**Abstract**

Human interest in space exploration is boundless. We are driven to investigate the unknown and push the limits of our understanding of our universe. Given that space flights are for extended periods of time—in the hazardous environments of space and the growth of the space tourism industry is credibly anticipated; the incidence of medical and surgical events is bound to increase during space travel. Airway management becomes an essential skill in such situations. Microgravity, shortage of medical personnel, inability of the crew to return to earth expeditiously or access real time assistance from earth are some of the reasons that warrant training and preparation of the crew, towards this end. The purpose of this chapter would be to explore the challenges and the various recourses available for airway management during space travel.

**Keywords:** space travel, airway management, space medicine, space flight, anaesthesia

#### **1. Introduction**

There is expanded access to space. Government agencies and private companies alike have planned manned missions to the moon and to Mars, for the coming years. Currently, we are also witnessing a meaningful growth in the space tourism sector.

It is now more important than ever to increase our understanding of human physiology and pathology in space. Furthermore, it is of prime importance that astronauts can manage medical and surgical emergencies, that may arise especially given that a space tourist—as against the typical astronaut—is unprepared for the rigours of space travel and therefore exposed to a higher risk of medical complications [1].

Man's tryst with space began in 1961. The International Space Station (ISS), which has been in orbit for almost 20 years now, has enabled humans to stay in space for long durations. This has provided a swifter and a more profound bioastronautics development.

The environment of space is harsh and challenging, with a prolonged exposure to multiple stressful stimuli, radiation, weightlessness, isolation, and confinement to tight enclosed spaces for long periods of time. Microgravity, which affects all organ systems, has the most profound effect on human physiology [2].

Travelling to Mars will require transitioning between three different gravitational fields: being weightless during a six month interplanetary flight, being at about one third of the Earth's gravity on Mars, and re-acclimatising to Earth's gravity upon return [3].

#### **2. Airway management in space**

With increasing flight durations, there is an increased prospect that a medical emergency will entail airway management. It is currently estimated that the probability of a medical intervention requiring general anaesthesia, over the course of a 950 day mission to Mars and with six crew members is 2.6%. This speaks to the importance of how even the unlikeliest of events could imperil the mission and lead to loss of life [1]. Airway management is an important skill that is required to manage a great many medical emergencies. Some of the possible scenarios necessitating airway management in space are listed in **Table 1** [1, 4, 5].

Seventeen medical emergencies were documented during spaceflight between the periods of 1961–1999 [1]. In one instance, in 1962, on the Mercury 7 flight, Scott Carpenter, an American astronaut, aspirated food crumbs in orbit and in 1975 several astronauts on the Apollo-Soyuz mission developed a mild form of chemical pneumonitis after accidentally inhaling propellent fluid during re-entry [4]. Incidentally, none of the seventeen cases have required intubation. Also, no one has required GA in space to date [1].

Medical evacuation is not an option, in case of an airway emergency, owing to the distance as well as the absolute need to maintain oxygenation to avoid brain death. It is therefore necessary that immediate care is provided, while on board [6]. This warrants a crew equipped with emergency care skills as well as continuous training, to prevent skill erosion [1, 6, 7]. Furthermore, communication delays prohibit real time telemedicine support. For example, the communication delay between Earth and Mars is about twenty minutes—one way [1]. Airway management skills are thus critical to the mission of exploring space safely.

In the first half of this chapter, we will deal with the physiology of airway management and the physiological adaptations of the human body in space. This would provide the essential foundation to understand the challenges associated with airway management in space.

The term 'Airway Management' refers to the maintenance of airway patency and ensuring adequate ventilation and oxygenation. Successful airway management entails that the practitioner anticipates and predicts difficult airway and at the same time devises an airway management plan. The practitioner should also be adequately skilled to execute that plan, with the available resources. In order to enable this plan, anaesthesia is typically required—to provide patient comfort, limit airway reflexes, and to moderate the hemodynamic response to airway instrumentation [8].

#### **3. Physiology of airway management**

#### **3.1 Pre-oxygenation**

Hypoxaemia can occur on induction of anaesthesia and muscle paralysis on account of hypoventilation and apnea. Pre-oxygenation or denitrogenation helps to replace the nitrogen in the lungs with oxygen. This, consequently, extends the apnea time and allows the anaesthesiologist to secure the airway and resume ventilation.

Pre-oxygenation is achieved by providing 100% oxygen via a face mask, at a flow rate of 10-12 L/min to prevent rebreathing. This can be achieved by asking the patient to breathe for 3 min using tidal volume ventilation; or by taking 8 vital capacity breaths over 60 seconds. During this process, it must be ensured that there are no leaks around the face mask [8].

