TENSION PNEUMOTHORAX DR.MALAV SHAH

CASE : MR P M 47 YRS OLD MALE MORBIDLY OBESE @ 115 KG SUBACUTE ONSET BREATHLESSNESS OVER FEW DAYS AND FEVER ADMITTED TO ICU FOR SEVERE HYPOXEMIA

DR C M

Chest X ray s/o bilateral airspace shadows – ARDS (SEVERE) INTUBATED AND VENTILATED. Invasive hemodynamic monitoring started

WHAT SHOULD BE INITIAL VENTILATOR SETTINGS? MODE : CONTROL : VOLUME FIO2 @PaO2 - 55-80 mmhg RATE : 20 / MIN TV : 6 ML/KG : 700- 800 ml/kg Target : to keep plateau pressure below 30-35 mmhg.

PLATEAU PRESSURE WAS MAINTAINED AROUND 30-34 mmhg overnight.

Next morning .. SINCE EARLY MORNING SLIGHT DROP IN BP, SAO2 AND INCREASES IN PLATEAU AND PEAK PRESSURE : worsening ARDS? PEEP increased further.. Sudden drop in blood pressure and SaO2 CHEST X RAY DONE IN THE MORNING

How my Mechanical Ventilation is Responsible for Pneumothorax ?

Back to basics .. The purpose of mechanical ventilation is to rest the respiratory muscles while providing adequate gas exchange. Despite the clear benefits , many patients eventually die after the initiation of mechanical ventilation, even though their arterial blood gases may have normalized.

In 1967, the term“respirator lung” was coined to describe the diffuse alveolar infiltrates and hyaline membranes that were found on postmortem examination of patients who had undergone mechanical ventilation.

VILI The constellation of pulmonary consequences of mechanical ventilation has been termed ventilator-induced lung injury (VILI).

PRESSURES IN THE LUNG When air flow is zero (e.g., at end inspiration), the principal force maintaining inflation is the trans pulmonary pressure (alveolar pressure minus pleural). lung volume and transpulmonary pressure are inextricably linked.

P TP TRANSPULMONARY PRESSURE = ALVEOLAR PRESSURE – PLEURAL PRESSURE.

Key factor ? Regional lung overdistention is a key factor in generating ventilator-induced lung injury. Limiting inflation pressure during mechanical ventilation is used as a surrogate strategy to limit overdistention.

Alveolar pressure is relatively easy to estimate clinically as the airway pressure during a period of zero flow. In a patient undergoing mechanical ventilation who is not making spontaneous breathing efforts, the airway pressure that is measured during a period when air flow is stopped at end inspiration is called the plateau pressure.

Unfortunately, pleural pressure — the other variable needed to calculate transpulmonary pressure - is more complicated. it can be estimated in the broader clinical setting only by measurement of esophageal pressure.

Therefore, the plateau pressure is the most common variable used in a clinical setting to indicate lung overdistention. If the patient is not making respiratory efforts, the plateau pressure represents the pressure that is distending the lungs plus the chest wall.

VILI: ventilation at high (absolute) lung volumes leads to alveolar rupture, air leaks, and gross barotrauma (e.g., pneumothorax, pneumomediastinum, and subcutaneous emphysema.

The term barotrauma can be misleading, because the critical variable leading to the air leaks is regional lung overdistention, not high airway pressure per se.

Dreyfuss et al …showed that volume (i.e., lung stretching), not airway pressure, was the most important factor in determining injury, a finding that led them to coin the term “volutrauma.”

More subtle injury that is manifested as pulmonary edema can occur as a result of lung overdistention.

Ventilation at low volumes ? Ventilation that occurs at low (absolute) lung volumes can also cause injury through multiple mechanisms, including repetitive opening and closing of airways and lung units, -Atelectotrauma

Amplified in lungs in which there are marked heterogeneities in ventilation.

VILI Barotrauma and Volutrauma Atelectrauma and biotrauma

Bio trauma Moderate degrees of stress and strain related to the cyclic opening and closing of alveoli - release of inflammatory mediators and noxious proteinases.

Back to our pt. : MR P M TIDAL VOLUME : 6 ml/kg ACTUAL BODY WEIGHT

Back to our pt. : MR P M TIDAL VOLUME : 6 ml/kg IDEAL BODY WEIGHT NOW WHAT ?

Tension Pneumothorax When the pleural pressure is positive throughout respiratory cycle “Ball-valve mechanism” Injury to pleura creates a tissue flap that opens on inspiration and closes on expiration

Radiological manifestations

Pneumothorax in erect position in supine position Air in apicolateral pleural space Air in anteromedial pleural space.

A MISSED CALL ? Unfortunately, it is difficult to make a radiographic diagnosis of a pneumothorax on portable x-ray films taken in the ICU setting. X-ray Upright-air in Apex X-ray In ICU; supine , semi supine In addition, concurrent lung disease may lead to different distributions of free air in the pleural space than in patients with relatively normal lungs.

Distribution of air

Pneumothorax Erect Small pneumothorax Apical lucency Visceral pleural line Large (>2cm in width) Tension Lung collapse Mediastinal shift Low flat diaphragm Supine Deep Costophrenic sulcus Lucent Cardiophrenic Sharp Mediastinal contour Double diaphragm

Signs of pneumothorax in supine position

Deep costophrenic sulcus

Sharp mediastinal contour

Double diaphragm sign subpulmonic pneumothorax

Lucent cardiophrenic sulcus

Large pneumothorax (without mediastinal shift)

Tension pneumothorax

Tension pneumothorax

U/S signs of pneumothorax Loss of lung sliding. Loss of comet tails. loss of seashore sign (M mode). Stratosphere sign or bar code sign(M mode).

LOSS OF LUNG SLIDING AND LOSS OF COMET TAIL

Stratosphere or bar code sign

CT Thorax

Tension pneumothorax : Treatment life-threatening. The immediate treatment is NEEDLE DECOMPRESSION followed by tube thoracostomy, or the insertion of a chest tube. The chest tube is left in place until the lung leak seals on its own.

Thoracostomy (Chest tube)

Prognosis Patients with procedure-related pneumothorax had a lower risk of mortality. Patients who had tension pneumothorax and concurrent septic shock had a higher risk of mortality. pneumothorax due to barotrauma, tension pneumothorax, and concurrent septic shock were significantly and independently associated with death.

TAKE HOME MESSAGE KEEP A TAB ON LUNG VOLUMES WITH RESPECT TO IBW …ALONG WITH PRESSURES. LEARN NEW STETHOSCOPE IN ICU : USG PROBE.