INTRODUCTION — The pneumonia associated with novel coronavirus disease 2019 (COVID-19 or nCoV) may lead to respiratory failure with profound hypoxemia requiring endotracheal intubation and mechanical ventilation. Regional surges in the pandemic resulted in utilization of all available intensive care unit (ICU) ventilators in some institutions. Repurposing of anesthesia machines for longer-term ventilation of COVID-19 or other critically ill patients is feasible, but somewhat unprecedented. Administration of inhalation anesthetics for sedation during longer-term ventilation with anesthesia machines has also been reported in a few institutions. However, ICU ventilators are preferred for prolonged use, if available, since critical care clinicians are familiar with them. Anesthesia machines are not designed for longer-term use and incur unique safety concerns.
This topic will address limitations and management issues associated with ventilating a critically ill patient with an anesthesia machine outside of an operating room (OR) or for longer than a few hours, emphasizing use for patients with COVID-19 pneumonia [1]. Use of standard ICU ventilators for critically ill COVID-19 patients is discussed separately. (See "COVID-19: Management of the intubated adult".)
Airway management and anesthetic care of patients with suspected or confirmed diagnosis of COVID-19 infection for surgical procedures, including preventing infection of anesthesia personnel or contamination of anesthesia machines and equipment are addressed in a separate topic. (See "COVID-19: Perioperative risk assessment and anesthetic considerations, including airway management and infection control".)
INFECTION CONTROL — Preventing contamination of the external parts of the anesthesia machine and attached monitoring equipment, and internal parts of the breathing system, ventilator, and gas analyzer while in use for patients with COVID-19 is described in another topic. (See "Safety in the operating room", section on 'Contamination of the anesthesia machine'.)
Thorough cleaning and sterilization between patients is prudent. Contamination of an anesthesia machine during longer-term use as an intensive care ventilator for patients with known COVID-19 infection is more likely than short-term use during a surgical procedure because of the duration and extent of machine exposure. After extended ventilation of a patient with COVID-19, we recommend thorough external cleaning and following the manufacturer's instructions for sterilizing the breathing system and ventilator prior to use on another patient. Based on studies of other coronaviruses, it is estimated that infected patients exhale 0 to 100,000 virus particles per 30 minutes, or as many as 4,800,000 particles per day [2]. To protect against internal contamination, a single filter with a viral filtration efficiency (VFE) of 99.9999 percent (ie, a good mechanical pleated filter at the expiratory limb) would allow 4.8 of these particles, on average, to pass. However, if two filters are used, such as a heat and moisture exchange filter (HMEF) containing an electrostatic filter placed at the airway plus a mechanical pleated filter placed at the expiratory limb of the breathing circuit (figure 1), the combined VFE (perhaps as high as 99.99999999 percent) would render internal contamination of the anesthesia machine unlikely, even when used for multiple days (with fresh filters each day). Typically, an HMEF is placed at the airway (figure 1), and a second high-quality viral filter (eg, a pleated mechanical filter that does not have heat and humidity exchange properties) is placed on the expiratory limb of the breathing circuit during ventilation of a COVID-19 patient. (See "Safety in the operating room", section on 'Contamination of the anesthesia machine'.).
All adjustments of anesthesia machine ventilator and fresh gas flow (FGF) settings are made by an anesthesia professional. This "hands-on," approach requires donning and doffing personal protective equipment (PPE) when caring for a COVID-19 patient [3]. Modification of one anesthesia machine model by reattaching the control and monitoring screen using a special extension cable allows changes to ventilation parameters from outside of the patient's room [4].
LOCATIONS FOR ANESTHESIA MACHINES — Location(s) selected for use of anesthesia machines to ventilate COVID-19-positive patients are institution-dependent due to considerations such as layout of selected hospital area(s), location of rooms with negative pressure capabilities, and availability of sources of electrical power, high-pressure oxygen, and medical air [1,5]. When multiple anesthesia machines are used in a single location, the compressed gas pipelines should be assessed to ensure that supply is adequate to meet consumption if supplying an area where multiple anesthesia ventilators are using high fresh gas flows (FGFs). The electrical supply should also be assessed to ensure that circuits will not be overloaded, particularly in areas outside the operating room (OR). (See 'Unique safety issues' below.)
Availability of compatible connections from the scavenger system to waste anesthesia gas disposal (WAGD) outlets or medical vacuum outlets is another consideration if inhalation anesthetic agents are to be administered via the anesthesia machine. However, gas scavenging is not necessary if inhalation agents are not administered. (See 'Anesthesia machine ventilators versus ICU ventilators: Differences' below and 'Use of inhalation anesthetics for sedation' below.)
Personnel considerations include availability of anesthesia professionals to manage ventilation with anesthesia machines, and convenience for critical care consultants. (See 'Collaboration with critical care consultants' below.)
Institutional options for location of anesthesia machine ventilators may include intensive care unit (ICU) rooms, step-down units, telemetry floors, the presurgical holding area, post-anesthesia care units (PACUs), or individual ORs [1,6-11]. In some institutions, it may be reasonable to treat two or more COVID-19 patients in the same OR if there are multiple sources of oxygen and medical air, and if anesthesia personnel (ie, anesthesiologists, Certified Registered Nurse Anesthetists [CRNAs], Certified Anesthesiologist Assistants [CAAs]) are deployed most easily in an OR setting. A single-institution study of ORs converted for use as ICU beds for 133 COVID-19 patients, with placement of multiple patients into each OR, reported an estimated probability of survival 30 days after hospitalization of 0.61 (95% CI 0.52-0.69), with higher mortality in those older than 65 years (hazard ratio [HR] 3.17, 95% CI 1.78-5.63) [10]. These results are similar to those reported after mechanical ventilation of COVID-19 patients in other settings [12-15]. Unique challenges were described for use of anesthesia machines as longer-term ventilators in this OR setting, including adequacy of medical gas supply (see 'Anesthesia machine ventilators versus ICU ventilators: Differences' below) and conversion of positive pressure ORs into negative pressure rooms [10]. Other concerns included lack of access to drainage pipes when disposal of large volumes of contaminated effluent from continuous renal replacement therapy (CRRT) devices was necessary, and the possibility of increased infection risk for health care workers exposed to multiple mechanically ventilated COVID-19 patients in each OR.