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is secured.

*Challenges to Airway Management in Space DOI: http://dx.doi.org/10.5772/intechopen.98932*

1. Hypoxic cardiopulmonary arrest

2. Airway obstruction 3. Foreign body aspiration 4. Burns or smoke inhalation

6. General Anaesthesia (GA)

*Indications for airway management in space.*

5. Coma

**Table 1.**

**3.2 Pulmonary aspiration of gastric contents**

prior to anaesthesia [9].

alone or in combination [8].

an increased intracranial pressure [8].

muscle relaxation [8, 10].

**3.4 Anaesthesia for airway management**

spasm [8].

Patients are required to have an empty stomach to reduce the risk of regurgitation and pulmonary aspiration of acidic gastric contents. The American Society of Anaesthesiologists task force recommends 4 hours of fasting from breast milk, 6 hours of fasting from infant formula, non-human milk and solid foods; and up to 8 hours or more from fried or fatty food. Clear fluids may be allowed up to 2 hours

Prophylactic drugs may be beneficial in patients with specific risk factors for aspiration. They help in decreasing gastric volume and increasing the gastric fluid pH. The commonly used drugs (alone or in combination) are—non-particulate antacids, promotility drugs and H2-receptor antagonists. These drugs may be used

**3.3 Airway reflexes and the physiological response to intubation of the trachea**

One of the main functions of the larynx is protection of the airway. Sensory receptors in the glottic and subglottic mucosa are triggered—on airway instrumentation—leading to the adduction of the vocal cords and laryngospasm. Furthermore, foreign body irritation of the lower airway can result in broncho-

Airway instrumentation causes an intense noxious stimulus via the vagal and glossopharyngeal afferents. This results in a reflex autonomic activation, manifesting as hypertension and tachycardia. Although this response lasts only for a short duration, it may have serious consequences in patients with significant cardiac disease. Also, CNS activation can occur leading to an increase in the electroencephalographic activity, cerebral metabolic rate and blood flow, which may result in

General anaesthesia is the most common technique employed in airway management. A rapid acting intravenous anaesthetic agent is most commonly used for induction of anaesthesia, followed by a neuromuscular blocking agent to provide

Rapid sequence induction is used when there is an appreciable risk for gastric regurgitation and pulmonary aspiration of gastric contents. In this technique, after pre-oxygenation, cricoid pressure is applied. This is followed by an induction dose of an intravenous anaesthetic and 1–1.5 mg/kg of intravenous succinylcholine. The trachea is then intubated without any attempts at positive pressure ventilation. The cricoid pressure is applied constantly until the airway


**Table 1.**

*Special Considerations in Human Airway Management*

airway management in space are listed in **Table 1** [1, 4, 5].

With increasing flight durations, there is an increased prospect that a medical emergency will entail airway management. It is currently estimated that the probability of a medical intervention requiring general anaesthesia, over the course of a 950 day mission to Mars and with six crew members is 2.6%. This speaks to the importance of how even the unlikeliest of events could imperil the mission and lead to loss of life [1]. Airway management is an important skill that is required to manage a great many medical emergencies. Some of the possible scenarios necessitating

Seventeen medical emergencies were documented during spaceflight between the periods of 1961–1999 [1]. In one instance, in 1962, on the Mercury 7 flight, Scott Carpenter, an American astronaut, aspirated food crumbs in orbit and in 1975 several astronauts on the Apollo-Soyuz mission developed a mild form of chemical pneumonitis after accidentally inhaling propellent fluid during re-entry [4]. Incidentally, none of the seventeen cases have required intubation. Also, no one has

Medical evacuation is not an option, in case of an airway emergency, owing to the distance as well as the absolute need to maintain oxygenation to avoid brain death. It is therefore necessary that immediate care is provided, while on board [6]. This warrants a crew equipped with emergency care skills as well as continuous training, to prevent skill erosion [1, 6, 7]. Furthermore, communication delays prohibit real time telemedicine support. For example, the communication delay between Earth and Mars is about twenty minutes—one way [1]. Airway manage-

In the first half of this chapter, we will deal with the physiology of airway management and the physiological adaptations of the human body in space. This would provide the essential foundation to understand the challenges associated

The term 'Airway Management' refers to the maintenance of airway patency and ensuring adequate ventilation and oxygenation. Successful airway management entails that the practitioner anticipates and predicts difficult airway and at the same time devises an airway management plan. The practitioner should also be adequately skilled to execute that plan, with the available resources. In order to enable this plan, anaesthesia is typically required—to provide patient comfort, limit airway reflexes, and to moderate the hemodynamic response to airway

Hypoxaemia can occur on induction of anaesthesia and muscle paralysis on account of hypoventilation and apnea. Pre-oxygenation or denitrogenation helps to replace the nitrogen in the lungs with oxygen. This, consequently, extends the apnea time and allows the anaesthesiologist to secure the airway and resume

Pre-oxygenation is achieved by providing 100% oxygen via a face mask, at a flow rate of 10-12 L/min to prevent rebreathing. This can be achieved by asking the patient to breathe for 3 min using tidal volume ventilation; or by taking 8 vital capacity breaths over 60 seconds. During this process, it must be ensured that there

ment skills are thus critical to the mission of exploring space safely.

