Effects of PEEP on Tension Pneumothorax
Applying PEEP to a patient with tension pneumothorax is extremely dangerous and can rapidly precipitate cardiovascular collapse—positive pressure ventilation converts any pneumothorax into a tension pneumothorax by maintaining the air leak and preventing air egress, thereby worsening mediastinal shift, venous return obstruction, and cardiac output reduction. 1, 2, 3
Pathophysiologic Mechanisms
Conversion of Simple to Tension Pneumothorax
Positive pressure ventilation, including PEEP, exacerbates the one-way valve mechanism by forcing air into the pleural space during each mechanical breath while preventing escape, causing progressive pressure accumulation that exceeds atmospheric pressure throughout the respiratory cycle. 1, 2, 3
The addition of positive pressure during mechanical ventilation converts a simple pneumothorax into a tension pneumothorax by maintaining continuous air leak without mechanism for egress. 3, 4
Positive pressure maintains the air leak—this is why all mechanically ventilated patients who develop pneumothorax require immediate tube thoracostomy rather than observation. 2
Hemodynamic Deterioration
PEEP increases pleural pressure (Ppl), which directly raises right atrial back pressure, thereby reducing the venous return gradient (normally only 4-8 mmHg) and causing profound decreases in cardiac output. 5
When PEEP is present, the gradient for venous return is decreased throughout the entire ventilatory cycle, not just during inspiration. 5
The increased intrathoracic pressure from PEEP reduces venous return and worsens right ventricular (RV) failure in patients with massive pulmonary embolism or other causes of elevated pulmonary vascular resistance. 5
Pulmonary Vascular Effects
PEEP increases pulmonary vascular resistance (PVR) in direct proportion to its effects on mean alveolar pressure, which further afterloads the already compromised RV in tension pneumothorax. 5
When regional pleural and interstitial pressures exceed pulmonary arterial pressure (West zone 1 conditions), pulmonary blood flow is largely obstructed, and alveolar pressure becomes the outflow pressure for the RV, considerably increasing RV afterload. 5
High PEEP (9 cmH₂O) increases diaphragm vascular resistance and reduces diaphragmatic blood flow compared to low PEEP (1 cmH₂O), demonstrating mechanical compression effects on vasculature. 6
Clinical Implications in Mechanically Ventilated Patients
High-Risk Scenarios
Patients on mechanical ventilation or non-invasive ventilation who suddenly deteriorate or develop pulseless electrical activity (PEA) arrest should be presumed to have tension pneumothorax until proven otherwise. 1, 2
In mechanically ventilated patients with severe asthma, tension pneumothorax is a rare but life-threatening complication that should be considered with sudden deterioration. 5, 2
The incidence of tension pneumothorax is greater in positive pressure ventilated patients, and the time to severe physiological impact is shorter, thus requiring a more aggressive treatment approach. 3
Management Modifications
When mechanical ventilation is required in patients at risk for pneumothorax, positive end-expiratory pressure should be applied with extreme caution—the European Society of Cardiology guidelines specifically warn that positive intrathoracic pressure can reduce venous return and worsen RV failure. 5
In asthmatic patients requiring mechanical ventilation, use low respiratory rate and tidal volume (6-8 mL/kg) with shorter inspiratory time and longer expiratory time (inspiratory:expiratory ratio 1:4 or 1:5) to minimize auto-PEEP and barotrauma risk. 5
If auto-PEEP develops and causes significant hypotension, immediately disconnect the patient from the ventilator circuit to allow passive exhalation, and assist exhalation by pressing on the chest wall. 5
Immediate Treatment Protocol
Recognition and Decompression
Diagnosis is purely clinical—never delay treatment for radiographic confirmation as tension pneumothorax is immediately life-threatening. 1
Perform immediate needle decompression using a 7-8 cm needle (minimum 4.5 cm) at the 2nd intercostal space, midclavicular line—shorter needles fail in 32.84% of cases. 1, 2
Follow immediately with tube thoracostomy at the 4th-5th intercostal space, midaxillary line, as needle decompression alone has a 32% recurrence rate. 1
Ventilator Management During Crisis
During cardiac arrest in an asthmatic patient with suspected tension pneumothorax, a brief disconnection from the bag-mask or ventilator may be considered, and compression of the chest wall to relieve air-trapping can be effective. 5
For all patients in cardiac arrest with difficult ventilation, strongly consider tension pneumothorax and treat empirically. 5
Critical Pitfalls
High levels of PEEP (18 torr or greater) increase the risk of pneumothorax—in one series, 14% of patients developed pneumothorax following institution of high PEEP therapy. 7
In mechanically ventilated patients whose ventilatory pressures are increasing with diminishing cardiac output, the possibility of tension pneumothorax converting from simple pneumothorax must be entertained immediately. 4
The dynamics of pneumothorax fundamentally change with positive pressure ventilation—what might be observed safely in a spontaneously breathing patient becomes immediately life-threatening under positive pressure. 3