LONG-TERM VENTILATION WITH ANESTHESIA MACHINES — Anesthesia personnel should be immediately available at all times to manage and monitor the anesthesia ventilator (and administration of inhalation anesthetic agents, if used), as well as to assist with respiratory care. Professional staff who are not anesthesiologists (eg, some intensivists, as well as respiratory therapists and intensive care unit [ICU] nurses) are experts in respiratory care, but are not familiar with anesthesia machines [7,10]. (See 'Monitoring during long-term ventilation' below and 'Monitoring during inhalation anesthetic administration' below.)
The American Society of Anesthesiologists (ASA), the Anesthesia Patient Safety Foundation (APSF), and other professional organizations have developed guidance for anesthesia care team members regarding repurposing of anesthesia machines for longer-term ventilation (refer to the APSF/ASA Guidance on Purposing Anesthesia Machines as ICU Ventilators and Quick Reference: Setup and Monitoring Instructions – Anesthesia Machine as an ICU Ventilator) [16-21]. Limited data regarding duration of mechanical ventilation for COVID-19 patients suggest that two or more weeks are often necessary. Collaboration with critical care teams throughout this period is clearly essential to achieve optimal respiratory care, and to manage other systemic problems in patients with severe COVID-19 disease. To manage limited resources, some institutions have used anesthesia machine to provide longer-term ventilation in patients who are not COVID-19-positive. (See "COVID-19: Management of the intubated adult", section on 'Ventilator management of acute respiratory distress syndrome'.)
Anesthesia machine ventilators versus ICU ventilators: Differences — Limited data address the ability of anesthesia machine ventilators developed by various manufacturers to mimic ICU ventilator parameters or to reliably provide continuous mechanical ventilation for a prolonged period [7,10,22]. Although newer anesthesia ventilators incorporate multiple controlled and assisted modes of ventilation that are nearly identical to intensive care ventilators, several important technical issues are unique to anesthesia machines, and must be considered during use for long-term ventilation.
Humidification of inspired gases — Intensive care ventilators differ from anesthesia machines in that they deliver fresh gas from a compressed gas source during each inspiration, and discharge all exhaled gas into the room. Because compressed gases have zero humidity, active warming and humidification is necessary.
Anesthesia machine breathing circuits recycle exhaled patient gas, and deliver part of it (scrubbed of carbon dioxide) during subsequent inspirations. The ability to alter FGF, and thereby the fraction of exhaled gas that is rebreathed, is a key feature distinguishing an anesthesia ventilator from an ICU ventilator. FGF is typically reduced during general anesthesia to conserve inhalation anesthetic agents. The low FGFs (ie, lower than minute ventilation) typically used for short-term ventilation during surgical cases result in rebreathing of exhaled gas that has been warmed and humidified by the body [23,24]. Furthermore, the reaction of exhaled carbon dioxide (CO2) with the CO2 absorbent in the anesthesia machine breathing circuit releases heat and produces additional humidity within the anesthesia breathing circuit [25].
Recommendations to manage humification of inspired gases administered via anesthesia machines during longer-term ventilation include:
●Set FGF initially to equal minute ventilation (approximately 6 to 8 L/minute in adult patients) to prevent buildup of humidity and accumulation of condensed water in the breathing circuit, as well as to decrease the use of CO2 absorbent [5,7]. Generally, it should be apparent in one to two hours if excess moisture is accumulating in the breathing circuit. If it is, FGF can be increased incrementally (eg, by 0.5 to 1 L/minute) until humidity is controlled. Alternately, FGF can be set higher (eg, 1.5 times minute ventilation) initially, and can then be reduced in increments of 500 mL/minute with vigilant monitoring for the appearance of humidity in the inspiratory limb. Once FGF exceeds 1.5 times minute ventilation, there is little rebreathing, and increasing FGF further does not provide any advantage and wastes compressed gas (oxygen and medical air).
Experience indicates that when an anesthesia machine is in long-term use as an ICU ventilator, reducing FGF to the usual low levels used during surgery (ie, 1 to 2 L/minute) leads to excessive humidity in the breathing circuit, and the need to change CO2 absorbent frequently. (See "Anesthesia machines: Prevention, diagnosis, and management of malfunctions", section on 'Carbon dioxide absorbent exhaustion or toxicity'.)
●Check the breathing circuit hoses and water trap for excessive condensed water every hour. Excessive humidity can be clinically significant leading to condensed water accumulation within the breathing circuit that can increase resistance to gas flow through the system, interfere with sensors such as respiratory gas analyzers and flow sensors, and increase risk for coinfections [5,10]. (See 'Machine monitoring and maintenance' below.)
Excessive accumulations of water in the breathing circuit (typically the expiratory limb) must be emptied. In patients with respiratory infections, this is accomplished by personnel wearing full personal protective equipment (PPE) since the water is likely to be contaminated. One institution reported the need to empty the water trap every 3.6 days (2.5 to 6.8 days) [26]. Issues with supply chains have limited purchase of water traps during COVID-19 pandemic surges; however, new options have been designed and tested [5].
●Despite the risks of excessive accumulation of condensed water as described above, drying of secretions and respiratory epithelium may occur if humidification of inspired gases is inadequate during long-term ventilation. The presence of condensate in the inspiratory hose indicates that relative humidity of the inspired gas is adequate (>100 percent) at room temperature. However, addition of a heat and moisture exchange filter (HMEF) is typically necessary when high FGFs are used in an effort to prevent excessive water accumulation in the breathing circuit. This HMEF aids in ensuring that adequate humidity is maintained in the lungs and also filters viral particles. It is placed at the endotracheal tube connection to the anesthesia machine breathing circuit (after the Y-piece and the gas sampling port (figure 1)).
●Devices that actively humidify inspired gas are not recommended. They cause problems with ventilation and monitoring since anesthesia machines are not designed to handle large amounts of condensed water within their breathing circuit.
●Inspect HMEF filter and other airway filters at least once every hour, and change the filter when obstruction is a concern, or once every 24 hours. One institution reported the need to change airway filters every day (1 to 1.5 days) [26]. During filter shortages, the filter placed at the expiratory limb may be left in place for a longer period of time than the filter placed at the airway because it is less prone to soiling and obstruction. Notably, when anesthesia machines are deployed to an ICU setting without constant attendance by an anesthesia professional, early detection of obstruction of a HMEF or other airway filter placed on the breathing circuit may be less likely compared with the operating room (OR) setting. (See 'Machine monitoring and maintenance' below.)