**2. Airway management in space**

required GA in space to date [1].

with airway management in space.

**3. Physiology of airway management**

are no leaks around the face mask [8].

instrumentation [8].

**3.1 Pre-oxygenation**

ventilation.

**194**

*Indications for airway management in space.*

#### **3.2 Pulmonary aspiration of gastric contents**

Patients are required to have an empty stomach to reduce the risk of regurgitation and pulmonary aspiration of acidic gastric contents. The American Society of Anaesthesiologists task force recommends 4 hours of fasting from breast milk, 6 hours of fasting from infant formula, non-human milk and solid foods; and up to 8 hours or more from fried or fatty food. Clear fluids may be allowed up to 2 hours prior to anaesthesia [9].

Prophylactic drugs may be beneficial in patients with specific risk factors for aspiration. They help in decreasing gastric volume and increasing the gastric fluid pH. The commonly used drugs (alone or in combination) are—non-particulate antacids, promotility drugs and H2-receptor antagonists. These drugs may be used alone or in combination [8].

## **3.3 Airway reflexes and the physiological response to intubation of the trachea**

One of the main functions of the larynx is protection of the airway. Sensory receptors in the glottic and subglottic mucosa are triggered—on airway instrumentation—leading to the adduction of the vocal cords and laryngospasm. Furthermore, foreign body irritation of the lower airway can result in bronchospasm [8].

Airway instrumentation causes an intense noxious stimulus via the vagal and glossopharyngeal afferents. This results in a reflex autonomic activation, manifesting as hypertension and tachycardia. Although this response lasts only for a short duration, it may have serious consequences in patients with significant cardiac disease. Also, CNS activation can occur leading to an increase in the electroencephalographic activity, cerebral metabolic rate and blood flow, which may result in an increased intracranial pressure [8].

#### **3.4 Anaesthesia for airway management**

General anaesthesia is the most common technique employed in airway management. A rapid acting intravenous anaesthetic agent is most commonly used for induction of anaesthesia, followed by a neuromuscular blocking agent to provide muscle relaxation [8, 10].

Rapid sequence induction is used when there is an appreciable risk for gastric regurgitation and pulmonary aspiration of gastric contents. In this technique, after pre-oxygenation, cricoid pressure is applied. This is followed by an induction dose of an intravenous anaesthetic and 1–1.5 mg/kg of intravenous succinylcholine. The trachea is then intubated without any attempts at positive pressure ventilation. The cricoid pressure is applied constantly until the airway is secured.

Inhalation induction of anaesthesia with volatile anaesthetics is commonly used in paediatric patients—to provide a needle free experience—and in adults where intravenous access is difficult or when this technique is desirable [8].

Intravenous induction without neuromuscular blocking drugs is used for LMA (laryngeal mask airway) placement. Propofol is the drug of choice for this technique due to its distinct ability to suppress airway reflexes and produce apnea [11, 12].

Awake airway management is indicated, but not limited to, difficult mask ventilation and difficult intubation [13]. In such a case, the pharyngeal muscle tone and patency of the upper airway is maintained. This allows for spontaneous ventilation and acts as a safeguard against aspiration. It also provides an opportunity for a quick neurological examination, if indicated. Awake airway management is achieved by topicalisation of the airway with local anaesthetics [8].

#### **3.5 Equipment for airway management**

Equipment for basic airway management includes face masks for pre-oxygenation and delivery of inhalational anaesthetic agents, supraglottic airways are devices that are inserted blindly into the pharynx to provide a conduit for ventilation without requiring tracheal intubation, and endotracheal tubes, that provide maximum protection against the risk of aspirating gastric contents while establishing a definitive airway and at the same time, allowing positive pressure ventilation with higher airway pressures.

In patients with known or predicted difficult airway, videolaryngoscopy, rather than direct laryngoscopy is indicated since videolaryngoscopy inherently provides better glottic visualisation as well as effortlessly employed by non-experts [8].

