Physical therapy is part of the treatment for patients admitted to ICU. Proprioceptive neuromuscular facilitation (PNF) is one of the physiotherapy concepts including manual techniques and verbal stimulation. The purpose of this paper is to examine the feasibility of PNF techniques in mechanically ventilated (MV) ICU patients. Another aim is to verify whether the technique using resistance during the patient’s inhalation will have a different effect than the technique used to teaching the correct breathing patterns. Methods: Patients admitted to tertiary ICU were enrolled in this study, randomly divided into two groups, and received four 90-second manual breathing stimulations each. The following vital signs were assessed: HR, SBP, DBP, and SpO2. Results: 61 MV ICU adult patients (mean age 67.8; 25 female and 36 male) were enrolled in this study. No significant differences in HR, SBP, and DBP were observed both for two techniques measured separately and between them. Statistically significant differences were noticed analysing SpO2 in the rhythmic initiation technique (RIT) group (p-value = 0.013). Conclusions: Short-term PNF interventions did not influence clinically relevant vital parameters among MV patients and seem to be feasible in this group of ICU patients.