Obstruction of the airway due to mucous plugging of the HMEF airway filter, the endotracheal tube, or within the airway is common due to airway desiccation, mucosal sloughing, and inspissated secretions in COVID-19 patients, even when humidification and warming of inspired gases is thought to be adequate [7,10,22]. In one report, nearly 30 percent (14/48) of COVID-19 patients receiving long-term ventilation with anesthesia machines developed such mucous plugging, causing catastrophic hypoxia requiring emergency bronchoscopy and/or tube exchange [22].
Unique safety issues — There are unique safety concerns during use of anesthesia machines as long-term ventilators. To minimize the potential for errors in setup of anesthesia machines, initiation of controlled ventilation, and respiratory monitoring in locations outside of the OR suite, deployment of multiple machines of the same model within any one outside location is ideal. Specific concerns include:
●Need to prevent accidental administration of inhalation anesthetic agents. If there are no plans to administer inhalation anesthetics for patient sedation, then the vaporizers for the volatile agents should be removed or drained. Also, the nitrous oxide (N2O) cylinder and pipeline hoses should be removed. These measures ensure that inhalation anesthetic agents are not accidentally administered.
However, some institutions with inadequate supplies of the intravenous (IV) sedatives and analgesic agents that are commonly used in the ICU may consider emergency use of low doses of a volatile inhalation anesthetic agent (isoflurane or sevoflurane), as explained below. (See 'Use of inhalation anesthetics for sedation' below.)
●Potential need to adjust the scavenger system of the anesthesia machine. Waste anesthetic gas scavenging is only necessary when use of inhalation anesthetic agents is planned (see 'Use of inhalation anesthetics for sedation' below). Waste anesthetic gas disposal (WAGD) outlets are typically only found in operating or procedure rooms, and waste gas hoses from the anesthesia machine may not be compatible with medical vacuum outlets found elsewhere (picture 1). Thus, when an anesthesia machine is deployed to other locations, it may not be possible to connect its scavenger system to a compatible vacuum outlet [27].
•If no inhaled anesthetics are used and the scavenger system is not connected to a WAGD or medical vacuum outlet in a machine with an open scavenger system, then no modifications are necessary.
•If the machine has a scavenger system with a reservoir bag (closed scavenger system), then the following modifications are necessary to prevent inappropriate continuous positive airway pressure (CPAP), excessive positive end-expiratory pressure (PEEP), and high peak pressures [27]:
-If no inhalation anesthetic agent is used, then options include disconnecting the scavenger system from the hoses coming from the breathing system and ventilator, or removing the reservoir bag altogether (picture 2).
-If an inhalation anesthetic agent will be used, then scavenging is required. Regardless of whether the anesthesia machine has an open or closed scavenger system it must be connected to an available WAGD or medical vacuum outlet. Alternate tubing or connectors or connection adapters may be necessary to make this connection. Also, if high FGF is being used, then the scavenger system requires high vacuum flow; thus, the scavenger suction must be adjusted upward to ensure proper function.
●Potential for the fraction of inspired oxygen (FiO2) concentration in the breathing circuit to be lower than the set oxygen gas concentration on the anesthesia machine (FgO2), especially at lower FGFs. Because of the recirculation of exhaled gases that occurs in an anesthesia machine breathing circuit, inspired oxygen concentration depends on both the ratio of oxygen to air in the delivered fresh gas (determined by the FGF setting) and the total FGF (which influences the amount of rebreathing). Thus, inspired oxygen concentration must be continuously monitored. (See 'Monitoring during inhalation anesthetic administration' below.)
●Potential for inability to deliver a FiO2 of 100 percent when the total FGF is higher than the maximum possible flow of oxygen (eg, >12 L/minute). For example, if a total FGF of 15 L/minute is necessary, and the maximum oxygen flow on the anesthesia machine is only 12 L/min, then 3 L/min of air must be added. This may be confusing on anesthesia machines that have separate controls for both total FGF and for oxygen percent.
●Potential need to modify oxygen utilization by the anesthesia machine ventilator if institutional oxygen supply is limited by factors such as [5,28]:
•Delay in delivery of liquid oxygen to the hospital
•Excessive use of oxygen by the hospital, such that the oxygen vaporizers (where liquid oxygen is converted to gas oxygen) become covered in ice, resulting in inefficiency
•Inability of the flow in an oxygen pipeline branch to keep up with demand due to caliber of the pipeline, and the number of ventilators, anesthesia machines, and oxygen flowmeters supplied by that branch [10]. This is more typically a problem in some older hospitals.
When the oxygen consumption outstrips the maximum oxygen supply, all the ventilators, anesthesia machines, and oxygen flowmeters on that pipeline branch will be affected. Thus, the inspired oxygen concentration delivered by an individual anesthesia machine may decrease if air is being used, and the machine alarm may activate during each inspiratory cycle.
Anesthesia machines with bellows ventilators typically use oxygen as the drive gas that compresses the bellows; these ventilators consume oxygen at a rate approximating minute ventilation plus additional oxygen used in the FGF at the rate of FGF times percent oxygen, with cyclic consumption that increases dramatically during inspiration. Modifications of these machines by a qualified clinical engineer are possible, so that they can be powered by compressed air instead of oxygen [5,28]. Such modifications must be made when the machine is not in use (refer to the APSF/ASA Guidance on Purposing Anesthesia Machines as ICU Ventilators).
Conversely, anesthesia machines with electrically powered (ie, piston or turbine) ventilators are similar to ICU ventilators, in that they typically consume oxygen at the rate of FGF times percent oxygen, and do not consume oxygen above what is delivered in the fresh gas.
●Potential need to change the CO2 absorbent when it becomes expired [10]. Inspired CO2 values and the color indicator of the CO2 absorbent are monitored. To avoid rebreathing excessive CO2, the absorbent should be replaced if inspired CO2 increases >5 mmHg, or if the CO2 absorbent color indicates that it has become exhausted. Furthermore, potential reactions may occur if a volatile anesthetic agent comes into contact with CO2 absorbent that has become too dry due to exposure to high FGF. (See "Anesthesia machines: Prevention, diagnosis, and management of malfunctions", section on 'Carbon dioxide absorbent exhaustion or toxicity'.)
