also reduces shunt (secondary to more homogeneous aeration of lung) and improved secretion clearance resulting in reduced hypoxemia. Various studies have documented the benefit of prone positioning in terms of shortening the duration of hospital stay, reduced need for mechanical ventilation, and lower mortality in hypoxemic respiratory failure.-
| Indications|| |
Conscious proning – FiO2 ≥ 28% or requiring basic respiratory support to achieve SaO2 92% to 96% (88%–92% if risk of hypercapnic respiratory failure).,
Mechanically ventilated – moderate to severe ARDS with PaO2:FiO2 ratio < 150 mm Hg and FiO2 ≥ 6 despite appropriate PEEP.
| Procedure|| |
Thirty minutes to 2 hours each of: fully prone → right side → sitting up (30°–60°) → left side → repeat.
Monitor oxygen saturation for 15 minutes after each position change.
Recommended duration is at least 12 to 16 hours/day.
| Conclusion|| |
Oxygen therapy is an important part of the management of hypoxemic respiratory failure. Timely diagnosis of hypoxemia and appropriate selection of ODDs can significantly alter the outcomes of disease. Prone positioning is standard of care and beneficial to both conscious and mechanically ventilated patients. Understanding pathophysiology is important in deciding the need of mechanical intubation. Though the choice of device depends on the patient’s status and availability of devices, guideline-based approach helps in the timely action and appropriate selection of devices.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2]