Non Invasive ventilation (NIV) in Postoperative Critically Ill Patient
Dr Prerana N. Shah,
Professor (Additional), Department of Anaesthesiology,
Seth G S Medical College & KEM Hospital, Mumbai
Non Invasive Ventilation (NIV):  It is delivery of ventilator support without endotracheal tube (ETT) or Tracheostomy tube via patient’s upper airway.  It is continuous spontaneous ventilation delivered via a sealed mask. Common modes used are Continuous Positive Airway pressure (CPAP) and Bi-level Positive Airway pressure (BIPAP). Tracheal intubation and mechanical ventilation (MV) have the risk of morbidity and mortality, including volutrauma, barotrauma, ventilator associated pneumonia (VAP), and the complications associated with sedation. More recently, NIV has been used in postoperative surgical patients.
History:  In the mid 20th century: Iron Lung for Polio myelitis with respiratory paralysis
1936: Successful use of NIV in ARF (respiratory)
1980s: CPAP via Nasal masks for OSA
Indication: The indications for NIV are COPD exacerbation, cardiogenic pulmonary oedema, asthma exacerbation, pneumonia, immunocompromised patient. Postoperatively it is often beneficial in thoracic, cardiac and upper abdominal surgeries.
Contraindication: The contraindications for NIV are need for emergency intubation, impaired level of consciousness, lack of respiratory drive, presence of excessive secretions, haemodynamic instability, uncontrolled vomiting, pregnancy, inability to protect airway, repeated haemoptysis or haematemesis, acute myocardial infarct, cardiac arrest, upper airway obstruction, preventing adequate mask seal e.g. facial trauma.
Abdominal surgery: Abdominal surgery is often followed by diaphragmatic dysfunction with decrease in vital capacity that leads to atelectasis and hypoxaemia. Surgeries which result in dysfunction of diaphragmatic movement tend to worsen respiratory impairment. The beneficial effects of postoperative NIV have been demonstrated following laparoscopic surgeries for cholecystectomy, bariatric surgeries and thoracoabdominal surgeries for aneurysm repair.
There have been several studies demonstrating the benefits of prophylactically applied NIV in patients undergoing abdominal surgeries. Patients receiving CPAP and incentive spirometry after cholecystectomy by laparotomy had a significantly improved functional residual capacity (FRC) and lesser roentgenographic evidence of atelectasis than those treated with coughing and deep breathing exercises. They have better oxygenation rates and shorter lengths of ICU. In morbidly obese patients undergoing abdominal surgeries, application of BiPAP set at 12 and 4 cm water PEEP improved the peak expiratory flow rate, the forced vital capacity and the oxygen saturation on the first postoperative day by improving lung inflation, preventing alveolar collapse and reducing inspiratory threshold load.
CPAP as therapeutic non-invasive ventilation reduced the incidence of endotracheal intubation, improved paO2/FiO2 and paCO2 levels, pneumonia, sepsis, anastomotic leaks, infection, length of ICU stay and death. However, there are concerns of increased incidence of anastomotic leaks.
Thoracic surgery: Postoperative lung dysfunction following lung resection surgeries occur due to inhibition of phrenic nerve, pain, reduced muscle tone due to general anaesthesia and loss of functioning lung parenchyma. These can lead to sputum retention, lobar atelectasis, pneumonia and respiratory failure. The prophylactic use of NIV in patients helps in significant improvements in pulmonary function like better forced vital capacity (FVC) and FEV1, improved oxygenation, lesser duration of hospital stay.
Cardiac surgery: Respiratory failure after cardiac surgery is associated with morbidity, mortality and decreased quality of life. Combined valve and coronary artery bypass graft was associated with the highest incidence of respiratory failure, followed by aortic procedures. Use of nasal CPAP following cardiac surgeries, lower reduction of lung volumes, improved oxygenation, reduced pulmonary complications and ICU readmission rates.
Obstructive sleep apnoea (OSA) often leads to upper airway obstruction in the postoperative period usually seen in the obese or patients with pre-existing neurological disorders. NIV is useful in laryngo tracheal surgeries, by providing ventilatory support and airway stenting till tracheal oedema and pulmonary dysfunction resolves, at the same time avoiding the risk of further tracheal mucosal injury from tracheal intubation.
Method: The patient must be in propped up position to at least 30 degrees and should receive adequate analgesia. In CPAP, EPAP is applied alone and in NPPV, both EPAP and IPAP are applied together.  Initially one must decide whether CPAP or BIPAP needs to be given, full face (Oronasal) or nasal mask to be used. Usually inspiratory support (IPAP) of 10 cm water and expiratory Support (EPAP) of 5 cm water is given. They are then titrated depending on pressure tolerance, respiratory rate, saturation and reduction in work of breathing. There should be good patient ventilator synchrony. It is better to avoid IPAP > 20 cm water. EPAP ensures flow to flush carbon dioxide from single ventilator tube and avoids rebreathing. It increases Functional Residual Capacity (FRC). It opens upper airway to prevent apnoea and hypopnoea. It also counterbalances intrinsic Positive End Expiratory pressure (PEEP) in Chronic Obstructive Pulmonary Disease (COPD) patients. If the patient is wearing dentures, they should be left in place to optimize the fitting of the mask. Warm and humidified gases minimize mouth leak and improve comfort. Humidification is required to prevent drying of upper airway.