There are three reasons not to simply remove the CO2 absorber canister, or use an empty absorber canister:
•CO2 absorption is important to prevent hypercarbia if FGF decreases below 1 to 1.5 times minute ventilation (purposely or inadvertently).
•The breathing system may leak if the canister is removed. The valve installed on some machines to prevent a leak is intended for use for short periods while the canister is being changed, and is not dependable for longer-term use.
•An empty canister would significantly increase the compliance of the breathing system.
As noted above, the patient must be temporarily ventilated by an alternative means when ventilation is interrupted to change the CO2 absorbent.
●Potential for kinking or compression of the anesthesia machine breathing circuit. This problem is more likely with anesthesia machine circuitry compared with ICU ventilators because there is no articulating arm on the anesthesia machine that can hold the breathing circuit up off the bed.
●Potential for accidental shutdown of the anesthesia machine. Loss of electrical supply to the anesthesia machine has been described during long-term ventilation in COVID-19 patients, and the machine continues to function with electrical supply from the backup battery. Visible and audible alarms should be functioning to alert clinicians that battery backup is being used with inherent potential for ventilation failure once the battery charge is depleted [3,22]. (See 'Patient monitoring' below.)
●Need for periodic performance of an anesthesia machine self-test (ie, power-up test) approximately every 24 to 72 hours [22]. The ASA and anesthesia machine manufacturers recommend a pre-use check every day prior to using the machine in the OR setting. For prolonged use, most manufactures have stated that this can be done approximately every three days. Experience has shown that problems such as inaccurate ventilation or monitor function may occur when anesthesia machines are not restarted and checked at three-day intervals.
Notably, an alternative means of ventilation is necessary during the machine performance check (eg, with a manual resuscitator or a second ventilator) while the machine is powered down, restarted, and checked. A step-by-step procedure should be followed to ensure that all equipment is available to prevent patient lung de-recruitment, as well as to limit spillage of breathing circuit gas and other contaminants and protect anesthesia personnel during this process (refer to APSF/ASA Guidance on Purposing Anesthesia Machines as ICU Ventilators and the ASA's Quick Reference: Setup and Monitoring Instructions – Anesthesia Machines as an ICU Ventilator) [16,17]. A suggested procedure has been developed by the APSF and ASA (refer to the APSF/ASA Procedure for Supporting Patients during the Anesthesia Machine Self-Test) [29].
Use of a single anesthesia machine to ventilate multiple patients simultaneously (ie, ventilator "splitting") is avoided [30]. Splitting of ICU ventilators has been used in some institutions as a means to alleviate ventilator shortages during regional surges of COVID-19 cases. However, anesthesia machines are ill-suited for this purpose, and the challenges noted above for long-term ventilation with an anesthesia machine are exacerbated. In one report, attempts to split an anesthesia machine for use in two patients resulted in the following problems: rapid HMEF obstruction due to excessive humidity; extremely rapid exhaustion of the CO2 absorbent; inability to adjust ventilator alarms due to highly unusual minute volume settings; and the need to use extra-long breathing circuit hoses which resulted in excessive compliance in the circuit [31].
Adjustment of ventilator settings — It is important to understand how specific capabilities differ among individual anesthesia machines, and differ from those of ICU ventilators [7,16].
General concepts include:
●Newer versus older anesthesia machines:
•Newer anesthesia machines, compared with older models, have ventilator capabilities similar to modern ICU ventilators, with more flexible settings that can deliver more modes of ventilation (including assist modes). In general, newer models with compliance compensation and tidal volume delivery unaffected by changes in FGF are preferred for longer-term ventilation (refer to the APSF/ASA Guidance on Purposing Anesthesia Machines as ICU Ventilators). Newer anesthesia machines are equipped with breathing systems and ventilators that can be sterilized between patients, and are better choices for those with COVID-19 infection.
•Older models are typically reserved for surgical patients and for ventilation of patients without COVID-19 respiratory disease.
●Modifications of default ventilatory parameters and alarm settings on the anesthesia machine are typically necessary to better match those of an ICU ventilator. These include default settings for minute ventilation, airway pressure, positive end-expiratory pressure (PEEP) levels, and alarms. Also, the default alarm volumes should be set to the maximum level.
●Anesthesia machines may not allow for optimal ventilator weaning in patients with improving lung mechanics. Compared with ICU ventilators, potential problems include increased dead space, added resistance caused by use of HMEF and other airway filters, and lack of typical weaning modes such as pressure support ventilation on some anesthesia machines [10].
Specific differences in performance of anesthesia machine compared with ICU ventilators include [7,16]:
●Anesthesia machines do not default to pressure support of extra breaths in control modes. Care must be taken to add this feature during changes in ventilator modes.
●Anesthesia machines are milliseconds slower to respond to patient effort because of the circle breathing system interposed between the patient and anesthesia ventilator [32], which can cause more hyperventilation in an air-hungry patient.
●Inspiratory time is not directly set on an anesthesia machine. Most anesthesia machines do not provide direct control of inspiratory time; instead, this is controlled indirectly by setting the inspiratory:expiratory (I:E) ratio and the respiratory rate.
●Anesthesia machines may have a lower peak inspiratory flow rate. Negative airway pressure occurs if the patient inhales faster than the maximum inspiratory flow rate provided by the ventilator. Options for setting the anesthesia machine inspiratory flow rate include:
•In volume control modes (including synchronized intermittent mandatory ventilation), the inspiratory flow rate can be increased by increasing tidal volume or by decreasing inspiratory time (accomplished by reducing the I:E ratio or by increasing the respiratory rate). Introducing an inspiratory pause (Tpause or TIP) will also increase the inspiratory flow rate during the active portion of inspiration, before the pause.
•In pressure control or support modes, the inspiratory flow rate can be increased by lowering the flow trigger level for ventilation (which also increases the speed at which pressure-support is provided), or by decreasing the rise time of pressure support (which increases the inspiratory flow rate). On Draeger anesthesia machine ventilators, the flow trigger level is called "Trigger L/min," and the rise time is called "Tslope." On GE Healthcare Systems anesthesia machine ventilators, the flow trigger level is called "Flow Trigger," and the rise time is called "Rise Rate." However, lowering the flow trigger level may cause extra mis-triggered breaths in some patients; if these occur, the flow trigger level must be increased. On some Draeger machine ventilators, the maximum inspiratory flow is governed by a facility-level setting, although on-site clinical engineers can adjust this parameter to allow a maximum inspiratory flow of 75 L/minute.
