Emergency Medical Services. Группа авторов

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      Patients may present with pleuritic pain, sudden onset of a sharp pain, minimal to severe shortness of breath, and hypoxemia. Physical exam findings that should prompt consideration of pneumothorax include decreased or absent unilateral breath sounds, subcutaneous emphysema, or evidence of thoracic trauma. Pulse oximetry may or may not decrease depending on the size of the pneumothorax and the underlying pulmonary function and comorbidities of the individual patient. Similarly, EtCO2 may or may not appreciably change and its interpretation may be further complicated by compensatory hyperventilation or other comorbid conditions. A potentially more sensitive indicator in patients already receiving mechanical ventilation may be decreases in tidal volumes and increases in peak pressures. Ultrasound, if available, can also be used to identify pneumothorax.

      The one case that must be recognized clinically is a tension pneumothorax. This occurs when the intrathoracic pressure is so great that ventilation and venous return to the heart are obstructed, leading to respiratory compromise and shock. Besides unilateral decreased or absent breath sounds and subcutaneous emphysema, tracheal deviation and jugular venous distension may be present, but these should not be relied upon. Tension physiology must be recognized and treated immediately.

      Trauma:

       Blunt

       Penetrating

      Medical:

       Acute asthma, especially if cardiac arrest

       Chronic obstructive pulmonary disease or other underlying lung disease

       Decompression‐associated barotrauma

       Marfan syndrome (or marfanoid habitus)

       Thoracic endometriosis (catamenial)

      Finger thoracostomy is an additional technique for emergent chest decompression [16, 17]. Some EMS physicians consider this more reliable than needle decompression and less likely to cause lung injury. This technique should be performed only by experienced EMS clinicians with specific training and credentialing. The procedure includes antisepsis of skin, identification of mid‐axillary line just above the nipple line, making a 3–4 cm skin incision with a scalpel, spreading subcutaneous and intercostal tissue with hemostats, and puncture of parietal pleura with finger. The site should then be covered as for a sucking chest wound. Vigilance for reaccumulation of the pneumothorax is essential just as after needle decompression.

      Subsequently, the patient should receive a formal thoracostomy tube placed on suction with water seal. This is typically deferred until arrival in the emergency department but may be considered in the prehospital setting under special circumstances (e.g., protracted transport interval) and if appropriately credentialed clinicians and resources are available.

      A patient with a penetrating wound to the chest should have an occlusive dressing applied with watchful monitoring for the development of tension physiology. If tension develops, the dressing should be immediately vented. Some types of occlusive dressings provide one‐way air flow (pleural space to environment) to prevent the accumulation of gas in the pleural space that leads to a tension pneumothorax. Alternatively, an occlusive dressing may be left unsealed on one side or corner, which allows it to act like a one‐way flap valve.

      A frequent concern with the management of patients with pneumothorax is air transport. Boyle’s law (P1 × V1 = P2 × V2) describes that the air in the pleural space will expand with decreasing atmospheric pressure associated with increasing altitude. The EMS clinician should be aware that helicopter transport is not typically associated with sufficient altitude to have a significant clinical effect. For example, most medical helicopters fly at 1,000–3,000 feet above the ground. But at 6,000 feet, an altitude sometimes associated with instrument flight conditions (e.g., inclement weather), the increase in size would be about 25% (e.g., V2 = P1 × V1/P2 = 760 mmHg × 100 cc/609 mmHg = 125 cc). The clinical effects of such an increase in pneumothorax size are very much patient specific, depending on such things as initial volume, lung compliance, and comorbid conditions. Patients generally should not be flown in fixed‐wing aircraft (especially without cabin pressurization) without tube thoracostomy decompression.

      Oxygenation and ventilation are distinctly different but interrelated physiological processes. In general, adequate oxygenation requires sufficient ventilation to deliver gas to alveolar spaces, where oxygen can then enter pulmonary capillaries for transport to peripheral tissues. Pulse oximetry is a useful tool, except in cases of carbon monoxide poisoning, to help determine the extent of tissue oxygenation. Patients with respiratory distress or SpO2 less than 94% should receive supplemental oxygen. However, use of oxygen should not be indiscriminate.

      Ventilation is about gas moving in and out of the lungs. Clearly, it can occur without oxygen, and, in that sense, is a distinct process. The adequacy of ventilation is generally assessed in terms of minute ventilation. Waveform capnography is a useful tool to both monitor ventilation and evaluate its effectiveness. NIPPV may provide needed support to an awake patient with inadequate ventilation but intact respiratory drive. Mechanical ventilation is the maximum ventilatory support tool. Especially in a dynamic prehospital environment, vigilant monitoring is imperative to promptly identify and address deficiencies in ventilation and oxygenation and complications arising from their treatment.

      1 1 Chan ED, Chan MM, Chan MM. Pulse oximetry: understanding its basic principles facilitates appreciation of its limitations. Respir Med. 2013; 107:789–99.

      2 2 Barker SJ, Curry J, Redford D, Morgan S. Measurement of carboxyhemoglobin and methemoglobin by pulse oximetry. Anesthesiology. 2006; 105:892–7.

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