#### **3.6 Laryngoscopy and endotracheal intubation**

Endotracheal intubation is established as the gold standard for airway management. It is typically achieved by direct laryngoscopy with patients placed in the sniffing position. A line of sight must be established from the mouth to the larynx. Direct laryngoscopy displaces the hyoid, tongue and epiglottis anterior to a line running from the upper teeth to the glottis.

In this technique, the mouth is opened, the laryngoscope blade is inserted and the tip is positioned to apply a lifting force exposing the glottis. The endotracheal tube is then inserted through the vocal cords into the trachea [8, 14].

#### **4. The human body in space**

The Earth's constant gravitational force is an important factor in the evolution of life on this planet. It has determined the development of all forms of life. All biological adaptations on land and water have been influenced by its interactions with gravity forming complex systems for stability, fluid regulation, gravity sensing, and locomotion.

The human body responds to microgravity in the same manner that it responds to senescence (ageing): Both ageing and microgravity produce a decline of biological function [15]. Also, like ageing, microgravity causes a negative calcium balance leading to a loss of bone density, muscle atrophy, cardiovascular and haematic changes, and metabolic, endocrine, and sleep disturbances. In microgravity, astronauts undergo rapid senescence. However, they subside over time on returning to Earth, departing from the typical path of the ageing process. This correspondence

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*Challenges to Airway Management in Space DOI: http://dx.doi.org/10.5772/intechopen.98932*

**4.1 Cardiovascular system**

alive to the issue of accelerated ageing in space [15].

puffiness coupled with reduced volume in the lower limbs [2, 16].

gravitational force on the cardiac muscle may even reduce it [15, 16].

dysfunction has been identified in astronauts [16].

arrhythmias in space due to catecholamine discharge [16].

to landing-day orthostatic stress [2].

**4.2 Endothelial changes**

vasodilation [15, 16].

Microgravity affects the heart rate and blood pressure minimally [16, 19]. The initial headward fluid shift increases the stroke volume and cardiac output. Subsequently, after a few days of adaptation, the resulting hypovolemia and cardiac atrophy, increase the ejection fraction and decrease the stroke volume. The left ventricle mass reduces by 8% due to reduced myocardial load in microgravity [16, 20–22]. The left ventricular systolic function is minimally affected even though diastolic

The nitric oxide release as a result of endothelial cell adaptation to microgravity and the loss of tone due to smooth muscle cell deconditioning causes vasodilation. Systemic vascular resistance reduces after 1 week of weightlessness due to this

The baroreflex response is weakened by 50% after just 24 hours of being in space. It is constrained after long-duration spaceflight and these changes linger on for up to 2 weeks after returning to Earth. There are changes in adrenergic-receptor sensitivity in microgravity: beta-adrenergic receptors sensitivity is increased and alpha-adrenergic receptors sensitivity is decreased. There is also an increased risk of

In space, aerobic capacity may be either maintained or increased. On return to Earth, there is an orthostatic challenge due to readaptation to gravity. As a result of this, astronauts experience reduced stroke volume and cardiac output which leads

Microgravity and reduced motor activity produces endothelial changes by altering the regional blood flow and vascular transmural pressure, which in turn,

of symptoms combined with a prolonged stationing in space requires that we are

Changes in the cardiovascular system because of microgravity are paramount from the standpoint of the anaesthesiologist. Gravity influences the equilibrium of the various functional fluid compartments of the vascular system and in particular that of the venous capacitance vessels [16]. In the upright posture, there is higher arterial pressure in the feet (200 mmHg) and lower pressure in the head (70 mmHg) relative to the heart (100 mmHg). In space, this gradient is absent, leading to redistribution of body fluids toward the head [2, 15, 17]. This phenomenon is referred to as "fluid shift". As a result of this, astronauts develop facial

Also, due to this 'fluid shift', there is engorgement of the central circulation. Mechanoreceptors sense this blood redistribution activating autonomic offloading and volume regulating reflexes leading to vasodilation and pooling of blood in the viscera and tissues, and initial renal fluid and salt loss. Most of these adaptations occur within 6–10 hours of spaceflight. After one week in space, the plasma volume reduces and the intracellular volume increases [15, 16]. In the same period, the RBC mass drops by about 10%. This "space anaemia" can again be attributed to the fluid shift toward the upper body, which is associated with an increase in kidney tissue oxygen partial pressure leading to the inhibition of erythropoiesis. A second hypothesis explains this as being due to haemolysis of recently formed RBCs [2, 16, 18]. Despite the headward fluid shift, paradoxically the central venous pressure is not increased. Further, a reduction in the intrathoracic pressure and the loss of

of symptoms combined with a prolonged stationing in space requires that we are alive to the issue of accelerated ageing in space [15].