Monitoring during long-term ventilation — An anesthesia professional should be available to start ventilation and subsequently monitor degree of moisture accumulation, inspired and expired CO2, filter integrity, overall anesthesia machine function, and effectiveness of ventilation [1,7]. (See "COVID-19: Management of the intubated adult", section on 'Ventilator management of acute respiratory distress syndrome'.)
The APSF/ASA guidelines address additional maintenance and monitoring requirements during use of anesthesia machines for long-term ventilation of COVID-19 patients (refer to APSF/ASA Guidance on Purposing Anesthesia Machines as ICU Ventilators and Quick Reference: Setup and Monitoring Instructions - Anesthesia Machine as an ICU Ventilator) [16,17]. These additional considerations are necessary due to use of extra filters which may become clogged, the tendency to accumulate condensed water in the breathing circuit, and risks for aerosolizing droplets containing COVID-19 virus.
Documentation of such enhanced monitoring of continuous and intermittent parameters is necessary. This may be accomplished manually using a template developed for this purpose by the anesthesia team, or automatically if the anesthesia machine connected to the hospital network for recording in the electronic medical record [1].
Patient monitoring — Baseline monitored parameters (eg, tidal volume, plateau pressure [Pplat], minute ventilation) are recorded when ventilation is initiated. If spirometry is available, saving or photographing the baseline tracings and reference loops may aid in later diagnosis of filter obstructions.
Continuously monitored parameters (with preset alarms) are recorded hourly including:
●Inspired oxygen concentration.
●Inspired and expired CO2.
●Inspiratory pressure.
●Tidal volume and respiratory rate.
●Low oxygen pressure alarm. If an anesthesia machine with an oxygen-driven bellows is being used, a low oxygen pressure alarm triggered by each inspiration may indicate a high demand on the institutional central oxygen pipeline system, particularly when multiple ventilators are simultaneously in use. (See 'Anesthesia machine ventilators versus ICU ventilators: Differences' above.)
●Alert or alarm messages. In particular, loss of the main electrical supply to the anesthesia machine may not be immediately recognized since temporary anesthesia machine function continues on backup battery power [3,22]. To prevent ventilation failure in such cases, the screen should display an alert and the audible alarm should be set to its loudest level.
Machine monitoring and maintenance — Intermittent inspection and maintenance of proper anesthesia machine and breathing circuit function includes:
●Inspect the breathing circuit hoses and water trap for excessive condensed water every hour. An oscillating obstructive gas flow tracing (figure 2) during exhalation indicates condensed water accumulation in the expiratory, scavenger, or ventilator hose. An oscillating obstructive gas flow tracing during inhalation indicates condensed water accumulation in the inspiratory or ventilator hose [33].
If fluid has accumulated in the breathing circuit and is threatening to impede ventilation, it must be removed [5]. Plans should be in place to ventilate the patient while the circuit is emptied. One novel method that has been described is placement of an airway filter casing with a Luer connector in the expiratory limb to serve as a water trap, enabling aspiration of condensed water by syringe without interrupting ventilation [5]. Furthermore, proper collection and disposal procedures for contaminated water and PPE for personnel performing this procedure are necessary since the fluid being removed may be contaminated with virus.
●Inspect the breathing circuit hoses for possible kinking or compression every hour.
●Inspect the filters in the airway and expiratory limb breathing circuit every hour (figure 1). Excessive humidity or secretions may cause obstruction of gas flow. Obstructed filters must be changed immediately. Otherwise, filters are typically replaced every 24 hours.
●Check for high peak airway pressure during volume ventilation or low tidal volume during pressure ventilation every hour, as these are signs of profound obstruction of the airway filters (figure 1) [5]. Decreased peak expiratory flow and prolongation of expiratory flow are earlier indications of partial obstruction of one of these filters (figure 3) [33]. Significant obstruction of either filter also creates additional PEEP, with a difference between the set and actual PEEP that can be seen in the airway pressure when the expiratory limb filter is obstructed. Notably, this additional PEEP is invisible when the airway filter is obstructed since airway pressure is measured downstream of that filter.
●Confirm there is no leak around the endotracheal tube cuff every hour because such a leak produces respiratory droplets and aerosolized viral particles. A leak around the endotracheal tube cuff typically manifests as measured exhaled tidal volume that is lower than measured inhaled tidal volume, and a flow-volume loop that does not close (figure 4) [33]. At low FGFs a bellows ventilator may progressively empty, while the reservoir bag will progressively deflate in machines with a piston or turbine ventilator. Notably, high FGF compensates for small leaks, obscuring these indicators of changes in breathing circuit volume.
●Check the CO2 absorbent color and inspired CO2 values every hour to ensure that the absorbent is still functioning properly and does not need to be exchanged. This is especially important if lower FGFs are being used.
●Check Pplat at least once every four hours, and after each change in PEEP or tidal volume, to ensure that Pplat is ≤30 cm H2O. Measurement of Pplat is accomplished during a 0.5 second inspiratory pause. Unlike many ICU ventilators, anesthesia machines do not have a control to manually initiate and hold an inspiratory pause [22]. On an anesthesia machine ventilator, a 0.5 second inspiratory pause can be generated by temporarily setting the mode to volume ventilation with the tidal volume that the patient has been receiving, at 10 breaths per minute, with an I:E ratio of 1:2 and a 50 percent inspiratory pause (Tpause or TIP). (See 'Adjustment of ventilator settings' above.)
●Check the flow readings approximately every four hours, since these may become less accurate over time. If the machine is equipped with both inspiratory and expiratory flow sensors, a gradual increase in the difference between inspired and exhaled tidal volume measurements usually indicates that a startup test is needed to recalibrate the breathing system flow sensors.
●Confirm that an anesthesia machine startup test was performed once every 24 to 72 hours (refer to the APSF/ASA Procedure for Supporting Patients during the Anesthesia Machine Self-Test) [29]. (See 'Unique safety issues' above.)
