Causes of ventilatory inefficiency in lung resection candidates

Ventilatory efficiency (V'_E/V'_CO ) has been shown to predict postoperative pulmonary complications (PPCs) in lung resection candidates. V'_E/V'_CO is determined by arterial partial pressure of carbon dioxide (P _aCO ) and by dead space to tidal volume ratio (V _D/V _T). We hypothesised P _aCO and V _D/V _T contribute equally to the increase in V'_E/V'_CO in lung resection patients.

Consecutive lung resection candidates from two prior prospective studies were included in this post hoc analysis. All subjects underwent preoperative spirometry, cardiopulmonary exercise testing and arterial blood gas analysis at rest and peak exercise. PPCs were prospectively assessed during the first 30 postoperative days, or hospital stay. A t-test, Mann-Whitney U-test and two-tailed Fisher's exact test were used to compare patients with and without PPCs. p-values <0.05 were considered statistically significant.

Of 398 patients, PPC developed in 64 (16%). Patients with PPCs more frequently underwent lobectomy by open thoracotomy, had longer hospital and ICU length of stay and higher 30- and 90-day mortality. Moreover, patients with PPCs exhibited a higher V'_E/V'_CO ratio both at rest and peak exercise. Both ratios were independently associated with PPCs. At rest, the contribution of P _aCO and V _D/V _T to the increase in V'_E/V'_CO ratio in patients with PPCs was 45% and 55%, respectively. At peak exercise, the contribution of P _aCO and V _D/V _T to the increase in V'_E/V'_CO ratio was 16% and 84%, respectively.

V _D/V _T (V'/Q' mismatch and/or rapid shallow breathing pattern) is the dominant contributor to the increase in V'_E/V'_CO in lung resection candidates who develop PPCs.