Göran Hedenstierna

Reexpansion of atelectasis during general anaesthesia may have a prolonged effect.

Pulmonary atelectasis, as found during general anaesthesia, may be reexpanded by hyper‐inflation of the lungs. The purpose of this study was to determine whether such a recruitment is maintained and whether this is accompanied by an improved gas exchange.

Atelectasis and pulmonary shunting during induction of general anaesthesia ‐ can they be avoided?

Background: Gas exchange is regularly impaired during general anaesthesia with mechanical ventilation. A major cause of this disorder appears to be atelectasis and consequently pulmonary shunt. After re‐expansion, atelectasis reappears very slowly if 30% oxygen in nitrogen is used, but much faster if 100% oxygen is used. The aim of the present study‐was to evaluate if early formation of atelectasis and pulmonary shunt may be avoided if the lungs are ventilated with 30% oxygen in nitrogen instead of 100% oxygen during the induction of general anaesthesia.

A comparison of pressure‐ and volume‐controlled ventilation at different inspiratory to expiratory ratios*

Background: Inverse ratio ventilation (IRV) is frequently used in severe acute respiratory failure. IRV may lead to intrinsic positive end‐expiratory pressure (PEEP) and is thought to improve oxygenation and to have advantageous effects on lung mechanics. Published data to support the use of IRV are scarce. This animal study compares external PEEP with intrinsic PEEP in pressure‐ and volume‐controlled ventilation.

Lung and Chest Wall Mechanics during Differential Ventilation with Selective PEEP

Eight patients free from cardio‐pulmonary disease and with a mean age of 46 years were studied during general anaesthesia in the lateral position. Measurements of hemithoracic mechanics were made during four different modes of ventilation: 1. Conventional ventilation (free distribution of ventilation) with no positive end‐expiratory pressure (PEEP) (CV), 2. differential ventilation (50% of ventilation to each lung) with no PEEP (DV:0), and 3 and 4. DV with selective PEEP of 0.8 and 1.6 kPa, respectively, to the dependent lung only (DV:8, DV:16). During CV, 60% of ventilation was distributed to the non‐dependent lung. Nondependent hemithoracic compliance was 64% greater and inspiratory resistance 39% lower than those of the dependent hemithorax. No significant differences between the two hemithoraces were noted during DV:0, but on application of selective PEEP the compliance of the dependent hemithorax increased and its resistance decreased. With DV:16, the compliances of the two hemithoraces were essentially equal, as were their resistances. Selective PEEP caused a larger volume increase in the dependent lung than general PEEP. Selective PEEP reduced the volume of the non‐dependent lung but only by 1/3 of the simultaneous increase in that of the dependent lung. Oesophageal pressure increased only slightly on selective inflation of the dependent lung, and remained negative within the 2 1 volume range studied. It is suggested that the altered mechanics of the dependent lung during selective PEEP result in a more even distribution of the inspired gas within that lung.

Effects of ventilatory pattern on exhaled nitric oxide in mechanically ventilated rabbits

Background: Nitric oxide [NOexp] is present in exhaled air in many species. During experiments on pressure‐controlled inverse ratio ventilation (PCIRV) in rabbits, increased [NOexp] was observed during PCIRV. The present study was undertaken to clarify which component of PCIRV increased [NOexp].

Open lung approach ventilation abolishes the negative effects of respiratory rate in experimental lung injury.

We recently reported that a high respiratory rate was associated with less inflammation than a low respiratory rate, but caused more pulmonary edema in a model of ARDS when an ARDSNet ventilatory strategy was used. We hypothesized that an open lung approach (OLA) strategy would neutralize the independent effects of respiratory rate on lung inflammation and edema. This hypothesis was tested in an ARDS model using two clinically relevant respiratory rates during OLA strategy.