USE OF INHALATION ANESTHETICS FOR SEDATION
General considerations — During the COVID-19 pandemic, shortages of the intravenous (IV) sedatives and analgesic agents that are routinely employed for sedation of critically ill patients during mechanical ventilation have led to use low doses of a potent volatile inhalation anesthetic agent (isoflurane or sevoflurane) in some institutions [34-37]. IV sedative-analgesic regimens that are routinely employed to sedate critically ill patients during mechanical ventilation are discussed in separate topics:
●(See "Pain control in the critically ill adult patient".)
Patients with acute respiratory distress syndrome (ARDS) due to COVID-19 have higher sedation requirements compared with other critically ill patients requiring mechanical ventilation, possibly due to younger age, higher respiratory drive, or a particularly intense inflammatory response [38-42]. In a study that included 24 COVID-19-positive patients requiring mechanical ventilation, opioid doses were more than three times higher than in historical cohorts with ARDS, and midazolam doses were also higher [43]. These unusually high sedation requirements have contributed to shortages of commonly used IV agents during regional COVID-19 surges [34,38]. (See "COVID-19: Management of the intubated adult", section on 'Sedation and analgesia'.).
When anesthesia machines are used to provide mechanical ventilation, the ready availability of inhalation agents is an advantage in institutions with impending or actual shortages of IV agents. The American Society of Anesthesiologists (ASA) and the Anesthesia Patient Safety Foundation (APSF) have developed guidelines for emergency use of low doses of a potent volatile inhalation anesthetic agent (isoflurane or sevoflurane; refer to the APSF/ASA Guidance for Use of Volatile Anesthetic for Sedation of ICU Patients) [44]. One study noted that initiation of isoflurane via anesthesia ventilators in 18 COVID-19 patients resulted in decreased dosing requirements for the sedative propofol (from a mean daily dose of 3656±1635 mg to 950±1804 mg) and the opioid hydromorphone (from a mean daily dose of 48±30 mg to 23±27 mg), although cumulative total opioid doses were similar to those in 17 COVID-19 patients who received standard IV sedation [37]. Notably, routine administration of inhalation anesthetic agents to critically ill patients for prolonged periods is not recommended due to scant safety data in this setting, as well as some disadvantages. (See 'Advantages and disadvantages' below.)
Dosing to achieve sedation — Titrated low doses of either sevoflurane (eg, 0.5 to 1.4%) or isoflurane (eg, 0.2 to 0.7%) achieve long-term sedation [36]. Factors influencing dosing include whether the targeted level of sedation is achieved with satisfactory patient comfort. The presence of ventilator dyssynchrony may necessitate deepening the anesthetic/sedation level. Conversely, if hypotension is present, the anesthetic level should be decreased. (See "Inhalation anesthetic agents: Clinical effects and uses", section on 'Clinical effects'.)
When the decision is made to allow the patient to awaken, the anesthetic vaporizer is turned off, and fresh gas flow (FGF) is increased. Washout of anesthetic agent is rapid and predictable, with patients typically able to respond to commands and be assessed for extubation within 10 to 15 minutes. (See "Emergence from general anesthesia", section on 'Inhalation agents'.)
Advantages and disadvantages — For sedation of mechanically ventilated patients with COVID-19 induced respiratory failure, potential advantages and disadvantages for long-term use of sevoflurane or isoflurane include (table 1):
●Advantages
•Effective sedative effects, with rapid onset and offset allowing easy titratability. (See "Inhalation anesthetic agents: Clinical effects and uses", section on 'Sedation and anesthesia'.)
•Minimal metabolism and likely minimal organ toxicity. (See "Inhalation anesthetic agents: Properties and delivery", section on 'Metabolism'.)
•Ready availability during shortages of the IV sedatives and analgesic agents [34].
•Potentially advantageous respiratory effects
-Bronchodilation, with attenuation of bronchospasm and decreased airway responsiveness. (See "Inhalation anesthetic agents: Clinical effects and uses", section on 'Respiratory effects'.)
-Potential anti-inflammatory pulmonary effects (eg, reduction of pro-inflammatory cytokine release) that may minimize the extent of lung injury [36,45-49]. (See "One lung ventilation: General principles", section on 'Intravenous versus inhalation anesthetics'.)
•Dose-dependent muscle relaxation during mechanical ventilation; thus, administration of a neuromuscular blocking agent (NMBA) may not be necessary. (See "Inhalation anesthetic agents: Clinical effects and uses", section on 'Skeletal and smooth muscle relaxation'.)
●Disadvantages
•Scant safety data regarding use of inhalation anesthetic agents for prolonged periods in critically ill patients [42]. However, long-term sedation with sevoflurane or isoflurane has been previously employed to sedate patients with adult respiratory distress syndrome (ARDS) or other critical illness in some regions of the world, without evidence of long-term renal or hepatic injury [36,48-52].
•Rapid consumption of volatile inhalation anesthetic agent when high FGFs are used. Thus, hourly inspection of the anesthetic vaporizer fill level and analysis of end-tidal anesthetic concentration are particularly important. (See 'Monitoring during inhalation anesthetic administration' below.)
Liquid anesthetic use can be estimated. One mL of a liquid volatile anesthetic agent yields approximately 200 mL of gas anesthetic (specific values are 195 mL for isoflurane or 184 mL for sevoflurane). Thus, at 10 L/minute of FGF, the liquid volatile anesthetic consumption is approximately 30 mL/hour if a 1 percent inhaled concentration is delivered. Most vaporizers hold approximately 200 mL of liquid, so refills would be needed multiple times each day even at the lower doses noted above to achieve sedation with isoflurane or sevoflurane. (See 'Dosing to achieve sedation' above.)
Reduced consumption of volatile anesthetic agent can be achieved by reducing FGF, but this leads to water accumulation in the breathing circuit. (See 'Humidification of inspired gases' above.)
Anesthetic reflector devices (eg, AnaConDa or Mirus devices) have been developed to conserve inhalation anesthetic agent during administration via traditional intensive care unit (ICU) ventilators; however, these devices are not available in the United States [53-58]. Such devices are placed between the Y-piece and patient, where it vaporizes small amounts of anesthetic liquid, and absorbs most of the exhaled anesthetic, which is then re-inhaled on the next breath (much like a heat and moisture exchanger absorbs and conserves humidity). Notably, room contamination still occurs with use of these devices unless a scavenging system is employed [56-58].
