Answer:

There are competing interests involved in managing the ventilation of this patient with COPD undergoing laparoscopic surgery. PIPs should be kept at a minimum, end-expiratory time needs to be adequate to overcome air trapping, and hypercarbia from insufflation with CO₂ must be compensated for.

A pressure control ventilation mode would be preferable to volume control because it results in lower PIPs at similar VTs. However, the laparoscopic technique leads to increasing airway resistance and increasing PIPs, so the VTs must be watched closely because they will decrease with insufflation of the abdomen and PIP set on the ventilator will need to be increased as the case proceeds.

High PIP should be avoided, especially in patients with emphysema and blebs, because a pneumothorax can result from barotrauma. PIP should never be greater than 50 cm H₂O, and plateau pressures should be kept below 30 cm H₂O to minimize barotrauma.

The inspiratory-to-expiratory time ratio (I:E ratio) can be increased in order to reduce PIP. However, in this patient, the I:E ratio will likely need to be reduced in order to allow for complete expiration in the setting of expiratory obstruction and avoid air trapping. Allowing for an adequate expiratory time is a key component in the ventilatory management of patients with obstructive pulmonary disease.

Adequate minute ventilation will need to be maintained and should be increased, as the case proceeds and insufflated CO₂ is absorbed into the bloodstream and exhaled through the alveoli. Minute ventilation may need to increase as much as 60% in order to maintain normocarbia. Absorbed CO₂ can result in hypercapnia that lingers well into the postoperative period.

Achieving adequate minute ventilation with sufficient expiratory time and reasonable PIP can be a difficult task. In patients with severe pulmonary disease, it may be impossible. In this scenario, alternatives to traditional laparoscopy should be discussed with the surgeon. Gasless laparoscopic techniques that do not require insufflation of the abdomen are preferable, when feasible. These techniques utilize abdominal wall lifting to avoid necessitating a pneumoperitoneum.

The application of PEEP during positive pressure ventilation is a controversial issue. This type of PEEP is also referred to as extrinsic PEEP and must be differentiated from intrinsic or auto-PEEP. Intrinsic PEEP occurs in patients with COPD or asthma because outflow obstruction leads to air trapping. In ventilators equipped with an expiratory hold control, intrinsic PEEP can be measured during positive pressure ventilation. PEEP applied by the ventilator should be subtracted from the airway pressure measured during the expiratory hold time in order to obtain intrinsic PEEP. When extrinsic PEEP is lower than intrinsic PEEP, it can improve ventilation, especially in the spontaneously ventilating patient. Extrinsic PEEP reduces the amount of negative pressure required to generate a breath and therefore reduces the work of breathing.

However, extrinsic PEEP that exceeds intrinsic PEEP can worsen air trapping and hyperinflation. Excessive PEEP also results in decreased venous return, decreased left ventricular compliance, and increased pulmonary capillary resistance. All of these changes lead to hypotension.

• Barash PG, Cullen BF, Stoelting RK, et al, eds. Clinical Anesthesia. 8th ed. Philadelphia, PA: Wolters Kluwer; 2017:379.
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• Slinger P. Don’t make things worse with your ventilator settings: how you manage the lungs during the perioperative period affects postoperative outcomes. In: IARS 2013 Review Course Lectures. San Francisco, CA: International Anesthesia Research Society; 2013:38-46.