**2. Physiological changes in microgravity**

The changes occur to human body during aviation can affect the anesthesia delivery if surgery is needed. Almost all the body organs will be affected, but what is more relevant to anesthesia administration is: cardiac systolic and diastolic changes, gastric motility, reduction in blood volume as well as neuromuscular junction changes.

#### **2.1 Pressure related effects**

At sea level, barometric pressure is 760 mmHg with a partial pressure of oxygen of 160 mmHg. The barometric pressure of ambient air declines as altitude increases, while the volume of air in a confined space will increase according to Boyle law, and this is why oxygen concentration remains at a constant 21% [1]. The intracranial air volume could be increased by 30% at the usual maximum cabin altitude of 8000 feet. These volume and pressure effects are sometimes associated with hemodynamic compromise (tension pneumothorax), barotrauma (sinuses), equipment malfunction (blood pressure cuffs), and possible injury or compromised monitoring as inflated gas bubble in the arterial line. Certain conditions such as pneumopericardium, subcutaneous emphysema, gas gangrene, systemic air emboli, decompression sickness, and gastric distension may be worsened at altitude [2]. Altitude sensitive equipment includes endotracheal and tracheostomy cuffs, pneumatic antishock garments (eg, medical antishock trousers), air splints, colostomy bags, foley catheters, orogastric and nasogastric tubes, ventilators, invasive monitors, and intra-aortic balloon pumps. Most aircraft cabins are usually pressurized to a pressure equivalent to 5000 to 8000 feet, giving an atmospheric partial pressure of oxygen of 118 mm Hg [3]. Thus, the oxygen requirement (Fio2) of a patient on mechanical ventilation may increase at altitude. ARDS in animal models were more responsive to increased PEEP, yet resistant to increases of (Fio2) [4].

Hypoxemia, even at low altitudes (3281–9843 feet), which is the usual flight range for the medical helicopter transport, could lead to global hypoxic pulmonary vasoconstriction and pulmonary edema. Hypoxemia is detrimental to patients with coronary ischemia, pulmonary compromise acute respiratory distress syndrome [ARDS], or neurologic injury. Besides, the hypoxia associated-tachycardia and hypertension increases the cardiac mechanical load and myocardial oxygen consumption.

Flying at low altitude is commonly known as "Altitude restrictions" which mainly for pressure sensitive conditions as in eye trauma, pneumothorax, intracerebral air, and sinusitis [5]. Those low altitude flying restrictions come with the cost of more turbulence and longer transport times, another risk factor for more vibration injury, anxiety and prolonged access to healthcare.

**219**

*Airway Management in Aviation, Space, and Microgravity*

The loss of gravity effect of the distribution of blood volume in different body compartments is notable in a microgravity environment. In normal environment at the earth surface there is a pressure gradient created by the gravity and the loss of this gradient during aviation result in more diuresis and by so reduction in blood volume [6–8]. The blood volume is one of the determinants of cardiac output, the reduction in the blood volume in microgravity will result in a 20% reduction in COP [6]. The reduction in these parameters will definitely reduce the body compensation capacity for hemorrhage, while the redistribution of the blood can affect intubation

Two main issues regarding musculoskeletal system changes in microgravity are the reduced bone mass [12] and the muscle atrophy which may lead to increase expression of extra junctional acetylcholine receptors [13, 14]. The abnormally expressed receptors can explain the risk of severe hyperkalemia after succinylcho-

Along with muscle atrophy changes in fat distribution affect the pharmacoki-

Some studies suggest that there is a decrease gastric emptying during aviation in the first three days [6, 15, 16]. Some studies used paracetamol absorption as an indicator of gastric emptying [17, 18]. In anesthesia, gastric emptying time is very important factor in the assessment of aspiration risk following anesthesia

**3. Special consideration in anesthesia and airway management in space** 

The first vehicles carrier used to carry humans to the stratosphere atmosphere, was the Balloons in 1783, the first round across the Earth had been achieved by the hybrid balloon. The increasing advancement of advanced life support programs and control systems progress had allowed to transport humans higher for more plans

Now recently aerospace companies are aiming to give scientists the chance to develop their clinical experience by arranging near space trips [20]. A great progress in Human spaceflight has expanded over the last 40 years leading to a larger, more sophisticated, and more distant journeys. As a result of this continuous advancement, space flight crews might require medical procedures, that mandates anesthesia, so the medical personnel on board should be well experienced to perform surgery and anesthesia during flights in deep space. So anesthesia strategies and techniques have to be adjusted to deal with specific problems and dangers that may

Airway management requires adequate training to maintain excellent medical care during aviation, our knowledge about airway management in microgravity is progressing and numbers of trials that examine the difference between different airway management methods is increasing. This justifies the importance of reviewing

and the preparation to colonize the Moon and the trip to Mars [19].

rise while patients are under the effects of microgravity [10].

*DOI: http://dx.doi.org/10.5772/intechopen.96603*

**2.2 Cardiovascular changes**

by causing facial edema [6, 9–11].

**2.3 Musculoskeletal changes**

line in space men [6, 10, 11].

netics of anesthetic medications.

**and microgravity conditions**

**2.4 Gastrointestinal changes**

induction.