•Potential for inadequate sedation if the anesthetic agent in the vaporizer is depleted (ie, runs dry), which is particularly distressing if an NMBA was administered. For this reason, the patient, anesthesia machine, and anesthetic vaporizer are carefully monitored.
•Need to use the anesthesia machine scavenger system during use of inhalation anesthetic agents, and potential difficulty with connection of the scavenger system to a compatible waste anesthesia gas disposal (WAGD) outlet in locations outside the operating room (OR). (See 'Unique safety issues' above.)
Alternatively, a charcoal filter can be placed at the exhaust valve of the ICU ventilator to capture anesthetic vapor [59]. The filter should be changed regularly because it loses its efficacy once saturated with anesthetic.
•Lack of familiarity among non-anesthesia professionals (eg, intensivists, nurses, respiratory therapists) regarding use of anesthesia machines to administer volatile inhalation anesthetic agents, dosing of these agents, and potential problems that may occur during administration (refer to the APSF/ASA Guidance for Use of Volatile Anesthetic for Sedation of ICU Patients) [44].
•Need for constant presence of anesthesia personnel as recommended by the ASA and APSF (refer to the APSF/ASA Guidance for Use of Volatile Anesthetic for Sedation of ICU Patients) [44]. Modifications to allow remote control and monitoring of some anesthesia machine models has been described to minimize infection risk for these personnel [4].
•Potentially undesirable systemic effects of a potent volatile anesthetic agent in critically ill patients, including:
-Cardiovascular effects that include myocardial depression and vasodilation resulting in dose-dependent reductions in blood pressure and cardiac output. (See "Inhalation anesthetic agents: Clinical effects and uses", section on 'Cardiovascular effects'.)
-Respiratory effects that include respiratory depression and airway irritation with more pungent agents such as isoflurane. (See "Inhalation anesthetic agents: Clinical effects and uses", section on 'Respiratory effects'.)
-Cerebral effects, particularly dose-dependent cerebral vasodilation and blunting of cerebral autoregulation by uncoupling cerebral blood flow (CBF) and metabolism, resulting in increased CBF and intracranial pressure (ICP). Thus, patients with known or suspected elevations in ICP are not candidates for sedation with inhalation anesthetic agents. (See "Inhalation anesthetic agents: Clinical effects and uses", section on 'Effects on cerebral physiology'.)
•Possible increased risk of nephrogenic diabetes insipidus (NDI) during prolonged ICU sedation with sevoflurane [60-62]. In one study, patients who developed NDI received higher sevoflurane concentrations and had longer durations of exposure to sevoflurane [61]. Notably, NDI resolved and did not recur after termination of sevoflurane administration.
•Although rare, malignant hyperthermia (MH) has been reported in patients receiving inhaled anesthetics for status asthmaticus [63]. When volatile anesthetics are used for ICU sedation, staff should be educated in the recognition and management of an MH reaction. (See "Inhalation anesthetic agents: Clinical effects and uses", section on 'Malignant hyperthermia (volatile inhalation agents)'.)
•Deleterious environmental effects of inhaled anesthetics, which are all greenhouse gases.
Specific advantages and disadvantages of sevoflurane versus isoflurane are discussed separately. (See "Inhalation anesthetic agents: Clinical effects and uses", section on 'Sevoflurane' and "Inhalation anesthetic agents: Clinical effects and uses", section on 'Isoflurane'.)
Monitoring during inhalation anesthetic administration — In addition to the suggested monitoring noted above for use of anesthesia machines for long-term ventilation (see 'Monitoring during long-term ventilation' above), specialized monitoring requiring the constant presence of an anesthesia provider is necessary during administration of inhalation anesthetic agents [36,44].
Patient monitoring during sedation
●Continuously monitored parameters include:
•End-tidal anesthetic concentration (ETAC), with titration of anesthetic dosing to the minimal effective end-tidal concentration. The low-level and high-level alarms on the anesthetic gas monitor should be enabled.
•Exhaled end-tidal carbon dioxide (ETCO2) to aid in management of ventilation and to monitor for the possibility of MH, which can severely and acutely increase ETCO2. (See 'Monitoring during long-term ventilation' above.)
•Temperature, since potent inhalation anesthetics lower core temperatures (see "Perioperative temperature management", section on 'Anesthetic effects on thermoregulation'), and to monitor for the possibility of MH, which can acutely increase temperature to >102°F (38.9°C).
●Other monitored parameters include:
•Hemodynamic monitoring per usual standards for care of each individual critically ill patient, which is also useful to evaluate cardiovascular responses to an inhalation anesthetic agent. (See "Acute respiratory distress syndrome: Supportive care and oxygenation in adults", section on 'Hemodynamic monitoring' and "Inhalation anesthetic agents: Clinical effects and uses", section on 'Cardiovascular effects'.)
•Serum creatinine and liver function tests obtained at intervals (typically daily) to check for renal or hepatic dysfunction.
Equipment monitoring during sedation — Intermittent inspection and maintenance of anesthetic administration includes:
●Check the fill level of the anesthetic vaporizer every hour since rapid utilization of volatile inhalation anesthetic agents occurs during high FGF. Refill the vaporizer when anesthetic level is <20 percent full.
●Check for proper functioning of the scavenging system during initiation of administration of an inhalation anesthetic agent, then every 24 hours or after any major change in the rate of FGF. (See 'Unique safety issues' above.)
COLLABORATION WITH CRITICAL CARE CONSULTANTS — Collaboration and coordination with critical care clinicians is essential for care of COVID-19 patients regarding decisions to use an anesthesia machine and for management of long-term ventilation and comorbid conditions (eg, cardiovascular and renal complications, coinfection with sepsis) [7,10,26,64-68]. These management issues are discussed elsewhere:
●(See "COVID-19: Management of the intubated adult".)
●(See "COVID-19: Evaluation and management of cardiac disease in adults".)
●(See "COVID-19: Issues related to acute kidney injury, glomerular disease, and hypertension".)
OUTCOMES AFTER VENTILATION WITH ANESTHESIA MACHINES — Intensive care unit (ICU) ventilators are preferred for prolonged use in critically ill patients because ICU personnel have limited familiarity with anesthesia machines and their unique safety concerns. (See 'Anesthesia machine ventilators versus ICU ventilators: Differences' above.)