Interface: The NIV mask is the most important component. It must be light weight, transparent, give comfortable airtight seal, have minimal dead space and must be optimized for fit and comfort. It is available in multiple sizes and shapes. Several modifications from straps to custom-molded masks are available.
Full face mask also called as oro nasal mask interferes with speech, expectoration and eating. It carries risks of claustrophobia, aspiration and rebreathing.
Nasal mask requires patent nasal passages and mouth closure to minimize air leaks.
Intra nasal pledgets or Nasal pillows are soft pledgets inserted directly into the nostrils, mouthpieces held in place by lip seals resembling a snorkel.
Total face mask are similar to plastic hockey goalie mask and helmet.
The causes of non- compliance include mask discomfort due to inadequate mask seal, air leak, lack of humidification and feeling of claustrophobia.
During NIV, patient must be comfortable, should not get the feeling of claustrophobia. Adequate time should be spent with patient to ensure proper fit, comfort and acclimatization with appropriate coaching and encouragement. The progress for therapy, tolerance of mode of support and signs of clinical deterioration needing ETT must be regularly assessed.
Monitoring: Mask comfort, tolerance of ventilator settings and respiratory distress, air leak, patient-ventilator synchrony, gas exchange by continuous oximetry, ABGs, (baseline, 1-2 hours, as indicated)
Advantages: NIV avoids laryngeal injury, reduces the risk of nosocomial infection, and less sedation is needed. Also, the patient can drink, eat, talk, and communicate. It prevents the need for intubation that has its own side effects. It reduces length of ICU and thereby hospital stay, reduction in rates of reintubation, pneumonia and hence has economic benefits.
Risk factors for failure: The risk factors for failure include pH < 7.25, Acute Physiology and Chronic Health Evaluation II (APACHE II) score > 29, acute lung injury/acute respiratory distress syndrome, pneumonia, severe hypoxemia, shock, metabolic acidosis and impaired mental status.
Effects: NIV delivers pressurized gas to increase transpulmonary pressure and inflate lungs. It reduces work of breathing and improves cardiac output, increases intra thoracic pressure, reduces left ventricular ejection pressure and transmural pressure thereby reducing the after load. Reduction in right ventricular preload improves left ventricular compliance. It has better patient tolerance with similar rates of efficacy with pressure-cycled modes than volume cycled.
Complications: Patient intolerance, abrasions, nasal congestion, sinus pain, oronasal dryness, raised intraocular pressure and intracranial pressure and fall in blood pressure are usually observed.
Paediatric patient: A paediatric patient has different pulmonary and chest wall mechanics. There are fewer alveoli and less surface area available for gas exchange. They are predisposed to manifest lung disease such as atelectasis, airway obstruction, increased pulmonary vascular resistance and pulmonary edema. Children have less ventilator muscle strength and endurance to infant’s susceptibility to respiratory fatigue. Neurologic control of breathing intrinsically unstable and predisposes to apnea and hypoventilation. Diurnal hypercapnia is also seen in children. Use of NIV in child is more empirical as less data is available. It is useful in chronic respiratory failure. It is contraindicated in upper airway obstruction, recent pneumothorax, swallowing problem, increased secretion and inadequate family support. Facial deformity after prolonged use is often seen.
Summary: NIV is an important part of the critical care ventilator armamentarium. NIV is useful for acute respiratory failure associated with COPD exacerbations, acute cardiogenic pulmonary oedema and immunocompromised states. Patients must be carefully selected for NIV. NIV should be reserved for patients who require ventilator assistance but have no contraindications. If patients are not improving within the first 1 or 2 hours of NIV, intubation should be performed without further delay.
Further Reading:

1. David Chang. Non Invasive Ventilation In Clinical Application of Mechancial Ventilation. Fourth Ed. Delmar 2014: 192-211
2. A. J. Glossop, N. Shepherd, D. C. Bryden and G. H. Mills. Non-invasive ventilation for weaning, avoiding reintubation after extubation and in the postoperative period: a meta-analysis. British Journal of Anaesthesia 109 (3): 305–14 (2012).
3. Mathai AS. Non-invasive ventilation in the postoperative period: Is there a role? Indian J Anaesth 2011; 55: 325-33.
4. Jaber S, Chanques G, Jung B. Postoperative noninvasive ventilation. Anesthesiology. 2010 Feb; 112(2): 453-61.