Limited mortality data comparing outcomes after long-term ventilation of critically ill COVID-19 patients with anesthesia machines versus ICU are available:
●A large institution in the United States that converted operating rooms for ICU care (OR ICU) with use of anesthesia machine ventilators for 133 COVID-19 patients reported an unadjusted mortality of 41.4 percent in these patients (calculated at the time of closure of the OR ICU when anesthesia ventilators were no longer needed after a median follow-up time of 33 days) [10]. None of these patients received inhalation anesthetic agents. Notably, the overall in-hospital mortality for all other critically ill COVID-19 patients who received care in that institution's non-OR ICUs was similar (39 percent).
Other centers in the United States accepting a high volume of COVID-19 patients requiring controlled mechanical ventilation have reported mortality ranging from 17 to 62 percent [12-15].
●An institution in Italy reported a higher unadjusted mortality of 70.6 percent in 17 COVID-19 patients ventilated with anesthesia machines in a converted OR ICU (14 received inhalation anesthetics) compared with an unadjusted mortality of 37.5 percent in 76 COVID-19 patients ventilated with an ICU ventilators in this OR ICU setting or in a traditional ICU (hazard ratio [HR] 4.05, 95% CI 1.75-9.33) [9]. These authors also reported more problems involving mucous plugging and other technical issues during use of anesthesia machines ventilators. (See 'Anesthesia machine ventilators versus ICU ventilators: Differences' above.)
Regarding other outcomes, one center reported ventilation parameters in 12 COVID-19 patients who had at least four days of mechanical ventilation with anesthesia ventilators compared with 20 COVID-19 patients who had ICU ventilators [69]. Changes in ventilation parameters over this four day period were acceptable with both types of ventilators, and were similar except for higher peak inspiratory pressures with use anesthesia machines, likely due to higher initial settings for this parameter on these machines.
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: COVID-19 – Index of guideline topics".)
INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5th to 6th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10th to 12th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.
Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)
●Basics topics (see "Patient education: COVID-19 overview (The Basics)")
SUMMARY AND RECOMMENDATIONS
●Infection control – Contamination of an anesthesia machine, its breathing system, ventilator, and connected gas analyzer is more likely during longer-term use as an intensive care ventilator compared with short-term use during surgical procedures for patients with novel coronavirus disease 2019 (COVID-19) infection because of the duration and extent of machine exposure. However, if two filters are used (eg, a heat and moisture exchange filter [HMEF] placed at the airway plus a mechanical pleated filter placed at the expiratory limb of the breathing circuit (figure 1)) and these are replaced daily, contamination of the anesthesia machine is unlikely. (See 'Infection control' above.)
●Locations for use – Locations selected for use of anesthesia machines to ventilate COVID-19 patients depend on availability of anesthesia personnel to manage the machines, rooms with negative pressure capabilities, sources of high-pressure oxygen and medical air, and compatible connections to waste anesthesia gas disposal (WAGD (picture 1)) outlets if inhalation anesthetics are used. (See 'Locations for anesthesia machines' above.)
●Differences between anesthesia machines versus ICU ventilators – Guidelines for repurposing anesthesia machines for longer-term ventilation address specific technical issues unique to their use including (refer to the APSF/ASA Guidance on Purposing Anesthesia Machines as ICU Ventilators and Quick Reference: Setup and Monitoring Instructions – Anesthesia Machine as an ICU Ventilator) (see 'Anesthesia machine ventilators versus ICU ventilators: Differences' above):
•Modifying the default ventilator parameters and alarm settings
•Adjusting fresh gas flow (FGF) to prevent condensed water accumulation in the breathing circuit
•Adjusting the scavenger system to prevent backpressure in the breathing system (picture 2)
•Providing long-term humification and warming of inspired gases
•Avoiding expiration of the carbon dioxide (CO2) absorbent
•Recognizing that the fraction of inspired oxygen (FiO2) concentration in the breathing circuit may be lower than the set oxygen gas concentration on the anesthesia machine (FgO2)
•Avoiding undesired (accidental) administration of inhalation anesthetic agents
●Monitoring during use – An anesthesia professional should be available to monitor ventilation and anesthesia machine function including (see 'Monitoring during long-term ventilation' above):
•Patient parameters (with preset alarms) (figure 2 and figure 3 and figure 4) – (See 'Patient monitoring' above.)
-Inspired oxygen concentration
-Inspired and expired CO2
-Inspiratory pressure
-Tidal volume and respiratory rate
-Low oxygen pressure alarm
-Plateau pressure (Pplat) checks every four hours, and after each change in tidal volume or positive end-expiratory pressure (PEEP)
-Flow reading checks every four hours
-Checks for leaking around the endotracheal tube cuff every hour
•Machine monitoring – (See 'Machine monitoring and maintenance' above.)
-Inspecting the breathing circuit hoses (for excessive condensed water, kinking, or compression), water trap, airway and expiratory limb breathing circuit (for secretions or excessive humidity) every hour
-Checking the inspired CO2 values and CO2 absorbent for color every hour
-Performing a startup test every 24 to 72 hours
●Use of inhalation anesthetic agents
•Advantages and disadvantages – Institutional shortages of intravenous (IV) sedative-analgesic agents may be addressed by using low doses of a potent volatile inhalation anesthetic agent (ie, sevoflurane [0.5 to 1.4%] or isoflurane [0.2 to 0.7%] via the anesthesia machine (APSF/ASA Guidance for Use of Volatile Anesthetic for Sedation of ICU Patients). Advantages and disadvantages are shown in the table (table 1). (See 'General considerations' above and 'Dosing to achieve sedation' above and 'Advantages and disadvantages' above.)
•Specialized additional monitoring – during administration of inhalation anesthetics includes (see 'Monitoring during inhalation anesthetic administration' above):
-Patient parameters – (See 'Patient monitoring during sedation' above.)
End-tidal anesthetic concentration, with low and high alarms
Exhaled end-tidal carbon dioxide (ETCO2)
Patient temperature
Intermittent serum creatinine and liver function tests
-Equipment monitoring – (See 'Equipment monitoring during sedation' above.)
Checks of anesthetic vaporizer fill level every hour
Confirmation of proper scavenging system functioning every 24 hours or after changes in FGF rate
●Collaboration with critical care clinicians – Collaboration is essential regarding decisions to use an anesthesia machine ventilator and to manage ventilation and comorbid conditions. (See 'Collaboration with critical care consultants' above.)
